Adult stem cells play an essential role in the maintenance of tissue homeostasis. Environmental and therapeutic insults leading to DNA damage dramatically impact stem cell functions and can lead to organ failure or cancer development. Yet little is known about the mechanisms by which adult stem cells respond to such insults by repairing their damaged DNA and resuming normal cellular functions. The blood (hematopoietic) system provides a unique experimental model to investigate the behaviors of specific cell populations. Our objective is to use defined subsets of mouse hematopoietic stem cells (HSCs) and myeloid progenitor cells to investigate how they respond to environmental and therapeutic insults by either repairing damaged DNA and restoring normal functions; accumulating DNA damage and developing cancer; or undergoing programmed cell death (apoptosis) and leading to organ failure. These findings will provide new insights into the fundamental mechanisms that regulate stem cell functions in normal tissues, and a better understanding of their deregulation during cancer development. Such information will identify molecular targets to prevent therapy-related organ damage or secondary cancers. These are severe complications associated with current cancer treatments and are among the leading causes of death worldwide. Originally discovered in blood cancers (leukemia), cancer stem cells (CSCs) have now been recognized in a variety of solid tumors. CSCs represent a subset of the tumor population that has stem cell-like characteristics and the capacity for self-renewal. CSCs result from the transformation of either stem or progenitor cells, which then generate the bulk of the cancer cells. Recent evidence indicates that CSCs are not efficiently killed by current therapies and that CSC persistence could be responsible for disease maintenance and cancer recurrence. Developing interventions that will specifically target CSCs is, therefore, an appealing strategy for improving cancer treatment, which is dependent on understanding how they escape normal regulatory mechanisms and become malignant. Few mouse models of human cancer are currently available in which the CSC population has been identified and purified. This is an essential prerequisite for identifying pathways and molecules amenable to interventional therapies in humans. We have previously developed a mouse model of human leukemia in which we have identified the CSC population as arising from the HSC compartment. We will use this model to understand how deregulations in apoptosis and DNA repair processes contribute to CSC formation and function during disease development. These results will provide new insights into the pathways that distinguish CSCs from normal stem cells and identify ways to prevent their transformation. Such information will be used to design novel and much-needed therapies that will specifically target CSCs while sparing normal stem cells.
This application investigates how environmental and therapeutic insults leading to DNA damage impact stem cell functions and can lead to organ failure or cancer development. The approach is to study how specific population of blood (hematopoietic) stem, progenitor, and mature cells respond to DNA damaging agents and chose a specific cellular outcome. Such information could identify molecular pathways that are available for interventional therapies to prevent end-organ damage in patients who are treated for a primary cancer and reduce the risk of a subsequent therapy-induced cancer. These are severe complications associated with current mutagenic cancer treatments (radiation or chemotherapeutic agents) that comprise a substantial public health problem in California and in the rest of the developed world. The hematopoietic system is the first to fail following cancer treatment and the formation of therapy-related blood cancer (leukemia) is a common event. The development of novel approaches to prevent therapy-related leukemia will, therefore, directly benefit the health of the Californian population regardless of the type of primary cancer. This application also investigates a novel paradigm in cancer research, namely the role of cancer stem cells (CSCs) in the initiation, progression and maintenance of human cancer. The approach is to study how dysregulations in important cancer-associated pathways (apoptosis and DNA repair processes) contribute to CSC aberrant properties using one of the few established mouse model of human cancer where the CSC population has already been identified. Leukemia, the disease type investigated in this application, has been the subject of many landmark discoveries of basic principles in cancer research that have then been shown to be applicable to a broad range of other cancer types. Accordingly, this research should benefit the people of California in at least two ways. First, the information gained about the properties of CSCs should improve the ability of our physicians and scientists to design, develop and evaluate the efficacy of innovative therapies to target these rare disease-initiating cells for death. This would place Californian cancer research at the forefront of translational science. Second, an average of 11.55 out of 100,000 Californian inhabitants are diagnosed with primary leukemia each year. Thus, in California, leukemia occurs at approximately the same frequency as brain, liver and endocrine cancers. As is true for many types of cancer, most cases of leukemia occur in older adults. At this time, the only treatment that can cure leukemia is allogeneic stem cell transplantation, which is a high-risk and expensive procedure that is most successful in younger patients. The development of novel and safe curative therapies for leukemia would, therefore, particularly benefit the health of our senior population and the economy of the state of California by realizing savings in the healthcare sector.
- Escape from apoptosis and increased genomic instability resulting from defective DNA repair processes are often associated with cancer development, aging and stem cell defects. Adult stem cells play an essential role in the maintenance of normal tissue. Removal of superfluous, damaged and/or dangerous cells is a critical process to maintain tissue homeostasis and protect against malignancy. Yet much remains to be learned about the mechanisms by which normal stem and progenitor cells respond to environmental and therapeutic genotoxic insults. Here, we have used the hematopoietic system as a model to investigate how cancer-associated mutations affect the behaviors of specific stem and progenitor cell populations. Our work during the first year of the CIRM New Faculty award has revealed the differential use of DNA double-strand break repair pathways in quiescent and proliferative hematopoietic stem cells (HSCs), which has clear implications for human health. Most adult stem cell populations, including HSCs, remain in a largely quiescent (G0), or resting, cell cycle state. This quiescent status is widely considered to be an essential protective mechanism stem cells use to minimize endogenous stress caused by cellular respiration and DNA replication. However, our studies demonstrate that quiescence may also have detrimental and mutagenic effects. We found both quiescent and proliferating HSCs to be similarly protected from DNA damaging genotoxic insults due to the expression and activation of cell type specific protective mechanisms. We demonstrate that both quiescent and proliferating HSCs resolve DNA damage with similar efficiencies but use different repair pathways. Quiescent HSCs preferentially utilize nonhomologous end joining (NHEJ) - an error-prone DNA repair mechanism - while proliferating HSCs essentially use homologous recombination (HR) - a high-fidelity DNA repair mechanism. Furthermore, we show that NHEJ-mediated repair in HSCs is associated with acquisition of genomic rearrangements. These findings suggest that the quiescent status of HSCs can, on one hand, be protective by limiting cell-intrinsic stresses but, on the other hand, be detrimental by forcing HSCs to repair damaged DNA with an error-prone mechanism that can generate mutations and eventually cause hematological malignancies. Our results have broad implications for cancer development and provide the beginning of a molecular understanding of why HSCs, despite being protected, are more likely than other cells in the hematopoietic system (i.e., myeloid progenitors) to become transformed. They also partially explain the loss of function occurring in HSCs with age, as it is likely that over a lifetime HSCs have acquired and accumulated numerous NHEJ-mediated mutations that hinder their cellular performance. Finally, our findings may have direct clinical applications for minimizing secondary cancer development. Many solid tumors and hematological malignancies are currently treated with DNA damaging agents, which may result in therapy-induced myeloid leukemia. Our results suggest that it might be beneficial to induce HSCs to cycle before initiating treatment, to avoid inadvertently mutating the patient's own HSCs by forcing them to undergo DNA repair using an error-prone mutagenic mechanism.
- Our work during the second year of the CIRM New Faculty award has lead to the discovery of at least one key reason why blood-forming stem cells can be susceptible to developing genetic mutations leading to adult leukemia or bone marrow failures. Most adult stem cells, including hematopoietic stem cells (HSCs), are maintained in a quiescent or resting state in vivo. Quiescence is widely considered to be an essential protective mechanism for stem cells that minimizes endogenous stress associated with cellular division and DNA replication. However, we demonstrate that HSC quiescence can also have detrimental effects. We found that HSCs have unique cell-intrinsic mechanisms ensuring their survival in response to ionizing irradiation (IR), which include enhanced pro-survival gene expression and strong activation of a p53-mediated DNA damage response. We show that quiescent and proliferating HSCs are equally radioprotected but use different types of DNA repair mechanisms. We describe how nonhomologous end joining (NHEJ)-mediated DNA repair in quiescent HSCs is associated with acquisition of genomic rearrangements, which can persist in vivo and contribute to hematopoietic abnormalities. These results demonstrate that quiescence is a double-edged sword that, while mostly beneficial, can render HSCs intrinsically vulnerable to mutagenesis following DNA damage. Our findings have important implications for cancer biology. They indicate that quiescent stem cells, either normal or cancerous, are particularly prone to the acquisition of mutations, which overturns the current dogma that cancer development absolutely requires cell proliferation. They help explain why quiescent leukemic stem cells (LSC), which currently survive treatment in most leukemia, do in fact represent a dangerous reservoir for additional mutations that can contribute to disease relapse and/or evolution, and stress the urgent need to develop effective anti-LSC therapies. They also have direct clinical applications for minimizing the risk of therapy-related leukemia following treatment of solid tumors with cytotoxic agents. By showing that proliferating HSCs have significantly decreased mutation rates, with no associated change in radioresistance, they suggest that it would be beneficial to induce HSCs to enter the cycle prior to therapy with DNA-damaging agents in order to enhance DNA repair fidelity in HSCs and thus reduce the risk of leukemia development. While this possibility remains to be tested in the clinic using FDA approved agents such as G-CSF and prostaglandin, it offers exciting new directions for limiting the deleterious side effects of cancer treatment. Our findings also have broad biological implications for tissue function. While the DNA repair mechanism used by quiescent HSCs can indeed produce defective cells, it is likely not detrimental for the organism in evolutionary terms. The blood stem cell system is designed to support the body through its sexually reproductive years, so the genome can be passed along. The ability of quiescent HSCs to survive and quickly undergo DNA repair in response to genotoxic stress supports this goal, and the risk of acquiring enough damaging mutations in these years is minimal. The problem occurs with age, as these long-lived cells have spent a lifetime responding to naturally occurring insults as well as the effects of X-rays, medications and chemotherapies. In this context, the accumulation of NHEJ-mediated DNA misrepair and resultant genomic damages could be a major contributor to the loss of function occurring with age in HSCs, and the development of age-related hematological disorders. We are now using this work on normal HSCs as a platform to understand at the molecular level how the DNA damage response and the mechanisms of DNA repair become deregulated in leukemic HSCs during the development of hematological malignancies.
- Our work during the third year of the CIRM New Faculty award has extended and broaden up our investigations in two novel directions that are still within the scope of our initial Aims: 1) identifying novel stress-response mechanisms that preserve hematopoietic stem cells (HSC) fitness during periods of metabolic stress; and 2) understanding how deregulations in DNA repair mechanisms contribute to the aberrant functions of old and transformed HSCs. Blood development is organized hierarchically, starting with a rare but well-defined population of HSCs that give rise to a series of committed progenitors and mature cells with exclusive functional and immunophenotypic properties. HSCs are the only cells within the hematopoietic system that self-renew for life, whereas other hematopoietic cells are short-lived and committed to the transient production of mature blood cells. Under steady-state conditions, HSCs are a largely quiescent, slowly cycling cell population, which, in response to environmental cues, are capable of dramatic expansion and contraction to ensure proper homeostatic replacement of all blood cells. While considerable work has deciphered the molecular networks controlling HSC activity, still little is known about how these mechanisms are integrated at the cellular level to ensure life-long maintenance of a functional HSC compartment. HSCs reside in hypoxic niches in the bone marrow microenvironment, and are mostly kept quiescent in order to minimize stress and the potential for damage associated with cellular respiration and cell division. Last year, we showed that HSCs can also engage specialized response mechanisms that protect them from the killing effect of environmental stresses such as ionizing radiation (IR) (Mohrin et al., Cell Stem Cell, 2010). We demonstrated that long-lived HSCs, in contrast to short-lived myeloid progenitors, have enhanced expression of pro-survival members of the bcl2 gene family and robust induction of p53-mediated DNA damage response, which ensures their specific survival and repair following IR exposure. We reasoned that HSCs have other unique protective features, which allow them to contend with a variety of cellular insults and damaged cellular components while maintaining their life-long functionality and genomic integrity. Now, we show that HSCs use the self-catabolic process of autophagy as an essential survival mechanism in response to metabolic stress in vitro or nutriment deprivation in vivo. Last year, we also reported that although HSCs largely survive genotoxic stress their DNA repair mechanisms make them intrinsically vulnerable to mutagenesis (Mohrin et al., Cell Stem Cell, 2010). We showed that their unique quiescent cell cycle status restricts them to the use of the error-prone non-homologous end joining (NHEJ) DNA repair mechanism, which renders them susceptible to genomic instability and transformation. These findings provide the beginning of an understanding of why HSCs, despite being protected at the cellular level, are more likely than other hematopoietic cells to initiate blood disorders (Blanpain et al., Cell Stem Cell, review, 2011). Such hematological diseases increase with age and include immunosenescence (a decline in the adaptive immune system) as well as the development of myeloproliferative neoplasms, leukemia, lymphoma and bone marrow failure syndromes. Many of these features of aging have been linked to changes in the biological functions of old HSCs. Gene expression studies and analysis of genetically modified mice have suggested that errors in DNA repair and loss of genomic stability in HSCs are driving forces for aging and cancer development. However, what causes such failures in maintaining HSC functionality over time remains to be established. We therefore asked whether the constant utilization of error-prone NHEJ repair mechanism and resulting misrepair of DNA damage over a lifetime could contribute to the loss of function and susceptibility to transformation observed in old HSCs. Similarly, we started investigating how mutagenic DNA repair could contribute to the genomic instability of HSC-derived leukemic stem cells (LSC).
- Our work during the fourth year of the CIRM New Faculty award has been focused on achieving the goals set forth last year for the two first aims of the grant: 1) identifying the stress-response mechanisms that preserve hematopoietic stem cells (HSC) fitness during periods of metabolic stress; and 2) understanding how deregulations in DNA repair mechanisms contribute to the aberrant functions of old HSCs and the aging of the blood system.
- Blood development is organized hierarchically, starting with a rare but well-defined population of HSCs that give rise to a series of committed progenitors and mature cells with exclusive functional and immunophenotypic properties. HSCs are the only cells within the hematopoietic system that self-renew for life, whereas other hematopoietic cells are short-lived and committed to the transient production of mature blood cells. Under steady-state conditions, HSCs are a largely quiescent, slowly cycling cell population, which, in response to environmental cues, are capable of dramatic expansion and contraction to ensure proper homeostatic replacement of all needed blood cells. While considerable work has deciphered the molecular networks controlling HSC activity, still little is known about how these mechanisms are integrated at the cellular level to ensure life-long maintenance of a functional HSC compartment.
- HSCs reside in hypoxic niches in the bone marrow microenvironment, and are mostly kept quiescent in order to minimize stress and the potential for damage associated with cellular respiration and cell division. Previously, we found that HSCs also have a unique pro-survival wiring of their apoptotic machinery, which contribute to their enhanced resistance to genotoxic stress (Mohrin et al., Cell Stem Cell, 2010). Now, we identified autophagy as an essential mechanism protecting HSCs from metabolic stress (Warr et al., Nature, in press). We show that HSCs, in contrast to their short-lived myeloid progeny, robustly induce autophagy following ex vivo cytokine withdrawal and in vivo caloric restriction. We demonstrate that FoxO3a is critical to maintain a gene expression program that poise HSCs for rapid induction of autophagy upon starvation. Notably, we find that old HSCs retain an intact FoxO3a-driven pro-autophagy gene program, and that ongoing autophagy is needed to mitigate an energy crisis and allow their survival. Our results demonstrate that autophagy is essential for the life-long maintenance of the HSC compartment and for supporting an old, failing blood system.
- Previous studies have also suggested that increased DNA damage could contribute to the functional decline of old HSCs. Therefore, we set up to investigate whether the reliance on the error-prone non-homologous end-joining (NHEJ) DNA repair mechanism we previously identified in young HSCs (Mohrin et al., Cell Stem Cell, 2010) could render old HSCs vulnerable to genomic instability. We confirm that old HSCs have increased numbers of γH2AX DNA foci but find no evidence of associated DNA damage. Instead, we show that γH2AX staining in old HSCs entirely co-localized with nucleolar markers and correlated with a significant decrease in ribosome biogenesis. Moreover, we observe high levels of replication stress in proliferating old HSCs leading to severe functional impairment in condition requiring proliferation expansion such as transplantation assays. Collectively, our results illuminate new features of the aging HSC compartment, which are likely to contribute to several facets of age-related blood defects (Flach et al, manuscript in preparation).
- Our work during the fifth and last year of our CIRM New Faculty award has been essentially focused on understanding how deregulations in DNA repair mechanisms contribute to the aberrant functions of old hematopoietic stem cells (HSC) and the aging of the blood system.
Cancer is the leading cause of death for people younger than 85. High cancer mortality rates related to resistance to therapy and malignant progression underscore the need for more sensitive diagnostic techniques as well as therapies that selectively target cells responsible for cancer propagation. Compelling studies suggest that human cancer stem cells (CSC) arise from aberrantly self-renewing tissue specific stem or progenitor cells and are responsible for cancer propagation and resistance to therapy. Although the majority of cancer therapies eradicate rapidly dividing cells within the tumor, the rare CSC population may be quiescent and then reactivate resulting in disease progression and relapse. We recently demonstrated that CSC are generated in chronic myeloid leukemia by activation of beta-catenin, a gene that allows cells to reproduce themselves extensively. However, relatively little is known about the sequence of events responsible for leukemic transformation in more common myeloproliferative disorders (MPDs) that express an activating mutation in the JAK2 gene. Because human embryonic stem cells (hESC) have robust self-renewal capacity and can provide a potentially limitless source of tissue specific stem and progenitor cells, they represent an ideal model system for generating and characterizing human MPD stem cells. Thus, hESC cell research harbors tremendous potential for developing life-saving therapy for patients with cancer by providing a platform to rapidly and rationally test new therapies that specifically target CSC. To provide a robust model system for screening novel anti-CSC therapies, we propose to generate and characterize BCR-ABL+ and JAK2+ MPD stem cells from hESC. We will investigate the role of genes that are essential for initiation of these MPDs such as BCR-ABL and JAK2 V617F as well as additional mutations in beta-catenin or GSK3betaï€ implicated in CSC propagation. The efficacy of a selective BCR-ABL and JAK2 inhibitors at blocking BCR-ABL+ and JAK2+ human ES cell self-renewal, survival and proliferation alone and in combination with a potent and specific beta-catenin antagonist will be assessed in robust in vitro and in vivo assays with the ultimate aim of developing highly active anti-MPD stem cell therapy that may halt progression to acute leukemia and obviate therapeutic resistance.
Although much is known about the genetic and epigenetic events involved in CSC production in a Philadelphia chromosome positive MPD like chronic myeloid leukemia (CML), comparatively little is known about the molecular pathogenesis of the five-fold more common Philadelphia chromosome negative (Ph-) MPDs. MPD patients have a moderately increased risk of fatal thrombotic events as well as a striking 36-fold increased risk of death from transformation to acute leukemia. Recently, a point mutation, JAK2 V617F(JAK2+), resulting in constitutive activation of the JAK2 cytokine signaling pathway was discovered in a large proportion of MPD patients. A critical barrier to developing potentially curative therapies for both BCR-ABL+ and JAK2+ MPDs is a comprehensive understanding of relative contribution of BCR-ABL and JAK2 V617F to disease initiation versus transformation to acute leukemia. We recently discovered that JAK2 V617F is expressed at the hematopoietic stem cell level in PV, ET and MF and that JAK2 skewed ifferentiation in PV is normalized with a selective JAK2 inhibitor, TG101348. However, a detailed molecular pathogenetic characterization has been hampered by the paucity of stem and progenitor cells in MPD derived blood and marrow samples. Because hESC have robust self-renewal capacity and can provide a potentially limitless source of tissue specific stem and progenitor cells in vitro, they represent an ideal model system for generating human MPD stem cells. Thus, California hESC research harbors tremendus potential for understanding the MPD initiating events that skew differentiation versus events that promote self-renewal and thus, leukemic transformation. Moreover, a more comprehensive understanding of primitive stem cell fate decisions may yield key insights into methods to expand blood cell production that may have major implications for blood banking. Clinical Benefit Generation of MPD stem cells from hESC would provide an experimentally amenable and relevant platform to expedite the development ofsensitive diagnostic techniques to predict disease progression and to develop potentially curative anti-CSC therapies. Economic Benefit The translational research performed in the context of this grant will not only speed the delivery of innovative MPD targeted therapies for Californians, it will help to train Californiaís future R&D workforce in addition to developing leaders in translational medicine. This grant will provide the personnel working on the project with a clear view of the importance of thir research to cancer therapy and a better perspective on future career opportunities in California as well as directly generate revenue through development and implementation of innovative therapies aimed at eradicating MPD stem cells that may be more broadly applicable to CSC in other malignances.
- Summary of Overall Progress
- This grant focuses on generation of MPN stem cells from hESC or CB and correlates leukemic potential with MPN patient samples. In the first year of this grant, we have demonstrated that 1) hESC differentiate on AGM stroma to the CD34+ stage, which is associated with increased GATA-1, Flk2, GATA-2 and ADAR1 expression; 2) hESC CD34+ differentiation is enhanced in vitro and in vivo in the presence of a genetically engineered mouse stroma, which produces human stem cell factor, IL-3 and G-CSF; 3) hESC CD34+ cells can be transduced with our novel lentiviral BCR-ABL vector, which, unlike retroviral BCR-ABL, can transduce quiescent stem cells; 4) BCR-ABL expression by CP CML progenitors does not sustain engraftment but rather leukemic transformation is predicated, in part, on bcl-2 overexpression; 5) JAK2V617F expression in hES or CB stem cells is insufficient to induce leukemic transformation; 6) BCR-ABL transduced hESC CD34+ cells have significantly higher BCR-ABL transplantation potential than CP CML progenitors suggesting that they have higher survival capacity; 7) lentiviral -catenin transduction of BCR-ABL hESC CD34+ cells leads to serial transplantation indicative of LSC formation; 8) CML BC LSC persist in vivo despite potent BCR-ABL inhibition with dasatinib therapy and will likely require combined inhibitor therapy to eradicate. Currently, HEEBO arrays and phospho-flow studies are underway to detect bcl-2 family members and self-renewal protein expression in BCR-ABL and JAK2 V617F transduced hESC and CB CD34+ cells compared with MPN patient derived progenitors. This will aid in development of combined MPN stem cell inhibitor strategies in this grant.
- This grant focuses on generation of myeloproliferative disorder or neoplasm (MPN) stem cells from pluripotent (hESC) or multipotent (CB) stem cells and seeks to correlate their leukemic potential with that of MPN patient sample-derived stem cells. To provide a platform for testing induction of stem cell differentiation, survival and self-renewal by BCR-ABL versus JAK2, hESC were utilized in the first year and as more patient samples and cord blood became available these were utilized.
- In the first year of this grant, we found that hESC undergo hematopoietic differentiation on AGM stroma to the CD34+ stage resulting in increased GATA-1, Flk2, ADAR1 and GATA-2 expression. Moreover, CD34+ differentiation was enhanced on a genetically engineered mouse stroma (SL/M2) secreting human SCF, IL-3 and G-CSF. Lentiviral BCR-ABL transduced hESC-derived CD34+ cells had higher BCR-ABL+ cellular transplantation potential than chronic phase (CP) CML progenitors, indicative of a higher survival capacity. However, they sustained self-renewal only when co-transduced with lentiviral -catenin (Rusert et al, manuscript in preparation) suggesting that blast crisis evolution requires acquisition of both enhanced survival and self-renewal potential. Similarly, lentiviral mouse mutant JAK2 expression in hESC or CB stem cells was insufficient to produce self-renewing MPN stem cells, indicating that the cellular context, nature of the genetic driver and responses to extrinsic cues from the microenvironment play seminal roles in regulating therapeutically resistant MPN stem cell properties such as aberrant survival, differentiation, self-renewal and dormancy.
- In the second year of this five year grant, we have focused on human cord blood (CB) stem cells compared with a large number of MPN patient samples propagated on SL/M2 stroma or in RAG2-/-c-/- mice to more adequately recapitulate the human MPN stem cell niche. Also, to more faithfully recapitulate human (rather than the previously published lentiviral mouse JAK2 vectors, Cancer Cell 2008) JAK2 driven MPNs, we cloned human wild-type JAK2 and human JAK2 V617F from MPN patient samples into lentiviral-GFP vectors (Court Recart A*, Geron I* et al, manuscript in preparation). We also incorporated full transcriptome RNA (ABI SOLiD 4.0) sequencing, PCR array and nanofluidic phosphoproteomics technology to better gauge the impact of JAK2 versus BCR-ABL on stem cell fate, survival, self-renewal and dormancy in the context of specific malignant microenvironments and the relative susceptibility of MPN stem cells in these niches to single agent molecularly targeted inhibitors.
- This grant focuses on generation of myeloproliferative disorder or neoplasm (MPN) stem cells from pluripotent human embryonic stem cells (hESC) or multipotent cord blood (CB) stem cells, and seeks to correlate their leukemic potential with that of disease progression in MPN patient sample-derived stem cells. In the first and second years of this grant, we found that lentiviral BCR-ABL transduced hESC-derived CD34+ cells had higher leukemic transplantation potential than chronic phase (CP) chronic myeloid leukemia (CML) progenitors. However, they sustained self-renewal only when co-transduced with lentiviral beta-catenin suggesting that blast crisis (BC) evolution requires acquisition of both enhanced survival and self-renewal potential. Similarly, we have shown using lentiviral vectors that mouse and human mutant JAK2 were insufficient to produce self-renewing MPN stem cells. New results in Year 3 demonstrate that BCR-ABL and JAK2 activation drive differentiation of hematopoietic progenitors towards an erthyroid/myeloid lineage bias. We have used full transcriptome RNA-Sequencing (RNA-Seq) technology to evaluate the genetic and epigenetic status of BCR-ABL and JAK2-transduced normal progenitor cells as well as patient-derived MPN progenitors. This has allowed us to probe the mechanisms of aberrant differentiation and self-renewal of MPN progenitors and identify unique gene expression signatures of disease progression.
- We previously found that overexpression and splice isoform switching of a key RNA editing enzyme – adenosine deaminase acting on dsRNA (ADAR), and splice isoform changes in pro-survival BCL2 family members, correspond with disease progression in CML. In the current reporting period, RNA-Seq analyses revealed that ADAR1-driven activation of RNA editing contributed to malignant progenitor reprogramming, promoting aberrant differentiation and self-renewal of MPN stem cells. Knocking down ADAR1 using lentiviral shRNA vectors reduced the self-renewal potential of CML progenitors. This work has culminated in a manuscript that has now been submitted to PNAS (Jiang et al.). Recent results also show that ADAR1 is activated in progenitors from patients with JAK2-driven MPNs. Thus, ADAR1 may be an important factor that works in concert with BCR-ABL or JAK2 to facilitate disease progression in MPNs.
- Our results show that another self-renewal factor that may drive BCR-ABL or JAK2-mediated propagation of disease from quiescent MPN progenitors is Sonic hedgehog (Shh). We have examined the expression patterns of this pathway in MPN progenitors using qRT-PCR and RNA-Seq, and have tested a pharmacological inhibitor of this pathway in a robust stromal co-culture model of MPN progression to Acute Myeloid Leukemia (AML).
- In sum, we have utilized full transcriptome RNA-Seq and qRT-PCR coupled with hematopoietic progenitor assays and in vivo studies to evaluate the impact of JAK2 versus BCR-ABL on stem cell fate, survival, self-renewal and dormancy. These techniques have allowed us to investigate in more detail the role of genetic and epigenetic alterations that drive disease progression in the context of specific malignant microenvironments, and the relative susceptibility of MPN stem cells in these niches to single agent molecularly targeted inhibitors.
- The main objectives of this project are generation of myeloproliferative disorder or neoplasm (MPN) stem cells from pluripotent human embryonic stem cells (hESC) or multipotent stem cells, and identification of crucial leukemia stem cell (LSC) survival and self-renewal factors that contribute to the development and progression of BCR-ABL and JAK2-driven hematopoietic disorders. A key finding of our work thus far is that in addition to activation of BCR-ABL or JAK2 oncogenes, generation of self-renewing MPN LSC requires stimulation of other pro-survival and self-renewal factors such as β-catenin, Sonic hedgehog (SHH), BCL2, and in particular the RNA editing enzyme ADAR1, which we identified as a novel regulator of LSC differentiation and self-renewal.
- We have now completed comprehensive gene expression analyses from next-generation RNA-sequencing studies performed on normal and leukemic human hematopoietic progenitor cells from primary cord blood samples and adult normal peripheral blood samples, along with normal cord blood transduced with BCR-ABL or JAK2 oncogenes, and primary samples from patients with BCR-ABL+ chronic phase and blast crisis chronic myeloid leukemia (CML). These studies revealed that gene expression patterns in survival and self-renewal pathways (SHH, JAK2, ADAR1) clearly distinguish normal and leukemic progenitor cells as well as MPN disease stages. These data provide a vast resource for identification of LSC-specific biomarkers with diagnostic and prognostic clinical applications, as well as providing new potential therapeutic targets to prevent disease progression.
- New results from RNA-sequencing studies reveal high levels of expression of inflammatory mediators in human blast crisis CML progenitors and in BCR-ABL transduced normal cord blood stem cells. Moreover, expression of the inflammation-responsive form of ADAR1 correlated with generation of an abnormally spliced GSK3β gene product that has been previously linked to LSC self-renewal. These results have now been published in the journal PNAS (Jiang et al.). Together, we have demonstrated that ADAR1 drives hematopoietic cell fate by skewing cell differentiation – a trend which occurs during normal bone marrow aging – and promotes LSC self-renewal through alternative splicing of critical survival and self-renewal factors. Notably, inhibition of ADAR1 through genetic knockdown strategies reduced self-renewal capacity of CML LSC, and may have important applications in treatment of other disorders that transform to acute leukemia. Thus, these results suggest that RNA editing (ADAR1) and splicing represent key therapeutic targets for preventing LSC self-renewal – a primary driver of leukemic progression.
- Whole transcriptome profiling studies coupled with qRT-PCR, hematopoietic progenitor assays and in vivo studies have shown that combined inhibition of BCR-ABL and JAK2 is another effective method to reduce LSC self-renewal in pre-clinical models. New results show that lentivirus-enforced BCR-ABL or JAK2 expression in normal cord blood stem cells drives generation of distinct splice isoforms of STAT5a. While inhibition of JAK2/STAT5a signaling or BCR-ABL tyrosine kinase activity alone did not eradicate self-renewing LSC, combined JAK2 and BCR-ABL inhibition dramatically impaired LSC survival and self-renewal in the protective bone marrow niche, and increased the lifespan of serial transplant recipients. These effects were associated with reduction in STAT5a isoform expression – which represents a novel molecular marker of response to combined BCR-ABL/JAK2 inhibition – and altered expression of cell cycle genes in human progenitor cells harvested from the bone marrow of transplanted mice. These results are the subject of a new manuscript currently under review (Court et al.). Moreover, this work has led to the development of new experimental tools that will facilitate study of LSC maintenance and cell cycle status in the context of normal versus diseased bone marrow microenvironments. In sum, studies completed thus far have uncovered a role for RNA editing and splicing alterations in leukemic progression, particularly in specific microenvironments. Using specific inhibitors targeting BCR-ABL and JAK2, along with strategies to block RNA editing and aberrant splicing activities, we have been able to establish the relative susceptibility of MPN stem cells to molecular inhibitors with activity against LSC residing in select hematopoietic niches that are difficult to treat with conventional chemotherapeutic agents.
- In the final year of this project, we focused on elucidating the mechanisms of leukemia stem cell (LSC) generation in JAK2 compared with BCR-ABL1 initiated myeloproliferative neoplasms (MPN, previously called myeloproliferative disorders). To this end, we investigated the MPN stem cell propagating effects of BCR-ABL1 or JAK2 alone or in combination with activation of the human embryonic stem cell RNA editase, ADAR1. Recently, we discovered that ADAR1, which edits adenosine to inosine bases in the context of primate specific Alu sequences, leads to GSK3β missplicing and β-catenin activation in chronic phase (CP) CML progenitors leading to blast crisis (BC) transformation and LSC generation. In addition, variant isoform expression of a Wnt/β-catenin target gene, CD44, was also characteristic of LSC. In a previous report (Jiang et al., PNAS 2013), identification of ADAR1 as a malignant reprogramming factor represented the first description of RNA editing as a regulator of reprogramming. When lentivirally overexpressed, ADAR1 endows committed CP myeloid progenitors with self-renewal capacity. Further studies revealed that JAK2/STAT5a activates ADAR1 leading to deregulation of cell cycle progression and global down-regulation of microRNA expression thereby uncovering two additional key mechanisms of LSC generation in MPNs. This is consistent with our findings from gene expression profiling studies performed in the previous year, along with functional classification and network analysis using Ingenuity Pathway Analysis (IPA), showing that cell cycle-related genes were significantly altered in human progenitors from xenografted mice treated with combination JAK2 and BCR-ABL inhibitor therapy compared with single agent therapies alone. Together these data suggest that combined BCR-ABL and JAK2 inhibition impairs LSC survival and self-renewal via cell cycle modulation. ADAR1 and other stem cell regulatory pathways such as CD44 represent novel targets to detect and eradicate the self-renewing LSC. We also performed new studies that elucidate the stem cell-intrinsic genetic changes that occur during human bone marrow aging, which may contribute to BCR-ABL or JAK2-dependent functional alterations.
- This work has led to discovery of a novel role for embryonic stem cell genes and splice isoforms, including ADAR1 p150 and a transcript variant of CD44, in the maintenance of LSC that promote MPN progression. In addition, through the course of this research we have 1) developed novel lentiviral tools for investigating normal hematopoietic stem and progenitor (HSPC) and malignant LSC survival, differentiation, self-renewal, and cell cycle regulation, and 2) devised innovative LSC diagnostic strategies and 3) tested therapeutic strategies targeting LSC-associated RNA editing and splice isoform generation that selectively inhibit LSC self-renewal.
Lung cancer is the most deadly cancer worldwide and accounts for more deaths than prostate cancer, breast cancer and colon cancer combined. Non small cell lung cancer (NSCLC) accounts for about 85% of all lung cancers. The current 5-year survival rate for all stages of NSCLC is only 15%. Although early stage lung cancer has a much better survival rate. Current therapeutic strategies of chemotherapy, radiation therapy and trials with new targeted therapies have only demonstrated, at best, extension in survival by a few months. Clearly, a novel approach is required to develop new therapies for this devastating disease and to detect the disease at an early stage. Cancer stem cells have been identified as the initial cell in the formation of carcinomas. Chemotherapy, radiation and even targeted therapies are all designed to eliminate dividing cells. However, cancer stem cells “hide out” in the quiescent phase of growth. This provides an explanation as to why our cancer therapies may produce an initial response but are often unsuccessful in curing patients. Lung cancer develops through a series of step wise changes that result in the progression of pre-malignant lesions to invasive lung cancer. The mechanisms of how lung cancer develops are not known and if we can prevent the formation of pre-malignant lesions, we will likely be able to prevent lung cancer. We have discovered a subpopulation of stem cells that circulates in the blood and is essential for normal lung repair. Blocking these cells from entering the lung results in a pre-malignant condition in the lungs. We have also identified a subpopulation of stem cells in the lung that is responsible for generating pre-malignant lung cancer lesions. We hypothesize that the interaction between the stem cells in the blood and the stem cells in the lung are critical to prevent lung cancer. We plan to use cutting edge technologies to characterize these different stem cell populations in the lung, and determine how they form pre-malignant lung cancer lesions. We also plan to use preclinical models to try to prevent lung cancer by giving additional stem cells derived from the blood as a therapy. Lastly, we plan to determine whether levels of stem cells in the blood in patients may be used as a blood test to measure the chance of recurrence of lung cancer after therapy. The long term goals of our work are to develop a screening test for lung cancer stem cells that can predict which patients are at high risk for developing lung cancer in order to diagnose lung cancer at an early stage, and to potentially develop a new stem cell based therapy for preventing and treating lung cancer.
According to the Center for Health Statistics, California Department of Health Services, 13,427 people died of lung cancer in the state of California in 2005. This is more than the deaths attributed to breast, prostate and colon cancers combined. The devastating effects of this disease on the citizens of California and the health care costs involved are enormous. Most cases of lung cancer occur in smokers, but non smokers, people exposed to second hand smoke and ex-smokers are also at risk. In addition, of special concern to California residents, is that exposure to air pollution is associated with an increased risk of lung cancer. Current therapeutic strategies for lung cancer are in general only able to prolong survival by a few months, especially for late stage disease. One reason for this may be that the cancer initiating stem cell is resistant to these therapies. Understanding the stem cell populations involved in repair of the lung and how these cells may give rise to lung cancer is important for potentially generating new therapeutic targets for lung cancer. We propose to study the stem cell populations of the lung that are crucial for normal airway repair and characterize the putative cancer initiating stem cell in the lung. We have also found stem cells in the blood that are critical for normal airway repair and we plan to test their role in the prevention of premalignant lung cancer lesions. We also plan to test whether levels of these stem cells in the blood may be used as a biomarker of lung cancer. Ultimately, the ability to perform a screening test to detect lung cancer at an early stage, and the development of new therapies for lung cancer will be of major benefit to the citizens of California.
- We identified a putative tumor-initiating stem/progenitor cell that goes rise to smoking-associated non small cell lung cancer (NSCLC). We examined 399 NSCLC samples for this tumor-initiating stem/progenitor cell and found that the presence of this cell in the tumor gave rise to a significantly worse prognosis and was associated with metastatic disease. This stem/progenitor cell is known to be important for repair of the airway and is present in precancerous lesions. We believe that this cell undergoes aberrant repair after smoking injury, which leads to lung cancer. We are currently trying to identify the genetic and epigenetic mechanisms involved in this aberrant repair as a means to identify a novel therapy to prevent the development of lung cancer. The presence of these stem/progenitor cells may also be used as a biomarker of poor prognostic NSCLC even in early stage disease.
- We have identified markers on these stem/progenitor tumor-initiating cells and identified sub-populations of these cells. We are now determining the stem cell capabilities of each of these sub-populations. We are using a model of the development of lung cancer to determine if giving a stem/progenitor cell sub-population for repair can prevent NSCLC from developing.
- We examined the blood of patients diagnosed with a lung nodule for circulating epithelial stem/progenitor cells. We found that the presence of these cells in the blood of patients predicted the presence of a subtype of NSCLC as compared to a benign lung nodule. We are currently obtaining many more blood samples from patients to further determine whether circulating epithelial stem/progenitor cells could be used as a biomarker of early NSCLC.
- We have found a stem cell that is important for lung repair after injury that is located in a protected niche in the airway. After repeated injury, for example in smokers, these stem cells persist in an abnormal location on the surface of the airway and replicate and form precancerous areas in the lung. The presence of these stem cells in lung cancer tumors was associated with a poor prognosis with an increased chance of relapse and metastasis.This was especially true in current and former smokers. We therefore believe we have found a putative stem cell that is a tumor initiating cell for lung cancer. We developed a method to isolate these lung stem cells and to profile these cells and developed in vitro and in vivo models to assess their stem cell properties. Finally, we examined human blood samples to assess levels of surrogate markers of these stem cells to assess whether we could use this as a biomarker to predict the presence or absence of lung cancer in patients with a lung nodule.
- We found a stem cell that is important for lung repair after injury that we believe may form precancerous areas in the lung. We are characterizing these stem cells and identifying pathways involved in normal repair and aberrant repair that leads to lung cancer. We are also isolating this stem cell population and other cell populations from the airway and inducing genetic changes to determine the tumor initiating cell/s for lung cancer. We are also examining the effect the environment may have on the regulation of genes in these stem cells, in precancerous areas and in lung cancers. Finally, we are examining human blood samples to assess levels of surrogate markers of these stem cells to assess whether we could use this as a biomarker to predict the presence or absence of lung cancer in patients with a lung nodule.
- During this period of funding we discovered a method to reproducibly recover stem cells from human airways and grow them in a dish into mature airway cells. We also discovered the role that certain metabolic cell processes play in regulating the repair after airway injury. We believe that an inability to shut off these processes leads to abnormal repair and lung cancer and are actively investigating this. We are also determining whether the stem cells we isolate from the airways are the stem cells for lung cancer and how they might give rise to lung cancer.
- In the last year of funding we identified a novel mechanism that tightly controls airway stem cell proliferation for repair after injury. We found that perturbing this pathway results in precancerous lesions that can ultimately lead to lung cancer. Correcting the abnormalities in this pathway that are seen in smokers could allow the development of targeted chemoprevention strategies to prevent the development of precancerous lesions and therefore lung cancer in at risk populations. We also continued our work on trying to identify a cell of origin for squamous lung cancer and identifying the critical drive mutations that are required for squamous lung cancer to develop.
- During this reporting period we discovered and published on how reactive oxygen species drive proliferation of airway basal stem cells. We found that this pathway is critical for homeostasis of the airway epithelium and perturbing this pathway results in precancerous lesions. Interestingly, these precancerous lesions are able to resolve over time, which is similar to the situation in smokers who develop precancerous lesions that almost always resolve. We now have a model to study the driver mutations that take precancerous lesions to invasive squamous lung cancer and with this model we can start to identify novel therapies to prevent the development of precancerous lesions and/or progression of precancerous lesions. We also developed a model of precancerous lesions in a dish which allows us to screen for compounds that promote or resolve these premalignant lesions. Our overall goal is to use these models to develop a targeted chemoprevention strategy for squamous lung cancer.
This proposal will define the biology of stem cell engineering to produce a cancer-fighting immune system. The immune system protects our body against most outside threats. However, it frequently fails to protect us from cancer. The T cell receptor (or TCR), a complex protein on the surface of an immune cell (or lymphocyte), allows to specifically recognize cancer cells. The TCR functions like a steering wheel for lymphocytes, allowing them to travel around the body and specifically find and attack cancercells. The goal of this research is to put TCR genes into stem cells to generate a renewable source of cancer-fighting lymphocytes. The studies in mice provide compelling evidence that inserting TCR genes into stem cells has several advantages for the progeny lymphocytes, allowing them to better fight cancer. The next step is to bring this approach to patients with cancer. The main reason is that the TCR genes inserted into stem cells allow the generation of a larger army of TCR re-directed cancer-fighting killer lymphocytes. I have dedicated most of my prior work to make the transition from studies in mice to the bedside. I have gaind the expertise to conduct clinical trials using cells as targeted drugs from patients. This experience has allowed me to design and start working on the clinical trials that will test the concept of inserting TCR genes into progenitors of lymphocytes and give them to patients. With my collaborators at other institutions, we have raised the adequate resources from private foundations and the NIH to initiate clinical trials inserting TCR genes into lymphocytes. I request additional funds from CIRM to allow me to extract the most information from the clinical trials and then help take them one step further by ultimately testing the use of hematopoietic stem cells (HSC) and induced pluripotent cells (iPS) to engineer a cancer-fighting immune system. There are several challenges tha need to be addressed, including what is the best approach to generate both immediate and long-term cancer fighting cells, what are the optimal stem cells to target, and how they should be manipulated and given to patients in the clinic. The study of samples obtained from patients participating in pilot clinical trials will provide information how to design new clinical trials using the method of inserting the cancer-specific TCR genes into stem cells. The experience of regenerating a cancer-fighting immune system in humans could then be applied to multiple cancer types and to infectious diseases that currently lack good treatment options.
Preclinical studies have validated the concept that the immune system can be harnessed to fight cancer. However, clinical testing has failed short of expectations. I propose to genetically program the immune system starting from stem cells with the hope of advancing cancer immunotherapy. Malignant melanoma will be the cancer for the initial testing of this approach. Melanoma has a track record of being “immune-sensitive” and there are well-defined antigens against which the immune system can be targeted. Melanoma is the cancer with the fastest rising incidence in the U.S. This disease impacts heavily in our society, since it strikes adults at the prime years of life (30-60 years old). In fact, melanoma is the second cancer cause of lost of productive years given its incidence early in life and its high mortality once it becomes metastatic. The problem is particularly worrisome in areas of the world like California, with large populations of persons originally from other latitudes with much lower sun exposure and with skin types unable to handle the increased exposure to ultraviolet (UV) light in California. Although most frequent in young urban Caucasians, melanoma also strikes other ethnicities. The incidence of acral melanoma (non-UV light induced melanoma that develops in the palms and soles) has also steadily increased in Hispanics and Blacks over the past decades. Early melanoma can be cured with surgery. Therefore, programs aimed at early detection have the highest impact in this disease. Once it becomes metastatic, melanoma has no curative standard therapy. Despite this grim outlook, it has been long known that occasional patients participating in experimental immunotherapy protocols have long remissions and are seemingly cured. This proposal aims at incorporating the most current knowledge arising from preclinical research and prior clinical experimentation of immunotherapy strategies to engineer the immune system genetically to better fight metastatic melanoma. Bringing new science from the laboratory to the bedside requires well-designed, well-organized and informative clinical trials. It is not enough to show some responses, we need to understand how they develop and why some patients respond and other do not. Therefore, the analysis of stem cell-based immune system engineering within clinical trials proposed herein requires thorough analysis of patient-derived samples to inform the follow-up clinical testing. Information resulting from the genetic engineering of the immune system in patients with melanoma will help develop studies to direct the immune system to fight other cancers and infectious diseases like HIV. Once optimized, I envision the ability to clone T cell receptor (TCR) genes specific for tumor or infectious disease antigens expressed by different cancers or infectious agents, and use these TCRs to genetically program the patient’s immune system to attack them.
- The awarded grant supports a patient-oriented research project to genetically engineer the human immune system to become cancer-targeted and provide benefit to patients with metastatic melanoma, a deadly form of skin cancer currently devoid of successful treatment options.
- During the first funding period we initiated a clinical trial where patients with metastatic melanoma receive immune cells that have been re-directed by gene engineering techniques to become melanoma-specific. The immune cells are obtained from the patient’s own blood and they are manipulated in an in-house clinical grade facility for one week to insert into the cells two genes (T cell receptor or TCR genes) that turn them specific melanoma killer cells, called the. The genetic reprogramming of the immune system cells to express TCR genes is done using a crippled virus called a gene transfer vector. These cells undergo extensive testing to meet the standards of the Food and Drug Administration (FDA) before they can be given back to patients.
- We give back the TCR re-directed immune cells to patients after receiving a chemotherapy preparative regimen to partially deplete their own immune system so the new cells have the ability to expand. In addition, the patients receive a treatment called high dose interleukin-2 (IL-2) to further allow these cells to expand. Furthermore, these patients receive three doses of dendritic cell vaccines, also generated from the patient’s own blood cells, which further helps the TCR re-directed immune cells to attack the melanoma lesions.
- Seven patients have been enrolled onto this study at this time. Two patients are too early to evaluate and in the other patients we have early encouraging evidence of antitumor activity. We are conducting studies to determine how these cells behave in the patients by analyzing if they acquire ability to persist long term, what we call T memory stem cells. These are ongoing studies that will continue to the next funding period.
- Finally, we have initiated the work to set up a follow up clinical trial where we will genetically modify patient’s blood stem cells, which we hypothesize will allow the continuous generation of TCR re-directed immune cells starting from the stem cells. This would provide means for immune system regeneration that would have applications to other cancers and non-cancer diseases like infectious diseases and autoimmune diseases. To this end, a new gene transfer vector has initiated clinical grade production to allow us to use it in the proposed next generation clinical trial.
- The awarded grant supports a patient-oriented research project to genetically engineer the human immune system to become cancer-targeted and provide benefit to patients with metastatic melanoma, a deadly form of skin cancer currently devoid of successful treatment options.
- During the second funding period we continued to conduct a clinical trial where patients with metastatic melanoma receive immune cells that have been re-directed by gene engineering techniques to become melanoma-specific. The immune cells are obtained from the patient’s own blood and they are manipulated in an in-house clinical grade facility for one week to insert into the cells two genes (T cell receptor or TCR genes) that turn them specific melanoma killer cells, called the. The genetic reprogramming of the immune system cells to express TCR genes is done using a crippled virus called a gene transfer vector. These cells undergo extensive testing to meet the standards of the Food and Drug Administration (FDA) before they can be given back to patients.
- Ten patients have been enrolled onto this study at this time. In nine of them there has been evidence of tumor shrinkage, demonstrating the strong therapeutic activity of TCR redirected lymphocytes. However, these have been transient beneficial effects. Our ongoing studies point to a loss of function of the TCR transgenic cells over time. Therefore, it is of key importance to develop means to optimize the presence of long lasting memory cells. As proposed in the initial grant we are conducting studies to characterize the presence of T memory stem cells, which are cells able to self-replicate and maintain a cancer-fighting immune system for long periods of time. These are ongoing studies that will continue to the next funding period.
- In addition, we have put a lot of work to set up a follow up clinical trial where we will genetically modify patient’s blood stem cells, which we hypothesize will allow the continuous generation of TCR re-directed immune cells starting from the stem cells. This would provide means for immune system regeneration that would have applications to other cancers and non-cancer diseases like infectious diseases and autoimmune diseases. To this end, we have generated new gene transfer vectors that are being studied for optimal function in relevant animal models to then allow an informed decision on the vector to take for clinical grade production and use it in the proposed next generation clinical trial.
- The awarded grant supports patient-oriented research with the ultimate goal of reconstituting a cancer-fighting immune system. The research is conducted in samples obtained from patients with metastatic melanoma, a deadly form of skin cancer, and using preclinical models.
- During the third funding period we have introduced modifications to enhance the ability of immune cell long term persistence within a clinical trial where patients with metastatic melanoma receive immune cells that have been re-directed by gene engineering techniques to become cancer-fighter cells. The immune cells are obtained from the patient’s own blood and they are manipulated in an in-house clinical grade facility for one week to insert into the cells two genes (T cell receptor or TCR genes) that turn them specific melanoma killer cells. The genetic reprogramming of the immune system cells to express TCR genes is done using a crippled virus called a gene transfer vector. These cells undergo extensive testing to meet the standards of the Food and Drug Administration (FDA) before they can be given back to patients.
- When using a higher number of the TCR genetically engineered lymphocytes that are not frozen before their infusion to patients we are now detecting a higher ability of these cancer-fighting immune system cells to persist for long periods of time. This may be because the protocol modifications were guided to foster a higher ability to generate immune system cells that have long term memory and ability to self-renew (termed T memory stem cells). The detection of these cells is one of the research projects in this grant, since there is no defined set of markers for them. We have been testing several strategies to detect these cells and these are ongoing studies that will continue to the next funding period.
- In addition, we have continued to move forward to set up a follow up clinical trial where we will genetically modify patient’s blood stem cells, which we hypothesize will allow the continuous generation of TCR re-directed immune cells starting from the stem cells. This would provide means for immune system regeneration that would have applications to other cancers and non-cancer diseases like infectious diseases and autoimmune diseases. To this end, we have tested the performance of two candidate gene transfer vectors for optimal function in humanized animal models. The results of these studies have demonstrated that one of the vectors is better suited for continued testing and it is the one that we plan to take into clinical grade production with the pre-IND activities being completed during the next funding period.
- This grant proposed the conduct of pre-clinical work to support the use of stem cells to regenerate a cancer-fighting immune system in mice and humans, and bedside-to-bench work to analyze populations of cells with potential ability to function as long term repopulating T lymphocytes obtained from patients treated within a phase 1 clinical trial. During this past year we have made progress to continue our study the biology of T cells with characteristics of long term memory immune cells, termed T memory stem cells (TMSC). We have recently studied the ability to use specific small molecule targeted inhibitors to increase the fraction of mature T cells with TMSC characgteristics, which will improve our ability to characterize them. We have also advanced our studies to test the transplantation of hematopoietic stem cells (HSC) genetically engineered to express T cell receptors (TCR) and provide a continuous progeny of TCR transgenic mature T cells in humanized mouse models. This work provides the rationale to allow us advancing our plans to conduct a clinical trial based on the transplantation of HSC genetically engineered to express TCR to regenerate a cancer-fighting immune system. We have successfully competed for a CIRM disease team award and have gone through a pre-IND meeting with the FDA to adequately plan for such a clinical trial to be started in approximately two years.
- We have continued to make progress to reach the proposed goals of this grant:
- We have further characterized immune cells that naturally express three transcription factors that transform normal cells into pluripotent stem cells. We are interested in determining if these immune cells with pluripotency transcription factors are long term memory cells able to maintain immune responses.
- In parallel, we have continued to advance our studies to bring a new approach to the clinic based on the genetic modification of blood stem cells to regenerate a cancer-fighting immune system. In the past year we have discussed our plans with the Food and Drug Administration and we have proceeded to follow their recommendations on what needs to be provided to open such a clinical trial. This clinical trial will be further developed within a newly approved CIRM disease team grant.
The therapeutic use of stem cells depends on the availability of pluripotent cells that are not limited by technical, ethical or immunological considerations. The goal of this proposal is to develop and bank safe and well-characterized patient-specific pluripotent stem cell lines that can be used to study and potentially ameliorate human diseases. Several groups, including ours have recently shown that adult skin cells can be reprogrammed in the laboratory to create new cells that behave like embryonic stem cells. These new cells, known as induced pluripotent stem (iPS) cells should have the potential to develop into any cell type or tissue type in the body. Importantly, the generation of these cells does not require human embryos or human eggs. Since these cells can be derived directly from patients, they will be genetically identical to the patient, and cannot be rejected by the immune system. This concept opens the door to the generation of patient-specific stem cell lines with unlimited differentiation potential. While the current iPS cell technology enables us now to generate patient-specific stem cells, this technology has not yet been applied to derive disease-specific human stem cell lines for laboratory study. Importantly, these new cells are also not yet suitable for use in transplantation medicine. For example, the current method to make these cells uses retroviruses and genes that could generate tumors or other undesirable mutations in cells derived from iPS cells. Thus, in this proposal, we aim to improve the iPS cell reprogramming method, to make these cells safer for future use in transplant medicine. We will also generate a large number of iPS lines of different genetic or disease backgrounds, to allow us to characterize these cells for function and as targets to study new therapeutic approaches for various diseases. Lastly, we will establish protocols that would allow the preparation of these types of cells for clinical use by physicians investigating new stem cell-based therapies in a wide variety of diseases.
Several groups, including ours have recently shown that adult skin cells can be reprogrammed in the laboratory to create new cells that behave like embryonic stem cells. These new cells, known as induced pluripotent stem (iPS) cells should have, similar to embryonic stem cells, the potential to develop into any cell type or tissue type in the body. This new technology holds great promise for patient-specific stem-cell based therapies, the production of in vitro models for human disease, and is thought to provide the opportunity to perform experiments in human cells that were not previously possible, such as screening for compounds that inhibit or reverse disease progression. The advantage of using iPS cells for transplantation medicine would be that the patient’s own cells would be reprogrammed to an embryonic stem cell state and therefore, when transplanted back into the patient, the cells would not be attacked and destroyed by the body's immune system. Importantly, these new cells are not yet suitable for use in transplantation medicine or studies of human diseases, as their derivation results in permanent genetic changes, and their differentiation potential has not been fully studied. The goal of this proposal is to develop and bank genetically unmodified and well-characterized iPS cell lines of different genetic or disease backgrounds that can be used to characterize these cells for function and as targets to study new therapeutic approaches for various human diseases. We will establish protocols that would allow the preparation of these types of cells for clinical use by physicians investigating new stem cell-based therapies in a wide variety of diseases. Taken together, this would be beneficial to the people of California as tens of millions of Americans suffer from diseases and injuries that could benefit from such research. Californians will also benefit greatly as these studies should speed the transition of iPS cells to clinical use, allowing faster development of stem cell-based therapies.
- The goal of this project is to develop and bank safe, well-characterized pluripotent stem cell lines that can be used to study and potentially ameliorate human diseases, and that are not limited by technical, ethical or immunological considerations. To that end, we proposed to establish protocols for generation of human induced pluripotent stem cells (hiPSC) that would not involve viral vector integration, and that would be compatible with Good Manufacturing Processes (GMP) standards. To establish baseline characteristics of hiPSCs, we performed a complete molecular characterization of all existing hiPSCs in comparison to human embryonic stem cells (hESCs). We found that all hiPSC lines created to date, regardless of the method by which they were reprogrammed, shared a common gene expression signature, distinct from that of hESCs. The functional role of this gene expression signature is still unclear, but any lines that are generated under the guise of this grant will be subjected to a similar analysis to set the framework by which these new lines are functionally characterized. Our efforts to develop new strategies for the production of safe iPS cells have yielded many new cell lines generated by various techniques, all of which are safer than the standard retroviral protocol. We are currently expanding many of the hiPSCs lines generated and will soon demonstrate whether their gene expression profile, differentiation capability, and genomic stability make them suitable for banking in our iPSC core facility. Once fully characterized, these cells will be available from our bank for other investigators.
- For hiPSC technology to be useful clinically, the procedures to derive these cells must be robust enough that iPSC can be obtained from the majority of donors. To determine the versatility of generation of iPS cells, we have now derived hiPSCs from commercially obtained fibroblasts derived from people of different ages (newborn through 66 years old) as well as from different races (Caucasian and mixed race). We are currently evaluating medium preparations that will be suitable for GMP-level use. Future work will ascertain the best current system for obtaining hiPSC, and establish GMP-compliant methodologies.
- The goal of this project is to develop and bank safe, well-characterized pluripotent stem cell lines that can be used to study and potentially ameliorate human diseases. To speed this process, we are taking approaches that are not limited by technical, ethical or immunological considerations. We are establishing protocols for generation of human induced pluripotent stem cells (hiPSCs) that would not involve viral vector integration, and that are compatible with Good Manufacturing Practices (GMP) standards. Our efforts to develop new strategies for the production of safe hiPSC have yielded many new cell lines generated by various techniques. We are characterizing these lines molecularly, and have found hiPSCs can be made that are nearly indistinguishable from human embryonic stem cells (hESC). We have also recently found in all the hiPSCs generated from female fibroblasts, none reactivated the X chromosome. This finding has opened a new frontier in the study and potential treatment of X-linked diseases. We are currently optimizing protocols to generate hiPSC lines that are derived, reprogrammed and differentiated in the absence of animal cell products, and preparing detailed standard operating procedures that will ready this technology for clinical utility.
- This project was designed to generate protocols whereby human induced pluripotent stem cells could be generated in a manner consistent with use in clinical trials. This required optimization of protocols and generation of standard operating procedures such that animal products were not involved in generation and growth of the cells. We have successfully identified such a protocol as a resource to facilitate widespread adoption of these practices.
Human embryonic stem cells (hESCs) are capable of unlimited self-renewal, a process to reproduce self, and retain the ability to differentiate into all cell types in the body. Therefore, hESCs hold great promise for human cell and tissue replacement therapy. Because DNA damage occurs during normal cellular proliferation and can cause DNA mutations leading to genetic instability, it is critical to elucidate the mechanisms that maintain genetic stability during self-renewal. This is the overall goal of this proposal. Based on our recent findings, I propose to investigate two major mechanisms that might be important to maintain genetic stability in hESCs. First, I propose to elucidate pathways that promote efficient DNA repair in hESCs. Second, based on our recent findings, I hypothesize that another primary mechanism to maintain genetic stability in self-renewing hESCs is to eliminate DNA-damaged hESCs by inducing their differentiation. Therefore, I propose to identify the pathways that regulate the self-renewing capability of hESCs in the presence and absence of DNA damage. In summary, the proposed research will contribute significantly to our understanding of the pathways important to maintain self-renewal and genetic stability in hESCs. This information will provide the foundation to improve the culturing condition of hESCs to promote efficient self-renewal with minimum genetic instability, a prerequisite for the development of hESCs into human therapeutics.
One major objective of the proposed research is to improve the genetic manipulation technologies in hESCs, including transgenic and gene targeting technologies. While mouse models are valuable tools to study the mechanisms of the pathogenesis in human diseases, many differences between mouse and human cells can lead to distinct phenotypes as well as the common phenomenon that certain therapeutic interventions work well in mouse models but poorly in humans. Therefore, it is of high priority to create disease-specific hESCs as powerful genetic tools to study the mechanism of the pathogenesis in human diseases. In addition, the unlimited supply of primary cells derived from the disease-specific hESCs will become valuable reagents for drug discovery. There are two ways to generate the disease-specific hESCs. One approach is through nuclear transfer that has been proven extremely difficult in human context and so far unsuccessful. The other is to employ the transgenic and gene targeting techniques to create disease-specific hESCs. Therefore, the proposed research will significantly improve our capability to generate disease-specific hESCs. After experimenting with various existing hESC lines, we found that only the non-federally-approved hESC lines developed recently at Harvard University is most suitable for genetic manipulation technologies. Since the research involving the HUES lines can not be supported by federal government, CIRM is in a unique position to support this proposed research.
Human embryonic stem cells (hESCs) are capable of unlimited self-renewal, a process to reproduce self, and retain the ability to differentiate into all cell types in the body. Therefore, hESCs hold great promise for human cell and tissue replacement therapy. The major goal of the human stem cell research supported by proposition 71 is to improve and even realize the therapeutic potential of hESCs. DNA damage occurs during normal cellular proliferation of hESCs and can cause genetic mutations that will be passaged to derivatives. Any cells with genetic mutations are not suitable for therapeutic purpose since they can cause cancers in the recipient. Therefore, to achieve the therapeutic potential of hESCs, it is critical to elucidate the mechanisms that prevent genetic mutations during the self-renewal of hESCs. This is the overall goal of this proposal. Successful completion of the proposed research will help to optimize the culturing conditions that promotes efficient self-renewal with minimum genetic instability.
One high-priority area of hESC research is to create disease-specific hESCs, which can be used as powerful genetic tools to study the mechanism of the pathogenesis in human diseases. In addition, the unlimited supply of primary cells derived from the disease-specific hESCs will become valuable reagents for drug discovery. There are two ways to generate the disease-specific hESCs. One approach is through nuclear transfer that has been proven extremely difficult in human context and so far unsuccessful. The other is to develop the transgenic and gene targeting techniques to create disease-specific hESCs. One major objective of my proposed research is to improve the genetic manipulation technologies in hESCs, including transgenic and gene targeting technologies. The successful completion of the proposed research will significantly improve our capability to generate disease-specific hESCs. In addition, the disease-specific hESCs (ATM-/- and p53-/- hESCs) generated in the course of the proposed studies are valuable tools to study the basis of neuronal degeneration in Ataxia-telangiectsia and development of human epithelial tumors as a result of p53-deficiency. Both of these phenotypes are not observed in mouse models.
In summary, the proposed research will benefit California citizens by contributing to the eventual realization of the therapeutic potential of hESCs.
- The goal of this proposal is to investigate the mechanisms that maintain the genomic stability of human ES cells (hESCs). We are focusing on the tumor suppression pathways ATM and p53, which are well established guardians of the genome in differentiated cells. In addition, we are investigating the pathways that govern the self-renewal of hESCs, which might be coordinated with DNA damage responses to maintain the genomic stability in hESCs. During the reporting period, we made significant progress towards our goals. First, we developed high efficiency homologous recombination technology to successfully disrupted ATM and p53 in hESCs. Analysis of the mutant ES cells indicate the roles of ATM and p53 in maintaining genomic stability in hESCs. Second, we identified pathways that are important for the self-renewal of hESCs. Third, we employed the knock-in tech
- The goal of this proposal is to investigate the mechanisms that maintain the genomic stability of human ES cells (hESCs). We are focusing on the tumor suppression pathways ATM and p53, which are well established guardians of the genome in differentiated cells. In addition, we are investigating the pathways that govern the self-renewal of hESCs, which might be coordinated with DNA damage responses to maintain the genomic stability in hESCs. During the reporting period, we made significant progress towards our goals. First, we developed a bacterial artificial chromosome based gene targeting technology that allows high efficiency homologous recombination in hESCs, and published the first homozygous knockout mutant hESCs in the world (Aims 1 and 3). This achievement, which was described in a publication in the top stem cell journal Cell Stem Cell, has attracted worldwide attention and will help to open up the entire field of hESCs (Song et al., 2010, Cell Stem Cell 6, 180-189). We employed the same technology to generate homozygous phosphorylation site knock-in mutant hESCs to study the mechanism underlying ATM activation in hESCs (Aim 3). Second, we identified a novel Pin1-Nanog pathway that is critical for the self-renewal of hESCs (Aim 2). Using small molecule compounds that inhibit this pathway, we were able to suppress the potential of ES cells to form teratomas. This finding, which is published in the Proceeding National Academy of Science, provides a druggable target to address the teratomas risk associated with the human ES cell based therapy (Moretto-Zita et al., 2010, PNAS, Epub 7/9). Third, to identify ES cell-specific DNA repair pathways, we have identified several ES cell-specific interaction between proteins and DNA breaks (Aim 3).
- We have made several significant progresses during the past year. We found the important roles of p53 in the differentiation of hESCs. We also identified that Nanog is a major coordinator of the self-renewal and proliferation of ES cells. We found that ATM is important to maintain the genetic stability of cells differentiated from hESCs. In addition, we identified an important phosphorylation event in activating ATM in hESCs. Finally, we identified a novel pathway to activate DNA damage in ES cells.
The roles of stem cells are to generate the organs of the body during development and to stand ready to repair those organs through repopulation after injury. In some cases these properties are not correctly regulated and cells with stem cell properties expand in number. Recent work is demonstrating that the genes that control stem cell properties are sometimes the same genes that are mutated in cancer. This means that a cell can simultaneously acquire stem cell properties and cancer properties. In order to effectively use stem cells for therapeutic purposes we need to understand the link between these two programs and devise ways to access one program without turning on the other. In other words, we would like to expand stem cell populations without them turning into cancer.
Recent work in our laboratory has found that the reduction of a specific tumor suppressor gene, p16, not only removes an important barrier to cancer but also confers stem cell properties within the cell. Cells that have reduced p16 activity can turn on a program that increases and reduces expression of specific genes that control differentiation. In this proposal we will test whether the continued reduction of this tumor suppressor gene creates human embryonic stem cells (hESC) that are unable to differentiate. We hypothesize that the lack of p16 represses multi-lineage potential by activating an epigenetic program and silencing genes that drive differentiation. To test this hypothesis we will first determine if lack of p16 activity is necessary for hESCs to develop into different cell types. Second, we will determine if continued lack of p16 activity is sufficient to inhibit differentiation of hESCs. Finally, we will determine if transient lack of p16 activity is sufficient for a non-stem cell to exhibit properties of a stem cell after propagation in a stem cell niche.
Since these types of events are potentially reversible, targeting such events may become clinically useful. These new observations identify novel opportunities. They provide potential markers for determining if someone is susceptible to cancer, as well as, providing potential targets for prevention and therapy. We hypothesize that these properties are critically relevant to the formation of cancer and will provide insights into the role of epigenetic modifications in disease processes and stem cell characteristics.
Stem cells hold great potential to help us in repairing injured body parts or replacing damaged organs. In order to realize this potential the rules that control stem cell behavior need to be understood. Recent work is demonstrating that the genes that control stem cell properties are sometimes the same genes that are mutated in cancer. In the proposed study we hypothesize that we may learn about a fundamental switch that not only controls stem cells but also controls the formation of a cancer cell. In understanding how this switch works we may be able to identify biomarkers that indicate when a normal looking cell will become a cancer cell or identify a drug that will allow us to stop the potential cancer cell from increasing in number. Since cancer is a common disease in California, any insights we can gain to battle this disease will benefit the citizens of our State.
There is also another side to the insights that may arise from the work in this proposal. Currently we believe the roles of stem cells are to generate the organs of the body during development and to stand ready to repair those organs through repopulation after injury. We do not know how to encourage a stem cell to repair, for example, some heart tissue rather than some bone tissue. If we could understand the code that directs the stem cells to differentiate in the proper fashion into one tissue or another, we could use these cells for clinical benefit. The pathways we are studying in this proposal tell the stem cells which genes to silence and which to activate. This is the program that allows the one original cells of your body (the embryo) to diversify into the multitude of specialized cells that work together to make a functioning person (eye cells, skin cells, nerve cells, etc.). In order to effectively use stem cells for therapeutic purposes we need to understand how they code their decisions and whether they can be changed after they have been set. These insights would allow us to aid in maintaining the health of the citizens of California.
Finally, if we do gain insight into the code that regulates the differences between cancer cells and stem cells, this information would be the basis of a new area of biotechnology. The generation of knowledge in this area would help in the development of companies, the recruitment of bright young minds and in the fiscal health of our State
- Stem cells hold great potential to help us in repairing injured body parts or replacing damaged organs. In order to realize this potential the rules that control stem cell behavior need to be understood. Our laboratory has found that repression of the tumor suppressor p16 in human mammary epithelial cells (HMECs) endows them with specific properties that are only found in classical stem cells and tumor cells. Indeed, repression of p16INK4a in HMECs enables them to grow in culture for a long time, something that HMECs expressing p16INK4a cannot achieve. Importantly, we have previously shown that repression of p16INK4a is accompanied by the acquisition of pre-malignant features.
- Thanks to the support of this CIRM grant, we have now established that a sub-population of these cells display stem cell properties. This means that these cells can self-renew but also differentiate in different breast cell types. Unexpectedly, these cells can also give rise to non-breast cells, such as brain cells, when grown in the appropriate cell culture conditions, making this unique cell model a powerful tool for cancer AND regenerative medicine research. Knowing that these cells can generate cells of different tissue types, we can now dissect the rules that dictate those different cell fates. We are also testing whether these exciting findings obtained in cell culture dishes (in vitro) can be confirmed in a mouse model (in vivo). In other words, can these cells generate a functional mammary gland? Other studies, beyond the scope of this application could also test whether these cells could rescue spinal injury.
- So why do we bother using breast cells to generate brain cells (or other types of cells)? The answer is that we believe that the sub-population of cells we have identified in breast likely exists as a stem cell pool in any tissue (with some tissue-specific variations of course). If this hypothesis is confirmed, these cells could turn out to represent a major advancement in regenerative medicine. Another major advantage of these naturally occurring stem cells, compared to the widely used embryonic stem cell lines, is that they are directly isolated from fresh breast tissue without introducing artifacts that may result from establishment in long-term cell culture systems. Their properties are an accurate reflection of a fully functional stem cell pool actually existing physiologically in our body.
- Understanding how stem cells code their decisions and whether cell fate can be changed after it has been set is key to the effective use of stem cells for therapeutic purposes. Gaining such insights will greatly improve our ability to manage wound repair and organ replacement. This should also help us characterize fundamental switches that control stem cells as well as control the formation of cancer cells since some of the genes that control stem cell properties are mutated in cancer. A mechanistic understanding of how these switches work may help us prevent adverse events that may result from the use of stem cells during regenerative medicine. Thus, we hope to contribute in improving the health of the citizens of California.
- An important feature of adult stem cells is the ability to bypass negative growth signals and participate in wound healing. Based on this premise, we identified a small subpopulation of human breast epithelial cells that is capable of bypassing negative growth signals. We identified a differential expression of genes that allowed for the rapid isolation of this novel somatic cell population from fresh disease-free human breast tissue. Importantly, this cell population is characterized by the over-expression of Bmi-1, a protein that plays an essential role in the self-renewal of stem cells and represses the cell cycle inhibitor, p16. This population of cells is therefore poised to express pluripotency markers at a level similar to that measured in human embryonic stem cells. It has the ability to self-renew and can express phenotypes of any of the three mammary lineages in vitro using cell culture differentiation assays. Importantly, these cells are also functional in vivo as observed after implantation in mice. Indeed, these human cells can differentiate into functional mammary outgrowths of human origin in the host mouse as we could document secretion of human milk in mice transplanted with these human somatic cells. We are currently investigating whether these cells can also differentiate into other lineages (tissue types) when cultured in the appropriate conditions. Our preliminary studies support that these cells will hold great promise in regenerative medicine and cell replacement therapy and may help overcome some of the important ethical and technical roadblocks related to the use of human embryonic stem cells.
The constant exposure of cells to endogenous and exogenous agents that inflict DNA damage requires active repair processes to eliminate potentially mutagenic events in stem cells leading to cancer. The same agents menace early human embryos with DNA damage that can ultimately lead to mutations, cancer, and birth defects. In vitro, human embryonic stem cells (HESCs) spontaneously undergo events leading to genetic instability and mutations. All these three types of genetic problems can have similar links to malfunctions in DNA repair systems, but little information now exists for HESCs. Therefore, the first step in understanding the causes of HESC genetic instability is to understand which DNA repair systems are defective. We will investigate the basis for this phenomenon in HESCs by evaluating their capacity to either repair DNA or form mutations. First, we will culture two HESC lines and compare HESC repair and mutation formation to that of control cells. We will use a new technique which simplifies the production and use of the feeder cells that support the growth of the HESCs. We will also test the genetic stability of HESCs grown on conventional feeder cells, as well as those grown in feeder free culture. We will use three types of DNA repair assays to monitor the genetic stability of the two HESC lines grown in these different ways. In the first of these assays, DNA molecules with different randomly-induced damage are transferred into HESCs, and DNA repair is followed by the re-establishment of the activity of a reporter protein that is coded for in the damaged DNA. A second assay will introduce specific DNA damage at a unique site in DNA that is transferred to HESCs and repair is determined using a polymerase chain reaction-based technique. Since aneuploidy is also known to be caused by double-strand DNA breaks, we will use two other assays to evaluate capacity of HESCs to repair that type of damage. These experiments will indicate if DNA repair pathways that eliminate DNA damage are dysfunctional and cause genetic instability. The final endpoint for these preliminary experiments is the formation of mutations. To study this, we have modified an assay system so that it will function in normal human cells to monitor mutations which arise spontaneously or those which are induced by various agents. In summary, these investigations will provide the basis for understanding genetic instability in HESCs that can direct cells to tumorgenic outcomes. The employment of HESCs clinically will require such knowledge. Moreover, these results will also yield information on susceptibility to mutations of cells early in development. The practical and basic science aspects of this seed grant proposal should lead to a complete proposal in the near future.
Human embryonic stem cells (HESCs) hold the potential to cure or alleviate many chronic illnesses, including cancer, but an immense gap exists between the achievement of the goals of stem cell based medicine and the current state of the art. Several stages of development including the following are required:
(1) Routine, standardized, simple protocols for the indefinite growth of HESC in the normal, undifferentiated state, in completely defined medium.(2) Control over differentiation of the cells in (1) to all adult cell types of interest. (3) Control over the maintenance of the differentiated state of derivatives of (1), in sufficient complexity to recreate normal functional histology. (4) Techniques, therapies, and protocols that allow immune tolerance of regenerated tissue, without rendering the human recipient immunodefficient.
Researchers are still struggling with steps 1 and 2. Although claims of feeder cell and animal product-free, long-term, undifferentiated HESC culture have been made, this is not the current state of the art in laboratories. These claims may be fortuitous or true for only a few HESC lines. The public anticipates a quick success of human stem cell technology and application to human disease, but the promise of stem cell therapy requires basic scientific work that is critical, but may not make headlines. Imprudent claims of miraculous cures could dim public enthusiasm. Few if any data exist regarding DNA repair systems or mutation frequencies of HESCs. We propose to investigate mechanisms underlying genetic instability in cultured HESCs. This instability limits HESC research and therapeutic applications. The data generated by this research according to Proposition 71 will be of lasting value to the People of the State of California for the following reasons:
(1) This proposal focuses on a serious, basic difficulty with respect to the growth of undifferentiated HESCs that is a barrier to their human therapeutic use.(2) In the future, if the focus of the stem cell field shifts to the as yet unavailable somatic nuclear transfer (SNT) methods, this proposed research, will provide a basis for the comparison of HESCs and SNT cell lines. (3) All humans begin as embryonic stem cells, therefore data generated by the proposed research will impact maternal health, well baby programs, early childhood development/learning, etc, because mutations are involved in birth defects as well as cancer. Therefore, understanding the causes of mutations in HESCs could assist in avoidance or reduction in birth defects that would aid both the families and the government of California.(5) All of the work described in this proposal will be conducted by individuals in California and most probably will result in the hiring of a graduate of a California institution of higher education, thus reducing unemployment and helping educate a new generation of California researchers in HESC use.
- Human embryonic stem cells (hESCs) originate directly from human embryos, whereas induced pluripotent stem cells (iPSCs) originate from body (somatic) cells that are re-programmed by producing or introducing proteins that control the process making specific RNAs. Together, both these pluripotent cell types are referred to as human pluripotent stem cells (hPSCs). Several reports have observed that in hESCs grown for long times, their genetic material, DNA, is unstable. The stable maintenance of DNA is performed by groups of proteins functioning in different systems globally known as DNA repair pathways. Since the development of aneuploidy is closely linked to cancer and to deficiencies in DNA repair, we have studied the propensity of hPSCs to repair their DNA efficiently by 4 major known DNA repair pathways. In addition, we are also investigating if specific damage to DNA in either hPSCs or somatic cells is processed differently and could lead to deleterious mutations.
- One major goal of the CIRM SEED grant mission is to bring new researchers into the hPSC field. The results we obtained during the funding period indicate that we have succeeded in that objective, since initially our laboratory had little experience with hESC culture. However, through courses and establishing critical collaborations with other hESC laboratories, we developed expertise in hPSC culture techniques. Most conditions for hPSCs growth require cells (feeder cells) that serve as a matrix and provide some factors needed for the pluripotent cells to divide. In accomplishing this aim, we perfected a method to generate reproducible feeder cells that significantly reduces the time and cost of feeder cell maintenance, and also developed a non-enzymatic and non-mechanical way to expand hPSCs. We now have experience with at least 5 hPSC lines and have methods to introduce foreign DNAs into hESCs and iPSCs to monitor DNA repair in hPSCs.
- In Aim II of our grant, we used our accumulated knowledge of hPSCs and DNA repair to investigate 4 DNA repair mechanisms in hPSCs and in somatic cells. Depending on the DNA damage, there is often a preferred DNA repair pathway that cells use to alleviate potential harm. We initiated our investigation by treating hPSCs using different DNA damaging agents, including ultraviolet light and gamma radiation. However, we found that hPSCs exposed to these agents rapidly died compared to treatments that allowed somatic cells to continue growing. Therefore, we developed methods to study DNA repair in hPSCs without directly treating the cells with external agents. We treated closed, circular DNA (plasmids) with damaging agents separately, outside the hPSCs and then introduced them into the hPSCs. The plasmid DNA has a sequence that codes for a protein that is produced only when the damage is repaired. The length of time for repair both in hPSCs and in somatic cells was followed by determining the protein production. We have shown superior DNA repair ability and elevated protection against DNA damage in hPSCs compared to somatic cells for ultraviolet light and oxidative damage, two common sources of damage in cells. A major pathway for joining double-strand DNA breaks in mammalian cells, non-homologous end-joining (NHEJ) repair (error prone), is greater in H9 cells than in iPSCs. Another way to repair double-strand DNA breaks that uses similar (i.e., homologous) sequences is lower in iPSCs compared to hESCs and somatic cells. Further study of these repair pathways is warranted, since several methods can be used to form iPSCs. Therefore, the genomic stability for iPSCs could depend on the method used for their generation.
- DNA repair analysis is critical to understanding how hPSCs protect against damage, but if left unrepaired, cells can turn damage into mutations when the damage is copied by enzymes (DNA polymerases) before repair occurs. Therefore, to monitor the mutations that ultimately lead to cancer or alter hPSC biology, we are using a plasmid that is damaged outside the cells and will make copies in hPSCs and somatic cells. That plasmid is introduced into cells and then the copies are recovered. The number of mutations found in the plasmid DNA indicates the likelihood of observing mutations in hPSCs compared to mutations in somatic cells. Together, these results will yield data on the stability of hPSCs and also a basis to monitor cells for stability which could serve as an indicator of safety for clinical use.
A variety of stem cells exist in humans throughout life and maintain their ability to divide and change into multiple cell types. Different types of adult derived stem cells occur throughout the body, and reside within specific tissues that serve as a reserve pool of cells that can replenish other cells lost due to aging, disease, trauma, chemotherapy or exposure to ionizing radiation. When conditions occur that lead to the depletion of these adult derived stem cells the recovery of normal tissue is impaired and a variety of complications result. For example, we have demonstrated that when neural stem cells are depleted after whole brain irradiation a subsequent deficit in cognition occurs, and that when muscle stem cells are depleted after leg irradiation an accelerated loss of muscle mass occurs. While an increase in stem cell numbers after depletion has been shown to lead to some functional recovery in the irradiated tissue, such recovery is usually very prolonged and generally suboptimal.Ionizing radiation is a physical agent that is effective at reducing the number of adult stem cells in nearly all tissues. Normally people are not exposed to doses of radiation that are cause for concern, however, many people are subjected to significant radiation exposures during the course of clinical radiotherapy. While radiotherapy is a front line treatment for many types of cancer, there are often unavoidable side effects associated with the irradiation of normal tissue that can be linked to the depletion of critical stem cell pools. In addition, many of these side effects pose particular threats to pediatric patients undergoing radiotherapy, since children contain more stem cells and suffer higher absolute losses of these cells after irradiation.Based on the foregoing, we will explore the potential utility and risks associated with using human embryonic stem cells (hESC) in the treatment of certain adverse effects associated with radiation-induced stem cell depletion. Our experiments will directly address whether hESCs can be used to replenish specific populations of stem cells in the brain and muscle depleted after irradiation in efforts to prevent subsequent declines in cognition and muscle mass respectively. In addition to using hESC to hasten the functional recovery of tissue after irradiation, we will also test whether implantation of such unique cells holds unforeseen risks for the development of cancer. Evidence suggests that certain types of stem cells may be prone to cancer, and since little is known regarding this issue with respect to hESC, we feel this critical issue must be addressed. Thus, we will investigate whether hESC implanted into animals develop into tumors over time. The studies proposed here comprise a first step in determining how useful hESCs will be in the treatment of humans exposed to ionizing radiation, as well as many other diseases where adult stem cell depletion might be a concern.
Radiotherapy is a front line treatment used in California for many types of cancer, including brain, breast, prostate, bone and other cancer types presenting surgical complications. Treatment of these cancers through the use of radiation is however, often associated with side effects caused by the depletion of critical stem cell pools contained within non-cancerous normal tissue. While radiotherapy is clearly beneficial overall, many of these side effects have no viable treatment options. If we can demonstrate that human embryonic stem cells (hESC) hold promise as a safe therapeutic agent for the treatment of radiation-induced stem cell depletion, then cancer patients may have a new treatment for countering many of the debilitating side effects associated with radiotherapy. Once developed this new technology could position California to attract cancer patients throughout the United States, and the state would clearly benefit from the increased economic activity associated with a rise in patient numbers.
- We have undertaken an extensive series of studies to delineate the radiation response of human embryonic stem cells (hESCs) and human neural stem cells (hNSCs) both in vitro and in vivo. These studies are important because radiotherapy is a frontline treatment for primary and secondary (metastatic) brain tumors. While radiotherapy is quite beneficial, it is limited by the tolerance of normal tissue to radiation injury. At clinically relevant exposures, patients often develop variable degrees of cognitive dysfunction that manifest as impaired learning and memory, and that have pronounced adverse effects on quality of life. Thus, our studies have been designed to address this serious complication of cranial irradiation.
- We have now found that transplanted human embryonic stem cells (hESCs) can rescue radiation-induced cognitive impairment in athymic rats, providing the first evidence that such cells can ameliorate radiation-induced normal-tissue damage in the brain. Four months following head-only irradiation and hESC transplantation, the stem cells were found to have migrated toward specific regions of the brain known to support the development of new brain cells throughout life. Cells migrating toward these specialized neural regions were also found to develop into new brain cells. Cognitive analyses of these animals revealed that the rats who had received stem cells performed better in a standard test of brain function which measures the rats’ reactions to novelty. The data suggests that transplanted hESCs can rescue radiation-induced deficits in learning and memory. Additional work is underway to determine whether the rats’ improved cognitive function was due to the functional integration of transplanted stem cells or whether these cells supported and helped repair the rats’ existing brain cells.
- The application of stem cell therapies to reduce radiation-induced normal tissue damage is still in its infancy. Our finding that transplanted hESCs can rescue radiation-induced cognitive impairment is significant in this regard, and provides evidence that similar types of approaches hold promise for ameliorating normal-tissue damage throughout other target tissues after irradiation.
- A comprehensive series of studies was undertaken to determine if/how stem cell transplantation could ameliorate the adverse effects of cranial irradiation, both at the cellular and cognitive levels. These studies are important since radiotherapy to the head remains the only tenable option for the control of primary and metastatic brain tumors. Unfortunately, a devastating side-effect of this treatment involves cognitive decline in ~50% of those patients surviving ≥ 18 months. Pediatric patients treated for brain tumors can lose up to 3 IQ points per year, making the use of irradiation particularly problematic for this patient class. Thus, the purpose of these studies was to determine whether cranial transplantation of stem cells could afford some relief from the cognitive declines typical in patients afflicted with brain tumors, and subjected to cranial radiotherapy. Human embryonic (hESCs) and neural (hNSCs) stem cells were implanted into the brain of rats following head only irradiation. At 1 and 4 months later, rats were tested for cognitive performance using a series of specialized tests designed to determine the extent of radiation injury and the extent that transplanted cells ameliorated any radiation-induced cognitive deficits. These cognitive tasks take advantage of the innate tendency of rats to explore novelty. Successful performance of this task has been shown to rely on intact spatial memory function, a brain function known to be adversely impacted by irradiation. Our data shows that irradiation elicits significant deficits in learning and spatial task recognition 1 and 4-months following irradiation. We have now demonstrated conclusively, and for the first time, that irradiated animals receiving targeted transplantation of hESCs or hNSCs 2-days after, show significant recovery of these radiation induced cognitive decrements. In sum, our data shows the capability of 2 stem cell types (hESC and hNSC) to improve radiation-induced cognitive dysfunction at 1 and 4 months post-grafting, and demonstrates that stem cell based therapies can be used to effectively to reduce a serious complication of cranial irradiation.
Embryonic stem cell-based therapies hold great promise for the treatment of many human diseases. These therapeutic strategies involve the culture and manipulation of embryonic stem cells grown outside the human body. Culture conditions outside the human body can encourage the development of changes to the cells that facilitate rapid and sustained cell growth. Some of these changes can resemble abnormal changes that occur in cancer cells. These include “epigenetic” changes, which are changes in the structure of the packaging of the DNA, as opposed to “genetic” changes, which are changes in the DNA sequence.
Cancer cells frequently have abnormalities in one type of epigenetic change, called “DNA methylation”. We have found that cultured embryonic stem cells may be particularly prone to develop the type of DNA methylation abnormalities seen in cancer cells. A single rogue cell with DNA methylation abnormalities predisposing the cell to malignancy can jeopardize the life of the recipient of stem cell therapy. We have developed highly sensitive and accurate technology to detect DNA methylation abnormalities in a single cell hidden among 10,000 normal cells.
In this seed grant, we propose to screen DNA methylation abnormalities at a large number of genes in different embryonic stem cells and compare their DNA methylation profiles to normal and cancer cells. This will allows us to identify the dangerous DNA methylation abnormalities most likely to occur in cultured embryonic stem cells. We will then develop highly sensitive assays to detect these DNA methylation abnormalities, using our technology. We will then use these assays to determine ES cell culture conditions and differentiation protocols most likely to cause these DNA methylation abnormalities to arise in cultured ES cells.
The long-term benefits of this project include 1) an increased understanding of the epigenetics of human embryonic stem cells, 2) insight into culture conditions to avoid the occurrence of epigenetic abnormalities, and 3) a technology to monitor for epigenetic abnormalities in ES cells intended for introduction into stem cell therapy patients.
The successful implementation of human embryonic stem cell therapy will require rigorous quality control measures to assure the safety of these therapies. Cells cultured outside the human body are known to be at risk of developing abnormalities similar to those found in cancer cells. Since a single rogue cell hidden among thousands of normal cells could cause cancer in an embryonic stem cell therapy recipient, it will be essential to have highly sensitive and accurate assays to detect these abnormalities in cultured embryonic stem cells before they are introduced into the patient. The goal of this proposal is to develop such sensitive and accurate assays. The citizens of the State of California will benefit from the availability of such assay technology to help assure the safety of human embryonic stem cell therapies.
- Embryonic stem cell-based therapies hold great promise for the treatment of many human diseases. These therapeutic strategies involve the culture and manipulation of embryonic stem cells grown outside the human body. Culture conditions outside the human body can encourage the development of changes to the cells that facilitate rapid and sustained cell growth. Some of these changes can resemble abnormal changes that occur in cancer cells. These include epigenetic changes, which are changes in the structure of the packaging of the DNA, as opposed to genetic changes, which are changes in the DNA sequence. Cancer cells frequently have abnormalities in one type of epigenetic change, DNA methylation. In this grant, we screened for DNA methylation abnormalities at a large number of genes in different embryonic stem cells and compare their DNA methylation profiles to normal and cancer cells. This allowed us to identify potentially dangerous DNA methylation abnormalities, which occur in cultured embryonic stem cells. In the first year of this seed grant, we have developed a custom microarray to screen for DNA methylation changes at predisposed genes. In addition, we have analyzed DNA methylation in embryonic stem cells at more than 14,000 genes on a generic platform. This has allowed us to identify hundreds of genes that are abnormally methylated in various types of human cancers, and that show some evidence of this alteration in ES cells.
- In the last phase of our study, we have screened the DNA methylation level of 1,536 genes in 142 different human embryonic stem cell pairs. Each member of the pair differed in the length of time it was in culture. Thus, our sample set was comprised of 284 paired specimens, one derived from an early passage and one derived from a late passage.
- Our results indicate that the levels of DNA methylation varied considerably at a significant portion of the screened genes, some of which gained and some of which lost DNA methylation. These results indicate that DNA methylation in human embryonic stem cells seems to be susceptible to change over, at least in the genes examined in this study. Overall, our results suggest that the monitoring of DNA methylation changes in human embryonic stem cells may have to be incorporated as a routine protocol in stem cell manipulation.
- During the past 12 months we have made significant progress on the data analysis of 141 paired (early passage-late passage) human embryonic stem cell lines (HESCs). The data in question was generated using a custom Illumina GoldenGate array of known Polycomb targets in HESCs, as described by Lee et al 2006. Briefly, we profiled the DNA methylation status of 1,536 loci on 282 specimens. This profiling was used to determine whether DNA methylation changes in HESCs arise as a result of time in culture at the examined loci. This determination was made by comparing the DNA methylation status of a sample of an early passage line with a late passage sample of the same line.
- Interestingly, we found that DNA methylation in Polycomb target genes is highly affected by time in culture in a cell line-specific manner. That is, in some cell lines few DNA methylation changes were observed, while in the majority of them a large number of loci showed either an increase or decrease in DNA methylation. Via collaboration with the University of Sheffield, we were able to determine that DNA methylation instability seems to be independent of genetic instability. Furthermore, genetic instability seems to be a function of passage time in culture.