In Vivo Imaging of Human Embryonic Stem Cell Derivatives and Tumorigenicity
Human embryonic stem cells (hESCs) are one of the most fascinating subjects of interest in all of biology and medicine these days. Under certain physiologic conditions, they can be induced to become specialized cells such as brain, cardiac, liver, pancreatic, and bone marrow cells. This opens up the exciting possibility that hESCs may one day be used to treat patients with Parkinson’s disease, heart conditions, hepatitis, diabetes, and leukemia, just to name a few currently intractable diseases that affect millions of Americans alone. This field of cell-based therapies to treat human diseases is generally referred to as “regenerative medicine.”
Scientists who want to study hESCs or their specialized cell derivatives typically inject them into small animal models such as mice and rodents. However, researchers currently are unable to monitor noninvasively these cells after transplant. Instead, these animals are typically sacrificed for postmortem biopsy, which precludes long-term follow-up of transplanted cells. Without the ability to follow the progress of transplanted cells over a longer period of time, important insights into hESC fates in vivo have not been forthcoming. Thus, developing a novel technology to track transplanted hESCs and their specialized cell derivatives would represent a major advancement in this field that will produce wide-ranging theoretical and practical implications.
Another problem with transplantation of hESCs is the potential to cause teratomas. Teratomas are disorganized arrays of cell differentiation that appear to recapitulate many of the events involved in early embryonic development. Clearly, the teratoma formation risk is a major obstacle to future clinical application of hESCs. In this proposal, we will evaluate how teratoma forms in living subjects over time using the imaging techniques that we have developed as well as how best to prevent them in the first place.
Due to the serious risks posed by teratoma formation, it is necessary to induce hESCs to become specialized cell derivatives first before transplantation for therapeutic purposes. However, this process is not efficient at present despite intense efforts searching for methods to expedite it. Our team plans to tackle this problem using the latest genomics and proteomics technology.
In summary, our proposal is a targeted response to the CIRM SEED grant. It seeks to develop a novel technology (molecular imaging) that will address a critical barrier in clinical translation of hESC therapy (teratoma formation) and provide a better understanding of cardiac cell differentiation process (genomics/proteomics). Our well-established multidisciplinary team has the required training, experience, and innovation to complete the project. Overall, we are confident that our proposed studies will generate significant progress in this field, in both scientific knowledge and useful therapies.
Stem cell based therapy holds great promise for treatment of numerous diseases. Human embryonic stem cells (hESCs), for example, can transform into brain, cardiac, pancreatic, liver, and bone marrow cells. This opens up the exciting possibility that hESCs may one day be used to treat diseases such as Parkinson’s, heart conditions, hepatitis, diabetes, and leukemia. This field of cell-based therapies to treat human diseases is generally referred to as “regenerative medicine.”
However, we are still at the very early stages of understanding the capability of hESCs. There are many basic research questions that need to be addressed before we can begin clinical trials involving specialized hESC-derived cells in the future. For example, we need to understand how to drive hESC differentiation into specific pathways, to control hESC proliferation, and to monitor their cell fate after transplantation.
One of the most serious problems is the potential for hESC to cause teratoma after transplantation. Teratomas are benign tumors that consist of cells from different lineages. Therefore, it is critical for scientists to understand how teratomas are formed as well as to develop techniques to monitor them noninvasively and repetitively. Our research proposal is designed to address all 3 questions: (1) how to image and monitor transplanted hESCs, (2) how teratomas are formed, and (3) how to reliably induce hESCs to become specialized derivatives such as cardiac cells.
We believe that answering these questions will lead to significant advances in hESC research and novel therapies. We have assembled a multidisciplinary team of experienced investigators to attack the challenges of this project. At the same time, we will train and mentor a new generation of bright students and junior scientists in the areas of technology development and hESC biology. This ensures that an essential knowledge base will be preserved and passed on for the foreseeable future.
Human embryonic stem cells (ESCs) are self-renewing and pluripotent cells derived from the inner cell mass of the blastocyst. Human ESCs are an unlimited and widely applicable cell source for regenerative medicine, making them desirable candidates for cell replacement therapy. However, the use of human ESCs also carries the danger of possible uncontrollable cellular proliferation and differentiation, a serious problem that is as yet unresolved. This potentially serious complication may occur if the transplanted human ESCs take an inappropriate path such as teratoma formation. Broadly defined, teratomas are haphazard arrays of cell differentiation that appears to recapitulate the main events involved in early embryonic development, but in a disorganized manner. Teratomas have been observed to grow from both undifferentiated mouse ESCs and human ESCs. Thus, the ability to visualize cellular proliferation and differentiation in vivo would be an invaluable next step toward monitoring and controlling cellular misbehavior.
The three specific aims of the project are as follow:
Aim 1: To develop a novel imaging platform for tracking human ESCs in vivo
Aim 2: To monitor the tumorigenicity profiles of different human ESC lines
Aim 3: To examine key regulatory processes involved in human ESC differentiation into cardiac cells
For Aim 1, we have created 3 human ESC lines (H1, H7, and H9) that stably express fusion reporter genes. Using novel imaging technology, we have successfully tracked human ESC teratom formation de novo in living subjects (Cao F et al, Cancer Research 2009). For Aim 2, we have shown that a minimum of 1x10(5) human ESCs in the myocardium and a minimum of 1x10(4) cells in the skeletal muscle was necessary for teratoma development, suggesting that cell number does play a critical factor (Lee A et al, Cell Cycle 2009). For Aim 3, we have performed detailed transcriptional and functional profiling analysis of human ESC derived cardiomyocytes in mouse model of myocardial infarction (Cao F et al, PLoS ONE 2008). Lastly, we have shown that the STAT3 signaling pathway is critical for the development and differentiation of cardiac cells.
In summary, we have made significant progress in understanding the divergent biology of human ESC differentiation and tumorigenicity. Over the past 2 years, we have published 8 papers that were supported by the CIRM Seed Grant.
- Stroke (2010) Human neural stem cell grafts modify microglial response and enhance axonal sprouting in neonatal hypoxic-ischemic brain injury. (PubMed: 20075340)
- Mol Imaging Biol (2010) Comparison of gene-transfer efficiency in human embryonic stem cells. (PubMed: 19551446)
- Mol Ther (2009) Molecular and magnetic resonance imaging of human embryonic stem cell-derived neural stem cell grafts in ischemic rat brain. (PubMed: 19436269)
- PLoS One (2009) Functional and transcriptional characterization of human embryonic stem cell-derived endothelial cells for treatment of myocardial infarction. (PubMed: 20046878)
- Cell Cycle (2009) Effects of cell number on teratoma formation by human embryonic stem cells. (PubMed: 19597339)
- Stem Cells Dev (2009) MicroRNA profiling of human-induced pluripotent stem cells. (PubMed: 19284351)
- Methods Mol Biol (2009) Molecular imaging of human embryonic stem cells. (PubMed: 19405224)
- Stem Cells Dev (2009) Imaging of STAT3 signaling pathway during mouse embryonic stem cell differentiation. (PubMed: 18576943)
- Cancer Res (2009) Noninvasive de novo imaging of human embryonic stem cell-derived teratoma formation. (PubMed: 19318556)
- Proc Natl Acad Sci U S A (2008) Immunosuppressive therapy mitigates immunological rejection of human embryonic stem cell xenografts. (PubMed: 18728188)
- PLoS One (2008) Transcriptional and functional profiling of human embryonic stem cell-derived cardiomyocytes. (PubMed: 18941512)
- Stem Cells Dev (2008) In vivo imaging of embryonic stem cells reveals patterns of survival and immune rejection following transplantation. (PubMed: 18491958)