In Utero Model to Assess the Fate of Transplanted Human Cells for Translational Research and Pediatric Therapies
Early Translational I
nfants with inherited blood diseases (such as sickle cell anemia, thalassemia, bleeding disorders) or other inherited metabolic disorders can be identified early in development using sophisticated diagnostic tests. Currently, the treatment for many of these childhood illnesses may include bone marrow transplantation which is complicated by: (1) the toxicity associated with chemotherapy or radiation-based regimens necessary to ensure the transplanted cells persist; (2) serious health complications associated with rejection of the donor cells; (3) the fact that only ~20-25% of children will have a matched donor, which is even less likely for ethnic populations and underrepresented minorities; and (4) the concern that significant damage, particularly to the brain, has occurred by the time the child is being considered for transplantation. Recent studies suggest that very early treatment before damage from the disease has occurred provides the best survival outcomes, and that immature cell sources may be most effective because they have characteristic features that are more compatible with the developmental stage of the patient. Human umbilical cord blood has been demonstrated to be a very effective source of hematopoietic stem cells (HSC) for transplantation, even if the donor cells do not match the recipient; in these cases the incidence and severity of disease post-transplant has been shown to be very low. However, there are significant limitations to more widespread use of umbilical cord blood HSC because of the low number of cells that are available each time cord blood units are collected. Human embryonic stem cells (hESC) provide another potential source of early stage blood cells for clinical transplantation for young patients. However, there remain significant concerns regarding the safety of use of cells obtained from hESC in all age groups. It is also currently unknown if early blood cells obtained from hESC will provide an advantage over other sources such as umbilical cord blood cells. These studies address crucial bottlenecks that prevent the use of therapeutically important cells for treating pediatric diseases, and methods and models to ensure that proposed approaches will be safe and effective for human use. The bottlenecks to be studied include: (1) the need to treat infants very early in their disease with sufficient and compatible cells; (2) the need to explore methods that will expand umbilical cord blood cells useful for transplantation, and to compare these cells to blood cells obtained from hESC; and (3) the need to use models for humans and related tools that can effectively predict outcome once cells are injected into the body, and to monitor where they travel and ultimately reside and function. The approaches proposed in this application will provide substantial advances in assessing the safety, for example, of new cell-based therapies with hESC, and provide new treatment options for many patients in need.
Statement of Benefit to California:
The benefits to the State of California and its citizens are critically needed effective and safe cellular therapies that could provide potential cures for infants and children diagnosed with an inherited blood cell or metabolic disorder. For example, current statistics on sickle cell disease, the most common inherited blood cell disease in the U.S., indicates approximately 20 children each day (about 8,000 each year) are born with this disease. Sickle cell disease and other blood cell disorders are present in all populations but are more prevalent in persons of African, Mediterranean, Asian, Southeast Asian, Caribbean, and South and Central American origins. The California Newborn Screening Program detects approximately 120 new cases of sickle cell disease every year. Thalassemia, another inherited blood disorder, is considered the most common genetic blood disease worldwide, with recent data indicating approximately 400,000 affected babies born annually. It is one of the most frequent disorders detected yearly in the California Newborn Screening Program of over 700,000 births. Millions of children world-wide suffer from the many serious complications associated with sickle cell disease and thalassemia that decrease life expectancy. These are just two of many inherited blood diseases that could substantially benefit from early treatment, and using stem cells from umbilical cord blood or pluripotent cells obtained from human embryonic stem cells. Similarly, more than 800 children and 400 adults in [REDACTED] alone have been diagnosed with inherited bleeding disorders including hemophilia. With current diagnostic capabilities, infants with these inherited blood diseases can be identified before they are born and cell therapies initiated at this time thus avoiding the damaging effects associated with these diseases. This could provide a means to ensure the delivery of healthy term newborns free of the many postnatal complications of these diseases that diminish quality of life and long-term survival.
The goal of this application is to establish an in utero preclinical model for monitoring the fate of transplanted cells, specifically hematopoietic precursors derived from umbilical cord blood or human embryonic stem cells (hESCs), with a long-term goal of treating inherited pediatric hematologic diseases. In the first aim, hematopoietic stem cells (HSCs) derived from cord blood and hESCs will be engrafted and the fate and distribution of the transplanted cells will be followed. For the second aim, a series of in vivo imaging methodologies will be employed to monitor the fate and migration of the engrafted cells. This proposal addresses several bottlenecks in clinical translation by: 1) addressing issues of hESC-derived cell optimization for clinical transplantation (e.g. expansion, safety); 2) providing insights into the fate and distribution of transplanted human cells in a preclinical model; and 3) conducting proof-of-principle studies for human transplantation in a relevant model. The reviewers agreed that the proposed effort represents a significant and interesting strategy for addressing several barriers to translation, particularly with regard to potential therapies for inherited pediatric diseases of the blood. Currently, there are few options for treating such disorders, and while cell therapies are thought to be promising, there remain many issues to resolve. One such obstacle is the threat of immune rejection, which the applicants have addressed by proposing a prenatal or early postnatal timing of cell administration. Due to the immaturity of the immune system at these stages, the threat of graft vs. host disease could be substantially reduced compared to current clinical scenarios. In addition, the reviewers appreciated the need for a preclinical model to address key safety and efficacy issues that must be resolved prior to testing in humans. In general, the reviewers were optimistic about the overall feasibility of this effort. The proposal was clear and well organized with realistic criteria for success. The research team was viewed as a considerable asset, comprised of successful and productive investigators covering complementary domains of expertise. Reviewers also noted as a strength the established model and imaging capabilities in the principal investigator’s (PI) laboratory. In addition to these qualifications, the reviewers discussed a number of strengths in the proposed experimental design. In particular, they appreciated the side-by-side comparisons for evaluating the fate of transplanted cell populations as well as the straightforward, bioluminescence imaging methodologies capable of detecting cell clusters. While their overall impressions were favorable, the reviewers expressed some concerns over specific aspects of this endeavor. The preliminary data were largely supportive. However, one reviewer commented that it was difficult to fully appreciate the preliminary data due to missing figure legends and an inadequate level of description. One reviewer questioned the feasibility of the positron emission tomography (PET) approach, as the proposed markers were not well described or supported by preliminary data. Even the citation provided for the PET methods did not reconcile the description provided by the applicants with the state of the art in the field. In addition to these minor points, the reviewers raised some questions about the immediate therapeutic potential of this work. Long-term engraftment and tolerance were discussed among the panelists as necessary preclinical translational milestones to assure life-long cure, and panelists were concerned that the proposal did not clearly address these issues. While noting that no diseases were specifically addressed, they recognized the utility of this model as a tool for development for a wide variety of disorders. They acknowledged, however, that similar studies using other models have been problematic, and wondered whether this particular preclinical system might be somewhat premature. Despite these reservations, most felt that potential benefits to be gained would outweigh the inherent risks. As a final point of discussion, several reviewers commented that the budget seemed excessive while others questioned whether the investigators might be overcommitted. In summary, the reviewers agreed that the proposed effort addressed several important barriers to translation. Overall, the experimental design was unique and feasible due to the strengths and experience of an outstanding research team. PROGRAMMATIC REVIEW During programmatic review, the Grants Working Group was instructed to consider the specific rank order of all applications in Tier I as an indicator of priority for funding. A motion was made to move this project below that of another with an identical score. The reviewers indicated that while in utero transplant models would be useful, studies similar to those proposed have been unproductive in other settings. Moreover, the overall immediate utility of this proposed project was less apparent than that of the project that achieved the same numerical score. The motion carried.