The human immune system is comprised of many different types of cells that all function, in different ways, to protect the body from infection and disease. There are many types of diseases that directly target or affect the human immune system. The list of such diseases includes AIDS, severe combined immunodeficiency, agammaglobulinemia, as well as other conditions that are the consequences of radiation, chemotherapy, burns, or other infections. Since the immune system is the key component protecting the body from infection, it is important that the various parts of the immune system function proficiently. There are a number of therapies that are designed to treat defects in the immune system. One such therapy involves the use of hematopoietic stem cells taken from the bone marrow or peripheral blood and then transplanted into the recipient patient. However, there are a number of important issues with these strategies that limit their success, including immune rejection by or against the transplanted cells. Further, the ability to obtain large quantities of transplantable cells to allow multiple treatments or cell manipulation is limited.
Human embryonic stem cells (hESC) have the ability to develop into any cell in the body, including those of the of the immune system. Because of this they hold a great amount of promise in developing approaches for treating and manipulating various types of immune defects. Hematopoietic stem cells derived from human embryonic stem cells (hESCs) could potentially provide such tissue to allow immune “matching” to the recipient, thus eliminating immune rejection. Further, hESCs could potentially allow infinite expansion of these cells and permit “tailoring” of the cells to regenerate defects in the immune response. Our proposal seeks to investigate the potential of hESC in forming functional immune cells. I t is necessary to closely examine the ability of hESC to become immune cells before a therapy can be developed.
Due to the fact that experimental transplantation of stem cells into human recipients is not feasible, there has been a strong interest in developing model systems to study the human immune response using a surrogate host. One such system has been developed using immunocompromised mice. Previous studies have shown that hematopoietic stem cells taken from human cord blood are capable of forming mature human immune cells in these mice. We propose to examine and compare the ability of hESCs to the ability of other hematopoietic stem cells to become mature human immune cells in the mice. We will further examine the ability of these cells to respond to infection with lymphocytic choriomeningitis virus (LCMV), which is a virus that infects both humans and mice and is widely used to study immune responses. These studies should provide insight into the feasibility of hESC-based therapies to regenerate human immune responses for a wide variety of diseases.
Statement of Benefit to California:
There are a number of diseases of the human immune system that would benefit from the development of new type of therapy. Such diseases include cancer, AIDS, SCID, allergy and other types of infections and non-infectious conditions. There are a number of therapies that are designed to treat defects in the immune system and there is a high demand for the development of more effective therapies. While exact numbers are difficult to attain, over 100,000 people undergo immune-suppressive therapy (radiation or chemotherapy) in the state of California each year. In roughly half of the patients undergoing stem cell transplantation procedures, the current stem cell transplantation methods are ineffective. Further, a recent study by the University of California estimated that 151,000 people in California were infected with HIV. While current drug regimes treating HIV are allowing greater survival, they are far from a cure. California is in the unique position to take the lead in therapies developed using human embryonic stem cells (hESC). Our proposal seeks to utilize the resources of the CIRM to investigate the potential of hESC in forming functional immune cells. These studies could lead to the development and understanding of the feasibility and the conditions that are necessary to develop a therapy that uses hESCs to treat a variety of defects in the immune response. This would greatly benefit the citizens of California that are directly affected by these conditions and help push California to the forefront in developing the state of the art hESC based therapies.
SYNOPSIS: The investigator proposes to pursue two specific aims: 1) Compare and contrast fetal derived and hESC derived hematopopoietic progenitor cells to reconstitute the surrogate immunocompromised mouse and 2) compare and contrast the abiltity of cells from hESC-derived and fetal-derived sources to generate a functional immune response. Animals which have been reconstituted with human lymphoid cells will be challenged with lymphocytic choriomeningitis virus and the immune response quantified.
INNOVATION AND SIGNIFICANCE: This proposal is of modest innovation in that the investigator proposes to replicate previous experiments in which he participated and to add LCMV challenge which is a conventional immunological strategy. The head-to head comparision of stem cells from fetal sources to hESC is of some interest and could yield interesting results. One reviewer noted that since the investigator proposes only one strategy to evaluate the immune response, the experiments are likely to have limited impact. Another reviewer noted that if positive results were obtained, the proposal is potentially highly significant . Evaluation of in vivo lymphocyte activity derived from human ES cells would be an important advance in this field.
STRENGTHS: This is a highly circumscribed proposal by a newly independent investigator who is familiar with the techniques and capable of performing the described experiments. In general, the proposal is a logical follow-up to the previous studies involving the investigator and there is data from other groups that suggest these types of studies may be feasible. Importantly, the group will use positive controls of hematopoietic stem cells from fetal liver or cord blood to compare immune activity. This direct comparision of fetal hematopoietic stem cell verses hESC is of potential interest. It would also be informative to study the response in normal mice to get an idea of how effective the immune reconstitution is with either source of stem cells. The proposal to utilize two different strains of immunodeficient mice and to study a number of different hESC lines is useful. The potential studies in aim 2 to test the response against LCMV is well thought out and again would be an important advance.
WEAKNESSES: The proposal has limited scope and lacks mechanistic focus. Unfortunately, the feasibility of these studies, based on other prior studies, is unclear. This proposal ignores three published studies by Bhatia, Zanjani, and Kaufman groups that have separately shown very minimal in vivo engraftment activity of hematopoietic precursor cells derived from hESC in immunodeficient mouse and fetal sheep models. These studies need to be referenced, and it should be more clearly stated why the models to be tested are more feasible. Also, few additional strategies are suggested to augment immmune reconstitution or dissect the important components that are required for function.
Another weakness is lack of details in experimental design. There is relatively little information about number of mice that will be tested in each group and the timeline for these analyses. It is also unclear what specific cell populations will be injected into these mice; only use of CD34-positive cells derived from hESC, fetal liver, or cord blood are described. It might be useful to consider other sub-populations of hematopoietic cells derived from hESC. Again, there is no statistical analysis that is described to test how these hematopoietic populations will be compared.
Most problematic is the fact that aim 2 is entirely dependent on aim 1, and there is a high risk that aim 1 may not give the desired positive results. In some respects, this potential pitfall is acknowledged and the PI states that in this case the anti-LCMV response of the fetal liver or cord-blood cells in this model will be assessed, though that is not the point of these seed grant proposals.
DISCUSSION: There was no further discussion following reviewers' comments.