The goal of our project is to study and develop immunological approaches to overcome rejection of embryonic stem cells (ESCs) and other cells and tissues derived from these pluripotent cells. We utilize animal modeling to study the impact of the immune system on survival and rejection of ESCs since we are better able to study specific cell populations and strategies involved in the underlying biology. We have further developed a strategy to study the survival and trafficking of injected cells using light emission in a process called bioluminescent imaging (BLI). This imaging approach is accomplished by introducing a light emitting protein called luciferase, generated from the North American firefly into cells of interest. In particular we have generated ESCs which express luciferase and therefore emit light. Using BLI we can study the growth and survival of these transplanted ESCs in living animals. Using this approach rejection and engraftment can be readily and non-invasively assessed. In the past year we have developed all of the necessary ESCs from different genetic backgrounds that express luciferase and can be imaged. We have demonstrated that animals with intact immune systems reject these transplanted cells over several weeks whereas animals with crippled immune systems do not. A goal of the research proposal was to study naturally occurring T and natural killer - T (NK-T) cells with known capacity to regulate immune responses. The goal is to develop strategies whereby injection of these regulatory cells will impact the rejection of the transplanted ESCs. Our initial studies have demonstrated that the simple co-injection of the regulatory T cells with the ESCs was not sufficient to prolong survival of the ESC grafts. This is not unexpected since the regulatory T cells may also be rejected by the recipient immune system. Current experiments are to study the survival and trafficking of the regulatory T cells in animals with and without ESCs and to explore ways to enhance survival of these grafts through manipulation of the immune system of the recipient animals. One approach under current study is to utilize a preparative regimen developed at Stanford including total lymphoid irradiation (TLI) and anti-lymphocyte serum (ALS) which in both animals and patients is very well tolerated and reduces immune function such that engraftment of foreign cells is possible. We are exploring the impact of TLI/ALS with and without the regulatory T cells and NK-T cells on ESC survival and engraftment. The ultimate goal is to develop approaches that will be translatable to the clinic to enhance the engraftment and survival of the transplanted ESC tissues. We have made excellent progress in the first year of funding and developed all of the necessary ESC lines emitting light and performed all of the control experiments demonstrating the immunological rejection of the ESCs. In the next 2 years we are well poised to study and develop immunological approaches to enhance ESC survival.
Reporting Period:
Year 2
In this proposal investigations are being performed to develop clinically relevant approaches to reduce the risk of rejection of embryonic stem cells (ESCs) and their derived cell products. We have identified that ESCs are readily rejected in the setting where they are mismatched to the recipient which is the clinical scenario for future intervention. We are exploring the role of naturally occurring immune regulatory cells such as regulatory T (Treg) cells and natural killer T (NK-T) cells in preventing rejection. We have found that these cells alone are not capable of preventing rejection but can be used in addition to total lymphoid irradiation (TLI) for the prevention of ESC rejection. We have observed that the use of TLI plus Treg is an effective and clinically relevant strategy for prevention of ESC rejection.
Additional studies are being performed on the analysis of strategies to prevent rejection of cells that are derived from ESCs. In the eventual clinical application of ESC based therapies it is likely that differentiated progeny will be the most likely cellular product since ESCs alone develop into tumors called teratomas. We are investigating the use of endothelial cells derived from ESCs which could be useful for re-vascularization for example following heart damage. These studies are just being initiated in the third year of this proposal.
In summary, immune regulatory strategies hold promise to overcome the rejection of ESCs and their derived progeny. It is expected that at the completion of this proposal we will have investigated how total lymphoid irradiation in combination with Treg or NK-T cells can be used as a strategy to avoid immune rejection.
Reporting Period:
Year 3
We have explored the use of clinically relevant strategies to promote the engraftment of embryonic stem cells (ESCs) and differentiated cells derived from ESCs. A major problem with the planned and future clinical use of ESCs as well as differentiated progeny is that they are likely to be rejected by the immune system of the patient. In our studies we have utilized two approaches that have already been tested in the clinic. One is the use of total body irradiation and anti-thymocyte serum which we have successfully utilized in hundreds of patients successfully both with hematologic malignancies and those with kidney failure to promote engraftment of donor derived hematopoietic cells and in some instances with combined hematopoietic cells and kidney transplants. A second approach was to utilize normal T cell populations that have been shown by our group and others to regulate immune reactions, termed regulatory T cells. In our studies in murine models we were able to show that both total lymphoid irradiation and antithymocyte serum alone resulted in the engraftment of ESCs from a genetically different donor, however, these cells grew into tumors called teratomas. When we utilized differentiated progreny derived from the ESCs, which is much more similar to the proposed clinically situation, the combination of total lymphoid irradiation and antithymocyte serum or total lymphoid irradation and regulatory T cells promoted engraftment whereas these strategies alone did not. These studies demonstrate that using clinically relevant strategies that we can promote engraftment of differentiated cells derived from embryonic stem cells. These findings could have high relevance as these therapies are considered for clinical application.
Reporting Period:
NCE
We have explored the use of clinically relevant strategies to promote the engraftment of embryonic stem cells (ESCs) and differentiated cells derived from ESCs. A major problem with the planned and future clinical use of ESCs as well as differentiated progeny is that they are likely to be rejected by the immune system of the patient. In our studies we have utilized two approaches that have already been tested in the clinic. One is the use of total body irradiation and anti-thymocyte serum which we have successfully utilized in hundreds of patients successfully both with hematologic malignancies and those with kidney failure to promote engraftment of donor derived hematopoietic cells and in some instances with combined hematopoietic cells and kidney transplants. A second approach was to utilize normal T cell populations that have been shown by our group and others to regulate immune reactions, termed regulatory T cells. In our studies in murine models we were able to show that both total lymphoid irradiation and antithymocyte serum alone resulted in the engraftment of ESCs from a genetically different donor, however, these cells grew into tumors called teratomas. When we utilized differentiated progreny derived from the ESCs, which is much more similar to the proposed clinically situation, the combination of total lymphoid irradiation and antithymocyte serum or total lymphoid irradation and regulatory T cells promoted engraftment whereas these strategies alone did not. These studies demonstrate that using clinically relevant strategies that we can promote engraftment of differentiated cells derived from embryonic stem cells. These findings could have high relevance as these therapies are considered for clinical application.
Grant Application Details
Application Title:
Regulatory T cell induced tolerance to ESC transplantation
Public Abstract:
The goals of this proposal are to utilize cell populations known to control immune reactions termed regulatory T cells and study their ability to protect embryonic stem cells (ESC) from immune rejection. Much has been learned about the control of immune reactions where it has been found that a variety of different factors control excessive and at times harmful immune reactions. Clearly the localization of immune responses, blood flow and both pro-inflammatory and anti-inflammatory cytokines or proteins play a major role in the control of immune reactions. More recently has been the discovery that there are specific populations of T cells, termed regulatory T cells, that have the capability of suppressing immune reactions which have enormous potential in clinical medicine. In this grant proposal, two distinct research groups with complementary expertise will come together to study this important problem. The laboratory of [REDACTED] has studied regulatory T cell biology in the setting of bone marrow transplantation and translated key findings to the clinic. The laboratory of [REDACTED] has studied ESC biology and has demonstrated that ESCs will be rejected in animal models. The goals of this research are to explore the biological activity of two distinct regulatory T cell populations in controlling ESC rejection and to develop strategies that could be directly translated to the clinic that are capable of enhancing survival of the ESCs and mature cells derived from ESCs in living animals. These studies will be performed largely in animals due to the complexity of studying immune reactions and the need to study these complex biological reactions in living animals but could be directly applied to humans. [REDACTED] has already established principles for translating regulatory T cell concepts into the clinic and have several ongoing clinical trials in the setting of bone marrow transplantation to explore the biological function of highly purified regulatory T cells. Therefore, results obtained from studies proposed in this application are intended to demonstrate the biological activity of immune regulatory mechanisms on the rejection of ESCs as well as mature progeny derived from ESC populations and develop strategies that are directly applicable to the human condition.
Statement of Benefit to California:
This research will directly benefit the residents of California but like all research also extend to individuals and corporations beyond the State. The goal of this research is to develop clinically applicable strategies to enhance the engraftment and survival of transplanted embryonic stem cells and mature differentiated cell populations derived from these critically important immature cell populations. The studies proposed here will provide important insights into developing clinical trials that will overcome the major problem of rejection of these cell populations which must be solved before this critically important research can reap clinical gains. Insights gained here could be of critical value when ESC based translational strategies are ready for clinical exploration. The studies proposed in this grant application utilize principles that are at the forefront of immunological research and also are directly applicable to the clinic. Importantly, the strategies that will be employed in these studies are being explored in clinical trials of bone marrow transplantation in an effort to reduce the risk of graft-versus-host disease and also to induce tolerance to organ transplantation. These clinical trials are being performed at [REDACTED] located in [REDACTED] which serves as a rich resource for advanced medical care in [REDACTED] and beyond. Therefore, many of the concepts developed in the studies proposed in this grant application will be directly applied to enhancing the biological activity and survival of transplanted embryonic stem cell populations and derived cells and tissues to enhance their function in clinical situations. These studies will be performed eventually in hospitals in the State of California which will be of direct value to the residents of this state, and also could attract other individuals to California for proposed treatments which would enhance the reputations, revenue and overall health of California residents, as well as individuals beyond. Further, many of the reagents, tools and equipment to be utilized in these studies and eventually in the translation of these concepts are under development by companies located in the state of California.
