Funding opportunities

Stem Cell Transplantation using Psoralen treated T-lymphocytes

Funding Type: 
Transplantation Immunology
Grant Number: 
RM1-01715
Funds requested: 
$1 323 182
Funding Recommendations: 
Not recommended
Grant approved: 
No
Public Abstract: 
While stem cell transplants of bone marrow have cured many patients, immune rejection of stem cell grafts, as well as the development of graft versus host disease remains a challenge. Immunosuppressive therapies have led to significant improvement in the survival of these patients, as well as patients receiving solid organs from donors. However, these treatments are non-specific and increase the risks for long term negative outcome. We propose a novel approach for inducing robust, and sustained tolerance of stem cell transplants, with the potential to be of major benefit not only for bone marrow stem cell replacement therapies, but also for regenerative medicine of other tissues. Our research has shown that we were able to overcome matching requirements in bone marrow transplants in the mouse, when we added miss-matched white blood cells (T-cells) treated with a chemical called psoralen to stem cells. This approach promoted stable engraftment of both bone marrow and cordblood derived stem cells, and avoided graft versus host disease. Our current data suggests that our protocols modulate the properties of the immune system in the recipient. In this proposal we aim to clarify the mechanisms that govern these changes. We speculate that modulation of the immune system by partially replacing bone marrow using our protocols may induce specific tolerance towards donor stem cells. This in turn may lead to graft acceptance, may modulate auto-immunity, and open a new opportunity for the successful cell therapy of a variety of diseases, as it leads to stable engraftment rather than rejection. These studies will have a major impact on clinical transplantation in sickle cell anemia as it addresses the acute lack of suitable donors. Partly mismatched units can overcome current compatibility barriers, prevent GVHD, and promote donor engraftment. Our proposed research will use human and murine stem cells in combination with psoralen treated T-cell add-back technology to: • Improve protocols to facilitate hematopoietic stem cell transplant in poorly matched donor-recipient pairs, with full T- and B- cell reconstitution. • Define the reprogramming of the host immune system to accept stem cell grafts, and optimize tolerance induction to stem cell derived grafts via hematopoietic and/or thymic chimerism. Our proposed studies will render a better understanding of the development of immune tolerance of pluripotent stem cell derivatives, the potential correction of autoimmunity, and will form the basis for a novel approach to improve clinical stem cell transplantation.
Statement of Benefit to California: 
While stem cell transplants of bone marrow have cured many patients, immune rejection of stem cell grafts, as well as the development of graft versus host disease remains a challenge. Immunosuppressive therapies have led to significant improvement in the survival of these patients, as well as patients receiving solid organs from donors. However, these treatments are non-specific and increase the risks for long term negative outcome. A better understanding of the mechanisms that lead to stable engraftment of stem cells to replace or restore tissues lost to injury or disease represents one of the most promising outcomes of regenerative medicine. We propose a novel approach for inducing robust, and sustained tolerance of stem cell transplants, with the potential to be of major benefit not only for bone marrow stem cell replacement therapies, but also for regenerative medicine of other tissues. Our research has shown that we were able to overcome matching requirements in bone marrow transplants in the mouse, when we added miss-matched white blood cells (T-cells) treated with a chemical called psoralen to stem cells. This approach promoted stable engraftment of both bone marrow and cordblood derived stem cells, and avoided graft versus host disease. Our current data suggests that our protocols modulate the properties of the immune system in the recipient. In this proposal we aim to clarify the mechanisms that govern these changes. We speculate that modulation of the immune system by partially replacing bone marrow using our protocols may induce specific tolerance towards donor stem cells. This in turn may lead to graft acceptance, may modulate auto-immunity, and open a new opportunity for the successful cell therapy of a variety of diseases, as it leads to stable engraftment rather than rejection. These studies will have a major impact on clinical transplantation in a variety of diseases that affect the residents of California. One such example with immediate benefit are patients with the sickle cell anemia as our study addresses the acute lack of suitable donors. Partly mismatched units can overcome current compatibility barriers, prevent GVHD, and promote donor engraftment. Our proposed research will use human and murine stem cells in combination with psoralen treated T-cell add-back technology to: • Improve protocols to facilitate hematopoietic stem cell transplant in poorly matched donor-recipient pairs, with full T- and B- cell reconstitution. • Define the reprogramming of the host immune system to accept stem cell grafts, and optimize tolerance induction to stem cell derived grafts via hematopoietic and/or thymic chimerism. Our proposed studies will render a better understanding of the development of immune tolerance of pluripotent stem cell derivatives, the potential correction of autoimmunity, and will form the basis for a novel approach to improve clinical stem cell transplantation.
Review Summary: 
This is a proposal to investigate the use of psoralen S59 photochemically treated T cells (T59 cells) to enhance the engraftment of allogeneic hematopoietic stem cells (HSCs) without inducing associated graft versus host disease (GVHD). The approach is based on the concept that appropriate doses of psoralen S59 and UV light exposure will induce DNA cross linking sufficient to prevent proliferation of T cells but not kill them, as evidenced by cytokine production and other immunological functions. These proliferation-defective T59 cells, when added back to HSC populations, should help engraftment without inducing GVHD. In Aim 1, the principal investigator (PI) proposes to improve protocols to facilitate HSC transplantation in poorly matched donor recipient pairs in mouse models of allogeneic transplantation. In Aim 2, the PI proposes to define the changes to the host immune system that are necessary to accept stem cell grafts, and optimize tolerance induction to stem cell derived grafts via hematopoietic and/or thymic chimerism. Although the rationale underlying this project is sound, reviewers were critical of this proposal. They commented that the experiments were not particularly novel or creative, which left them unconvinced that the project would have a strong impact on the field. The preliminary data was limited and poorly presented, and previous research on this topic in the lab was not as thorough as the reviewers would have expected, raising concerns about project feasibility. Finally, the proposal itself was described as poorly organized and unfocused. Overall, reviewers were concerned about the team’s ability to provide novel information to the field. The modification of T cells to preserve engraftment of HSC without GVHD has been a major focus in transplantation biology for many years, and a successful strategy for doing this would have major impact on the field. However, the use of psoralen S59 photochemical treatment has been used, with moderate success, by these investigators and others for over a decade. Reviewers commented that the experiments described in this application were not particularly novel, and did not use state-of-the-art technologies. Reviewers were unconvinced that the research proposed would impact the field substantially. The scientific rationale for the project is sound, and investigators have used the approach in different bone marrow transplant models with variable success. The basic questions addressed in this proposal - whether third party T59 cells can promote engraftment, whether the animals are immunologically competent, whether they have associated donor specific tolerance, and where T59 cells migrate to – are not difficult questions. However, reviewers felt that the PI did not adequately define the model system to be used, and that the experiments and controls were inadequate. For instance, reviewers commented that the proposed time points of analysis of “long-term” chimerism are not adequate for assessing the long-term engraftment of HSCs. At least twice that duration is standard in the field. Some of the key experiments to study the kinetics of T59 cell survival, proliferation and homing in the allogeneic host were not described. The assessment of donor specific tolerance is also rudimentary, as the chimeric animals would be expected to be tolerant of additional cells from the same donor. Reviewers were concerned that this group had not conducted these studies already, given that their first publication on improved engraftment with T59 cells was several years ago and all of these questions are relatively easy to address with a few basic experiments. Reviewers commented that the experiments described in the second specific aim will not provide much new or useful information regarding the mechanism of enhancement of engraftment or reduction of GVHD. The PI describes in vitro co-culture studies to assess changes in donor and recipient T cell populations, but does not include in vivo experiments, which would be easy to perform. Others have described upregulation of regulatory T cells (Tregs) by psoralen treated lymphocytes in vivo. This mechanism could be easily investigated in chimeric mice with both a quantitative and functional read out of Treg activity. Finally, reviewers commented that the preliminary data was not compelling, that the aims as presented are unfocused, without defining exactly what experiments are planned and what hypotheses will be addressed. This made it difficult to assess whether the PI could accomplish the aims in three years. The PI has a moderate track record of publications, and is only moderately funded. The proposal calls for a large team of co-investigators, but it is not clear what role each will play. Given the team’s lack of progress on basic questions related to the T59 approach over the past several years, there is concern regarding the team’s ability to provide new and important information with the proposed experiments in this application. In conclusion, although the area of research was scientifically valid, reviewers were unconvinced that the project would have an important impact on the field.
Conflicts: 

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