Early Translational I
Blood stem cells (BSC) within bone marrow, are responsible for producing all the cells found in blood, from red blood cells that carry oxygen, to disease fighting T cells. Many types of cancer, including leukemia, are treated by BSC transplantation, especially after treatment with chemotherapy or radiation. Ideally, a patient should use his own bone marrow for transplantation. However, this is not always possible; a significant number of patients receiving blood stem cell transplantation cannot find a related donor. Instead, they rely on blood stem cells donated by an unrelated donor. Receiving blood stem cells from an unrelated donor has significant benefits, but might have some serious side effects. Often, there are donor T cells present in the blood stem cell sample. T cells uses markers called HLA antigens to recognize cells. Once inside the patient, donor T cells recognize the host HLA antigens as different and attack the patient’s cells. This is beneficial if the attacked cell is a lingering cancer cell, but it is harmful if the attacked cell is a normal cell. The beneficial anti-cancer response is called graft-versus-tumor (GVT) effect. Attacks on normal cells result in a serious condition called graft-versus-host disease or GVHD. Doctors can treat GVHD with drugs that will prevent T cell function. However, these treatments reduce the beneficial graft-versus-tumor effect and weaken the immune system, leaving the patient defenseless against infections. The possibility of infection represents another complication resulting from blood stem cell transplantation. Blood stem cells take a long time to produce enough disease fighting T cells to protect the patient against infection, up to 2 years in some cases. Without T cells, the body does not have a way to fight off germs. This leaves the patient vulnerable to fungal and viral infections. The possibilities of GVHD and infections offset the benefits of blood stem cell transplantation from unrelated donors. Therefore, it is imperative to figure out ways to reduce the possibility of GVHD and infections, while maintaining graft-versus-tumor activity. With this in mind, we intend to transplant human committed T cell progenitors (CTP), cells that are programmed to become T cells, together with unrelated blood stem cells. This treatment has several advantages over traditional blood stem cell transplantation: First, neither CTP nor the T cells they produce cause GVHD. Second, CTP can produce T cells faster than blood stem cells, rapidly providing an army of disease fighting T cells to the patient. These T cells could control lingering tumor cells too, allowing the blood stem cell to establish itself in the patient. Third, few CTPs are needed to achieve these beneficial results, making CTP transplantation feasible. Taken together, the simple addition of CTP to blood stem cell transplants could result in a significant increase in the success of blood stem cell transplantation from unrelated donors.
Statement of Benefit to California:
The State of California and its citizens will benefit from the proposed research in the following ways: Direct impact: The National Marrow Donor Program reports that 2,198 unrelated blood stem cell transplants were conducted in 13 different transplant centers in California, from January 2001 to December 2005. These patients often suffer from devastating graft-versus-host disease and infection. The research proposed here has the potential to significantly increase the capacity of the immune system to fight viral infections, while significantly decreasing the severity of graft-versus-host disease. This will: 1) reduce the amount and time of use of drugs that control GVHD by suppressing the immune system, 2) reduce the rate of infections and 3) reduce the time of hospitalization. Together, these benefits expedite the time of recovery while reducing cost, resulting in a net improvement in quality of life for patients receiving blood stem cell transplants. Health Care: We will test our hypothesis in well-characterized models of transplantation, leukemia and viral infection. If successful, this research would identify a novel developmental candidate that will improve immune function in patients receiving blood stem cell therapies. Most likely, Californians would be the primary recipients of life-saving therapies designed using my research. Moreover, my research is designed to have broad applicability, so that other conditions where T cells are dysfunctional could be tested and improved. Biotechnology: My work already depends on a number of products and instruments made by California companies. If our proof-of-concept studies are successful, bringing this project to the clinic will require a scaled-up version of the protocols described in my studies, using Good Manufacturing Practices. This could attract new biotechnology companies in the state, boosting its tax revenue and providing new jobs for Californians. Public opinion and educational benefits: If successful, my work has the potential to positively affect the public opinion and educational climate in the state of California. Patients who benefited from improved blood stem cell transplants, as well as their friends and family, would become advocates for stem cell research, encouraging the government to adopt better stem cell research policies. This will incite universities to promote science education, generating highly skilled graduates to fill the jobs created by stem cell research in the state. California and out-of-state students interested in biomedical research and health professions will remain in the state, reducing the brain drain of California’s talent. I foresee that K-12 education will also benefit, by receiving funding to improve and promote science education at all levels.
This development candidate proposal focuses on the development of a cell therapy to increase the success of allogeneic hematopoietic stem cell transplant (HSCT) by reducing the incidence and severity of graft-versus-host disease (GVHD). HSCT is used to treat patients with malignant and nonmalignant blood disorders. GVHD is caused when donor T-cells present in the allogeneic hematopoietic stem cell (HSC) graft recognize patient antigens and initiate an immune response. Immunosuppressive drugs are used for prevention and treatment of GVHD but also make patients susceptible to infection. The applicant hypothesizes that GVHD can be avoided by transplanting committed T-cell progenitors (CTPs) along with purified HSCs. The applicant proposes to characterize the cellular and molecular phenotype of isolated CTPs from human bone marrow, determine their developmental potential and test their functionality in immunodeficient mouse models. Reviewers agreed that this proposal addresses important issues in allogeneic HSCT but cautioned that its findings may not be easily translated to the clinic. Specifically a reviewer noted that xenogeneic transplants into an immunodeficient mouse model cannot address the problem of graft failure, which has haunted T-cell depletion and repletion studies in humans. This reviewer also pointed out that most HSCT involves HLA-matched donors, a scenario that’s difficult to model using xenogeneic transplants. It was pointed out that human into mouse model does not typically show human GVHD and mouse to mouse models have not been very predictive of human GVHD development. One reviewer did feel that the authors made a good case for the co-transplantation of CTPs with HSCs and other reviewers agreed that if these cells could convey all of the benefits hypothesized by the applicant the proposal would have significant impact. The reviewers raised a number of doubts about the feasibility of the research plan. They noted that Aims 2 & 3 both depend on experiments described in Aim 1, involving the isolation of CTPs from human bone marrow, yet no preliminary data is presented suggesting this is possible. One reviewer pointed out that human T-cell depletion studies, while effective in reducing the risk of GVHD, have frequently been plagued by high rates of graft rejection and loss of beneficial graft-versus-tumor (GVT) activity. This reviewer had difficulty accepting the hypothesis that CTP co-transplantation strategy could eliminate GVHD while both avoiding graft rejection and retaining GVT effects. A reviewer raised issue with the GVT studies that will use human cell lines that will generally be HLA disparate with most marrows tested. This reviewer noted that while most human HSCT involves HLA-matching, GVT effects in HLA-mismatched settings are thought to involve NK cells, which seem to be removed in the process of generating CTPs. Furthermore, the applicant failed to take into consideration the issue of decreased thymic function specifically in older patients. It is unclear what effect that will have on the CTP responses. For these reasons the reviewer expressed doubt that GVT effects would be seen in the mouse model. Reviewers also pointed out that testing the capacity of human CTP transplants to control murine cytomegalovirus (CMV) may not be the best approach as it presumes not only cross-reactivity between human and murine CMV immunologic epitopes, but also that the human marrow donor is CMV+. Another reviewer noted that the applicant’s argument for a dose advantage of CTPs over common lymphoid progenitors is irrelevant given the lack of data describing how easily CTPs can be harvested, processed and isolated. Furthermore the applicant does not propose to isolate CTPs in a clinically-relevant, GMP-compliant manner or evaluate efficiency of recovery. The applicant has relevant expertise and has published several papers dealing with T-cell development and NK function. The collaborators include appropriate clinical and non-clinical investigators with skill sets needed for the proposal. Reviewers commented that the budget seems large, specifically the amount requested for supplies and equipment. Overall, the reviewers agreed that the proposal addresses important issues surrounding HSCT but they raised significant questions about the feasibility of the research plan and considered the proposed research premature for early translation.