Role of intracytoplasmic pattern recognition receptors in HSC engraftment

The research performed through this project is very important for the fields of solid organ and bone marrow transplantation because it focuses on a potential new target to increase engraftment of stem cells. Currently, patients that receive stem cell transplants from a non-identical donor must take medications to suppress their immune system; otherwise the stem cells will be rejected. In our first year of this project we were able to develop a reliable model to delete specific receptors which directly influence stem cell engraftment in genetically different hosts. We have also found that deletion of defined receptors greatly improves stem cell engraftment for up to 20 weeks after injection in a murine model of bone marrow transplantation. The plan for the next reporting period is to continue to focus our studies on characterizing the lodging and fate of the engrafted stem cells in long-lasting chimeric animals and to look into ways to improve the opportunities for long-term transplant survival without the use of toxic immunosuppressive medications.

The scientific progress on this award has been extensive. The purpose of this project was to determine whether we could improve the efficiency of hematopoietic stem cell (HSC) engraftment in order to downregulate the host response to transplanted organs, by essentially tricking the host into accepting a foreign organ as it's own. There were two aims of the project. The first aim was to essentially optimize the engraftment of HSC and the second aim was to test how improved engraftment yielded improvements in transplantation efficiency and understand the immunologic mechanisms by which the transplant was accepted. In Aim 1 we developed a murine model of hematopoietic stem cell-induced mixed chimerism and discovered that the deletion of specific receptors that resided on the cells, but not others, directly influenced HSCs engraftment in allogeneic hosts. During the first funding period we focused on defining which specific receptors contributed to HSC engraftment. During the second funding period we defined whether engraftment was specific to the specific receptors and determined the fate of the engrafted cells. In Aim 2, we studied whether the receptor deficiency resulted in host unresponsiveness to donor antigens and we conducted extensive experiments to analyze the role of the specific receptors in host T cell activation and T cell unresponsiveness, using mixed lymphocyte experiments, cytokine analyses, flow cytometric and molecular biology experiments. There were two foci to this aim. The first was to determine whether HSC engraftment resulted in host unresponsiveness to donor antigens and the second was to define those mechanisms that caused downregulation of host responses. In this aim we were able to define the mechanisms by which the host unresponsiveness occurred, which set the stage for future manuscript submissions and future grant proposals directed at how to manipulate these receptors on human hematopoietic stem cells.