PROJECT SUMMARY/ABSTRACT Alloimmunization is the physiological response to allogeneic antigens encountered by the host during pregnancy, blood transfusion, or transplantation. B cell-derived alloantibodies are generated in this response which do not contribute to infection control but instead constitute a barrier to life-saving blood transfusion or transplantation. The most prominent allogeneic humoral barriers are MHC class I human leukocyte antigens (HLA) due to their strong immunogenicity and broad tissue expression. Donor-specific antibodies to these antigens are leading causes of antibody-mediated graft rejection and ineffective platelet transfusion. To target HLA-specific antibody- producing B cells, we have engineered MHC-Fc fusion proteins by linking an HLA class I antigen with the Fc portion of an antibody molecule. Our preliminary data show that such HLA class I-Fc fusion proteins potently kill B cell hybridomas with cognate specificities. This effect occurs in an antigen-specific and Fc-dependent manner in vitro and in vivo. Here, we will extend our findings to examine these lead biologics in pre-clinical settings to demonstrate their applicability. We hypothesize that MHC-Fc treatment can modify antibody-mediated disease processes and attenuate alloimmunization to specific MHC class I antigens. We will test this central hypothesis in three aims. In Aim 1, we will evaluate the efficacy and specificity of MHC-Fc treatment in a platelet refractoriness model. In Aim 2, we will test the feasibility of desensitization by MHC-Fc treatment in a skin transplant model. In Aim 3, we will test whether MHC-Fc treatment can induce antigen-specific humoral suppression in a murine alloimmunization model involving bone fide polyclonal B cells producing anti-MHC class I antibodies. Our proposed work allows critical evaluation of MHC-Fc prototypes in models that either mimic the settings of their anticipated clinical applications (Aims 1 and 2) or offer a physiological source of B cells as the therapeutic target (Aim 3). The results from these experiments will open a novel avenue of research in precision medicine for the selective induction of antigen-specific humoral tolerance.

PROJECT NARRATIVE Alloimmunization is the physiological response to foreign proteins encountered during pregnancy, blood transfusion, or transplantation. The resultant immune response to these foreign proteins constitutes a barrier to life-saving blood transfusion or transplantation. Here, we aim to develop a therapy to eliminate the B cell- derived portion of the alloimmunization to specific antigens as a means to eliminate this barrier.