Transplantation is curative treatment for end-stage organ failure. Antibodies that are directed against donor HLA, termed donor specific antibodies (DSA), are associated with rejection and are increasingly recognized as a barrier to improving long-term transplant outcomes. DSA are serially monitored in transplant patients using advanced methods, but treatment strategies are resource intensive and have limited efficacy. Memory B cells that differentiate following allogeneic sensitization form a cellular reservoir that differentiates into antibody secreting plasma cells in the presence of antigen. Despite their role in contributing to DSA formation, the memory B cell compartment is not assessed clinically and there are no effective therapeutic strategies that inhibit it. Recent work has established the importance of the PD-1 pathway in restraining adaptive immunity, but the role of PD-L2 on B cells is not well understood. In this proposal, we have developed a cutting-edge approach to study murine allogeneic B cells through all stages of differentiation from nave to memory. Using an approach of selective PD-L2 ablation on B cells, we will assess the requirements for germinal center dependent and independent formation of allogeneic memory. In the mentored K99 Phase in Aim 1, we will assess the role of PD-L2 on the differentiation of secondary germinal centers and plasmablasts following restimulation.
In Aim 2, we will investigate the effect of B cell expressed PD-L2 on PD-1+ CD4+ T follicular populations using MHC Class II tetramers to identify allogeneic CD4+ T cells. Finally, in Aim 3, during the independent R00 phase, I will investigate activated B cell subsets in the blood of renal transplant patients who form DSA following transplantation. We will examine the possibility that the proliferating activated B cell subsets can be used as a biomarker of DSA formation and rejection in conjunction with the degree of known epitope mismatches at MHC Class II loci. Finally, we will assess the ability of PD-L2 blockade with a monoclonal antibody to inhibit B cell proliferation and antibody production in vitro. The proposed work is aligned with the NIAID strategic priority of identifying therapeutic targets for the enhancement of translational efforts to extend renal allograft survival through preclinical research. These findings will lead to new understanding of the key factors that determine the potency of memory B cells and the cellular processes that lead to DSA formation. Through this work we hope to identify new therapeutic checkpoints that can be exploited to inhibit memory B cell formation and prevent DSA formation and antibody mediated rejection. I am applying for this K99/R00 as a clinical histocompatibility fellow with extensive experience as a T cell immunologist. This application will support extensive advanced training as a B cell immunologist. My long-term career goal is to become an HLA laboratory director with an independently funded basic science laboratory.
Memory B cells play a critical role in the formation of anti-HLA antibodies that mediate immunologic injury following solid organ transplantation. Programmed death ligand 2 (PD-L2) is a B cell surface receptor that plays a crucial role in the formation of memory B cells and is an attractive therapeutic target for restraining donor-specific antibody formation. Improved outcomes following transplantation will reduce the public health burden associated with end-stage organ failure and lifelong immunosuppression.
