Chimeric HLA antibody receptor T cells to target HLA-specific B cells in solid organ transplantation

HLA-sensitized patients on the transplant waiting list harbor antibodies and memory B cells directed against allogeneic HLA molecules, which decreases the chance to receive a compatible donor organ. Current desensitization strategies non-specifically target circulating antibodies and B cells, warranting the development of therapies that specifically affect HLA-directed humoral immune responses. We developed Chimeric HLA Antibody Receptor (CHAR) constructs comprising the extracellular part of HLA-A2 or HLA-A3 coupled to CD28-CD3ζ domains. CHAR-transduced cells expressing reporter constructs encoding T-cell activation markers, and CHAR-transduced CD8⁺ T cells from healthy donors were stimulated with HLA-specific monoclonal antibody-coated microbeads, and HLA-specific B cell hybridomas. CHAR T cell activation was measured by upregulation of T cell activation markers and IFNγ secretion, whereas CHAR T cell killing of B cell hybridomas was assessed in chromium release assays and by IgG ELISpot. HLA-A2- and HLA-A3-CHAR expressing cells were specifically activated by HLA-A2- and HLA-A3-specific monoclonal antibodies, either soluble or coated on microbeads, as shown by CHAR-induced transcription factors. HLA-A2 and HLA-A3 CHAR T cells efficiently produced IFNγ with exquisite specificity and were capable of specifically lysing hybridoma cells expressing HLA-A2- or HLA-A3-specific B-cell receptors, respectively. Finally, we mutated the α3 domain of the CHAR molecules to minimize any alloreactive T-cell reactivity against CHAR T cells, while retaining CHAR activity. These data show proof of principle for CHAR T cells to serve as precision immunotherapy to specifically desensitize (highly) sensitized solid organ transplant candidates and to treat antibody-mediated rejection after solid organ transplantation.