Chimeric <scp>HLA</scp> antibody receptor T cells to target <scp>HLA</scp>‐specific B cells in solid organ transplantation

Abstract

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.