Advanced Genetic Engineering to Unravel Tumor-Specific B Cell Responses - RESEARCH SUMMARY B cells are among the most abundant tumor-infiltrating immune cells, and their presence in several solid tumors is associated with a more favorable prognosis. Yet, investigations on the role of B cells in cancer have so far yielded contradicting results, with some studies indicating a tumor-promoting role and others suggesting anticancer activity. In addition to their role in the production of antibodies, naturally occurring cancer-specific B cells can directly participate in tumor suppression by i) direct killing of tumor cells via granzyme B, TRAIL, and FasL expression and ii) by triggering robust T cell immunity, through activation of inflammatory responses and/or through their professional antigen-presenting cell (APC) function. Indeed, tumor-infiltrating B cells often form immune compartments called tertiary lymphoid structures (TLS), the presence of which in human tumors is associated with a favorable response to immunotherapy. Preclinical studies have shown that adoptive transplant of effector B cells collected from the tumor-draining lymph nodes (TDLN) of BC-bearing mice mediate the reduction of lung metastases and trigger the establishment of tumor-specific T cell immunity. However, tumor- specific B cells within TDLN are rare and difficult to specifically select and expand from the extensive polyclonal repertoire of patient B cells. Here, we hypothesized that homology-driven gene editing could be exploited to rapidly generate tumor-specific B cells that can be used to study the role of antigen-specific B cells in tumor progression, with the ultimate goal of developing innovative immunotherapeutic strategies. We will exploit an optimized B cell gene editing protocol we have recently developed to redirect the specificity of the endogenous B cell receptor (BCR) towards the HER2 tumor-associated antigen. The efficacy and tolerability of this adoptive immunotherapy strategy will be evaluated in vivo by exploiting both mouse models of breast tumors expressing human HER2 and xenogeneic murine models of human cell transplantations. The bidirectional interaction of transplanted B cells with immune cells of the tumor microenvironment will be investigated by single-cell transcriptome analyses. Establishment of epitope spreading and T cell immunity will be assessed by measuring tumor cytotoxicity and cytokine production of T cells harvested from the transplanted mice. If successful, this novel precision medicine strategy will redirect both the humoral and cellular immunity against cancer, thus introducing a new and powerful weapon to the oncologic therapeutic armamentarium and opening new avenues for empowered cancer-adoptive immunotherapies.
