BiTE-secreting T cells effectively target ovarian cancer and prolong antitumor immunity by persisting in the extratumoral peritoneal cavity

Cancer immunotherapies can produce complete therapeutic responses, however outcomes in ovarian cancer (OC) are modest and while adoptive transfer of engineered T cells (ACT) has been evaluated in OC, durable effects are rarely observed. T cells lacking tumor specificity (bystander T cells) readily accumulate in tumors and leveraging bystander T cell activity represents a promising opportunity to enhance antitumor immunity following ACT. To this end, we have generated T cells that stably secrete a FRa-directed bispecific T cell engager (FR-B T cells), which robustly targeted FRa+ tumor cells in OC patient specimens and effectively engaged patient T cells present in the tumor microenvironment (TME). Therapeutic testing of FR-B T cells using an immunocompetent OC model demonstrated robust activity, with response duration dependent on both endogenous T cells and FR-B T cell persistence. Cytokine preconditioning prior to infusion produced less differentiated FR-B T cells and improved therapeutic efficacy, with mechanistic studies revealing preferential accumulation of TCF-1+ CD69-CD39- stem-like CD8+ FR-B T cells in the peritoneal cavity over solid tumors. These findings highlight the potential of FR-B T cell therapy in OC and suggest the peritoneal TME permits FR-B T cells to persist in the extratumoral space while actively directing antitumor immunity. Overall design: RNAseq analysis of sorted CD8+ FR-B TALs pre-conditioned with IL-2/IL-7 or IL-2/IL-15 was conducted using the Takara Bio USA, Inc. SMART-Seq® v4 PLUS Kit