293 Development of a MUC16-specific CAR-T cell exhibiting potent antitumor activity for the treatment of patients with recurrent ovarian cancer

BackgroundDespite significant improvements in surgical and medical treatments, ovarian cancer remains the most lethal gynecologic malignancy, with a 2-to 3-year recurrence rate, highlighting an unmet need for effective therapeutic options for patients.1 Mucin 16 (MUC16) is a type I integral membrane glycoprotein that is overexpressed in more than 80% of ovarian cancers.2 Proteolytic cleavage of full length MUC16 results in the shedding of CA125 into the bloodstream, leading to a truncated ectodomain at the cell surface.3 Here, we report the development of a chimeric antigen receptor (CAR) T cell product (BB4015) targeting the membrane-retained MUC16 ectodomain for the treatment of patients with recurrent ovarian cancer.Methods in vitro assessment: Human ovarian tumor samples were evaluated for MUC16 expression via immunohistochemistry. BB4015’s phenotypic and functional assessments were evaluated using anti-MUC16 CAR T cells derived from LVV transduction of healthy donor PBMCs. BB4015 phenotype was defined via flow cytometry by CD4, CD8, CD62L, and CD45RA expression. BB4015 function was assessed for antigen-dependent cytokine release/cytotoxicity where BB4015 was co-incubated with antigen positive/negative tumor or primary cells. To determine the off-target binding potential of BB4015’s scFv, we employed a cellular microarray platform (Retrogenix/Charles River) encoding 5,868 full-length human plasma membrane and secreted proteins. in vivo assessment: BB4015 efficacy was evaluated for tumor growth suppression in female NSG mice inoculated with OVCAR3 tumor cells via intraperitoneal injection. Tumor burden and animal weight were measured 3 times a week from tumor-bearing mice infused with BB4015. Live blood draws were taken at various time points following infusion to determine BB4015 pharmacokinetics.Results96% of ovarian tumor biopsies evaluated stained positive for MUC16 expression with an antibody raised against the membrane-retained MUC16 ectodomain. BB4015 reactivity to recombinant MUC16 ectodomain elicited specific and dose-dependent cytokine release, with no detectable reactivity to soluble CA125 protein. BB4015’s scFv displayed no observable off-target binding. BB4015 exhibited phenotypic skewing toward a more central memory/naïve-like T cell subtype. This has been attributed to increased antitumor efficacy/greater antigen recall, compared to more effector memory subtypes.4 5 In mice bearing OVCAR3 ovarian tumors, BB4015 infusion inhibited tumor gr