Evaluating Novel Therapeutic Strategies to Enhance CAR-T Cell Efficacy Using Patient-Derived Organotypic Tumor Spheroids

Novel therapeutic strategies are needed to improve the efficacy of chimeric antigen receptor (CAR)-T cells in the treatment of solid tumors. Multiple tumor microenvironmental factors are thought to contribute to CAR-T cell therapy resistance in solid tumors, and appropriate model systems to identify and examine these factors using clinically relevant biospecimens are limited. Here, we examined the activity of B7-H3 (CD276) directed CAR-T (B7-H3.CAR-T) using 3D microfluidic cultures of patient-derived organotypic tumor spheroids (PDOTS) and confirmed activity of B7-H3.CAR-T in PDOTS. While B7-H3 expression in PDOTS was associated with B7-H3.CAR-T sensitivity, mechanistic studies revealed dynamic upregulation of co-inhibitory receptors on CAR-T cells following target cell encounter that led to CAR-T cell dysfunction and limited efficacy against B7-H3 expressing tumors. PD-1 blockade restored CAR-T activity in monotypic and organotypic tumor spheroids with improved tumor control and upregulation of effector cytokines. Given the emerging role of TANK-binding kinase 1 (TBK1) as an immune evasion gene, we examined the effect of TBK1 inhibition on CAR-T efficacy. Similar to PD-1 blockade, TBK1 inhibition restored CAR-T activity in monotypic and organotypic tumor spheroids, prevented CAR-T cell dysfunction, and enhanced T cell proliferation. Inhibition or deletion of TBK1 also enhanced sensitivity of cancer cells to immune-mediated killing. Taken together, our results demonstrate the feasibility and utility of ex vivo profiling of CAR-T cells using PDOTS and suggest that targeting TBK1 is a novel strategy to enhance CAR-T efficacy by overcoming tumor-intrinsic and -extrinsic resistance mechanisms.