IMMU-10. ENGINEERED PD-L1 RECEPTORS AUGMENT ANTI-TUMOR ACTIVITY OF HER2 CAR T CELLS IN HIGH GRADE GLIOMA. (31st May 2017) - Landi, Daniel
Abstract: HER2-specific chimeric antigen receptor (CAR) T cells induced objective yet transient responses in children with high grade glioma (HGG; NCT01109095; JAMA Oncology in press). At this stage, it becomes mandatory to seek conceptual "tumor specific" innovations in preclinical models if complete tumor elimination is to be achieved. For HGG, a strategy to combat the immunosuppressive tumor microenvironment is necessary. We endowed HER2 CAR T cells with resistance to programmed cell death-1 (PD-1) using chimeric checkpoint reversal receptors (CPRs). CPRs consisted of the native PD-1 extracellular domain followed by a transmembrane domain fused to an intracellular signaling domain. The signaling domain contained co-stimulatory T cell molecules such as CD28 and 4-1BB. Engagement of the CPRs with PD-L1 molecules within the tumor bed would thus elicit co-stimulatory survival signals rather than the native inhibitory signal. We designed a panel of candidate CPRs and co-expressed these with our clinical-grade HER2-CAR (FRP5.CD28ζ) on HGG patients' T cells using a bicistronic transgene. HER2 CAR T cells expressing CPRs exhibited higher activation potential and sustained in vitro anti-tumor activity against autologous HGG over unmodified HER2-CAR T cells. CAR T cells with CPRs containing the 4-1BB domain preferentially developed a central memory phenotype optimal for sustained anti-tumor activity in patients. Three-dimensional reconstitution and quantification of super-resolution confocal images of the CAR T-cell/tumor-cell interface revealed a more stable immunological synapse and demonstrated higher levels of activated signaling kinases in T-cell co-stimulatory pathways. Interestingly, activated CAR T cells expressing CPRs exhibited increased aerobic glycolysis while unmodified HER2-CAR T cells exhibited higher lipid oxidation denoting metabolic stress. HER2 CAR T cells with 4-1BB CPRs also significantly improved survival in a murine xenograft model. We conclude that CPRs, the synthetic PD-1 fusion molecules, improve the differentiation, metabolism, and molecular signaling of HER2 CAR T cells, thereby increasing their anti-glioma activity.