Simultaneous, cell-intrinsic downregulation of PD-1 and TIGIT can enhance effector function of CD19-targeting CAR T cells and promote early memory phenotype

CD19-targeting chimeric antigen receptor (CAR) T cell have become an important therapeutic option for patients with relapsed and refractory B cell malignancies. However, according to the recent clinical data, a significant portion of patients still do not benefit from the therapy, due various resistance mechanisms including the high expression of multiple inhibitory immune checkpoint receptors on activated CAR-T cells. Studies of checkpoint blockade immunotherapy using monoclonal antibodies have shown that simultaneously targeting inhibitory receptors that are functionally non-redundant can synergistically enhance anti-tumor responses. Here we report a lentiviral two-in-one CAR T approach in which two checkpoint receptors can be downregulated simultaneously by a dual short-hairpin RNA (shRNA) cassette integrated into a CAR vector. Using this system, we evaluated CD19-targeting CAR T cells in the context of four different checkpoint combinations, PD-1/TIM-3, PD-1/LAG-3, PD-1/CTLA-4, and PD-1/TIGIT, and found that the CAR T with PD-1/TIGIT downregulation uniquely exhibited synergistic anti-tumor effect in mouse xenograft models compared to the single PD-1 downregulation and maintained cytolytic and proliferative capacity upon repeated antigen exposure. Importantly, functional and phenotypic analysis of CAR T cells as well as analysis of transcriptomic profiles suggests that downregulation of PD-1 enhances short-term effector function while downregulation of TIGIT is primarily responsible for maintaining a less-differentiated/exhausted state, providing a potential mechanism of the synergy. The PD-1/TIGIT downregulated CAR T cells generated from DLBCL patient-derived T cells following clinically applicable manufacturing process also showed a robust anti-tumor activity and significantly improved persistence in vivo compared to conventional CD19-targeting CAR T cells. Overall, our results demonstrate that the cell-intrinsic PD-1/TIGIT dual downregulation strategy may provide an effective way to overcome the immune checkpoint-mediated resistance in CAR T therapy. RNAseq profiling of first and second restimulation CD19 specfic CAR T cells with GFP, PD-1, TIGIT, or PD-1/TIGIT downregualtion