Human CAR T cells with cell-intrinsic PD-1 checkpoint blockade resist tumor-mediated inhibition

TLDR

Solid tumors upregulate coinhibitory ligands after immune attack, creating adaptive resistance that hampers CAR T cell therapy efficacy. The study examined whether PD‑1–mediated exhaustion impairs mesothelin‑targeted CAR T cells and tested cell‑intrinsic methods to counteract this inhibition. The authors used PD‑1/PD‑L1 blockade via antibody, shRNA, or a dominant‑negative receptor to restore CD28 CAR T‑cell function. In a pleural mesothelioma mouse model, high‑dose CD28‑ and 4‑1BB‑based CAR T cells eradicated tumors, whereas at lower doses 4‑1BB CAR T cells outperformed CD28 CAR T cells in persistence and survival; PD‑1 blockade restored CD28 CAR T‑cell function, showing that PD‑1/PD‑L1 inhibition limits CAR T‑cell efficacy and that its blockade can improve potency.

Abstract

Following immune attack, solid tumors upregulate coinhibitory ligands that bind to inhibitory receptors on T cells. This adaptive resistance compromises the efficacy of chimeric antigen receptor (CAR) T cell therapies, which redirect T cells to solid tumors. Here, we investigated whether programmed death-1-mediated (PD-1-mediated) T cell exhaustion affects mesothelin-targeted CAR T cells and explored cell-intrinsic strategies to overcome inhibition of CAR T cells. Using an orthotopic mouse model of pleural mesothelioma, we determined that relatively high doses of both CD28- and 4-1BB-based second-generation CAR T cells achieved tumor eradication. CAR-mediated CD28 and 4-1BB costimulation resulted in similar levels of T cell persistence in animals treated with low T cell doses; however, PD-1 upregulation within the tumor microenvironment inhibited T cell function. At lower doses, 4-1BB CAR T cells retained their cytotoxic and cytokine secretion functions longer than CD28 CAR T cells. The prolonged function of 4-1BB CAR T cells correlated with improved survival. PD-1/PD-1 ligand [PD-L1] pathway interference, through PD-1 antibody checkpoint blockade, cell-intrinsic PD-1 shRNA blockade, or a PD-1 dominant negative receptor, restored the effector function of CD28 CAR T cells. These findings provide mechanistic insights into human CAR T cell exhaustion in solid tumors and suggest that PD-1/PD-L1 blockade may be an effective strategy for improving the potency of CAR T cell therapies.