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

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.

Is autoimmunity the Achilles' heel of cancer immunotherapy?

“…These attempts to create checkpoint-resistant T cells are likely to increase both their general efficacy and autoantigen-mediated effects 63,64,102 . Thus, controlling potential off-target effects of CAR and TCR-transduced T cells will depend on choosing an appropriate tumor-specific antigen, eliminating the endogenous TCR, engineering CAR T cells reliant on multiple tumor-associated antigens for activation 103 , and inserting suicide genes, such as iCaspase-9 or other regulated receptors 75 , that allow for quick inactivation in the event of off-target effects.…”

Axicabtagene ciloleucel, a first-in-class CAR T cell therapy for aggressive NHL

“…Like their endogenous counterparts, CAR T cells express and upregulate programed cell death protein 1 (PD-1) [68], a pathway that can be co-opted by tumor cells to impair T cell function. Results of preclinical experiments in mouse models have demonstrated that combining CAR T cell therapy with PD-1 pathway blockade maximizes CAR T cell activity and results in increased tumor reduction [69,70]. The first interventional clinical studies of CAR T cells in combination with checkpoint blockade agents are accruing.…”

CARs on the Highway: Chimeric Antigen Receptor Modified T Cells for the Adoptive Cell Therapy of Malignant Diseases

“…With that respect, the 4-1BB CAR initiates a long-lasting central memory and the CD28 CAR a more short-lived effector cell response. Both CD28 and 4-1BB CAR T cells in high doses eradicates large established tumors in preclinical models; at lower doses, CD28 CAR T cells show larger degree of exhaustion than the 4-1BB CAR T cells and treatment with 4-1BB CAR T cells more efficiently eradicated tumors [25]. T cells with 4-1BB CAR are still sensitive to tumor-mediated inhibition, however, show less exhaustion and decline in cytolytic capacities and cytokine secretion upon repeated antigen encounter than CD28 CAR T cells.…”

“…Suppression by TGF-β can moreover be prevented by engineering T cells with a dominant negative mutant of TGF-β [104,105]. PD-1 upregulation within the tumor suppresses the T cell anti-tumor response; blocking the PD-1/PD-1 ligand pathway through PD-1 antibody checkpoint blockade, cell-intrinsic PD-1 shRNA blockade, or a PD-1 dominant negative receptor, improves CAR T cell activity in a preclinical model [25].…”