Suppression of tumor/host intrinsic CMTM6 drives anti-tumor cytotoxicity in a PD-L1 independent manner

CKLF-like MARVEL transmembrane domain-containing 6 (CMTM6) has been identified as a regulator of membranal programmed death ligand 1 (PD-L1) stability and a factor associated with malignancy progression, but the effects and mechanisms of CMTM6 on tumor growth, as well as its potential for therapy, are still largely unknown. Here, we show that tumor CMTM6 increased with progression in both clinical patients and mice. Ablation of CMTM6 resulted in significant retardation of human and murine tumor growth dependent on T-lymphocyte immunity. Tumor CMTM6 suppression broke resistance to immune checkpoint inhibitors and remodeled the tumor immune microenvironment, as specific antitumor cytotoxicity was enhanced and contributed primarily to tumor inhibition. Further, without the PD-1/PD-L1 axis, CMTM6 suppression still significantly dampened tumor growth dependent on cytotoxic cells. Notably, we identified that CMTM6 was widely expressed on immune cells. T-cell CMTM6 increased with sustained immune activation and intratumoral immune exhaustion and affected the T-cell-intrinsic PD-L1 levels. Host CMTM6 knockout significantly restrained tumor growth dependent on CD8 + T-cells, and similarly, not entirely dependent on PD-L1. Thus, we developed and evaluated the antitumor efficacy of CMTM6-targeting adeno-associated virus (AAV), which effectively mobilized antitumor immunity and could be combined with various antitumor drugs. Our findings reveal that both tumor and host CMTM6 are deeply involved in tumor immunity with or without the PD-1/PD-L1 axis and that gene therapy targeting CMTM6 is a promising strategy for cancer immunotherapy. One Sentence Summary Even in the absence of the PD-1/PD-L1 axis, tumor or host CMTM6 deficiency can mediate cytotoxicity-dependent anti-tumor immune responses, allowing CMTM6 to be a novel target for scAAV-mediated oncoimmunology gene therapy and combination treatment.