PARP inhibition elicits NK cell-associated immune evasion via potentiating HLA-G expression in tumor

Resistance to poly(ADP-ribose) polymerase inhibitors (PARPi) poses a significant challenge to enhancing the efficacy of cancer treatments. Beyond the cellular mechanisms intrinsic to tumor cells, the modulation of the tumor immune microenvironment is crucial in dictating the responsiveness to pharmacological interventions. Thus, there is a pressing need to elucidate the intricate interplay between PARPi and antitumor immune responses and to develop an optimized combinatorial therapeutic approach. In this study, using matched tumor samples before and after neoadjuvant monotherapy with the PARPi niraparib in a prospective clinical trial (NCT04507841), we observed a significant increase in natural killer (NK) cell infiltration post-treatment. However, this was not accompanied by the expected enhancement in their cytotoxic functions. This observation underscores the necessity to optimize the antitumor potential of NK cells by enhancing their cytotoxic capabilities. Upon exposure to niraparib, tumor cells, particularly those with wild-type EGFR, exhibited a pronounced upregulation of human leukocyte antigen G (HLA-G), an immune checkpoint impeding NK cell functions. Niraparib promotes EGFR internalization, which in turn diminishes AKT/mTOR signaling, leading to the increased transcriptional activity of the transcription factor EB (TFEB) and subsequent enhancement of HLA-G expression. The combination of niraparib with HLA-G blockade not only augmented NK cell-mediated tumor lysis in vitro but also synergistically inhibited tumor growth in humanized patient-derived xenograft models. Collectively, our results shed light on a previously unrecognized immune evasion mechanism and offer a compelling argument for the integration of HLA-G blockade with PARPi in cancer therapy.