Blockade of PD-L1 expression on tumor cells via anti–PD-L1 monoclonal antibody (mAb) has shown great promise for successful cancer treatment by overcoming T-cell exhaustion; however, the function of PD-L1 on natural killer (NK) cells and the effects of anti–PD-L1 mAb on PD-L1+ NK cells remain unknown. Moreover, patients with PD-L1− tumors can respond favorably to anti–PD-L1 mAb therapy for unclear reasons. Here, we show that some tumors can induce PD-L1 on NK cells via AKT signaling, resulting in enhanced NK-cell function and preventing cell exhaustion. Anti–PD-L1 mAb directly acts on PD-L1+ NK cells against PD-L1− tumors via a p38 pathway. Combination therapy with anti–PD-L1 mAb and NK cell–activating cytokines significantly improves the therapeutic efficacy of human NK cells against PD-L1− human leukemia when compared with monotherapy. Our discovery of a PD-1–independent mechanism of antitumor efficacy via the activation of PD-L1+ NK cells with anti–PD-L1 mAb offers new insights into NK-cell activation and provides a potential explanation as to why some patients lacking PD-L1 expression on tumor cells still respond to anti–PD-L1 mAb therapy. Significance: Targeting PD-L1 expressed on PD-L1+ tumors with anti–PD-L1 mAb successfully overcomes T-cell exhaustion to control cancer, yet patients with PD-L1− tumors can respond to anti–PD-L1 mAb. Here, we show that anti–PD-L1 mAb activates PD-L1+ NK cells to control growth of PD-L1− tumors in vivo, and does so independent of PD-1. This article is highlighted in the In This Issue feature, p. 1325

IL15 is a pleiotropic cytokine with multiple roles that improve immune responses to tumor cells. Oncolytic viruses (OV) specifically lyse tumors and activate immune responses. Systemic administration of IL15 or its complex with the IL15Rα and chimeric antigen receptor (CAR) natural killer (NK) cells are currently being tested in the clinic. Here, we generated a herpes simplex 1–based OV-expressing human IL15/IL15Rα sushi domain fusion protein (named OV-IL15C), as well as off-the-shelf EGFR-CAR NK cells, and studied their monotherapy and combination efficacy in vitro and in multiple glioblastoma (GBM) mouse models. In vitro, soluble IL15/IL15Rα complex was secreted from OV-IL15C–infected GBM cells, which promoted GBM cytotoxicity and improved survival of NK and CD8+ T cells. Frozen, readily available off-the-shelf EGFR-CAR NK cells showed enhanced killing of tumor cells compared with empty vector–transduced NK cells. In vivo, OV-IL15C significantly inhibited tumor growth and prolonged survival of GBM-bearing mice in the presence of CD8+ T cells compared with parental OV. OV-IL15C plus EGFR-CAR NK cells synergistically suppressed tumor growth and significantly improved survival compared with either monotherapy, correlating with increased intracranial infiltration and activation of NK and CD8+ T cells and elevated persistence of CAR NK cells in an immunocompetent model. Collectively, OV-IL15C and off-the-shelf EGFR-CAR NK cells represent promising therapeutic strategies for GBM treatment to improve the clinical management of this devastating disease. Significance: The combination of an oncolytic virus expressing the IL15/IL15Rα complex and frozen, ready-to-use EGFR-CAR NK cells elicits strong antitumor responses in glioblastoma.

The pandemic of coronavirus disease 2019 (COVID-19) has reached nearly 240 million cases, caused nearly 5 million deaths worldwide as of October 2021, and has raised an urgent need for the development of novel drugs and therapeutics to prevent the spread and pathogenesis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). To achieve this goal, an animal model that recapitulates the features of human COVID-19 disease progress and pathogenesis is greatly needed.

N 6-methyladenosine (m6A) is the most prevalent posttranscriptional modification on RNA. NK cells are the predominant innate lymphoid cells that mediate antiviral and antitumor immunity. However, whether and how m6A modifications affect NK cell immunity remain unknown. Here, we discover that YTHDF2, a well-known m6A reader, is upregulated in NK cells upon activation by cytokines, tumors, and cytomegalovirus infection. Ythdf2 deficiency in NK cells impairs NK cell antitumor and antiviral activity in vivo. YTHDF2 maintains NK cell homeostasis and terminal maturation, correlating with modulating NK cell trafficking and regulating Eomes, respectively. YTHDF2 promotes NK cell effector function and is required for IL-15–mediated NK cell survival and proliferation by forming a STAT5–YTHDF2 positive feedback loop. Transcriptome-wide screening identifies Tardbp to be involved in cell proliferation or survival as a YTHDF2-binding target in NK cells. Collectively, we elucidate the biological roles of m6A modifications in NK cells and highlight a new direction to harness NK cell antitumor immunity.