IL21 Therapy Combined with PD-1 and Tim-3 Blockade Provides Enhanced NK Cell Antitumor Activity against MHC Class I-Deficient Tumors

Increased expression of coinhibitory molecules such as PD-1 and Tim-3 on NK cells has been demonstrated in advanced cancer patients who harbor MHC class I-deficient tumors. However, even in preclinical models, the antitumor effects of checkpoint blockade on NK cells have not been clearly elucidated. Here, we show that anti-PD-1/anti-Tim-3 treatment suppressed tumor progression in mice bearing MHC class I-deficient tumors, and the suppression was further enhanced by recombinant IL21 (rIL21) treatments through an NK-cell-dependent mechanism. We also show that the intratumoral delivery of rIL21 attracted NK cells to the tumor site in a CXCR3-dependent fashion. A combination of IL21 and checkpoint blockade facilitated the effector function of exhausted NK cells in cancer patients. Given the effects of the checkpoint blockade and rIL21 combination on NK cells infiltrating into MHC class I-deficient tumors, we suggest that the efficacy of checkpoint blockade can be enhanced through the administration of IL21 for advanced cancer patients with MHC class I-low/deficient tumors. (C) 2018 AACR.