Abstract
Inhibitor of apoptosis protein (IAP) antagonists are in clinical trials for a variety of cancers, and mouse models show synergism between IAP antagonists and anti-PD-1 immunotherapy. Although IAP antagonists affect the intrinsic signaling of tumor cells, their most pronounced effects are on immune cells and the generation of antitumor immunity. Here, we examined the effects of IAP antagonism on T-cell development using mouse fetal thymic organ culture and observed a selective loss of iNKT cells, an effector cell type of potential importance for cancer immunotherapy. Thymic iNKT-cell development probably failed due to increased strength of TCR signal leading to negative selection, given that mature iNKT cells treated with IAP antagonists were not depleted, but had enhanced cytokine production in both mouse and human ex vivo cultures. Consistent with this, mature mouse primary iNKT cells and iNKT hybridomas increased production of effector cytokines in the presence of IAP antagonists. In vivo administration of IAP antagonists and α-GalCer resulted in increased IFNγ and IL-2 production from iNKT cells and decreased tumor burden in a mouse model of melanoma lung metastasis. Human iNKT cells also proliferated and increased IFNγ production dramatically in the presence of IAP antagonists, demonstrating the utility of these compounds in adoptive therapy of iNKT cells. Cancer Immunol Res; 6(1); 25-35. ©2017 AACR.