The pd-l1/pd-1 axis blocks neutrophil cytotoxicity in cancer

ABSTRACT The PD-L1/PD-1 axis was shown to promote tumor growth and progression via the inhibition of anti-tumor immunity. Blocking this axis was shown to be beneficial in maintaining the anti-tumor functions of the adaptive immune system. Still, the consequences of blocking the PD-L1/PD-1 axis on innate immune responses remain largely unexplored. In this context, neutrophils were shown to consist of different subpopulations, which possess either pro- and anti-tumor properties. PD-L1-expressing neutrophils are considered pro-tumor as they can suppress cytotoxic T-cells. That said, we found that PD-L1 expression is not limited to tumor promoting neutrophils but is also evident in anti-tumor neutrophils. We show that neutrophil cytotoxicity is effectively and efficiently blocked by tumor cell expressed PD-1. Furthermore blocking of either neutrophil PD-L1 or tumor cell PD-1 maintains neutrophil cytotoxicity resulting in enhanced tumor cell apoptosis. Importantly, we show that tumor cell PD-1 blocks neutrophil cytotoxicity and promotes tumor growth via a mechanism independent of adaptive immunity. Taken together, these findings highlight the therapeutic potential of enhancing anti-tumor innate immune responses via blocking of the PD-L1/PD-1 axis.