The PD-L1/PD-1 Axis Blocks Neutrophil Cytotoxicity in Cancer

Introduction

Blocking PD-L1 and/or PD-1 is therapeutically utilized for maintaining the anti-tumor functions of the adaptive immune system. However, the consequences of blocking the PD-L1/PD-1 axis on innate immune responses remains largely unexplored. In cancer, neutrophils were shown to consist of different subpopulations, which possess either pro- and anti-tumor properties. We found that PD-L1 expression is not limited to the tumor promoting neutrophil subset but is also evident in the anti-tumor neutrophil subset. In this study we evaluated the role played by PD-L1 in regulating anti-tumor neutrophil cytotoxicity.

Materials and methods

The expression of PD-1/PD-L1 on tumor cells and neutrophils respectively was evaluated by flow cytometry. The consequences of manipulating the PD-1/PD-L1 axis on neutrophil cytotoxicity were evaluated in a tumor cell-neutrophil co-culture setting. The effect of manipulating neutrophil PD-1/PD-L1 interactions with tumor cells in vivo was evaluated in NOD-SCID mice which lack adaptive immunity.

Results and discussion

We show that neutrophil cytotoxicity is efficiently blocked by tumor cell expressed PD-1. Furthermore, blocking of either neutrophil PD-L1 or tumor cell PD-1 maintains neutrophil cytotoxicity and enhances tumor cell apoptosis. Importantly, we show that high tumor cell PD-1 levels block neutrophil cytotoxicity and promotes tumor growth regardless the adaptive immune system. Taken together, these findings highlight the therapeutic potential of enhancing anti-tumor innate immune responses via blocking of the PD-L1/PD-1 axis.

Conclusion

In summary, our study provides novel insight into the interaction of neutrophil PD-L1 and tumor cell PD-1. We demonstrate that tumor cell PD-1 blocks neutrophil cytotoxicity and has a dramatic impact on the anti-metastatic function of neutrophils.