SiglecFhigh neutrophils in lung tumor tissues suppress local CD8 T cell responses and limit the efficacy of anti PD-L1 antibodies

BackgroundTumor infiltrating neutrophils generally correlates to worst prognosis and refractoriness to immunotherapy yet the complexity and significance of diverse subsets resident in tumor tissues has just begun to emerge. In lung tumors, a network of neutrophils states with graded protumorigenic properties is conserved between mouse and humans and include a subset of mature, long lived cells expressing the sialic-acid-binding protein SiglecF (SiglecFhigh neu). The mechanism of recruitment of SiglecFhigh neu into tumor tissues and the impact on local anti-tumor T cell responses and interference with immunotherapy is still elusive. MethodsWe used an immunogenic model of KrasG12D Tp53 null adenocarcinoma of the lung to screen for factors inducing the recruitment of SiglecFhigh neu, followed by gene editing to delete selected candidates. We analyzed frequencies and effector functions of endogenous CD8 T cell responses in controls and SiglecFhigh neu depleted tumors by flow cytometry and functional assays. Tissues fluorescence and confocal imaging of lung sections was used to explore the relative distribution of neu and CD8 T cells. To establish the impact of SiglecFhigh neu on anti-tumoral immune responses we treated cohort of animals with anti-PD-L1 antibodies to evaluate tumor growth in control conditions and under therapy. ResultsWe found that tumor tissues express high levels of CXCL5, mapping to cancer cells. Upon deletion of chemokine expression by gene editing, the recruitment of SiglecFhigh neu was almost entirely abrogated. In tumors depleted of SiglecFhigh neu, the density of tumor specific endogenous CD8 T cells was 3-fold higher than in controls and showed significantly enhanced activation and effector functions. Importantly, checkpoint blockade with anti PD-L1 antibodies was ineffective in control tumors but showed a significant benefit in SiglecFhigh neu depleted tumors. ConclusionThis study demonstrates that SiglecFhigh neu differentiating in lung tumor tissues inhibit local CD8 T cell responses and interfere with the success of checkpoint blockade. These data suggest that blocking selectively tissue resident neu may promote better responses to immunotherapy.