Pertussis toxin-induced lymphocytosis enhances anti-tumor immune environments and improves the anti-PD1 treatment response in a squamous cell carcinoma model.

Elevation of the neutrophil-to-lymphocyte ratio (NLR) in cancer patients predicts a worse prognosis, and NLR is a good discriminator in response to anti-tumor immune checkpoint inhibitors. However, the therapeutic potential of NLR normalization to enhance the efficacy of anti-tumor immunotherapy has not been investigated. In this study, we chose pertussis toxin (PTX) as an agent to induce lymphocytosis and lower NLR. PTX decreased NLR in squamous cell carcinoma (SCC)-tumor-bearing mice and shifted the tumors from low to high immune scores. PTX-induced elevation of CXCL9 led to lymphocytosis and increased immune cell infiltration in tumor tissues. The combination treatment with PTX and anti-PD1 antibody significantly suppressed in vivo SCC tumor growth, compared to anti-PD1 treatment alone. The combination treatment induced a larger proportion of T cells in the tumor microenvironment, and these findings were associated with an increase in terminally differentiated CD8 T cells and their augmented Ki-67 expression. In addition, tumor-specific IFN-γ production was augmented in animals treated with anti-PD1 antibody and combination treatments, but not with PTX alone. In summary, PTX can induce high lymphocyte infiltration into tumor tissue, leading to the NLR normalization and a favorable immune environment for immune checkpoint inhibitors.