The role of sex in the innate and adaptive immune environment of metastatic colorectal cancer

Background Women with colorectal cancer (CRC) have a significant survival advantage over men. Sex influences on the tumour microenvironment (TME) are not well characterised, despite the importance of immune response in CRC. We hypothesised that sex-divergent immune responses could contribute to survival. Methods Using a murine model of metastatic CRC, we examined T cells, macrophages, and cytokines locally and systemically. TME and serum cytokines were measured by multiplex bead-based arrays, while FCA was used to identify cells and phenotypes. IHC provided spatial confirmation of T cell infiltration. Results Females had increased survival and T cell infiltration. CD8, CD4 and Th2 populations correlated with longer survival. Males had increased serum levels of chemokines and inflammation-associated cytokines. Within the TME, males had lower cytokine levels than females, and a shallower cytokine gradient to the periphery. Female tumours had elevated IL-10+ macrophages, which correlated with survival. Conclusions These data demonstrate survival-associated differences in the immune response of males and females to metastatic CRC. Females showed changes in cytokine production accompanied by increased immune cell populations, biased toward Th2-axis phenotypes. Key differences in the immune response to CRC correlated with survival in this model. These differences support a multi-faceted shift across the TME.