**8. Induction of regulatory T cells by tumors**

Tregs, in addition to natural killer cells, are CD4 T cells capable of directly suppressing CD4+ and CD8+ T cells. Thus, the presence of Tregs in the tumor microenvironment may be involved in a decrease in the immune response, and many studies have demonstrated that an increase in these cells is correlated with worse prognosis. Muir et al. [31] demonstrated the prognostic role of Tregs in canine lymphomas, with dogs with higher levels of Tregs showing worse prognoses. A study by Curiel et al. [32] also demonstrated that an increase in the number of these cells in ovarian carcinoma predisposes dogs to a lower survival rate.
