Regulatory T-cells (T_reg) protect the host from autoimmune disease by suppressing self-reactive immune cells. As such, T_reg may also block antitumor immune responses. Recent observations by us and others showed that the prevalence of T_reg is increased in cancer patients, particularly in the tumor environment. Our studies in a mouse pancreas cancer model suggest that the tumor actively promotes the accural of T_reg through several mechanisms involving activation of naturally occurring T_reg as well as conversion of non-T_reg into T_reg. Our studies focus on further defining these mechanisms with the ultimate goal of designing strategies that block T_reg-mediated suppression in cancer patients.