CTLA4 and breast cancer: In addition, they subsequently demonstrated that sitagliptin, a DPP4 inhibitor, exerted an anti-tumor effect by increasing CC motif chemokine ligand 11 (CCL11)-mediated eosinophil chemotaxis in syngeneic mouse models of liver and breast cancer, and combining sitagliptin with the inhibition of PD-1 and CTLA-4 significantly suppressed tumors expressing IL-33 [26].