The biological functions and mechanisms of oncogenic KRASG12D (KRAS*) in resistance to immune checkpoint blockade (ICB) therapy are not fully understood. We demonstrate that KRAS* represses the expression of interferon regulatory factor 2 (IRF2), which in turn directly represses CXCL3 expression. KRAS*-mediated repression of IRF2 results in high expression of CXCL3, which binds to CXCR2 on myeloid-derived suppressor cells (MDSCs) and promotes their migration to the tumor microenvironment. Anti-PD-1 resistance of KRAS*-expressing tumors can be overcome by enforced IRF2 expression or by the inhibition of CXCR2. Colorectal cancer (CRC) showing higher IRF2 expression exhibited increased responsiveness to anti-PD-1 therapy. The KRAS*-IRF2-CXCL3-CXCR2 axis provides a framework for patient selection and combination therapies to enhance the effectiveness of ICB therapy in CRC.