Tumor-Derived Complement C3 Overexpression in <i>STK11</i> -Mutant Lung Adenocarcinoma Drives Tumor Growth and Immune Checkpoint Inhibitor Resistance

Loss-of-function STK11 mutations occur in 15% to 20% of lung adenocarcinomas (LUAD) and correlate with immunotherapy failure and worse survival. By integrating analysis of human tumor samples, a human LUAD cell line panel, and Cancer Cell Line Encyclopedia and The Cancer Genome Atlas datasets, we found that C3 production was increased in human STK11-mutant versus STK11-wildtype (WT) LUAD, modulated by LKB1 loss, whereas high C3 expression in STK11-mutant LUAD was associated with worse survival. STK11 knockout (STK11-KO) in syngeneic murine LUAD tumors resulted in increased neutrophil and reduced T-cell infiltration and anti-PD-1 resistance. STK11-KO tumor growth was similar in C3-/- versus WT mice. In contrast, C3 deletion in STK11-KO tumors resulted in dramatic inhibition of tumor growth and enhanced sensitivity to anti-PD-1 in immunocompetent mice but had no significant effect in CD8-depleted WT mice or nude mice, pointing to tumor-derived C3 promoting immune evasion. Mechanistically, STK11 loss drove tumor-derived C3 production and downstream CXCL2 and complement factor H production that promoted immune evasion and impaired anti-PD-1 efficacy. Our results show a C3-driven signaling axis for STK11-mutant LUAD promoting immune evasion and identify therapeutic targets to render these tumors sensitive to anti-PD-1.