Coordinated Immune Activation Following KRAS Inhibition in Syngeneic Models Reveals Molecular Pathways that Potentiate and Limit Antitumor Immunity.

Although mutant-specific KRAS inhibitors are approved to treat cancer, a deeper understanding of intratumoral changes driven specifically by KRAS inhibition is needed to maximize therapeutic responses. In this study, we used single-cell RNA sequencing, flow cytometry, and spatial transcriptomics to distinguish mechanisms of tumor control after KRASG12C inhibition [KRAS(G12C)i] or MEK inhibition (MEKi). Despite both inhibiting the MAPK pathway, KRAS(G12C)i and MEKi drive the adaptation of distinct neoplastic cell fates affecting metabolism and cell-cycle regulation, and additive tumor suppression is observed after co-administration. KRAS(G12C)i results in the emergence of a specific, cDC1-driven mature conventional dendritic cell (cDC) state. Coculture of treated neoplastic cells with cDC1s is sufficient to upregulate maturation markers such as CCR7, and intercellular communication analyses suggest that activation is augmented through nonimmune mediators. Both KRAS(G12C)i and MEKi increase infiltration of cytotoxic T cells, but MEKi, which also targets nonmalignant cells, is associated with a reduced capacity for T-cell proliferation and degranulation, consistent with distinct adaptive immune activation mechanisms. We observe that combination treatment of KRAS(G12C)i with anti-PD-1 immunotherapy further expands effector T-cell states, increases clonal persistence, and induces proinflammatory macrophages associated with higher overall survival that were largely absent after KRAS(G12C)i alone. Furthermore, combination treatment enhances intercellular communication networks among non-PD-1+-expressing cells that can perpetuate cDC activation. Our findings delineate distinct tumor and immune responses to KRAS and MEK inhibition and identify molecular features of the responding tumor microenvironment that may be leveraged to improve therapeutic efficacy.