Tumor-draining lymph nodes shape the tumor microenvironment through enrichment of tumor-reactive effector-exhausted CD8+ T cells.

Tumor-draining lymph nodes are central to anti-tumor immunity and influence the response to immunotherapy. Colorectal cancers with microsatellite instability and microsatellite stability differ substantially in tumor biology, prognosis and sensitivity to immune checkpoint blockade. However, the differences in tumor-draining lymph nodes between these two subtypes and their contribution to distinct anti-tumor immune responses remain poorly understood. Here, we performed an integrative multi-omics analysis to systematically compare tumor-draining lymph nodes and tumor microenvironments in these two colorectal cancer subtypes. We identified a distinct population of CD8+ T cells that displayed terminal exhaustion while retaining strong anti-tumor activity. These cells were highly tumor reactive, associated with tertiary lymphoid structure formation and enriched in microsatellite instability colorectal cancers. Lineage tracing indicated that they originated in tumor-draining lymph nodes. In microsatellite instability colorectal cancers, tumor-draining lymph nodes contained more pre-exhausted T cells, dendritic cells with enhanced antigen-presenting capacity and fewer regulatory T cells, thereby providing both precursors and a supportive niche for the development of these effector-exhausted T cells. Meanwhile, within tumors, IL21+CD4+ T cells and CXCL10+ myeloid cells promoted the differentiation and recruitment of these cells through cytokine signaling and increased major histocompatibility complex expression. Colorectal cancer cells with microsatellite instability further reinforced this immune ecosystem by activating the cyclic GMP-AMP synthase-stimulator of interferon genes pathway. Collectively, our findings identify effector-exhausted CD8+ T cells as key mediators of favorable immunity in microsatellite instability colorectal cancers and highlight the pivotal role of tumor-draining lymph nodes in shaping the tumor immune landscape.