Colorectal cancers with distinct metastatic potential trigger divergent early T cell responses

Colorectal cancer is a common malignancy, and the prognosis for patients with advanced disease remains limited. Even with endoscopic, surgical, radiotherapy, chemotherapy, targeted therapy, and immunotherapy options, treatment outcomes for metastatic cases remain unsatisfactory^[1]. The efficacy of immunotherapy also depends heavily on the tumor’s molecular background: mismatch repair-deficient tumors harbor more somatic mutations that may generate immunogenic antigens, and PD-1 blockade has demonstrated clinical activity in this advanced colorectal cancer population, whereas the objective response rate in mismatch repair-proficient tumors is 0%^[2]. However, tumor immunity is not determined solely by mutation burden. Clinical cohorts show that immune cell type, density, and spatial distribution within the tumor predict survival in colorectal cancer patients more effectively than conventional pathological staging^[3], while pan-cancer analyses suggest that antigen presentation defects and alterations in apoptosis pathways can help tumors evade immune killing^[4]. The key question therefore shifts from whether tumors harbor identifiable antigens to how early tumors shape the initial T cell response as they acquire metastatic capacity, and why an effective local immune response often fails to develop.

This study orthotopically transplanted colorectal cancer organoids with differing metastatic potential and combined T cell fate mapping with single-cell analysis to compare early T cell trajectories during tumor formation. Non-metastatic tumors recruited CD8αβ+ and CD4+ T cells earlier and induced cytotoxic and Th1-like programs, whereas metastasis-promoting tumors caused infiltrating T cells to remain naïve-like and poorly activated. The study further found that tumor-infiltrating CD4+ T cells underwent clonal expansion, with some clones recognizing microbial and dietary antigens. After labeling physical contacts using universal LIPSTIC, T cells interacting directly with tumors were enriched among expanded, cytotoxic clones. Functional experiments showed that fate-mapped T cells in non-metastatic tumors suppressed tumor growth in an IFN-γ-dependent manner.

Mechanistically, metastasis-promoting tumors downregulated MHCII, while targeting Ciita in non-metastatic organoids reduced CD4+ T cell clonal expansion and led to tumor progression. The study thus linked the early T cell response with metastatic potential through two complementary observations: MHCII- and antigen presentation-associated CD4+ T cell expansion and cytotoxic differentiation, and the coexistence of a poorly activated state with metastatic propensity. This advances existing understanding. Previous studies established the prognostic significance of immune cell composition and spatial location^[3] and revealed tumor escape mechanisms associated with antigen presentation and cytotoxicity^[4]. The present study moves the observation window earlier in tumor evolution and traces early T cell fates induced by different metastatic potentials within the same experimental system, proposing that inadequate local immune priming precedes metastatic dissemination. uLIPSTIC can record physical contacts between immune cells and between immune and non-immune cells without depending on a specific receptor–ligand combination, and can be integrated with single-cell transcriptomics^[5], providing a key tool for identifying T cells that directly contact tumors.

However, this study primarily relies on an orthotopic organoid model, and the available findings alone cannot establish whether early T cell trajectories can reliably predict metastasis or guide immunotherapy in patients. The factors determining whether clones tolerant to microbial and dietary antigens ultimately develop effective antitumor activity, and how to restore MHCII and CD4+ T cell priming in metastasis-promoting tumors without disrupting mucosal homeostasis, remain to be addressed.