Colorectal Cancers with Distinct Metastatic Potential Trigger Divergent Early T Cell Responses

Author

• Marwa Ahmed Saad

Date of Award

2026

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Thesis Advisor

Daniel Mucida

Abstract

The intestinal mucosa harbors the largest immune compartment in the mammalianbody, where resident and recruited immune cells must maintain tolerance to commensal and dietary antigens while preserving their ability to mount effective responses against pathogens and malignant transformation. Uncontrolled epithelial proliferation leads to colorectal cancer (CRC), the second leading cause of cancer-related deaths worldwide. More than 85% of human CRC cases arise from accumulating sporadic or hereditary mutations in the tumor suppressor genes Apc, Tp53, Smad4, and the oncogene Kras. Although immune checkpoint blockade has transformed the treatment of certain solid tumors, most CRCs, particularly those with a proficient mismatch repair system (pMMR), remain refractory to immunotherapy and are prone to metastasis. In contrast, mismatch repair-deficient (dMMR) tumors harbor a high mutational burden that promotes immunogenicity and responsiveness to T cell-mediated therapies. This dichotomy underscores the pivotal yet incompletely understood role of local T cell responses in shaping CRC progression and its metastatic propensity. Although adaptive immunity can eliminate nascent tumor cells, it can also become functionally silenced or co-opted in an evolving tumor microenvironment. In the gut tissue, this challenge is compounded by the constant need to restrain damaging immune activation toward abundant luminal antigens, creating an environment in which tumor- specific responses must arise amid pre-existing tolerance mechanisms. However, how T cells integrate these conflicting cues, especially during the early stages of tumor growth and metastatic dissemination, remains unclear. Previous studies have largely focused on either highly immunogenic dMMR CRC models or non-physiological subcutaneous transplants, providing limited insight into gut-resident or metastasis-associated T cell response. Additionally, polyclonal T cell responses in non-metastatic versus pro- metastatic CRC, distinct from “background” gut immune responses, remain unexplored. To address these gaps, we combined orthotopic CRC models with distinct metastatic potentials and a temporal T cell fate-mapping strategy that enabled discrimination between pre-existing intestinal T cells and newly recruited potential antitumor clones. We demonstrated that metastatic competency is associated with an early T cell hypoactivation state rather than a late collapse of established immunity. Non- metastatic AKP tumors elicited an early accumulation of CD8+ and CD4+ T cells that acquired cytotoxic and Th1 transcriptional programs. In contrast, pro-metastatic tumors failed to induce these programs; newly recruited T cells retained a naïve-like, hyporesponsive phenotype from the outset. Direct tumor–T cell interactions were readily detected in non-metastatic tumors but were markedly reduced in pro-metastatic tumors despite physical proximity, indicating an early immune disengagement. Although CD8+ cells contributed to restraining primary tumor growth, depletion of CD4+ or CD8+ T cells did not confer metastatic potential on AKP tumors, demonstrating that adaptive immunity alone does not dictate systemic dissemination. At the clonal level, AKP tumors induced robust CD4+ T cell expansion, with overlap between tumor-infiltrating and adjacent mucosal repertoires. A subset of expanded clones in both CRC models exhibited reactivity to dietary and microbial antigens, suggesting that tumor immunity can recruit components of the pre-existing mucosal T cell repertoire. Functionally, tumor-infiltrating T cells from AKP tumors displayed cytotoxic activity in vitro, mediated by both IFN-g-dependent and IFN-g-independent mechanisms depending on cellular context. In the non-metastatic setting, AKP tumors exhibited higher tumor-intrinsic MHC class II (MHCII) expression in vivo at early stages. In parallel, T cells isolated from these tumors were capable of inducing MHCII upregulation on tumor organoids in vitro, consistent with an IFN-g-dependent mechanism. Genetic ablation of MHCII in AKP tumors modestly reduced CD4_⁺T cell accumulation and increased TCR repertoire diversity at the early tumor stage, and was accompanied by the emergence of liver metastases in a subset of animals at the late stage. Conversely, enforced MHCII expression in pro- metastatic tumors did not reverse their aggressive phenotype, suggesting that MHCII alone is insufficient to restore immune control. Collectively, this work defines temporally distinct T cell differentiation trajectories associated with metastatic potential in CRC and demonstrates that immune divergence emerges at the earliest stages of tumor development. Rather than reflecting a late collapse of established immunity, metastatic progression is preceded by an early failure of productive local T cell engagement. These findings indicate that early immune activation dynamics is a feature of CRC disease trajectory and provide a framework for exploring how tumor-intrinsic programs and host immune context interact during metastatic progression. Further investigation across additional models and metastatic settings will be necessary to determine the broader applicability of these observations.

Comments

A Thesis Presented to the Faculty of The Rockefeller University in Partial Fulfillment of the Requirements for the degree of Doctor of Philosophy

License and Reuse Information

This work is licensed under a Creative Commons Attribution-NonCommercial-Share Alike 4.0 International License.

Recommended Citation

Saad, Marwa Ahmed, "Colorectal Cancers with Distinct Metastatic Potential Trigger Divergent Early T Cell Responses" (2026). Student Theses and Dissertations. 863.
https://digitalcommons.rockefeller.edu/student_theses_and_dissertations/863