Unconventional T cells in colorectal cancer

Abstract

The aim of this thesis is to provide in-depth information about two unconventional T cell population in colorectal cancer, MAIT cells and γδ T cells. These cells are characterized by a TCR with limited diversity that does not recognize targets within the classical MHC class II context. These unconventional T cells are usually low in frequency, except in mucosal tissues, such as the colon, where colorectal cancer arises. The following thesis first focuses on the homing receptors that MAIT cells in colorectal cancer patients express, with the goal of providing a comprehensive overview of their migration to tumour sites and potential interactions. The following articles focus on γδ T cells in colorectal cancer and in peritoneal metastases, a relatively rare complication with very poor prognosis. All manuscripts rely heavily on flow cytometry as the method to identify various cell populations and receptors, as well as cell culture of both immune cells and tumoroids, and bulk TCR sequencing. This thesis shows that MAIT cells employ a variety of receptors in order to successfully migrate towards colon tumours; these include integrins such as CD18 and CD103 and chemokine receptors such as CCR6, CXCR6 and GPR15. MAIT cells display a high expression of these receptors during stimulation and expansion, without the need of any additional cytokines outside of IL-2 and IL-7. The role of γδ T cells is also explored, with a study showing the distinct presence of Vδ3, a subtype that was, until recently, undetectable with flow cytometry. The published article demonstrates that this subtype possesses pro-tumourigenic capacity, via the release of IL-17 and other pro-tumorigenic proteins, while the two most common subtypes, Vδ1 and Vδ2, retain a cytotoxic profile. The unpublished manuscript focuses on CRC and peritoneal metastasis in an attempt to profile the γδ T cells present and gain some insight in their phenotype. The most notable conclusion is the presence of the circulating Vδ2 cells in solid tissues at levels comparable with Vδ1; however, these Vδ2 cells display few activation markers and skew towards either a central memory or effector memory phenotype. There are also marked clonotype similarities between the metastatic and tumour tissue, and some similarities between those tissues and blood; but little with the unaffected tissue. Altogether, this manuscript concludes that γδ T cells display an unexpected repertoire diversity and tissue-specific phenotypes in the peritoneal metastases of CRC.