Intratumoral regulatory T cells from colon cancer patients comprise several activated effector populations

Abstract

Background Intratumoral regulatory T cells (Treg) in colon cancer are a heterogeneous cell population, with potential impact on patient outcome. Generally, a high Treg infiltration has been correlated to a worse patient outcome, but it is still unclear how the composition of different Treg subsets affects patient relapse and survival. In this study, we used mass and flow cytometry to characterize Treg in colon tumors and corresponding unaffected tissue, followed by a correlation to clinical parameters and patient outcome. Results Using mass cytometry, we defined 13 clusters of intestinal Treg, three of which were enriched in the tumors. The two most enriched clusters were defined by their expression of the proliferation marker Ki67 and CD56, respectively. The Treg accumulating in the tumors expressed inducible T-cell co-stimulator (ICOS), OX-40, and CD39, indicating that they were effector Treg (eTreg). Intratumoral CD39+ Treg also had a higher expression of Foxp3, suggesting a higher suppressive activity, and we subsequently used CD39 as a marker for eTreg. Our further studies showed that colon tumors can be divided into two tumor groups, based on the proportion of CD39+ putative eTreg in the tumors. This property was independent of both tumor microsatellite status and tumor stage, which are important factors in predicting cancer disease progression. In a prospective study of forty-four colon cancer patients, we also showed that patients with a high CD39 expression on tumor-infiltrating Treg have a tendency towards a less favorable patient outcome in terms of cumulative cancer-specific survival. Conclusions This study uncovers novel subsets of tumor-infiltrating Treg in colon cancer, and suggests that CD39 may be a potential therapeutic target in patients with microsatellite stable colon tumors, which are usually refractory to checkpoint blockade therapy.

Colorectal Cancer-Infiltrating Regulatory T Cells: Functional Heterogeneity, Metabolic Adaptation, and Therapeutic Targeting

“…As already discussed, TI-Treg cells express high levels of CD39/CD73 ectonucleotidases that convert ATP to adenosine, a potent suppressor of tumor immunity (Figure 1f) (258). CD39+ TI-Treg cells have been found to play an important role during CRC tumor growth (150) and inhibition of CD39 enzymatic activity has been evaluated in a CRC hepatic-metastatic murine model. Here, CD39+ Treg cells modulate NK reactivity against the tumor, and targeting CD39 was found to both inhibit Treg cell activity in vitro and reduce tumor growth in vivo (259).…”

“…The subgroups with the highest and intermediate expression of CD39 were found in the tumor, while the subgroup with the lowest expression was found in healthy colon tissue. Higher expression of CD39 correlated with poorer outcome (150).…”

“…Novel immune checkpoint targets such as TIGIT, LAG-3 and TIM-3 are currently under pre-clinical investigation and are being evaluated for their safety profiles in phase I trials (244,245). In CRC, these receptors are highly expressed on TI-Treg cells compared to healthy colon tissue (150). TIGIT is a co-inhibitory molecule, a member of the CD28 family, expressed preferentially in T cells and NK cells.…”

Associations of different immune checkpoints-expressing CD4+ Treg/ T cell subsets with disease-free survival in colorectal cancer patients

“…In contrast to other solid tumors, high levels of tumor-infiltrating FoxP3 + Tregs were related with increased survival in CRC patients [ 9 , 24 ]. Recent studies reported that tumor-infiltrating CD39 + Tregs in CRC patients expressed different markers such as OX-40, CTLA-4 and ICOS, implicating their high immunosuppressive abilities in inhibiting anti-tumor immune responses [ 25 , 26 ]. Correale et al, showed that a higher level of FoxP3 + T-lymphocyte tumor infiltration in CRC patients receiving chemotherapy or chemo-immunotherapy was a favorable prognostic marker [ 27 ].…”

Mucosal tissue regulatory T cells are integral in balancing immunity and tolerance at portals of antigen entry

“…However, the role of Tregs in CRC is nuanced and context-dependent, as Tregs can also protect the mouse and human host from cancer-associated inflammation 162 , 163 and BLIMP-1+ Tregs and Treg-derived IL-10 have been associated with decreased polyps and increased CRC survival in both mice and humans 164 – 166 . Together, these conflicting results suggest that distinct Treg subsets may perform different functions in intestinal cancers 167 , 168 . For example, in mice, Treg-specific loss of transcription factor TCF-1 expression, a suppressor of genes co-bound by FoxP3, increases Treg-mediated T cell suppression and promotes tumor growth in polyposis, demonstrating a role for Treg TCF-1 expression in tumor clearance 169 .…”