Abstract 6112: Clinical relevance of intra-tumoral density of regulatory T cells as a predictive factor for chemotherapy response in metastatic colorectal cancer
Authors: Oshi Masanori , Sarkar Joy , Wu Rongrong , Tokumaru Yoshihisa , Yan Li , Matsuyama Ryusei , Endo Itaru , Takabe Kazuaki 
Published: June 2022

Background: Within the tumor microenvironment, regulatory T cells (Tregs) are potent facilitators of immune tolerance, and in most solid tumors a higher proportion of Tregs compared to cytotoxic T cells predicts a worse outcome. However, the role of Tregs in colorectal cancer (CRC) is more controversial, possibly due in part to the effect of the gut microbiome on colorectal tumors. We explore the association between colorectal cancer (CRC) Treg density, cancer biology, and clinical outcome. The aim of the study is to investigate the clinical relevance of the fraction of Tregs within the colorectal cancer TME using xCell score with mRNA expression data across several CRC cohorts.

Methods: We used xCell to estimate intra-tumoral Tregs in 898 CRC patients in the Cancer Genome Atlas (TCGA) and GCE39582 cohorts. into two groups based on high versus low proportions of Tregs. We studied the correlation between intra-tumoral Treg density and cancer biology including host immune response, ICM expression, and the tumor microbiome by comparing gene ex-pression between the two groups. We further examined two CRC cohorts which contained data on response to neoadjuvant chemotherapy using mFOLFOX6 and bevacizumab, in order to explore the association between Treg infiltration and response to treatment.

Results: High-Treg CRCs enriched immune response-related gene sets; inflammatory response, IFN-γ and IFN-α response, IL2/IL6 signaling, and allograft rejection, and had significantly high infiltration of CD8, CD4, M1/M2 macrophage, and dendritic cells in both cohorts. While high-Treg CRCs enriched multiple pro-cancer signaling pathways compared to low-Treg CRCs, such as Epithelial Mesenchymal Transition, K-ras, Hypoxia, TGF-β, TNF-α, and angiogenesis, Treg infiltration was surprisingly associated with earlier CRC stage in TCGA. Metastatic CRCs with more Tregs showed a significantly better response to mFOLFOX6 versus low-Treg CRC metastases (88.9% response vs. 16.7%, p &lt; 0.001). Finally, high-Treg CRCs were associated with increased expression of immune check-point molecules PD-L1/PD-L2, CTLA4, TIGIT and BTLA, implying susceptibility to immunotherapy.

Conclusion: We show that unlike in other cancers, Tregs in CRC are not necessarily a marker of poor prognosis. High-Treg CRC enriched not only cancer aggravating gene sets, such as EMT, KRAS, TGF-β and angiogenesis, but also immune response-related gene sets, which is consistent with high infiltration of anti-cancerous immune cells. High Treg density was a predictor of response to chemotherapy in metastatic CRC.

Citation Format: Masanori Oshi, Joy Sarkar, Rongrong Wu, Yoshihisa Tokumaru, Li Yan, Ryusei Matsuyama, Itaru Endo, Kazuaki Takabe. Clinical relevance of intra-tumoral density of regulatory T cells as a predictive factor for chemotherapy response in metastatic colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6112.