Abstract 2505: Immune dynamics and response predictors to regorafenib, ipilimumab, and nivolumab (RIN) treatment in chemotherapy resistant microsatellite stable (MSS) metastatic colorectal cancer (mCRC)

Abstract Background: In our previous study, RIN therapy in MSS mCRC patients, excluding those with liver metastases, yielded a notable 36.4% objective response rate. RIN treatment was observed to remodel the local tumor microenvironment by enhancing immune infiltration, especially in responders. Systemic immunity, as assessed through peripheral blood analysis, showed that responders had lower baseline immune activity, which increased markedly post-treatment. Patients with liver metastases demonstrated a reduced CD4/CD8 T cell ratio, indicative of immunosenescence. Methods: Building on our prior research, we analyzed blood samples from 29 chemotherapy-resistant MSS mCRC patients undergoing RIN therapy, collected at baseline and after two consecutive treatment cycles. Two 28-marker spectral flow cytometry panels were used to assess immune senescence and cytokine production in lymphocytes. Additionally, T cell receptor repertoires and transcriptional profiles were analyzed using RNA sequencing from sorted non-naïve T cells. Results: The study unveiled distinct immunological profiles in MSS mCRC patient responders vs non-responders to RIN treatment. Responders demonstrated increased numbers of newly expanding CD8 T cell clones on-treatment, indicative of an active immune responses. In contrast, non-responders displayed evidence of increased DNA damage in circulating lymphocytes (T, B, and NK cells), as marked by elevated γ-H2AX levels. We also identified divergent cytokine production profiles patterns at baseline: T cells in non-responders demonstrated increased capacity for production of IL-2, IL-10, IL-4/-13, and IL-22, while production of IFN-γ in both T cells and NK cells correlated with improved outcomes. Notably, patients with liver metastases exhibited greater frequencies of senescent T cells, characterized by increased expression of senescence markers (SA-βGal, CD57, Granzyme B/K) and a reduction in CD27 and CD28 in CD4 T cells, along with an accumulation of terminally differentiated CD8 T cells both pre- and post-treatment. Additionally, RNA sequencing revealed an upregulation of FOXO1 related genes in non-naive T cells of responder patients, which is consistent with its important role for this pathway in attenuating senescence and maintenance of stem-like properties in T cells. Conclusions: The effectiveness of RIN therapy is associated with baseline functional potential of circulating T cells and an on-treatment expansion of T cell clonotypes. Pre-existing and persistent features of senescence and DNA damage in circulating lymphocytes may be a major barrier to RIN treatment efficacy in MSS colorectal cancer and should be validated further in future studies. Citation Format: Jian Ye, Chongkai Wang, Colt Egelston, Weihua Guo, Peter Lee, Marwan Fakih. Immune dynamics and response predictors to regorafenib, ipilimumab, and nivolumab (RIN) treatment in chemotherapy resistant microsatellite stable (MSS) metastatic colorectal cancer (mCRC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2505.