Abstract 4967: Neoadjuvant chemotherapy promotes a transient increase of intratumoral T-cell density in colorectal liver metastases

Abstract

Abstract Background: In metastatic colorectal cancer, only the microsatellite instable (MSI) subgroup of cases has so far demonstrated major responses to immune checkpoint inhibition. Increased infiltration of T lymphocytes in presumed non-responsive tumors has been shown to facilitate response to immune checkpoint inhibition. Cytotoxic chemotherapy might induce immunogenic cell death and cause infiltration of immune cells, turning “cold” tumors into “hot”. In this work we investigated whether standard-of-care neoadjuvant chemotherapy (NACT) would influence T-cell infiltration in the tumor microenvironment of colorectal liver metastases (CLM) in a substudy of patients included in the OSLO-COMET trial (n=280; NCT01516710). Materials and methods: Patients (n=92; bearing 144 metastatic tumors) had resectable CLM, and of these, 45 patients received NACT, in most cases fluoropyrimidine-based, with the addition of oxaliplatin (n=36) or irinotecan (n=8). Quantification of total T-cells (Ttot), cytotoxic T-cells, T-helper cells, and regulatory T-cells was performed by immunohistochemical staining of serial sections with antibodies against CD3, CD8, CD4, and FOXP3, respectively. Hotspots from the invasive margin (IM), intratumoral region (IT), and adjacent liver tissue (NLi) were analyzed. T-cell density was reported as number of T-cells/mm2. Results: The density of Ttot in the IM region (median 2360 cells/mm2) was 7 times greater than in the IT region (319 cells/mm2) and 13 times greater than in the NLi region (183 cells/mm2), with similar findings for T-cell subtypes. Comparing patients that had received NACT to patients that had not, there was no difference in T-cell infiltration in the IM and NLi regions, but a non-significant trend towards increased T-cell density was detected in the IT region after NACT, exemplified by Ttot 353 vs 292 cells/mm2 (p=0.2). Exploring the influence of the time interval between NACT completion and surgery by receiver operating characteristic curve analysis, 9.5 weeks was identified as the time point that separated the cases most clearly by T-cell density. Interestingly, cases with a shorter than 9.5-week interval had a significantly higher intratumoral T-cell count than cases with the longer interval; with median Ttot 491 vs 236 cells cells/mm2; p<0.0001. Similar findings were detected for all T-cell subsets in the IT region. Conclusion: The main finding of this work was that NACT administration was associated with a transient increase of intratumoral T-cell density in CLM, potentially promoting an MSI-like tumor immune phenotype. The results suggest that when exploring combinations of cytotoxic therapy and immune checkpoint inhibition, the timing of individual treatment components may be essential. To further optimize treatment schedules, biomarkers reflecting T-cell infiltration may be a useful tool for tailoring personalized therapy. Citation Format: Kjersti Flatmark, audun E. Berstad, Vegar Dagenborg, Bjørn Edwin, Åsmund A. Fretland, Krzysztof Grzyb, Eirik Høye, Marius Lund-Iversen, Serena E. Marshall, Anne H. Ree, Sheraz Yaqub. Neoadjuvant chemotherapy promotes a transient increase of intratumoral T-cell density in colorectal liver metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4967.