616P - Microsatellite instability and immunogenicity in colorectal cancer: Do resident memory Tcells (Trm) play a role in colorectal cancer?

Abstract

BackgroundColorectal cancers with microsatellite instability (MSI) are associated with abundance of tumour infiltrating lymphocytes (TILs). Recent studies have shown that a proportion of TILs may actually be resident memory T cells, not just a continuous circulation of T cells. MethodsPatients with known MSI and BRAF status were eligible for inclusion in this study. Histopathology slides prepared with haematoxylin and eosin were reviewed using an Olympus BX53 microscope to examine the tumour invading edge and core. These slides were then scanned electronically and reexamined with both the investigator and a pathologist. Blocks from these representative slides were recut using a microtome in preparation for quantitative multiplex immunofluorescence staining. All immunofluorescence staining was carried out on 4-µm-thick sections using an Autostainer Plus (Dako – Agilent Technologies) with appropriate positive and negative controls. Opal Multiplex IHC Assay kit (PerkinElmer) was used. Statistical analysis was performed using Graphpad Prism Version 7 and Stata Version 15. Results72 patients with known MSI and BRAF status were eligible for inclusion in this study. 36 of these patients were successfully underwent quantitative multiplex immunofluorescence staining. Overall, there was a statistically significant increase in T cells in the MSI BRAF mutant and wild type group over the MSS group. There was a statistically significant difference in Trm between MSI-H BRAF mutant vs. MSS (mean/mm2: 2.922 (2.4239-3.4201) vs. 0.9854 (0.8162-1.1546) p=0.0002). There was also a statistically significant difference between MSI-H BRAF wt vs. MSS (mean/ mm2: 2.119 (1.7603-2.4777) vs. 0.9854 (0.8162-1.1546) p=0.0002). The difference between MSI-H BRAF mutant and wild type was not statistically significant. ConclusionsThis study has shown that resident memory T cells are in greater abundance in MSI-H colorectal cancers compared to their MSS counterpart. Trms may play a role in the immunogenicity of MSI-H colorectal cancers, and may be a target for immune-related therapy. Legal entity responsible for the studyThe authors. FundingHas not received any funding. DisclosureAll authors have declared no conflicts of interest.