Immunological profiles in Lynch syndrome colorectal cancers are not specific to mismatch repair gene defects

Background and aims: Colorectal carcinomas (CRCs) in patients with Lynch syndrome (LS) exhibit heightened immunogenicity due to mismatch repair deficiency (MMR-d), often resulting in favorable responses to T cell immune checkpoint therapies. Recent studies indicate that the phenotype and genotype of LS-associated CRCs vary depending on the specific MMR gene mutated. Here, we investigated whether the immune profiles of LS-associated CRCs differ based on the MMR gene defects. Methods: Tissue material from 18 MLH1-, 16 MSH2-, 40 MSH6-, and 23 PMS2-mutated CRCs and 35 sporadic MMR-d CRCs were included in the study. Imaging mass cytometry (IMC) analysis, along with targeted multiplex immunofluorescence imaging (mIF) and immunohistochemistry, were applied to examine the tumor immune microenvironment, including Human Leukocyte Antigen (HLA) class I and programmed death-ligand 1 (PD-L1) expression. Results: Unsupervised hierarchical clustering of cell phenotypes identified by IMC, followed by mIF validation, revealed comparable lymphoid and myeloid cell infiltration levels across CRCs from all MMR groups. Infiltrating T cell levels negatively correlated with the number of mutations at coding microsatellite sequences, particularly in MLH1-mutated CRCs. HLA class I defects were observed in 76% of all CRCs. These defects were more frequently accompanied by β2M defects in hereditary MMR-d CRCs (67%) compared to sporadic MMR-d CRCs (37%), and did not associate with the number of γδ T cells, which were present in CRCs from all MMR groups. PD-L1 expression in tumor cells was only detected in 8% of all CRCs. Conclusion: Our findings illustrate that, from an immunological perspective, there is no evidence of differing immunogenic features across MMR defects. This is important to consider when developing preventive vaccine strategies and evaluating immunotherapy for LS patients and those with MMR-d CRCs.