Colorectal cancers associated with
Lynch syndrome are characterized by defective mismatch repair,
microsatellite instability, high mutation rates, and a highly immunogenic environment. These features define a subset of
cancer with a favorable prognosis and high likelihood to respond to treatment with anti-programmed death 1 (PD-1)/
programmed death ligand 1 (PD-L1) drugs. With the aim to define immune-evasive mechanisms and a potential impact hereof in
colorectal cancers from
Lynch syndrome versus hereditary cases with retained mismatch repair function, we immunohistochemically and transcriptionally profiled 270
tumors.
Lynch syndrome-associated
tumors showed an overrepresentation of
tumor-infiltrating CD3, CD8 and CD68 positive cells, loss of beta-2-microglobulin (B2M) and up-regulation of PD-L1 on
tumor cells. The gene expression signature of
Lynch syndrome tumors was characterized by upregulation of genes related to antigen processing and presentation, apoptosis, natural killer cell-mediated cytotoxicity, and T cell activation.
Tumors with loss of B2M and up-regulation of PD-L1 showed distinctive immunogenic profiles. In summary, our data demonstrate a complex
tumor-host interplay where B2M loss and PD-L1 up-regulation influence immunological pathways and clinical outcome in
Lynch syndrome tumors. Immunological classification may thus aid in the preselection of
colorectal cancers relevant for treatment with anti-PD-1/PD-L1
therapies.