Lynch Syndrome (LS) represents a hereditary, autosomal dominant form of colorectal cancer with a high lifetime penetrance that is caused by germline mutations in any of several DNA repair genes, leading to microsatellite instability. LS develops as a highly immune-sensitive tumor, due to the immunogenic frame-shifted products from genes bearing microsatellites, which leads to effective cycles of “recognition and elimination” until any of several immune escape mechanisms thwart control. LS is an ideal target in which to evaluate various immune-mediated modalities, including preventative vaccines, as reviewed by Pastor and Scholm.
Contributed by Ed Fritsch
PURPOSE OF REVIEW: Patients with Lynch syndrome have a high probability of developing colorectal and other carcinomas. This review provides a comprehensive assessment of the immunologic aspects of Lynch syndrome pathogenesis and provides an overview of potential immune interventions for patients with Lynch syndrome polyps and Lynch syndrome-associated carcinomas. RECENT FINDINGS: Immunogenic properties of the majority of Lynch syndrome polyps and associated cancers include microsatellite instability leading to a high mutational burden and the development of novel frameshift peptides, i.e., neoantigens. In addition, patients with Lynch syndrome develop T cell responses in the periphery and in the tumor microenvironment (TME) to tumor-associated antigens, and a proinflammatory cytokine TME has also been identified. However, Lynch syndrome lesions also possess immunosuppressive entities such as alterations in MHC class I antigen presentation, TGF_ receptor mutations, regulatory T cells, and upregulation of PD-L1 on tumor-associated lymphocytes. The rich immune microenvironment of Lynch syndrome polyps and associated carcinomas provides an opportunity to employ the spectrum of immune-mediating agents now available to induce and enhance host immune responses and/or to also reduce immunosuppressive entities. These agents can be employed in the so-called prevention trials for the treatment of patients with Lynch syndrome polyps and for trials in patients with Lynch syndrome-associated cancers.