Every living cell has a set of proteins constituting the DNA Mismatch Repair (MMR) system. The MMR system is responsible for correcting nucleotide mismatches occurring in the DNA during cell replication.
Short repetitive sequences, so-called microsatellites, are particularly prone to accumulation of such mismatches. Therefore, when the MMR system does not function, insertion-deletion mutations accumulate at microsatellites causing Microsatellite Instability (MSI) and leading to cancer development. MSI has dramatic consequences on the pathogenesis and immunogenicity of cancer cells, opening possibilities for immunotherapy and immune prevention of MSI cancers.