To establish an in vitro model for JCV T-Ag expression, we transfected a JCV T-Ag carrying plasmid into two prototypic colon cancer cell lines; HCT116, which is a microsatellite unstable cell line and is representative of Lynch syndrome colorectal cancers due to an underlying germline mutation in the DNA mismatch repair gene, MLH1; and SW837 cells, which are microsatellite stable but harbor mutations in the p53 tumor suppressor gene (Figure 1A). Here, MLH1 is linked to colorectal cancer.