Chapuis’s group first observed a complete response in 2 of 3 metastatic lesions of a 67-year-old man with metastatic MCPyV-expressing MCC who was treated with autologous ex vivo expanded, HLA-A*2402-epitope-restricted specific T cells (MCPyV-STs).88 They later treated 2 more patients with autologous HLA B*3502- and HLA-A*0201-epitope-restricted MCPyV-STs.89 Notwithstanding the observed tumor lesion regressions, both patients relapsed, thus confirming the risk of tumor escape from single-epitope-targeting T cells. This evidence concerns the gene HLA-A and Merkel cell skin cancer.