CD19 and melanoma: Such escape on the level of viral epitope recognition is paralleled by the phenomenon of “antigen loss” in tumors—for example, the loss of MART-1 antigen in melanoma patients after adoptive transfer of MART-1 specific T cells (97, 98), or the loss of CD19 following CD19 targeted CAR T cell therapy for acute myeloid leukemia (99) [reviewed in (100)].