CD274 and neoplasm: Although blockade of the PD-1/PDL1 pathway in antigen-specific CTLs presents a potential clinical strategy to treat tumor and chronic viral infection (Ha et al, 2008; Dotti, 2009; Brahmer et al, 2012; Topalian et al, 2012), it is not fully understood how PD-1 expression and CD8+ CTL cytotoxic efficacy are regulated during immunotherapy.