Recent studies have found that tumor-infiltrating lymphocytes (TIL) expressing PD-1 can recognize autologous tumor cells, suggesting that cells derived from PD-1(+) TILs can be used in adoptive T-cell therapy (ACT). However, no study thus far has evaluated the antitumor activity of PD-1-selected TILs in vivo. In two mouse models of solid tumors, we show that PD-1 allows identification and isolationof tumor-specific TILs without previous knowledge of their antigen specificities. Importantly, despite the high proportion of tumor-reactive T cells present in bulk CD8 TILs before expansion, only T-cell products derived fromsorted PD-1(+), but not from PD-1(-) or bulk CD8 TILs, specifically recognized tumor cells. The fold expansion of PD-1(+) CD8 TILs was 10 times lower than that of PD-1(-) cells, suggesting that outgrowth of PD-1(-) cells was the limiting factor in the tumor specificity of cells derived from bulk CD8 TILs. The highly differentiated state of PD-1(+) cells was likely the main cause hampering ex vivo expansion of this subset. Moreover, PD-1 precisely identified marrow-infiltrating, myeloma-specific T cells in a mouse model of multiple myeloma. In vivo, only cells expanded from PD-1(+) CD8 TILs contained tumor progression, and their efficacy was enhanced by PDL-1 blockade. Overall, our data provide a rationale for the use of PD-1-selected TILs in ACT. (C) 2017 AACR.