Studies from Rosenberg and colleagues performed in patients with melanoma and ovarian cancer have shown that expression of PD-1 on CD8+ T cells in circulating blood identified the repertoire of tumor-reactive cells, suggesting that the CD8+PD-1+ T cells in peripheral blood might be isolated and expanded to provide a surrogate of TILs for use in ACT (15–17). The gene discussed is CD8A; the disease is ovarian carcinoma.