Implication of chemo‐resistant memory T cells for immune surveillance in patients with sarcoma receiving chemotherapy

Chemotherapy has improved the prognosis of patients with sarcomas. However, it may suppress anti‐tumor immunity. Recently, we reported a novel CD8(+) memory T cell population with a chemo‐resistance property, “young memory” T (T(YM)) cells. In this study, we investigated the proportion and function of T(YM) cells in peripheral blood of healthy donors and sarcoma patients who received chemotherapy and those who did not. The proportion of T(YM) cells was significantly decreased in patients compared with that in healthy donors. In healthy donors, anti‐EBV CTLs were induced using mixed lymphocyte peptide culture, from not only T(YM) cells but also T(CM) and T(EM) cells. No CTLs directed to tumor‐associated antigens were induced. In sarcoma patients who did not receive chemotherapy, in addition to anti‐EBV CTLs, CTLs directed to the tumor‐associated antigen PBF were induced from T(YM), T(CM) and T(EM) cells. In sarcoma patients who received chemotherapy, EBV‐specific CTLs were induced from T(YM) cells but were hardly induced from T(EM) cells. Interestingly, CTLs directed to the anti‐tumor‐associated antigen PBF were induced from T(YM) cells but not from the T(CM) and T(EM) cells in sarcoma patients who received chemotherapy. The findings suggest that T(YM) cells are resistant to chemotherapy and can firstly recover from the nadir. T(YM) cells might be important for immunological memory, especially in sarcoma patients receiving chemotherapy.