TNFRSF9 and leukemia: To identify the specific T-cell receptors (TCRs) that recognize leukemic blasts and fusion gene-derived neoantigens, the expanded T cells were co-cultured with autologous blasts, and then the leukemia-reactive T cells were enriched by sorting for 4-1BB+ on the CD8+ population [43] and for 4-1BB+, OX40+, or 4-1BB+ OX40+ on the CD4+ population [44] (Fig. 4A).