TGF-β1 induces preferential rapid expansion and persistence of tumor antigen-specific CD8⁺ T cells for adoptive immunotherapy

Adoptive cell transfer of expanded, autologous tumorinfiltrating lymphocytes (TIL) into lymphodepleted melanoma patients can induce the regression of bulky, metastatic disease. To generate the large numbers of T cells needed for infusion, TIL undergo a rapid expansion protocol (REP) in vitro using anti-CD3 antibody, interleukin-2, and irradiated peripheral blood feeder cells that typically results in an approximately 1000-fold expansion over 14 days. However, we have found that the conventional REP (C-REP) often favors the expansion of CD4⁺ T cells at the expense of tumor antigen-specific CD8⁺ T cells, which are the most potent cytolytic effector cells. In this study, we demonstrate that addition of transforming growth factor (TGF)-β1 to the TIL culture at the onset of rapid expansion (T-REP) maintained the percentage of CD8⁺ T cells while not inhibiting overall T-cell expansion. Of T cells expanded from different melanoma patient tumors, 13 of 15 TIL demonstrated improved yields and percentages of both CD8⁺ and MART-1 melanoma antigen-specific T cells after 14 days of expansion in TGF-β1 compared with the C-REP. This was associated with a marked improvement in the antitumor activity of the resulting bulk TIL culture in terms of interferon-γ production and melanoma tumor-specific cytotoxic T-lymphocyte activity. In addition, T-REP T cells demonstrated a higher potential for continued expansion in vitro for up to 3 weeks after the expansion compared with C-REP T cells, suggesting that they may also be capable of increased persistence after adoptive cell transfer. Our results suggest that TGF-β1-expanded TIL have attributes that might predict efficacy superior to that of conventional TIL.