Absence of amplification of CD4+CD25high regulatory T cells during in vitro expansion of tumor‐infiltrating lymphocytes in melanoma patients

Abstract

The exact role of CD4+CD25(high) regulatory T cells (Treg) in adoptive immunotherapy of melanoma is still to be determined, and an association between an expansion of Treg cells and the expansion of therapeutic tumor-infiltrating lymphocytes (TIL) remains unelucidated. In this context, the aim of our study was to determine whether functional Treg cells were detectable and amplified among in vitro-expanded TIL from 10 metastatic melanoma lymph nodes (LNs). In this study, we investigated the expression of forkhead/winged helix transcription factor 3 (Foxp3) in melanoma-invaded LNs and determined proportion and functionality of Treg cells among TIL extracted from these 10 metastatic melanoma LNs at different steps of their in vitro expansion. We found that metastatic melanoma LNs expressed very heterogeneous levels of Foxp3 and that CD4+CD25(high) Treg cells extracted from these LNs were detectable at each step of the in vitro culture of TIL but decreasing during the culture. In addition, functional assays demonstrated that these CD4+CD25(high) T cells were capable of suppressing autologous CD8+ and CD4+CD25- T cell proliferation. These cells were indeed Treg cells as they expressed Foxp3. In conclusion, our work suggests that CD4+CD25(high) Foxp3 expressing T cells are not expanded during in vitro amplification of TIL obtained from melanoma-invaded LNs.