Lentivirally Transduced Recipient-derived Dendritic Cells Serve to Ex Vivo Expand Functional FcRγ-sufficient Double-negative Regulatory T Cells.

αβTCRCD4CD8 double-negative (DN) T regulatory (Treg) cells have recently been shown to suppress antigen-specific immune responses mediated by CD8 and CD4 T cells in mice and humans. In this study, we developed a system to expand DN Treg cells for transplantation therapy that exclusively uses recipient-derived immune cells and confers a high degree of safety as the protocol does not involve the direct injection of lentiviral vectors. Recipient-derived dendritic cells (DCs) were transduced with lentiviral vectors that express major histocompatibility complex class I L antigen (LV-L), which is expressed by the donor graft but is allogeneic to the graft recipient. LV-L-transduced mature DCs (mDCs) were able to expand effectively both FcRγ and FcRγ DN T cells. After expansion with LV-L-transduced mDCs, only the FcRγ DN Treg cells maintained their ability to suppress CD8 T cells in vitro. In addition, adoptive transfer of the FcRγex vivo expanded DN Treg cells significantly prolonged the survival of L skin grafts. This study is the first description of successful ex vivo expansion of antigen-specific DN Treg cells using genetically modified syngeneic DCs for adoptive immunotherapy and demonstrates that although FcRγ DN T cells can be expanded, they do not gain regulatory ability.