Regulatory CD8+ T cells induced by exposure to all-trans retinoic acid and TGF-β suppress autoimmune diabetes

Antigen-specific regulatory CD4+ T cells have been described but there are few reports on regulatory CD8+ T cells. We generated islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-specific regulatory CD8+ T cells from 8.3-NOD transgenic mice. CD8+ T cells from 8.3-NOD splenocytes were cultured with IGRP, splenic dendritic cells (SpDCs), TGF-β, and all-trans retinoic acid (ATRA) for 5 days. CD8+ T cells cultured with either IGRP alone or IGRP and SpDCs in the absence of TGF-β and ATRA had low Foxp3+ expression (1.7 ± 0.9% and 3.2 ± 4.5%, respectively). In contrast, CD8+ T cells induced by exposure to IGRP, SpDCs, TGF-β, and ATRA showed the highest expression of Foxp3+ in IGRP-reactive CD8+ T cells (36.1 ± 10.6%), which was approximately 40-fold increase compared with that before induction culture. CD25 expression on CD8+ T cells cultured with IGRP, SpDCs, TGF-β, and ATRA was only 7.42%, whereas CD103 expression was greater than 90%. These CD8+ T cells suppressed the proliferation of diabetogenic CD8+ T cells from 8.3-NOD splenocytes in vitro and completely prevented diabetes onset in NOD-scid mice in cotransfer experiments with diabetogenic splenocytes from NOD mice in vivo. Here we show that exposure to ATRA and TGF-β induces CD8+Foxp3+ T cells ex vivo, which suppress diabetogenic T cells in vitro and in vivo.