Protection of acute GVHD by all-trans retinoic acid through suppression of T cell expansion and induction of regulatory T cells through IL-2 signaling.

All-trans retinoic acid (atRA), the active derivative of vitamin A, has been shown to regulate Treg and T effector cell differentiation. However, the potential use of atRA as a treatment for acute graft-verse-host disease (aGVHD) has not been realized. Here we studied the ability of atRA to prevent and treat acute-GVHD in the B6-to-F1(D2B6F1) murine model. Our results showed that atRA consistently displayed a potent ability to control aGVHD development and reduce mortality by suppressing the expansion of donor T cells and inhibiting cytokine expression from donor CD8 cells. Interestingly, CD4(+)Foxp3(+) regulatory T cells were markedly increased in the spleens of atRA-treated mice. In vitro treatment with atRA inhibited T cell proliferation in a dose-dependent manner. Injection of an anti-IL-2 antibody impaired the protection by atRA in aGVHD. Therefore, these results strongly implicate atRA as a novel therapeutic strategy for controlling aGVHD progression and treating other inflammatory diseases.