Enforced ROR(gamma)t expression in haematopoietic stem cells increases regulatory T cell number, which reduces immunoreactivity and attenuates hypersensitivity in vivo.

BACKGROUND The retinoic acid receptor-related orphan receptor gammat (ROR(gamma)t) is a key transcription factor involved in the generation of T-helper 17 (Th17) cells, which mediate tissue inflammation and autoimmunity. However, recent studies indicated that less than half of all ROR(gamma)t(+) Talphabeta cells express IL-17, while the others are Foxp3(+) Talphabeta cells expressing IL-10. These observations raise questions regarding the role of ROR(gamma)t in the early differentiation process of T cells from haematopoietic stem cells. METHODS To examine the role of RORyt in T cell differentiation, mice were reconstituted with ROR(gamma)t cDNA-transduced haematopoietic stem cells and the role of ROR(gamma)t in T cell differentiation was studied in a mouse bone marrow transplantation model in vivo. RESULTS While the number of Th17 cells increased with the reduction in Thl cell number in transplanted mice, peripheral blood Foxp3(+) Talphabeta cell number also increased, which attenuated the severity of contact hypersensitivity on skin exposed to 2,4-dinitrofluorobenzene. The number of non-transduced Foxp3(+) regulatory T cells (Treg cells) also increased in these mice. CONCLUSION These observations suggest that the enforced expression of ROR(gamma)t in haematopoietic stem cells induces differentiation of Thl7 cells and results in an increase in Foxp3(+) Treg cell number to limit self-tissue damage.