Donor Th17 cells and IL-21 may contribute to the development of chronic graft-versus-host disease after allogeneic transplantation.

The roles of Th17 cells and IL-21 in the pathogenesis of chronic graft-versus-host disease (cGVHD) in patients who undergo allogeneic transplantation are still unknown. Here, we examined this question by monitoring eight patients with new-onset cGVHD for the presence of Th17 cells, Th1 cells, and IL-21. Allografts from an additional 41 patients were also analyzed for Th17 and Th1 cells. Out of these 41 patients, the last 32 enrolled patients were further analyzed for Th17 cells, Th1 cells, and plasma IL-21 levels at day 30 post-transplantation regarding cGVHD. Th17 cells and IL-21 plasma levels were significantly increased at cGVHD onset and drastically decreased after complete remission. Patients who received a higher number of Th17 cells in their allograft had a higher incidence of cGVHD compared with patients who received a lower number of Th17 cells. Meanwhile, positive plasma IL-21 levels at day 30 post-transplantation predicted cGVHD occurrence. These results suggest that Th17 cells and IL-21 may contribute to the development of cGVHD.