Regulatory γδT cells induced by G-CSF participate in acute graft-versus-host disease regulation in G-CSF-mobilized allogeneic peripheral blood stem cell transplantation

Background: The immunomodulatory effects of granulocyte colony-stimulating factor (G-CSF) on T cells result in a low incidence of acute graft-versus-host disease (aGVHD) in G-CSF-mobilized allogeneic peripheral blood stem cell transplantation (G-PBSCT). However, the exact mechanism remains unclear Regulatory gamma delta T cells (gamma delta Tregs), characterized by the presence of TCR gamma delta and Foxp3, have aroused great concern in the maintenance of immune tolerance. We hypothesized that gamma delta Tregs might involve in the immunomodulatory effects of G-CSF mobilization. Methods: The expression and immunomodulatory function of gamma delta Treg subsets in peripheral blood of donors before and after G-CSF treatment in vivo and in vitro were evaluated by flow cytometry and CFSE assays. To investigate the effects of gamma delta Tregs on aGVHD, the association between gamma delta Treg subsets in grafts and aGVHD in recipients was estimated. Results: The proportions of V delta 1 Tregs, CD27(+)V delta 1Tregs and CD25(+)V delta 1Tregs were significantly increased in peripheral blood after G-CSF treatment in vivo gamma delta Tregs could be generated in vitro by stimulating with anti-TCR gamma delta in the presence of G-CSF. The immune phenotype, proliferation suppression function, and cytokine secretion of G-CSF-induced gamma delta Tregs were similar to that of transforming growth factor-beta (TGF-beta)-induced gamma delta Tregs The clinical data demonstrated that the proportion of CD27(+)V delta 1Tregs in grafts was significantly lower in the patients who experienced aGVHD than in those who did not develop aGVHD (P=0.028), and the proportions of other gamma delta Treg subsets in grafts did not differ significantly between the two groups. The best cutoff value for CD27(+)V delta 1Treg proportion in grafts in prediction of aGVHD was 0.33%, with an area under the curve value of 0.725 (P=0.043). Eight patients (26.7%) were classified as the low-CD27(+)V delta 1Treg group (< 0.33%), and 22 patients (73.3%) as the high-CD27(+)V delta 1Treg group (>= 0.33%). The incidence of aGVHD was higher in the low-CD27(+)V delta 1Treg group than in the high-CD27(+)V delta 1Treg group (75.0% versus 22.7%, P=0.028). Conclusions: G-CSF could induce the generation of gamma delta Tregs in vivo and in vitro, and gamma delta Tregs might participate in aGVHD regulation in G-PBSCT.