Increase of Regulatory γδ T Cells Reduces the Incidence of Acute Graft-Versus-Host Disease after Allogeneic Hematopoietic Stem Cell Transplantation

Background Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the primary means for treatment of hematologic and non-hematologic malignancies. Acute graft-versus-host disease (aGVHD) is a major complication associated with high morbidity and mortality after transplantation. Regulatory γδ T cells (γδ Tregs), as a novel subset of γδ T cells with Foxp3 expression and immunosuppressive effect, are found to effectively alleviate aGVHD in mice model. However, whether γδ Tregs involve in the occurrence of aGVHD in recipients of allo-HSCT remains unclear. Therefore, the aim of this study is to investigate the effect of γδ Tregs in the occurrence of aGVHD in recipients of allo-HSCT.

Methods The immunophenotyping of γδ Tregs was analyzed in peripheral blood from 24 aGVHD and 24 paired non-aGVHD patients (undergoing transplantation at the same time, basic data matched), using flow cytometry. The expression levels of immunoregulatory-associated molecules (Foxp3, CD25, CTLA-4, GITR, TLR8, RORc, STAT-1 and STAT-3) were analyzed in peripheral blood, using real-time RT-PCR with SYBR GreenⅠstaining. Liquichip technology was used to analyze the concentration of interferon-γ (IFN-γ), interleukin-4 (IL-4), IL-10, IL-17 and tumour necrosis factor-α (TNF-α) in cultural supernatant.

Results The proportions of total γδ T and Vδ2 T cells in non-aGVHD patients were significantly higher than that in aGVHD patients (P=0.044, P=0.000), and the proportion of Vδ1 T cells was similar between the two groups (P=0.061). Compared with aGVHD patients, the proportions of Foxp3⁺γδ T, Foxp3⁺Vδ1 T, Foxp3⁺Vδ2 T cells and Tregs were increased in non-aGVHD patients (P=0.005, P=0.014, P=0.026 and P=0.000). There was a negative correlation between the incidence of aGVHD and the percentages of Foxp3⁺γδ T, Foxp3⁺Vδ1 T and Foxp3⁺Vδ2 T cells (P=0.014, r_s=-0.477; P=0.001, r_s=-0.610; P=0.040, r_s=-0.405). The mRNA expression levels of Foxp3 and TLR8 genes were significantly increased in non-aGVHD patients compared with aGVHD patients (P=0.042, P=0.002). There were no significant difference in the expression levels of CD25, RORc, CTLA-4, GITR, STAT-1 and STAT-3 genes (P=0.234, P=0.194, P=0.056, P=0.524, P=0.142 and P=0.775). In addition, the concentrations of IL-10 and TNF-α were significantly increased in aGVHD patients (P=0.002, P=0.036), and the concentrations of IL-4, IL-17 and IFN-γ were similar between the two groups (P=0.379, P=0.414, P=0.170).

Conclusions Increase of γδ Tregs might reduce the incidence of aGVHD after allo-HSCT.