This study aimed to determine the frequencies of CD4⁺CD25⁺ T cells in donor graft and peripheral blood CD4⁺CD25⁺ T cells in recipients after hematopoietic stem cell transplantation (HSCT) and their association with graft-versus-host disease (GVHD).

Seventeen children who underwent HSCT were investigated. CD4⁺CD25⁺ T cells in samples from donor grafts and recipient peripheral blood were assessed by flow cytometry at 1 and 3 months after transplantation.

CD4⁺CD25⁺ T cell frequencies in the grafts showed no significant difference between patients with and without acute GVHD (0.90% vs. 1.06%, P =0.62). Absolute CD4⁺CD25⁺ T cell number in grafts were lower in patients with acute GVHD than in those without acute GVHD (6.18×10⁵/kg vs. 25.85×10⁵/kg, P =0.09). Patients without acute GVHD showed a significant decrease in peripheral blood CD4⁺CD25⁺ T cell percentage at 3 months compared to those at 1 month after HSCT (2.11% vs. 1.43%, P =0.028). However, in patients with acute GVHD, CD4⁺CD25⁺ T cell percentage at 3 months was not different from the corresponding percentage at 1 month after HSCT (2.47% vs. 2.30%, P =0.5).

The effect of frequencies of CD4⁺CD25⁺ T cells in donor grafts on acute GVHD after HSCT could not be identified, and the majority of peripheral blood CD4⁺CD25⁺ T cells in patients who underwent HSCT may be activated T cells related to acute GVHD rather than regulatory T cells. Further studies with additional markers for regulatory T cells are needed to validate our results.