Mechanism of Suppression Effect of Myeloid-Derived Suppressor Cells on Hyperacute Graft-Versus-Host Disease

Allogeneic HSCT (allo-HSCT) is associated with serious side effects and its most common complication is graft-versus-host disease (GVHD). Hyperacute GVHD is a clinical syndrome that occurs within the first 14 days after allo-HSCT associated with significant morbidity and mortality. The large sample size of clinical study indicated that the incidence of hyperacute GVHD in patient who underwent an allo-HSCT was about 9%, but the pathological process and crucial factor of this complication have incompletely defined.

Myeloid-derived suppressor cells (MDSCs) have been found that had a beneficial role in treatment of GVHD, on account of suppressing ability on alloreactive T-cell-response in vitro and in vivo. It was reported that reactive oxygen species (ROS) have been implicated in MDSCs-mediated T cell suppression and MDSCs from NOX2-deficient mice, chronic granulomatous disease (CGD) mice, failed to suppress T cell function. However, the investigation of whether and how MDSCs and ROS play in CGD mice receiving allo-HSCT is lacking.

In our research, WT mice receiving allo-HSCT began to appear typical acute GVHD clinical manifestations in about 20 days and died within 30 days after transplantation, while CGD mice receiving allo-HSCT suddenly suffered from hyperacute GVHD at day 3 after allo-HSCT: performed continuous weight loss, demonstrated poor grooming and impairs movement with or without hunching or skin integrated and animals died within 2 days after onset of symptoms. Further study shown that the donor spleen derived T cells was indispensable for hyperacute GVHD of CGD mice after receiving allo-HSCT. T lymphocyte subsets and proportional change in bone marrow and spleen of each group were detected by flow cytommeter after transplantation. The percentage and absolute number of donor derived CD3⁺CD8⁺T cell from both BM and spleen of CGD were significant higher than that of WT mice received allo-HSCT. Moreover, cell size and expression of activation marker CD25, CD44, and CD69 of CD3⁺CD8⁺T cell from both BM and spleen of CGD mice were significant higher than that of WT mice. The killing ability of donor derived CD3⁺T cells was observed by the living cells workstation and it was obviously to see that allo-reactive T cells from CGD mice had stronger killing ability. The levels of different cytokines in serum of recipient mice were detected by protein chip at day 3 after allo-HSCT. Comparing to C57BL/6 mice, more than ten kinds of inflammatory factors, including IL-6, were increased in the serum of CGD mice, which indicated that the cytokine storm related to T cells might be occur during hyperacute GVHD. In addition, using this hyperacute mouse model, we revealed that application of ROS agonist, L-buthionine-S, R-sulfoximine (BSO), rescued the CGD mice receiving allo-HSCT from hyperacute GVHD.

In General, this study pioneering established a stable murine model of hyperacute GVHD and proved that allo-reactive T cells massively activated and proliferated since ROS production defective MDSCs lose the ability of inhibiting T cell immune reaction and caused hyperacute GVHD. These data provided new insights into the pathogenesis of GVHD and may improve the clinical management of this common complication.