Peripheral blood stem cells (PBSCs) obtained from granulocyte colony-stimulating factor (G-CSF)-mobilized donors have been used more frequently than bone marrow stem cells as the source of cells in allogeneic hematopoietic stem cell transplantation (allo-HSCT). Although G-CSF–mobilized PBSC grafts contain more mature T cells than bone marrow cell grafts, the incidence and severity of graft-versus-host disease (GVHD) were not elevated. G-CSF-induced immune tolerance might be via inducing T helper type 2 (Th2) polarization, the promotion of regulatory T cell and tolerogenic dendritic cell (DC) differentiation. However, these mechanisms are not fully understood. Human leucocyte antigen-G (HLA-G) is a tolerogenic molecule which participates in the regulation of immune response. In this study, to explore the mechanisms of G-CSF-induced immunoregulation, the effect of G-CSF on blood cells expressing HLA-G was studied.
Membrane-bound HLA-G (mHLA-G) was detected using flow cytometry analysis; soluble HLA-G (sHLA-G), interferon gamma (IFN-γ) and interleukin 10 (IL-10) were determined by enzyme-linked immunosorbent assay (ELISA); HLA-Gpos cells were isolated using flow cytometry, and mixed leukocytes reaction (MLR) was carried out to assess the suppressive effect of HLA-Gpos cells.
CD3+CD4+ T cells, CD3+CD8+ T cells, CD19+ cells and CD14+ cells all expressed mHLA-G in peripheral blood (PB) and bone marrow (BM) from 18 healthy donors before and after G-CSF mobilization. The levels of sHLA-G and mHLA-G on these cells in PB and BM all increased significantly after G-CSF mobilization (all P<0.05). The levels of sHLA-G and mHLA-G on these cells in BM were all higher than that in PB, including before and after G-CSF mobilization (all P<0.05). Bone marrow mononuclear cells (BMMCs) were stimulated with G-CSF in vitro, and the levels of mHLA-G on these cells and sHLA-G in culture supernatant all increased significantly after BMMCs cultivated with G-CSF for 24 hours (all P<0.001). In addition, the levels of IFN-γ and IL-10 also elevated in culture supernatant (both P<0.05). Antibodies blocking experiments for IL-10 and IFN-γ showed that IL-10 and IFN-γ were not necessary for G-CSF-induced HLA-G expression of blood cells. The results of MLR showed that HLA-Gpos cells were able to suppress the proliferation of allogeneic lymphocytes.
G-CSF could directly induce blood cells expressing HLA-G, which might be another mechanism of G-CSF-mediated immunoregulation in G-CSF–mobilized PBSC transplants.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.