Suppression of B-Cell Activation by Human Cord Blood-Derived Stem Cells (CB-SC) through the Galectin-9-Dependent Cell Contact Mechanism

BackgroundWe developed the Stem Cell Educator therapy among multiple clinical trials based on the immune modulations of multipotent cord blood-derived stem cells (CB-SC) on different compartments of immune cells such as T cells and monocytes/macrophages in diabetes and other autoimmune diseases. However, the effects of CB-SC on the B cells remained unclear. To better understand the molecular mechanisms underlying the immune education of CB-SC, we explored the modulations of CB-SC on human B cells. MethodsCB-SC were isolated from human cord blood units and confirmed by flow cytometry with different markers for their purity. B cells were purified by using anti-CD19 immunomagnetic beads from human peripheral blood mononuclear cells (PBMC). Next, the activated B cells were treated in the presence or absence of coculture with CB-SC for 7 days before undergoing flow cytometry analysis of phenotypic change with different markers. RT-PCR was utilized to evaluate the levels of galectin expressions with or without treatment of activated B cells in order to find the key galectin contributing to the B-cell modulation. ResultsFlow cytometry demonstrated that the proliferation of activated B cells was markedly suppressed in the presence of CB-SC, leading to the down-regulation of immunoglobulin productions from the activated B cells. Phenotypic analysis revealed that treatment with CB-SC increased the percentage of IgD+CD27- naive B cells, but decreased the percentage of IgD-CD27+ switched B cells. Transwell assay showed that the immune suppression of CB-SC on B cells was dependent on the manner of cell-cell contact via Gal-9 molecule, as confirmed by the blocking experiment with the anti-Gal-9 monoclonal antibody. Mechanistic studies demonstrated that both calcium levels of cytoplasm and mitochondria were down-regulated after the treatment with CB-SC, causing the decline of mitochondrial membrane potential in the activated B cells. Western blot exhibited that the levels of phosphorylated Akt and Erk1/2 signaling proteins in the activated B cells were also markedly reduced in the presence of CB-SC. ConclusionsCB-SC displayed multiple immune modulations on B cells through the Gal-9-mediated cell-cell contact mechanism and calcium flux/Akt/Erk1/2 signaling pathways. The data advances current understanding about the molecular mechanisms underlying the Stem Cell Educator therapy to treat autoimmune diseases in clinics.