Figure 6.

Steroids potentiate TNFα‐induced VEGF‐C expression in MSCs. A) VEGF‐C levels in mouse plasma during aGvHD progression at indicated time points as assayed by ELISA. B) VEGF‐C levels in the plasma of aGvHD patients sensitive or resistant to steroid treatment. Pre/post aGvHD (sensitive) (n = 12), pre/post aGvHD (insensitive) (n = 16), and ongoing aGvHD (insensitive) (n = 16). C) VEGF‐C levels in the supernatant of MSCs with or without TNFα stimulation as assayed by ELISA. D,E) Expressions of VEGF‐C mRNA (D) and protein (E) in MSCs treated with Dex (10 ng mL⁻¹), TNFα (10 ng mL⁻¹), or their combination for 24 h. F) Vegfc mRNA expression in MSCs stimulated with or without TNFα. Tnfr1 expression was knockdown using siRNA. G) MSCs with Tnfr1 knockdown impaired Dex‐induced CD8⁺ T cell proliferation. Anti‐CD3 and anti‐CD28 activated CD8⁺ T cells were co‐cultured with Ctrl‐MSCs or siRNA‐Tnfr1 MSCs with or without Dex. Cell proliferation was assessed by ³H‐thymidine incorporation. H,I) Expressions of Vegfc mRNA (H) and protein (I) in MSCs stimulated with TNFα (3 ng mL⁻¹), in presence or absence of Dex (50 ng mL⁻¹) with or without RU486 (1 µm) for 12 h. J) Graphical abstract. The immunoregulatory property of MSCs is highly plastic. The final read‐out of MSCs depends on the strength and types of inflammatory cytokine and the presence of immunosuppressants. In the presence of IFN‐γ and TNFα, MSCs elicit immunosuppressive property to alleviate aGvHD progression through suppressing the function of a panel of immune cells, including NK cells, neutrophils, CD8⁺ T cells, CD4⁺ T cells, macrophages, and DCs. However, in the presence of Dex and TNFα, MSCs promote immune response via enhancing VEGF‐C‐mediated CD8⁺ T cell response. Mechanistically, Dex and TNFα synergistically induce MSCs to produce abundant VEGF‐C. Subsequently, VEGF‐C binds to VEGFR3 on CD8⁺ T cells to augment PI3K/AKT signaling and elevate Cyclin D1 expression, eventually enhancing CD8⁺ T cell response and exacerbating aGvHD progression. Data are presented as mean ± SEM. n.s: no significance, ^* p < 0.05, ^** p < 0.01, and ^*** p < 0.001.