Immunomodulatory effects of vitamin D: implications for GVHD

Abstract

GVHD remains a major source of morbidity and mortality after allogeneic BMT. GVHD is mediated by alloreactive T cells derived from the hematopoietic graft that target host tissues. Pre-clinical models have shown that presentation of alloantigens by host DCs results in the activation of donor-derived T cells that mediate GVHD. Strategies that interfere with the Ag-presenting capacity of DCs after allogeneic transplantation may decrease the risk of developing GVHD. Vitamin D is a hormone essential for calcium metabolism that shows immunomodulatory properties. We showed that correction of vitamin D deficiency appeared to mitigate manifestations of GVHD. In pre-clinical studies, we have shown that vitamin D inhibits DC maturation, polarizes T-cell populations toward the expression of Th2 as compared with Th1 cytokines, and blunts allogeneic T-cell proliferation in response to DC stimulation. Exposure to vitamin D resulted in increased expression of IDO, an enzyme responsible for tryptophan metabolism that is upregulated in tolerizing DCs. These data suggest that exposure to vitamin D results in immature DC populations that bias toward tolerizing rather than stimulatory T-cell populations. Vitamin D may therefore have a role in the prevention of GVHD.

Figure 1

(a) A representative example showing the expression of CD80, CD83, CD86 on DCs generated in the presence and absence of 10 ηm vitamin D. Upper panels: Expression of CD80, CD83 and CD86 on DCs generated by culturing adherent mononuclear cells isolated from leukopak collections with GM-CSF, IL-4 and TNFα. Lower panels: Expression of CD80, CD83 and CD86 on DCs generated by culturing adherent mononuclear cells isolated from leukopak collections with GM-CSF, IL-4 and TNFα in the presence of 10 ηm vitamin D. (b) Summary data showing the expression of CD80, CD83 and CD86 on DCs generated in the presence and absence of 10 ηm vitamin D. Phenotypic analysis was performed on paired samples of DCs generated in the presence and absence of vitamin D. Cells were incubated with the appropriate Ab and analyzed by flow cytometry. Each dot represents the percent expression of CD80, CD83 and CD86 in an individual experiment, and the line represents the median percent expression of the indicated surface molecule.

Figure 2

Expression of IDO protein by DCs generated in the presence and absence of vitamin D. DCs were generated by culturing adherent mononuclear cells isolated from leukopak collections with GM-CSF, IL-4 and TNFα in the presence or absence of 10 ηm vitamin D. IDO protein expression was assessed by western blot analysis.

Figure 3

(a) Ratio of IFN gamma/IL-10 expressing CD4 and CD8T cells in the presence and absence of vitamin D. Mean values of three experiments are presented, with associated s.e. of the means. (b) Allogeneic T-cell proliferation after stimulation with mature DCs in the presence or absence of vitamin D. Allogeneic T cells were cocultured with mature DCs for 5 days in the presence or absence of vitamin D. Proliferation was measured by uptake of tritiated thymidine after an overnight pulse. Results are expressed as a stimulation index (T-cell proliferation following coculture/proliferation of unstimulated T cells). Each dot represents the stimulation index (SI) of an individual experiment, and the line represents the median SI.

Figure 4

Analysis of DCs generated in the presence and absence of vitamin D for P-STAT1 levels. DCs were generated from adherent mononuclear cells in the presence and absence of 10 ηm vitamin D, and the level of P-STAT1 was assessed by western blot analysis.