Low-dose oral cholecalciferol is associated with higher numbers of Helios+ and total Tregs than oral calcitriol in renal allograft recipients: an observational study

BACKGROUND: Regulatory T cells (Tregs) are a cornerstone of graft acceptance. High numbers of Tregs are associated with better long-term graft survival. Recently, Vitamin D was suggested as an immunomodulator, in addition to its classical role in calcium metabolism. Vitamin D modulates Tregs and might, thereby, promote graft acceptance and long-term graft survival. METHODS: One hundred twenty-three renal allograft recipients attending either Heidelberg nephrology or Giessen internal medicine clinic were enrolled in this cross- sectional study. Sixteen healthy controls were studied in addition. Sixty-nine patients were receiving no vitamin D, 38 calcitriol, and 16 cholecalciferol supplementations. We evaluated whether there was a difference in the absolute numbers of Helios(+), Helios(-), CTLA-4(+), IFNg(+), and total Tregs among the patient groups. RESULTS: Cholecalciferol supplementation was associated with higher absolute numbers of Helios(+), CTLA-4(+), and total Tregs than calcitriol (p < 0.001, p = 0.004, p = 0.001 respectively). Helios(+) Tregs were also higher in cholecalciferol than no vitamin D supplementation patients (p = 0.001), whereas CTLA-4(+) and total Tregs were similar in both groups (p = NS). Helios(+), Helios(-), CTLA-4(+), IFNg(+), and total Tregs were similar in the cholecalciferol and healthy control groups (p = NS). CONCLUSION: Our findings indicate that cholecalciferol, even when administered at low dosages, has a stabilizing effect on Tregs (particularly the Helios + subset), in contrast to calcitriol which showed neither a stabilizing nor a proliferation-inducing effect on the same cell population.