Determination of optimal strength of alloantigen Treg stimulation.

<p>(A) Treg were stimulated with indicated ratios of irradiated allogeneic PBMC in the presence of IL-2 and IL-15. Proliferation was determined by measurement of [³H]Thymidine incorporation at day 5. Data are representative of three independent experiments. (B) Treg primed with alloantigen were restimulated with indicated ratios of irradiated allogeneic PBMC in the presence of IL-2 and IL-15. Proliferation was determined by measurement of [³H]Thymidine incorporation at day 3. Data are representative of three independent experiments. (C) Efficiency of primary alloantigen stimulated expansion is related to the number of HLA-DRB1 mismatches. Freshly isolated Treg were expanded in one cycle in the presence of IL-2 and IL-15 and stimulation by gamma irradiated allogeneic PBMC with one (N = 10) or two (N = 6) mismatches on HLA class II DRB1 genes. Expansion values were calculated by relating the number of cells set up in the initial culture to the number of cells after expansion (after two days rest). Expansion was higher with alloantigen mismatched on two HLA-DRB1 genes as compared to alloantigen with one mismatch. This difference was found to be statistically significant in a Mann Whitney test (P = 0.025).