Fig. 1.

BM-MSC and CMPC co-cultures with T cells after 6 days of stimulation. A. Light microscopical representation of T cell co-cultures after 6 days. In the non-stimulated samples, small individual cells are spread throughout the well. Upon stimulation, T cells form proliferating colonies. In the presence of BM-MSC and CMPC, the formation of these colonies is strongly reduced or even absent. Bar is 200 μm. B. Proliferation of T cells as measured by flow cytometry. Non-stimulated T cells have a single FL1 peak at a high fluorescent intensity. Upon stimulation, lower intensity peaks form, halving the fluorescent signal upon each cell division. C. Quantification of proliferation of T cells in different co-cultures. The first bar represents the unstimulated control, while the second bar is the stimulated T cells. Proliferation of T cells is significantly reduced in the presence of BM-MSC (65% ± 8) and CMPC (97% ± 0.6) (BM-MSC and CMPC: n = 12). D. Differences in suppressive capacity based on donor age. Both fetal and adult cells suppress T cell proliferation significantly. Adult BM-MSC suppress similar to fetal BM-MSC (40% ± 7.5 and 43% ± 11, resp.), while adults CMPC perform worse than fetal CMPC (51% ± 3.1 and 95% ± 0.4, resp.). E. The additional effect on T cell suppression due to ‘licensing’ was investigated. Progenitor cells were preconditioned with 20 ng/mL IFN-gamma (red bars) and compared to the unconditioned cells (black bars). Preconditioning had no effect on fetal stem cells. Adult BM-MSC improved to 65% ± 3 suppression, while adult CMPC improved to 83% ± 5.8 suppression (p = 0.006). ***p < 0.001 and **p < 0.01 compared to stimulated T cells. °°°p < 0.001 compared to T cells + fCMPC.