Lack of suppression of T-cell proliferation by T_reg cells in MGUS and myeloma. (A) Anti-CD3–mediated T-cell proliferation of PBMCs incubated with or without CD25⁺ T cells for 72 hours was measured by ³H-thymidine uptake during the last 8 hours of culture. Results are mean ± SEM CPM, and the number of samples analyzed is shown in parentheses. ^*P < .05 by Student t test analysis. Compared with healthy donor cells, T_reg cells from MGUS and MM patients were unable to significantly suppress T-cell proliferation. (B) CD25⁺ T-cell–depleted PBMCs were cocultured with increasing numbers of CD25⁺ T cells at different ratios, and anti-CD3–mediated proliferation was then measured at 72 hours by ³H-thymidine uptake during the last 8 hours of culture. Adding excess CD25⁺ cells failed to suppress T-cell proliferation in patients with MGUS or MM compared with healthy donors. Results are from 1 of 7 representative experiments.