CD4 and plasma cell myeloma: In PB, the proportion of circulating CD4+CD28−FoxP3+ Treg-like cells among CD4+ T cells significantly increased in MGUS patients (4.61% ± 1.46%, n = 10, P = 0.0002) and untreated myeloma patients (6.19% ± 0.1.58%, n = 16, P < 0.0001) compared to healthy individuals (2.33% ± 0.58%, n = 10); the frequency of Treg-like cells in MM patients was even remarkably higher than those in MGUS patients (P = 0.014) (Fig. 3a).