Increase of naive CD4⁺CD25^high T cells in MGUS and MM patients. Frequencies of CCR7⁺CD45RA⁺ naive T cells (T_naive), CCR7⁺CD45RA^– central memory T cells (T_CM), and CCR7^–CD45RA^– effector memory T cells (T_EM) were assessed in peripheral blood (PB, n = 18) and bone marrow (BM, n = 6) of MM patients, MGUS patients (MGUS, n = 8), and healthy individuals (control, n = 30). CD4⁺ T cells were further subdivided into conventional CD4⁺CD25^–, CD4⁺CD25^low, and regulatory CD4⁺CD25^highT cells according to their CD25 expression. Significant differences (P < .05, Student t test) between healthy donors, MGUS patients, and MM patients are marked by an asterisk. Error bars represent SD. (A) Increase of naive CD4⁺CD25^highT cells in PB of patients with MGUS or MM as well as in BM of MM patients. (B) Enrichment of CD4⁺CD25^highT_CM cells in PB and BM of patients with MM as well as in MGUS patients. (C) PB of MM patients shows higher frequencies of CD4⁺CD25^high T_EM cells. (D) In PB and BM of MM as well as in MGUS patients, we observed an increase of T_naive cells (F) with a concomitant decrease of T_EM cells in the CD4⁺CD25^low T-cell subsets, (E) whereas T_CM cells were increased in BM of MM patients. (H) Higher frequencies of T_CM cells were also observed in CD4⁺CD25^– T cells in BM of MM patients as well as in PB of MGUS patients, (G) while reduced naive conventional CD4⁺CD25^– T cells were detected in PB and BM of MM patients. (I) CD4⁺CD25^– T_EM cells were diminished only in BM of MM patients.