Increased activated regulatory T cell subsets and aging Treg-like cells in multiple myeloma and monoclonal gammopathy of undetermined significance: a case control study

BACKGROUND: Accumulating evidence have indicated that regulatory T cells (Tregs) play an essential role in T cell-mediated immune response and development of multiple myeloma (MM). CD4(+)FoxP3(+) T cells are composed of three phenotypically and functionally distinct subpopulations: CD45RA(+)FoxP3(lo) resting Tregs (rTregs), CD45RA(−)FoxP3(hi) activated Tregs (aTregs) and CD45RA(−)FoxP3(lo) non-suppressive T cells (non-Tregs). We aimed to clarify the frequency and function of these three subpopulations in newly diagnosed multiple myeloma and monoclonal gammopathy of undetermined significance (MGUS) patients. In addition, CD28(−)CD4(+)FoxP3(+) Treg-like cell is a senescent regulatory T cell subset with partial suppressive function, which could be impaired during myelomagenesis. METHODS: we examined 20 patients with MGUS, 26 patients with newly diagnosed MM and 18 healthy volunteers. Flow cytometric analysis in peripheral blood and bone marrow was performed for frequency study. The immunosuppressive function of Treg subsets was assessed by their ability to suppress the proliferation of responder cells in co-culture. Concentration of cytokine from the culture supernatants of proliferation assay was measured using ELISA. RESULTS: The proportion of activated Tregs in CD4(+) T cells was significantly higher in MGUS and MM patients than healthy controls (P = 0.01, P < 0.001) in both PB and BM; while the proportion of rTregs in MGUS, MM patients was significantly lower than that of controls (P = 0.02, P < 0.01) only in BM. There was no significant difference in frequencies of non-Tregs from MGUS to MM patients with normal controls (P = 0.14, P = 0.88). Significant increase in PB and BM Treg-like cells was observed in MGUS and MM cohort compared with healthy controls (P < 0.01, P < 0.01). Treg-like cells in MM patients were significantly higher than those in MGUS patients (P < 0.01). The inhibition rate of aTreg in bone marrow of MM patients was significantly higher than that of rTreg (P < 0.01), while the inhibition rate of non-Treg was significantly lower than that of rTreg cells (P < 0.01). Functional assays revealed the suppressive and secretory abilities of three Treg subsets were intact in MM patients. CONCLUSIONS: In summary, aTregs and aging Treg-like cells were quantitatively altered in MGUS and MM patients, which might be associated with disease progression and prognosis. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12935-018-0687-8) contains supplementary material, which is available to authorized users.