Increased level of both CD4+FOXP3+ regulatory T cells and CD14+HLA-DR⁻/low myeloid-derived suppressor cells and decreased level of dendritic cells in patients with multiple myeloma.

Patients with multiple myeloma (MM) suffer from a general impaired immunity comprising deficiencies in humoral responses, T-cell responses as well as dendritic cell (DC) function. Thus, to achieve control of tumour growth through immune therapy constitutes a challenge. Careful evaluation of the immune status in patients with MM seems crucial prior to active immune therapy. We evaluated the proportion of both, DC, Treg cells and myeloid-derived suppressor cells (MDSC) in peripheral blood from patients with MM at diagnosis and in remission as well as patients with monoclonal gammopathy of undetermined significance (MGUS). We found that the proportion of both myeloid (m) DC and plasmacytoid (p) DC in patients at diagnosis was lowered compared to control donors, while only the proportion of pDC in patients in remission and with MGUS was significantly lower than in controls. The proportion of CD4+FOXP3+ Treg cells was increased in patients at diagnosis and not in patients in remission or with MGUS. Also, Treg cells from patients with MM were functionally intact as they were able to inhibit proliferation of both CD4 and CD8 T cells. Finally, we observed an increase in the proportion of CD14+HLA-DR⁻/low MDSC in patients with MM at diagnosis, illustrating that this cell fraction is also distorted in patients with MM. Taken together, our results illustrate that, both mDC, pDC, Treg cells and MDSC are affected in patients with MM underlining the fact that the immune system is dysregulated as a consequence of the disease.