Monophosphoryl lipid A induces bone marrow precursor cells to differentiate into myeloid-derived suppressor cells.

Myeloid-derived suppressor cells (MDSCs) and dendritic cells (DCs) are important in the immune response. In vitro, DCs are derived from myeloid precursors by stimulation with granulocyte macrophage colony‑stimulating factor and interleukin‑4. Previous studies demonstrated that lipopolysaccharide (LPS) in combination with interferon‑γ inhibited DC development but enhanced MDSC functions. Monophosphoryl lipid A (MPL), derived from LPS, is a unique immunomodulatory Toll‑like receptor 4 agonist. In the present study, MPL was used to disturb DC differentiation from myeloid precursors and it was observed that prolonged stimulation with MPL led to the accumulation of MDSCs in vitro and in vivo. In conclusion, it was demonstrated that stimulation by MPL from the beginning of cell differentiation disturbed the development of DCs and led to the accumulation of MDSCs.