Myelodysplastic syndromes (MDS) are age-dependent stem cell malignancies that share biological features of activated adaptive immune response and ineffective hematopoiesis. Here we report that myeloid-derived suppressor cells (MDSC), which are classically linked to immunosuppression, inflammation, and cancer, were markedly expanded in the bone marrow of MDS patients and played a pathogenetic role in the development of ineffective hematopoiesis. These clonally distinct MDSC overproduce hematopoietic suppressive cytokines and function as potent apoptotic effectors targeting autologous hematopoietic progenitors. Using multiple transfected cell models, we found that MDSC expansion is driven by the interaction of the proinflammatory molecule S100A9 with CD33. These 2 proteins formed a functional ligand/receptor pair that recruited components to CD33’s immunoreceptor tyrosine-based inhibition motif (ITIM), inducing secretion of the suppressive cytokines IL-10 and TGF-β by immature myeloid cells.
Xianghong Chen, Erika A. Eksioglu, Junmin Zhou, Ling Zhang, Julie Djeu, Nicole Fortenbery, Pearlie Epling-Burnette, Sandra Van Bijnen, Harry Dolstra, John Cannon, Je-in Youn, Sarah S. Donatelli, Dahui Qin, Theo De Witte, Jianguo Tao, Huaquan Wang, Pingyan Cheng, Dmitry I. Gabrilovich, Alan List, Sheng Wei