CD33 and myelodysplastic syndrome: Expanded populations of myeloid-derived suppressor cells (MDSC), representing CD33+CD123+ immature myeloid cells within the bone marrow mononuclear cell fraction contribute to the immunosuppressive tumor microenvironment (TME) by inhibiting both memory and cytotoxic effector T-cell populations as well as natural killer (NK) cells, thereby promoting the immune evasion of MDS clones (Sallman and List, 2019; Younos et al., 2015; Chen et al., 2013; Gañán-Gómez et al., 2015; Parker et al., 2015; Movahedi et al., 2008; Marvel and Gabrilovich, 2015) (Figure 1).