CD33 and acute myeloid leukemia: For instance, exosomes derived from plasma of acute myelogenous leukemia (AML) patients, containing CD33, CD34, CD117, MICA/MICB, and TGF-β, were shown to decrease cytotoxic activity of NK cells, in a process involving Smad phosphorylation and down-regulation of NKG2D receptor in NK cells (Szczepanski et al., 2011; Whiteside, 2013), which was reversible by IL-15 (Szczepanski et al., 2011).