The human CD34⁺ cells acquire a morphologic polarity upon in vitro cultivation. (A-C) Light micrographs of human CD34⁺ cells freshly isolated from the umbilical cord blood (A) or cultured for 1 day (d1) in serum-free medium in the presence (B) or absence (C) of early acting cytokines as growth factors (GF). (D) The human CD34⁺ cells were cultured in serum-free medium in the presence of early acting cytokines and PI3K inhibitor Ly294002 (Ly). All panels are shown at the same magnification. Note, CD34⁺ cells that were cultured for 1 day in the presence of early acting cytokines (B) increase in size and acquire a polarized cell shape forming a leading edge at the front (arrowheads) and a uropod at the rear pole (arrows). Even in the absence of early acting cytokines, CD34⁺ cells can acquire a polarized cell shape, although they do not increase in size (C). The cell polarization and the growth process are inhibited by the PI3K inhibitor (D).