Inhibition of HSC homing by antibodies against integrin α6 and α4. (A) Peripheral blood reconstitution of CD 45.1 cells and CD 45.1 myeloid cells at 3, 6, and 16 weeks. The CD 45.1 BM cells were incubated with rat IgG2a antibody (rIgG) or antibodies against integrin α4 (α4), α6 (α6), or both α4 and α6 (α4 + α6) before the homing and competitive repopulation assay. Data are pooled from 3 independent experiments. *P < .05; **P < .01; and ***P < .001, compared with reconstitution from cells incubated with rIgG; #P < .05 and ##P < .01, compared with reconstitution from cells treated with anti–integrin α4 antibody. The horizontal bars show mean values for each measurement. The numbers in bottom panels show the number of mice with myeloid CD 45.1 cell reconstitution more than 1% and the number of mice analyzed. (B) Representative fluorescence-activated cell sorting (FACS) dot plots showing blood reconstitution 16 weeks after secondary transplantation. The left panels show reconstitution of CD45.1 BM cells and CD45.2 competitor/recipient cells. The right panels show blood reconstitution of myeloid (Mac-1) and lymphoid (B220, CD4, CD8) cells derived from CD45.1 cells. The numbers indicate the mean percentage of cells in each fraction (n = 13-22).