Competitive repopulation analysis to assess HSC homing. BM cells from CD45.1 mice were incubated with rat IgG2a antibody or antibodies against integrin α4, α6, or both α4 and α6, and were injected into lethally irradiated CD45.2 mice. BM cells were harvested 3 hours after injection and cells from one femur were injected together with CD45.2 competitor BM cells into lethally irradiated CD45.2 secondary recipient mice. Blood was harvested at 3, 6, and 16 weeks after transplantation and CD45.1⁺ and CD45.2⁺ cells as well as B-cell (B220), T-cell (CD4/CD8), and myeloid cell (Mac-1) reconstitution of CD 45.1 cells were analyzed by flow cytometry.