BMP4 increases ITGA4 expression in human BM-derived HSPCs resulting in better homing after transplantation in mice. Human BM derived Lin⁻CD34⁺ cells were cultured with SCF+TPO with or without BMP4 alone or with SB203580 for 5 days (ST = SCF/TPO; STB = SCF/TPO/BMP4; STBS = SCF/TPO/BMP4/ SB203580). Levels of ITGA4 mRNA were assessed by qRT-PCR, expression of phospho-p38 MAPK and ITGA4 by FACS, or cells were used for in vivo homing assays. (A) qRT-PCR analysis for ITGA4 in hBM derived Lin⁻CD34⁺ progeny from ST, STB and STBS cultures. (n = 5; * P < .01). (B-C) Lin⁻CD34⁺ BM progeny were harvested and stained with antibodies against Lineage markers, CD34, phospho-p38 MAPK or ITGA4. Lin⁻CD34⁺ cells were gated (B), and phosphorylated p38 MAPK levels (C, left) and ITGA4 levels (C, right) were compared among different conditions by FACS. Representative example of 5 experiments. (D) Freshly isolated or cultured hBM Lin⁻CD34⁺ cells (0.1 × 10⁶) were transplanted intravenously in lethally irradiated Rag2^−/−Il2Rγc^−/− mice, BM was harvested after 16 hours and CFU-Cs enumerated in the recipient BM. Percentage homing was determined by comparing total CFU-Cs homed with CFU-Cs injected (n = 8, P < .005).