Reduced competitive repopulation of Hoxb4^-/- BM cells. Contribution of wt (□) and Hoxb4^-/- (▪) cells in peripheral blood of primary (A) and secondary (B) recipients after 6 and 12 weeks, in competition with B6.SJL BM cells. Primary recipients showed significantly reduced reconstitution at 6 weeks after BMT, whereas the difference at 12 weeks was only marginal. In secondary recipients, reduced reconstitution by Hoxb4^-/- BM was even more pronounced at 6 weeks after transplantation (P < .05), but at 12 weeks the difference was no longer significant (P = .05) (mean ± SD; n = 4).