Competitive repopulation experiments with 1:1 or 3:1 α4^Δ/Δ (= test) to α4^+/+ (= competitive) cell ratio. (A) FACS profiles of pooled 1:1 BM or 3:1 BM samples showing proportions of α4^- () versus α4⁺ (▪) cells (CFU-C ratio of T:C cells was 6:1 in the latter). (B) PB-cell evaluation for α4 positivity shows an early and progressive reconstitution by α4⁺ competitor cells from 6 to 36 weeks after transplantation (P = .04, , percent α4^-; ▪, percent α4⁺). (C) Genomic PCR in 14 surviving mice (7 from 1:1 and 7 from 3:1) from competitive repopulation at 36 weeks. Note the predominant presence of floxed (f) allele (= competitor) compared to deleted (Δ) one and a minor presence of WT allele from hosts (likely contaminating CD45^- cells). Predominant reconstitution by α4^f/f (= competitors) was also corroborated by CFU-C cultures, showing mostly G418-resistant colonies (α4^f/f are neo⁺) from competitor cells. Only 2 mice (no. 1 from 1:1 and no. 2 from 3:1) show appreciable numbers of (Δ) allele corresponding to higher proportions of α4^- cells. Error bars represent standard error of the mean.