Competitive repopulation with pooled α4^+/+ (competitor cells) and α4^Δ/Δ (test cells) BM cells. (A) Proportion of α4⁺ cells in the pooled BM sample used for transplantation is depicted in the left panel, and proportion of kit⁺/α4⁺ cells is shown in the right panel. (B) Blood samples from recipients who received transplants were assessed 16 to 42 weeks after transplantation for the presence of α4⁺ (▪) or α4^- () cells. At all times tested, the proportion of α4⁺ cells was 2:1 in PB (compared to input ratio of 1:1). (C) Comparison of PB and BM positivity (right panels) for α4 integrin in mice that received transplants and were killed at 30 (n = 4) or 42 (n = 5) weeks after transplantation (PB, ▪; BM from the same group of mice, ). Reconstitution by α4⁺ cells was higher in BM compared to concurrently tested PB cells (total cells or kit⁺ cells, left panels), suggesting ongoing replacement of hematopoiesis by α4⁺ competitor cells. Error bars represent standard error of the mean.