Enhanced thymocyte cellularity in KGF + leuprolide acetate-treated BMT recipients correlates with increased T-cell export into the periphery and diminished homeostatic proliferation early after BMT. (A,B) Lethally irradiated B6 recipients of allogeneic (BALB/c) bone marrow that were left untreated (BMT Control) or pretreated with KGF, leuprolide acetate, or KGF + leuprolide acetate were intrathymically injected (one thymic lobe) with biotin at 28 days after BMT. After 24 hours of in vivo labeling, the export of thymus-derived CD4 (A) and CD8 (B) T cells into the periphery was assessed by staining total splenocytes with fluorescently labeled streptavidin in combination with monoclonal antibodies specific for CD4 and CD8. Absolute numbers of recent thymic emigrants (RTE) were normalized to absolute numbers of donor-derived CD4⁺ or CD8⁺ T cells in panels A and B, respectively. (C-F) Homeostatic proliferation in the CD4⁺ and CD8⁺ T-cell compartment was also assessed between days 30 and 35 after BMT. Treated and untreated BMT recipients and non-BMT control mice were injected intraperitoneally with BrdU (1 mg) on day 30, followed by continuous administration of BrdU in the drinking water (0.8 mg/mL) through day 35 after BMT, at which point CD4⁺ and CD8⁺ T cells were analyzed for BrdU incorporation and concomitant up-regulation of CD44, thus indicating that proliferation had occurred within the 5-day labeling window. Data shown are the mean percentages of BrdU⁺CD44⁺ (± SEM) of total CD4⁺ T cells (C,E) and CD8⁺ T cells (D,F) isolated from the spleens and lymph nodes of these mice. These data are representative of one experiment with 4 mice per group; *P < .05 compared with BMT control mice; #P < .05 compared with KGF- or leuprolide acetate-treated BMT recipients.