Pretransplantation administration of KGF in middle-aged recipients of allogeneic BM transplant increases thymopoiesis. Lethally irradiated (1300 cGy) 12-month-old CBA mice were transplanted with T-cell-depleted B10.BR BM (10 × 10⁶). Recipients received either KGF (5 mg/kg/d) or PBS subcutaneously from days -6 to -4. Mice were harvested at day 56, and thymic and splenic cellularities were determined. (A-C) Thymic subpopulations were calculated as described in Figure 1. (D) The number of donor- or host-derived splenic CD4⁺ and CD8⁺ T cells from recipients of allogeneic BM transplant are shown. (E) Splenocytes stained with anti-CD4, -CD8, -CD44, and -Ly9.1 antibodies and donor-derived naive and memory T-cell numbers were calculated as described in Figure 5. Values represent mean (± SEM) and n = 6 mice per group. ^*P < .05.