Rapamycin and anti-CD28 mAb limit expansion of alloreactive T cells. Lethally irradiated (1200 cGy) B10.BR recipients were given transplants of 10 × 10⁶ CFSE-labeled T cells from B6 donors. Recipients were treated intraperitoneally with either anti-CD28 mAb at 20 μg × 1 day (αCD28), or rapamycin at 1.5 mg/kg × 4 days (rapamycin) or both combined (αCD28 + rapamycin). Splenocytes were harvested on day 4 after transplantation and stained for H2-K^b, CD4, and CD8. (A) CFSE profile is shown separately for donor type (H2-K^b) CD4⁺ and CD8⁺ cells. (B) Absolute numbers of donor CD4⁺ and CD8⁺ cells are shown for each group. Samples were pooled from 3 to 4 recipients per group. Results are representative of 2 replicate experiments.