Recent thymic emigrants and CD44^lo T cells are less sensitive to peripheral apoptosis. Lethally irradiated (850 cGy) 8- to 10-week-old BALB/c mice were transplanted with 5 × 10⁶ TCD Rag2-eGFP Tg BM. n = 5. DATA are representative of 1 of 3 independent experiments. (A) Percentages of eGFP^hi splenic CD4⁺ and CD8⁺ T cells in 2-, 8-, and 12-month-old RAG2-eGFP animals that did not receive transplants, and percentages of CD4⁺ and CD8⁺ donor-derived eGFP^hi splenic T cells in animals that received transplants at days 32 and 48 were determined. Donor cells were defined as H-2D^d negative. (B,C) Donor CD4⁺ and CD8⁺ splenocytes (H-2D^d–negative cells) from TCD-BMT recipients were subsetted according to eGFP expression and analyzed for apoptosis by annexin-V staining on days 18, 32, 45, and 56 after transplantation. Mice that did not receive transplants were also analyzed and are denoted by “N” in these figures. (D) Donor splenocytes (H-2D^d–negative cells) from TCD-BMT recipients were subsetted according to eGFP and CD44 expression. T-cell apoptosis was evaluated by annexin-V staining. (F) Donor splenocytes (H-2D^d–negative cells) from TCD-BMT recipients were subsetted according to eGFP and CD44 expression. Intracellular Bcl-2 levels were measured.