Rapid spontaneous proliferation of nonalloreactive donor T cells enhances peripheral apoptosis. Lethally irradiated (1100 cGy) B6 Ly5.1 recipients were transplanted with 2 × 10⁷ CFSE-labeled B6 purified T cells. (A) Apoptosis of donor (Ly5.2⁺) T cells as defined by annexin V staining was measured on day 7 after adoptive transfer. Top histograms reveal the CD4⁺ and CD8⁺ T-cell proliferation pattern. (B) Annexin V staining on proliferating donor CD4⁺ and CD8⁺ T cells is shown. (C) The mean percentages of apoptotic, annexin V⁺ T cells with data from 5 combined independent experiments is shown (n = 7).