Donor CD4⁺ T cells are deleted by AICD after 4-1BB stimulation in cGVHD. (A-C) CFSE-labeled DBA/2 spleen/lymph node cells (8 × 10⁷) were adoptively transferred into BDF₁ mice. Immediately thereafter, 200 μg 3H3 or control Ig was injected. Forty hours later, splenocytes were isolated and stained with anti-CD4 with or without anti-CD62L mAb. (A) Representative FACS plots of CFSE staining of donor CD4⁺ T cells. (B) Percent of donor CD4⁺ T cells that divided for more than 4 generations (indicated by lines in the FACS plots in panel A). (C) Percent CD62L^low donor CD4⁺ T cells in these populations (n = 3). ^*P < .05 between the 2 groups. (D-F) Splenocytes prepared on day 5 after disease induction were analyzed for annexin V staining of donor CD4⁺ T cells immediately after isolation (0 h) or after in vitro culture for 12 hours (12 h). H-2K^b–negative CD4⁺ T cells were gated and analyzed for annexin V staining. (D) Representative FACS plots of annexin V⁺ donor CD4⁺ T cells. (E,F) Percent of annexin V⁺ donor CD4⁺ T cells at 0 hours (E) and 12 hours (F); n = 4. ^*P < .05 between the 2 groups at the indicated times.