Early tolerance of CD8 T cells. Cytolytic capacity of tolerized donor-reactive CD8 T cells was analyzed with a ⁵¹Cr release assay following a 5-day restimulation in vitro. 2C/B6 mice were prepared 7 weeks before allo-BMT and received 3 Gy TBI on day −1 and allo-BM transplant on day 0. 2C/B6 mice received a transplant of either L^d+ (B10.A) (A) or L^d− (A.SW or B10.S) BM (B) and were injected with anti-CD154 on day 0 or received L^d+ (B10.A) BM without anti-CD154 (MR1) (C). Four days after BMT, splenocytes were tested against donor (B10.A) stimulator and target cells (■) and against third-party (B10.RIII) stimulator and target cells (□). One representative experiment of 3 is shown (n = 2-3 animals per group; mean ± SEM shown).