Tc2-type donor CD8⁺ T cells abrogate marrow graft rejection. Host B6 (H-2^b) mice were irradiated at 950 or 650 cGy; all mice received 1 × 10⁷ TCD bone marrow cells from B6D2F1 (H-2^b/d) donor mice. Engraftment control mice (950/−) and rejection control mice (650/−) received only the donor bone marrow at the time of transplant; other groups received additional donor CD8⁺ T cells (1 × 10⁷cells) of Tc1-type (650/Tc1) or Tc2-type (650/Tc2). Peripheral blood lymphocytes were isolated on days 30 and 90 posttransplant and stained with H-2^b FITC (common to both donor and host cells) and H-2^d PE (specific for donor cells); the percentage of donor and host chimerism was then determined by flow cytometry. Each data point represents the donor chimerism result for an individual animal.