CD28^−/− donor T cells engraft in both unirradiated and irradiated hosts. (A) DNA was extracted from splenocytes of normal BDF1 or BDF1 recipients of CD28^−/− spleen cell grafts 28 days after transplant. (B) DNA was extracted from splenocytes of irradiated (B6 × bm12)F1 mice or (B6 × bm12)F1 recipients of CD28^−/− CD4⁺ cells 103 days after transplant. (C) DNA was extracted from splenocytes of irradiated (B6 × bm1)F1 mice or (B6 × bm1)F1 recipients of CD28^−/− CD8⁺ cells 101 days after transplant. DNA was amplified by PCR as described in Materials and Methods. Ethidium bromide-stained agarose gels show the DNA bands for β-actin or neo in each sample.