CD28-driven T-cell expansion in thymectomized rats. ATXBM PVG rats were reconstituted with 5 million CD45 allotype-marked T cells and injected with a single dose of 1 mg CD28 superagonist (•) or isotype control mAb (○). Peripheral blood was analyzed for total lymphocytes, donor-derived total T cells, and their CD4 and CD8 subsets as indicated. Means and SDs of 6 animals per group are shown. *P < .05; **P < .01.