Echinomycin treatment does not affect long-term HSC activity as revealed by composition of spleen cells. Spleen cells from the CD45.2⁺ recipients of competitive BMT were analyzed for composition of CD45.1⁺ donor-type leukocytes. (A) Frequency of CD45.1⁺ cells. (B) Frequency of B and T cells. (C) Frequency of granulocytes. (D) Summary data of A-C. Data shown represent the mean and standard error of the mean for 5 mice. These data have been repeated in 2 independent experiments.