ABT007 stimulates formation of transgenic mouse erythroid colonies. (A) ABT007 supports the growth of erythroid colonies from bone marrow cells of transgenic mice. Error bars represent SD calculated from the average of duplicate counts. Typical colonies, identified microscopically, are shown on the right for (B) the isotype control–, (C) EPO-, and (D) ABT007-treated cells. The colonies were red in color. All images are at the same magnification.