Phenotype of nonleukemic hCG–PML-RARα transgenic mice. (A) Photograph of nontransgenic bone marrow cells stained with Wright's Giemsa. (B) Photograph of bone marrow cells from a nonleukemic, transgene-expressing mouse from founder line 83, stained with Wright's Giemsa. Note that the marrow of this mouse contains predominantly myeloid cells at all stages of differentiation. (C and D) Photographs of spleen sections from (C) a nontransgenic mouse or (D) a nonleukemic, transgene-expressing mouse after histochemical staining for myeloperoxidase activity. A marked increase in cells staining for MPO activity (black stain) is observed in the transgenic spleen.