Induction of spontaneous monocytic differentiation in M1 cells transfected with WT1 +KTS isoforms. M1 cells stably transfected with retroviral vectors containing cDNAs encoding individual WT1 isoforms were compared with parental cells or control M1.Neo cells generated by transfection with a retroviral vector encoding neomycin-resistance. Differences in morphology were examined in culture (original magnification ×200) and by Leishman's staining of cytospin preparations (original magnification ×800).