MN1-induced inhibition of myeloid differentiation can be selectively abolished. (A) Western blot using an antihuman MN1 and antimouse Gapdh antibody in lysates of control (ctl)- and MN1VP16-transduced BM cells (left panels). RT-PCR using VP16 specific primers in the same cells used in the Western blot (right panel). (B) Total number of colonies in serial replating. Cumulative yield is shown for an initial plating of 4000 transduced BM cells (mean ± SD of 3 independent experiments). (C) In vitro differentiation assay with MN1 or MN1VP16 cells using either DMSO (1/1000th of total volume, equal to control) or ATRA (1 μM). Cell cultures were propagated every 3 days, and DMSO or ATRA were re-added. Morphology was analyzed after 10 days (magnification, × 1000; see “Materials and methods” for more image acquisition information). (D) Relative gene expression of p21, p27, PU.1, and C/ebpa in MN1 or MN1VP16 cells comparing ATRA-treated (1 μM) to DMSO-treated cells after 7 days of treatment (mean ± SD of 3 independent experiments; *P < .02). (E) FACS analysis of CMP-, GMP-, and MEP-like populations in MN1 and MN1VP16 cells (representative blot from 2 independent experiments). (F) In vitro cytotoxicity assay with 1 μM ATRA over time. Cumulative cell numbers were determined at the given time points for MN1 and MN1VP16 cells (mean ± SD of 3 independent experiments). (G) Survival curves for mice given transplants of MN1- or MN1VP16-transduced BM cells (n = 6 and 4, respectively; P = .004).