The Lnk SH2 domain is required to inhibit Epo-dependent erythroid differentiation. (A) CD71/Ter119 FACS profile of freshly isolated e14.5 fetal liver cells. About 15% of the cells are Ter119^- (R1 and R2). (B) Differentiation profile of erythroid cells immediately after Ter119^- purification. Ter119^- population is enriched to 96%. Erythroid progenitor cells were subsequently infected and cultured as described in Figure 4. (C) Median FITC-CD71 fluorescence (± SD) after 16 to 18 hours of culture. (D-E) Differentiation of vector-infected erythroblasts cultured in Epo (D), vector-infected erythroblasts in the absence of Epo (E), and Lnk-infected erythroblasts cultured in Epo (F). The left panels show the CD71/Ter119 FACS profiles and cytology of cells after 16 to 18 hours of culture. The right panels show the FACS profiles and cytology of cells after 42 to 48 hours of culture. Dashed line outlined regions (R0) indicate nonerythroid cells. The FACS plots were gated for the hCD4⁺ population, that is, for expression of the transduced genes, in all the plots. For cytology the cells were centrifuged onto slides and stained with benzidine (brown) and Giemsa (purple for the nuclei). The arrowheads indicate benzidine-positive enucleated reticulocytes, and the thin arrows point to nonerythroid cells. Scale bars are 20 μm.