In vivo, ES-EP terminally differentiate and do not induce tumor formation. GFP-expressing ES-EPs (1.5 × 10⁷) were intravenously injected into sublethally irradiated syngeneic mice. FACS analysis for GFP and erythroid (Ter119), lymphoid (B220), and myeloid (Mac-1) markers of cells derived from spleens 2 days and 4 days after injection is shown. Sorting of GFP⁺ cells from spleen and bone marrow by FACS at day 2 reveals the presence of erythroblasts and enucleated erythrocytes in the GFP-transduced population. Original magnification, × 100.