Embryonic mesenchymal progenitor cells (MPCs) support long-term hematopoiesis in vitro. To determine whether embryonic MPCs are able to regulate hematopoiesis, weekly colony-forming cell (CFC) assay is carried out on the nonadherent fraction collected from the cocultures over 6 weeks. Statistical analysis of one representative from 3 independent experiments shows that the CFC frequencies in the AGM-MSC group exceed that of BM-MSCs at multiple time points (A). Furthermore, the LTC-IC assay using bulk culture is carried out 3 times. After 7-week incubation, the total CFCs in individual wells including the adherent layers are quantified. As shown in panel B, there are 37.5 (± 5.9) CFCs in the cultures with AGM-MSCs, resembling those with BM-MSCs (32 ± 3.4, P > .05). (C) RT-PCR assay shows that embryonic MPCs express a set of early-acting hematopoietic cytokines, including BMP4, TGF-β1, and FL, and all lineage-specific cytokine GM-CSFs (except G-CSF). The results are expressed as means (± SEM). Significance was determined using the Student t test: *P < .05; **P < .01, compared with the data of BM control.