Characterization of CD34⁺ cells from PB cultured in serum-free medium in presence of EPO, SCF, DXM, and IL3 at day 4 (when the cells were retrovirally infected for the first time) and at day 6 (when the cells were sorted) (n = 3). (A) Flow cytometry analysis of one representative experiment showing that at day 4, most of the cells were still CD34 positive (71%), expressed CD36 but not GPA. At day 6, expression of CD34 was lost (17% positive), and cells were in majority CD36⁺/GPA^–. (B) Colony-assay. 1 000 cells were plated in semisolid medium in presence of G-CSF, EPO, SCF, and IL3. Colonies were counted at day 7 for CFU-E and at day 14 for BFU-E and CFU-GM. Results are expressed as the number of colonies per 5 000 cells. Cells plated at day 4 are BFU-E (left). Infected CD36⁺/GPA^– cells sorted after 6 days in culture gave rise to CFU-E (right). Data are expressed as mean ± SD.