Relative expansion of CD34⁺ cells in the presence (•, ○) or absence (▪, □) of 6 μmol/L PD98059 induced by MGDF (A) or a mixture of SCF + IL-3 +IL-6 (B). The data have been normalized to the number of purified CD34⁺ cells seeded on day 0. The results presented are those from a representative experiment of 8 (A) or 3 (B) performed.