Epo (R103A) inhibits primary human erythroblasts.

(A) Inhibition of primary erythroblast proliferation by Epo (R103A). UCB CD34⁺ cells were expanded as described in “Materials and methods.” Day 9 proerythroblasts were cultured for 5 days in differentiation medium containing recombinant Epo (7.5 ng/mL) in the absence or presence of increasing concentrations of Epo (R103A) as indicated (range, 0-10 μg/mL). As a negative control, cells were cultured in the absence of any added recombinant Epo or Epo (R103A) (no Epo). Comparable results were obtained in 3 independent experiments. (B) Epo (R103A) results in decreased viability of primary erythroblasts. Day 9 proerythroblasts were cultured in triplicate in differentiation medium in 96-well plates (10 000 cells/well) in the absence or presence of increasing concentrations or Epo (R103A) (range, 0-10 μg/mL). MTT colorimetric assay was performed after 5 days as described in “Materials and methods.” Viability of cells was expressed as a percentage of maximum viability in the absence of any Epo antagonist. As a negative control, cells were cultured in differentiation medium without added recombinant Epo and without any Epo antagonist (no Epo). Asterisks indicate inhibition of viability that is significantly different from viability in Epo alone (P < .05). Comparable results were obtained in several experiments.