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Different Sensitivities of Granulocyte‐Macrophage and Erythroid Progenitor Cells of Normal Human Bone Marrow to S‐Phase‐Specific Agents

The extraordinary sensitivity of early erythroid progenitor cells (BFU‐e) of normal human bone marrow to tritiated thymidine ([3H]TdR) was studied. While exposure of bone‐marrow cells to [3H]TdR for 1 hr resulted in the death of only 40% of the granulocyte‐macrophage progenitor cells (CFU‐c), 90% of BFU‐e were killed. Experiments in which normal bone‐marrow cells were mixed with bone‐marrow cells which had been exposed to [3H]TdR demonstrated that the excessive killing of BFU‐e by [3H]TdR reflected carry‐over of the [3H]TdR by the exposed cells. A carry‐over effect was not observed for CFU‐c, suggesting the presence of a fundamental difference in the metabolism of TdR between CFU‐c and BFU‐e. There was a suggestion of a carry‐over effect regarding two other S‐phase‐specific agents, hydroxyurea and 1‐β‐D‐arabinofuranosylcytosine.