Chemotherapeutic susceptibility of human bone marrow progenitor cells and human myelogenous leukemia cells (HMO) in co‐culture: Preliminary report

We determined the chemotherapeutic susceptibility of normal human granulocyte progenitor cells (CFU‐C) and acute myelogenous leukemia cells (HL‐60) in co‐culture. Nucleated bone marrow cells and HL‐60 cells were mixed in 0.3% agar containing McCoy's 5A medium, fetal bovine serum, human placenta‐conditioned medium, and various concentrations of chemotherapeutic agents. They were incubated in 5% humidified CO₂ at 37°C for 8–10 days. CFU‐C and HL‐60 colonies were differentiated morphologically. The formation of CFU‐C was progressively inhibited with the increasing number of HL‐60 cells, whereas the presence or absence of bone marrow cells did not influence the number of HL‐60 colonies. In separate culture, HL‐60 cells were more sensitive to vincristine than were CFU‐C cells. In co‐culture, however, the CFU‐C became more sensitive to vincristine than in the separate culture. Similarly, co‐culture CFU‐C were more sensitive to daunorubicin than in separate culture. These data indicate that HL‐60 leukemic cells exert inhibitory effects on normal bone marrow CFU‐C; in such an inhibited state, normal bone marrow is more susceptible to certain chemotherapeutic agents.