Regulator-induced suppression of myelomonocytic leukemic cells: clonal analysis of early cellular events.

Mouse WEHI-3B myelomonocytic leukemic cells were cloned in semi-solid agar in the presence of post-endotoxin serum (ES) or semi-purified differentiation factor (DF). At the 2-cell, 4-cell and 8-32-cell stage, individual cells were washed and recloned in control cultures to test for clonogenicity and the ability to form differentiating progeny. With increasing clone size, an increasing proportion of treated cells either failed to proliferate or generated differentiating colonies of reduced size. The observed suppression indicated that both ES and DF exert irreversible effects on leukemic stem cell self-replication within one or two cell cycles. The stem cell suppression observed was markedly asymmetric and most often involved premature differentiation and death of progeny of the affected cells rather than immediate death of the cell. The results are consistent with the possibility that the regulator DF irreversibly modifies one or more of the newly synthesised daughter chromatids of myeloid leukemic cells during the induction of stem cell suppression and differentiation.