Direct Determinationof the Influenceof the Cell Cycle on the Sijrvival of TumorCells Exposedto CytotoxicAntibodies'

indicated that cells in the G1 phase of@thecell cycle are most susceptible to Iysis by cytotoxic antib4dy. However, there are other studies that have indicated either that G1 cells can be more resistant to antibody (18) or thattthere are no cell cycle specific changes in susceptibility (10)@The major problem in interpreting these results is that all @f the studies involved artificial synchronization or physical 4eparation of the target cells before they were exposed to th4 antibodies. The drugs used to synchronize populations or th4 changes produced by the separation techniques may by then'@selves alter the suscep tibility of the cells to cytotoxic [email protected], such studies are not necessarily analogous@tothe effect one might observe when untreated, exponentialI@1growing cells are ex posed to antibody. We report here a methodby which @synchronous cell pop ulations exposed to a lethal agent (@,hetherit be cytotoxic antibodies, antineoplastic drugs, or irr@diation)can be directly analyzed in order to determine how rna@iycells were killed from each phase of the cell cycle. Usin@exponentially growing murine Si 07 myeloma cells, we found no major loss of cells from one phase of the cell cycle priorj to the death of cells in other phases, and, therefore, there we@eonly small differences in the susceptibility of cells in diffei1@ent phases to specific antibodies.