Biology of the human myeloma cell population. II. Cytokinetic characteristics.

A kinetic study of five human myeloma cell populations before and after chemotherapy using cytochemical and autoradiographical techniques showed: 1. a large number of cells, with a DNA content intermediate between 2c and 4c, that did not incorporate thymidine ('U' cells) and were indicative of ineffective myelomapoiesis; 2. non cell cycle-specific (cyclophosphamide) followed by cell cycle-specific (vincristine) treatment led to an increase in the 3H-thymidine labelling index (LI) and activation of macromolecular synthesis (increased uridine and leucine uptake and actinomycin binding capacity) pointing to early cell recruitment. A high percentage of 'U' cells can be found even after therapy. The LI variations make it clear that recruitment after therapy is overestimated by at least 40\% due to ineffective myelomapoiesis. In the light of this and previous personal studies, we propose a kinetic pattern: the myeloma population may be seen as a highly differentiating population whose non-proliferating cells cannot re-enter the cycle. By contrast, the acute leukemia populations are unable to differentiate, and the non-proliferating cells (G0) can be recalled into the cell cycle.