Adherent cell-mediated inhibition of human leukemic myelopoiesis.

We investigated the possibility that the control of leukemic growth by autologous adherent marrow cells may explain the indolent behavior of oligoleukemia. Leukemic cluster growth was measured by in vitro agar culture. The following marrow fractions (Fr) were examined from 13 patients for leukemic growth: Fr I: ficollisopaque interface cells (density less than 1.077 g/ml); Fr II: adherent-cell depleted Fr I (4.8% +/- 2.1 (SE) monocytes); Fr III: adherent and phagocytic cell depleted Fr I (0.3% +/- 0.2 monocytes); and Fr IV: adherent cells removed from plastic surfaces by lidocaine plus EDTA (74% +/- 10.9 monocytes). Two patient groups were recognized: Group A showed cluster growth in Fr IV with no absolute increase in Fr III and no suppression of Fr III cluster growth with addition of Fr IV. In Group B, Fr III showed an absolute increase in cluster growth. Fr IV did not show cluster growth and addition of Fr IV to Fr III suppressed growth. This suggested that in Group B, monocytes may suppress leukemic growth, the failure to observe this in Group A indicated the possible leukemic nature of the adherent cell fraction and the absence of residual normal monocytes. Other possible explanations are discussed.