Conditions Required For the Inhibition of In Vitro Growth of A Mouse Myeloma Cell Line By Adherent Bone-Marrow Cells

The in vitro growth of the MPC-11 myeloma cell line was inhibited when these cells were co-cultured with adherent cells from mouse bone marrow. This growth inhibition involved prolongation of the specific population doubling time of the MPC-11 cell line. Control cultures of MPC-11 cells exhibited an average doubling time of 14–15 hr, whereas in the presence of adherent layers the length of the doubling time was up to 28 hr. This prolongation in the doubling time did not depend on the duration of incubation, but on the relative proportions of tumour cells and adherent cells employed. MPC-11 cells seeded in relatively high starting cell concentrations partially overcame the growth inhibition. the inhibitory activity of adherent cells from the bone marrow did not appear to be due to production of soluble factor(s), since media conditioned by adherent cells did not affect cell growth. Moreover, in modified co-cultures in which MPC-11 cells grew physically separated from the adherent layers, only marginal growth inhibition activity was observed. the possibility that cell-to-cell interactions lead to the inhibition of growth of MPC-11 cells by adherent cells from the bone marrow, and the implications of these findings to the control of cell growth by the haemopoietic microenvironment, are discussed.