Separation on Percoll density gradients of cells derived from malignant ascites of mice

In an attempt to separate malignant from normal and reactive stromal cells, we fractionated ascites cells from BALB/c mice bearing a transplantable myeloma (MPC-11) by isopyknic centrifugation in continuous density gradients of povidone-coated silica gels (Percoll). Cells from different fractions were then analyzed by morphologic and immunologic criteria. The ability of cells from the different fractions to form colonies in soft agar and to produce tumors in BALB/c mice was also examined. Although most fractions contained morphologically identifiable plasma cells, colony-forming cells (CFC), derived from multiply passaged tumors, separated in a sharp peak at 1.072 g/ml. CFC peaked at 1.078-1.082 g/ml for tumors passed less than three times and were invariably markedly depleted from the low-density portions of the gradients. Cells recovered from different fractions of the gradients were cultured in soft agar and inoculated sc into syngeneic mice. In these experiments, a highly significant correlation was observed between the ability of cells to form colonies in soft agar and to form tumors in vivo. This correlation suggests that CFC and tumorigenic cells have similar distributions.