A simple density gradient for enriching subfractions of solid tumor cells.

Cell suspensions of human solid tumors could be separated into 5 or 6 subfractions for flow cytometry by centrifugation on a continuous silica gel (Percoll, Pharmacia Fine Chemicals, Upsalla, Sweden) density gradient. In all cases, there were one or more subfractions with enrichment of the aneuploid tumor cells. The greatest enrichment occurred in cases with fewer than 20% aneuploid cells in the original specimen; for these cases the enrichment factor ranged from 2.8- to 11.7-fold increase. In six cases with fewer than 7% aneuploid G0/1 cells initially, the aneuploid G0/1 DNA peak was difficult to demonstrate on the original specimen but became quite obvious in the subfraction. In no case were the tumor cells confined to a single subfraction. The distribution of tumor cells within two or more subfractions appeared related to differentiation in the case of squamous cells and to RNA content for other tumor cells. DNA/RNA flow cytometry proved useful in defining subpopulations of tumor cells with different DNA stemlines and varying positions in the cell cycle according to the RNA content of the respective subpopulation.