Results with a modified human myeloma stem cell assay.

The human tumor stem cell assay (HTSCA) introduced by Hamburger and Salmon [2] was modified in several details. It was found that a short period of treatment with deoxyribonuclease (DNase) of the material aspirated from the patients bone marrow greatly enhances the production of single cell suspensions and thereby may improve the assay. Instead of the dextran sedimentation method, we used the density gradient centrifugation method according to Bøyum [1] for the isolation of mononuclear cells from the bone marrow. Another methodical modification introduced by us is the use of the same medium for culturing the cells before plating them and in the agar after plating. Under the conditions reported here the formation of colonies was observed in 8 of 11 samples from individual myeloma patients. The average plating efficiency was 0.024% with a range of 0.009% to 0.039% showing that possibly an improvement was achieved when compared to the results obtained with the original method showing an average plating efficiency of 0.014% [2].