Effects of cloned human leukocyte interferons in the human tumor stem cell assay.

Clonogenic tumor cells from fresh biopsies of human cancers were cultivated in vitro and tested for sensitivity by continuous exposure to pharmacologically achievable concentrations of either of two highly purified human leukocyte interferon subtypes (IFN-alpha A and IFN-alpha D) prepared by recombinant DNA methods. The interferons were compared on a weight basis at concentrations of 0.4 and 4.0 ng/ml (equivalent to 80 and 800 units of interferon activity for IFN-alpha A and 2.0 and 20 units for IFN-alpha D). Inhibition of tumor colony-forming units (50% of control or less) was observed in 38.1% of the 273 tumors tested against IFN-alpha A, and in 16% of the 71 tumors tested against IFN-alpha D. Of the tumor types with at least ten samples tested against IFN-alpha A, the percentage of cases exhibiting inhibition was as follows: melanoma (51.7%), lung cancer (50%), myeloma (33.4%), ovarian cancer (33.9%), sarcoma (33.3%), adenocarcinoma of unknown primary (30.4%), breast cancer (28%), acute leukemia (30.8%...