Influence of fetal calf serum on growth-inhibitory activity of human recombinant gamma-interferon (GI-3) in vitro.

The growth-inhibitory activity of human recombinant gamma-interferon (rIFN-gamma: GI-3) against 30 human cultured cell lines derived from leukemias and lymphoma (9 T-cell, 13 B-cell, 2 nonTnonB and 6 myeloid cell lines) was measured quantitatively by in vitro regrowth assay. Only three myelomonocytoid cell lines (HL-60, U937 and THP-1-0) were found to be sensitive, and HL-60 was the most sensitive. However, the sensitivity of HL-60 was found to be much influenced by both the batch and the concentration of fetal calf serum (FCS) used in the experiment. In the experiments using a certain FCS, GI-3 had a high antiproliferative activity against HL-60 at the optimal concentration (10(4)-10(5) U/ml), when assayed in medium containing 10% FCS. Both lower and higher concentrations of the interferon than 10(4)-10(5) U/ml resulted in decreased antiproliferative activity. When a high concentration (30%) of the FCS was employed in the assay, the antiproliferative activity of GI-3 was also much reduced. In the experiments using the other FCS, no antiproliferative activity of GI-3 against HL-60 was observed on assay in the medium containing 10% FCS, but significant antiproliferative activity was observed in the medium containing 30% FCS from the same source. Experiments using serum-free culture medium revealed that GI-3 itself had both a slight growth-inhibitory action at the optimal concentrations (at about 10(4) U/ml) and growth-enhancing activity at high (10(6) U/ml) concentration. The antiviral titer of GI-3 was stable during 72 hr of incubation in growth medium with or without cells. These findings suggest that there are cofactors in the serum which positively or negatively influence the growth-regulatory activity of GI-3 against HL-60 cells.