Antitumor effects of a normal human serum factor (normal human globulin fraction 1) on human tumor cells in vitro

Normal human globulin fraction 1 (NHG-1) produced cytotoxicity and/or cytostasis as well as inhibition of protein synthesis in 8 well-characterized human tumor cell lines (4 breast cancer, 1 colon cancer, 1 melanoma, and 2 leukemia) and in 2 variants of murine B-16 melanoma. NHG-1 was not cytotoxic for the Chang liver cell line, a normal kidney embryo line, or for normal lymphocytes or macrophages when used in lower concentrations but was growth inhibitory for normal cells in higher concentrations. Although lymphocyte blastogenesis with phytohemagglutinin (PHA) was inhibited by high concentrations of NHG-1, augmentation of the lymphocyte PHA response was seen at lower concentrations, suggesting a lymphokine-like effect. Preincubation with the mitogen partially nullified these NHG-1 effects (suggesting the need for cell surface binding). Although NHG-1 antitumor activity was confirmed in selected human and murine tumor cell lines, the mechanism of its activity is unknown. Occurrence of NHG-1 in the alpha 2-globulin region (an area rich in immune-regulating factors) suggests that NHG-1 may have general "cytokine"-like effects and may be capable of regulating replication of both normal and transformed cells.