Utilization of homologous proteins to evaluate the safety of recombinant human proteins--case study: recombinant human interferon-gamma (rhIFN-gamma).

Interferon-gamma is an immunomodulatory cytokine that has an extremely restricted host range of activities. RhIFN-gamma was one of the first species-specific recombinant proteins to be assessed in conventional safety models typically utilized for xenobiotics. Acute, subchronic and Segment I and II reproductive studies in rats revealed no evidence of toxicity at any of the doses tested; these results were not predictive of clinical toxicity, which is not unexpected since rodents are known to be pharmacologically nonresponsive to rhIFN-gamma. In contrast, 4- and 13-week multidose toxicity studies in cynomolgus monkeys with rhIFN- were predictive of many of the dose-limiting clinical toxicities. RhIFN- is active on non-human primate cells, though not at the same level as on human cells. In addition, qualitative similarities were observed between toxicity studies employing rhIFN-gamma in the cynomolgus monkey and recombinant murine interferon-gamma (rmuIFN-gamma) in the mouse. These results suggest that in situations where a high degree of species specificity is encountered, studies employing a recombinant protein in a homologous species may provide a useful test system for preclinical safety assessment. This information should be evaluated in conjunction with data from studies conducted with the human protein in pharmacologically responsive animal models when possible.