The Chimpanzee as a Model to Test the Side Effects of Human Interferons

Type I IFNs and their role in the development of autoimmune diseases

BACKGROUND

Since their initial use in the 1980s, IFNs have become an essential component of the therapy for many diseases such as hepatitis and multiple sclerosis. Although they have been extremely useful in conditions that pose therapeutic challenges, complications associated with their use have been widely reported including emerging reports of several autoimmune diseases. Many of these reports have shed light on the pathogenesis of autoimmune disorders and helped to highlight not only the critical role of type I IFNs in defense against viral infections but also the pivotal role they occupy in the interface between innate and adaptive immunity. Many patients with autoimmune disease have increased responsiveness to type I IFNs (alpha/beta), and therapy with these cytokines has induced or unmasked autoimmune disease in many additional patients.

OBJECTIVE

The objective of this paper is to discuss the role of type I IFNs in autoimmunity.

METHODS

The literature regarding type I IFNs and autoimmunity was reviewed using the Medline database from 1950 to 2009. Search terms included 'interferon alpha' and 'autoimmune disease' and 'interferon beta' and 'autoimmune disease'. Case reports, case series, reviews and prospective studies were included in the analysis.

RESULTS/CONCLUSIONS

In the literature a variety of autoimmune disorders have reportedly been induced by the use of type I IFNs, being used, although these are primarily in the form of case reports and case series. Nevertheless, there is a growing body of molecular evidence to support the clinical association. The role of IFNs in the induction of autoimmunity is complex with interplay of many genetic and environmental factors that influence the balance between normal and aberrant immune responsiveness, ultimately leading to the observed clinical manifestations.

Nonclinical safety evaluation of biotechnologically derived pharmaceuticals

The primary objectives of nonclinical safety evaluation for pharmaceutical products are to identify potential target organ toxicity, provide a safe starting dose for clinical trials, and establish dose-response relationships. These objectives do not differ in concept for either small molecular weight compounds or biotechnologically derived pharmaceuticals; they are important for both. The complex structural and biological characteristics of biotechnologically derived pharmaceuticals, however, dictate that different approaches to their safety evaluation are needed. Although their novel mode of production initially raised concerns about their safety, improvements in analytical and manufacturing procedures have largely minimized the perceived risks. It is primarily their exaggerated pharmacodynamic properties that produce the toxicity observed in nonclinical studies. Even though most of these products will require a case-by-case, scientifically based approach, knowledge gained from both nonclinical and clinical evaluation of these novel products have highlighted some general principles with regards to their safety evaluation. These principles include the importance of evaluating species in which the biotechnologically derived pharmaceutical is biologically active, the potential impact of immunogenicity on the interpretation of multiple dose toxicity study results, and the need for both highly sensitive and specific analytical methods to measure their pharmacodynamic properties. An understanding of these principles forms the basis for the development of a scientifically sound nonclinical safety evaluation program.

Comparative pathology of recombinant murine interferon-gamma in mice and recombinant human interferon-gamma in cynomolgus monkeys

Interferon-gamma is a highly species-specific cytokine and has the most restricted host range of activity of the interferons. Recombinant human IFN-gamma was one of the first species-specific recombinant proteins to be thoroughly assessed in conventional safety models used for xenobiotics. Acute single-dose intravenous toxicity studies with rHuIFN-gamma were performed in rats, marmosets, and squirrel monkeys with no indications of toxicity. A complete series of subchronic toxicity studies and segment I and II reproductive studies in the rat revealed no evidence of toxicity at any of the doses tested. These results suggested that studies conducted in pharmacologically nonresponsive species may not be predictive of clinical toxicity. Human IFN-gamma is active on nonhuman primate cells, though not at the same level as on human cells. Multidose studies in cynomolgus monkeys with rHuIFN-gamma for 28 or 90 days were predictive of many of the dose-limiting clinical toxicities. Qualitative similarity was observed between toxicity studies employing rHuIFN-gamma in the cynomolgus monkey and rMuIFN-gamma in the mouse. The adverse effects seen in toxicity studies with cytokines and growth factors are often exaggerated pharmacological effects of the molecules, and therefore can only be studied in a responsive species. In situations in which 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.

Do the interferons act singly or in combination?

Our views of interferon production and action have evolved from the simple to the complex. We review evidence that interferon-gamma (IFN-gamma) may induce a portion of its antiviral activity through the induction of another interferon. This is shown by demonstrating IFN-alpha in the supernatant fluids of IFN-gamma-treated mouse cells and showing that, under certain conditions, the antiviral activity of IFN-gamma in mouse and human cells can be reduced by antibody to IFN-alpha or IFN-beta, respectively. Induction of mouse spleen, bone marrow, and peritoneal exudate cells also results in their production of IFNs-alpha and/or -beta. In addition, new preliminary data indirectly suggests the presence of IFN-gamma in poly(IC):poly(LC)-treated mouse cells. In both of these systems, the maximal antiviral activity appears to develop as a consequence of the induction of a second interferon.

Preclinical safety testing of species-specific proteins produced with recombinant DNA-techniques. An attempt to transfer current experience into future testing strategies

Preclinical toxicity studies in animals with species-specific recombinant DNA products have now been performed for several years. An interim statement on the significance of these animal tests and their ability to predict adverse effects in humans therefore appears indicated, with the aim of deducing future testing strategies. The experience accumulated so far shows that the animal models have failed to predict adverse effects subsequently observed in man. Immunogenicity of these proteins further restricted the usefulness of standard toxicity tests. There is also increasing evidence that animal tests on the toxic potential of impurities contained in the products are markedly inferior in sensitivity to analytical and quality control methods. Thus, modified testing programs are proposed to demonstrate safety rather than target organ toxicity using rodents and small non-rodent species and restricted dosing; furthermore the study duration should be limited by the detection of immunogenic responses.

Inhibition of development of exoerythrocytic forms of malaria parasites by gamma-interferon

A specific DNA probe was used to study the effect of recombinant rat, mouse, and human gamma-interferon (gamma-IFN) on the course of sporozoite-induced malaria infections. In mice and rats infected with sporozoites of Plasmodium berghei, mouse and rat gamma-IFN's strongly inhibited the development of the exoerythrocytic forms in the liver liver cells of the hosts, but not the development of the erythrocytic stages. The degree of inhibition of the exoerythrocytic forms was proportional to the dose of gamma-IFN administered, but was independent of the number of sporozoites used for challenge. A 30 percent reduction in the development of exoerythrocytic forms in rat liver was achieved when 150 units (about 15 nanograms of protein) of rat gamma-IFN were injected a few hours before sporozoite challenge; the reduction was 90 percent or more with higher doses of gamma-IFN. The effect was less pronounced if the gamma-IFN was administered 18 hours before or a few hours after challenge. Human gamma-IFN also diminished the parasitemia in chimpanzees infected with sporozoites of the human malaria parasite Plasmodium vivax. The target of gamma-IFN activity may be the infected hepatocytes themselves, as shown by in vitro experiments in which small doses of the human lymphokine inhibited the development of exoerythrocytic forms of Plasmodium berghei in a human hepatoma cell line. These results suggest that immunologically induced interferon may be involved in controlling malaria infection under natural conditions.