Impact of Infections and Normal Flora in Nonhuman Primates on Drug Development

Preclinical safety studies that are required for the marketing approval of a pharmaceutical include single and repeat dose studies in rodent and nonrodent species. The use of nonhuman primates (NHPs), primarily macaques, as the nonrodent species has increased in recent years, in part due to the increase in development of biopharmaceuticals and immunomodulatory agents. Depending on the source of the macaques, they may vary in genetic background, normal flora, and/or the incidence of preexisting pathogens and inflammatory conditions. As the use of alternative sources of macaques rises to meet the increased demand for these animals in biomedical research, the toxicologic pathologist should be well versed in NHP pathology to adequately assess potential drug-related effects in the context of these variations. Such knowledge is particularly important in studies involving immunomodulatory drugs as the toxicologic pathologist should anticipate which type(s) of infections are most likely to arise depending on which arm of the immune system is modulated. The purpose of this review is to discuss the immunosuppressive (e.g., simian type D retrovirus, simian immunodeficiency virus) and opportunistic viruses (e.g., cytomegalovirus, adenovirus, simian virus 40, rhesus rhadinovirus, and lymphocryptovirus), primary and opportunistic bacteria (e.g., Campylobacter spp., Shigella flexneri, Yersinia enterocolitica, Moraxella catarrhalis, Mycobacterium avium complex, enteropathogenic Escherichia coli), and parasites (e.g., Plasmodium spp., Schistosoma spp., Strongyloides fulleborni) that have had the most profound impact on the interpretation of drug safety studies and/or that may reemerge as alternative sources of NHPs are used for drug safety studies.