Prevention of infection in xenotransplantation: Designated pathogen-free swine in the safety equation.

Post-transplantation infections are common. In immunosuppressed human xenograft recipients, infection is most likely to be due to the same pathogens seen in human allotransplantation. However, organisms derived from swine and transmitted with xenografts have the potential to cause novel infections in xenograft recipients. The specific organisms likely to cause infection or "xenosis" are unknown but are postulated to be like those causing infection in allograft recipients. On this basis, theoretical exclusion criteria have been developed to guide the development of source animal herds. Herds developed based on the exclusion of potential human pathogens have been termed "designated pathogen-free" (DPF). Lists of potential pathogens will require revision with changing epidemiology of infection in swine worldwide and clinical experience. Development of new microbiological assays is required both for animal screening and in clinical diagnosis should infections occur. Genetic modifications of swine have the potential to eliminate certain infectious agents such as the porcine endogenous retrovirus; infectious complications of such modifications have not been observed. Unexpected, off target effects of genetic modifications require further study. Monitoring for infection in asymptomatic recipients is important to define infectious risks which are unknown in the absence of clinical trials data. Advanced microbiological techniques may be applied to diagnose and prevent infection in xenograft recipients.