Inactivation of porcine endogenous retrovirus by human serum as a function of complement activated through the classical pathway

Abstract

Background: The clinical use of organs and cells of pig donors as a source of tissue for xenotransplantation and extracorporeal therapies has been problematic due to the risk for zoonotic infection of porcine endogenous retroviruses (PERV). Methods: The effect of human serum on PERV was evaluated using an infectivity assay and virolysis assay. Cell-free PERV infection to human 293 cells was determined by the presence of proviruses 5 days post-infection by a highly sensitive nested PCR, and the lysis of PERV virions was determined by the reverse transcriptase activities released into the supernatant. Results: Treatment of PERV-PK, the culture supernatant of a pig kidney cell line containing the virus titer of 10 2.8 TCID 50 units/ml, with a quarter volume of human serum completely inactivated the infectivity. This activity was heat-labile and sensitive to an anti-complement agent, nafamostat mesilate, and a Ca 2+-chelator, EGTA, indicating the crucial involvement of complement activated through the classical pathway. Since a synthetic galactosyl α1–3 galalactose (Galα1–3Gal) largely absorbed the activity from the serum, natural antibodies to the Galα1–3Gal epitopes are likely to trigger the complement activation. Conclusion: Cell-free PERV seems no longer be infectious in human serum. This greatly encourages the clinical application of pig tissues in particular for extracorporeal therapies such as a bioartificial liver, in which pig cells do not come in direct contact with a recipient.