Unusual permeability of porcine endogenous retrovirus subgroup A through membrane filters

In xenotransplantation from pigs to humans, a bio-artificial endocrine pancreas (Bio-AEP), in which pancreatic endocrine cells are encapsulated within a semipermeable membrane of 100 nm pore size, has been developed. We evaluated the permeability of porcine endogenous retroviruses (PERVs) through membrane filters using a pseudotype virus (LacZ(PERV-A)) containing a viral core derived from murine leukemia virus and an envelope (Env) from PERV subgroup A. Contrary to our expectations, LacZ(PERV-A) lost its infectivity by filtration through a 200 nm membrane filter. This unusual phenotype was not observed in pseudotype viruses harboring Envs from other gammaretroviruses. The infectivity of LacZ(PERV-A) was significantly decreased by repeated freeze/thaw treatment, indicating that LacZ(PERV-A) was physically labile. In addition, LacZ(PERV-A) may be agglutinated because copy numbers of viral RNA after filtration were significantly reduced by filtration through the 200 nm membrane. This phenotype is advantageous to develop a safe Bio-AEP blocking PERV infection.