Endogenous retroviruses in swine cell lines and evaluation of possible transmission to primate cellular systems

The need to prepare a vaccine against influenza virus infection by using cell cultures instead of the traditional biological system, such as chicken embryos, has arisen recently. This, requires an evaluation of the susceptibility of several cell lines to different influenza virus types. Newborn swine kidney (NSK) and trachea (NPTr) cells, both set up in our laboratory, were both able to support replication not only of viruses of swine derivation but also of influenza subtypes isolated from different species. However, the two cell lines, despite their high viral susceptibility, cannot be used for large-scale production because of their infection by endogenous retroviruses. Furthermore, the reverse transcriptase activity test (Phan-Thanh et al., 1992) carried out on NSK cells showed retrovirus secretion into the culture medium. The pig endogenous retroviruses, known to be endogenous retroviruses of C-type, are integrated in about 50 copies in all domestic and wild swine genomes. These have been studied for a long time, because of their potential risk in xenotransplantation. Recently, the transmission of pig endogenous retroviruses to several cell cultures from different species, including those from humans, has been demonstrated. In particular, the different cell lines can secrete viruses that are sometimes ecotropic, while in others they may be xenotropic or amphotropic. On the basis of their tropism and the env gene structure, three PERV classes have been identified, A, B, and C (Takeuchi et al., 1998).
The aim of this study was to standardize a method capable of evaluating the transmission of PERVs from NSK and NPTr cell lines to other cell cultures and possible virus secretion from the infected cells. [...]