Comparison of replication-competent molecular clones of porcine endogenousretrovirus class A and class B derived from pig and human cells

Vertically transmitted endogenous retroviruses pose an infectious risk in t he course of pig-to-human transplantation of cells, tissues, and organs. Tw o classes of polytropic type C porcine endogenous retroviruses (PERV) which are infectious for human cells in vitro are known. Recently, we described the cloning and characterization of replication-competent PERV-B sequences from productively infected human cells (F, Czauderna, N, Fischer, K, Boiler , R, Kurth, and R, R, Tonjes, J, Virol, 74:4028-4038, 2000). Here, we repor t the isolation of infectious molecular PERV-A and PERV-B clones from pig c ells and compare these proviruses with clones derived from infected human 2 93 cells, In addition to clone PERV-A(42) derived from 293 cells, four "nat ive" full-length proviral PERV sequences derived from a genomic library of the porcine cell line PK15 were isolated, Three identical class A clones, d esignated PK15-PERV-A(42), PK15-PERV-A(45), and PK15-PERV-A(58), and one cl ass B clone, PK15-PERV-B(213), were characterized. PK15-PERV-B(213) is high ly homologous but distinct from the previously described clone PERV-B(43). PK15-PERV-A(58) demonstrates close homology to PERV-A(42) in env and to PER V-C in long terminal repeat, gag, and pro/pol sequences. All three PERV clo nes described here were replication competent upon infection of susceptible cell lines. The findings suggest that the pig genome harbors a limited num ber of infectious PERV-A and -B sequences.