Xenotransplantation using pig cells, tissues or organs may be associated with the transmission of porcine zoonotic or xenozoonotic microorganisms. Porcine endogenous retroviruses (PERVs) pose a special risk for xenotransplantation as these viruses can infect human cells and are integrated in multiple copies in the genome of all pigs and, therefore, they cannot be eliminated as other viruses can. To prevent PERV transmission to the recipient, several strategies have been developed: PERV-C-free animals, siRNA and genomic editing. Another strategy is the generation of vaccines based on neutralizing antibodies in order to protect the recipient. To investigate whether a protective vaccine is feasible in the case of PERV, the recombinant transmembrane (p15E) and the surface envelope (gp70) protein of PERV were cloned, produced, purified and used to immunize rats. For the first time, an adjuvant type that is approved for human use was used. In all cases we obtained virus binding antibodies as shown in Western blot assays and neutralizing antibodies as shown in neutralization assays, indicating the potential for a protective vaccine. The epitopes recognized by the antisera against p15E were determined using overlapping peptides. Two main epitopes were found in the sequence of p15E, one in the membrane proximal external region (MPER) and one in the fusion peptide proximal region (FPPR). The epitopes correspond to epitopes determined previously when immunizing different animal species with p15E of PERV. Antibodies against these epitopes block the conformational changes in the transmembrane envelope proteins that are required for membrane fusion, thereby inhibiting infection. The epitope in the MPER is related by sequence and location to an epitope in the transmembrane envelope protein of the human immunodeficiency virus-1 (HIV-1) recognized by a broadly neutralizing antibody from infected patients.
