E^rns is a highly glycosylated envelope protein of classical swine fever virus (CSFV) with RNase activity. E^rns can induce neutralizing antibodies and provide immune protection against CSFV infection. In this study, the RNase domain of the E^rns was produced in Escherichia coli. Its reactivity with CSFV-positive sera and its ability to induce antibodies and to provide protective immunity were then investigated. The serological tests showed that the prokaryotically expressed RNase domain of the E^rns retained its antigenicity and induced high titers of humoral responses. However, only partial protection and a limited amount of neutralizing antibodies were demonstrated by an in vitro neutralization test and an immunization/challenge test. The results suggest that other essential factors rather than simply enhancing the immunogenicity of E^rns should be taken into consideration when E^rns is enrolled as one of the components of a candidate vaccine.

The epitope ELDKWA, which is located in the membrane-proximal external region (MPER) of HIV-1 gp41, is an important neutralizing epitope. The human monoclonal antibody (mAb) 2F5 against this epitope shows broad neutralizing activity toward many HIV strains. However, several reports have shown that the epitope-specific mAbs induced by peptides containing MPER did not exhibit the same neutralizing activities as human mAb 2F5. In this study, four ELDKWA epitope specific mAbs (9E7, 7E10, 6B5, and 2B4) induced by immunization with the ELDKWA epitope in varied molecular contexts, all showed inhibitory activities with different potencies in HIV-1 Env-mediated membrane fusion assays and pseudovirus neutralization assays. This result indicates that though these antibodies recognize the epitope ELDKWA, their characterizations differ from that of neutralizing antibodies, implying that the neutralizing mAbs can be induced but also need to be screened, and the protective ability of a related vaccine antigen depends on the concentration of the neutralizing mAbs in the induced polyclonal antibodies.

A multi-epitope-vaccine MEV^ABC consisting of two linear neutralizing determinants (BC1: aa693-716; A6: aa844-865) located on antigenic unit B/C and unit A of glycoprotein E2 was prepared to evaluate whether a combination strategy is effective in the design of peptide vaccines. After immunization, pig sera collected every one to two weeks were evaluated by enzyme linked immunosorbent assay. C-strain-induced anti-sera and hyper-immune sera cannot recognize overlapping peptides that cover the E2 N-terminus, while MEV^ABC is able to elicit high levels of peptide-specific antibody response. When compared with previously studied peptide vaccines PV-BC1 and PV-A6, the same dose of either component in the MEV^ABC increases the BC1- or A6-specific antibodies (to 1/3-1/2 of the levels of the separate vaccines). However, the synergy between the antibodies may make MEV^ABC much more potent. Moreover, anti-C-strain immunity pre-existing in pigs does not disturb the sequent MEV^ABC vaccination. Thus, MEV^ABC can be administrated to pigs which already possess anti-classical swine fever virus immunity. MEV^ABC is a promising candidate marker vaccine.

Some monoclonal antibodies (mAbs) could inhibit infection by HIV-1. In this study, four mAbs against HIV-1 gp41 were prepared in mice. All four mAbs could bind to the recombinant soluble gp41 and recognize the native envelope glycoprotein gp160 expressed on the HIV-Env⁺ CHO-WT cell in flow cytometry analysis. Interestingly, the results show that all four mAbs purified by affinity chromatography could inhibit HIV-1 Env-mediated membrane fusion (syncytium formation) by 40%-60% at 10 µg/mL, which implies potential inhibitory activities against HIV-1.