Japanese Encephalitis DNA Vaccine Candidates Expressing Premembrane and Envelope Genes Induce Virus-Specific Memory B Cells and Long-Lasting Antibodies in Swine

Abstract

Swine are an important amplifier of Japanese encephalitis (JE) virus in the paradomestic environment. In this study, two JE DNA vaccine candidates were evaluated for immunogenicity in swine. Both vaccine plasmids encode a cassette consisting of the signal of premembrane (prM), prM, and envelope (E) coding regions of JE virus. One plasmid, designated pcJEME, is based on a commercial vector (pcDNA3), whereas the other plasmid, designated pNJEME, is based on a vector (pNGVL4a) designed to address some of the safety concerns of DNA vaccine use. No differences were detected in the immunogenicity of these two plasmids in mice or swine. Swine immunized with the DNA vaccines at a dose of 100 to 450 microgram at an interval of 3 weeks developed neutralizing and hemagglutination-inhibitory (HAI) antibody titers of 1:40 to 1:160 at 1 week after the second immunization. However, swine administered two doses of a commercial JE vaccine (formalin-inactivated virus preparation; JEVAX-A) developed low (1:10) or undetectable antibody responses after their boost. Interestingly, serum antibody titers elicited by DNA vaccines in swine were higher than those detected in mice. Eight days after boosting with viral antigen (JEVAX-A) to detect an anamnestic response, swine immunized two times with the DNA vaccine showed a >100-fold elevation in HAI titer, indicating a strong recall of antibody response. Swine maintained detectable levels of HAI antibody for at least 245 days after two immunizations with a DNA vaccine. These results indicate that these DNA vaccines are able to induce virus-specific memory B cells and long-lasting antibodies in swine, which were of higher levels than those obtained with a commercial formalin-inactivated JE vaccine.

Production of Pseudoinfectious Yellow Fever Virus with a Two-Component Genome

“…The lack of nucleocapsid-packaged replication-competent RNA makes the application of SVPs as potential vaccines very advantageous but requires the development of a new means for the largescale production or delivery of the expression constructs. The prM/E-expressing cassettes can be designed on the basis of viral and nonviral vectors (1,6,7,14,15,21,22,29,33,36,39). In the case of viral vectors (19,36), there is always a concern of either the development or preexistence of an immune response to the viral vector used.…”

Development of New Vaccines against Dengue Fever and Japanese Encephalitis

“…a prM = Premembrane protein; E = envelope glycoprotein; NS1, NS2A, NS3, and NS5 = nonstructural proteins 1, 2A, 3, and 5, respectively; 50%, 80%, 90%, 92% E = amino-terminal portion of E protein expressed in the plasmid construct; carboxyl 50% E = carboxyl-terminal portion of E expressed in the plasmid; part NS2A = co-expression of amino-terminal region of NS2A. Same plasmid designated as pcJEME in reference [156]. Plasmid DNA vectors usually contain SV40 virus-specific sequences and the bacterial ampicillin resistance gene.…”

“…The longer signal peptide sequence may aid translocation of the translated polypeptide into the ER lumen, which in turn may enhance the processing of prM and E proteins of more authentic conformation and increase the release of EPs. An optimized Kozak's sequence, which was also designed into the pcDNA3JEME and pNJEME plasmids [154][155][156], might increase the expression level of the prM and E genes. The low levels of neutralizing antibodies that were induced by most of the DNA vaccine constructs expressing the prM/E of DEN or JE virus may not prevent infection by the challenge virus, but immunized animals usually developed strong anamnestic neutralizing antibody responses and were protected from disease after virus challenge [155,156,163].…”

“…An optimized Kozak's sequence, which was also designed into the pcDNA3JEME and pNJEME plasmids [154][155][156], might increase the expression level of the prM and E genes. The low levels of neutralizing antibodies that were induced by most of the DNA vaccine constructs expressing the prM/E of DEN or JE virus may not prevent infection by the challenge virus, but immunized animals usually developed strong anamnestic neutralizing antibody responses and were protected from disease after virus challenge [155,156,163]. It is thought that such candidate DNA vaccines induce memory B and T cells which protect immunized animals from DEN or JE disease.…”

Immunogenicity of a Recombinant MVA and a DNA Vaccine for Japanese Encephalitis Virus in Swine

“…This was primarily due to differences in the two vectors used (16). Also, DNA vaccine systems for JEV have been developed and elicit neutralizing antibodies in mice and swine (1,7,9). However, a DNA vaccine system must be proved safe in humans and overcome poor immunity.…”