Protection of rainbow trout against infectious hematopoietic necrosis virus four days after specific or semi-specific DNA vaccination.

A DNA vaccine against a fish rhabdovirus, infectious hematopoietic necrosis virus (IHNV), was shown to provide significant protection as soon as 4 d after intramuscular vaccination in 2 g rainbow trout (Oncorhynchus mykiss) held at 15 degrees C. Nearly complete protection was also observed at later time points (7, 14, and 28 d) using a standardized waterborne challenge model. In a test of the specificity of this early protection, immunization of rainbow trout with a DNA vaccine against another fish rhabdovirus, viral hemorrhagic septicemia virus, provided a significant level of cross-protection against IHNV challenge for a transient period of time, whereas a rabies virus DNA vaccine was not protective. This indication of distinct early and late protective mechanisms was not dependent on DNA vaccine doses from 0.1 to 2.5 microg.

Nanogram quantities of a DNA vaccine protect rainbow trout fry against heterologous strains of infectious hematopoietic necrosis virus.

The efficacy of a DNA vaccine containing the glycoprotein gene of infectious hematopoietic necrosis virus (IHNV), a rhabdovirus affecting trout and salmon, was investigated. The minimal dose of vaccine required, the protection against heterologous strains, and the titers of neutralizing antibodies produced were used to evaluate the potential of the vaccine as a control pharmaceutical. Results indicated that a single dose of as little as 1-10 ng of vaccine protected rainbow trout fry against waterborne challenge by IHNV. An optimal dose of 100 ng per fish was selected to assure strong protection under various conditions. Neutralizing antibody titers were detected in fish vaccinated with concentrations of DNA ranging from 5 to 0.01 microg. Furthermore, the DNA vaccine protected fish against a broad range of viral strains from different geographic locations, including isolates from France and Japan, suggesting that the vaccine could be used worldwide. A single dose of this DNA vaccine induced protection in fish at a lower dose than is usually reported in mammalian DNA vaccine studies.

Fish DNA vaccine against infectious hematopoietic necrosis virus: efficacy of various routes of immunisation.

The DNA vaccine, pIHNVw-G, contains the gene for the glycoprotein (G) of the rhabdovirus infectious hematopoietic necrosis virus (IHNV), a major pathogen of salmon and trout. The relative efficacy of various routes of immunisation with pIHNVw-G was evaluated using 1.8 g rainbow trout fry vaccinated via intramuscular injection, scarification of the skin, intraperitoneal injection, intrabuccal administration, cutaneous particle bombardment using a gene gun, or immersion in water containing DNA vaccine-coated beads. Twenty-seven days after vaccination neutralising antibody titres were determined, and 2 days later groups of vaccinated and control unvaccinated fish were subjected to an IHNV immersion challenge. Results of the virus challenge showed that the intramuscular injection and the gene gun immunisation induced protective immunity in fry, while intraperitoneal injection provided partial protection. Neutralising antibodies were not detected in sera of vaccinated fish regardless of the route of immunisation used, suggesting that cell mediated immunity may be at least partially responsible for the observed protection.

Evaluation of the protective immunogenicity of the N, P, M, NV and G proteins of infectious hematopoietic necrosis virus in rainbow trout oncorhynchus mykiss using DNA vaccines.

The protective immunogenicity of the nucleoprotein (N), phosphoprotein (P), matrix protein (M), non-virion protein (NV) and glycoprotein (G) of the rhabdovirus infectious hematopoietic necrosis virus (IHNV) was assessed in rainbow trout using DNA vaccine technology. DNA vaccines were produced by amplifying and cloning the viral genes in the plasmid pCDNA 3.1. The protective immunity elicited by each vaccine was evaluated through survival of immunized fry after challenge with live virus. Neutralizing antibody titers were also determined in vaccinated rainbow trout Oncorhynchus mykiss fry (mean weight 2 g) and 150 g sockeye salmon Oncorhynchus nerka. The serum from the 150 g fish was also used in passive immunization studies with naive fry. Our results showed that neither the internal structural proteins (N, P and M) nor the NV protein of IHNV induced protective immunity in fry or neutralizing antibodies in fry and 150 g fish when expressed by a DNA vaccine construct. The G protein, however, did confer significant protection in fry up to 80 d post-immunization and induced protective neutralizing antibodies. We are currently investigating the role of different arms of the fish immune system that contribute to the high level of protection against IHNV seen in vaccinated fish.

Involvement of the complement system in the protection of mice from challenge with respiratory syncytial virus Long strain following passive immunization with monoclonal antibody 18A2B2.

Passive immunization of mice with 131 micrograms of the non-neutralizing monoclonal antibody (mAb) 18A2B2, directed against the A subgroup epitope of the G glycoprotein of respiratory syncytial virus Long strain (RSV), confers protection against viral i.n. challenge. The role of the Fc fragment of this antibody as well as the involvement of antibody-dependent cellular cytotoxicity (ADCC) and complement-mediated cytolysis towards protection was evaluated in vivo. Passive immunization with the Fab fragment alone (618-907 micrograms mouse-1) was unable to confer protection in mice. Furthermore, we passively immunized with the mAb 18A2B2 SCID beige mice, which are deficient in natural killer (NK) cell activity, to ascertain the role of NK cells in the protective mechanism. These mice were free of virus 5 days following viral challenge, indicating that NK cells do not contribute significantly towards the protective action of this antibody. Moreover, passively immunized BALB/c mice decomplemented with 8-10 U of cobra venom factor (CoVF) and DBA/2J mice (C5 deficient) were only partially protected. These findings suggest that in mice the alternative and classical pathways of the complement system are involved in the passive protection mechanism conferred by the non-neutralizing mAb 18A2B2. To our knowledge, it is the first description of a protective mechanism in mice that involves a non-neutralizing antibody and the complement system.