Humoral and cell-mediated immune responses in DNA immunized mink challenged with wild-type canine distemper virus

Immunogenicity and protective efficacy of a novel bacterium-like particle-based vaccine displaying canine distemper virus antigens in mice and dogs

Canine distemper virus (CDV) poses a severe threat to both domesticated and wild animals, including multiple carnivores. With the continued expansion of its host range, there is an urgent need for the development of a safer and more effective vaccine. In this study, we developed subunit vaccines based on a bacterium-like particle (BLP) delivery platform containing BLPs-F and BLPs-H, which display the CDV F and H glycoprotein antigens, respectively, using the antigen-protein anchor fusions produced by a recombinant baculovirus insect cell expression system. The combination of BLPs-F and BLPs-H (CDV-BLPs), formulated with colloidal manganese salt [Mn jelly (MnJ)] adjuvant, triggered robust CDV-specific antibody responses and a substantial increase in the number of interferon gamma (IFN-γ)-secreting CD4+ and CD8+ T cells in mice. Dogs immunized intramuscularly with this vaccine not only produced CDV-specific IgG but also displayed elevated concentrations of IFN-γ and interleukin 6 in their serum, along with an increase of the CD3+CD4+ and CD3+CD8+ T cell subsets. Consequently, this heightened immune response provided effective protection against disease development and reduced viral shedding levels following challenge with a virulent strain. These findings suggest that this BLP-based subunit vaccine has the potential to become a novel canine distemper vaccine.

IMPORTANCE

Many sensitive species require a safe and effective distemper vaccine. Non-replicating vaccines are preferred. We constructed subunit particles displaying canine distemper virus (CDV) antigens based on a bacterium-like particle (BLP) delivery platform. The CDV-BLPs formulated with theMn jelly adjuvant induced robust humoral and cell-mediated immune responses to CDV in mice and dogs, thereby providing effective protection against a virulent virus challenge. This work is an important step in developing a CDV subunit vaccine.

DNA Vaccine Co-Expressing Hemagglutinin and IFN-γ Provides Partial Protection to Ferrets against Lethal Challenge with Canine Distemper Virus

Canine distemper (CD), caused by canine distemper virus (CDV), is a highly contagious and lethal disease in domestic and wild carnivores. Although CDV live-attenuated vaccines have reduced the incidence of CD worldwide, low levels of protection are achieved in the presence of maternal antibodies in juvenile animals. Moreover, live-attenuated CDV vaccines may retain residual virulence in highly susceptible species and cause disease. Here, we generated several CDV DNA vaccine candidates based on the biscistronic vector (pIRES) co-expressing virus wild-type or codon-optimized hemagglutinin (H) and nucleocapsid (N) or ferret interferon (IFN)-γ, as a molecular adjuvant, respectively. Apparently, ferret (Mustela putorius furo)-specific codon optimization increased the expression of CDV H and N proteins. A ferret model of CDV was used to evaluate the protective immune response of the DNA vaccines. The results of the vaccinated ferrets showed that the DNA vaccine co-expressing the genes of codon-optimized H and ferret IFN-γ (poptiH-IRES-IFN) elicited the highest anti-CDV serum-neutralizing antibodies titer (1:14) and cytokine responses (upregulated TNF-α, IL-4, IL-2, and IFN-γ expression) after the third immunization. Following vaccination, the animals were challenged with a lethal CDV 5804Pe/H strain with a dose of 105.0 TCID50. Protective immune responses induced by the DNA vaccine alleviated clinical symptoms and pathological changes in CDV-infected ferrets. However, it cannot completely prevent virus replication and viremia in vivo as well as virus shedding due to the limited neutralizing antibody level, which eventually contributed to a survival rate of 75% (3/4) against CDV infection. Therefore, the improved strategies for the present DNA vaccines should be taken into consideration to develop more protective immunity, which includes increasing antigen expression or alternative delivery routes, such as gene gun injection.

A highly efficient recombinant canarypox virus-based vaccine against canine distemper virus constructed using the CRISPR/Cas9 gene editing method

Canine distemper virus (CDV) is the causative agent of canine distemper (CD), which is one of the most important infectious diseases affecting wild and domestic carnivores. Vaccination represents an effective approach to prevent CDV infection among domestic carnivores. Canarypox-vectored recombinant CD vaccines (such as Recombitek CDV, PureVax Ferret Distemper, and Merial) with the CDV hemagglutinin (H) and fusion (F) genes can induce a potent immune response in dogs and ferrets. However, the vaccine's effectiveness varies with the species. In the current study, we developed a highly efficient recombinant canarypox virus termed as "ALVAC-CDV-M-F-H/C5^-" that contained CDV virus-like particles (VLPs) by using the CRISPR/Cas9 gene editing method, which enabled concurrent expression of the matrix (M), H, and F genes. The recombinant strain provided faster seroconversion than the parent strain among minks as well as provided higher rates of antibody positivity than the parent strain among foxes and minks even before the administration of a second booster vaccination. We demonstrated, for the first time, that the CRISPR/Cas9 system can be applied for the rapid and efficient modification of the ALVAC-CDV-F-H genome and also that a high-dose new recombinant strain that produces CDV VLPs may present good outcomes in the prevention of CD among foxes and minks.

Morbillivirus Experimental Animal Models: Measles Virus Pathogenesis Insights from Canine Distemper Virus

Morbilliviruses share considerable structural and functional similarities. Even though disease severity varies among the respective host species, the underlying pathogenesis and the clinical signs are comparable. Thus, insights gained with one morbillivirus often apply to the other members of the genus. Since the Canine distemper virus (CDV) causes severe and often lethal disease in dogs and ferrets, it is an attractive model to characterize morbillivirus pathogenesis mechanisms and to evaluate the efficacy of new prophylactic and therapeutic approaches. This review compares the cellular tropism, pathogenesis, mechanisms of persistence and immunosuppression of the Measles virus (MeV) and CDV. It then summarizes the contributions made by studies on the CDV in dogs and ferrets to our understanding of MeV pathogenesis and to vaccine and drugs development.

Preparation and Identification of a Single-chain Variable Fragment Antibody Against Canine Distemper Virus

The variable regions of the heavy chain (VH) and light chain (VL) were amplified by RT-PCR from the hybridoma 1N8, which secretes the monoclonal antibody against CDV N protein (aa 277-471). The VL and VH amplicons were combined using SOE-PCR by a 12 amino acid flexible linker (SSGGGGSGGGGS), which produced the scFv gene (named scFv/1N8). After sequence analysis, the scFv/1N8 gene was cloned into the prokaryotic expression vector PET32a with a His-tag. The recombinant scFv/1N8 protein was successfully expressed in recombinant Escherichia coli by IPTG induction. Moreover, the binding activity and specificity of the scFv were determined by indirect ELISA (His-tag) and competitive ELISA. The recombinant scFv/1N8 protein reported here will provide some basis for further antiviral drug research based on the scFv molecule.

Canine distemper virus DNA vaccination of mink can overcome interference by maternal antibodies

Canine distemper virus (CDV) is highly contagious and can cause severe disease against which conventional live vaccines are ineffective in the presence of maternal antibodies. Vaccination in the presences of maternal antibodies was challenged by vaccination of 5 days old and 3 weeks old mink kits with CDV DNA vaccines. Virus neutralising (VN) antibody responses were induced in mink kits vaccinated with a plasmid encoding the haemaglutinin protein (H) of CDV (n=5, pCDV-H) or a combination of the H, fusion (F) and nucleoprotein (N) of CDV (n=5, pCDV-HFN). These DNA vaccinated kits were protected against virulent experimental infection with field strains of CDV. The pCDV-H was more efficient in inducing protective immunity in the presence of maternal antibodies compared to the pCDV-HFN. The results show that DNA vaccination with the pCDV-H or pCDV-HFN (n=4) only given once at 5 days of age induces virus specific immune response in neonatal mink and protection against virulent CDV exposure later in life.

DNA vaccines encoding proteins from wild-type and attenuated canine distemper virus protect equally well against wild-type virus challenge

Immunity induced by DNA vaccines containing the hemagglutinin (H) and nucleoprotein (N) genes of wild-type and attenuated canine distemper virus (CDV) was investigated in mink (Mustela vison), a highly susceptible natural host of CDV. All DNA-immunized mink seroconverted, and significant levels of virus-neutralizing (VN) antibodies were present on the day of challenge with wild-type CDV. The DNA vaccines also primed the cell-mediated memory responses, as indicated by an early increase in the number of interferon-gamma (IFN-γ)-producing lymphocytes after challenge. Importantly, the wild-type and attenuated CDV DNA vaccines had a long-term protective effect against wild-type CDV challenge. The vaccine-induced immunity induced by the H and N genes from wild-type CDV and those from attenuated CDV was comparable. Because these two DNA vaccines were shown to protect equally well against wild-type virus challenge, it is suggested that the genetic/antigenic heterogeneity between vaccine strains and contemporary wild-type strains are unlikely to cause vaccine failure.