Evaluation of safety and immunogenicity of feline vaccines with reduced volume

Revolutionizing Veterinary Health with Viral Vector-Based Vaccines

Vaccines signify one of the economical and reasonable means to prevent and eradicate the important infectious diseases. Conventional vaccines like live attenuated and inactivated vaccines comprise of whole pathogen either in attenuated or killed form. While, new generation vaccines have been designed to elicit immune response by genetically modifying only the nucleic acid portion of that pathogen. These new generation therapeutics include mRNA vaccines, DNA plasmid vaccines, chimeric vaccines and recombinant viral vector-based vaccines. Nucleic acid based vaccines use genetic material itself thus, they are highly stable and potent in nature to induce long-lasting immune response. Amongst these novel vaccine platforms, viral vector-based vaccines is one such emerging field which has proven to be extremely effective and potent. Nowadays, veterinary medicine has also accepted this innovative vectored vaccine platform to develop an effective control strategy against certain important viral diseases of animals. Viral vector-based vaccine uses various DNA and RNA viruses of human or animal origin to carry an immunogenic transgene of target pathogen. These vaccines enhance both humoral and cell mediated immune response without use of any accessory immune-stimulants. Till today, several viruses have been modified to be characterized as vaccine vectors. Currently, large number of research programs are going on to develop vectored vaccines and novel viral vector for veterinary use. In the present review, different kinds of viral vectored vaccines having veterinary importance have been discussed.

Immunogenicity evaluation of a bivalent vaccine based on a recombinant rabies virus expressing gB protein of FHV-1 in mice and cats

Feline viral rhinotracheitis (FVR) is caused by the feline herpesvirus-1 (FHV-1), which commonly results in upper respiratory symptoms, and can result in death in the kittens and weak cats. Rabies is an infectious disease with zoonotic characteristics highly relevant to public health and also poses a serious threat to cats. Vaccines are the most effective method to control the spread of both FHV-1 and RABV and have the advantage that they produce long-term specific immune responses. In this study, we constructed a bivalent vaccine against FHV-1 and rabies virus (RABV) simultaneously. The vaccine was constructed by cloning FHV-1 gB into a RABV based vector, and the recombinant RABV (SRV9-FHV-gB) expressing the FHV-1 gB protein was rescued. The growth characteristics of SRV9-FHV-gB were analyzed on NA and BSR cells. To assess the immunogenicity of the vaccine, mice and cats were immunized with SRV9-FHV-gB supplemented with Gel02 adjuvant. The SRV9-FHV-gB exhibited the same growth characteristics as the parent virus SRV9 in both BSR cells and NA cells. The safety of SRV9-FHV-gB was evaluated using 5-day-old and 14-day-old suckling mice. The results showed that mice infected with the SRV9-FHV-gB survived for longer than those in the SRV9 group. Mice immunized with inactivated SRV9-FHV-gB produced high titers of specific antibodies against FHV-1 and neutralizing antibodies against RABV. Cats that received three immunizations with SRV9-FHV-gB also produced neutralizing antibodies against both FHV-1 and RABV. This study represents the first time that a bivalent vaccine targeting FHV-1 and RABV has been constructed, laying the foundations and providing inspiration for the development of other multivalent vaccines.

A bacterium-like particle vaccine displaying protective feline herpesvirus 1 antigens can induce an immune response in mice and cats

Feline herpesvirus 1 (FHV-1) is a highly transmissible virus that mainly causes ocular and upper respiratory infections in cats and seriously threatens the health of domestic cats and captive or wild cats (such as tigers, cheetahs, and lions). Vaccination is crucial to reduce the incidence rate and mortality of cats infected with FHV-1. In this study, three bacterium-like particles (BLPs) displaying the gB, gC, and gD proteins of FHV-1 were constructed based on a gram-positive enhancer matrix-protein anchor (GEM-PA) surface display system. Indirect immunofluorescence assay, western blot, and electron microscopy results showed that gB, gC or gD protein of FHV-1 was successfully displayed on the surface of GEM particles. Additionally, we designed one more BLPs, designated gB&gC&gD-GEM, which consisted of a mixture of gB-GEM, gC-GEM, and gD-GEM at a protein content ratio of 1:1:1. Mice were immunized with the four BLPs mixed with Gel02 adjuvant, and the results indicated that neutralizing antibody level in the gB&gC&gD-GEM group was superior than those in the other groups. Moreover, gB&gC&gD-GEM significantly increased the secretion of cytokines, as well as the activation and maturation of B cells. It also boosted the production of central memory T cells among CD4 + and CD8 + T cells. Moreover, gB&gC&gD-GEM mixed with Gel02 adjuvant provoked an antibody response in cats. In conclusion, the BLPs vaccine prepared from gB&gC&gD-GEM induced specific humoral and cellular immune responses to FHV-1 and be used as a potential vaccine candidate for the control of FHV-1 infection in cats.

Prevalence of Serum Antibody Titers against Core Vaccine Antigens in Italian Cats

Feline core vaccines strongly recommended for all cats are against Feline panleukopenia virus (FPV), Felid herpesvirus type 1 (FeHV-1), and Feline calicivirus (FCV), but cats can be classified as low- and high-risk based on their lifestyle. The aim of this study was to determine the actual seroprotection against FPV, FeHV-1, and FCV in a large cohort of Italian cats by using the VacciCheck test. A total of 740 cats (567 owned and 173 stray cats; 435 vaccinated and 305 unvaccinated) were analyzed for Protective Antibody Titers (PATs). Differences related to origin, sex, age, breed, FIV/FeLV status, health status, and time elapsed since last vaccination were evaluated. Less than half of the entire cohort (36.4%) had PATs for all three diseases simultaneously, increasing to 48.6% if weak positive values were also considered and 50.3% when considering only the 435 vaccinated cats. Particularly, antibodies were detected against FCV, FPV, and FeHV-1 at protective titers (PATs) in 78.6%, 68.1, and 49.1% of the cats, respectively. In general, owned, neutered, and adult FIV- and/or FeLV-negative cats were the most protected categories, even if not always for the three viruses. Most cats maintained high PATs for 3 years or longer after vaccination against FPV and FCV but not FeHV-1. Long-lasting protective immunity persisted for many years after the last vaccination (more than 18 years in the oldest cats). Nevertheless, since not all cats were protected after so many years and for all pathogens, checking protection via antibody titration could be the best choice to prevent immunity breakdowns. The discussion also focuses on the reliability of antibody titration for the two URTD (upper respiratory tract disease) viruses which, unlike for FPV, is not widely accepted as a valid index of protection.

Feline Injection-Site Sarcoma and Other Adverse Reactions to Vaccination in Cats

Vaccine-associated adverse events (VAAEs), including feline injection-site sarcomas (FISSs), occur only rarely but can be severe. Understanding potential VAAEs is an important part of informed owner consent for vaccination. In this review, the European Advisory Board on Cat Diseases (ABCD), a scientifically independent board of feline medicine experts, presents the current knowledge on VAAEs in cats, summarizing the literature and filling the gaps where scientific studies are missing with expert opinion to assist veterinarians in adopting the best vaccination practice. VAAEs are caused by an aberrant innate or adaptive immune reaction, excessive local reactions at the inoculation site, an error in administration, or failure in the manufacturing process. FISS, the most severe VAAE, can develop after vaccinations or injection of other substances. Although the most widely accepted hypothesis is that chronic inflammation triggers malignant transformation, the pathogenesis of FISS is not yet fully understood. No injectable vaccine is risk-free, and therefore, vaccination should be performed as often as necessary, but as infrequently as possible. Vaccines should be brought to room temperature prior to administration and injected at sites in which FISS surgery would likely be curative; the interscapular region should be avoided. Post-vaccinal monitoring is essential.

Comparison of the local safety of two multi-component feline vaccines, adjuvanted (1 mL) versus non-adjuvanted at reduced volume (0.5 mL), using computed tomography imaging

In 2020, a new 0.5 mL presentation of PUREVAX® RCP FeLV was registered and introduced in Europe. The objectives of this study were to investigate the local safety of this non-adjuvanted vaccine at reduced volume by classical methods (clinical examination, histopathology) and to evaluate the suitability of an alternative non-invasive methodology, the computed tomography (CT). For this purpose, the course of local reactions was assessed for 3 months after subcutaneous injection of PUREVAX® RCP FeLV 0.5 mL and compared to an adjuvanted vaccine, LEUCOFELIGEN® FeLV/RCP 1.0 mL. Injection site reactions consisted mainly of swelling reactions, which were more frequent, more pronounced and long-lasting in the adjuvanted vaccine group. Microscopically, in this group, moderate to severe inflammatory reactions were observed on day 7 (D7) and D21 post-injection and still present on D84, while mild inflammatory lesions were observed in the non-adjuvanted vaccine group only on D7 and D21. With the adjuvanted vaccine, inflamed areas were measurable by CT scan in all cats on D7 and D21, whereas they were detected only on D7 and only in 20 % of cats from the non-adjuvanted vaccine group. Besides the higher frequency, the mean inflamed volume was nearly 300 times larger in adjuvanted vaccine group on D7. Using different methodologies, the favorable safety profile of PUREVAX® RCP FeLV 0.5 mL was confirmed. Furthermore, the vaccine is aligned with current vaccination guidelines by inducing less inflammatory reactions, being adjuvant-free and injectable under a reduced volume, thus improving the convenience of administration in recommended sites (eg, legs). CT scan proved to be a suitable non-invasive method for the experimental follow-up of injection site reactions, yielding results consistent with clinical assessment and histopathology on D7 and D21. CT scan substantiated large differences between the investigated vaccines with a more prominent inflammatory reaction after injection of an adjuvanted vaccine.

Safety and immunogenicity of a TK/ gI/gE gene-deleted feline herpesvirus-1 mutant constructed via CRISPR/Cas9 in feline

Feline herpesvirus-1 (FHV-1) is the aetiological agent of feline viral rhinotracheitis, which accounts for approximately 50 % of all viral upper respiratory diseases in cats. Commercially available modified live vaccines containing FHV-1 are generally safe and effective, but these FHV-1 vaccines retain full virulence genes and can establish latency and reactivate to cause infectious rhinotracheitis in vaccine recipients, raising safety concerns. To address this shortcoming, we constructed a novel TK/gI/gE -gene-deleted recombinant FHV-1 (WH2020-ΔTK/gI/gE) through CRISPR/Cas9-mediated homologous recombination. The growth kinetics of WH2020-ΔTK/gI/gE were slightly delayed compared to those of the parent strain WH2020. Recombinant FHV-1 had severely impaired pathogenicity in cats. Felines immunized with WH2020-ΔTK/gI/gE produced high levels of gB-specific antibodies, neutralizing antibodies and IFN-β. Additionally, WH2020-ΔTK/gI/gE provided greater protection against challenge with FHV-1 field strain WH2020 than did the commercial modified live vaccine. After challenge, the cats vaccinated with WH2020-ΔTK/gI/gE showed significantly fewer clinical signs, pathological changes, viral shedding, and viral loads in the lung and trigeminal ganglia than those vaccinated with the commercial vaccine or unvaccinated. Our results suggest that WH2020-ΔTK/gI/gE is a promising candidate as a safer and more efficacious live FHV-1 vaccine, with a decreased risk of vaccine-related complications, and could inform the design of other herpesvirus vaccines.

Calicivirus Infection in Cats

Feline calicivirus (FCV) is a common pathogen in domestic cats that is highly contagious, resistant to many disinfectants and demonstrates a high genetic variability. FCV infection can lead to serious or even fatal diseases. In this review, the European Advisory Board on Cat Diseases (ABCD), a scientifically independent board of experts in feline medicine from 11 European countries, presents the current knowledge of FCV infection and fills gaps with expert opinions. FCV infections are particularly problematic in multicat environments. FCV-infected cats often show painful erosions in the mouth and mild upper respiratory disease and, particularly in kittens, even fatal pneumonia. However, infection can be associated with chronic gingivostomatitis. Rarely, highly virulent FCV variants can induce severe systemic disease with epizootic spread and high mortality. FCV can best be detected by reverse-transcriptase PCR. However, a negative result does not rule out FCV infection and healthy cats can test positive. All cats should be vaccinated against FCV (core vaccine); however, vaccination protects cats from disease but not from infection. Considering the high variability of FCV, changing to different vaccine strain(s) may be of benefit if disease occurs in fully vaccinated cats. Infection-induced immunity is not life-long and does not protect against all strains; therefore, vaccination of cats that have recovered from caliciviral disease is recommended.