Pathogenicity and immunogenicity of gI/gE/TK-gene-deleted Felid herpesvirus 1 variants in cats.

BACKGROUND: Felid herpesvirus 1 (FHV-1) is a major pathogenic agent of upper respiratory tract infections and eye damage in felines worldwide. Current FHV-1 vaccines offer limited protection of short duration, and therefore, do not reduce the development of clinical signs or the latency of FHV-1. METHODS: To address these shortcomings, we constructed FHV ∆gIgE-eGFP, FHV ∆TK mCherry, and FHV ∆gIgE/TK eGFP-mCherry deletion mutants (ΔgI/gE, ΔTK, and ΔgIgE/TK, respectively) using the clustered regularly interspaced palindromic repeats (CRISPR)/CRISP-associated protein 9 (Cas9) system (CRISPR/Cas9), which showed safety and immunogenicity in vitro. We evaluated the safety and efficacy of the deletion mutants administered with intranasal (IN) and IN + subcutaneous (SC) vaccination protocols. Cats in the vaccination group were vaccinated twice at a 4-week interval, and all cats were challenged with infection 3 weeks after the last vaccination. The cats were assessed for clinical signs, nasal shedding, and virus-neutralizing antibodies (VN), and with postmortem histological testing. RESULTS: Vaccination with the gI/gE-deleted and gI/gE/TK-deleted mutants was safe and resulted in significantly lower clinical disease scores, fewer pathological changes, and less nasal virus shedding after infection. All three mutants induced virus-neutralizing antibodies after immunization. CONCLUSIONS: In conclusion, this study demonstrates the advantages of FHV-1 deletion mutants in preventing FHV-1 infection in cats.

Safety and Efficacy of Felid Herpesvirus-1 Deletion Mutants in Cats.

Felid herpesvirus-1 (FeHV-1) is an important respiratory and ocular pathogen of cats and current vaccines are limited in duration and efficacy because they do not prevent infection, viral nasal shedding and latency. To address these shortcomings, we have constructed FeHV-1 gE-TK- and FeHV-1 PK- deletion mutants (gE-TK- and PK-) using bacterial artificial chromosome (BAC) mutagenesis and shown safety and immunogenicity in vitro. Here, we compare the safety and efficacy of a prime boost FeHV-1 gE-TK- and FeHV-1 PK- vaccination regimen with commercial vaccination in cats. Cats in the vaccination groups were vaccinated at 3-week intervals and all cats were challenge infected 3 weeks after the last vaccination. Evaluations included clinical signs, nasal shedding, virus neutralizing antibodies (VN), cytokine mRNA gene expression, post-mortem histology and detection of latency establishment. Vaccination with gE-TK- and PK- mutants was safe and resulted in significantly reduced clinical disease scores, pathological changes, viral nasal shedding, and viral DNA in the trigeminal ganglia (the site of latency) following infection. Both mutants induced VN antibodies and interferons after immunization. In addition, after challenge infection, we observed a reduction of IL-1ß expression, and modulation of TNFα, TGFß and IL10 expression. In conclusion, this study shows the merits of using FeHV-1 deletion mutants for prevention of FeHV-1 infection in cats.

Calicivirus co-infections in herpesvirus pneumonia in kittens.

Felid herpesvirus-1 (FeHV-1) and feline calicivirus (FCV) are the most important infectious causes of respiratory disease in cats. FeHV-1 and FCV co-infections are common in cats with upper respiratory tract disease, but it is unknown whether such co-infections also occur in cats with pneumonia. This study examined the lungs of naturally infected cats with FeHV-1 pneumonia for FCV co-infection by histopathology and immunohistochemistry. The frequency of FCV (13/21, 62%) in this group of cats suggests that co-infection is common in kittens with FeHV-1 pneumonia. FCV infected macrophages were often found in the lumen of FeHV-1 affected airways. In 8/13 (62%) cats, typical FCV lesions were distant from changes induced by FeHV-1. FCV infection of type II pneumocytes/alveolar macrophages was apparent in histologically unaltered areas. It is likely that damage to airways induced by FeHV-1 facilitates secondary infection with FCV due to reduced mucociliary clearance and impaired immune defences.

In vitro characterization of felid herpesvirus 1 (FHV-1) mutants generated by recombineering in a recombinant BAC vector.

Felid herpesvirus 1 (FHV-1) mutants were constructed using two-step Red-mediated recombination techniques based on a virulent full-length FHV-1 BAC clone. The individual mutant viruses generated were deficient in glycoprotein C (gC), glycoprotein E (gE), US3 serine/threonine protein kinase (PK), or both gE and thymidine kinase (TK). The gC- mutant virus produced plaques that were similar in size to those resulting from infection with the C-27 parent strain. In contrast, the gE(-), PK(-), and gE(-)PK(-) deletion mutants produced plaques that were significantly smaller. Multistep in vitro growth kinetics of the gE(-), PK(-), and gE(-)PK(-) viruses were slightly delayed compared to those of the C-27 parent strain. Peak progeny titers of these three mutants were approximately 10-fold lower than those generated with the C-27 strain. There was no delay in the growth kinetics of the gC- mutant, but the progeny virus titer obtained with this mutant was at least 3 logs lower compared to the parental strain titer. Based upon their in vitro characteristics, these mutants will be useful for the development of novel immunization strategies against this important feline pathogen.