Mutations in feline infectious peritonitis virus nonstructural protein 14/16 methyltransferase attenuate the pathogenicity of the virus in cats.
Mutations in the FIPV methyltransferase proteins can reduce pathogenicity in cats, with the dnsp14 strain showing better immune response than dnsp16.
Where it sits
this study against the rest of the dnsp-11 (dopamine neuron stimulating peptide-11) corpusSummary and findings
This study investigated the effects of mutations in the methyltransferase activity of feline infectious peritonitis virus (FIPV) nonstructural proteins nsp14 and nsp16 on pathogenicity in cats. Two mutant strains, dnsp14 and dnsp16, were created and administered at doses of 10^5 TCID50 and 10^4 TCID50. The dnsp14 strain resulted in a 75% reduction in mortality compared to the wild type and induced higher neutralizing antibody titers than dnsp16.
Abstract
Feline infectious peritonitis virus (FIPV) can cause an immune-mediated disease that is fatal to felines, but there is a lack of clinically effective protection conferred by vaccines. The methyltransferase (MTase) activity of the coronavirus nonstructural proteins nsp14 and nsp16 affects virulence, but there are no studies on the effect of nsp14 and nsp16 mutations affecting enzyme activity on the virulence of FIPV. In this study, we successfully rescued two mutant strains based on the previous infectious clone QS-79, named FIPV QS-79 dnsp14 and dnsp16, by mutating the MTase active sites of nsp14 (N415) and nsp16 (D129). The dnsp14 and dnsp16 exhibited similar syncytium formation ability and growth kinetics as their parental strains <i>in vitro</i>. Moreover, both mutants stimulated increased expression of interferon and cytokines in a macrophage lineage cell line. The dnsp14 and dnsp16 exhibited significantly lower pathogenicity in cats, with a 75% reduction in mortality compared to the wild type. The dnsp14 and dnsp16 were administered to cats at high (10<sup>5</sup> TCID<sub>50</sub>) and low (10<sup>4</sup> TCID<sub>50</sub>) doses for immunization purposes. The dnsp14 resulted in the production of high neutralizing antibody titers (>1:156) at both doses, whereas the dnsp16 only induced low neutralizing antibody titers (<1:64). And the dnsp14 provided protection to 50% of the cats at both immunization doses, whereas the dnsp16 failed to provide protection to cats of the challenge assays. The above results show that these two mutant strains are less pathogenic in cats, and dnsp14 induces a better humoral immune response and protection than dnsp16.IMPORTANCEFeline infectious peritonitis virus is a significant pathogen that affects felines worldwide, and its high fatality rate has long been a concern in the pet medical industry. Previous studies have indicated that the virus encodes nsp14 and nsp16 methyltransferases, which play a crucial role in viral genome replication and evasion of innate immunity. In this study, we aimed to inhibit the MTase activity by mutating the methyltransferase of feline infectious peritonitis virus nonstructural protein 14/16. This mutation resulted in the construction of a vaccine candidate with reduced virulence, efficient replication in the host, and the ability to provide partial protection from the virulent parental virus. Our findings offer valuable insights for the development of live attenuated vaccines that target the nsp14/nsp16 MTase of feline coronaviruses.
Background
Feline infectious peritonitis virus (FIPV) is a significant pathogen causing fatal immune-mediated disease in felines, with limited effective vaccines available. Previous research has established that the methyltransferase activity of nonstructural proteins nsp14 and nsp16 is crucial for the virus's virulence. This study aims to explore how mutations in these proteins can affect FIPV pathogenicity, potentially leading to the development of safer vaccine candidates.
Methods
The study involved creating two mutant strains of FIPV, dnsp14 and dnsp16, by mutating the methyltransferase active sites of nsp14 (N415) and nsp16 (D129). These strains were administered to cats at high (10^5 TCID50) and low (10^4 TCID50) doses. The primary outcomes measured included mortality rates and neutralizing antibody titers following immunization.
Results
The primary endpoint showed a 75% reduction in mortality for cats infected with the dnsp14 and dnsp16 strains compared to the wild type. The dnsp14 strain produced high neutralizing antibody titers (>1:156) at both doses, while dnsp16 produced low titers (<1:64). Additionally, dnsp14 provided protection to 50% of the cats, whereas dnsp16 did not confer any protection in challenge assays.
Interpretation
The findings suggest that the dnsp14 strain is less pathogenic and induces a stronger immune response compared to dnsp16. While the reduction in mortality is statistically significant, the clinical relevance may be limited by the small sample size and the lack of long-term follow-up. The study's results could inform future vaccine development, but confounding factors such as the specific immune responses in a broader feline population need consideration.
Key findings
- 75% reduction in mortality compared to wild type in cats.
- dnsp14 resulted in high neutralizing antibody titers (>1:156) at both doses.
- dnsp16 only induced low neutralizing antibody titers (<1:64).
- 50% protection provided by dnsp14 at both immunization doses.
- dnsp16 failed to provide protection in challenge assays.
Limitations
- small sample size in cats
- short follow-up duration
- no long-term effects evaluated
- single-site study
- no human data available