# Donor Plasmid Optimization Enhances Expression of Feline Parvovirus VP2 Protein in the Baculovirus Expression Vector System

## TL;DR

Researchers improved a protein expression system to produce more feline parvovirus protein, leading to better vaccine candidates for cats.

## Contribution

A baculovirus expression system was optimized to significantly increase FPV VP2 protein yield and vaccine efficacy.

## Key findings

- Optimized BEVS increased VP2 transcription by 1.5-fold and viral titers by 3.7-fold.
- Vaccinated cats showed normal health metrics and minimal viral shedding after FPV challenge.
- Purified VP2 self-assembled into uniform 25 nm virus-like particles.

## Abstract

Background: Feline panleukopenia virus (FPV) causes acute and frequently fatal disease in cats, underscoring the urgent need for safe, rapidly effective, and scalable vaccines. While virus-like particle (VLP) vaccines are inherently safe and immunogenic, their development is constrained by low yields of recombinant protein in insect cell expression systems. Methods: An optimized baculovirus expression vector system (BEVS) incorporating the hr1-p6.9-p10 transcriptional enhancer and the Ac-ie-01 anti-apoptotic gene was employed to enhance recombinant protein production. VP2 expression levels, viral titers, and hemagglutination activity were quantified using qPCR, SDS-PAGE/Western blotting, transmission electron microscopy (TEM), and functional assays. Immunogenicity and protective efficacy were assessed in both mice and cats through serological analysis, neutralizing antibody detection, and post-challenge clinical monitoring. Results: The optimized BEVS enhanced recombinant protein transcription by 1.5-fold, viral titers by 3.7-fold, and hemagglutination activity by 15-fold. The purified protein self-assembled into uniform 25 nm virus-like particles (VLPs). Immunization elicited earlier responses compared to commercial vaccines. Vaccinated cats maintained normal body temperature, stable leukocyte counts, and minimal viral shedding following FPV challenge. Conclusions: This study validates an enhanced BEVS that effectively overcomes VP2 yield constraints and generates highly immunogenic FPV VLPs. The platform enables rapid-onset protection and offers a scalable strategy for next-generation FPV vaccine development.