# Heterologous signal peptide grafting enhances the immune efficacy of Salmonella vectors delivering hemagglutinin against H7N9 avian influenza virus

## TL;DR

Scientists improved Salmonella bacteria to better deliver a vaccine against H7N9 bird flu by using a new protein signal system, leading to stronger immune protection.

## Contribution

A novel approach combining a modified hemagglutinin leader sequence and a tPA signal peptide significantly enhances H7N9 HA protein expression in Salmonella vectors.

## Key findings

- Replacing the H9N2 HA precursor sequence with that from H7N9 AIV improved HA protein expression in Salmonella.
- Combining the H9N2 HA leader sequence with a tPA signal peptide significantly increased H7N9 HA protein expression.
- The modified Salmonella vector improved protective efficacy against H7N9 AIV challenge in a mouse model.

## Abstract

Salmonella enterica serovar Typhimurium (S. Typhimurium) vectors, which induce broad cellular and humoral immune responses, are excellent candidates for delivering foreign antigens. However, S. Typhimurium strains display limitations, including low levels of antigen protein expression when delivering viral antigens. In this study, we found that replacing the hemagglutinin (HA) precursor sequence of H9N2 AIV (avian influenza virus) with that from H7N9 AIV significantly improved HA protein expression. Building on this, we combined the H9N2 HA leader sequence with a tissue plasminogen activator (tPA) signal peptide and delayed lysis Salmonella mRNA interferase regulation vector (SIRV) system previously developed by our team. This novel approach markedly enhanced the expression of viral antigens delivered by Salmonella vectors. Our results demonstrate that both the H9N2 HA leader sequence and the tissue plasminogen activator (tPA) signal peptide significantly increased H7N9 AIV HA protein expression and substantially improved the protective efficacy of the attenuated S. Typhimurium vector delivering the H7N9 HA protein vaccine against H7N9 AIV challenge. These findings offer valuable insights for developing more effective attenuated Salmonella-based recombinant H7N9 AIV vaccines and provide a valuable reference for vaccine strategies against other infectious diseases.