# Immunoproteomic Screening of Candidate Antigens for the Preliminary Development of a Novel Multi-Component and Multi-Epitope Vaccine Against Streptococcus suis Infection

## TL;DR

Researchers developed a multi-component vaccine against Streptococcus suis that offers cross-protection against multiple strains.

## Contribution

A novel multi-component subunit vaccine using PdhA, Ldh, and MalX proteins was shown to provide cross-protection against multiple SS serotypes.

## Key findings

- Eight immunogenic cell wall proteins were identified, inducing high IgG antibody titers.
- A multi-component subunit vaccine (PdhA, Ldh, MalX) protected mice against SS2 and SSChz strains with 62.5% and 75% efficacy.
- A multi-epitope vaccine derived from these proteins showed limited protection in challenge tests.

## Abstract

Background/Objectives: Streptococcus suis (SS), an important zoonotic pathogen, has caused significant economic losses to the global pig industry. Existing commercial vaccines for SS mainly provide effective protection against a single serotype. Due to the existence of many serotypes and their robust immune evasion capabilities, the development of multi-component subunit vaccines or multi-epitope vaccines that provide effective cross-protection against different strains of SS is a key focus of current research. Methods: We applied two-dimensional electrophoresis (2-DE) and immunoblotting to screen for candidate immunogens among the immunogenic cell wall proteins of SS. BALB/c mice were immunized intradermally with a multi-component, multi-epitope vaccine. The vaccine’s safety and immunogenicity were assessed via clinical monitoring, antibody titer detection, cytokine assays, and survival curve analyses. Results: In this study, eight immunogenic cell wall proteins (GH25, Pk, PdhA, Ldh, ExoA, Pgk, MalX, and Dnak) were successfully identified using MALDI-TOF-MS, all of which could induce high IgG antibody titers. Based on the conservation and immunoprotection demonstrated by these eight protective antigenic proteins, PdhA, Ldh, and MalX were screened to construct a multi-component subunit vaccine as a candidate vaccine for providing cross-protection against SS isolates of multiple serotypes. Challenge studies showed that mice immunized with the multi-component subunit vaccine (PdhA, Ldh, and MalX) were protected against challenges with the SS2 virulent strain ZY05719 (62.5% protection) and the SSChz virulent strain CZ130302 (75% protection). Subsequently, we utilized immunoinformatics techniques to design a novel multi-epitope vaccine (MVPLM) derived from the immunogenic proteins PdhA, Ldh, and MalX. However, challenge tests revealed that the MVPLM offered limited protection against SS. Conclusions: These data demonstrate that a multi-component subunit vaccine composed of PdhA, Ldh, and MalX proteins shows promise as a candidate universal vaccine against multiple SS serotypes.