# Viral Vector-Based Chlamydia trachomatis Vaccines Encoding CTH522 Induce Distinct Immune Responses in C57BL/6J and HLA Transgenic Mice

## TL;DR

This study explores how different C. trachomatis vaccines affect immune responses in two types of mice, showing that antigen design and mouse strain matter for vaccine effectiveness.

## Contribution

The study demonstrates that antigen localization and mouse strain influence distinct immune responses in C. trachomatis vaccine development.

## Key findings

- Both vaccines induced CD4+ T-cell responses in C57BL/6J mice but failed to generate CD8+ T cells.
- Only the membrane-anchored CTH522 elicited strong IgG2b and IgG2c antibody responses in C57BL/6J mice.
- In HLA transgenic mice, both vaccines induced Th1-directed CD4+ and multifunctional CD8+ T cells, but only CTH522:B7 generated antibody responses.

## Abstract

Chlamydia trachomatis remains a major global health problem with increasing infection rates, requiring innovative vaccine solutions. Modified Vaccinia Virus Ankara (MVA) is a well-established, safe and highly immunogenic vaccine vector, making it a promising candidate for C. trachomatis vaccine development. In this study, we evaluated two novel MVA-based recombinant vaccines expressing spCTH522 and CTH522:B7 antigens. Our results show that while both vaccines induced CD4+ T-cell responses in C57BL/6J mice, they failed to generate antigen-specific systemic CD8+ T cells. Only the membrane-anchored CTH522 elicited strong IgG2b and IgG2c antibody responses. In an HLA transgenic mouse model, both recombinant MVAs induced Th1-directed CD4+ T cell and multifunctional CD8+ T cells, while only the CTH522:B7 vaccine generated antibody responses, underscoring the importance of antigen localization. Collectively, our data indicate that distinct antigen formulations can induce different immune responses depending on the mouse strain used. This research contributes to the development of effective vaccines by highlighting the importance of careful antigen design and the selection of appropriate animal models to study specific vaccine-induced immune responses. Future studies should investigate whether these immune responses provide protection in humans and should explore different routes of immunization, including mucosal and systemic immunization.