# Efficacy of genetically modified Mycoplasma hyopneumoniae strains and their effect on local and cell-mediated immune responses in pigs

## TL;DR

This study explores genetically modified strains of Mycoplasma hyopneumoniae to improve pig vaccination, showing reduced infection symptoms and bacterial load after challenge.

## Contribution

The study introduces novel genetically modified M. hyopneumoniae strains (ΔmmsA and ΔmnuA) as potential live vaccine candidates.

## Key findings

- The ΔmnuA strain reduced clinical signs and challenge strain DNA load in broncho-alveolar lavage fluid.
- Both vaccinated groups showed increased IgA and decreased pro-inflammatory cytokines in broncho-alveolar lavage.
- ΔmnuA led to lower percentages of IFN-γ+ and TNF-α+IFN-γ+ CD8+ T cells post-vaccination.

## Abstract

Vaccination against Mycoplasma hyopneumoniae is still carried out worldwide, but unfortunately current commercial vaccines only provide partial protection. Therefore, two M. hyopneumoniae strains were genetically modified by transposon-mediated gene disruption of mmsA and mnuA, encoding methylmalonate semialdehyde dehydrogenase and membrane nuclease A, respectively. We investigated how immune responses elicited by these genetically modified M. hyopneumoniae strains protected pigs against challenge infection. An endotracheal single dose vaccination with genetically modified M. hyopneumoniae strain 1 (ΔmmsA) or 2 (ΔmnuA), or physiological saline solution (Control) was followed by challenge infection. Piglets from ΔmnuA had a higher respiratory disease score post-vaccination, but this group coughed significantly less after challenge. Significantly fewer DNA copies of the challenge strains were observed in broncho-alveolar lavage fluid (BAL) from ΔmnuA after challenge. Two weeks post-challenge, significantly more BAL IgG and BAL IgA was observed in ΔmnuA, but at euthanasia significantly more IgA and less pro-inflammatory cytokines were detected in BAL from both vaccinated groups. Furthermore, a significantly lower percentage of IFN-γ+ and TNF-α+IFN-γ+ CD8+ T cells was observed after administration of ΔmnuA. The percentage of IFN-γ+ CD8+ T cells was significantly lower in ΔmmsA at euthanasia. To conclude, the results of this exploratory study show that a single endotracheal administration of ΔmnuA resulted in coughing post-vaccination, but reduced clinical signs post-challenge and challenge strain DNA load in BAL. Therefore, a strain mutated in the mnuA gene might be an interesting mutant strain that could be promising as a potential live vaccine candidate strain as it can reduce M. hyopneumoniae infection burden under field conditions.

The online version contains supplementary material available at 10.1186/s13567-025-01653-2.