Contributions of lipopolysaccharide and the type IVB secretion system to Coxiella burnetii vaccine efficacy and reactogenicity

Carrie M Long,Robert A Heinzen,Paul A Beare,Diane C Cockrell,Carl I Shaia,Jonathan Fintzi,Mahelat Tesfamariam

doi:10.1038/s41541-021-00296-6

Carrie M Long, Robert A Heinzen + Show 5 more

Open Access

https://doi.org/10.1038/s41541-021-00296-6

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Abstract

Coxiella burnetii is the bacterial causative agent of the zoonosis Q fever. The current human Q fever vaccine, Q-VAX®, is a fixed, whole cell vaccine (WCV) licensed solely for use in Australia. C. burnetii WCV administration is associated with a dermal hypersensitivity reaction in people with pre-existing immunity to C. burnetii, limiting wider use. Consequently, a less reactogenic vaccine is needed. Here, we investigated contributions of the C. burnetii Dot/Icm type IVB secretion system (T4BSS) and lipopolysaccharide (LPS) in protection and reactogenicity of fixed WCVs. A 32.5 kb region containing 23 dot/icm genes was deleted in the virulent Nine Mile phase I (NMI) strain and the resulting mutant was evaluated in guinea pig models of C. burnetii infection, vaccination-challenge, and post-vaccination hypersensitivity. The NMI ∆dot/icm strain was avirulent, protective as a WCV against a robust C. burnetii challenge, and displayed potentially altered reactogenicity compared to NMI. Nine Mile phase II (NMII) strains of C. burnetii that produce rough LPS, were similarly tested. NMI was significantly more protective than NMII as a WCV; however, both vaccines exhibited similar reactogenicity. Collectively, our results indicate that, like phase I LPS, the T4BSS is required for full virulence by C. burnetii. Conversely, unlike phase I LPS, the T4BSS is not required for vaccine-induced protection. LPS length does not appear to contribute to reactogenicity while the T4BSS may contribute to this response. NMI ∆dot/icm represents an avirulent phase I strain with full vaccine efficacy, illustrating the potential of genetically modified C. burnetii as improved WCVs.

Highlights

Coxiella burnetii is a gram-negative, intracellular bacterium with near worldwide dissemination
Crazy RSA514 (NMC), and Nine Mile RSA439 phase II, clone 4 (NMII). Were utilized in these studies due to their historic experimental use, known virulence, and shared genetic background[29,30,43]. These isogenic strains are genetically similar with the exception of large genomic deletions of LPS biosynthesis genes in NMC and NMII44
As LPS length is an important determinant of virulence and vaccine efficacy[29], the LPS content of all C. burnetii stocks used for infections or as whole cell vaccine (WCV) were characterized by silver stain (Fig. 2a–c) and immunoblot using antibodies specific for phase I, intermediate, and phase II LPS30 (Supplementary Fig. 1)

Summary

Introduction

Coxiella burnetii is a gram-negative, intracellular bacterium with near worldwide dissemination. This bacterium is the causative agent of the zoonosis Q fever. Human Q fever generally presents as an acute influenza-like illness many individuals remain asymptomatic throughout infection[1]. A potentially severe post-vaccination delayed-type hypersensitivity (DTH) skin response can occur at the inoculation site in individuals with pre-existing immunity due to previous symptomatic or asymptomatic infection[11]. This response necessitates extensive pre-screening of potential vaccinees by serologic and skin testing[11,12]. A WCV derived from the Nine Mile strain, Coxevac®, has been approved for veterinary use in the European Union since

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