T-Bet Controls Susceptibility of Mice to Coxiella burnetii Infection

Q fever immunology: the quest for a safe and effective vaccine

Q fever is an infectious zoonotic disease, caused by the Gram-negative bacterium Coxiella burnetii. Transmission occurs from livestock to humans through inhalation of a survival form of the bacterium, the Small Cell Variant, often via handling of animal parturition products. Q fever manifests as an acute self-limiting febrile illness or as a chronic disease with complications such as vasculitis and endocarditis. The current preventative human Q fever vaccine Q-VAX poses limitations on its worldwide implementation due to reactogenic responses in pre-sensitized individuals. Many strategies have been undertaken to develop a universal Q fever vaccine but with little success to date. The mechanisms of the underlying reactogenic responses remain only partially understood and are important factors in the development of a safe Q fever vaccine. This review provides an overview of previous and current experimental vaccines developed for use against Q fever and proposes approaches to develop a vaccine that establishes immunological memory while eliminating harmful reactogenic responses.

QuilA® adjuvanted Coxevac® sustains Th1-CD8+-type immunity and increases protection in Coxiella burnetii-challenged goats

Coxevac® is the EMA-approved veterinary vaccine for the protection of cattle and goats against Q fever, a zoonotic bacterial disease due to Coxiella burnetii. Since Coxevac® reduces bacterial shedding and clinical symptoms but does not prevent infection, novel, ready-to-use vaccine formulations are needed to increase its immunogenicity. Here, a goat vaccination-challenge model was used to evaluate the impact of the commercially available saponin-based QuilA® adjuvant on Coxevac® immunity. Upon challenge, the QuilA®-Coxevac® group showed a stronger immune response reflected in a higher magnitude of total IgG and an increase in circulating and splenic CD8⁺ T-cells compared to the Coxevac® and challenged-control groups. The QuilA®-Coxevac® group was characterized by a targeted Th1-type response (IFNγ, IP10) associated with increased transcripts of CD8⁺ and NK cells in spleens and γδ T cells in bronchial lymph nodes. Coxevac® vaccinated animals presented an intermediate expression of Th1-related genes, while the challenged-control group showed an immune response characterized by pro-inflammatory (IL1β, TNFα, IL12), Th2 (IL4 and IL13), Th17 (IL17A) and other immunoregulatory cytokines (IL6, IL10). An intriguing role was observed for γδ T cells, which were of TBX21- and SOX4-types in the QuilA®-Coxevac® and challenged control group, respectively. Overall, the addition of QuilA® resulted in a sustained Th1-type activation associated with an increased vaccine-induced bacterial clearance of 33.3% as compared to Coxevac® only. QuilA® could be proposed as a readily-applied veterinary solution to improve Coxevac® efficacy against C. burnetii infection in field settings.

Infection and Persistence of Coxiella burnetii Clinical Isolate in the Placental Environment

Infection by Coxiella burnetii, the etiological agent of Q fever, poses the risk of causing severe obstetrical complications in pregnant women. C. burnetii is known for its placental tropism based on animal models of infection. The Nine Mile strain has been mostly used to study C. burnetii pathogenicity but the contribution of human isolates to C. burnetii pathogenicity is poorly understood. In this study, we compared five C. burnetii isolates from human placentas with C. burnetii strains including Nine Mile (NM) as reference. Comparative genomic analysis revealed that the Cb122 isolate was distinct from other placental isolates and the C. burnetii NM strain with a set of unique genes involved in energy generation and a type 1 secretion system. The infection of Balb/C mice with the Cb122 isolate showed higher virulence than that of NM or other placental isolates. We evaluated the pathogenicity of the Cb122 isolate by in vitro and ex vivo experiments. As C. burnetii is known to infect and survive within macrophages, we isolated monocytes and placental macrophages from healthy donors and infected them with the Cb122 isolate and the reference strain. We showed that bacteria from the Cb122 isolate were less internalized by monocyte-derived macrophages (MDM) than NM bacteria but the reference strain and the Cb122 isolate were similarly internalized by placental macrophages. The Cb122 isolate and the reference strain survived similarly in the two macrophage types. While the Cb122 isolate and the NM strain stimulated a poorly inflammatory program in MDM, they elicited an inflammatory program in placenta macrophages. We also reported that the Cb122 isolate and NM strain were internalized by trophoblastic cell lines and primary trophoblasts without specific replicative profiles. Placental explants were then infected with the Cb122 isolate and the NM strain. The bacteria from the Cb122 isolate were enriched in the chorionic villous foetal side. It is likely that the Cb122 isolate exhibited increased virulence in the multicellular environment provided by explants. Taken together, these results showed that the placental isolate of C. burnetii exhibits a specific infectious profile but its pathogenic role is not as high as the host immune response in pregnant women.

Q Fever Vaccine Development: Current Strategies and Future Considerations

Q fever is a zoonotic disease caused by the intracellular pathogen Coxiella burnetii. This disease typically manifests as a self-limiting, febrile illness known as acute Q fever. Due to the aerosol transmissibility, environmental persistence, and infectivity of C. burnetii, this pathogen is a notable bioterrorism threat. Despite extensive efforts to develop next-generation human Q fever vaccines, only one vaccine, Q-Vax®, is commercially available. Q-Vax® is a phase I whole-cell vaccine, and its licensed use is limited to Australia, presumably due to the potential for a post-vaccination hypersensitivity response. Pre-clinical Q fever vaccine development is a major area of interest, and diverse approaches have been undertaken to develop an improved Q fever vaccine. Following a brief history of Q fever vaccine development, current approaches will be discussed along with future considerations for an improved Q fever vaccine.