Soluble antigens derived from <i>Coxiella burnetii</i> elicit protective immunity in three animal models without inducing hypersensitivity.

Abstract

Q fever is caused by the intracellular bacterium <i>Coxiella burnetii</i>, for which there is no approved vaccine in the United States. A formalin-inactivated whole-cell vaccine (WCV) from virulent <i>C. burnetii</i> NMI provides single-dose long-lived protection, but concerns remain over vaccine reactogenicity. We therefore sought an alternate approach by purifying native <i>C. burnetii</i> antigens from the clonally derived avirulent NMII strain. A soluble bacterial extract, termed Sol II, elicits high-titer, high-avidity antibodies and induces a CD4 T cell response that confers protection in naive mice. In addition, Sol II protects against pulmonary <i>C. burnetii</i> challenge in three animal models without inducing hypersensitivity. An NMI-derived extract, Sol I, enhances protection further and outperforms the WCV gold standard. Collectively, these data represent a promising approach to design highly effective, non-reactogenic Q fever vaccines.