Septic bacterial pneumonias are a major cause of death worldwide. Several of the highest priority bioterror concerns, including anthrax, tularemia, and plague, are caused by bacteria that acutely infect the lung. Bacterial resistance to multiple antibiotics is increasingly common. Although vaccines may be our best defense against antibiotic-resistant bacteria, there has been little progress in the development of safe and effective vaccines for pulmonary bacterial pathogens. The Gram-negative bacterium Yersinia pestis causes pneumonic plague, an acutely lethal septic pneumonia. Historic pandemics of plague caused millions of deaths, and the plague bacilli's potential for weaponization sustains an ongoing quest for effective countermeasures. Subunit vaccines have failed, to date, to fully protect nonhuman primates. In mice, they induce the production of Abs that act in concert with type 1 cytokines to deliver high-level protection; however, the Y. pestis Ags recognized by cytokine-producing T cells have yet to be defined. In this study, we report that Y. pestis YopE is a dominant Ag recognized by CD8 T cells in C57BL/6 mice. After vaccinating with live attenuated Y. pestis and challenging intranasally with virulent plague, nearly 20% of pulmonary CD8 T cells recognize this single, highly conserved Ag. Moreover, immunizing mice with a single peptide, YopE 69-77, suffices to confer significant protection from lethal pulmonary challenge. These findings suggest YopE could be a valuable addition to subunit plague vaccines and provide a new animal model in which sensitive, pathogen-specific assays can be used to study CD8 T cell-mediated defense against acutely lethal bacterial infections of the lung.
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