The threat of a pandemic spread of highly virulent influenza A viruses currently represents a top global public health problem. Mass vaccination remains the most effective way to combat influenza virus. However, current vaccination strategies face the challenge to meet the demands in a pandemic situation. In a mouse model of severe influenza virus-induced pneumonitis, we observed that prior nasal administration of an attenuated strain of Bordetella pertussis (BPZE1) provided effective and sustained protection against lethal challenge with two different influenza A virus subtypes. In contrast to most cross-protective effects reported so far, the protective window offered upon nasal treatment with BPZE1 lasted up to at least 12 weeks, suggesting a unique mechanism(s) involved in the protection. No significant differences in viral loads were observed between BPZE1-treated and control mice, indicating that the cross-protective mechanism(s) does not directly target the viral particles and/or infected cells. This was further confirmed by the absence of cross-reactive antibodies and T cells in serum transfer and in vitro restimulation experiments, respectively. Instead, compared to infected control mice, BPZE1-treated animals displayed markedly reduced lung inflammation and tissue damage, decreased neutrophil infiltration, and strong suppression of the production of major proinflammatory mediators in their bronchoalveolar fluids (BALFs). Our findings thus indicate that protection against influenza virus-induced severe pneumonitis can be achieved through attenuation of exaggerated cytokine-mediated inflammation. Furthermore, nasal treatment with live attenuated B. pertussis offers a potential alternative to conventional approaches in the fight against one of the most frightening current global public health threats.

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Our study demonstrates the broad anti-inflammatory properties of the attenuated B. pertussis BPZE1 vaccine candidate and supports its development as a promising agent to prevent and/or treat allergic diseases.

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Whereas the great majority of the current vaccines are delivered through the parenteral route, mucosal administration has been increasingly considered for controlling infection and preventing disease. Mucosal vaccination can trigger both humoral and cell-mediated protection, not only at the targeted mucosal surface, but also systemically. In this regard, nasal vaccination has shown great potential. The live attenuated strain of Bordetella pertussis, BPZE1, is particularly attractive and promising as a nasal vaccine delivery vector of heterologous antigen vaccine candidates. BPZE1 was originally developed as a live nasal pertussis vaccine candidate, and is currently undergoing phase I clinical trial in human (http://www.child-innovac.org). Highly adapted to the human respiratory tract and offering several potential protein carriers for presentation of the heterologous antigen vaccine candidates, BPZE1 represents an appealing platform for the development of live recombinant vaccines delivered via the nasal route that would confer simultaneous protection against pertussis and the targeted infectious disease(s).