Cross-protective immunity of the haemagglutinin stalk domain presented on the surface of Lactococcus lactis against divergent influenza viruses in mice.

Most of the current approaches to influenza vaccine design focus on antibodies against influenza (HA). However, these influenza vaccines typically provide strain-specific protection against mostly homologous subtypes. There is an urgent need to develop a universal vaccine that confers cross-protection against influenza viruses. Of note, the HA stalk domain (HAsd) is a promising target for such an influenza vaccine. In this study, we generated recombinant Lactococcus lactis ( L. lactis )/pNZ8150-phosphatidylglycerophosphate synthetase A (pgsA)-HAsd, in which pgsA was used as an anchor protein, and investigated the immunogenicity of HAsd in a mouse model by oral administration without the use of a mucosal adjuvant. Compared with L. lactis /pNZ8150-pgsA, mice were orally vaccinated with L. lactis /pNZ8150-pgsA-HAsd and then produced strong humoral and mucosal immune responses. Importantly, L. lactis /pNZ8150-pgsA-HAsd provided cross-protection against H5N1, H3N2 and H1N1 virus infections. Our data support the hypothesis that HAsd presented on the surface of L. lactis can provide cross-protective immunity against divergent influenza A viruses. Taken together, these findings suggest that L. lactis /pNZ8150-pgsA-HAsd can be considered an alternative approach to developing a novel universal vaccine during an influenza A pandemic. Abbreviations: HA, HAsd, HA stalk domain; L. lactis, Lactococcus lactis ; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis; IFA, immunofluorescence assay; PBS, phosphate-buffered saline; pgsA, phosphatidylglycerophosphate synthetase A; SPF, specific pathogen-free; CFU, colony-forming unit; BSL-3, biosafety level-3 laboratory; TCID ₅₀ , 50% tissue culture infective dose; ELISA, enzyme-linked immunosorbent assay; OD, optical density; LTB, liable enterotoxin B subunit; CTB, cholera toxin B subunit.