Cross-protection of Lactococcus lactis-displayed HA2 subunit against homologous and heterologous influenza A viruses in mice.

Current influenza vaccines provide strain-specific protection against homologous subtypes and need to be updated annually. Therefore, it is essential to develop a universal vaccine that would induce broadly cross-protective immunity against homologous and heterologous influenza A viruses. The highly conserved HA2 subunit is a promising candidate for developing a universal influenza vaccine. Here, we hypothesized that the HA2 subunit could be displayed on the surface of Lactococcus lactis (L. lactis), using Spax as an anchor protein (L. lactis/pNZ8008-Spax-HA2) and that L. lactis/pNZ8008-Spax-HA2 would have immunogenicity by oral administration without the use of adjuvant in the mouse model. To address this hypothesis, we show that oral vaccination of mice with L. lactis/pNZ8008-Spax-HA2 elicited significant humoral and mucosal immune responses. Importantly, L. lactis/pNZ8008-Spax-HA2 provided 100% protection against homologous H5N1 or heterologous H1N1 virus challenge. These results suggest that an HA2 subunit presented on the surface of L. lactis is an effective universal vaccine candidate against influenza A viruses in the poultry industry and in humans.