M2e-based universal vaccine protects against Influenza A virus challenge and enhances heterosubtypic immunity during subsequent infections

MICHAEL SCHOTSAERT; TINE YSENBAERT; KATRIJN NEYT; LORENA ITATI IBAÑEZ; PIETER BOGAERT; BART LAMBRECHT; WALTER FIERS; XAVIER SAELENS

Brussels

Jornada; Life, Death and Survival of Micro-organisms; 2011

BELGIAN SOCIETY FOR MICROBIOLOGY

Influenza is responsible for circa half a million deaths and three to five million severely ill subjects, yearly. Influenza vaccines are assumed to protect by raising antibodies that bind and potentially neutralize hemagglutinin (HA) and neuraminidase (NA), on the surface of the virion thereby preventing further infection. However, due to sequence drift or even complete shift of the HA and NA genes, the virus is able to escape neutralizing immunity raised by vaccination in a previous season which can lead to an epidemic or pandemic, respectively. It has been shown before in both animals and humans that infection with a seasonal influenza virus correlates with protection against a subsequent infection with a heterotypic or heterologous virus, and that this heterosubtypic immunity (HSI) very often is accompanied by the activation of an antiviral T-cell response in mice and humans.However, vaccination with licensed inactivated vaccines protects against a homologous  infection but also impairs the induction of cellular HSI. We here demonstrate that Matrix 2 protein ectodomain (M2e)-based vaccines not only protect against influenza A virus challenge but also allow the induction of cellular HSI. In a BALB/c mouse model vaccination with a recombinant M2e-virus like particle (M2e-VLP) strongly reduced morbidity and virus replication after a sublethal infection with a seasonal strain (H1N1 or H3N2) and protects from mortality following a lethal challenge with a pandemic strain (H3N3 or the 2009 pandemic H1N1). Vaccination with whole inactivated virus (WIV) also protected mice against the homologous sublethal infection with a seasonal strain but failed to protect against a subsequent lethal heterologous pandemic challenge. Inducible BALT formation was observed by microscopy in naïve and control VLP vaccinated mice but not in WIV and to a lesser extent in M2e-VLP immune mice following their recovery from infection with pandemic virus. Flow cytometric quantification of GL7+ B-cells confirms that iBALT was present in M2e-VLP  immune mice, be it to a lower extent as in PBS- or VLP-vaccinated mice, but more than in WIV-vaccinated mice. Vaccination with M2e-VLP, similar to naïve but not WIV-vaccinated mice, followed by a sublethal infection with seasonal virus resulted in the induction of a qualitative and functional cellular immune response directed against HA and NP-derived CTL epitopes as demonstrated by intracellular cytokine staining, pentamer staining and in vivo target cell killing. We hereby showed that, contrary to vaccination with WIV, vaccination with M2e-VLP universal vaccine does not only protect against challenge with viruses from different subtypes, but also permits the induction of cross-reactive cellular immunity induced by encounters with influenza virus.