UNDERSTANDING IMMUNE PROTECTION MECHANISMS OF AN INFLUENZA A VIRUS M2 PEPTIDE VACCINE (52.3)

Abstract

Abstract M2 peptide is under clinical investigation as a target for universal flu vaccines. Studies have shown that Abs induced by M2 vaccines can provide cross-strain protection against flu A virus challenge. Because of the high level expression of M2 protein on the cell surface of flu virus infected cells and minimal neutralizing activities of M2 Abs in vitro, Ab-mediated cytotoxicity by NK cells has been implicated as a protection mechanism by M2 peptide vaccines. However, the studies were mostly based on the observations using M2 immune sera. Thus, to better understand immune protection mechanisms by M2 vaccines, we generated 4 mAbs. Although all mAbs showed little antiviral activity in vitro, adoptive transfer of 2 of 4 mAbs could confer protection against lethal flu A virus challenge in naïve mice. More importantly, the protection was not affected by depletion of NK cells in mice. Further characterizations revealed that the 2 protective mAbs recognize core epitopes located at the N-terminal 10 amino acids of M2 peptide, different from those reported previously, such as clone 14C2. Interestingly, both protective mAbs preferentially reacted with M2 peptides in multimeric form and in parallel orientation, while non protective mAb showed no such substrate preference. Our findings dispute the notion that M2 vaccine-induced protection is medicated by NK cells, and clearly show that the epitopes recognized by protective M2 mAbs are complex and conformational.