A non-VH1-69 heterosubtypic neutralizing human monoclonal antibody protects mice against H1N1 and H5N1 viruses

Influenza viruses are among the most important human pathogens and are responsible for annual epidemics and sporadic,potentially devastating pandemics. The humoral immune response plays an important role in the defense against theseviruses, providing protection mainly by producing antibodies directed against the hemagglutinin (HA) glycoprotein.However, their high genetic variability allows the virus to evade the host immune response and the potential protectionoffered by seasonal vaccines. The emergence of resistance to antiviral drugs in recent years further limits the optionsavailable for the control of influenza. The development of alternative strategies for influenza prophylaxis and therapy istherefore urgently needed. In this study, we describe a human monoclonal antibody (PN-SIA49) that recognizes a highlyconserved epitope located on the stem region of the HA and able to neutralize a broad spectrum of influenza virusesbelonging to different subtypes (H1, H2 and H5). Furthermore, we describe its protective activity in mice after lethalchallenge with H1N1 and H5N1 viruses suggesting a potential application in the treatment of influenza virus infections.