The human transmembrane protease serine 2 is necessary for the production of Group 2 influenza A virus pseudotypes

The monomer of influenza haemagglutinin (HA) is synthesised as a single polypeptide precursor that during maturation is cleaved by proteases into two active subunits. Other studies have demonstrated that the human Transmembrane Protease Serine 2 (TMPRSS2) can cleave the HA of human seasonal influenza viruses and therefore has an important role in pathogenesis. As a model of this cleavage we have investigated the use of human TMPRSS2 to produce high-titre influenza HA lentiviral pseudotypes from Group 2 influenza viruses. Such pseudotypes represent powerful and safe tools to study viral entry mechanisms and immune responses. Influenza pseudotype particles are obtained by co-transfecting human embryonic kidney HEK293T/17 cells using plasmids coding for the influenza HA, HIV gag-pol and a retroviral vector incorporating firefly luciferase. However, in order to successfully produce Group 2 pseudotypes, it was necessary to co-transfect a plasmid expressing the TMPRSS2 endoprotease to achieve the necessary HA cleavage for infective particle generation. These lentiviral pseudotypes were shown to transduce HEK293T/17 cells with high efficiency. This demonstrates that TMPRSS2 can cleave, in vitro, both the HA of human seasonal influenza and also other Group 2 HA influenza strains. Pseudotypes represent an adjunct tool for predicting pandemic potential of emerging influenza viruses.