Lysosome-targeting live attenuated influenza vaccines elicit robust and broad immunity in mice

The lysosome is a cell’s endogenous machinery responsible for degrading proteins. Here we describe two lysosome-targeting live attenuated vaccine approaches, LYTAR 1.0 and LYTAR 2.0, by harnessing the lysosome to conditionally degrade viral proteins of influenza virus. LYTAR 1.0 incorporates a conditionally removable lysosome-targeting motif at the N- or C-terminus of viral proteins. LYTAR 2.0 allows flexible placement of lysosome-targeting motifs at internal or terminal sites of viral proteins. The resulting lysosome-targeting vaccine strains are attenuated by lysosome-mediated viral protein degradation in conventional cells, while maintaining replication efficiencies comparable to the wild-type virus in producer cell lines. In mouse models, these vaccine candidates are attenuated, induce strong and broad adaptive immune responses, and provide cross-reactive protection against H1N1 and H3N2 influenza viral challenges. This study establishes a lysosome-targeting vaccine platform for developing safe and effective live attenuated vaccines. Host cell protein degradation machinery including the lysosome is involved in the processing and degradation of protein antigens. Here the authors develop lysosomal targeting vaccine approaches and test these in murine models of influenza infection.