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.