The present invention relates to a new method for rescuing an influenza virus and a composition therefor. The method comprises providing a host cell stably integrated with and expressing influenza virus PA, PB1, PB2 and NP genes, and introducing an influenza virus rescue system in which a stop codon is introduced into the PA, PB1, PB2 and NP genes respectively into the host cell to achieve virus rescue. The produced virus particles can be used as a live attenuated influenza vaccine, which is characterized in that, since the genes encoding the related proteins are mutated, it has no replication and proliferation ability in human and normal animal cells, and replication and proliferation can be achieved only in the host cells constructed above and it can fully stimulate the body immunity and effectively protect the body while ensuring the safety.

Provided herein are genetically modified yeast cells capable of producing one or more human milk oligosaccharides. The yeast cells include one or more heterologous nucleic acids that encode enzymes of a human milk oligosaccharide biosynthetic pathway. The yeast cells do not include a heterologous nucleic acid encoding a fucokinase. Also provided are fermentation compositions including the disclosed genetically modified yeast cells, and related methods of producing and recovering human milk oligosaccharides generated by the yeast cells.