BCL2L1 and influenza: To reduce MDCK cells’ tumorigenicity and ensure the safety of influenza vaccine production, a B-cell lymphoma extra-large (Bcl-xL) gene, which plays a pivotal role in apoptosis regulation, was knocked-out in original MDCK cells by CRISPR-Cas9 gene editing technology, so that a homozygous MDCK-Bcl-xL-/- cell strain was acquired and named as BY-02.