TPST Gene Knock-Out Eliminates Tyrosine Sulfation on a Recombinant Antibody Produced in CHO Cells

Tyrosine sulfation is a post-translational modification that has been reported to occur infrequently on recombinant monoclonal antibodies (mAbs). We recently demonstrated that tyrosine sulfation occurred on a bispecific antibody (bsAb) produced in Chinese hamster ovary (CHO) cells, using a multi-enzymatic approach in combination with intact mass and peptide-based mass spectrometry analysis supplemented with the use of synthetic peptides. Tyrosine sulfation needs to be controlled during the manufacturing process due to potential undesired effects, such as impact on potency and immunogenicity. Here, we report that tyrosine sulfation was not significantly inhibited by the addition of chemical inhibitors, such as sodium chlorate. Individual knockout and double knockout (DKO) of two key genes in the tyrosine sulfation pathway were carried out sequentially. Tyrosyl protein sulfotransferase 1/2 (TPST1/2) DKO by CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein-9 nuclease)-mediated gene editing eliminated tyrosine sulfation while maintaining cell growth, antibody production, and overall product quality.