Conclusion
PLBD2 is a host cell protein lipase present in many drug substances, A prior study suggested that PLBD2 was responsible for the degradation of polysorbates3, an enzymatic activity that at high levels, compromises drug product’s quality and stability. In contrast to this notion our data indicate that PLBD2 is largely not involved in the polysorbate degradation. This conclusion is supported by three observations: PLBD2-gene knockout did not reduce lipase activity; PLBD2-depleted mAb samples did not show any reduction or elimination of lipase activity; and lack of correlation between PLBD2 concentration and lipase activity. To reconcile our data and the previously observed PS degradation by purified recombinant PLBD2 we examined the purity of the recombinant PLBD2 enzymes. Several lipases were identified, raising the likelihood that the previously identified lipase activity in the recombinant human PLBD2 material was due to contaminating lipases that co-purified with human PLBD2. Our findings provide an explanation for the lack of correlation between the levels of PLBD2 in drug substances and the rates of polysorbate degradation, which has been observed by several companies in the industry. In addition, our data suggest that the clearance of PLBD2 may not be used as the sole indicator for successful removal of lipase activities in the final therapeutic protein products.
In addition to showing that PLBD2 was largely not responsible for the observed polysorbate degradation, our study offered insights that a low activity but high abundance lipase like PLBD2 could mask other active lipases present at low levels, making them less likely to be identified by common analytical methods. This study provides a novel methodology to identify other problematic host cell protein lipases, which in turn could guide the downstream purification process in developing effective strategies to remove these HCPs that may have significant impact on the therapeutic protein product quality.