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.