Vanderlaan, M., Sandoval,W., Liu, P., et al., Hamster phospholipase B-like 2 (PLBL2).  A host-cell protein impurity in therapeutic monoclonal antibody derived from Chinese hamster ovary cells, Bioprocess International April, 2015, pps 18-29.   

I have found an article which deserves some comment.  A recent article from workers at Genentech described the identification of an impurity which copurified with a monoclonal antibody obtained from CHO (Chinese Hamster Ovary) cells.  Specifically a hamster phospholipase B-like 2 protein was identified as an impurity in therapeutic monoclonal antibody produced in CHO cells.  The works starts with thoughtful interpretation of ELISA assays for CHO protein (CHOP) and ends with the identification of the protein impurity by mass spectrometry sequencing of tryptic peptides obtained from gel electrophoresis.  Confirmation of identification was obtained from reaction with a polyclonal antibody to recombinant hamster phospholipase B-like 2.

The authors do state that this impurity was not found in current Genentech commercial products. The material was found in several products in development.  Furthermore, the purification process was modified to separate the impurity from the active pharmaceutical ingredient.

The reader is referred to below articles for background on host-cell protein issues in recombinant therapeutics

1.  Xue, L., Johnson, R., and Gorovits, B., Prevalence and isotopic complexity of the anti-Chinese hamster ovary host cell protein antibodies in normal human serum, AAPS J. 12, 98-106, 2010.
2.  Eon-Duval, A., Broly, H., and Gleixner, R., Quality attributes of recombinant therapeutic proteins: An assessment of impact on safety and efficacy as part of a quality by design development approach, Biotechnology Progress 28, 608-622, 2012.
3.  Zhu-Shimoni, J., Yu, C., Nishihara, J., et al., Host cell protein testing by ELISAs and the use of orthogonal methods, Biotechnol.Bioengineer. 111, 236702378, 2014.