N‐terminal or signal peptide sequence engineering prevents truncation of human monoclonal antibody light chains

Monoclonal antibodies (mAbs) contain short N‐terminal signal peptides on each individual polypeptide that comprises the mature antibody, targeting them for export from the cell in which they are produced. The signal peptide is cleaved from each heavy chain (Hc) and light chain (Lc) polypeptide after translocation to the ER and prior to secretion. This process is generally highly efficient, producing a high proportion of correctly cleaved Hc and Lc polypeptides. However, mis‐cleavage of the signal peptide can occur, resulting in truncation or elongation at the N‐terminus of the Hc or Lc. This is undesirable for antibody manufacturing as it can impact efficacy and can result in product heterogeneity. Here, we describe a truncated variant of the Lc that was detected during a routine developability assessment of the recombinant human IgG1 MEDI8490 in Chinese hamster ovary cells. We found that the truncation of the Lc was caused due to the use of the murine Hc signal peptide together with a lambda Lc containing an SYE amino acid motif at the N‐terminus. This truncation was not caused by mis‐processing of the mRNA encoding the Lc and was not dependent on expression platform (transient or stable), the scale of the fed‐batch culture or clonal lineage. We further show that using alternative signal peptides or engineering the Lc SYE N‐terminal motif prevented the truncation and that this strategy will improve Lc homogeneity of other SYE lambda Lc‐containing mAbs. Biotechnol. Bioeng. 2017;114: 1970–1977. © 2017 Wiley Periodicals, Inc.