ASSESSING GENETIC-HETEROGENEITY IN PRODUCTION CELL-LINES - DETECTION BY PEPTIDE-MAPPING OF A LOW-LEVEL TYR TO GLN SEQUENCE VARIANT IN A RECOMBINANT ANTIBODY

A recombinant antibody directed against the human epidermal growth fac tor receptor-2 extracellular domain was subjected to detailed structur al characterization. Heterogeneity in the heavy chain was demonstrated by recovery of two forms of a tryptic peptide, with either glutamine or the expected tyrosine at residue 376. Subsequent experiments indica ted that the Y376Q variant developed during transfection of the antibo dy heavy and light chain genes into Chinese hamster ovary cells. Level s of the Y376Q variant (range: 27% to 1 %) in the purified antibody we re inversely proportional to cell age. The established cell line was s ubcloned and found to be heterogeneous by polymerase chain reaction an alysis of cell extracts and protein analysis of the purified antibody. Ten percent of subclones produced high levels of the Y376Q variant wh ile 90% of the subclones produced antibody with only the expected heav y chain sequence. This report demonstrates the utility of peptide mapp ing as a sensitive tool for assessing genetic heterogeneity of recombi nant cell lines.