Variant antibody identification by peptide mapping

During development of CGP56901, a monoclonal antibody (MAb) specific for a unique epitope on human IgE, the protein A‐purified IgG from one of the candidate production cell lines, showed an additional minor heavy chain (H‐chain) band with a molecular weight slightly lower than that of the principal H‐chain band on SDS‐PAGE. The N‐terminal amino acid sequence of this minor H‐chain species indicated that at least the first 30 amino acids were identical to those of the antibody light‐chain (L‐chain) variable domain. More detailed studies using peptide mapping and amino acid sequencing analysis confirmed a crossover event between the V genes of the antibody. The position is between Arg¹⁰⁸ of the L chain and Ala¹²⁴ of the H chain. This crossover resulted in a variant H chain, which had 16 fewer amino acid residues than the normal CGP56901 H chain. These results show that peptide mapping is a useful “first‐line” analytical tool in the characterization of the quality of the monoclonal antibody. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 62: 485–488, 1999.