title: Epitope mapping of a chimeric CD137 mAb: a necessary step for assessing the biologic relevance of non-human primate models.
abstract: Antibody based manipulation of the CD137 (4-1BB) co-signaling pathway is an attractive option for the treatment of cancer and autoimmune disease. We developed a chimeric anti-human CD137 monoclonal antibody (GG) and characterized its function. As a component of planned preclinical studies, we evaluated the binding of GG to activated peripheral blood mononuclear cells (PBMCs) from cynomolgus macaque and baboon against human. Interestingly, GG only recognized human CD137, while a commercial anti-CD137 mAb (4B4-1), recognized activated PBMCs from both human and non-human primates (NHP). Subsequent analysis revealed that the amino acid sequence of CD137 is largely conserved between primate species ( approximately 95% identical), with the extracellular domain differing by only 9-10 amino acids. Based on these data, we generated mutant constructs in the extracellular domain, replacing NHP with human CD137 sequences, and identified 3 amino acids critical for GG binding. These residues are likely part of a conformational epitope, as a peptide spanning this region is unable to block mAb binding. These data demonstrate that subtle sequence variations of defined co-stimulatory molecules amongst primate species can be employed as a strategy for mapping residues necessary for antibody binding to conformational epitopes.
authors.affiliation: Department of Otorhinolaryngology-Head and Neck Surgery, University of Maryland School of Medicine, 685 West Baltimore Street, HSFI Rm332, Baltimore, MD 21201, USA.
authors.forename: Siaw-Lin
authors.initials: SL
authors.lastname: Chan
authors.forename: Caroline J
authors.initials: CJ
authors.lastname: Voskens
authors.forename: Wei
authors.initials: W
authors.lastname: Lin
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Schindler
authors.forename: Agnes
authors.initials: A
authors.lastname: Azimzadeh
authors.forename: Lai-Xi
authors.initials: LX
authors.lastname: Wang
authors.forename: Rodney J
authors.initials: RJ
authors.lastname: Taylor
authors.forename: Scott E
authors.initials: SE
authors.lastname: Strome
authors.forename: Dan H
authors.initials: DH
authors.lastname: Schulze
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D018604:Epitope Mapping; D000939:Epitopes / Q000737:chemistry; D006031:Glycosylation; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000276:immunology; D023421:Models, Animal; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D011323:Primates / Q000276:immunology*; D011485:Protein Binding; D011994:Recombinant Proteins / Q000276:immunology*; D053261:Tumor Necrosis Factor Receptor Superfamily, Member 9 / Q000737:chemistry / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; D010455:Peptides; D011994:Recombinant Proteins; D053261:Tumor Necrosis Factor Receptor Superfamily, Member 9