Anti-PD1 'SHR-1210' aberrantly targets pro-angiogenic receptors and this polyspecificity can be ablated by paratope refinement

• Published in: mAbs 2019-01, Vol.11 (1), p.26-44
• Main Authors: Finlay, William J J, Coleman, James E, Edwards, Jonathan S, Johnson, Kevin S
• Format: Article
• Language: English
• Subjects: Animals; Antibodies, Monoclonal, Humanized - genetics; Antibodies, Monoclonal, Humanized - immunology; Antibody Specificity - genetics; Antibody Specificity - immunology; Binding Sites, Antibody - genetics; Binding Sites, Antibody - immunology; Complementarity Determining Regions - genetics; Complementarity Determining Regions - immunology; Humans; Macaca fascicularis; Mice; Programmed Cell Death 1 Receptor - antagonists & inhibitors; Protein Engineering - methods; Vascular Endothelial Growth Factor Receptor-2 - agonists
• ISSN: 1942-0862; 1942-0870
• DOI: 10.1080/19420862.2018.1550321

Monoclonal anti-programmed cell death 1 (PD1) antibodies are successful cancer therapeutics, but it is not well understood why individual antibodies should have idiosyncratic side-effects. As the humanized antibody SHR-1210 causes capillary hemangioma in patients, a unique toxicity amongst anti-PD1 antibodies, we performed human receptor proteome screening to identify nonspecific interactions that might drive angiogenesis. This screen identified that SHR-1210 mediated aberrant, but highly selective, low affinity binding to human receptors such as vascular endothelial growth factor receptor 2 (VEGFR2), frizzled class receptor 5 and UL16 binding protein 2 (ULBP2). SHR-1210 was found to be a potent agonist of human VEGFR2, which may thereby drive hemangioma development via vascular endothelial cell activation. The v-domains of SHR-1210's progenitor murine monoclonal antibody 'Mab005' also exhibited off-target binding and agonism of VEGFR2, proving that the polyspecificity was mediated by the original mouse complementarity-determining regions (CDRs), and had survived the humanization process. Molecular remodelling of SHR-1210 by combinatorial CDR mutagenesis led to deimmunization, normalization of binding affinity to human and cynomolgus PD1, and increased potency in PD1/PD-L1 blockade. Importantly, CDR optimization also ablated all off-target binding, rendering the resulting antibodies fully PD1-specific. As the majority of changes to the paratope were found in the light chain CDRs, the germlining of this domain drove the ablation of off-target binding. The combination of receptor proteome screening and optimization of the antibody binding interface therefore succeeded in generating novel, higher-potency, specificity-enhanced therapeutic IgGs from a single, clinically sub-optimal progenitor. This study showed that highly-specific off-target binding events might be an under-appreciated phenomenon in therapeutic antibody development, but that these unwanted properties can be fully ameliorated by paratope refinement.