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Anti-PD1 'SHR-1210' aberrantly targets pro-angiogenic receptors and this polyspecificity can be ablated by paratope
William J J Finlay1, James E Coleman1, Jonathan S Edwards1
1a UltraHuman Limited, Codebase , Edinburgh , UK.
Abstract:
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.
Insights
Anti-programmed cell death 1 (PD1) antibody SHR-1210 caused unique toxicities due to off-target binding to vascular endothelial growth factor receptor 2 (VEGFR2). Optimizing complementarity-determining regions (CDRs) enhanced specificity and potency, eliminating side effects.
Area of Science:
- Immunology and Cancer Therapeutics
- Protein Engineering and Antibody Design
Background:
- Monoclonal anti-programmed cell death 1 (PD1) antibodies are effective cancer treatments.
- Unique toxicities, like capillary hemangioma caused by SHR-1210, are not fully understood.
- Off-target interactions of therapeutic antibodies may drive idiosyncratic side effects.
Purpose of the Study:
- To identify the cause of SHR-1210's unique toxicity, capillary hemangioma.
- To investigate non-specific binding interactions driving angiogenesis.
- To engineer a more specific and potent anti-PD1 antibody.
Main Methods:
- Human receptor proteome screening to identify off-target binding.
- Biochemical assays to assess binding affinity and functional activity (agonism).
- Combinatorial complementarity-determining region (CDR) mutagenesis for antibody engineering.
- Assessment of binding specificity, potency, and deimmunization of engineered antibodies.
Main Results:
- SHR-1210 exhibited selective, low-affinity binding to vascular endothelial growth factor receptor 2 (VEGFR2), frizzled class receptor 5, and UL16 binding protein 2 (ULBP2).
- SHR-1210 acted as a potent agonist of VEGFR2, potentially causing hemangioma via vascular endothelial cell activation.
- Off-target binding and VEGFR2 agonism originated from the murine progenitor antibody's CDRs and persisted after humanization.
- Molecular remodeling via CDR mutagenesis successfully ablated off-target binding and VEGFR2 agonism, yielding highly PD1-specific antibodies.
- Engineered antibodies showed normalized binding affinity to PD1, increased potency in PD1/PD-L1 blockade, and were deimmunized.
Conclusions:
- Highly specific off-target binding is an under-appreciated factor in therapeutic antibody development.
- Paratope refinement, particularly in light chain CDRs, can effectively ameliorate unwanted binding properties.
- Receptor proteome screening combined with CDR optimization can generate superior therapeutic antibodies with enhanced potency and specificity.