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Structure of full-length human anti-PD1 therapeutic IgG4 antibody pembrolizumab
Giovanna Scapin1, Xiaoyu Yang2, Winifred W Prosise1, Mark McCoy1, Paul Reichert1, Jennifer M Johnston1, Ramesh S Kashi3 & Corey Strickland1
ImmunoglobulinG4antibodiesexhibitunusualpropertieswithimportantbiologicalconsequences.Wereportthestructureof thehumanfull-lengthIgG4S228Panti-PD1antibodypembrolizumab,solvedto2.3-resolution.Pembrolizumabisacompact molecule,consistentwiththepresenceofashorthingeregion.TheFcdomainisglycosylatedattheCH2domainonbothchains, butoneCH2domainisrotated120withrespecttotheconformationobservedinallreportedstructurestodate,andits glycanchainfacesthesolvent.Wespeculatethatthisnewconformationisdrivenbytheshorterhinge.Thestructuresuggests arolefortheS228PmutationinpreventingtheIgG4armexchange.Inaddition,thisunusualFcconformationsuggestspossible structuraldiversitybetweenIgGsubclassesandshowsthatuseofisolatedantibodyfragmentscouldmaskpotentiallyimportant interactions,owingtomolecularflexibility.
npg 201 5 Nature America, Inc. All rights reserved.
Human cancers produce antigens that can allow a patients immune system to mount an endogenous antitumor response. However, this response is often ineffective because tumor cells can activate key immune checkpoints that cause localized immune suppression. Cancer immunotherapies using immune-checkpoint inhibitors can be used to block this localized suppression mechanism, thus promoting an effective endogenous immune response1. Pembrolizumab, a recently approved treatment for advanced melanoma, targets the mechanism of immune suppression by blocking the interaction of the immune-checkpoint PD-1 receptor and its ligand PD-L1 (ref. 2). Pembrolizumab belongs to the immunoglobulin (Ig) G4 subclass of human antibodies, which have been shown to exhibit unusual properties. IgG4 antibodies can be functionally monovalent in vivo3, because of the possibility of exchanging half-molecules (one heavy and one light chain) among themselves, a process known as Fab-arm exchange4. They also display affinities for Fc receptors different from those of the other immunoglobulin G subclasses (IgG1, IgG2 and IgG3)5. The biological consequences of these differences influence the selection of the appropriate IgG isotype for antibody therapeutics6. Because IgG4 only weakly induces complement and cell activation, owing to low affinity for C1q and Fc receptors, this isotype has become the preferred class for immunotherapy when recruitment of host effector function is undesirable.
Structures of only four intact IgG1 antibodies (PDB http://www.rcsb.org/pdb/explore/explore.do?structureId=2IG2
Web End =2IG2 , Fab only7; PDB http://www.rcsb.org/pdb/explore/explore.do?structureId=1MCO
Web End =1MCO , with a hinge deletion8; and PDB http://www.rcsb.org/pdb/explore/explore.do?structureId=1IGY
Web End =1IGY 9 and PDB http://www.rcsb.org/pdb/explore/explore.do?structureId=1HZH
Web End =1HZH 10) and one IgG2a antibody (PDB http://www.rcsb.org/pdb/explore/explore.do?structureId=1IGT
Web End =1IGT 11) have been published to date. The best resolution is 2.7 for PDB http://www.rcsb.org/pdb/explore/explore.do?structureId=1HZH
Web End =1HZH 10, but in general these are structures of less than 3- resolution, with poorly detailed
maps and missing portions. In contrast, many structures of individual Fab and Fc domains, including the recently published first structure of an IgG4 Fc domain12, and related receptor complexes are available. The structures of...