LitCovid-sample-sentences  

PMC:7228307 / 2471-62115 JSONTXT 27 Projects

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Id Subject Object Predicate Lexical cue
T17 0-12 Sentence denotes Introduction
T18 13-148 Sentence denotes The regulatory approval of the first therapeutic monoclonal antibodies (mAbs) in the 1980s ushered in the modern era of immune therapy.
T19 149-274 Sentence denotes Since then, mAbs have become one of the most clinically successful therapeutic modalities across a diverse array of diseases.
T20 275-728 Sentence denotes They have revolutionized the treatment of chronic inflammatory diseases and of some cancers including otherwise incurable malignancies.1 They are commercially important and in 2017, five mAbs collectively grossed $45.6 billion in sales, placing them in the top ten drugs globally.2 MAb development is expanding rapidly with over 100 mAbs approved for clinical use or in late‐stage clinical trials and over 600 in various stages of clinical development.1
T21 729-1103 Sentence denotes The therapeutic actions of mAbs can take many forms—neutralization of the target such as cytokines in autoimmune disease, clearance of the target such as virus in infection or immunoglobulin (Ig)E in allergy, induction of innate effector cell activation that leads to target destruction by direct killing or the induction of apoptosis and the induction of adaptive immunity.
T22 1104-1496 Sentence denotes Most therapeutic mAbs are IgG in origin and the heavy‐chain subclass determines many of their biological properties including their long plasma half‐life3; complement activation, which is important in the action of some cytotoxic mAbs4, 5, 6 and importantly engagement by their fragment crystallizable (Fc) region with specific cell surface receptors, called FcγR, the subject of this review.
T23 1497-1830 Sentence denotes In normal homeostatic immunity, there is a balance between IgG immune complex activation of proinflammatory responses through the activating‐type FcγRs—which leads to the destruction of opsonized pathogens—and of the modulation of these destructive effector responses by the inhibitory‐type FcγR, thereby avoiding injury to the host.
T24 1831-2019 Sentence denotes Thus, therapeutic mAbs powerfully exploit these opposing activities, making them versatile drugs whose therapeutic potency can be improved by specific engineering of Fc–FcγR interactions.7
T25 2020-2183 Sentence denotes Many therapeutic mAbs depend, to varying degrees, on FcγR function (Figure 1, Table 1) for their mechanism of action (MOA) and/or their pharmacokinetic properties.
T26 2184-2436 Sentence denotes For some mAbs interaction with FcγR is central to their MOA, such as the destruction of a target cell by antibody‐dependent cell‐mediated cytotoxicity (ADCC; Figure 1a) or antibody‐dependent cell‐mediated phagocytosis (phagocytosis or ADCP; Figure 1b).
T27 2437-2655 Sentence denotes This also includes mAbs that may harness the inhibitory action of FcγRIIb to modulate the proinflammatory responses of immunoreceptor tyrosine activation motif (ITAM)‐dependent receptor signaling complexes (Figure 1c).
T28 2656-2982 Sentence denotes For other mAbs, FcγR may play a secondary role, such as the removal or “sweeping” of all immune complexes formed by cytokine or virus‐specific neutralizing antibodies or of opsonized fragments of lysed target cells which in antigen‐presenting cells may also feed the antigen into the antigen‐presentation pathways (Figure 1d).
T29 2983-3275 Sentence denotes In addition, FcγRs, particularly FcγRIIb (Figure 1e), are also key participants in the MOA of immune‐stimulating agonistic mAbs or apoptotic mAbs by acting as a scaffold for the additional cross‐linking of mAbs already bound to a cellular target, thereby inducing a signal in the target cell.
T30 3276-3601 Sentence denotes Figure 1 Graphical representation of the FcγR effector functions. (a) Natural killer cell antibody‐dependent cell‐mediated cytotoxicity via FcγRIIIa. (b) Antibody‐dependent cell‐mediated phagocytosis, and/or trogocytosis of large immune complexes, by professional phagocytes via activating FcγR such as FcγRIIIa and FcγRIIa.
T31 3602-3816 Sentence denotes Biological sequelae include the destruction of the ingested complexes which may also feed antigen into antigen‐presentation pathways of antigen‐presenting cells (APCs). (c) Inhibition of cell activation by FcγRIIb.
T32 3817-4117 Sentence denotes The immunoreceptor tyrosine activation motif (ITAM)‐mediated signaling of B‐cell antigen receptors (left) or of activating FcγR (right) on innate immune cells such as macrophages and basophils is inhibited by IgG Fc‐mediated co‐cross‐linking of these activating receptors with the inhibitory FcγRIIb.
T33 4118-4529 Sentence denotes This leads to phosphorylation of the FcγRIIb immunoreceptor tyrosine‐based inhibitory motif (ITIM) and consequently recruits the phosphatases that modulate the ITAM‐driven signaling responses leading to diminished cell responses. (d) Sweeping or internalization of small immune complexes leading to their removal and, in APC, to enhanced immune responses. (e) Scaffolding in which the FcγRs play a passive role.
T34 4530-4848 Sentence denotes Typically involving FcγRIIb, no signal is generated in the effector cell but “super‐cross‐linking” of the opsonizing antibody by the FcγR on one cell generates a signal in the conjugated target cell, for example, induction of apoptosis or activation in agonistic expansion of cells and/or their secretion of cytokines.
T35 4849-4913 Sentence denotes In extreme cases, this leads to life‐threatening cytokine storm.
T36 4914-5041 Sentence denotes ADCC, antibody‐dependent cell‐mediated cytotoxicity; Ag, antigen; BCR, B‐cell receptor; Ig, immunoglobulin; NK, natural killer.
T37 5042-5119 Sentence denotes Table 1 FcγR responses relevant to therapeutic monoclonal antibodies (mAbs).
T38 5120-5200 Sentence denotes FcγR‐mediated mechanism of action Effector responses Action Dominant receptor
T39 5201-5299 Sentence denotes Activation Antibody‐dependent cell‐mediated cytotoxicity Direct killing of target cell FcγRIIIa
T40 5300-5416 Sentence denotes Antibody‐dependent cell‐mediated phagocytosis, trogocytosis Direct killing of target cell FcγRIIIa, FcγRIIa, FcγRI
T41 5417-5503 Sentence denotes Antigen presentation Vaccine‐like immunity post‐mAb therapy FcγRIIa, FcγRI, FcγRIIIa
T42 5504-5688 Sentence denotes Inhibition Reduce B‐cell proliferation or innate cell activation by antibody complexes Inhibition of ITAM cell activation (i.e. BCR) or activating‐type FcR (i.e. FcγR, FcεRI, FcαRI).
T43 5689-5769 Sentence denotes Note that the FcγRIIb must be co‐cross‐linked with the ITAM activating receptor.
T44 5771-5778 Sentence denotes FcγRIIb
T45 5779-5850 Sentence denotes Sweeping Internalization Removal of small immune complexes FcγRIIb a
T46 5851-6045 Sentence denotes Scaffolding Target agonism or apoptosis Passive “super‐cross‐linking” of mAb on opsonized target cell, for example, CD40, CD28, CD20, by FcγR on an adjacent cell FcγRIIb; also FcγRIIa, FcγRI?
T47 6046-6115 Sentence denotes BCR, B‐cell receptor; ITAM, immunoreceptor tyrosine activation motif.
T48 6116-6179 Sentence denotes a Activating FcγR can also contribute to removal of complexes.
T49 6180-6327 Sentence denotes John Wiley & Sons, Ltd This article is being made freely available through PubMed Central as part of the COVID-19 public health emergency response.
T50 6328-6510 Sentence denotes It can be used for unrestricted research re-use and analysis in any form or by any means with acknowledgement of the original source, for the duration of the public health emergency.
T51 6511-6998 Sentence denotes This review focuses on the cell‐based effector functions that arise from the interaction of IgG with the classical human leukocyte FcγR.7 Although beyond the scope of this review, it should be noted that the IgG‐Fc portion dictates other aspects of an antibody’s biology, including its serum half‐life mediated by the neonatal FcR (FcRn), 3 the activation of complement C1,8 antiviral protection via the intracellular receptor TRIM219 and interactions with the Fc receptor‐like family.10
T52 7000-7029 Sentence denotes Human FcγR General Properties
T53 7030-7397 Sentence denotes The human leukocyte receptors fall into two functional groups, namely, proinflammatory, activating‐type receptors (FcγRI, FcγRIIa, FcγRIIc, FcγRIIIa and FcγRIIIb, which are also known as CD64, CD32a, CD32c, CD16a and CD16b, respectively) and the anti‐inflammatory, inhibitory‐receptor group (FcγRIIb also called CD32b) which was the first immune checkpoint described.
T54 7398-7505 Sentence denotes These FcγRs are high‐avidity sensors of immune complexes which initiate, and then modulate, cell responses.
T55 7506-7714 Sentence denotes In the context of normal immune physiology, opsonized target molecules can engage various FcγRs and induce a spectrum of effector responses which can be harnessed by many therapeutic mAbs (Figure 1, Table 1).
T56 7715-7862 Sentence denotes These responses are not mutually exclusive and one therapeutic mAb may initiate various responses via different FcγRs and via different cell types.
T57 7863-8118 Sentence denotes Understanding the importance of cell‐based effector functions in the MOA of therapeutic mAbs requires an appreciation of FcγR biology (Tables 1, 2, 3) which also underpins future efforts to tailor new mAbs for the exploitation‐specific effector responses.
T58 8119-8261 Sentence denotes In this review, we address only key aspects of the extensive knowledge of the human leukocyte FcγR family as it relates to effector functions.
T59 8262-8762 Sentence denotes A number of other reviews more comprehensively explore FcγR biology physiology, biochemistry, genetics and structure.7, 11, 12, 13, 14 Notwithstanding the recognized differences between the immunobiology of human FcγR and of rodents or nonhuman primates, animal models of FcR effector function in vivo have helped shape the strategies for the development of current therapeutic mAbs and are well reviewed.12, 15 Furthermore, humanized FcγR models will provide even greater insights into the future.16
T60 8763-8791 Sentence denotes Table 2 Properties of FcγR.
T61 8792-8846 Sentence denotes Receptor Affinity IgG specificity Cell distribution
T62 8847-8983 Sentence denotes FcγRI High IgG1, IgG3, IgG4 Induced by interferon‐γ on monocytes, neutrophils, macrophages, dendritic cell subpopulations; mast cells
T63 8984-9130 Sentence denotes FcγRIIa Low IgG1, IgG3, but IgG2 binding limited to the FcγRIIa‐H131 form, ~70% people) All leukocytes and platelets except T and B lymphocytes
T64 9131-9173 Sentence denotes FcγRIIc a Low IgG1, IgG3, IgG4 NK cells
T65 9174-9200 Sentence denotes FcγRIIIa Low IgG1, IgG3.
T66 9202-9320 Sentence denotes NK cells, macrophages, subpopulation of circulating monocytes, myeloid dendritic cells, neutrophils at very low levels
T67 9321-9367 Sentence denotes Binding avidity reduced by Phe at position 158
T68 9368-9406 Sentence denotes FcγRIIIb Low IgG1, IgG3 Neutrophils
T69 9407-9514 Sentence denotes FcγRIIb Low IgG1, IgG3, IgG4 B lymphocytes, some monocytes (can be upregulated); basophils; eosinophils?
T70 9515-9626 Sentence denotes Plasmacytoid and myeloid dendritic cells; NK cells only of individuals with FcγRIIIb gene copy number variation
T71 9627-9690 Sentence denotes Airway smooth muscle, LSEC, placenta, follicular dendritic cell
T72 9691-9740 Sentence denotes Ig, immunoglobulin; NK cell, natural killer cell.
T73 9741-9771 Sentence denotes a Expressed in 20% of people.
T74 9772-9919 Sentence denotes John Wiley & Sons, Ltd This article is being made freely available through PubMed Central as part of the COVID-19 public health emergency response.
T75 9920-10102 Sentence denotes It can be used for unrestricted research re-use and analysis in any form or by any means with acknowledgement of the original source, for the duration of the public health emergency.
T76 10103-10157 Sentence denotes Table 3 Unique features of IgG subclass Fc and hinge.
T77 10158-10258 Sentence denotes IgG subclass FcγR specificity Light‐chain attachment Hinge characteristics Fc stability Comment
T78 10259-10369 Sentence denotes IgG1 All FcγR Upper hinge Light‐chain attachment Stable Fc is >100× times more stable than IgG4 and IgG2.
T79 10370-10387 Sentence denotes Stable core hinge
T80 10388-10524 Sentence denotes IgG2 FcγRIIa His131 CH1 of Fab and/or upper hinge Stable core hinge with additional inter H‐chain disulfide bonds in the upper hinge.
T81 10526-10607 Sentence denotes Unstable CH3:CH3 Alternative light‐chain attachment creates distinct conformers.
T82 10608-10739 Sentence denotes Unlike IgG4, the CH3:CH3 instability does not lead to half‐molecule exchange as a result of stable core and upper hinge disulfides.
T83 10740-10901 Sentence denotes IgG4 FcγRI, FcγRIIb, FcγRIIc CH1 of Fab Labile core hinge Unstable CH3:CH3 Combined instability of core hinge and CH3:CH3 permits half‐IgG molecule exchange
T84 10902-10921 Sentence denotes Ig, immunoglobulin.
T85 10922-11069 Sentence denotes John Wiley & Sons, Ltd This article is being made freely available through PubMed Central as part of the COVID-19 public health emergency response.
T86 11070-11252 Sentence denotes It can be used for unrestricted research re-use and analysis in any form or by any means with acknowledgement of the original source, for the duration of the public health emergency.
T87 11254-11290 Sentence denotes FcγR expression on hemopoietic cells
T88 11291-11555 Sentence denotes The tissue distribution of the human leukocyte FcγR is well documented and reviewed comprehensively elsewhere.7, 11, 17 In the context of effector functions harnessed by therapeutic mAbs, several aspects of the cellular distribution (Table 2) should be emphasized.
T89 11556-11701 Sentence denotes FcγR expression profiles differ between cell lineages but almost all mature human leukocytes, and platelets, express at least one FcγR (Table 2).
T90 11702-12143 Sentence denotes It should also be appreciated that the cellular expression levels and receptor diversity as will be described later is also influenced by the activation state of the cells, anatomical location and the cytokine environment which modulates FcγR expression, particularly for FcγRI and FcγRIIb.18 For example, resting monocyte subpopulations may express only FcγRIIa but activated macrophages express FcγRI, FcγRIIa and FcγRIIIa and/or FcγRIIb.7
T91 12144-12230 Sentence denotes Thus, specific characteristics of leukocyte FcγR expression are summarized as follows:
T92 12231-12412 Sentence denotes FcγRI is not usually expressed until induced by cytokines such as interferon‐γ on monocytes, neutrophils, macrophages, microglial cells in the brain, dendritic cells and mast cells.
T93 12413-12698 Sentence denotes The sensitivity of FcγRI to interferon‐γ suggests that its in vivo activity is closely tied to immune activation events, and mouse studies have suggested that it has a critical role early in immune responses.19, 20 Its role in the MOA of antibodies may vary with anatomical location.21
T94 12699-12824 Sentence denotes FcγRIIa is expressed only in primates and shows the broadest expression of all FcγRs, being present on all innate leukocytes.
T95 12825-12967 Sentence denotes It is also present on platelets but its role in effector functions is not established but it is important in certain immune thrombocytopenias.
T96 12968-13046 Sentence denotes A polymorphic form of this receptor is the only human receptor for human IgG2.
T97 13047-13221 Sentence denotes This, together with its limited species expression and unique ITAM‐containing cytoplasmic tail (reviewed by Anania et al. 11), suggests a unique function in human leukocytes.
T98 13222-13468 Sentence denotes Interestingly, polymorphism of the receptor is associated with systemic lupus erythematosus and resistance to Gram‐negative organisms.11 A rare, hyper‐responsive form is a risk factor for neutrophil‐driven anaphylaxis in Ig replacement therapy.22
T99 13469-13908 Sentence denotes FcγRIIc is an activating FcγR whose expression is regulated single nucleotide polymorphism that permits expression in approximately 20% of humans and in whom it is present at low levels on natural killer (NK) and B cells.11 It has arisen by gene duplication/recombination resulting in an extracellular region  derived from  FcγRIIb, which binds IgG4, and with an ITAM‐containing cytoplasmic tail related to the activating receptor FcγRIIa.
T100 13909-14027 Sentence denotes Thus FcγRIIc provides IgG4 with an activation receptor pathway and confers a new biology of IgG4 in these individuals.
T101 14028-14160 Sentence denotes Its low frequency in the population may also confound in vivo mAb clinical testing or use, but as yet there is no evidence for this.
T102 14161-14235 Sentence denotes FcγRIII forms are two highly related gene products, FcγRIIIa and FcγRIIIb.
T103 14236-14328 Sentence denotes The FcγRIIIa is expressed on NK cells and professional phagocytes, particularly macrophages.
T104 14329-14576 Sentence denotes It is only recently apparent that FcγRIIIa is expressed on neutrophils, albeit at low levels, but plays a role in their function.23 FcγRIIIb is unique to humans and unlike other FcγRs it is attached to cell membrane via a glycophosphatidyl anchor.
T105 14577-14718 Sentence denotes It is expressed, predominantly and abundantly, on human neutrophils.7 Its effector function depends in part on its coexpression with FcγRIIa.
T106 14719-14832 Sentence denotes The lack of FcγRIIIb on macaque neutrophils appears to be compensated for by an increase in FcγRIIa expression.15
T107 14833-14900 Sentence denotes FcγRIIbs are the inhibitory‐type FcγR and arise from a single gene.
T108 14901-14982 Sentence denotes They lack intrinsic proinflammatory signaling and are instead immune checkpoints.
T109 14983-15113 Sentence denotes They provide feedback regulation by antibodies, in the form of immune complexes, to inhibit B‐cell activation by specific antigen.
T110 15114-15178 Sentence denotes They also control activating‐type FcγR function on innate cells.
T111 15179-15272 Sentence denotes Two major splice variant forms of FcγRIIb exist with differential tissue expression profiles.
T112 15273-15457 Sentence denotes FcγRIIb1 preferentially expressed on B lymphocytes contains a 20‐amino acid cytoplasmic insertion necessary for membrane retention and cocapping with the B‐cell antigen receptor (BCR).
T113 15458-15633 Sentence denotes FcγRIIb2 is the predominant inhibitory receptor found on basophils and neutrophils, as well as on subpopulations of mast cells, dendritic cells and some monocytes/macrophages.
T114 15634-15850 Sentence denotes FcγRIIb2 lacks the cytoplasmic insertion of FcγRIIb1 and consequently can internalize rapidly including with the activating FcR when they are co‐cross‐linked.11 It is not clear which form is present on human T cells.
T115 15851-15978 Sentence denotes One additional comment on tissue distribution is that FcγR expression on T cells has been difficult to establish unequivocally.
T116 15979-16060 Sentence denotes However, there is increasing evidence that T‐lymphocyte populations express FcγR.
T117 16061-16272 Sentence denotes Some γδ T cells express FcγRIIIa and αβ T cells reportedly express FcγRIIa, FcγRIIb or FcγRIIIa but the significance with respect to effector function mediated by antibody is presently unclear.24, 25, 26, 27, 28
T118 16274-16308 Sentence denotes Expression on nonhemopoietic cells
T119 16309-16532 Sentence denotes The immunobiology of FcγR is studied and understood almost exclusively in the context of hematopoietic cell function but relatively recent investigations have identified and explored FcγR expression on nonhemopoietic cells.
T120 16533-16637 Sentence denotes These studies suggest important roles in normal immune function and in the MOA of some therapeutic mAbs.
T121 16638-16796 Sentence denotes The most extensively characterized receptor expression is FcγRIIb which is expressed on follicular dendritic cell, airway smooth muscle and liver endothelium.
T122 16797-17187 Sentence denotes Its abundant expression on liver sinusoidal endothelial cells (LSECs) is estimated to represent the majority of in vivo FcγRIIb expression.17, 29, 30, 31 As FcγRIIb lacks intrinsic proinflammatory signaling function, its role on these nonhemopoietic cells involves immune complex handling without the danger of, or the need for, induction of local tissue destructive inflammatory responses.
T123 17188-17525 Sentence denotes On LSEC its major role appears to be immune complex sweeping, a process of removal of small immune complexes such as opsonized virus or macromolecules.17 This scavenging role by FcγRIIb on LSEC can be exploited in principle by mAbs forming small soluble complexes with their targets such as antiviral, anticytokine or similar antibodies.
T124 17527-17566 Sentence denotes FcγR activating or inhibitory signaling
T125 17567-17694 Sentence denotes Effector functions that are initiated via the activating‐type FcγR occur by signaling via the ITAM pathway of immune receptors.
T126 17695-17879 Sentence denotes This well‐characterized pathway is used by BCR and T‐cell antigen receptors, the IgE receptor FcεRI and IgA receptor FcαRI (reviewed extensively by Hogarth and Pietersz 7 Anania et al.
T127 17880-18047 Sentence denotes 11 and Getahun and Cambier 32) Induction of an activating signal requires the aggregation of activating FcγR by immune complexes, or by antigen in the case of the BCR.
T128 18048-18208 Sentence denotes This aggregation at the cell membrane results in specific tyrosine phosphorylation of the ITAM by Src kinases, thus initiating the activation cascade.32, 33, 34
T129 18209-18842 Sentence denotes The inhibitory‐type FcγRs, FcγRIIb1 and FcγRIIb2, whose expression is cell lineage restricted, modulate the ITAM signaling of the BCR or the activating‐type FcγRs, respectively.11 Their function is dependent on the immunoreceptor tyrosine inhibition motif in their cytoplasmic tail.32, 33 This checkpoint action requires that FcγRIIbs are coaggregated with the tyrosine‐phosphorylated ITAM‐signaling receptor complex which results also in immunoreceptor tyrosine inhibition motif tyrosine phosphorylation and consequential recruitment of lipid or protein tyrosine phosphatases that powerfully dampen the ITAM‐induced cell activation.
T130 18844-18877 Sentence denotes FcγR‐Dependent Effector Responses
T131 18879-18970 Sentence denotes Not all opsonized targets are equal: size, distance, valency and Fc geometry affect potency
T132 18971-19266 Sentence denotes To understand the immunobiology of FcγR effector responses particularly in the therapeutic mAb context, it is important to appreciate that the quality and potency of such effector responses is greatly affected by the nature of the IgG immune complex and/or the state of potential effector cells.
T133 19267-19410 Sentence denotes First, opsonization, per se, of a target is not necessarily sufficient to ensure FcγR interaction in a way that initiates an effector response.
T134 19411-20085 Sentence denotes Although it is the IgG Fc that interacts with and clusters the FcγR to induce a response, the nature of the Fab interaction with its epitope can strongly influence the likelihood or potency of FcγR effector responses by influencing the density of appropriately presented Fc portions.35 and also the size of the immune complex.36 Furthermore, the display/orientation and geometry of the Fc portions, as a consequence of the fragment antigen‐binding (Fab) interaction with the target epitope, can result in effector responses such as ADCC that differ substantially in potency, presumably because the orientation of the Fc makes FcγR engagement more, or less, accessible.37, 38
T135 20086-20441 Sentence denotes Second, in innate effector cells at rest, the largely linear actin cytoskeleton and the extracellular glycosaminoglycan glycocalyx regulate function by interacting with large glycoproteins, such as CD44, arranging these into ordered “picket” fences.39, 40 These corral receptors, including the FcγRs, and sterically inhibit their interaction with ligands.
T136 20442-21140 Sentence denotes Upon cell activation, cytoskeletal remodeling is associated with the loss of the receptor corrals, allowing FcγRs and other receptors to freely diffuse, engage ligand, cluster and signal.39 The influence of such surface constraints on receptors and effector cell function helps explain some of the observed epitope distance requirements for optimal mAb function,39, 41 which were apparent in a comparative study of ADCC and ADCP.42 ADCC was optimal when the epitope was displayed close, 0.3 nm “flush” or 1.5 nm, to the target membrane where close conjugation of effector and target by the mAb presumably facilitates the delivery of pore‐forming proteins to the target membrane as required by ADCC.
T137 21141-21286 Sentence denotes Interestingly, complement‐dependent cytotoxicity which also utilizes pore‐forming proteins for its cytotoxicity has similar distance constraints.
T138 21287-21580 Sentence denotes By contrast, ADCP was poor  when targeting epitopes displayed close or "flush" to the target cell membrane (within ~0.3 nm) but ADCP activity was restored when the epitope was displayed 1.5 nm off the membrane, demonstrating different optimal epitope distance requirements for ADCC and ADCP.42
T139 21581-21776 Sentence denotes Although the action of agonistic/antagonistic mAbs is mechanistically distinct to those eliciting cytotoxicity and ADCP, the distance segregation between target and FcγR+ cells is also important.
T140 21777-21908 Sentence denotes Indeed, the membrane proximal epitopes of CD28 and CD40 are important for the FcγR function in the complex MOA of these mAbs.43, 44
T141 21909-22153 Sentence denotes Clearly, the effects of immune complex valency, Fc density, presentation and geometry together with FcγR organization in the cell membrane suggest that the development of mAbs to certain targets will be heavily influenced by the context of use.
T142 22154-22270 Sentence denotes Thus, improved mAb potency may not necessarily be achieved by engineering of the Fc polypeptide or its glycan alone.
T143 22271-22491 Sentence denotes A more function‐oriented approach early in mAb selection and development by, for example, application of rapid screening technologies that select for effector potency,34 followed by Fc engineering may be more productive.
T144 22493-22514 Sentence denotes ADCC and phagocytosis
T145 22515-22726 Sentence denotes ADCC and ADCP are the most widely appreciated FcγR‐dependent effector functions (Figure 1a, b) and are, respectively, mediated primarily via  FcγRIIIa on NK cells and professional phagocytes such as macrophages.
T146 22727-22880 Sentence denotes These effector functions, particularly NK cell ADCC, are believed to be major components of the MOA of cytotoxic therapeutic mAbs used in cancer therapy.
T147 22881-23054 Sentence denotes In addition, ADCP can also occur via FcγRIIa and FcγRI,45 but the extent to which cytotoxic anticancer therapeutic mAbs depend on these for their MOA in patients is unclear.
T148 23055-23326 Sentence denotes The improvement in clinical utility of mAbs engineered for selectively increased FcγRIII binding suggests that FcγRIIa and FcγRI may be less important in vivo in cell killing effects but perhaps are more important in other aspects of therapeutic efficacy—discussed later.
T149 23328-23368 Sentence denotes Inhibition of cell activation by FcγRIIb
T150 23369-23493 Sentence denotes FcγRIIb is an immune checkpoint46, 47 and its splice variants are potent modulators of ITAM‐dependent signaling (Figure 1c).
T151 23494-23592 Sentence denotes This modulatory function occurs only when FcγRIIb is coaggregated with an ITAM signaling receptor.
T152 23593-24006 Sentence denotes Thus, B‐cell activation by the binding of the antigen in the immune complex to the BCR is regulated by the simultaneous binding of the Fcs of the immune complex to FcγRIIb1 on the same cell. In innate leukocytes, the activating‐type FcR (i.e. FcγRI, FcγRIIa, FcγRIIc, FcγRIII) and the high‐affinity IgE receptor, FcεRI, and the IgA receptor, FcαRI, are all modulated by immune complex co‐engagement with FcγRIIb2.
T153 24007-24212 Sentence denotes The inhibitory function contributes to the MOA of therapeutic antibodies that target cell‐activating molecules where the target cells also express the inhibitory FcγRIIbs such as the BCR (discussed later).
T154 24213-24411 Sentence denotes Thus, B‐cell activation is modulated by the simulatenous binding of the antigen in the immune complex to the BCR and the binding of the Fcs, also in the immune complex, to FcγRIIB1 on the same cell.
T155 24413-24458 Sentence denotes Sweeping: clearance of small immune complexes
T156 24459-24586 Sentence denotes The removal of immune complexes in humans depends primarily on the complement receptor pathway and to a lesser degree the FcγR.
T157 24587-24724 Sentence denotes Among the FcγRs, it has been widely believed that immune complex removal only occurs by phagocytosis/endocytosis of activating‐type FcγR.
T158 24725-25045 Sentence denotes Surprisingly, the inhibitory FcγRIIb, which lacks intrinsic activating function, plays a major role in clearance, and rapidly “sweeps” away small complexes from the circulation (Figure 1d).48, 49 A major tissue involved in the clearance is likely to be the LSEC, where FcγRIIb is expressed abundantly in mice and humans.
T159 25046-25297 Sentence denotes This role is potentially important in resistance to viruses and toxins but may also be key to optimal performance of therapeutic IgG mAbs whose primary MOA is believed to be only neutralization of soluble macromolecules, for example, cytokines or IgE.
T160 25299-25373 Sentence denotes FcγR uptake of antigen: antibody complexes and shaping the immune response
T161 25374-25436 Sentence denotes Monoclonal antibody therapy is a form of passive immunization.
T162 25437-25758 Sentence denotes Indeed, longer‐term vaccine‐like or vaccinal immunity has been demonstrated in anti‐CD20‐treated mice via FcγRIIa50, 51 and in vitro recall memory responses from CD20‐treated patients.52 Although this is dependent on FcγR and anti‐CD20, the mechanism by which long‐term anti‐tumor response is established remains unclear.
T163 25759-26460 Sentence denotes Nonetheless, the active involvement of FcγR in the enhancement of antigen‐specific immunity by uptake of immune complexes through FcγR is historically well documented in experimental systems where FcγRs bind immune complexes and thereby feed antigens into the antigen‐presentation pathways.53 This has been demonstrated in vivo for small immune complexes via human FcγRI on human antigen‐presenting cells54 and in mice.19 Similarly, the capacity of FcγRIIbs to bind and rapidly internalize antigen–antibody complexes suggests that it too may significantly influence feeding antigens into professional antigen‐presenting cells of hematopoietic origin such as dendritic cells and possibly B lymphocytes.
T164 26461-26745 Sentence denotes Although not a classical major histocompatibility complex‐dependent antigen presentation, FcγRIIb on the stroma‐derived follicular dendritic cells influences antibody immunity by recycling antigen–antibody complexes to the cell surface for presentation of intact antigen to B cells.55
T165 26746-26968 Sentence denotes Although somewhat speculative, FcγRIIb’s rapid internalization/sweeping of complexes by the abundant LSEC, which interact with lymphocytes and can present antigen,56 may have a significant role in shaping immune responses.
T166 26970-27015 Sentence denotes Scaffolding of cell‐bound mAbs by FcγR+ cells
T167 27016-27117 Sentence denotes FcγR‐expressing cells can be critical, but passive, participants in the MOA of some mAbs (Figure 1e).
T168 27118-27330 Sentence denotes In FcγR scaffolding, IgG mAb molecules that have opsonized the cell surface of a target cell are additionally cross‐linked by their Fc portions engaging the FcγRs that are arrayed on the surface of a second cell.
T169 27331-27543 Sentence denotes This “super‐cross‐linking” of the target‐bound mAb by the FcγR lattice or “scaffold” on the adjacent cell greatly exceeds the target cross‐linking by the mAb alone, thereby inducing a response in the target cell.
T170 27544-28137 Sentence denotes Scaffolding was originally identified as the basis of T‐cell mitogenesis induced by anti‐CD3 mAb.57, 58 The CD3 mAbs alone were poor mitogens but the “super‐cross‐linking” of the T‐cell‐bound CD3 mAb by the membrane FcγR on adjacent cells, particularly by monocytes, induced rapid T‐cell expansion and cytokine secretion but did not require activation of FcγR‐expressing cells.57 Regrettably, FcγR scaffolding came to prominence and clinical relevance because of its causal role in the catastrophic adverse events resulting from the administration of anti‐CD357 and anti‐CD28 (TGN1412)59 mAbs.
T171 28138-28273 Sentence denotes Nonetheless, FcγR scaffold‐based induction of intracellular responses in a target cell can also lead to beneficial therapeutic effects.
T172 28274-28496 Sentence denotes Such examples are the induction of apoptotic death in a target cell, which is likely part of the MOA of daratumumab in multiple myeloma60 or the controlled agonistic expansion of cells, for example, via CD40 mAb agonism.43
T173 28498-28547 Sentence denotes IgG subclasses: specificity and affinity for FcγR
T174 28548-28771 Sentence denotes Most FcγRs (Table 2) are weak, low‐affinity receptors (affinities in the micromolar range) for IgG‐Fc, irrespective of whether the IgG is uncomplexed, monomeric or when it is complexed with antigen (i.e. an immune complex).
T175 28772-29013 Sentence denotes The very avid binding of immune complexes to an effector cell surface that displays an array of FcγR molecules is the result of the collective contributions of the low‐affinity interactions of each Fc of the IgGs in the complex with an FcγR.
T176 29014-29166 Sentence denotes This avidity effect is necessary as the FcγRs operate in vivo in environments of high concentrations of uncomplexed monomeric IgG (normally 3–12 g L–1).
T177 29167-29257 Sentence denotes Thus, the avid multivalent binding of the complex out competes uncomplexed, monomeric IgG.
T178 29258-29311 Sentence denotes The notable exception to this is the enigmatic FcγRI.
T179 29312-29488 Sentence denotes This receptor shows high, nanomolar affinity for uncomplexed monomeric IgG and thus would be expected to be constantly occupied in vivo by the normal circulating monomeric IgG.
T180 29489-29556 Sentence denotes However, IgG dissociation permits engagement with immune complexes.
T181 29557-29723 Sentence denotes Furthermore, FcγRI is not expressed or expressed poorly on resting cells, requiring interferon‐γ for induction of its expression, presumably at sites of inflammation.
T182 29724-29905 Sentence denotes Although the human IgG heavy‐chain constant domains have greater than 90% identity, key amino acid differences confer each subclass with unique structural and functional properties.
T183 29906-29977 Sentence denotes IgG1 and IgG3 are “universal” ligands, that is, they bind to all FcγRs.
T184 29978-30300 Sentence denotes Formal measurement of the weak, micromolar KD interactions of the low‐affinity receptors with monomeric IgG1 also revealed differing affinities between the low‐affinity FcγRs, with inhibitory FcγRIIb generally having the lowest affinity and FcγRIII the higher, sometimes referred to as a “moderate” affinity receptor.7, 61
T185 30301-30464 Sentence denotes The strength of IgG1 interaction can also be affected by FcγR polymorphism and in the context of therapeutic mAbs, variation in FcγRIIIa is particularly important.
T186 30465-30676 Sentence denotes The most common and possibly clinically significant polymorphism is phenylalanine/valine variation at position 158 in the IgG‐binding site, wherein FcγRIIIa‐F158 binds IgG1 less well than the FcγRIIIa‐V158 form.
T187 30677-30729 Sentence denotes IgG4 and IgG2 have more restricted FcγR specificity.
T188 30730-30867 Sentence denotes IgG4 has low affinity (KA = ~2 × 105 m –1) for the inhibitory FcγRIIb, but is also a high‐affinity ligand for FcγRI (KA = ~4 × 108 m –1).
T189 30868-31113 Sentence denotes IgG2 exhibits a highly restricted specificity, showing functional activity with only one polymorphic form of FcγRIIa (binding affinity KA = ~4.5 × 105 m –1) which is permitted by the presence of histidine at position 131 of its IgG‐binding site.
T190 31114-31324 Sentence denotes This FcγRIIa–H131 form is expressed in approximately 70% of the population, whereas IgG2 has no functional activity on the other common allelic form, FcγRIIa‐R131, which contains arginine at position 131.11, 61
T191 31326-31341 Sentence denotes IgG Subclasses:
T192 31342-31366 Sentence denotes Structure and Properties
T193 31368-31416 Sentence denotes The molecular basis of IgG and FcγR interactions
T194 31417-31480 Sentence denotes The extracellular regions of the FcγR are structurally similar.
T195 31481-31627 Sentence denotes Each low‐affinity FcγR has two ectodomains, whereas the high‐affinity FcγRI has a third domain but this is not directly involved in IgG binding.62
T196 31628-31922 Sentence denotes The interaction between the IgG subclasses and the FcγR is most comprehensively defined for human IgG1 by both X‐ray crystallographic7, 62, 63 and mutagenesis structure/function analyses.64, 65, 66 These studies defined key regions of the IgG sequence required for interaction with their FcγRs.
T197 31923-32089 Sentence denotes Crystallographic analyses of the human IgG1‐Fc complexed with FcγRI, FcγRII or FcγRIII show that these interactions are similar in topology, and asymmetric in nature.
T198 32090-32171 Sentence denotes The second extracellular domain of the FcγR inserts between the two heavy chains.
T199 32172-32322 Sentence denotes Here it makes contacts with the lower hinge of both H chains and with residues of the adjacent BC loop of one CH2 domain and the FG loop of the other.
T200 32323-32504 Sentence denotes The N‐linked glycan at asparagine 297 (N297) of the heavy chain is essential for the structural integrity of the IgG‐Fc by affecting the spacing and conformation of the CH2 domains.
T201 32505-32759 Sentence denotes Indeed, its removal ablates FcγR binding.67 Of particular relevance to therapeutic mAb development is that the normal low‐affinity IgG interaction with FcγRIIIa is profoundly increased by the removal of the core fucose from the N297 Fc oligosaccharide.68
T202 32760-33011 Sentence denotes No crystallographic data are available for IgG2 or IgG4 Fc in complex with FcγR, but mutagenesis studies of the Fc and the FcγR revealed general similarity, but with critical differences, in the interaction of these subclasses with their cognate FcγR.
T203 33013-33060 Sentence denotes Unique features of the IgG2 and IgG4 subclasses
T204 33061-33268 Sentence denotes In IgG1, the stable interaction of the two heavy chains results from the combined effects of stable covalent inter H‐chain disulfide bonds and strong noncovalent interaction of the two CH3 domains (Table 3).
T205 33269-33364 Sentence denotes In stark contrast, in IgG2 and IgG4 the interaction of the CH3 domains of each H‐chain is weak.
T206 33365-33460 Sentence denotes Residues 392, 397 and 409 (Eu numbering) profoundly affect the stability of these interactions.
T207 33461-33657 Sentence denotes The difference at position 409 (R409 in IgG4 and K409 in IgG1) confers a 100‐fold decrease in stability of the interface between the two CH3 domains of IgG4 compared with that of IgG1 (Table 3).69
T208 33658-33817 Sentence denotes Furthermore, the core hinge of IgG4 differs from IgG1 at position 228 (P228 in IgG1 and S228 in IgG4), resulting in unstable inter‐heavy‐chain disulfide bonds.
T209 33818-34286 Sentence denotes This, together with the destabilizing amino acids in the CH3, confers the unique property of half‐antibody (Fab arm) exchange between different IgG4 antibodies,69 thereby creating monovalent, bispecific IgG4 antibodies in vivo.69, 70 The similarly unstable interactions between the CH3 domains in IgG2 are conferred by the interface residue M397; however, the stable inter‐H‐chain disulfide bonds of the core and upper hinge prevent half‐molecule exchange (Table 3).69
T210 34287-34360 Sentence denotes In addition, IgG2 uniquely has three disulfide bond conformers (Table 3).
T211 34361-34970 Sentence denotes The distinct conformers are formed when (1) each light chain is attached to the Cys131 residue of CH1 in the heavy chain (IgG2‐A conformer), (2) both light chains attach to the upper hinge (IgG2‐B) or (3) one light chain is attached to the CH1 Cys131 and one to the upper hinge of the other heavy chain (IgG2‐AB).71 This results in distinct positioning of the Fabs relative to the Fc portions in the different conformers, which has implications for the interaction with antigen and the capacity of IgG2 to cross‐link target molecules in the absence of FcγR binding, for example, in an agonistic mAb setting.72
T212 34971-35070 Sentence denotes It should also be noted that IgG3 has not been used in therapeutic mAbs despite its unique biology.
T213 35071-35336 Sentence denotes The main impediment to its use are its physicochemical properties such as susceptibility to proteolysis and propensity to aggregate that present challenges to industry‐scale production and stability but protein engineering is attempting to overcome these hurdles.73
T214 35338-35388 Sentence denotes Therapeutic antibody design: improving mAb potency
T215 35389-35479 Sentence denotes Many factors affecting FcγR‐dependent responses in vivo come into play during mAb therapy.
T216 35480-35786 Sentence denotes The experience of three decades of clinical use of mAbs taken together with our extensive, albeit incomplete, knowledge of IgG and FcγR structure and immunobiology provides a war chest for the innovative development of new and highly potent mAbs through the manipulation of their interaction with the FcγR.
T217 35787-36085 Sentence denotes Therapeutic mAb engineering strategies are directed by many factors including the biology of the target, the nature of the antigen, the desired MOA and possibly the anatomical location of the therapeutic effect,21 and thus to optimize potency for a desired response, the context of use is critical.
T218 36087-36116 Sentence denotes The nature of the IgG isotype
T219 36117-36284 Sentence denotes Different capabilities for the recruitment and activation of the different immune effector functions are naturally found in the Fc regions of the human IgG subclasses.
T220 36285-36432 Sentence denotes Thus, to achieve a desired MOA, the different IgG subclasses are important starting points for the selection and engineering of the optimal mAb Fc.
T221 36433-36763 Sentence denotes IgG1 is, in many ways, a proinflammatory or “effector‐active” subclass, as it can initiate the complement cascade and is a “universal” FcγR ligand.74 Notwithstanding it is also a ligand for the inhibitory FcγRIIb, IgG1 elicits proinflammatory responses through all activating‐type FcγRs, including ADCC, ADCP and cytokine release.
T222 36764-36940 Sentence denotes Because of their more restricted FcγR‐binding profile, IgG2 and IgG4 have offered some choice in potentially avoiding FcR effector function without the need for Fc engineering.
T223 36941-37410 Sentence denotes They have been used as the backbone for therapeutic mAbs either because recruitment of patients’ effector functions was unlikely to be necessary for the primary MOA of the mAb or is possibly detrimental to the desired therapeutic effect.75 However, the use of these unmodified “inert” subclasses is not without consequences and underscores the need for Fc engineering to modify FcγR interactions—See the “Attenuating and ablating FcγR related functions of IgG” section.
T224 37411-37577 Sentence denotes Thus, the choice of IgG subclass for therapeutic mAb engineering is an important first step for engineering of novel mAbs of improved specificity, potency and safety.
T225 37579-37630 Sentence denotes Fc engineering for enhanced anticancer therapeutics
T226 37631-37810 Sentence denotes IgG1 is the predominant subclass used in the development of cytotoxic mAbs where induction of an activation‐type response, ADCC or phagocytosis, is considered desirable.45, 76, 77
T227 37811-37903 Sentence denotes Cytotoxic mAb cancer therapeutics can control disease progression by one or more mechanisms.
T228 37904-38060 Sentence denotes Their MOAs include direct induction of apoptotic cell death of the cancer cell (anti‐CD20, anti‐CD52) or blocking receptor signaling (anti‐HER2, anti‐EGFR).
T229 38061-38473 Sentence denotes They may also harness FcγR effector functions, including ADCC in the tumor microenvironment.78 The approved mAbs, rituximab (anti‐CD20), trastuzumab (anti‐HER2) and cetuximab (anti‐EGFR), are formatted on a human IgG1 backbone and all require activating‐type FcγR engagement for optimal therapeutic activity.79, 80 This presents an example where context of therapeutic use is critical for therapeutic mAb design.
T230 38474-38563 Sentence denotes IgG1 antibodies bind both the activating FcγR (e.g. FcγRIIIa) and the inhibitory FcγRIIb.
T231 38564-38713 Sentence denotes In some environments effector cells will coexpress FcγRIIb together with FcγRI, FcγRIIa and FcγIIIa, as may occur on a tumor‐infiltrating macrophage.
T232 38714-38970 Sentence denotes Therapy with an IgG1 anti‐cancer cell mAb may then be compromised by the inhibitory action of FcγRIIb upon the ITAM signaling of the activating FcγR as both types of receptor would be coengaged on  such an effector cell by the mAb bound to the target cell.
T233 38971-39017 Sentence denotes This leads to reduced therapeutic mAb potency.
T234 39018-39467 Sentence denotes Thus, the relative contributions of the activating (A) and inhibitory (I) FcγR to the response by an effector cell, the A‐to‐I ratio, may be an important determinant in clinical outcome of therapeutic mAb activity,76, 81, 82 that is, the higher the A‐to‐I ratio, the greater the proinflammatory response induced by the therapeutic mAb or conversely the lower the A‐to‐I ratio, the greater the inhibition or dampening of the proinflammatory response.
T235 39468-39579 Sentence denotes Thus, the challenge for the development of more potent FcγR effector mAbs is to overcome three major obstacles.
T236 39580-39772 Sentence denotes First, improving activation potency by selectively enhancing interaction with activating‐type FcγR, particularly FcγRIIIa owing to its predominant role in ADCC‐mediated killing of tumor cells.
T237 39773-39839 Sentence denotes Second, reducing binding interactions with the inhibitory FcγRIIb.
T238 39840-39914 Sentence denotes These two approaches improve the FcγR A‐to‐I ratio of cytotoxic IgG1 mAbs.
T239 39915-40185 Sentence denotes Third, overcoming the significant affinity difference in the interaction with the main FcγRIII allelic forms of FcγRIIIa‐V158 and FcγRIIIa‐F158 76, 83, 84 which appears to be an important source of patient variability in responses to therapeutic mAb treatment of cancer.
T240 40186-40271 Sentence denotes At the time of writing, some mAbs with improved potency are coming into clinical use.
T241 40272-40404 Sentence denotes Their improved action has been achieved by modifying the N‐linked glycan or the amino acid sequence of the heavy‐chain Fc (Table 4).
T242 40405-40511 Sentence denotes Table 4 Fc or hinge‐engineered monoclonal antibodies (mAbs) approved or in advanced clinical development.
T243 40512-40621 Sentence denotes mAb name Target IgG backbone Fc modification Effect on mAb Therapy area Most advanced development stage
T244 40622-40726 Sentence denotes Andecaliximab Matrix Metalloproteinase 9 (MMP9) IgG4 S228P Stabilize core hinge Oncology Phase III
T245 40727-40887 Sentence denotes Anifrolumab Interferon alpha/beta receptor 1 IgG1 L234F; L235E; P331S Mimic IgG4 hinge and its CH2/F/G loop; plus ablate FcγR binding Immunology Phase III
T246 40888-40977 Sentence denotes Atezolizumab PD‐L1 IgG1 Aglycosylated (N297A) Ablate FcγR binding Oncology Marketed
T247 40978-41171 Sentence denotes Benralizumab Interleukin 5 IgG1 Afucosylated Selectively enhance FcγRIII interaction Respiratory dermatology; ear nose throat disorders; gastrointestinal; hematology; immunology; Marketed
T248 41172-41301 Sentence denotes Durvalumab PD‐L1 IgG1 L234F; L235E; P331S Mimic IgG4 hinge and its CH2 F/G loop; plus ablate FcγR binding Oncology Marketed
T249 41302-41411 Sentence denotes Evinacumab Angiopoietin‐related protein 3 IgG4 S228P Stabilize core hinge Metabolic disorders Phase III
T250 41412-41536 Sentence denotes Inebilizumab CD19 IgG1 Afucosylated Selectively enhance FcγRIII interaction Central nervous system; oncology Phase III
T251 41537-41661 Sentence denotes Ixekizumab Interleukin 17A IgG4 S228P Stabilize core hinge Dermatology; immunology; musculoskeletal disorders Marketed
T252 41662-41783 Sentence denotes Margetuximab HER2 IgG1 F243L; L235V; R292P; Y300L; P396L Selectively enhance FcγRIII interaction Oncology Phase III
T253 41784-41940 Sentence denotes Mogamulizumab C–C chemokine receptor type 4 (CCR4) IgG1 Afucosylated Selectively enhance FcγRIII interaction Central nervous system; oncology Marketed
T254 41941-42059 Sentence denotes Tafasitamab (MOR208 XmAb 5574) CD19 IgG1 S239D; I332E Selectively enhance FcγRIII interaction Oncology Phase III
T255 42060-42150 Sentence denotes Nivolumab PD‐1 IgG4 S228P Stabilize core hinge Infectious disease; oncology Marketed
T256 42151-42262 Sentence denotes Obinutuzumab CD20 IgG1 Afucosylated Selectively enhance FcγRIII interaction Immunology; oncology Marketed
T257 42263-42363 Sentence denotes Ocaratuzumab CD20 IgG1 P247I; A339Q Selectively enhance FcγRIII interaction Oncology Phase III
T258 42364-42449 Sentence denotes Pembrolizumab PD‐1 IgG4 S228P Stabilize core hinge Infection; oncology Marketed
T259 42450-42566 Sentence denotes Roledumab Rhesus D IgG1 Afucosylated Selectively enhance FcγRIII interaction Hematological disorders Phase III
T260 42567-42679 Sentence denotes Spesolimab (BI‐655130) IL‐36R IgG1 L234A; L235A Ablate FcγR binding Gastrointestinal; immunology Phase III
T261 42680-42767 Sentence denotes Teplizumab CD3 IgG1 L234A; L235A Ablate FcγR binding Metabolic disorders Phase II
T262 42768-42988 Sentence denotes Tislelizumab PD‐1 IgG4 S228P; E233P; F234V; L235A; D265A; L309V; R409K Stabilize core hinge; mimic IgG2 lower hinge for restricted FcγR specificity; ablate FcγR binding; stabilize CH3 interaction Oncology Phase III
T263 42989-43071 Sentence denotes Toripalimab (JS 001) PD‐1 IgG4 S228P Stabilize core hinge Oncology Phase III
T264 43072-43195 Sentence denotes Ublituximab CD20 IgG1 Afucosylated Selectively enhance FcγRIII interaction Central nervous system; oncology Phase III
T265 43196-43215 Sentence denotes Ig, immunoglobulin.
T266 43216-43363 Sentence denotes John Wiley & Sons, Ltd This article is being made freely available through PubMed Central as part of the COVID-19 public health emergency response.
T267 43364-43546 Sentence denotes It can be used for unrestricted research re-use and analysis in any form or by any means with acknowledgement of the original source, for the duration of the public health emergency.
T268 43548-43577 Sentence denotes Modification of the Fc glycan
T269 43578-43858 Sentence denotes The typical complex N‐linked glycan attached to N297 of the heavy chain includes a core fucose.85 Antibodies that lack this fucose have approximately 50‐fold improved binding to FcγRIIIa and FcγRIIIb and importantly retain the weak, low‐affinity binding to the inhibitory FcγRIIb.
T270 43859-44233 Sentence denotes Furthermore, this glycoengineering increased binding affinity of the modified IgG1 mAb for both FcγRIIIa V158 and F158 allelotypes.86, 87, 88 Afucosyl versions of the tumor targeting mAbs such as anti‐HER2, anti‐EGFR and anti‐CD20 had greater antitumor effects and increased survival,68, 88, 89 which is a reflection of the greatly increased, and selective, FcγRIII binding.
T271 44234-44559 Sentence denotes Compared with their unmodified counterparts, the afucosyl mAbs showed dramatic improvement of FcγRIII‐related effector responses such as stronger NK cell‐mediated ADCC, or enhanced neutrophil‐mediated phagocytosis through FcγRIIIb and/or FcγRIIIa.23 However, certain neutrophil functions via FcγRIIa may be compromised.90, 91
T272 44560-44664 Sentence denotes There are six afucosylated antibodies in late‐stage clinical trials or approved for treatment (Table 4).
T273 44665-45015 Sentence denotes Notable is obinutuzumab, an afucosyl anti‐CD20 mAb which nearly doubles progression‐free survival in chronic lymphocytic leukemia patients as compared with the fucose‐containing rituximab.68 This dramatic improvement in clinical utility reinforces the value of glycan engineering specifically and of Fc engineering generally in anticancer treatments.
T274 45017-45047 Sentence denotes Mutation of the Fc amino acids
T275 45048-45160 Sentence denotes Alteration of the amino acids in the heavy‐chain Fc can alter IgG specificity and affinity for activating FcγRs.
T276 45161-45441 Sentence denotes The anti‐CD19 antibody MOR208 (XmAb 5574) is currently in phase III trials for the treatment of chronic lymphocytic leukemia.92 It contains two mutations in its IgG1 Fc, S329D and I332E, which increases affinity to FcγRIIIa, particularly the “lower‐affinity” FcγRIIIa F158 allele.
T277 45442-45559 Sentence denotes The mAb shows increased FcγRIII‐mediated ADCC and phagocytosis in vitro, and reduced lymphoma growth in mouse models.
T278 45560-45939 Sentence denotes Margetuximab is an ADCC‐enhanced IgG1 Fc‐engineered variant of the approved anti‐HER2 mAb trastuzumab in phase III for HER2‐expressing cancers.66, 93 Alteration of five amino acids (L235V, F243L, R292P, Y300L and P396L) enhanced binding to FcγRIIIa which also had the additional effect of decreasing binding to the inhibitory FcγRIIb, and thereby increased its A‐to‐I FcγR ratio.
T279 45940-46154 Sentence denotes This was apparent when compared with unmodified trastuzumab the  margetuximab showed enhanced ADCC against HER2+ cells in vitro and demonstrated superior antitumor effects in an HER2‐expressing tumor model in mice.
T280 46155-46526 Sentence denotes The anti‐CD20 ocaratuzumab is an Fc‐engineered IgG1 mAb in late‐stage clinical trials for the treatment of a range of cancers, including non‐Hodgkin lymphoma and chronic lymphocytic leukemia.94 Two Fc mutations, P247I and A339Q, conferred about 20‐fold increase in binding to both major allelic variants of FcγRIIIa and elicited sixfold greater ADCC than unmodified IgG1.
T281 46527-46688 Sentence denotes Thus, the engineering of the Fc domain or glycan for improved FcγRIIIa binding is a powerful tool to create more potent and clinically effective anticancer mAbs.
T282 46690-46744 Sentence denotes Attenuating and ablating FcγR‐related functions of IgG
T283 46745-46853 Sentence denotes There are circumstances where binding to FcγR is unnecessary or undesirable in the MOA of a therapeutic mAb.
T284 46854-47191 Sentence denotes Unmodified IgG irrespective of its subclass or intended therapeutic effect has the potential to engage an FcγR which may lead to suboptimal therapeutic performance or to unexpected and catastrophic consequences.57, 59 Clearly reducing or eliminating FcγR interactions, when they are not required for therapeutic effect, may be desirable.
T285 47192-47284 Sentence denotes Indeed, this had been addressed by the choice of IgG subclass or by modifying the Fc region.
T286 47285-47446 Sentence denotes Indeed, most efforts in Fc engineering mAbs that have translated to an approved drug have focused on the reduction or elimination of FcγR interactions (Table 4).
T287 47447-47714 Sentence denotes One approach to minimize interactions with the activating FcγR has been the use of IgG4 or IgG2 backbones, which show a more restricted specificity for the activating FcγR and consequently have been traditionally, and simplistically, viewed as “inert” IgG subclasses.
T288 47715-47896 Sentence denotes Notwithstanding the unexpected, and FcγR‐dependent, severe adverse reaction induced by the IgG4 TGN1412 mAb, the IgG4 or IgG2 backbones have been successfully used in many settings.
T289 47897-48131 Sentence denotes Indeed, checkpoint inhibitors, such as mAbs targeting CTLA‐4 or the PD‐L1/PD‐1 interaction for the suppression of inhibitory signals that contribute to immune tolerance in the tumor microenvironment, are formatted on an IgG4 backbone.
T290 48132-48356 Sentence denotes Pembrolizumab, nivolumab and cemiplimab are all anti‐PD‐1 antibodies currently used for cancer therapy and have been formatted on an IgG4 backbone95, 96, 97 with a stabilized core hinge (S228P) to prevent half‐IgG4 exchange.
T291 48357-48513 Sentence denotes Similarly, the checkpoint inhibitor tremelimumab is an anti‐CTLA‐4 antibody formatted on an IgG2 backbone to avoid potential ADCC killing of target cells.98
T292 48514-48585 Sentence denotes However, the use of IgG2 and IgG4 as “inert” subclasses is problematic.
T293 48586-48981 Sentence denotes Both bind to the activating receptors FcγRIIa‐H131 and FcγRI, respectively (Table 2), and initiate effector functions such as neutrophil activation and apoptosis induction.75, 99 Interestingly, in experimental systems, cross‐linking of anti‐PD‐1 IgG4‐based mAb by FcγRI switched its activity from blocking to activatory.10 Moreover, IgG4 binds to FcγRIIb, which may scaffold the therapeutic mAb.
T294 48982-49299 Sentence denotes Although scaffolding may be beneficial in some contexts, for example, in immune agonism,43 it can be disastrous and unexpected in others as it was for the anti‐CD28 TGN1412 mAb.59 Thus, the IgG2 and IgG4 subclasses are not the optimum choice for “FcR‐inactive” mAbs, and so modifying the Fc is a more direct approach.
T295 49300-49594 Sentence denotes The complete removal of the heavy‐chain N‐linked glycan is well known to ablate all FcγR binding by dramatically altering the Fc conformation.36, 67, 101, 102 Atezolizumab, an IgG1 anti‐PD‐L1 checkpoint inhibitor mAb, utilizes this strategy and eliminates FcγR and also complement activation.13
T296 49595-49706 Sentence denotes Modification to the Fc amino acid sequence of the FcγR‐contact regions can also be used to reduce FcγR binding.
T297 49707-49862 Sentence denotes A widely used modification of IgG1 is the substitution of leucine 234 and 235 in the lower hinge sequence (L234 L235 G236 G237) with alanine (L234A L235A).
T298 49863-50031 Sentence denotes It is often referred to as the “LALA mutation” and effectively eliminates FcγR binding by more than 100 fold104, 105 and is used in teplizumab and spesolimab (Table 4).
T299 50032-50236 Sentence denotes A separate strategy has used combinations of amino acid residues from the FcγR‐binding regions of IgG2 and IgG4, which have restricted FcγR specificity, together with other binding‐inactivating mutations.
T300 50237-50415 Sentence denotes The lower hinge amino acids of the IgG1 mAbs durvalumab (anti‐PD‐L1) and anifrolumab (anti‐interferon‐α receptor; Table 4) were modified to mimic the lower hinge of IgG4 (L234F).
T301 50416-50633 Sentence denotes They additionally incorporated L235E in the lower hinge and P331S in the F/G loop of the CH2 domain to ablate FcγR binding by disrupting two major FcγR contact sites7 and also coincidently decreasing C1q activation.16
T302 50634-50729 Sentence denotes IgG4 mAbs have been similarly engineered to eliminate their interaction with FcγRI and FcγRIIb.
T303 50730-51004 Sentence denotes The IgG4 anti‐PD‐1 antibody tislelizumab has had its FcγR contact residues in the lower hinge E233, F234, L235 substituted with the equivalent residues of IgG2 P, V, A (E233P, F234V, L235A) as well as the additional D265A mutation which disrupts a major FcγR contact in CH2.
T304 51005-51222 Sentence denotes It also has substitutions in the core hinge S228P and the CH3 L309V and R409K to stabilize the H‐chain disulfides and CH3 interactions, respectively, thereby preventing half‐Ig exchange characteristic of natural IgG4.
T305 51223-51327 Sentence denotes Collectively, these modifications create a stable IgG4 with no FcγR binding nor complement activation.17
T306 51328-51590 Sentence denotes Thus, Fc engineering is an effective way to remove FcγR effector functions and may be preferable to using unmodified IgG2 or IgG4 backbones that have a more restricted repertoire of FcγR interactions but which are still able to induce certain effector functions.
T307 51592-51622 Sentence denotes Improving FcγRIIb interactions
T308 51623-51792 Sentence denotes Preferential or specific Fc engagement of FcγRIIb over the activating FcγR offers several potential therapeutic advantages for new mAbs in distinct therapeutic settings.
T309 51794-51896 Sentence denotes Improved recruitment of FcγRIIb immunoreceptor tyrosine inhibition motif‐dependent inhibitory function
T310 51897-52383 Sentence denotes Harnessing the physiological inhibitory function of FcγRIIb by mAbs that target ITAM receptors has the potential to shut down ITAM‐dependent signaling pathways of major importance in antibody pathologies.32, 108 Such ITAM signaling receptors include the BCR complex on B cells which is active in systemic lupus erythematosus, the FcεRI on basophils and mast cell subsets in allergies or the activating‐type FcγR on a variety of innate leukocytes in antibody‐mediated tissue destruction.
T311 52384-52548 Sentence denotes In such scenarios, the ITAM signaling receptor complex that is targeted by the therapeutic mAb must be co‐expressed on the cell surface with the inhibitory FcγRIIb.
T312 52549-52752 Sentence denotes This permits coengagement with ITAM signaling receptor by the Fab of the mAb and inhibitory FcγRIIb by its Fc which is the critical requirement in the inhibitory MOA for such therapeutic mAbs (Figure 1).
T313 52753-53178 Sentence denotes Obexelimab (also known as XmAb5871; Table 4), currently in early clinical testing in inflammatory autoimmune disease, is an IgG1 mAb that targets CD19 of the BCR complex.19 It contains two Fc modifications, S267E and L328F (also known as “SELF” mutations), that selectively increased FcγRIIb binding by 400‐fold to about 1 nm, which results in powerful suppression of BCR signaling and the proliferation of primary B cells.19
T314 53179-54143 Sentence denotes The anti‐IgE mAb omalizumab is an IgG1 mAb approved for the treatment of allergic disorders.110, 111 A similar but Fc‐engineered IgG1 mAb XmAb7195, currently in early clinical testing, contains the affinity‐enhancing SELF modifications.112 Both mAbs sterically neutralize the interaction between IgE and its high‐affinity receptor FcεRI to prevent basophil and mast cell activation.113, 114 However, XmAb7195 exhibited more efficient removal (sweeping; discussed later) of circulating IgE and also inhibited B‐cell IgE production, presumably by binding to the IgE BCR on the B‐cell surface and coclustering with FcγRIIb via its affinity‐enhanced Fc domain.112 Thus, XmAb7195’s selective modulation of IgE production by IgE+ B cells in addition to its enhanced clearance of IgE may offer significantly improved therapeutic benefits in allergy therapy beyond simple IgE neutralization.112 The “SELF” mutations have also been used in agonistic mAbs (discussed later).
T315 54144-54375 Sentence denotes One cautionary note is that the arginine 131 (R131) of the IgG‐binding site in FcγRIIb is critical for the enhanced affinity binding of “SELF”‐mutated Fcs but it is also present in the activating‐type “high responder” FcγRIIa‐R131.
T316 54376-54638 Sentence denotes Thus, antibodies modified with “SELF” have very‐high‐affinity binding to FcγRIIa‐R131 115 with a potentially increased risk of FcγRIIa‐dependent complications in patients expressing this allelic form, although, so far, none have been reported in clinical trials.
T317 54639-54829 Sentence denotes However, an alternative set of six Fc mutations, termed “V12” (P238D, E233D, G237D, H268D, P271G and A330R), potently enhanced FcγRIIb binding without increasing FcγRIIa–R131 interaction.115
T318 54831-54879 Sentence denotes Enhancing the sweeping of small immune complexes
T319 54880-55252 Sentence denotes The expression of FcγRIIb on LSEC and its action in the “sweeping” or removal of small immune complexes has opened up new possibilities for the application of FcγRIIb‐enhancing modifications.17 Antibodies or Fc fusion proteins, whose primary MOA is the neutralization of soluble molecules such as IgE or cytokines, are particularly attractive candidates for this approach.
T320 55253-55561 Sentence denotes Proof‐of‐concept for this strategy has been demonstrated in experimental models.48 Indeed, this may be a significant component of the rapid disappearance of IgE from the circulation of patients treated with the anti‐IgE XmAb7195 containing the FcγRIIb enhancing “SELF” modifications, as described previously.
T321 55563-55602 Sentence denotes Immune agonism through FcγR scaffolding
T322 55603-55702 Sentence denotes Agonistic mAbs induce responses in target cells by stimulating signaling of their molecular target.
T323 55703-55948 Sentence denotes Typically, this is to either enhance antitumor immunity by engaging costimulatory molecules on antigen‐presenting cells or T cells (i.e. CD40, 4‐1BB, OX40) or promote apoptosis by engaging death receptors on cancer cells (i.e. DR4, DR5, Fas).116
T324 55949-56041 Sentence denotes The role of FcγR in the action of these types of mAbs appears to be primarily as a scaffold.
T325 56042-56138 Sentence denotes FcγRIIb is often the predominate receptor involved and the extent of its involvement is complex.
T326 56139-56459 Sentence denotes In the case of CD40, the degree of FcγRIIb scaffolding potency is linked to the epitope location of the targeting mAb with greater potency seen for membrane proximal epitopes.43, 117 It is also noteworthy that depending on the epitope location, the scaffolding of anti‐CD40 mAbs may convert antagonist mAbs to agonistic.
T327 56460-56952 Sentence denotes Engineering of the IgG1 Fc region for enhanced and/or specific binding to FcγRIIb can greatly improve agonistic function.72, 118, 119, 120 Such mutations induced significantly greater agonistic activity in an anti‐DR5 model through increased induction of apoptotic death and decreased tumor growth compared with unmodified IgG1.121 The “SELF” modifications that dramatically and selectively increase affinity for FcγRIIb have also been used to enhance immune agonism in an anti‐OX40 model.122
T328 56953-57156 Sentence denotes The incorporation of the "V12" Fc mutations into IgG1 specifically enhance FcγRIIb interaction 200‐fold, conferring the enhanced agonistic activity of an anti‐CD137 antibody and an anti‐OX40 mAb.115, 122
T329 57158-57187 Sentence denotes Future Engineering Strategies
T330 57188-57284 Sentence denotes Monoclonal antibodies are potent therapeutics in a number of chronic or once incurable diseases.
T331 57285-57414 Sentence denotes However, there is still extensive unmet clinical need as well as considerable room for improvement in many existing therapeutics.
T332 57415-57555 Sentence denotes Further understanding of how antibody structure affects FcγR function is essential for future development of more potent and effective mAbs.
T333 57556-57823 Sentence denotes Already, engineering of the IgG Fc and its glycan has proved a potent and effective approach for increasing the clinical effectiveness, functional specificity and safety of therapeutic mAbs and is an emerging pathway to the development of the “next‐gen” therapeutics.
T334 57824-58167 Sentence denotes Future directions in the development and use of therapeutic antibodies should increasingly mimic normal protective antibody responses, which are polyclonal and elicited in the context of innate receptor engagement which includes the FcR as well as other powerfully responsive systems including the Toll‐like receptors and complement receptors.
T335 58168-58421 Sentence denotes Furthermore, the mixed subclass nature of these normal antibody responses suggests that circumstances may arise in therapeutic strategies where there is value in having distinctly modified Fcs for the nuanced engagement of different FcγR family members.
T336 58422-58573 Sentence denotes Treatments comprising multiple mAbs and immune stimulants are under investigation in infectious disease for neutralization coverage of variant strains.
T337 58574-58731 Sentence denotes Indeed, such an approach may be most effective in emerging infectious disease such as severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection.
T338 58732-58930 Sentence denotes The use of multiple mAbs tailored for distinct effector functions and targeting different epitopes will maximize the opportunity for cocktailing of effector functions in different types of diseases.
T339 58931-59134 Sentence denotes Indeed, in a small but contemporary example outside of infectious disease, the FDA‐approved combination in adenocarcinoma therapy uses a cocktail of two mAbs, pertuzumab and trastuzumab, against Her2.123
T340 59135-59412 Sentence denotes Rather than one type of Fc to conquer all, the combined use of appropriately selected mAbs whose individual components are enhanced for the engagement of different FcγR members may utilize multiple components of the spectrum of effector responses on offer by the immune system.
T341 59413-59616 Sentence denotes Such “next‐gen” biologics will begin to realize the full potential of FcγR‐mediated antibody immune therapeutics and offer transformational change for the treatment of intractable and incurable diseases.
T342 59618-59638 Sentence denotes Conflict of Interest
T343 59639-59644 Sentence denotes None.