Different Adaptations of IgG Effector Function in Human and Nonhuman Primates and Implications for Therapeutic Antibody Treatment (original) (raw)
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IgG Binding Characteristics of Rhesus Macaque FcγR
Journal of immunology (Baltimore, Md. : 1950), 2016
Indian rhesus macaques (Macaca mulatta) are routinely used in preclinical studies to evaluate therapeutic Abs and candidate vaccines. The efficacy of these interventions in many cases is known to rely heavily on the ability of Abs to interact with a set of Ab FcγR expressed on innate immune cells. Yet, despite their presumed functional importance, M. mulatta Ab receptors are largely uncharacterized, posing a fundamental limit to ensuring accurate interpretation and translation of results from studies in this model. In this article, we describe the binding characteristics of the most prevalent allotypic variants of M. mulatta FcγR for binding to both human and M. mulatta IgG of varying subclasses. The resulting determination of the affinity, specificity, and glycan sensitivity of these receptors promises to be useful in designing and evaluating studies of candidate vaccines and therapeutic Abs in this key animal model and exposes significant evolutionary divergence between humans and...
Frontiers in Immunology
The field of HIV research relies heavily on non-human primates, particularly the members of the macaque genus, as models for the evaluation of candidate vaccines and monoclonal antibodies. A growing body of research suggests that successful protection of humans will not solely rely on the neutralization activity of an antibody's antigen binding fragment. Rather, immunological effector functions prompted by the interaction of the immunoglobulin G constant region and its cognate Fc receptors help contribute to favorable outcomes. Inherent differences in the sequences, expression, and activities of human and non-human primate antibody receptors and immunoglobulins have the potential to produce disparate results in the observations made in studies conducted in differing species. Having a more complete understanding of these differences, however, should permit the more fluent translation of observations between model organisms and the clinic. Here we present a guide to such translations that encompasses not only what is presently known regarding the affinity of the receptor-ligand interactions but also the influence of expression patterns and allelic variation, with a focus on insights gained from use of this model in HIV vaccines and passive antibody therapy and treatment.
IgG Fc variant cross-reactivity between human and rhesus macaque FcγRs
mAbs, 2017
Non-human primate (NHP) studies are often an essential component of antibody development efforts before human trials. Because the efficacy or toxicity of candidate antibodies may depend on their interactions with Fcg receptors (FcgR) and their resulting ability to induce FcgR-mediated effector functions such as antibody-dependent cell-meditated cytotoxicity and phagocytosis (ADCP), the evaluation of human IgG variants with modulated affinity toward human FcgR is becoming more prevalent in both infectious disease and oncology studies in NHP. Reliable translation of these results necessitates analysis of the cross-reactivity of these human Fc variants with NHP FcgR. We report evaluation of the binding affinities of a panel of human IgG subclasses, Fc amino acid point mutants and Fc glycosylation variants against the common allotypes of human and rhesus macaque FcgR by applying a high-throughput array-based surface plasmon resonance platform. The resulting data indicate that amino acid variation present in rhesus FcgRs can result in disrupted, matched, or even increased affinity of IgG Fc variants compared with human FcgR orthologs. These observations emphasize the importance of evaluating species cross-reactivity and developing an understanding of the potential limitations or suitability of representative in vitro and in vivo models before human clinical studies when either efficacy or toxicity may be associated with FcgR engagement.
Biophysical and Functional Characterization of Rhesus Macaque IgG Subclasses
Frontiers in Immunology, 2016
Antibodies raised in Indian rhesus macaques [Macaca mulatta (MM)] in many preclinical vaccine studies are often evaluated in vitro for titer, antigen-recognition breadth, neutralization potency, and/or effector function, and in vivo for potential associations with protection. However, despite reliance on this key animal model in translation of promising candidate vaccines for evaluation in first in man studies, little is known about the properties of MM immunoglobulin G (IgG) subclasses and how they may compare to human IgG subclasses. Here, we evaluate the binding of MM IgG1, IgG2, IgG3, and IgG4 to human Fc gamma receptors (FcγR) and their ability to elicit the effector functions of human FcγR-bearing cells, and unlike in humans, find a notable absence of subclasses with dramatically silent Fc regions. Biophysical, in vitro, and in vivo characterization revealed MM IgG1 exhibited the greatest effector function activity followed by IgG2 and then IgG3/4. These findings in rhesus are in contrast with the canonical understanding that IgG1 and IgG3 dominate effector function in humans, indicating that subclass-switching profiles observed in rhesus studies may not strictly recapitulate those observed in human vaccine studies.
IgG-effector functions: “The Good, The Bad and The Ugly”
Immunology Letters, 2014
IgG-antibodies are potent and versatile mediators of host protection. They elicit their biological effects through specific interaction of the Fc-part with complement, specific cellular receptors, or both. Several factors should be taken into consideration when analyzing the nature and intensity of the immunological response elicited via IgG-effector functions, especially for the family of IgG-Fc receptors (Fc␥Rs) exclusively expressed on immune cells. These include the various classes of leukocyte Fc␥R, expressed variably on different immune cells, each with distinct affinity for every IgG subclass, as well as genetic Fc␥R-polymorphisms affecting expression and affinity for IgG. Furthermore, various aspects of the IgG itself are also crucial for the outcome of the biological response. These include endogenously encoded IgG-polymorphisms, such as IgG3 polymorphisms, and post-transcriptional IgG-modifications, in particular IgG-Fc-glycosylation, affecting IgG effector functions through modified binding affinity to Fc␥R. These latter aspects concerning the variability in IgG3 on its half-life and placental transport and the clinical consequences of altered IgG-quality through glycosylation, will be the focus of this review.
Clinical Immunology, 2001
Keliximab, a Primatized IgG1 CD4 mAb, was reconfigured to an IgG4 antibody. The ␥4 constant region was further modified by substituting glutamic acid for serine at position 235 in the CH2 domain (IgG4-E), to remove residual binding to Fc␥ receptors, and substitution of serine with proline at position 228 in the hinge region (IgG4-PE) for greater stability. Pharmacokinetic analysis in rats gave a t 1/2 of approximately 4 days for IgG4-E and 9 days for IgG4-PE, consistent with a greater stability of the IgG4-PE molecule. The effects on T cell subsets were assessed in chimpanzees given escalating doses of IgG4-PE: 0.05 mg/kg on Day 16, 1.5 mg/kg dose on Day 43, and 15 mg/kg on Day 85. Receptor modulation was observed at the two highest doses, but no depletion of T cells at any dose. The in vitro and in vivo results demonstrate the potential of this IgG4-PE mAb for use in human trials.
Transfusion Clinique et Biologique, 2002
Sixty four IgG Rh monoclonal antibodies (Mabs) submitted to the Fourth International Workshop on Monoclonal Antibodies Against Human Red Blood Cells and Related Antigens were characterised and tested in quantitative functional assays at five laboratories. The biological assays measured the ability of anti-D to mediate phagocytosis or extracellular lysis of RBC by IgG Fc receptor (FcγR)-bearing effector cells. Interactions of RBC pre-sensitised with anti-D (EA-IgG) with monocytes in chemiluminescence (CL) assays were found proportional to the amount of IgG anti-D on the RBC. Using antibodies to inhibit FcγRI, FcγRII or FcγRIII, the only receptor utilised in the monocyte CL and ADCC assays for interactions with EA-IgG1 was found to be FcγRI. In these assays, enhanced interactions were promoted by EA-IgG3 and additional Fcγ receptors may have contributed. IgG2 anti-D was not reactive in these assays and EA-IgG4 promoted weak reactions through FcγRI. A macrophage ADCC assay showed that haemolysis of EA-IgG3 was greater than that of EA-IgG1, mediated mainly through FcγRIII. In ADCC assays using lymphocytes (NK cells) as effector cells and papainised RBC target cells, only a minority of IgG1 anti-D Mabs were shown to be able to mediate haemolysis in the presence of monomeric IgG (AB serum or IVIg). These interactions were mediated solely through FcγRIII. Haemolysis via FcγRIII may depend on the presence of certain sugars on the oligosaccharide moiety of IgG. Most Mabs (IgG1, IgG2, IgG3 and IgG4) elicited intermediate, low or no haemolysis in these assays. Blocking studies indicated that low activity IgG1 and IgG4 anti-D utilised only FcγRI. Other IgG1 and IgG3 Mabs appeared to promote haemolysis through FcγRI and FcγRIII while IgG2 was inhibited by Mabs to both FcγRII and FcγRIII, suggesting a variety of FcγR are utilised for anti-D of low haemolytic activity. Excellent agreement between the results of the lymphocyte ADCC assays and antibody quantitation was observed between the participating laboratories.
Immunogenetics, 2014
Macaques are the most widely used experimental nonhuman primate (NHP) species. Rhesus (Macaca mulatta, Macmul), cynomolgus (Macaca fascicularis, Macfas), and pigtail (Macaca nemestrina, Macnem) macaques continue to be popular models for vaccine and infectious diseases research, especially HIV infection and AIDS, and for the development of antibody-based therapeutic strategies. Increased understanding of the immune system of these species is necessary for their optimal use as models of human infections and intervention. In the past few years, the antibody/Fc receptor system has been characterized in a stepwise manner in these species. We have continued this characterization by identifying the four IG heavy gamma (IGHG) genes of Macfas and Macnem in this study. Our results show that these genes share a high degree of similarity with those from other NHP species, while presenting consistent differences when compared to human IGHG genes. Furthermore, comparison of Macfas IGHG genes with...
IgG subclasses and allotypes: from structure to effector functions
Of the five immunoglobulin isotypes, immunoglobulin G (IgG) is most abundant in human serum. The four subclasses, IgG1, IgG2, IgG3, and IgG4, which are highly conserved, differ in their constant region, particularly in their hinges and upper CH2 domains. These regions are involved in binding to both IgG-Fc receptors (FcγR) and C1q. As a result, the different subclasses have different effector functions, both in terms of triggering FcγR-expressing cells, resulting in phagocytosis or antibody-dependent cell-mediated cytotoxicity, and activating complement. The Fc-regions also contain a binding epitope for the neonatal Fc receptor (FcRn), responsible for the extended half-life, placental transport, and bidirectional transport of IgG to mucosal surfaces. However, FcRn is also expressed in myeloid cells, where it participates in both phagocytosis and antigen presentation together with classical FcγR and complement. How these properties, IgG-polymorphisms and post-translational modification of the antibodies in the form of glycosylation, affect IgG-function will be the focus of the current review.