Rhesus macaque antibody molecules: sequences and heterogeneity of alpha and gamma constant regions

Multivariate analysis of FcR-mediated NK cell functions identifies unique clustering among humans and rhesus macaques

Rhesus macaques (RMs) are a common pre-clinical model used to test HIV vaccine efficacy and passive immunization strategies. Yet, it remains unclear to what extent the Fc-Fc receptor (FcR) interactions impacting antiviral activities of antibodies in RMs recapitulate those in humans. Here, we evaluated the FcR-related functionality of natural killer cells (NKs) from peripheral blood of uninfected humans and RMs to identify intra- and inter-species variation. NKs were screened for FcγRIIIa (human) and FcγRIII (RM) genotypes (FcγRIII(a)), receptor signaling, and antibody-dependent cellular cytotoxicity (ADCC), the latter mediated by a cocktail of monoclonal IgG1 antibodies with human or RM Fc. FcγRIII(a) genetic polymorphisms alone did not explain differences in NK effector functionality in either species cohort. Using the same parameters, hierarchical clustering separated each species into two clusters. Importantly, in principal components analyses, ADCC magnitude, NK contribution to ADCC, FcγRIII(a) cell-surface expression, and frequency of phosphorylated CD3ζ NK cells all contributed similarly to the first principal component within each species, demonstrating the importance of measuring multiple facets of NK cell function. Although ADCC potency was similar between species, we detected significant differences in frequencies of NK cells and pCD3ζ+ cells, level of cell-surface FcγRIII(a) expression, and NK-mediated ADCC (P<0.001), indicating that a combination of Fc-FcR parameters contribute to overall inter-species functional differences. These data strongly support the importance of multi-parameter analyses of Fc-FcR NK-mediated functions when evaluating efficacy of passive and active immunizations in pre- and clinical trials and identifying correlates of protection. The results also suggest that pre-screening animals for multiple FcR-mediated NK function would ensure even distribution of animals among treatment groups in future preclinical trials.

IgG1-Dominant Antibody Response Induced by Recombinant Trimeric SARS-CoV-2 Spike Protein with PIKA Adjuvant

Recombinant trimeric SARS-CoV-2 Spike protein with PIKA (polyI:C) adjuvant induces potent and durable neutralizing antibodies that protect against multiple SARS-CoV-2 variants. The immunoglobulin subclasses of viral-specific antibodies remain unknown, as do their glycosylation status on Fc regions. In this study, we analyzed immunoglobulins adsorbed by plate-bound recombinant trimeric SARS-CoV-2 Spike protein from serum of Cynomolgus monkey immunized by recombinant trimeric SARS-CoV-2 Spike protein with PIKA (polyI:C) adjuvant. The results showed that IgG1 was the dominant IgG subclass as revealed by ion mobility mass spectrometry. The average percentage of Spike protein-specific IgG1 increased to 88.3% as compared to pre-immunization. Core fucosylation for Fc glycopeptide of Spike protein-specific IgG1 was found to be higher than 98%. These results indicate that a unique Th1-biased, IgG1-dominant antibody response was responsible for the effectiveness of PIKA (polyI:C) adjuvant. Vaccine-induced core-fucosylation of IgG1 Fc region may reduce incidence of severe COVID-19 disease associated with overstimulation of FCGR3A by afucosylated IgG1.

Gingival tissue antibody gene utilization in aging and periodontitis

OBJECTIVE

This study used a nonhuman primate model of ligature-induced periodontitis to document the characteristics of immunoglobulin (Ig) gene usage in gingival tissues with disease and affected by age.

BACKGROUND

Adaptive immune responses to an array of oral bacteria are routinely detected in local gingival tissues and the systemic circulation across the human population. The level and diversity of antibody increases with periodontitis, reflecting the increased quantity of B cells and plasmacytes in the tissues at sites of periodontal lesions.

METHODS

Macaca mulatta (n = 36) in four groups (young - ≤3 years; adolescent >3-7 years; adult - 12-15 years; aged - 17-23 years) were used in this study. Gingival tissues were sampled at baseline (health), 2 weeks (initiation), 1 and 3 months (progression), and 5 months (resolution) of the lesion development and transcriptomic analysis included 78 Ig-related genes.

RESULTS

The results demonstrated extensive variation in Ig gene usage patterns and changes with the disease process that was substantially affected by the age of the animal. Of note was that the aged animals generally demonstrated elevated expression on multiple Ig genes even in the baseline/healthy gingival tissues. The expression levels revealed 5 aggregates of Ig gene change profiles across the age groups. The number of gene changes were greatly increased in adult animals with the initiation of disease, while the young and adolescent animals showed extensive changes with disease progression. Elevated Ig gene transcripts remained with disease resolution except in the aged animals. The response profiles demonstrated selective heavy/light change gene transcripts that differed with age and clustering of the transcript expression was dominated by the age of the animals.

CONCLUSIONS

The results suggested potential critical variations in the molecular aspects of Ig gene expression in gingival tissues that can contribute to understanding the kinetics of periodontal lesions, as well as the variation in episodes, rapidity of progression, and role in resolution that are impacted by age.

Molecular characterisation of parvorder Platyrrhini IgG sub-classes

Non-human primates (NHP) are essential in modern biomedical research; New World monkeys (NWM) are mainly used as an experimental model regarding human malaria as they provide useful information about the parasite's biology and an induced immune response. It is known that a vaccine candidate's efficacy is mediated by a protection-inducing antibody response (IgG). Not enough information is available concerning IgG subclasses' molecular characteristics regarding NHP from parvorder Platyrrhini. Understanding the nature of the humoral immune response and characterising the IgG subclasses' profile will provide valuable information about the immunomodulator mechanisms of vaccines evaluated using an NHP animal model. This article has characterised IgG subclasses in NWM (i.e. genera Aotus, Cebus, Ateles and Alouatta) based on the amplification, cloning and sequencing of the immunoglobulin heavy constant gamma (IGHG) gene's CH1 to CH3 regions. The resulting sequences enabled elucidating IGHG gene organisation; two IgG variants were found in the Aotus and Ateles monkey group and three IgG variants in the Cebus and Alouatta group. The sequences were highly conserved in Platyrrhini and had a similar structure to that reported for monkeys from parvorder Catarrhini. Such information will help in developing tools for a detailed characterisation of the humoral immune response in an NWM experimental animal model.

Development of anti-thrombotic vaccine against human S100A9 in rhesus monkey

In post-stroke patients, a decreased adherence to antiplatelet drugs is a major challenge in the prevention of recurrent stroke. Previously, we reported an antiplatelet vaccine against S100A9 in mice, but the use of Freund’s adjuvant and the difference in amino acid sequences in epitopes between mice and humans were problematic for clinical use. Here, we redesigned the S100A9 vaccine for the common sequence in both humans and monkeys and examined its effects in cynomolgus monkeys with Alum adjuvant. First, we assessed several candidate epitopes and selected 102 to 112 amino acids as the suitable epitope, which could produce antibodies. When this peptide vaccine was intradermally injected into 4 cynomolgus monkeys with Alum, the antibody against human S100A9 was successfully produced. Anti-thrombotic effects were shown in two monkeys in a mixture of vaccinated serum and fresh whole blood from another cynomolgus monkey. Additionally, the anti-thrombotic effects were partially inhibited by the epitope peptide, indicating the feasibility of neutralizing anti-thrombotic effects of produced antibodies. Prolongation of bleeding time was not observed in vaccinated monkeys. Although further studies on increasing the effect of vaccine and safety are necessary, this vaccine will be a promising approach to improve adherence to antiplatelet drugs in clinical settings.

Functional Homology for Antibody-Dependent Phagocytosis Across Humans and Rhesus Macaques

Analyses of human clinical HIV-1 vaccine trials and preclinical vaccine studies performed in rhesus macaque (RM) models have identified associations between non-neutralizing Fc Receptor (FcR)-dependent antibody effector functions and reduced risk of infection. Specifically, antibody-dependent phagocytosis (ADP) has emerged as a common correlate of reduced infection risk in multiple RM studies and the human HVTN505 trial. This recurrent finding suggests that antibody responses with the capability to mediate ADP are most likely a desirable component of vaccine responses aimed at protecting against HIV-1 acquisition. As use of RM models is essential for development of the next generation of candidate HIV-1 vaccines, there is a need to determine how effectively ADP activity observed in RMs translates to activity in humans. In this study we compared ADP activity of human and RM monocytes and polymorphonuclear leukocytes (PMN) to bridge this gap in knowledge. We observed considerable variability in the magnitude of monocyte and PMN ADP activity across individual humans and RM that was not dependent on FcR alleles, and only modestly impacted by cell-surface levels of FcRs. Importantly, we found that for both human and RM phagocytes, ADP activity of antibodies targeting the CD4 binding site was greatest when mediated by human IgG3, followed by RM and human IgG1. These results demonstrate that there is functional homology between antibody and FcRs from these two species for ADP. We also used novel RM IgG1 monoclonal antibodies engineered with elongated hinge regions to show that hinge elongation augments RM ADP activity. The RM IgGs with engineered hinge regions can achieve ADP activity comparable to that observed with human IgG3. These novel modified antibodies will have utility in passive immunization studies aimed at defining the role of IgG3 and ADP in protection from virus challenge or control of disease in RM models. Our results contribute to a better translation of human and macaque antibody and FcR biology, and may help to improve testing accuracy and evaluations of future active and passive prevention strategies.

Coming together at the hinges: Therapeutic prospects of IgG3

The human IgG3 subclass is conspicuously absent among the formats for approved monoclonal antibody therapies and Fc fusion protein biologics. Concern about the potential for rapid degradation, reduced plasma half-life, and increased immunogenicity due to marked variation in allotypes has apparently outweighed the potential advantages of IgG3, which include high affinity for activating Fcγ receptors, effective complement fixation, and a long hinge that appears better suited for low abundance targets. This review aims to highlight distinguishing features of IgG3 and to explore its functional role in the immune response. We present studies of natural immunity and recombinant antibody therapies that elucidate key contributions of IgG3 and discuss historical roadblocks that no longer remain clearly relevant. Collectively, this body of evidence motivates thoughtful reconsideration of the clinical advancement of this distinctive antibody subclass for treatment of human diseases. Abbreviations: ADCC - Antibody-Dependent Cell-mediated CytotoxicityADE - Antibody-dependent enhancementAID - Activation-Induced Cytidine DeaminaseCH - Constant HeavyCHF - Complement factor HCSR - Class Switch RecombinationEM - Electron MicroscopyFab - Fragment, antigen bindingFc - Fragment, crystallizableFcRn - Neonatal Fc ReceptorFcγR - Fc gamma ReceptorHIV - Human Immunodeficiency VirusIg - ImmunoglobulinIgH - Immunoglobulin Heavy chain geneNHP - Non-Human Primate.

Functional Interactions of Common Allotypes of Rhesus Macaque FcγR2A and FcγR3A with Human and Macaque IgG Subclasses

The rhesus macaque is an important animal model for AIDS and other infectious diseases. However, the investigation of Fc-mediated Ab responses in macaques is complicated by species-specific differences in FcγRs and IgG subclasses relative to humans. To assess the effects of these differences on FcγR-IgG interactions, reporter cell lines expressing common allotypes of human and rhesus macaque FcγR2A and FcγR3A were established. FcγR-mediated responses to B cells were measured in the presence of serial dilutions of anti-CD20 Abs with Fc domains corresponding to each of the four subclasses of human and rhesus IgG and with Fc variants of IgG1 that enhance binding to FcγR2A or FcγR3A. All of the FcγRs were functional and preferentially recognized either IgG1 or IgG2. Whereas allotypes of rhesus FcγR2A were identified with responses similar to variants of human FcγR2A with higher (H131) and lower (R131) affinity for IgG, all of the rhesus FcγR3A allotypes exhibited responses most similar to the higher affinity V158 variant of human FcγR3A. Unlike responses to human IgGs, there was little variation in FcγR-mediated responses to different subclasses of rhesus IgG. Phylogenetic comparisons suggest that this reflects limited sequence variation of macaque IgGs as a result of their relatively recent diversification from a common IGHG gene since humans and macaques last shared a common ancestor. These findings reveal species-specific differences in FcγR-IgG interactions with important implications for investigating Ab effector functions in macaques.

Igh locus structure and evolution in Platyrrhines: new insights from a genomic perspective

Non-human primates have been used as animal models because of their phylogenetic closeness to humans. However, the genetic differences between humans and non-human primates must be considered to select the appropriate animal models. Recently, New World monkeys (Platyrrhines) have generated a higher interest in biomedical research, especially in assessing vaccine safety and immunogenicity. Given the continued and renewed interest in Platyrrhines as biomedical models, it is a necessary to have a better and more complete understanding of their immune system and its implications for research. Immunoglobulins (Ig) are the main proteins that mediate humoral immunity. These proteins have evolved as part of an adaptive immune response system derived from ancient vertebrates. There are at least four Ig classes in Prosimians, whereas five have been reported in Catarrhines. Information on the structure and evolution of the loci containing immunoglobulin heavy chain constant genes (Igh) in Platyrrhines, however, is limited. Here, Igh loci were characterized in 10 Platyrrhines using the available whole genome sequences. Human and Macaca Igh loci were also assessed to compare them with their Platyrrhines counterparts. Differences in Igh locus structure were observed between Platyrrhines and Catarrhines. Noteworthy changes occur in the γ gene, which encodes a key Ig involved in organism defense that would favor protection after vaccination. The remarkable differences between the immunoglobulin proteins of Platyrrhines and Catarrhines warrant a cautionary message to biomedical researchers.

Knowns and Unknowns of Assaying Antibody-Dependent Cell-Mediated Cytotoxicity Against HIV-1

It is now well-accepted that Fc-mediated effector functions, including antibody-dependent cellular cytotoxicity (ADCC), can contribute to vaccine-elicited protection as well as post-infection control of HIV viremia. This picture was derived using a wide array of ADCC assays, no two of which are strictly comparable, and none of which is qualified at the clinical laboratory level. An earlier comparative study of assay protocols showed that while data from different ADCC assay formats were often correlated, they remained distinct in terms of target cells and the epitopes and antigen(s) available for recognition by antibodies, the effector cells, and the readout of cytotoxicity. This initial study warrants expanded analyses of the relationships among all current assay formats to determine where they detect overlapping activities and where they do not. Here we summarize knowns and unknowns of assaying ADCC against HIV-1.

Mind the Gap: How Interspecies Variability in IgG and Its Receptors May Complicate Comparisons of Human and Non-human Primate Effector Function

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.

From Rhesus macaque to human: structural evolutionary pathways for immunoglobulin G subclasses

The Old World monkey, Rhesus macaque (Macaca mulatta, Mm), is frequently used as a primate model organism in the study of human disease and to test new vaccines/antibody treatments despite diverging before chimpanzees and orangutans. Mm and humans share 93% genome identity with substantial differences in the genes of the adaptive immune system that lead to different functional IgG subclass characteristics, Fcγ receptors expressed on innate immune cells, and biological interactions. These differences put limitations on Mm use as a primary animal model in the study of human disease and to test new vaccines/antibody treatments. Here, we comprehensively analyzed molecular properties of the Fc domain of the four IgG subclasses of Rhesus macaque to describe potential mechanisms for their interactions with effector cell Fc receptors. Our studies revealed less diversity in the overall structure among the Mm IgG Fc, with MmIgG1 Fc being the most structurally like human IgG3, although its CH2 loops and N297 glycan mobility are comparable to human IgG1. Furthermore, the Fcs of Mm IgG3 and 4 lack the structural properties typical for their human orthologues that determine IgG3's reduced interaction with the neonatal receptor and IgG4's ability for Fab-arm exchange and its weaker Fcγ receptor interactions. Taken together, our data indicate that MmIgG1-4 are less structurally divergent than the human IgGs, with only MmIgG1 matching the molecular properties of human IgG1 and 3, the most active IgGs in terms of Fcγ receptor binding and Fc-mediated functions. PDB accession numbers for deposited structures are 6D4E, 6D4I, 6D4M, and 6D4N for MmIgG1 Fc, MmIgG2 Fc, MmIgG3 Fc, and MmIgG4 Fc, respectively.

Adeno-Associated Virus Delivery of Anti-HIV Monoclonal Antibodies Can Drive Long-Term Virologic Suppression

Long-term delivery of anti-HIV monoclonal antibodies (mAbs) using adeno-associated virus (AAV) vectors holds promise for the prevention and treatment of HIV infection. We describe a therapy trial in which four rhesus monkeys were infected with SHIV-AD8 for 86 weeks before receiving the AAV-encoded mAbs 3BNC117, 10-1074, and 10E8. Although anti-drug antibody (ADA) responses restricted mAb delivery, one monkey successfully maintained 50-150 μg/mL of 3BNC117 and 10-1074 for over 2 years. Delivery of these two mAbs to this monkey resulted in an abrupt decline in plasma viremia, which remained undetectable for 38 successive measurements over 3 years. We generated two more examples of virologic suppression using AAV delivery of a cocktail of four mAbs in a 12-monkey study. Our results provide proof of concept for AAV-delivered mAbs to produce a "functional cure." However, they also serve as a warning that ADAs may be a problem for practical application of this approach in humans.

Anti-drug Antibody Responses Impair Prophylaxis Mediated by AAV-Delivered HIV-1 Broadly Neutralizing Antibodies

Adeno-associated virus (AAV) delivery of potent and broadly neutralizing antibodies (bNAbs is a promising approach for the prevention of HIV-1 infection. The immunoglobulin G (IgG)1 subtype is usually selected for this application, because it efficiently mediates antibody effector functions and has a somewhat longer half-life. However, the use of IgG1-Fc has been associated with the generation of anti-drug antibodies (ADAs) that correlate with loss of antibody expression. In contrast, we have shown that expression of the antibody-like molecule eCD4-Ig bearing a rhesus IgG2-Fc domain showed reduced immunogenicity and completely protected rhesus macaques from simian-HIV (SHIV)-AD8 challenges. To directly compare the performance of the IgG1-Fc and the IgG2-Fc domains in a prophylactic setting, we compared AAV1 expression of rhesus IgG1 and IgG2 forms of four anti-HIV bNAbs: 3BNC117, NIH45-46, 10-1074, and PGT121. Interestingly, IgG2-isotyped bNAbs elicited significantly lower ADA than their IgG1 counterparts. We also observed significant protection from two SHIV-AD8 challenges in macaques expressing IgG2-isotyped bNAbs, but not from those expressing IgG1. Our data suggest that monoclonal antibodies isotyped with IgG2-Fc domains are less immunogenic than their IgG1 counterparts, and they highlight ADAs as a key barrier to the use of AAV1-expressed bNAbs.

Antibody-Dependent Cellular Phagocytosis in Antiviral Immune Responses

Antiviral activities of antibodies may either be dependent only on interactions between the antibody and cognate antigen, as in binding and neutralization of an infectious virion, or instead may require interactions between antibody-antigen immune complexes and immunoproteins or Fc receptor expressing immune effector cells. These Fc receptor-dependent antibody functions provide a direct link between the innate and adaptive immune systems by combining the potent antiviral activity of innate effector cells with the diversity and specificity of the adaptive humoral response. The Fc receptor-dependent function of antibody-dependent cellular phagocytosis (ADCP) provides mechanisms for clearance of virus and virus-infected cells, as well as for stimulation of downstream adaptive immune responses by facilitating antigen presentation, or by stimulating the secretion of inflammatory mediators. In this review, we discuss the properties of Fc receptors, antibodies, and effector cells that influence ADCP. We also provide and interpret evidence from studies that support a potential role for ADCP in either inhibiting or enhancing viral infection. Finally, we describe current approaches used to measure antiviral ADCP and discuss considerations for the translation of studies performed in animal models. We propose that additional investigation into the role of ADCP in protective viral responses, the specific virus epitopes targeted by ADCP antibodies, and the types of phagocytes and Fc receptors involved in ADCP at sites of virus infection will provide insight into strategies to successfully leverage this important immune response for improved antiviral immunity through rational vaccine design.

Rhesus macaque and mouse models for down-selecting circumsporozoite protein based malaria vaccines differ significantly in immunogenicity and functional outcomes

BACKGROUND

Non-human primates, such as the rhesus macaques, are the preferred model for down-selecting human malaria vaccine formulations, but the rhesus model is expensive and does not allow for direct efficacy testing of human malaria vaccines. Transgenic rodent parasites expressing genes of human Plasmodium are now routinely used for efficacy studies of human malaria vaccines. Mice have however rarely predicted success in human malaria trials and there is scepticism whether mouse studies alone are sufficient to move a vaccine candidate into the clinic.

METHODS

A comparison of immunogenicity, fine-specificity and functional activity of two Alum-adjuvanted Plasmodium falciparum circumsporozoite protein (CSP)-based vaccines was conducted in mouse and rhesus models. One vaccine was a soluble recombinant protein (CSP) and the other was the same CSP covalently conjugated to the Qβ phage particle (Qβ-CSP).

RESULTS

Mice showed different kinetics of antibody responses and different sensitivity to the NANP-repeat and N-terminal epitopes as compared to rhesus. While mice failed to discern differences between the protective efficacy of CSP versus Qβ-CSP vaccine following direct challenge with transgenic Plasmodium berghei parasites, rhesus serum from the Qβ-CSP-vaccinated animals induced higher in vivo sporozoite neutralization activity.

CONCLUSIONS

Despite some immunologic parallels between models, these data demonstrate that differences between the immune responses induced in the two models risk conflicting decisions regarding potential vaccine utility in humans. In combination with historical observations, the data presented here suggest that although murine models may be useful for some purposes, non-human primate models may be more likely to predict the human response to investigational vaccines.

Biophysical and Functional Characterization of Rhesus Macaque IgG Subclasses

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.

Enhanced protective antibody to a mutant meningococcal factor H-binding protein with low-factor H binding

Meningococcal factor H-binding protein (FHbp) is an antigen in 2 serogroup B meningococcal vaccines. FHbp specifically binds human and some nonhuman primate complement FH. To investigate the effect of binding of FH to FHbp on protective antibody responses, we immunized infant rhesus macaques with either a control recombinant FHbp antigen that bound macaque FH or a mutant antigen with 2 amino acid substitutions and >250-fold lower affinity for FH. The mutant antigen elicited 3-fold higher serum IgG anti-FHbp titers and up to 15-fold higher serum bactericidal titers than the control FHbp vaccine. When comparing sera with similar IgG anti-FHbp titers, the antibodies elicited by the mutant antigen gave greater deposition of complement component C4b on live meningococci (classical complement pathway) and inhibited binding of FH, while the anti-FHbp antibodies elicited by the control vaccine enhanced FH binding. Thus, the mutant FHbp vaccine elicited an anti-FHbp antibody repertoire directed at FHbp epitopes within the FH binding site, which resulted in greater protective activity than the antibodies elicited by the control vaccine, which targeted FHbp epitopes outside of the FH combining site. Binding of a host protein to a vaccine antigen impairs protective antibody responses, which can be overcome with low-binding mutant antigens.

IgG Binding Characteristics of Rhesus Macaque FcγR

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 macaques.

Cynomolgus macaque (Macaca fascicularis) immunoglobulin heavy chain locus description

Cynomolgus macaques (Macaca fascicularis) have become an important animal model for biomedical research. In particular, it is the animal model of choice for the development of vaccine candidates associated with emerging dangerous pathogens. Despite their increasing importance as animal models, the cynomolgus macaque genome is not fully characterized, hindering molecular studies for this model. More importantly, the lack of knowledge about the immunoglobulin (IG) locus organization directly impacts the analysis of the humoral response in cynomolgus macaques. Recent advances in next generation sequencing (NGS) technologies to analyze IG repertoires open the opportunity to deeply characterize the humoral immune response. However, the IG locus organization for the animal is required to completely dissect IG repertoires. Here, we describe the localization and organization of the rearranging IG heavy (IGH) genes on chromosome 7 of the cynomolgus macaque draft genome. Our annotation comprises 108 functional genes which include 63 variable (IGHV), 38 diversity (IGHD), and 7 joining (IGHJ) genes. For validation, we provide RNA transcript data for most of the IGHV genes and all of the annotated IGHJ genes, as well as proteomic data to validate IGH constant genes. The description and annotation of the rearranging IGH genes for the cynomolgus macaques will significantly facilitate scientific research. This is particularly relevant to dissect the immune response during vaccination or infection with dangerous pathogens such as Ebola, Marburg and other emerging pathogens where non-human primate models play a significant role for countermeasure development.

Efficient generation of monoclonal antibodies from single rhesus macaque antibody secreting cells

Nonhuman primates (NHPs) are used as a preclinical model for vaccine development, and the antibody profiles to experimental vaccines in NHPs can provide critical information for both vaccine design and translation to clinical efficacy. However, an efficient protocol for generating monoclonal antibodies from single antibody secreting cells of NHPs is currently lacking. In this study we established a robust protocol for cloning immunoglobulin (IG) variable domain genes from single rhesus macaque (Macaca mulatta) antibody secreting cells. A sorting strategy was developed using a panel of molecular markers (CD3, CD19, CD20, surface IgG, intracellular IgG, CD27, Ki67 and CD38) to identify the kinetics of B cell response after vaccination. Specific primers for the rhesus macaque IG genes were designed and validated using cDNA isolated from macaque peripheral blood mononuclear cells. Cloning efficiency was averaged at 90% for variable heavy (VH) and light (VL) domains, and 78.5% of the clones (n = 335) were matched VH and VL pairs. Sequence analysis revealed that diverse IGHV subgroups (for VH) and IGKV and IGLV subgroups (for VL) were represented in the cloned antibodies. The protocol was tested in a study using an experimental dengue vaccine candidate. About 26.6% of the monoclonal antibodies cloned from the vaccinated rhesus macaques react with the dengue vaccine antigens. These results validate the protocol for cloning monoclonal antibodies in response to vaccination from single macaque antibody secreting cells, which have general applicability for determining monoclonal antibody profiles in response to other immunogens or vaccine studies of interest in NHPs.

Host Anti-antibody Responses Following Adeno-associated Virus-mediated Delivery of Antibodies Against HIV and SIV in Rhesus Monkeys

Long-term delivery of antibodies against the human immunodeficiency virus (HIV) using adeno-associated virus (AAV) vectors is a promising approach for the prevention or treatment of HIV infection. However, host antibody responses to the delivered antibody are a serious concern that could significantly limit the applicability of this approach. Here, we describe the dynamics and characteristics of the anti-antibody responses in monkeys that received either rhesus anti-simian immunodeficiency virus (SIV) antibodies (4L6 or 5L7) in prevention trials or a combination of rhesusized human anti-HIV antibodies (1NC9/8ANC195/3BNC117 or 10-1074/10E8/3BNC117) in therapy trials, all employing AAV1 delivery of IgG1. Eight out of eight monkeys that received the anti-HIV antibodies made persisting antibody responses to all three antibodies in the mix. Six out of six uninfected monkeys that received the anti-SIV antibody 4L6 and three out of six of those receiving anti-SIV antibody 5L7 also generated anti-antibodies. Both heavy and light chains were targeted, predominantly or exclusively to variable regions, and reactivity to complementarity-determining region (CDR)-H3 peptide could be demonstrated. There was a highly significant correlation of the magnitude of anti-antibody responses with the degree of sequence divergence of the delivered antibody from germline. Our results suggest the need for effective strategies to counteract the problem of antibody responses to AAV-delivered antibodies.

Immunoglobulin VH gene diversity and somatic hypermutation during SIV infection of rhesus macaques

B cell functional defects are associated with delayed neutralizing antibody development in pathogenic lentivirus infections. However, the timeframe for alterations in the antibody repertoire and somatic hypermutation (SHM) remains unclear. Here, we utilized the SIV/rhesus macaque (RM) model to investigate the dynamics of immunoglobulin V(H) gene diversity and SHM following infection. Three RMs were infected with SIVmac239, and V(H)1, V(H)3, and V(H)4 genes were amplified from peripheral blood at 0, 2, 6, 24, and 36 weeks postinfection for next-generation sequencing. Analysis of over 3.8 million sequences against currently available RM germline V(H) genes revealed a highly biased V(H) gene repertoire in outbred RMs. SIV infection did not significantly perturb the predominant IgG1 response, but overall immunoglobulin SHM declined during the course of SIV infection. Moreover, SHM at the AID deamination hotspot, WRC, rapidly decreased and was suppressed throughout SIV infection. In contrast, a transient increase in mutations at the APOBEC3G deamination hotspot, CCC, coincided with a spike in APOBEC3G expression during acute SIV infection. The results outline a timetable for altered V(H) gene repertoire and IgG SHM in the SIV/RM model and suggest a burst of APOBEC3G-mediated antibody SHM during acute SIV infection.

Defense-in-depth by mucosally administered anti-HIV dimeric IgA2 and systemic IgG1 mAbs: complete protection of rhesus monkeys from mucosal SHIV challenge

Although IgA is the most abundantly produced immunoglobulin in humans, its role in preventing HIV-1 acquisition, which occurs mostly via mucosal routes, remains unclear. In our passive mucosal immunizations of rhesus macaques (RMs), the anti-HIV-1 neutralizing monoclonal antibody (nmAb) HGN194, given either as dimeric IgA1 (dIgA1) or dIgA2 intrarectally (i.r.), protected 83% or 17% of the RMs against i.r. simian-human immunodeficiency virus (SHIV) challenge, respectively. Data from the RV144 trial implied that vaccine-induced plasma IgA counteracted the protective effector mechanisms of IgG1 with the same epitope specificity. We thus hypothesized that mucosal dIgA2 might diminish the protection provided by IgG1 mAbs targeting the same epitope. To test our hypothesis, we administered HGN194 IgG1 intravenously (i.v.) either alone or combined with i.r. HGN194 dIgA2. We enrolled SHIV-exposed, persistently aviremic RMs protected by previously administered nmAbs; RM anti-human IgG responses were undetectable. However, low-level SIV Gag-specific proliferative T-cell responses were found. These animals resemble HIV-exposed, uninfected humans, in which local and systemic cellular immune responses have been observed. HGN194 IgG1 and dIgA2 used alone and the combination of the two neutralized the challenge virus equally well in vitro. All RMs given only i.v. HGN194 IgG1 became infected. In contrast, all RMs given HGN194 IgG1+dIgA2 were completely protected against high-dose i.r. SHIV-1157ipEL-p challenge. These data imply that combining suboptimal defenses at the mucosal and systemic levels can completely prevent virus acquisition. Consequently, active vaccination should focus on defense-in-depth, a strategy that seeks to build up defensive fall-back positions well behind the fortified frontline.

Common features of mucosal and peripheral antibody responses elicited by candidate HIV-1 vaccines in rhesus monkeys

Human immunodeficiency virus type 1 (HIV-1) vaccines that elicit protective antibody responses at mucosal sites would be highly desirable. Here, we report that intramuscular immunization of candidate HIV-1 vaccine vectors and purified Env proteins elicited potent and durable humoral immune responses in colorectal mucosa in rhesus monkeys. The kinetics, isotypes, functionality, and epitope specificity of these mucosal antibody responses were similar to those of peripheral responses in serum. These data suggest a close immunological relationship between mucosal and systemic antibody responses following vaccination in primates.

Differential expression of anti-glycan antibodies in schistosome-infected humans, rhesus monkeys and mice

Schistosomiasis is a debilitating parasitic disease of humans, endemic in tropical areas, for which no vaccine is available. Evidence points to glycan antigens as being important in immune responses to infection. Here we describe our studies on the comparative humoral immune responses to defined schistosome-type glycan epitopes in Schistosoma mansoni-infected humans, rhesus monkeys and mice. Rhesus anti-glycan responses over the course of infection were screened on a defined glycan microarray comprising semi-synthetic glycopeptides terminating with schistosome-associated or control mammalian-type glycan epitopes, as well as a defined glycan microarray of mammalian-type glycans representing over 400 glycan structures. Infected rhesus monkeys generated a high immunoglobulin G (IgG) antibody response to the core xylose/core α3 fucose epitope of N-glycans, which peaked at 8-11 weeks post infection, coinciding with maximal ability to kill schistosomula in vitro. By contrast, infected humans generated low antibody levels to this epitope. At 18 months following praziquantel therapy to eliminate the parasite, antibody levels were negligible. Mice chronically infected with S. mansoni generated high levels of anti-fucosylated LacdiNAc (GalNAcβ1, 4(Fucα1, 3)GlcNAc) IgM antibodies, but lacked a robust response to the core xylose/core α3 fucose N-glycan antigens compared with other species studied, and their sera demonstrated an intermediate level of schistosomula killing in vitro. These differential responses to parasite glycan antigens may be related to the ability of rhesus monkeys to self-cure in contrast to the chronic infection seen in humans and mice. Our results validate defined glycan microarrays as a useful technology to evaluate diagnostic and vaccine antigens for schistosomiasis and perhaps other infections.

Cynomolgus and pigtail macaque IgG subclasses: characterization of IGHG genes and computational analysis of IgG/Fc receptor binding affinity

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 those described in other studies suggests the existence of polymorphism. Using sequence- and structure-based computational tools, we performed in silico analysis on multiple polymorphic Macfas IgG and their interactions with human IgG Fc receptors (FcγR), thus predicting that Macfas IGHG polymorphisms influence IgG protein stability and/or binding affinity towards FcγR. The presence of macaque IGHG polymorphisms and macaque/human amino acid changes at locations potentially involved in antibody functional properties indicate the need for cautious design and data interpretation of studies in these models, possibly requiring the characterization of antibody/Fc receptor interactions at the individual level.

Opening the door to innovation

Open innovation is the new buzz, with initiatives popping up left and right. Here, we give a personal perspective on a very successful, knowledge-driven innovation initiated in an academia- industry alliance, which culminated in technology platforms that enable the generation of therapeutic antibodies with novel properties. To start, we provide a general background on open innovation in the drug development field.

The FcγR of humans and non-human primates and their interaction with IgG: implications for induction of inflammation, resistance to infection and the use of therapeutic monoclonal antibodies

Considerable effort has focused on the roles of the individual members of the FcγR receptor (FcγR) family in inflammatory diseases and humoral immunity. Recent work has revealed major roles in infection and in particular HIV pathogenesis and immunity. In addition, FcγR functions underpin the action of many of the successful therapeutic monoclonal antibodies. This emphasises the need for a greater understanding of FcγR function in humans and in the NHP which provides a key model for human immunity and preclinical testing of antibodies. We discuss recent key aspects of the human FcγR receptor biology and structure to define differences and similarities in activity between the human and macaque Fc receptors. These differences and similarities nuance the interpretation of infection and vaccine studies in the macaque. Indeed passive IgG antibody protection in lentivirus infection models in the macaque provided early evidence for the role of Fc receptors in anti-HIV immunity that have subsequently gained support from human vaccine trials. None-the-less the diverse functions and cellular contexts of FcγR receptor expression ensure there is much still to understand of the protective and deleterious effects of FcγRs in HIV infection. Careful comparative studies of human and non-human primate FcγRs will facilitate our appreciation of what attributes of HIV specific IgG antibodies, either acquired naturally or via vaccination, are most important for protection.

Nonhuman primate models for HIV/AIDS vaccine development

The development of HIV vaccines has been hampered by the lack of an animal model that can accurately predict vaccine efficacy. Chimpanzees can be infected with HIV-1 but are not practical for research. However, several species of macaques are susceptible to the simian immunodeficiency viruses (SIVs) that cause disease in macaques, which also closely mimic HIV in humans. Thus, macaque-SIV models of HIV infection have become a critical foundation for AIDS vaccine development. Here we examine the multiple variables and considerations that must be taken into account in order to use this nonhuman primate (NHP) model effectively. These include the species and subspecies of macaques, virus strain, dose and route of administration, and macaque genetics, including the major histocompatibility complex molecules that affect immune responses, and other virus restriction factors. We illustrate how these NHP models can be used to carry out studies of immune responses in mucosal and other tissues that could not easily be performed on human volunteers. Furthermore, macaques are an ideal model system to optimize adjuvants, test vaccine platforms, and identify correlates of protection that can advance the HIV vaccine field. We also illustrate techniques used to identify different macaque lymphocyte populations and review some poxvirus vaccine candidates that are in various stages of clinical trials. Understanding how to effectively use this valuable model will greatly increase the likelihood of finding a successful vaccine for HIV.

Rapid Generation of Human-Like Neutralizing Monoclonal Antibodies in Urgent Preparedness for Influenza Pandemics and Virulent Infectious Diseases

BACKGROUND

The outbreaks of emerging infectious diseases caused by pathogens such as SARS coronavirus, H5N1, H1N1, and recently H7N9 influenza viruses, have been associated with significant mortality and morbidity in humans. Neutralizing antibodies from individuals who have recovered from an infection confer therapeutic protection to others infected with the same pathogen. However, survivors may not always be available for providing plasma or for the cloning of monoclonal antibodies (mAbs).

METHODOLOGY/PRINCIPAL FINDINGS

The genome and the immunoglobulin genes in rhesus macaques and humans are highly homologous; therefore, we investigated whether neutralizing mAbs that are highly homologous to those of humans (human-like) could be generated. Using the H5N1 influenza virus as a model, we first immunized rhesus macaques with recombinant adenoviruses carrying a synthetic gene encoding hemagglutinin (HA). Following screening an antibody phage display library derived from the B cells of immunized monkeys, we cloned selected macaque immunoglobulin heavy chain and light chain variable regions into the human IgG constant region, which generated human-macaque chimeric mAbs exhibiting over 97% homology to human antibodies. Selected mAbs demonstrated potent neutralizing activities against three clades (0, 1, 2) of the H5N1 influenza viruses. The in vivo protection experiments demonstrated that the mAbs effectively protected the mice even when administered up to 3 days after infection with H5N1 influenza virus. In particular, mAb 4E6 demonstrated sub-picomolar binding affinity to HA and superior in vivo protection efficacy without the loss of body weight and obvious lung damage. The analysis of the 4E6 escape mutants demonstrated that the 4E6 antibody bound to a conserved epitope region containing two amino acids on the globular head of HA.

CONCLUSIONS/SIGNIFICANCE

Our study demonstrated the generation of neutralizing mAbs for potential application in humans in urgent preparedness against outbreaks of new influenza infections or other virulent infectious diseases.

Neutralizing capacity of monoclonal antibodies that recognize peptide sequences underlying the carbohydrates on gp41 of simian immunodeficiency virus

Extensive glycosylation of the envelope spikes of human and simian immunodeficiency virus (HIV and SIV) is an important factor for the resistance of these viruses to neutralization by antibodies. SIVmac239 gp41 has three closely spaced sites for N-linked carbohydrate attachment. Rhesus macaques experimentally infected with mutant versions of SIVmac239 lacking two or three of these carbohydrate sites developed strong serum reactivity against mutated peptide sequences at the site of these glycosylations, as well as high titers of neutralizing activity to the mutant viruses (E. Yuste et al., J. Virol. 82:12472-12486, 2008). However, whether antibodies that recognize these underlying peptides have neutralizing activity has not been directly demonstrated. Here we describe the isolation and characterization of three gp41-specific monoclonal antibodies (4G8, 6G8, and 7D6) from one of these mutant-infected monkeys. All three antibodies reacted with mutant gp41 from viral particles and also with peptides corresponding to mutated sequences. Slight differences in peptide specificities were observed among the three antibodies. Sequence analysis revealed that the heavy chains of all three antibodies were derived from the same germ line heavy-chain segment (IGHV4-59*01), but they all had very different sequences in complementarity-determining region 3. The light chains of all three antibodies were very closely related to one another. All three antibodies had neutralizing activity to mutant viruses deficient in gp41 carbohydrate attachment, but they did not neutralize the parental SIVmac239. These results demonstrate unambiguously that antibodies with specificity for peptide sequences underlying gp41 carbohydrates can effectively neutralize SIV when these carbohydrates are absent. However, the presence of these gp41 carbohydrates effectively shields the virus from antibodies that would otherwise neutralize viral infectivity.

A three-dose intramuscular injection schedule of anthrax vaccine adsorbed generates sustained humoral and cellular immune responses to protective antigen and provides long-term protection against inhalation anthrax in rhesus macaques

A 3-dose (0, 1, and 6 months) intramuscular (3-IM) priming series of a human dose (HuAVA) and dilutions of up to 1:10 of anthrax vaccine adsorbed (AVA) provided statistically significant levels of protection (60 to 100%) against inhalation anthrax for up to 4 years in rhesus macaques. Serum anti-protective antigen (anti-PA) IgG and lethal toxin neutralization activity (TNA) were detectable following a single injection of HuAVA or 1:5 AVA or following two injections of diluted vaccine (1:10, 1:20, or 1:40 AVA). Anti-PA and TNA were highly correlated (overall r(2) = 0.89 for log(10)-transformed data). Peak responses were seen at 6.5 months. In general, with the exception of animals receiving 1:40 AVA, serum anti-PA and TNA responses remained significantly above control levels at 28.5 months (the last time point measured for 1:20 AVA), and through 50.5 months for the HuAVA and 1:5 and 1:10 AVA groups (P < 0.05). PA-specific gamma interferon (IFN-γ) and interleukin-4 (IL-4) CD4(+) cell frequencies and T cell stimulation indices were sustained through 50.5 months (the last time point measured). PA-specific memory B cell frequencies were highly variable but, in general, were detectable in peripheral blood mononuclear cells (PBMC) by 2 months, were significantly above control levels by 7 months, and remained detectable in the HuAVA and 1:5 and 1:20 AVA groups through 42 months (the last time point measured). HuAVA and diluted AVA elicited a combined Th1/Th2 response and robust immunological priming, with sustained production of high-avidity PA-specific functional antibody, long-term immune cell competence, and immunological memory (30 months for 1:20 AVA and 52 months for 1:10 AVA). Vaccinated animals surviving inhalation anthrax developed high-magnitude anamnestic anti-PA IgG and TNA responses.

Different adaptations of IgG effector function in human and nonhuman primates and implications for therapeutic antibody treatment

Safety of human therapeutic Abs is generally assessed in nonhuman primates. Whereas IgG1 shows identical FcγR interaction and effector function profile in both species, fundamental differences in the IgG2 and IgG4 Ab subclasses were found between the two species. Granulocytes, the main effector cells against IgG2- and IgG4-opsonized bacteria and parasites, do not express FcγRIIIb, but show higher levels of FcγRII in cynomolgus monkey. In humans, IgG2 and IgG4 adapted a silent Fc region with weak binding to FcγR and effector functions, whereas, in contrast, cynomolgus monkey IgG2 and IgG4 display strong effector function as well as differences in IgG4 Fab arm exchange. To balance this shift toward activation, the cynomolgus inhibitory FcγRIIb shows strongly increased affinity for IgG2. In view of these findings, in vitro and in vivo results for human IgG2 and IgG4 obtained in the cynomolgus monkey have to be cautiously interpreted, whereas effector function-related effects of human IgG1 Abs are expected to be predictable for humans.

Isolation of potent neutralizing monoclonal antibodies from an SIV-Infected rhesus macaque by phage display

The humoral immune response is a mechanism that potently suppresses or prevents viral infections. However, genetic diversity and resistance to antibody-mediated neutralization are serious obstacles in controlling HIV-1 infection. In this study, we isolated monoclonal antibodies from an SIV-infected macaque by using the phage display method to characterize antibodies in SIV infection. Variable regions of immunoglobulin genes were amplified by rhesus macaque-specific primers and inserted into the phagemid pComb3X, which produced the Fab fragment. Antibodies against SIV proteins were selected by biopanning using an SIV protein-coated 96-well plate. A total of 20 Fab clones obtained included 14 clones directed to gp41, four clones to gp120, and two clones to p27. The anti-gp120 Fab clones completely neutralized the homologous neutralization-sensitive SIVsmH635FC and the genetically divergent SIVmac316, and showed at least 50% inhibition against the neutralization-resistant strain, SIVsmE543-3. Competition ELISA revealed that these anti-gp120 Fab clones recognize the same epitope on gp120 including the V3 loop. Identification of antibodies with potent neutralizing activity will help to elucidate the mechanisms for inducing broadly neutralizing antibodies.

Characterization and allelic polymorphisms of rhesus macaque (Macaca mulatta) IgG Fc receptor genes

Macaque models are invaluable for AIDS research. Indeed, initial development of HIV-1 vaccines relies heavily on simian immunodeficiency virus-infected rhesus macaques. Neutralizing antibodies, a major component of anti-HIV protective responses, ultimately interact with Fc receptors on phagocytic and natural killer cells to eliminate the pathogen. Despite the major role that Fc receptors play in protective responses, there is very limited information available on these molecules in rhesus macaques. Therefore, in this study, rhesus macaque CD32 (FcγRII) and CD64 (FcγRI) homologues were genetically characterized. In addition, presence of CD16 (FcγRIII), CD32, and CD64 allelic polymorphisms were determined in a group of nine animals. Results from this study show that the predicted structures of macaque CD32 and CD64 are highly similar to their human counterparts. Macaque and human CD32 and CD64 extracellular domains are 88-90% and 94-95% homologous, respectively. Although all cysteines are conserved between the two species, macaque CD32 exhibits two additional N-linked glycosylation sites, whereas CD64 lacks three of them when compared to humans. Five CD32, three CD64, and three CD16 distinct allelic sequences were indentified in the nine animals examined, indicating a relatively high level of polymorphism in macaque Fcγ receptors. Together, these results validate rhesus macaques as models for vaccine development and antibody responses, while at the same time, underscoring the need to take into account the high degree of genetic heterogeneity present in this species when designing experimental protocols.

Naïve and memory B cells in the rhesus macaque can be differentiated by surface expression of CD27 and have differential responses to CD40 ligation

The rhesus macaque (RM) model has the potential to be an invaluable tool for studying B cell populations during pathogenic infections, however, to date, there has been no definitive delineation of naïve and memory B cell populations in the RM. This has precluded a rigorous analysis of the generation, persistence and resolution of a pathogen-specific memory B cell response. The present study utilized multiple analyses to demonstrate that CD27 expression on B cells is consistent with a memory phenotype. Compared to CD20+CD27- B cells, CD20+CD27+ B cells were larger in size, and preferentially accumulated at effector sites. Direct sequence analysis revealed that CD20+CD27+ B cells had an increased frequency of point mutations that were consistent with somatic hypermutation and at a functional level, CD40 ligation improved CD20+CD27- but not CD20+CD27+ B cell survival in vitro. These data provide definitive evidence that the naïve and memory B cell populations of the RM can be differentiated using surface expression of CD27.

Human immunoglobulin allotypes: possible implications for immunogenicity

More than twenty recombinant monoclonal antibodies are approved as therapeutics. Almost all of these are based on the whole IgG isotype format, but vary in the origin of the variable regions between mouse (chimeric), humanized mouse and fully human sequences; all of those with whole IgG format employ human constant region sequences. Currently, the opposing merits of the four IgG subclasses are considered with respect to the in vivo biological activities considered to be appropriate to the disease indication being treated. Human heavy chain genes also exhibit extensive structural polymorphism(s) and, being closely linked, are inherited as a haplotype. Polymorphisms (allotypes) within the IgG isotype were originally discovered and described using serological reagents derived from humans; demonstrating that allotypic variants can be immunogenic and provoke antibody responses as a result of allo-immunization. The serologically defined allotypes differ widely within and between population groups; therefore, a mAb of a given allotype will, inevitably, be delivered to a cohort of patients homozygous for the alternative allotype. This publication reviews the serologically defined human IgG allotypes and considers the potential for allotype differences to contribute to or potentiate immunogenicity.

Energy expenditure in chow-fed female non-human primates of various weights

BACKGROUND

Until now no technology has been available to study energy metabolism in monkeys. The objective of this study was to determine daily energy expenditures (EE) and respiratory quotients (RQ) in female monkeys of various body weights and ages.

METHODS

16 socially reared Bonnet Macaque female monkeys [5.5 +/- 1.4 kg body weight, modified BMI (length measurement from head to base of the tail) = 28.8 +/- 6.7 kg/crown-rump length, m2 and 11.7 +/- 4.6 years] were placed in the primate Enhanced Metabolic Testing Activity Chamber (Model 3000a, EMTAC Inc. Santa Barbara, CA) for 22-hour measurements of EE (kcal/kg) and RQ (VCO2/VO2). All were fed monkey chow (4.03 kcal/g) ad-libitum under a 12/12 hour light/dark cycle. Metabolic data were corrected for differences in body weight. Results were divided into day (8-hours), dark (12 hours) and morning (2-hours) periods. Data analysis was conducted utilizing SPSS (Version 13).

RESULTS

Modified BMI negatively correlated with 22-hour energy expenditure in all monkeys (r = -0.80, p < 0.01). The large variability of daily energy intake (4.5 to 102.0 kcal/kg) necessitated division into two groups, non-eaters (< 13 kcal/kg) and eaters (> 23 kcal/kg). There were reductions (p < 0.05) in both 22-hour and dark period RQs in the "non-eaters" in comparison to those who were "eaters". Monkeys were also classified as "lean" (modified BMI < 25) or "obese" (modified BMI > 30). The obese group had lower EE (p < 0.05) during each time period and over the entire 22-hours (p < 0.05), in comparison to their lean counterparts.

CONCLUSION

The EMTAC proved to be a valuable tool for metabolic measurements in monkeys. The accuracy and sensitivity of the instrument allowed detection of subtle metabolic changes in relation to energy intake. Moreover, there is an association between a reduction of energy expenditure and a gain in body weight.

Nonhuman primate IgA: genetic heterogeneity and interactions with CD89

Nonhuman primates are extremely valuable animal models for a variety of human diseases. However, it is now becoming evident that these models, although widely used, are still uncharacterized. The major role that nonhuman primate species play in AIDS research as well as in the testing of Ab-based therapeutics requires the full characterization of structure and function of their Ab molecules. IgA is the Ab class mostly involved in protection at mucosal surfaces. By binding to its specific Fc receptor CD89, IgA plays additional and poorly understood roles in immunity. Therefore, Ig heavy alpha (IGHA) constant (C) genes were cloned and sequenced in four different species (rhesus macaques, pig-tailed macaques, baboons, and sooty mangabeys). Sequence analysis confirmed the high degree of intraspecies polymorphism present in nonhuman primates. Individual animals were either homozygous or heterozygous for IGHA genes. Highly variable hinge regions were shared by animals of different geographic origins and were present in different combinations in heterozygous animals. Therefore, it appears that although highly heterogeneous, hinge sequences are present only in limited numbers in various nonhuman primate populations. A macaque recombinant IgA molecule was generated and used to assess its interaction with a recombinant macaque CD89. Macaque CD89 was able to bind its native ligand as well as human IgA1 and IgA2. Presence of Ag enhanced macaque IgA binding and blocking of macaque CD89 N-glycosylation reduced CD89 expression. Together, our results suggest that, despite the presence of IgA polymorphism, nonhuman primates appear suitable for studies that involve the IgA/CD89 system.

The xenoantibody response and immunoglobulin gene expression profile of cynomolgus monkeys transplanted with hDAF-transgenic porcine hearts

BACKGROUND

Recent work has indicated a role for anti-Gal alpha 1-3Gal (Gal) and anti-non-Gal xenoantibodies in the primate humoral rejection response against human-decay accelerating factor (hDAF) transgenic pig organs. Our laboratory has shown that anti-porcine xenograft antibodies in humans and non-human primates are encoded by a small number of germline IgV(H) progenitors. In this study, we extended our analysis to identify the IgV(H) genes encoding xenoantibodies in immunosuppressed cynomolgus monkeys (Macaca fascicularis) transplanted with hDAF-transgenic pig organs.

METHODS

Three immunosuppressed monkeys underwent heterotopic heart transplantation with hDAF porcine heart xenografts. Two of three animals were given GAS914, a poly-L-lysine derivative shown to bind to anti-Gal xenoantibodies and neutralize them. One animal rejected its heart at post-operative day (POD) 39; a second animal rejected the transplanted heart at POD 78. The third monkey was euthanized on POD 36 but the heart was not rejected. Peripheral blood leukocytes (PBL) and serum were obtained from each animal before and at multiple time points after transplantation. We analyzed the immune response by enzyme-linked immunosorbent assay (ELISA) to confirm whether anti-Gal or anti-non-Gal xenoantibodies were induced after graft placement. Immunoglobulin heavy-chain gene (V(H)) cDNA libraries were then produced and screened. We generated soluble single-chain antibodies (scFv) to establish the binding specificity of the cloned immunoglobulin genes.

RESULTS

Despite immunosuppression, which included the use of the polymer GAS914, the two animals that rejected their hearts showed elevated levels of cytotoxic anti-pig red blood cell (RBC) antibodies and anti-pig aortic endothelial cell (PAEC) antibodies. The monkey that did not reject its graft showed a decline in serum anti-RBC, anti-PAEC, and anti-Gal xenoantibodies when compared with pre-transplant levels. A V(H)3 family gene with a high level of sequence similarity to an allele of V(H)3-11, designated V(H)3-11(cyno), was expressed at elevated levels in the monkey that was not given GAS914 and whose graft was not rejected until POD 78. IgM but not IgG xenoantibodies directed at N-acetyl lactosamine (a precursor of the Gal epitope) were also induced in this animal. We produced soluble scFv from this new gene to determine whether this antibody could bind to the Gal carbohydrate, and demonstrated that this protein was capable of blocking the binding of human serum xenoantibody to Gal oligosaccharide, as had previously been shown with human V(H)3-11 scFv.

CONCLUSIONS

DAF-transgenic organs transplanted into cynomolgus monkeys induce anti-Gal and anti-non-Gal xenoantibody responses mediated by both IgM and IgG xenoantibodies. Anti-non-Gal xenoantibodies are induced at high levels in animals treated with GAS914. Antibodies that bind to the Gal carbohydrate and to N-acetyl lactosamine are induced in the absence of GAS914 treatment. The animal whose heart remained beating for 78 days demonstrated increased usage of an antibody encoded by a germline progenitor that is structurally related, but distinct from IGHV311. This antibody binds to the Gal carbohydrate but does not induce the rapid rejection of the xenograft when expressed at high levels as early as day 8 post-transplantation.

IgG Fc receptor III homologues in nonhuman primate species: genetic characterization and ligand interactions

Ig Fc receptors bind to immune complexes through interactions with the Fc regions of specific Ab subclasses to initiate or inhibit the defense mechanisms of the leukocytes on which they are expressed. The mechanism of action of IgG-based therapeutic molecules, which are routinely evaluated in nonhuman primate models, involves binding to the low-affinity FcRIII (CD16). The premise that IgG/CD16 interactions in nonhuman primates mimic those present in humans has not been evaluated. Therefore, we have identified and characterized CD16 and associated TCR zeta-chain homologues in rhesus macaques, cynomolgus macaques, baboons, and sooty mangabeys. Similar to humans, CD16 expression was detected on a lymphocyte subpopulation, on monocytes, and on neutrophils of sooty mangabeys. However, CD16 was detected only on a lymphocyte subpopulation and on monocytes in macaques and baboons. A nonhuman primate rCD16 generated in HeLa cells interacted with human IgG1 and IgG2. By contrast, human CD16 binds to IgG1 and IgG3. As shown for humans, the mAb 3G8 was able to block IgG binding to nonhuman primate CD16 and inhibition of nonhuman primate CD16 N-glycosylation enhanced IgG binding. Clearly, differences in interaction with IgG subclasses and in cell-type expression should be considered when using these models for in vivo evaluation of therapeutic Abs.

Sooty mangabey (Cercocebus torquatus atys) IGHG and IGHA genes

Antibodies are adaptor molecules of the immune system that link antigen recognition with the effector mechanisms responsible for antigen clearance. Several nonhuman primate species are widely used in biomedical research, especially for vaccine development and for AIDS-related studies. However, nonhuman primate antibody molecules have been characterized only partially and only in a few species. Here, we describe sooty mangabey (Cercocebus torquatus atys) IGHG and IGHA genes, which encode the heavy-chain constant region of IgG and IgA molecules, respectively. The four mangabey IGHG genes are highly homologous to the rhesus macaque and baboon IGHG genes (percent identity varies between 94.0 and 98.8, depending on the subclass), with most amino acid differences located in the hinge regions. Results obtained by real-time reverse transcription polymerase chain reaction show that the four IGHG genes are expressed at least at the mRNA level. The mangabey IGHA gene is highly homologous to the corresponding gene from rhesus macaques (percent identity ranges from 88.6 to 96.7, depending on the allele considered), the only other nonhominoid primate species for which the complete sequence of the IGHA gene is currently available. In the mangabey analyzed, two IGHA alleles are present, confirming that high levels of IGHA gene heterozygosity are present in monkey species. These results show that nonhuman primate gamma and alpha heavy chains differ from each other mostly at the level of the hinge region and that alpha sequence heterogeneity in nonhuman primate species is also present in other gamma regions. In addition, these results provide sequence information that can be used for residue frequency analysis of antibody heavy-chain constant region sequences.

Molecular characterization of immunoglobulin D in mammals: immunoglobulin heavy constant delta genes in dogs, chimpanzees and four old world monkey species

Antibodies are adaptor molecules that neutralize pathogens and link humoral and cellular defence mechanisms. Immunoglobulin D (IgD), one of the five antibody classes present in mammals, is expressed as an antigen receptor on naïve B cells. The functional role that IgD plays in the immune response is still poorly understood, but the recent characterization of immunoglobulin heavy constant delta genes (IGHD) in a variety of species challenges the view that IgD is of minor importance and is not present in many animals. On the basis of serological studies, IgD appears to be expressed in the majority of mammalian species examined. To confirm, at the molecular level, that IgD is present in different species, we cloned and sequenced IGHD cDNA from dogs and five non-human primate species (chimpanzee, rhesus macaque, cynomolgus macaque, baboon and sooty mangabey). Our results show that in all six species, IgD heavy chains possess three immunoglobulin domains and a long hinge region encoded by two exons. Only the hinge region of non-human primates is similar to the human hinge region, with conservation of O-glycosylation sites and multiple charged residues at opposing ends. The preservation of IgD in primates, dogs and previously characterized species suggests an important functional role for IgD, possibly involving binding to a receptor. The high degree of similarity existing between the structural features of human and non-human primate IgD suggests that non-human primates are suitable for in vivo studies designed to define the role that IgD plays in the immune response.

Similarities in the immunoglobulin response and VH gene usage in rhesus monkeys and humans exposed to porcine hepatocytes

Background

The use of porcine cells and organs as a source of xenografts for human patients would vastly increase the donor pool; however, both humans and Old World primates vigorously reject pig tissues due to xenoantibodies that react with the polysaccharide galactose α (1,3) galactose (αGal) present on the surface of many porcine cells. We previously examined the xenoantibody response in patients exposed to porcine hepatocytes via treatment(s) with bioartficial liver devices (BALs), composed of porcine cells in a support matrix. We determined that xenoantibodies in BAL-treated patients are predominantly directed at porcine αGal carbohydrate epitopes, and are encoded by a small number of germline heavy chain variable region (V_H) immunoglobulin genes. The studies described in this manuscript were designed to identify whether the xenoantibody responses and the IgV_H genes encoding antibodies to porcine hepatocytes in non-human primates used as preclinical models are similar to those in humans. Adult non-immunosuppressed rhesus monkeys (Macaca mulatta) were injected intra-portally with porcine hepatocytes or heterotopically transplanted with a porcine liver lobe. Peripheral blood leukocytes and serum were obtained prior to and at multiple time points after exposure, and the immune response was characterized, using ELISA to evaluate the levels and specificities of circulating xenoantibodies, and the production of cDNA libraries to determine the genes used by B cells to encode those antibodies.

Results

Xenoantibodies produced following exposure to isolated hepatocytes and solid organ liver grafts were predominantly encoded by genes in the V_H3 family, with a minor contribution from the V_H4 family. Immunoglobulin heavy-chain gene (V_H) cDNA library screening and gene sequencing of IgM libraries identified the genes as most closely-related to the IGHV3-11 and IGHV4-59 germline progenitors. One of the genes most similar to IGHV3-11, V_H3-11^cyno, has not been previously identified, and encodes xenoantibodies at later time points post-transplant. Sequencing of IgG clones revealed increased usage of the monkey germline progenitor most similar to human IGHV3-11 and the onset of mutations.

Conclusion

The small number of IGV_H genes encoding xenoantibodies to porcine hepatocytes in non-human primates and humans is highly conserved. Rhesus monkeys are an appropriate preclinical model for testing novel reagents such as those developed using structure-based drug design to target and deplete antibodies to porcine xenografts.

Despite extensive similarity in germline DH and JH sequence, the adult Rhesus macaque CDR-H3 repertoire differs from human

Rhesus macaques (Macaca mulatta) and chimpanzees (Pan troglodytes) are frequently used models for the study and treatment of human infectious diseases, including AIDS. Confidence in the equivalence to human of the humoral immune responses of these higher primates has grown as studies of immunoglobulin germline sequences have documented average identities of 90% or greater to human counterparts. The most variable component of the immunoglobulin heavy chain, complementarity determining region 3 (CDR-H3) is the product of somatic (junctional) as well as germline (combinatorial) mechanisms of diversity. Located at the center of the antigen binding site, CDR-H3 often exerts a dominant role in antibody specificity and affinity. To test whether similarity in germline DH and JH sequence would yield similarity in CDR-H3 composition in the expressed repertoire, we compared IgM CDR-H3 transcripts from Rhesus and chimpanzee blood to human. In fetal Rhesus, the range and mean of CDR-H3 lengths was similar to that observed in fetal human. However, the Rhesus repertoire of adult muCDR-H3 transcripts did not contain the longer hypervariable intervals that humans begin to express late in the second trimester of fetal life. Conversely, the adult chimpanzee repertoire included more long CDR-H3 structures than human. The differences between these adult repertoires reflected fine changes in N addition and terminal nucleotide loss. We conclude that the same mechanisms that refine and shape CDR-H3 diversity during ontogeny can also be used to fine tune and individualize species-specific antibody repertoires despite germline immunoglobulin sequence similarity.