Host IgG Research Articles

Comparison Study of the Bio-Plex and Meso Scale Multiplexed SARS-CoV-2 Serology Assays Reveals Evidence of Diminished Host Antibody Responses to SARS-CoV-2 after Monoclonal Antibody Treatment.

Assessing the breadth and duration of antigen-specific binding antibodies provides valuable information for evaluating interventions to treat or prevent SARS-CoV-2 infection. Multiplex immunoassays are a convenient method for rapid measurement of antibody responses but can sometimes provide discordant results, and antibody positive percent agreement for COVID-19 diagnosis can vary depending on assay type, disease severity, and population sampled. Therefore, we compared two assays marked for research applications, MSD and Bio-Plex Pro, to evaluate qualitative interpretation of serostatus and quantitative detection of antibodies of varying isotypes (IgG, IgM, and IgA) against receptor binding domain (RBD) and nucleocapsid (N) antigens. Specimens from ACTIV-2/A5401, a placebo-controlled clinical trial of the SARSCoV-2 monoclonal antibody (mAb) bamlanivimab to prevent COVID-19 disease progression, were used to evaluate the concordance of the Bio-Rad Bio-Plex Pro Human SARS-CoV-2 Serology Assay and the Meso Scale Discovery (MSD) V-PLEX COVID-19 Panel 1 serology assay in detecting and quantifying IgG, IgA, and IgM binding anti-SARS-CoV-2 antibody responses against the RBD and N antigens. Data were disaggregated by study arm, bamlanivimab dose, days post-enrollment, and presence of emerging resistance. We observed 90.5% (412 of 455 tests) concordance for anti-RBD IgG and 87% (396 of 455) concordance for anti-N IgG in classifying samples as negative or positive based on assay-defined cutoffs. Antibody levels converted to the WHO standard BAU/mL were significantly correlated for all isotypes (IgG, IgM, and IgA) and SARS-CoV-2 antigen targets (RBD and N) tested that were common between the two assays (Spearman r 0.65 to 0.92, P < 0.0001). Both assays uncovered evidence of diminished host-derived IgG immune responses in participants treated with bamlanivimab compared to placebo. Assessment of immune responses in the four individuals treated with the 700 mg of bamlanivimab with emerging mAb resistance demonstrated a stronger anti-N IgG response (MSD) at day 28 (median 2.18 log BAU/mL) compared to participants treated with bamlanivimab who did not develop resistance (median 1.55 log BAU/mL). These data demonstrate the utility in using multiplex immunoassays for characterizing the immune responses with and without treatment in a study population and provide evidence that monoclonal antibody treatment in acute COVID-19 may have a modest negative impact on development of host IgG responses.

Extracellular vesicles of Trypanosoma cruzi and immune complexes they form with sialylated and non-sialylated IgGs increase small peritoneal macrophage subpopulation and elicit different cytokines profiles.

American trypanosomiasis, or Chagas disease, is caused by the protozoan parasite Trypanosoma cruzi and is characterized by the presence of cardiac or gastrointestinal symptoms in a large number of patients during the chronic phase of the disease. Although the origin of the symptoms is not clear, several mechanisms have been described involving factors related to T. cruzi and the host immune response. In this sense, the extracellular vesicles (EVs) secreted by the parasite and the immune complexes (ICs) formed after their recognition by host IgGs (EVs-IgGs) may play an important role in the immune response during infection. The aim of the present work is to elucidate the modulation of the immune response exerted by EVs and the ICs they form by analyzing the variation in the subpopulations of small and large peritoneal macrophages after intraperitoneal inoculation in mice and to evaluate the role of the sialylation of the host IgGs in this immunomodulation. Both macrophage subpopulations were purified and subjected to cytokine expression analysis by RT-qPCR. The results showed an increase in the small peritoneal macrophage subpopulation after intraperitoneal injection of parasite EVs, but a greater increase in this subpopulation was observed when sialylated and non-sialylated ICs were injected, which was similar to inoculation with the trypomastigote stage of the parasite. The cytokine expression results showed the ability of both subpopulations to express inflammatory and non-inflammatory cytokines. These results suggest the role of free EVs in the acute phase of the disease and the possible role of immune complexes in the immune response in the chronic phase of the disease, when the levels of antibodies against the parasite allow the formation of immune complexes. The differential expression of interleukins showed after the inoculation of immune complexes formed with sialylated and non-sialylated IgGs and the interleukins expression induced by EVs, demonstrates that the IgG glycosilation is involved in the type of immune response that dominates in each of the phases of the Chagas disease.

Ultrastructural characterization of the tegument in protoscoleces of Echinococcus ortleppi

Cystic echinococcosis is a globally distributed zoonosis caused by cestodes of the Echinococcus granulosus sensu lato (s.l.) complex, with Echinococcus ortleppi mainly involved in cattle infection. Protoscoleces show high developmental plasticity, being able to differentiate into either adult worms or metacestodes within definitive or intermediate hosts, respectively. Their outermost cellular layer is called the tegument, which is important in determining the infection outcome through its immunomodulating activities. Herein, we report an in-depth characterization of the tegument of E. ortleppi protoscoleces performed through a combination of scanning and transmission electron microscopy techniques. Using electron tomography, a three-dimensional reconstruction of the tegumental cellular territories was obtained, revealing a novel structure termed the ‘tegumental vesicular body’ (TVB). Vesicle-like structures, possibly involved in endocytic/exocytic routes, were found within the TVB as well as in the parasite glycocalyx, distal cytoplasm and close inner structures. Furthermore, parasite antigens (GST-1 and AgB) were unevenly localised within tegumental structures, with both being detected in vesicles found within the TBV. Finally, the presence of host (bovine) IgG was also assessed, suggesting a possible endocytic route in protoscoleces. Our data forms the basis for a better understanding of E. ortleppi and E. granulosus s.l. structural biology.

Novel Models of Streptococcus canis Colonization and Disease Reveal Modest Contributions of M-Like (SCM) Protein.

Streptococcus canis is a common colonizing bacterium of the urogenital tract of cats and dogs that can also cause invasive disease in these animal populations and in humans. Although the virulence mechanisms of S. canis are not well-characterized, an M-like protein, SCM, has recently identified been as a potential virulence factor. SCM is a surface-associated protein that binds to host plasminogen and IgGs suggesting its possible importance in host-pathogen interactions. In this study, we developed in vitro and ex vivo blood component models and murine models of S. canis vaginal colonization, systemic infection, and dermal infection to compare the virulence potential of the zoonotic S. canis vaginal isolate G361 and its isogenic SCM-deficient mutant (G361∆scm). We found that while S. canis establishes vaginal colonization and causes invasive disease in vivo, the contribution of the SCM protein to virulence phenotypes in these models is modest. We conclude that SCM is dispensable for invasive disease in murine models and for resistance to human blood components ex vivo, but may contribute to mucosal persistence, highlighting a potential contribution to the recently appreciated genetic diversity of SCM across strains and hosts.

The Guinea pig cytomegalovirus GP119.1 gene encodes an IgG-binding glycoprotein that is incorporated into the virion.

Cytomegaloviruses (CMVs) encode various immunoevasins, including viral receptors for the Fc domain of host IgG (vFcγR), to evade host immune responses. Although guinea pig CMV (GPCMV) provides a useful animal model for congenital CMV infection, the GPCMV genes encoding such receptors have not yet been characterized. In this study, we analyzed a locus that may encode gene products for the GPCMV immune evasion mechanisms and identified the following. (a) RACE analyses identified four transcripts in the GP117 to GP122 locus. One of the transcripts contained the GP119.1 ORF, which has weak homologies with human CMV UL119/UL118 encoding a viral FcγR and with guinea pig FcγR. (b) A transient transfection assay with plasmids expressing EGFP-tagged GP119.1 or its mutated forms identified its true translational initiation site, localization mainly in the endoplasmic reticulum, and N-glycosylation. (c) Importantly, GP119.1 bound to guinea pig IgG or the IgG-Fc fragment. (d) GP119.1 is present in the virion with a molecular mass of 15 and 23~30 kDa, and a portion of the GP119.1 products are N-glycosylated. (e) GP119.1 was dispensable for viral growth on guinea pig fibroblasts and epithelial cells in vitro. Taken together, our findings indicate that GP119.1 is an IgG-Fc binding glycoprotein incorporated into the virion, and this finding warrants further studies on the functions of GP119.1 in animal models.

MiR-1929-3p Overexpression Alleviates Murine Cytomegalovirus-Induced Hypertensive Myocardial Remodeling by Suppressing Ednra/NLRP3 Inflammasome Activation.

MicroRNAs (miRNAs) play crucial roles in the development of essential hypertension (EH). Previously, we found that the expression of miR-1929-3p was decreased in C57BL/6 mice with hypertension induced by murine cytomegalovirus (MCMV). In this study, we explored the role of miR-1929-3p in hypertension myocardial remodeling in MCMV-infected mice. First, we measured MCMV DNA and host IgG and IgM after infection and determined the expression of miR-1929-3p and its target gene endothelin A receptor (Ednra) mRNA in the myocardium of mice. Then, we performed invasive blood pressure (BP) monitoring. Heart-to-body weight ratio (HW/BW%), along with mRNA levels of B-type natriuretic peptide (BNP) and beta myosin heavy chain (β-MHC), revealed myocardial remodeling. Hematoxylin/eosin and Masson's trichrome staining indicated morphological changes in the myocardium. Cardiac function was assessed via echocardiography. Moreover, MCMV-infected mice were injected with recombinant adeno-associated virus- (rAAV-) miR-1929-3p overexpression vector. Immunohistochemistry and western blotting showed the expression of Ednra and the activation of NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome. And enzyme-linked immunosorbent assay (ELISA) revealed the concentrations of endothelin-1 (ET-1), interleukin-1β (IL-1β), and interleukin-18 (IL-18). In this study, we found that decreased expression of miR-1929-3p in MCMV-infected mice induced high BP and further development of myocardial remodeling cardiac function injury through increased expression of Ednra. Strikingly, overexpression of miR-1929-3p ameliorated these pathological changes of the heart. The positive effect was shown to be associated with inhibition of NLRP3 inflammasome activation and decreased expression of key proinflammatory cytokine IL-1β. Collectively, these results indicate that miR-1929-3p overexpression may effectively alleviate EH myocardial remodeling by suppressing Ednra/NLRP3 inflammasome activation in MCMV-infected mice.

Expanding the Scope of Antibody Rebridging with New Pyridazinedione-TCO Constructs.

Disulfide rebridging methods have recently emerged as a route to hinge region-specific antibody modification, and there exist numerous examples of successful rebridging chemistry applied to clinically relevant human IgG1 antibodies. Here, dibromopyridazinedione disulfide rebridging is adapted to fast trans-cyclooctene/tetrazine (TCO/Tz) bioorthogonal ligations and extended beyond therapeutic human IgG1 antibodies for the first time to include mouse and rat monoclonal antibodies integral to multiplexed analytical diagnostics. In spite of a common architecture, only a subset of antibody host species and IgG isotype subclasses can be rebridged, highlighting the intricate relationship between hinge region sequence, structure, biological activity, and the conjugation chemistry of IgG antibodies.

Streptococcus pyogenes evades adaptive immunity through specific IgG glycan hydrolysis.

Streptococcus pyogenes (Group A streptococcus; GAS) is a human pathogen causing diseases from uncomplicated tonsillitis to life-threatening invasive infections. GAS secretes EndoS, an endoglycosidase that specifically cleaves the conserved N-glycan on IgG antibodies. In vitro, removal of this glycan impairs IgG effector functions, but its relevance to GAS infection in vivo is unclear. Using targeted mass spectrometry, we characterized the effects of EndoS on host IgG glycosylation during the course of infections in humans. Substantial IgG glycan hydrolysis occurred at the site of infection and systemically in the severe cases. We demonstrated decreased resistance to phagocytic killing of GAS lacking EndoS in vitro and decreased virulence in a mouse model of invasive infection. This is the first described example of specific bacterial IgG glycan hydrolysis during infection and thereby verifies the hypothesis that EndoS modifies antibodies in vivo. This mechanisms of immune evasion could have implications for treatment of severe GAS infections and for future efforts at vaccine development.

Fate of uptaken host proteins in Taenia solium and Taenia crassiceps cysticerci.

During the study of host–parasite relationships in taeniid parasite diseases, including cysticercosis and hydatidosis, reports have described the presence of host proteins in the cyst fluid and tissue of metacestodes. However, the fate or role of host elements inside the parasite remains barely explored. After the publication of genomes of four cestode species, it became clear that these organisms possess a limited biosynthetic capability. The initial goal of the present study was to determine if uptaken host proteins could be a source of essential amino acids for cysticerci. To track the utilization of uptaken proteins, we added metabolically labeled IgG-3H and GFP-3H to the culture medium of Taenia crassiceps cysticerci. Incorporation of labeled amino acid was evaluated by fluorography in cysticerci extracts. Our results showed that the use of uptaken proteins by cysticerci as a source of amino acids appeared negligible. Exploring alternative fates for the host proteins, proteomic analysis of the protein matrix in calcareous corpuscles was carried out. Since T. crassiceps does not contain calcareous corpuscles, proteomic analyses were performed in corpuscles of Taenia solium cysticerci. Our results demonstrated that host proteins represented approximately 70% of protein content in the calcareous corpuscles. The presence of the two major uptaken host proteins, namely albumin and IgG, was also demonstrated by Western blot in the matrix of corpuscles. Our findings strongly suggested that the uptake and disposal of host proteins involve calcareous corpuscles, expanding the physiological role of these mineral concretions to a far more important level than previously proposed.

Antibody Repertoires Identify β-Tubulin as a Host Protective Parasite Antigen in Mice Infected With Trypanosoma cruzi.

Few studies investigate the major protein antigens targeted by the antibody diversity of infected mice with Trypanosoma cruzi. To detect global IgG antibody specificities, sera from infected mice were immunoblotted against whole T. cruzi extracts. By proteomic analysis, we were able to identify the most immunogenic T. cruzi proteins. We identified three major antigens as pyruvate phosphate dikinase, Hsp-85, and β-tubulin. The major protein band recognized by host IgG was T. cruzi β-tubulin. The T. cruzi β-tubulin gene was cloned, expressed in E. coli, and recombinant T. cruzi β-tubulin was obtained. Infection increased IgG reactivity against recombinant T. cruzi β-tubulin. A single immunization of mice with recombinant T. cruzi β-tubulin increased specific IgG reactivity and induced protection against T. cruzi infection. These results indicate that repertoire analysis is a valid approach to identify antigens for vaccines against Chagas disease.

Mycobacterium tuberculosis thymidylate kinase antigen assays for designating incipient, high-risk latent M.tb infection

BackgroundPrecise designation of high risk forms of latent Mycobacterium tuberculosis-M.tb infections (LTBI) is impossible. Delineation of high-risk LTBI can, however, allow for chemoprophylaxis and curtail majority cases of active tuberculosis (ATB). There is epidemiological evidence to support the view that LTBI in context of HIV-1 co-infection is high-risk for progression to ATB relative to LTBI among HIV-ve persons. We recently showed that assays of M.tb thymidylate kinase (TMKmt) antigen and host specific IgG can differentiate ATB from LTBI and or no TB (NTB, or healthy controls). In this study, we aimed to expose the differential levels of TMKmt Ag among HIV+ve co-infected LTBI relative to HIV-ve LTBI as a strategy to advance these assays for designating incipient LTBI.MethodsTMKmt host specific IgM and IgG detection Enzyme Immuno-Assays (EIA) were conducted on 40 TB exposed house-hold contacts (22 LTBI vs. 18 no TB (NTB) by QunatiFERON-TB GOLD®); and TMKmt Ag detection EIA done on 82 LTBI (46 HIV+ve vs 36 HIV-ve) and 9 NTB (American donors). Purified recombinant TMKmt protein was used as positive control for the Ag assays.ResultsIgM levels were found to be equally low across QuantiFERON-TB GOLD® prequalified NTB and TB exposed house-hold contacts. Higher TMKmt host specific IgG trends were found among TB house-hold contacts relative to NTB controls. TMKmt Ag levels among HIV+ve LTBI were 0.2676 ± 0.0197 (95% CI: 0.2279 to 0.3073) relative to 0.1069 ± 0.01628 (95% CI: 0.07385 to 0.14) for HIV-ve LTBI (supporting incipient nature of LTBI in context of HIV-1 co-infection). NTB had TMKmt Ag levels of 0.1013 ± 0.02505 (5% CI: 0.0421 to 0.1606) (intimating that some were indeed LTBI).ConclusionsTMKmt Ag levels represent a novel surrogate biomarker for high-risk LTBI, while host-specific IgG can be used to designate NTB from LTBI.

Abstract 2217: Detection of circulating immune biomarkers of cervical disease using proteome arrays

Abstract Introduction: More than 260,000 women die of cervical cancer every year. Screening methods have reduced the incidence of cervical cancer in high-income countries, but detection continues to lag in low and middle income countries (LMICs). IgG antibody (Ab) immunity to early (E) HPV antigens (Ags) are potential biomarkers of disease progression. Since HPV16 accounts for only ~50% of invasive cervical cancers, we developed protein microarrays expressing the proteomes of 12 HPV types to detect host IgG Abs to a broad spectrum of viral Ags to detect pre-invasive and invasive cervical disease. Methods: We developed custom HPV protein microarrays displaying the proteomes of two low-risk HPV types (HPV6 and 11) and ten oncogenic high-risk HPV types (HPV16, 18, 31, 33, 35, 39, 45, 51, 52 and 58). Arrays were probed with serum samples obtained from women with invasive cervical cancer (ICC; n=80), no or low-grade cervical disease (CIN 0/I; n=60), and high-grade cervical dysplasia (CIN II/III; n=60). To identify positive serologic responses, arrays were scanned and the signal intensity of each protein spot was quantified and normalized. Visual examination of diffused signal (ring) around each spot was performed and the Ab response to each protein was scored on a scale from 0 to 5. Results: To verify array quality and reproducibility, we confirmed high protein expression levels for 98% (96/98) of the antigens printed and high correlation (R ≥ 0.90) of protein expression signals between different randomly selected arrays. Epitope expression was confirmed using four commercial monoclonal Abs raised against HPV16 Ags. Host Abs to at least one early antigen (E1, E2, E4, E6, or E7) were detected in the sera of 31.2% and 43.3% of ICC and CINII/III patients, respectively, compared with 11.7% of women with CIN 0/I. 73.1% of CINII/III cases detected had Abs only to non-HPV16 Ags. Abs to E1, E2, E4, E6, and E7 Ags were detected in 3.8%, 7.7%, 54%, 19%, and 31% of CINII/III versus 16%, 16%, 32%, 32%, and 40% of ICC cases that were positive. The immunodominant Ags in women with CINII/III and ICC were E4 (54%) and E7 (40%), respectively. These results are consistent with the difference in tissue expression levels of these proteins in these two disease stages. This emphasizes the importance of broadening the scope of serological detection to include non-HPV16 proteomes. Conclusions: This study demonstrates that Abs against high risk HPV16 and non-HPV16 serotypes are potential biomarkers for both the diagnosis of cervical cancer and the differentiation between high grade and low-grade pre-invasive cervical lesions. These results suggest that serology is a potential minimally invasive tool for early detection of cervical cancer. High-throughput immunoprofiling of HPV-associated cancers and pre-invasive lesions may be informative for understanding the diversity of host immunity and viral progression. Citation Format: Radwa Ewaisha, Ian Meshay, Jack Resnik, Tirinder Bharaj, Karen S. Anderson. Detection of circulating immune biomarkers of cervical disease using proteome arrays [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2217. doi:10.1158/1538-7445.AM2017-2217

Characterization of Calflagin, a Flagellar Calcium-Binding Protein from Trypanosoma congolense.

BackgroundIdentification of species-specific trypanosome molecules is important for laboratory- and field-based research into epidemiology and disease diagnosis. Although Trypanosoma congolense is the most important trypanosome pathogen of cattle in Africa, no species-specific molecules found in infective bloodstream forms (BSF) of the parasites have been identified, thus limiting development of diagnostic tests.MethodsImmuno-mass spectrometric methods were used to identify a protein that is recognized by a T. congolense-specific monoclonal antibody (mAb) Tc6/42.6.4. The identified molecule was expressed as a recombinant protein in E. coli and was tested in several immunoassays for its ability to interact with the mAb. The three dimensional structure of the protein was modeled and compared to crystal- and NMR-structures of the homologous proteins from T. cruzi and T. brucei respectively, in order to examine structural differences leading to the different immunoreactivity of the T. congolense molecule. Enzyme-linked immunosorbent assays (ELISA) were used to measure antibodies produced by trypanosome-infected African cattle in order to assess the potential for use of T. congolense calflagin in a serodiagnostic assay.ResultsThe antigen recognized by the T. congolense-specific mAb Tc6/42.6.4 was identified as a flagellar calcium-binding protein, calflagin. The recombinant molecule showed immunoreactivity with the T. congolense-specific mAb confirming that it is the cognate antigen. Immunofluorescence experiments revealed that Ca2+ modulated the localization of the calflagin molecule in trypanosomes. Structural modelling and comparison with calflagin homologues from other trypanosomatids revealed four non-conserved regions on the surface of the T. congolense molecule that due to differences in surface chemistry and structural topography may form species-specific epitopes. ELISAs using the recombinant calflagin as antigen to detect antibodies in trypanosome-infected cattle showed that the majority of cattle had antibody responses. Area under the Receiver-Operating Characteristic (ROC) curves, associated with host IgG and IgM, were calculated to be 0.623 and 0.709 respectively, indicating a positive correlation between trypanosome infection and the presence of anti-calflagin antibodies.ConclusionsWhile calflagin is conserved among different species of African trypanosomes, our results show that T. congolense calflagin possesses unique epitopes that differentiate this protein from homologues in other trypanosome species. MAb Tc6/42.6.4 has clear utility as a laboratory tool for identifying T. congolense. T. congolense calflagin has potential as a serodiagnostic antigen and should be explored further for its utility in antigen-detection assays for diagnosis of cattle infections.

A peptide immunization approach to counteract a Staphylococcus aureus protease defense against host immunity

Pathogens that induce acute and chronic infections, as well as certain cancers, employ numerous strategies to thwart host cellular and humoral immune defenses. One proposed evasion mechanism against humoral immunity is a localized expression of extracellular proteases that cleave the IgG hinge and disable host IgG functions. Host immunity appears to be prepared to counter such a proteolytic tactic by providing a group of autoantibodies, denoted anti-hinge antibodies that specifically bind to cleaved IgGs and provide compensating functional restoration in vitro. These respective counter-measures highlight the complex interrelationships among pathogens and host immunity and suggested to us a possible means for therapeutic intervention. In this study, we combined an investigation of pathogen-mediated proteolysis of host IgGs with an immunization strategy to boost host anti-hinge antibodies. In a Staphylococcus aureus infection model using an artificial tissue cage (wiffle ball) implanted into rabbits, cleaved rabbit IgGs were detected in abundance in the abscesses of untreated animals early after infection. However, in animals previously immunized with peptide analogs of the cleaved IgG hinge to generate substantial anti-hinge antibody titers, S. aureus colony formation was markedly reduced compared to control animals or those similarly immunized with a scrambled peptide sequence. The results of this study demonstrate that extensive local proteolysis of IgGs occurs in a test abscess setting and that immunization to increase host anti-hinge antibodies provided substantial acute protection against bacterial growth.

Characterization of Antibody Bipolar Bridging Mediated by the Human Cytomegalovirus Fc Receptor gp68.

The human cytomegalovirus glycoprotein gp68 functions as an Fc receptor for host IgGs and can form antibody bipolar bridging (ABB) complexes in which gp68 binds the Fc region of an antigen-bound IgG. Here we show that gp68-mediated endocytosis transports ABB complexes into endosomes, after which the complex is routed to lysosomes, presumably for degradation. These results suggest gp68 contributes to evasion of IgG-mediated immune responses by mediating destruction of host IgG and viral antigens.

CXCL12-delivery by double microcapsules and dual costimulatory blockade synergistically prolong the survival of porcine islet xenografts in diabetic NOD mice

Event Abstract Back to Event CXCL12-delivery by double microcapsules and dual costimulatory blockade synergistically prolong the survival of porcine islet xenografts in diabetic NOD mice Susan Safley1, Graham F. Barber1, Stephanie M. Duncanson2, Robert W. Holdcraft3, Lawrence S. Gazda3, Mark C. Poznansky4, Athanassios Sambanis2 and Collin J. Weber1 1 Emory University, Surgery, United States 2 Georgia Institute of Technology, School of Chemical and Biomolecular Engineering, United States 3 The Rogosin Institute, Xenia Division, United States 4 Massachusetts General Hospital, Vaccine and Immunotherapy Center, United States Introduction: Our goal is to improve islet transplantation for patients with Type I diabetes mellitus. Because human donor islets are in short supply, we are studying the efficacy of microencapsulated adult porcine islets (APIs) transplanted intraperitoneally in diabetic NOD mice. We have developed a biocompatible and durable double alginate microcapsule that excludes host IgG and that prevents islets from protruding through the capsule wall. The objective of this study was to test the effectiveness of our double microcapsule for therapeutic delivery of CXCL12 (SDF-1), a chemokine that provides pro-survival signals to islets and also recruits regulatory T cells while repelling effector T cells[1],[2]. In NOD mice, we have evaluated delivery of CXCL12 via our double microcapsule, alone and in combination with: (1) belatacept (CTLA4-Ig)[3], (2) anti-CD154 mAb, and (3) the combination of CTLA4-Ig plus anti-CD154 mAb. Since CD4+ T cells are the primary effectors in the rejection of islet xenografts[4],[5], we also have assessed the efficacy of a non-depleting anti-CD4 mAb (YTS177.9) that spares regulatory T cells[6], alone and in combination with CXCL12. Materials and Methods: APIs were isolated from adult pig pancreata, prepared as described[7], encapsulated in our double capsules as described[8] and transplanted i.p. in diabetic NOD mice (9,000 IEQ/mouse) given no immunosuppresssion, CTLA4-Ig (Orencia, Bristol-Myers Squibb, New York, NY,400 mg i.p. on day 0, QOD for 21 days, then once weekly), anti-CD154 mAb (BioXCell, West Lebanon, NH, 500 mg i.p. days 0, 2, 4, and 6 then once weekly), or non-depleting anti-CD4 mAb (YTS177.9, BioXCell, 250 mg i.p. days -3, -2, -1, then weekly). CXCL12 (Preprotech, Rocky Hill, NJ) was incorporated into the matrix of our double capsule (1μg/mL alginate). Graft function was monitored by measuring random blood glucose (BG) and histologic analyses of graft biopsies. Results and Discussion: APIs in double capsules functioned for 45 ± 33 days in diabetic NOD mice given no immunosuppression (n=24). Intracapsular CXCL12 alone prolonged graft survival for 90 ± 123 days (n=10), similar to the effects of CTLA4-Ig alone (77 ± 66, n=9), and not significantly longer than survival in untreated mice. The combination of CXCL12 and CTLA4-Ig (n=5) has augmented graft survival for 105 ± 52 days to date (n=5) with two animals still living with functioning grafts on day 146 post-transplant. Anti-CD4 mAb (YTS177.9) alone yielded significantly prolonged graft survival compared to untreated controls (217 ± 56, p<0.001, n=6). The addition of CTLA4-Ig to YTS177.9 did not further improve graft function (168 ± 44, n=6). Dual costimulatory blockade (CTLA4-Ig plus anti-CD154 mAb) (n=25) significantly prolonged graft function to 144 ± 74 days (p<0.001, vs no treatment). The most durable and consistent results to date were found when NOD mice were treated with CTLA4-Ig and anti-CD154 mAb plus CXCL12 (n=5), which resulted in encapsulated API xenograft function for 438 ± 133 days. Conclusions: Single therapy with a non-depleting anti-CD4 mAb (YTS177.9) significantly augmented API xenograft function in diabetic NOD mice for up to 301 days, suggesting that our double capsule may allow reduced immuno-suppression. Notably, CXCL12 plus CTLA4-Ig and anti-CD154 mAb has resulted in robust graft function for >300 days in all mice tested, up to 645 days in one animal. Both CXCL12 and YTS177.9 enhance regulatory T cell responses, and therefore we hypothesize that recruitment of these immunoregulatory T cells may be an important mechanism for the survival and function of encapsulated porcine islet xenografts. Our data suggest that combining CXCL12 or YTS177.9 with CTLA4-Ig and anti-CD154 mAb may be an effective means of augmenting the survival and function of encapsulated APIs. Funding from the Juvenile Diabetes Research Foundation

Dysfunctional Antibodies in the Tumor Microenvironment Associate with Impaired Anticancer Immunity.

Studies have demonstrated that cancer-associated matrix metalloproteinases (MMP) can generate single peptide bond cleavages in the hinge region of immunoglobulin G1 (IgG1). This study investigated the cleavage of endogenous IgGs by MMPs in the tumor microenvironment and the consequences of the IgG hinge cleavage for humoral immunity. We investigated the occurrence of single peptide bond cleaved IgGs (scIgG) in tumor tissues and plasma samples collected from a cohort of breast cancer patients (n = 60). Samples from healthy people (n = 20) were used as the control. Antibody hinge cleavage was detected by multiple assays, including IHC, ELISA, and flow cytometry. A correlation analysis was conducted between scIgG levels and patient clinical parameters. Levels of scIgGs in tumors were significantly higher than in normal tissues. In addition, scIgG levels in tumors were enriched compared with that in the plasma of the same patients. The appearance of scIgGs in tumor tissues was associated with altered host IgG content and decreased IgG1. Increased tumor scIgGs were found to be positively correlated with adverse clinical factors, such as elevated tumor-associated macrophages, increased expression of MMP9 and other MMPs, and local metastasis to axillary lymph nodes. The study contributes to mounting evidence for the presence of hinge-cleaved antibodies with reduced Fc immune effector function in the tumor microenvironment. The results highlight a link between tumor scIgGs and poor patient outcomes, and reveal a component of compromised humoral immunity within tumors that could point to new immunotherapeutic strategies to rescue host immunity.

Distinct Intracellular Trafficking Patterns of Host IgG by Herpes Virus Fc‐Receptors

Members of both alpha and beta herpes viruses affects 50–98% of people around the world. They cause severe symptoms in congenitally infected newborns, a lifelong latent infection that is lethal in immuno‐compromised individuals, and are associated with several types of cancer. Human cytomegalovirus (HCMV) and herpes simplex virus type 1 (HSV‐1) viruses express proteins (HCMV gp68 and gp34; HSV‐1 gE‐gI) that function as Fcγ receptors (FcγRs) by binding to the Fc regions of human IgG. In addition to binding free IgG, these viral FcγRs can bind to IgG complexed with an antigen to form an antibody bipolar bridged (ABB) complex. The effects of Fcγ binding by these viral molecules are poorly understood. Although HCMV gp68 and HSV‐1 gE‐gI have an overlapping binding site on Fc, the finding that the gp68/Fc interaction is stable at pH values between 5.6 and 8.1 but that gE‐gI binds only at neutral or basic pH suggests distinct pH‐based downstream events after IgG is internalized via receptor‐mediated endocytosis into intracellular compartments. Here we developed a cell‐based in vitromodel system and performed 4D‐confocal fluorescence imaging to define the fates of ABB complexes formed by the two types of viral FcγRs. We found that alpha (HSV‐1) and beta (HCMV) herpes virus FcγRs displayed distinct intracellular trafficking patterns to target internalized ligands: HSV‐1 gE‐gI dissociates from its IgG‐antigen ligand in acidic endosomal compartments and recycles back to the cell surface (Ndjamen et al., 2014), whereas HCMV FcγRs (gp68) are transported together with IgG‐antigen complexes to lysosomes for degradation. In both cases, anti‐viral IgGs and their viral targets are selectively degraded, a potential immune evasion strategy allowing herpes viruses to escape from IgG‐mediated immune responses.

The genetic control of immunity to Plasmodium infection.

BackgroundMalaria remains a major worldwide public health problem with ~207 million cases and ~627,000 deaths per year, mainly affecting children under five years of age in Africa. Recent efforts at elaborating a genetic architecture of malaria have focused on severe malaria, leading to the identification of two new genes and confirmation of previously known variants in HBB, ABO and G6PD, by exploring the whole human genome in genome-wide association (GWA) studies. Molecular pathways controlling phenotypes representing effectiveness of host immunity, notably parasitemia and IgG levels, are of particular interest given the current lack of an efficacious vaccine and the need for new treatment options.ResultsWe propose a global causal framework of malaria phenotypes implicating progression from the initial infection with Plasmodium spp. to the development of the infection through liver and blood-stage multiplication cycles (parasitemia as a quantitative trait), to clinical malaria attack, and finally to severe malaria. Genetic polymorphism may control any of these stages, such that preceding stages act as mediators of subsequent stages. A biomarker of humoral immunity, IgG levels, can also be integrated into the framework, potentially mediating the impact of polymorphism by limiting parasitemia levels. Current knowledge of the genetic basis of parasitemia levels and IgG levels is reviewed through key examples including the hemoglobinopathies, showing that the protective effect of HBB variants on malaria clinical phenotypes may partially be mediated through parasitemia and cytophilic IgG levels. Another example is the IgG receptor FcγRIIa, encoded by FCGR2A, such that H131 homozygotes displayed higher IgG2 levels and were protective against high parasitemia and onset of malaria symptoms as shown in a causal diagram.ConclusionsWe thus underline the value of parasitemia and IgG levels as phenotypes in the understanding of the human genetic architecture of malaria, and the need for applying GWA approaches to these phenotypes.

The Herpes Virus Fc Receptor gE-gI Mediates Antibody Bipolar Bridging to Clear Viral Antigens from the Cell Surface

The Herpes Simplex Virus 1 (HSV-1) glycoprotein gE-gI is a transmembrane Fc receptor found on the surface of infected cells and virions that binds human immunoglobulin G (hIgG). gE-gI can also participate in antibody bipolar bridging (ABB), a process by which the antigen-binding fragments (Fabs) of the IgG bind a viral antigen while the Fc binds to gE-gI. IgG Fc binds gE-gI at basic, but not acidic, pH, suggesting that IgG bound at extracellular pH by cell surface gE-gI would dissociate and be degraded in acidic endosomes/lysosomes if endocytosed. The fate of viral antigens associated with gE-gI–bound IgG had been unknown: they could remain at the cell surface or be endocytosed with IgG. Here, we developed an in vitro model system for ABB and investigated the trafficking of ABB complexes using 4-D confocal fluorescence imaging of ABB complexes with transferrin or epidermal growth factor, well-characterized intracellular trafficking markers. Our data showed that cells expressing gE-gI and the viral antigen HSV-1 gD endocytosed anti-gD IgG and gD in a gE-gI–dependent process, resulting in lysosomal localization. These results suggest that gE-gI can mediate clearance of infected cell surfaces of anti-viral host IgG and viral antigens to evade IgG-mediated responses, representing a general mechanism for viral Fc receptors in immune evasion and viral pathogenesis.