Divergent immunoglobulin g subclass activity through selective Fc receptor binding

Role of Antibodies and Their Specificities in Atherosclerotic Cardiovascular Disease

Atherosclerosis is a lipid-driven chronic inflammatory disease that is modulated by innate and adaptive immunity including humoral immunity. Importantly, antibody alterations achieved by genetic means or active and passive immunization strategies in preclinical studies can improve or aggravate atherosclerosis. Additionally, a wide range of epidemiological data demonstrate not only an association between the total levels of different antibody isotypes but also levels of antibodies targeting specific antigens with atherosclerotic cardiovascular disease. Here, we discuss the potential role of atherogenic dyslipidemia on the antibody repertoire and review potential antibody-mediated effector mechanisms involved in atherosclerosis development highlighting the major atherosclerosis-associated antigens that trigger antibody responses.

Fc gamma receptors: Their evolution, genomic architecture, genetic variation, and impact on human disease

Fc gamma receptors (FcγRs) are a family of receptors that bind IgG antibodies and interface at the junction of humoral and innate immunity. Precise regulation of receptor expression provides the necessary balance to achieve healthy immune homeostasis by establishing an appropriate immune threshold to limit autoimmunity but respond effectively to infection. The underlying genetics of the FCGR gene family are central to achieving this immune threshold by regulating affinity for IgG, signaling efficacy, and receptor expression. The FCGR gene locus was duplicated during evolution, retaining very high homology and resulting in a genomic region that is technically difficult to study. Here, we review the recent evolution of the gene family in mammals, its complexity and variation through copy number variation and single-nucleotide polymorphism, and impact of these on disease incidence, resolution, and therapeutic antibody efficacy. We also discuss the progress and limitations of current approaches to study the region and emphasize how new genomics technologies will likely resolve much of the current confusion in the field. This will lead to definitive conclusions on the impact of genetic variation within the FCGR gene locus on immune function and disease.

Immunomodulatory and anti-inflammatory properties of immunoglobulin G antibodies

Antibodies provide an essential layer of protection from infection and reinfection with microbial pathogens. An impaired ability to produce antibodies results in immunodeficiency and necessitates the constant substitution with pooled serum antibodies from healthy donors. Among the five antibody isotypes in humans and mice, immunoglobulin G (IgG) antibodies are the most potent anti-microbial antibody isotype due to their long half-life, their ability to penetrate almost all tissues and due to their ability to trigger a wide variety of effector functions. Of note, individuals suffering from IgG deficiency frequently produce self-reactive antibodies, suggesting that a normal serum IgG level also may contribute to maintaining self-tolerance. Indeed, the substitution of immunodeficient patients with pooled serum IgG fractions from healthy donors, also referred to as intravenous immunoglobulin G (IVIg) therapy, not only protects the patient from infection but also diminishes autoantibody induced pathology, providing more direct evidence that IgG antibodies play an active role in maintaining tolerance during the steady state and during resolution of inflammation. The aim of this review is to discuss different conceptual models that may explain how serum IgG or IVIg can contribute to maintaining a balanced immune response. We will focus on pathways depending on the IgG fragment crystallizable (Fc) as pre-clinical data in various mouse model systems as well as human clinical data have demonstrated that the IgG Fc-domain recapitulates the ability of intact IVIg with respect to its ability to trigger resolution of inflammation. We will further discuss how the findings already have or are in the process of being translated to novel therapeutic approaches to substitute IVIg in treating autoimmune inflammation.

Polyhedral oligomeric silsesquioxane-modulated mesoporous amorphous bimetallic organic frameworks for the efficient isolation of immunoglobulin G

The efficient and accurate separation of immunoglobulin G (IgG) plays a vital role for disease diagnosis and therapy, but it is always hampered by the huge geometric size and complex structure of IgG. In this work, an amorphous Fe/Co bimetallic organic framework (denoted as PMOF-Fe/Co) is fabricated for IgG separation, with octa-carboxyl polyhedral oligomeric silsesquioxane (OCPOSS) as modulator for the first time. Benefiting from the rigid nanostructure and competitive coordination of OCPOSS, the aperture of PMOF-Fe/Co is enlarged to ∼20 nm along with the generation of enormous structural defects, which enables the accommodation of protein species with high molecular weights and large sizes. OCPOSS is also found exerting a positive impact on mediating the specific recognition and adsorption ability of PMOF-Fe/Co towards IgG through metal affinity, hydrophilic and hydrophobic interactions. Consequently, the multimode and multivalent affinity of PMOF-Fe/Co gives rise to an extraordinary adsorption capacity (2691.7 mg g-1) and satisfactory practical application performance. This study is convinced to provide a simple avenue for the efficient separation of specific large-sized proteins, as well as the engineering of abiotic affinity reagents with compositional and architectural complexity.

Influenza virus antibodies inhibit antigen-specific de novo B cell responses in mice

Antibody responses to influenza vaccines tend to be focused on epitopes encountered during prior influenza exposures, with little production of de novo responses to novel epitopes. To examine the contribution of circulating antibodies to this phenomenon, we passively transferred a hemagglutinin (HA)-specific monoclonal antibody (mAb) into mice before immunizing with whole inactivated virions. The HA mAb inhibited de novo HA-specific antibodies, plasmablasts, germinal center B cells, and memory B cells, while responses to a second antigen in the vaccine, neuraminidase (NA), were uninhibited. The HA mAb potently inhibited de novo antibody responses against epitopes near the HA mAb binding site. The HA mAb also promoted IgG1 class switching, an effect that, unlike the inhibition of HA responses, relied on signaling through Fc-gamma receptors. These studies suggest that circulating antibodies inhibit de novo B cell responses in an antigen-specific manner, which likely contributes to differences in antibody specificities elicited during primary and secondary influenza virus exposures.IMPORTANCEMost humans are exposed to influenza viruses in childhood and then subsequently exposed to antigenically drifted influenza variants later in life. It is unclear if antibodies elicited by earlier influenza virus exposures impact immunity against new influenza virus strains. Here, we used a mouse model to investigate how an anti-hemagglutinin (HA) monoclonal antibody (mAb) affects de novo B cell and antibody responses to the protein targeted by the monoclonal antibody (HA) and a second protein not targeted by the monoclonal antibody [neuraminidase (NA)]. Collectively, our studies suggest that circulating anti-influenza virus antibodies can potently modulate the magnitude and specificity of antibody responses elicited by secondary influenza virus exposures.

Fc-FcγR interactions during infections: From neutralizing antibodies to antibody-dependent enhancement

Advances in antibody technologies have resulted in the development of potent antibody-based therapeutics with proven clinical efficacy against infectious diseases. Several monoclonal antibodies (mAbs), mainly against viruses such as SARS-CoV-2, HIV-1, Ebola virus, influenza virus, and hepatitis B virus, are currently undergoing clinical testing or are already in use. Although these mAbs exhibit potent neutralizing activity that effectively blocks host cell infection, their antiviral activity results not only from Fab-mediated virus neutralization, but also from the protective effector functions mediated through the interaction of their Fc domains with Fcγ receptors (FcγRs) on effector leukocytes. Fc-FcγR interactions confer pleiotropic protective activities, including the clearance of opsonized virions and infected cells, as well as the induction of antiviral T-cell responses. However, excessive or inappropriate activation of specific FcγR pathways can lead to disease enhancement and exacerbated pathology, as seen in the context of dengue virus infections. A comprehensive understanding of the diversity of Fc effector functions during infection has guided the development of engineered antiviral antibodies optimized for maximal effector activity, as well as the design of targeted therapeutic approaches to prevent antibody-dependent enhancement of disease.

Sustained release of inactivated H1N1 virus from degradable microparticles for extended vaccination

Influenza vaccines administered as intramuscularly injected inactivated viruses or intranasally administered live-attenuated viruses usually provide short-term protection against influenza infections. Biodegradable particles that provide sustained release of the antigen has been studied as an approach to extend vaccine protection. Here, we investigate sustained release of ultraviolet killed influenza A virus (A/PR/8/34(H1N1)) (kPR8) loaded into poly(D,L-lactic-co-glycolic acid) (PLGA) microparticles. Particles were prepared using the double emulsion method, and polymer molecular weight (MW), polymer hydrophobicity, polymer concentration in the organic phase, and the amount of killed virus were varied to obtain a range of particles. Formulations included PLGA 50:50 (2-6, 7-17 kDa), PLGA 75:25 (4-15 kDa), and 50/50 PLGA 75:25 (4-15 kDa)/PCL (14 kDa). Additionally, NaOH was co-encapsulated in some cases to enhance particle degradation. The structure of the particles was explored by size measurements and electron microscopy. The kPR8 release profiles were measured using hemagglutinin ELISA. The concentration of the polymer (PLGA) in the organic phase and polymer MW significantly influenced virus loading, while polymer MW and co-encapsulation of NaOH modulated the release profiles. Mice receiving a single intramuscular injection of NaOH microparticle-encapsulated kPR8 were partially protected against a lethal influenza challenge 32 weeks post immunization. Microparticle (MP) vaccination induced a gradual increase in PR8-specific IgGs dominated by IgG1 in contrast to the rapid IgG2a-biased response elicited by soluble kPR8 immunization. Our results indicate that vaccine-NaOH co-loaded PLGA particles show potential as a single dose vaccination strategy for extended protection against influenza virus infection.

Core fucosylation within the Fc-FcγR degradation pathway promotes enhanced IgG levels via exogenous L-fucose

α1,6-Fucosyltransferase (Fut8) is the enzyme responsible for catalyzing core fucosylation. Exogenous L-fucose upregulates fucosylation levels through the GDP-fucose salvage pathway. This study investigated the relationship between core fucosylation and immunoglobulin G (IgG) amounts in serum utilizing WT (Fut8+/+), Fut8 heterozygous knockout (Fut8+/-), and Fut8 knockout (Fut8-/-) mice. The IgG levels in serum were lower in Fut8+/- and Fut8-/- mice compared with Fut8+/+ mice. Exogenous L-fucose increased IgG levels in Fut8+/- mice, while the ratios of core fucosylated IgG versus total IgG showed no significant difference among Fut8+/+, Fut8+/-, and Fut8+/- mice treated with L-fucose. These ratios were determined by Western blot, lectin blot, and mass spectrometry analysis. Real-time PCR results demonstrated that mRNA levels of IgG Fc and neonatal Fc receptor, responsible for protecting IgG turnover, were similar among Fut8+/+, Fut8+/-, and Fut8+/- mice treated with L-fucose. In contrast, the expression levels of Fc-gamma receptor Ⅳ (FcγRⅣ), mainly expressed on macrophages and neutrophils, were increased in Fut8+/- mice compared to Fut8+/+ mice. The effect was reversed by administrating L-fucose, suggesting that core fucosylation primarily regulates the IgG levels through the Fc-FcγRⅣ degradation pathway. Consistently, IgG internalization and transcytosis were suppressed in FcγRⅣ-knockout cells while enhanced in Fut8-knockout cells. Furthermore, we assessed the expression levels of specific antibodies against ovalbumin and found they were downregulated in Fut8+/- mice, with potential recovery observed with L-fucose administration. These findings confirm that core fucosylation plays a vital role in regulating IgG levels in serum, which may provide insights into a novel mechanism in adaptive immune regulation.

Functional Fc receptors are crucial in antibody-mediated protection against cytomegalovirus

Human cytomegalovirus is a medically important pathogen. Previously, using murine CMV (MCMV), we provided evidence that both neutralizing and nonneutralizing antibodies can confer protection from viral infection in vivo. In this study, we report that serum derived from infected animals had a greater protective capacity in MCMV-infected RAG-/- mice than serum from animals immunized with purified virus. The protective activity of immune serum was strictly dependent on functional Fcγ receptors (FcγR). Deletion of individual FcγRs or combined deletion of FcγRI and FcγRIV had little impact on the protection afforded by serum. Adoptive transfer of CD115-positive cells from noninfected donors demonstrated that monocytes represent important cellular mediators of the protective activity provided by immune serum. Our studies suggest that Fc-FcγR interactions and monocytic cells are critical for antibody-mediated protection against MCMV infection in vivo. These findings may provide new avenues for the development of novel strategies for more effective CMV vaccines or antiviral immunotherapies.

Impact of isotype on the mechanism of action of agonist anti-OX40 antibodies in cancer: implications for therapeutic combinations

BACKGROUND

OX40 has been widely studied as a target for immunotherapy with agonist antibodies taken forward into clinical trials for cancer where they are yet to show substantial efficacy. Here, we investigated potential mechanisms of action of anti-mouse (m) OX40 and anti-human (h) OX40 antibodies, including a clinically relevant monoclonal antibody (mAb) (GSK3174998) and evaluated how isotype can alter those mechanisms with the aim to develop improved antibodies for use in rational combination treatments for cancer.

METHODS

Anti-mOX40 and anti-hOX40 mAbs were evaluated in a number of in vivo models, including an OT-I adoptive transfer immunization model in hOX40 knock-in (KI) mice and syngeneic tumor models. The impact of FcγR engagement was evaluated in hOX40 KI mice deficient for Fc gamma receptors (FcγR). Additionally, combination studies using anti-mouse programmed cell death protein-1 (mPD-1) were assessed. In vitro experiments using peripheral blood mononuclear cells (PBMCs) examining possible anti-hOX40 mAb mechanisms of action were also performed.

RESULTS

Isotype variants of the clinically relevant mAb GSK3174998 showed immunomodulatory effects that differed in mechanism; mIgG1 mediated direct T-cell agonism while mIgG2a acted indirectly, likely through depletion of regulatory T cells (Tregs) via activating FcγRs. In both the OT-I and EG.7-OVA models, hIgG1 was the most effective human isotype, capable of acting both directly and through Treg depletion. The anti-hOX40 hIgG1 synergized with anti-mPD-1 to improve therapeutic outcomes in the EG.7-OVA model. Finally, in vitro assays with human peripheral blood mononuclear cells (hPBMCs), anti-hOX40 hIgG1 also showed the potential for T-cell stimulation and Treg depletion.

CONCLUSIONS

These findings underline the importance of understanding the role of isotype in the mechanism of action of therapeutic mAbs. As an hIgG1, the anti-hOX40 mAb can elicit multiple mechanisms of action that could aid or hinder therapeutic outcomes, dependent on the microenvironment. This should be considered when designing potential combinatorial partners and their FcγR requirements to achieve maximal benefit and improvement of patient outcomes.

Three in one: An effective and universal vaccine expressing heterologous tandem RBD trimer by rabies virus vector protects mice against SARS-CoV-2

The rapid emergence of Severe Acute Respiratory Syndrome Coronavirus type 2 (SARS-CoV-2) variants, coupled with severe immune evasion and imprinting, has jeopardized the vaccine efficacy, necessitating urgent development of broad protective vaccines. Here, we propose a strategy employing recombinant rabies viruses (RABV) to create a universal SARS-CoV-2 vaccine expressing heterologous tandem receptor-binding domain (RBD) trimer from the SARS-CoV-2 Prototype, Delta, and Omicron strains (SRV-PDO). The results of mouse immunization indicated that SRV-PDO effectively induced cellular and humoral immune responses, and demonstrated higher immunogenicity and broader SARS-CoV-2 neutralization compared to the recombinant RABVs that only expressed RBD monomers. Moreover, SRV-PDO exhibited full protection against SARS-CoV-2 in the challenge assay. This study demonstrates that recombinant RABV expressing tandem RBD-heterotrimer as a multivalent immunogen could elicit a broad-spectrum immune response and potent protection against SARS-CoV-2, making it a promising candidate for future human or veterinary vaccines and offering a novel perspective in other vaccine design.

Immunization with a Mu-class glutathione transferase from Echinococcus granulosus induces efficient antibody responses and confers long-term protection against secondary cystic echinococcosis

Cystic echinococcosis, a zoonosis caused by cestodes belonging to the Echinococcus granulosus sensu lato (s.l.) genetic complex, affects humans and diverse livestock species. Although a veterinary vaccine exhibiting high levels of antibody-mediated protection has successfully reached the market, the large genetic diversity among parasite isolates and their particular host preferences, makes still necessary the search for novel vaccine candidates. Glutathione transferases (GSTs) constitute attractive targets for immunoprophylaxis due to their outstanding relevance in helminth detoxification processes, against both exogenous and endogenous stressors. Among the six GSTs known to be expressed in E. granulosus s.l., EgGST1 (Mu-class), EgGST2 (Sigma-class), and EgGST3 (a still non-classifiable isoenzyme), show the highest proteomic expression. Therefore, their recombinant forms -rEgGST1, rEgGST2 and rEgGST3- were herein analyzed regarding their potential to induce long-term antiparasite protection in mice. Only immunization with rEgGST1 induced long-lasting protection; and accordingly, rEgGST1-specific antibodies enhanced the parasite killing through both the classical activation of the host complement system and the antibody-dependent cellular cytotoxicity by macrophages. These results support further testing of rEgGST1 as a vaccine candidate in diverse hosts due to the broad expression of EgGST1 in different parasite stages and tissues.

Selective IgG binding to the LPS glycolipid core found in bovine colostrum, or milk, during Escherichia coli mastitis influences endotoxin function

The dynamic interplay between intramammary IgG, formation of antigen-IgG complexes and effector immune cell function is essential for immune homeostasis within the bovine mammary gland. We explore how changes in the recognition and binding of anti-LPS IgG to the glycolipid "functional" core in milk from healthy or clinically diagnosed Escherichia coli (E. coli) mastitis cows' controls endotoxin function. In colostrum, we found a varied anti-LPS IgG repertoire and novel soluble LPS/IgG complexes with direct IgG binding to the LPS glycolipid core. These soluble complexes, absent in milk from healthy lactating cows, were evident in cows diagnosed with E. coli mastitis and correlated with endotoxin-driven inflammation. E. coli mastitis milk displayed a proportional reduction in anti-LPS glycolipid core IgG compared to colostrum. Milk IgG extracts showed that only colostrum IgG attenuated LPS induced endotoxin activity. Furthermore, LPS-stimulated reactive oxygen species (ROS) in milk granulocytes was only suppressed by colostrum IgG, while IgG extracts of neither colostrum nor E. coli mastitis milk influenced N-formylmethionine-leucyl-phenylalanine (fMLP)-stimulated ROS in LPS primed granulocytes. Our findings support bovine intramammary IgG diversity in health and in response to E. coli infection generate milk anti-LPS IgG repertoires that coordinate appropriate LPS innate-adaptive immune responses essential for animal health.

Immunogenicity of PvCyRPA, PvCelTOS and Pvs25 chimeric recombinant protein of Plasmodium vivax in murine model

In the Americas, P. vivax is the predominant causative species of malaria, a debilitating and economically significant disease. Due to the complexity of the malaria parasite life cycle, a vaccine formulation with multiple antigens expressed in various parasite stages may represent an effective approach. Based on this, we previously designed and constructed a chimeric recombinant protein, PvRMC-1, composed by PvCyRPA, PvCelTOS, and Pvs25 epitopes. This chimeric protein was strongly recognized by naturally acquired antibodies from exposed population in the Brazilian Amazon. However, there was no investigation about the induced immune response of PvRMC-1. Therefore, in this work, we evaluated the immunogenicity of this chimeric antigen formulated in three distinct adjuvants: Stimune, AddaVax or Aluminum hydroxide (Al(OH)3) in BALB/c mice. Our results suggested that the chimeric protein PvRMC-1 were capable to generate humoral and cellular responses across all three formulations. Antibodies recognized full-length PvRMC-1 and linear B-cell epitopes from PvCyRPA, PvCelTOS, and Pvs25 individually. Moreover, mice's splenocytes were activated, producing IFN-γ in response to PvCelTOS and PvCyRPA peptide epitopes, affirming T-cell epitopes in the antigen. While aluminum hydroxide showed notable cellular response, Stimune and Addavax induced a more comprehensive immune response, encompassing both cellular and humoral components. Thus, our findings indicate that PvRMC-1 would be a promising multistage vaccine candidate that could advance to further preclinical studies.

Alum/CpG adjuvant promotes immunogenicity of inactivated SARS-CoV-2 Omicron vaccine through enhanced humoral and cellular immunity

The SARS-CoV-2 Omicron variant, which was classified as a variant of concern (VOC) by the World Health Organization on 26 November 2021, has attracted worldwide attention for its high transmissibility and immune evasion ability. The existing COVID-19 vaccine has been shown to be less effective in preventing Omicron variant infection and symptomatic infection, which brings new challenges to vaccine development and application. Here, we evaluated the immunogenicity and safety of an Omicron variant COVID-19 inactivated vaccine containing aluminum and CpG adjuvants in a variety of animal models. The results showed that the vaccine candidate could induce high levels of neutralizing antibodies against the Omicron variant virus and binding antibodies, and significantly promoted cellular immune response. Meanwhile, the vaccine candidate was safe. Therefore, it provided more foundation for the development of aluminum and CpG as a combination adjuvant in human vaccines.

Human neutralizing antibodies target a conserved lateral patch on H7N9 hemagglutinin head

Avian influenza A virus H7N9 causes severe human infections with >30% fatality. Currently, there is no H7N9-specific prevention or treatment for humans. Here, from a 2013 H7N9 convalescent case in Hong Kong, we isolate four hemagglutinin (HA)-reactive monoclonal antibodies (mAbs), with three directed to the globular head domain (HA1) and one to the stalk domain (HA2). Two clonally related HA1-directed mAbs, H7.HK1 and H7.HK2, potently neutralize H7N9 and protect female mice from lethal H7N9/AH1 challenge. Cryo-EM structures reveal that H7.HK1 and H7.HK2 bind to a β14-centered surface and disrupt the 220-loop that makes hydrophobic contacts with sialic acid on an adjacent protomer, thereby blocking viral entry. Sequence analysis indicates the lateral patch targeted by H7.HK1 and H7.HK2 to be conserved among influenza subtypes. Both H7.HK1 and H7.HK2 retain HA1 binding and neutralization capacity to later H7N9 isolates from 2016-2017, consistent with structural data showing that the antigenic mutations during this timeframe occur at their epitope peripheries. The HA2-directed mAb H7.HK4 lacks neutralizing activity but when used in combination with H7.HK2 moderately augments female mouse protection. Overall, our data reveal antibodies to a conserved lateral HA1 supersite that confer neutralization, and when combined with a HA2-directed non-neutralizing mAb, augment protection.

Preclinical Evaluation of virus-like particle Vaccine Against Carbonic Anhydrase IX Efficacy in a Mouse Breast Cancer Model System

Carbonic anhydrase IX (CAIX) is a cancer-associated membrane protein frequently overexpressed in hypoxic solid tumours leading to enhanced tumour cell survival and invasion, and it has been proposed to be an attractive tumour-specific molecule for antibody-mediated targeting. This study aimed to generate a virus-like particle (VLP)-based CAIX vaccine candidate and evaluate its efficacy in a mouse model of breast cancer. The prototype murine vaccine was developed based on the ssRNA bacteriophage Qbeta VLPs with chemically coupled murine CAIX protein catalytic domains on their surfaces. The vaccine was shown to efficiently break the natural B cell tolerance against autologous murine CAIX and to induce high-titre Th1-oriented IgG responses in the BALB/c mice. This vaccine was tested in a therapeutic setting by using a triple-negative breast cancer mouse model system comprising 4T1, 4T1-Car9KI and 4T1-Car9KO cells, the latter representing positive and negative controls for murine CAIX production, respectively. The humoural immune responses induced in tumour-bearing animals were predominantly of Th1-type and higher anti-mCAIXc titres correlated with slower growth and lung metastasis development of 4T1 tumours constitutively expressing mCAIX in vivo in the syngeneic host.

Engaging natural antibody responses for the treatment of inflammatory bowel disease via phosphorylcholine-presenting nanofibres

Inflammatory bowel disease lacks a long-lasting and broadly effective therapy. Here, by taking advantage of the anti-infection and anti-inflammatory properties of natural antibodies against the small-molecule epitope phosphorylcholine (PC), we show in multiple mouse models of colitis that immunization of the animals with self-assembling supramolecular peptide nanofibres bearing PC epitopes induced sustained levels of anti-PC antibodies that were both protective and therapeutic. The strength and type of immune responses elicited by the nanofibres could be controlled through the relative valency of PC epitopes and exogenous T-cell epitopes on the nanofibres and via the addition of the adjuvant CpG. The nanomaterial-assisted induction of the production of therapeutic antibodies may represent a durable therapy for inflammatory bowel disease.

SARS-CoV-2 membrane protein-specific antibodies from critically ill SARS-CoV-2-infected individuals interact with Fc receptor-expressing cells but do not neutralize the virus

The membrane (M) glycoprotein of SARS-CoV-2 is one of the key viral proteins regulating virion assembly and morphogenesis. Immunologically, the M protein is a major source of peptide antigens driving T cell responses, and most individuals who have been infected with SARS-CoV-2 make antibodies to the N-terminal, surface-exposed peptide of the M protein. We now report that although the M protein is abundant in the viral particle, antibodies to the surface-exposed N-terminal epitope of M do not appear to neutralize the virus. M protein-specific antibodies do, however, activate antibody-dependent cell-mediated cytotoxicity and cytokine secretion by primary human natural killer cells. Interestingly, while patients with severe or mild disease make comparable levels of M antigen-binding antibodies, M-specific antibodies from the serum of critically ill patients are significantly more potent activators of antibody-dependent cell-mediated cytotoxicity than antibodies found in individuals with mild or asymptomatic infection.

Influenza virus antibodies inhibit antigen-specific de novo B cell responses in mice

Antibody responses to influenza vaccines tend to be focused on epitopes encountered during prior influenza exposures, with little production of de novo responses to novel epitopes. To examine the contribution of circulating antibody to this phenomenon, we passively transferred a hemagglutinin (HA)-specific monoclonal antibody (mAb) into mice before immunizing with whole inactivated virions. The HA mAb inhibited de novo HA-specific antibodies, plasmablasts, germinal center B cells, and memory B cells, while responses to a second antigen in the vaccine, neuraminidase (NA), were uninhibited. The HA mAb potently inhibited de novo antibody responses against epitopes near the HA mAb binding site. The HA mAb also promoted IgG1 class switching, an effect that, unlike the inhibition of HA responses, relied on signaling through Fc-gamma receptors. These studies suggest that circulating antibodies inhibit de novo B cell responses in an antigen-specific manner, which likely contributes to differences in antibody specificities elicited during primary and secondary influenza virus exposures.

Recombinant CD5 and CD6 Ectodomains Induce Antiparasitic and Immunomodulatory Effects in Secondary Cystic Echinococcosis

Scavenger receptors participate in a wide range of biological functions after binding to multiple non-self or altered self-ligands. Among them, CD5 and CD6 are lymphocyte scavenger receptors known to interact with different microbial-associated molecular patterns, and the administration of the recombinant soluble ectodomains of human CD5 (rshCD5) and/or CD6 (rshCD6) has shown therapeutic/prophylactic potential in experimental models of fungal, bacterial and echinococcal infections. The latter is a zoonosis caused by the larval stage of the cestode parasite Echinococcus granulosus sensu lato, which in humans can induce secondary cystic echinococcosis (CE) after the spillage of protoscoleces contained within fertile cysts, either spontaneously or during surgical removal of primary hydatid cysts. Herein, we have analysed the mechanisms behind the significant protection observed in the mouse model of secondary CE following prophylactic administration of rshCD5 or rshCD6. Our results show that both molecules exhibit intrinsic antiparasitic activities in vitro, as well as immunomodulatory functions during early secondary CE, mainly through Th1/Th17 cytokine bias and promotion of peritoneal polyreactive antibodies. These data support the relevance of the parasite components bound by rshCD5 and rshCD6, as well as the potential of their prophylactic administration as a useful strategy to reduce secondary CE in patients.

NADPH oxidase exerts a B cell-intrinsic contribution to lupus risk by modulating endosomal TLR signals

Genome-wide association studies in systemic lupus erythematosus (SLE) have linked loss-of-function mutations in phagocytic NADPH oxidase complex (NOX2) genes, including NCF1 and NCF2, to disease pathogenesis. The prevailing model holds that reduced NOX2 activity promotes SLE via defective efferocytosis, the immunologically silent clearance of apoptotic cells. Here, we describe a parallel B cell-intrinsic mechanism contributing to breaks in tolerance. In keeping with an important role for B cell Toll-like receptor (TLR) pathways in lupus pathogenesis, NOX2-deficient B cells exhibit enhanced signaling downstream of endosomal TLRs, increased humoral responses to nucleic acid-containing antigens, and the propensity toward humoral autoimmunity. Mechanistically, TLR-dependent NOX2 activation promotes LC3-mediated maturation of TLR-containing endosomes, resulting in signal termination. CRISPR-mediated disruption of NCF1 confirmed a direct role for NOX2 in regulating endosomal TLR signaling in primary human B cells. Together, these data highlight a new B cell-specific mechanism contributing to autoimmune risk in NCF1 and NCF2 variant carriers.

Proof of concept in utilizing the peptidoglycan skeleton of pathogenic bacteria as antigen delivery platform for enhanced immune response

Subunit vaccines are becoming increasingly important because of their safety and effectiveness. However, subunit vaccines often exhibit limited immunogenicity, necessitating the use of suitable adjuvants to elicit robust immune responses. In this study, we demonstrated for the first time that pathogenic bacteria can be prepared into a purified peptidoglycan skeleton without nucleic acids and proteins, presenting bacterium-like particles (pBLP). Our results showed that the peptidoglycan skeletons screened from four pathogens could activate Toll-like receptor1/2 receptors better than bacterium-like particles from Lactococcus lactis in macrophages. We observed that pBLP was safe in mouse models of multiple ages. Furthermore, pBLP improved the performance of two commercial vaccines in vivo. We confirmed that pBLP successfully loaded antigens onto the surface and proved to be an effective antigen delivery platform with enhanced antibody titers, antibody avidity, balanced subclass distribution, and mucosal immunity. These results indicate that the peptidoglycan skeleton of pathogenic bacteria represents a new strategy for developing subunit vaccine delivery systems.

Distinctive domains and activity regulation of core fucosylation enzyme FUT8

BACKGROUND

Core fucose, a structure added to the reducing end N-acetylglucosamine of N-glycans, has been shown to regulate various physiological and pathological processes, including melanoma metastasis, exacerbation of chronic obstructive pulmonary disease, and severe outcomes in COVID-19.

SCOPE OF REVIEW

Recent research has shed light on regulation of the activity and subcellular localization of a1,6-fucosyltransferase (FUT8), the glycosyltransferase responsible for core fucose biosynthesis, unraveling the mechanisms for controlling core fucosylation in vivo.

MAJOR CONCLUSIONS

This review summarizes the various features of FUT8, including its domains, structures, and substrate specificity. Additionally, we discuss the potential involvement of FUT8-binding proteins, such as oligosaccharyltransferase subunits, in the regulation of FUT8 activity, substrate specificity, and the secretion of FUT8.

GENERAL SIGNIFICANCE

We anticipate that this review will contribute to a deeper understanding of the control of core fucose levels in vivo and involvement of core fucosylation in FUT8-relevant functions and diseases.

Delivery of CD47-SIRPα checkpoint blocker by BCMA-directed UCAR-T cells enhances antitumor efficacy in multiple myeloma

In the treatment of relapsed or refractory multiple myeloma patients, BCMA-directed autologous CAR-T cells have showed excellent anti-tumor activity. However, their widespread application is limited due to the arguably cost and time-consuming. Multiple myeloma cells highly expressed CD47 molecule and interact with the SIRPα ligand on the surface of macrophages, in which evade the clearance of macrophages through the activation of "don't eat me" signal. In this study, a BCMA-directed universal CAR-T cells, BC404-UCART, secreting a CD47-SIRPα blocker was developed using CRISPR/Cas9 gene-editing system. BC404-UCART cells significantly inhibited tumor growth and prolonged the survival of mice in the xenograft model. The anti-tumor activity of BC404-UCART cells was achieved via two mechanisms, on the one hand, the UCAR-T cells directly killed tumor cells, on the other hand, the BC404-UCART cells enhanced the phagocytosis of macrophages by secreting anti-CD47 nanobody hu404-hfc fusion that blocked the "don't eat me" signal between macrophages and tumor cells, which provides a potential strategy for the development of novel "off-the-shelf" cellular immunotherapies for the treatment of multiple myeloma.

Comparative study of acetalated-dextran microparticle fabrication methods for a clinically translatable subunit-based influenza vaccine

The most common influenza vaccines are inactivated viruses produced in chicken eggs, which is a time-consuming production method with variable efficacy due to mismatches of the vaccine strains to the dominant circulating strains. Subunit-based vaccines provide faster production times in comparison to the traditional egg-produced vaccines but often require the use of an adjuvant to elicit a highly protective immune response. However, the current FDA approved adjuvant for influenza vaccines (MF59) elicits a primarily helper T-cell type 2 (Th2)-biased humoral immune response. Adjuvants that can stimulate a Th1 cellular response are correlated to have more robust protection against influenza. The cyclic dinucleotide cGAMP has been shown to provide a potent Th1 response but requires the use of a delivery vehicle to best initiate its signalling pathway in the cytosol. Herein, acetalated dextran (Ace-DEX) was used as the polymer to fabricate microparticles (MPs) via double-emulsion, electrospray, and spray drying methods to encapsulate cGAMP. This study compared each fabrication method's ability to encapsulate and retain the hydrophilic adjuvant cGAMP. We compared their therapeutic efficacy to Addavax, an MF59-like adjuvant, and cGAMP Ace-DEX MPs provided a stronger Th1 response in vaccinated BALB/c mice. Furthermore, we compared Ace-DEX MPs to spray dried MPs composed from a commonly used polymer for drug delivery, poly(lactic-co-glycolic acid) (PLGA). We observed that all Ace-DEX MPs elicited similar humoral and cellular responses to the PLGA MPs. Overall, the results shown here indicate Ace-DEX can perform similarly to PLGA as a polymer for drug delivery and that spray drying can provide an efficient way to produce MPs to encapsulate cGAMP and stimulate the immune system.

FcγRIIB Is an Immune Checkpoint Limiting the Activity of Treg-Targeting Antibodies in the Tumor Microenvironment

Preclinical murine data indicate that fragment crystallizable (Fc)-dependent depletion of intratumoral regulatory T cells (Treg) is a major mechanism of action of anti-CTLA-4. However, the two main antibodies administered to patients (ipilimumab and tremelimumab) do not recapitulate these effects. Here, we investigate the underlying mechanisms responsible for the limited Treg depletion observed with these therapies. Using an immunocompetent murine model humanized for CTLA-4 and Fcγ receptors (FcγR), we show that ipilimumab and tremelimumab exhibit limited Treg depletion in tumors. Immune profiling of the tumor microenvironment (TME) in both humanized mice and humans revealed high expression of the inhibitory Fc receptor, FcγRIIB, which limits antibody-dependent cellular cytotoxicity/phagocytosis. Blocking FcγRIIB in humanized mice rescued the Treg-depleting capacity and antitumor activity of ipilimumab. Furthermore, Fc engineering of antibodies targeting Treg-associated targets (CTLA-4 or CCR8) to minimize FcγRIIB binding significantly enhanced Treg depletion, resulting in increased antitumor activity across various tumor models. Our results define the inhibitory FcγRIIB as an immune checkpoint limiting antibody-mediated Treg depletion in the TME, and demonstrate Fc engineering as an effective strategy to overcome this limitation and improve the efficacy of Treg-targeting antibodies.

Nanoparticle-Based Secretory Granules Induce a Specific and Long-Lasting Immune Response through Prolonged Antigen Release

Developing prolonged antigen delivery systems that mimic long-term exposure to pathogens appears as a promising but still poorly explored approach to reach durable immunities. In this study, we have used a simple technology by which His-tagged proteins can be assembled, assisted by divalent cations, as supramolecular complexes with progressive complexity, namely protein-only nanoparticles and microparticles. Microparticles produced out of nanoparticles are biomimetics of secretory granules from the mammalian hormonal system. Upon subcutaneous administration, they slowly disintegrate, acting as an endocrine-like secretory system and rendering the building block nanoparticles progressively bioavailable. The performance of such materials, previously validated for drug delivery in oncology, has been tested here regarding the potential for time-prolonged antigen release. This has been completed by taking, as a building block, a nanostructured version of p30, a main structural immunogen from the African swine fever virus (ASFV). By challenging the system in both mice and pigs, we have observed unusually potent pro-inflammatory activity in porcine macrophages, and long-lasting humoral and cellular responses in vivo, which might overcome the need for an adjuvant. The robustness of both innate and adaptive responses tag, for the first time, these dynamic depot materials as a novel and valuable instrument with transversal applicability in immune stimulation and vaccinology.

Tissue niche occupancy determines the contribution of fetal- versus bone-marrow-derived macrophages to IgG effector functions

Understanding the mechanisms underlying cytotoxic immunoglobulin G (IgG) activity is critical for improving therapeutic antibody activity and inhibiting autoantibody-mediated tissue pathology. While prior research highlights the important role of the mononuclear phagocytic system for removing opsonized target cells, it remains unclear which monocyte or macrophage subsets stemming from fetal or post-natal bone-marrow (BM)-associated definitive hematopoiesis are involved in target cell depletion. By using a titrated irradiation approach as well as Kupffer-cell-specific deletion of activated Fcγ receptor signaling, we establish conditions under which the contribution of BM-derived monocytes versus yolk-sac-derived liver-resident macrophages to cytotoxic IgG activity can be studied. Our results demonstrate that liver-resident macrophages originating from either fetal or adult hematopoiesis play a central role in IgG-mediated depletion of opsonized target cells from the peripheral blood under steady-state conditions, highlighting the impact of the tissue niche and not macrophage origin for cytotoxic antibody activity.

Conserved molecular chaperone PrsA stimulates protective immunity against group A Streptococcus

Group A Streptococcus (GAS) is a significant human pathogen that poses a global health concern. However, the development of a GAS vaccine has been challenging due to the multitude of diverse M-types and the risk of triggering cross-reactive immune responses. Our previous research has identified a critical role of PrsA1 and PrsA2, surface post-translational molecular chaperone proteins, in maintaining GAS proteome homeostasis and virulence traits. In this study, we aimed to further explore the potential of PrsA1 and PrsA2 as vaccine candidates for preventing GAS infection. We found that PrsA1 and PrsA2 are highly conserved among GAS isolates, demonstrating minimal amino acid variation. Antibodies specifically targeting PrsA1/A2 showed no cross-reactivity with human heart proteins and effectively enhanced neutrophil opsonophagocytic killing of various GAS serotypes. Additionally, passive transfer of PrsA1/A2-specific antibodies conferred protective immunity in infected mice. Compared to alum, immunization with CFA-adjuvanted PrsA1/A2 induced higher levels of Th1-associated IgG isotypes and complement activation and provided approximately 70% protection against invasive GAS challenge. These findings highlight the potential of PrsA1 and PrsA2 as universal vaccine candidates for the development of an effective GAS vaccine.

Effector functions are required for broad and potent protection of neonatal mice with antibodies targeting HSV glycoprotein D

Multiple failed herpes simplex virus (HSV) vaccine candidates induce robust neutralizing antibody (Ab) responses in clinical trials, raising the hypothesis that Fc-domain-dependent effector functions may be critical for protection. While neonatal HSV (nHSV) infection results in mortality and lifelong neurological morbidity in humans, it is uncommon among neonates with a seropositive birthing parent, supporting the hypothesis that Ab-based therapeutics could protect neonates from HSV. We therefore investigated the mechanisms of monoclonal Ab (mAb)-mediated protection in a mouse model of nHSV infection. For a panel of glycoprotein D (gD)-specific mAbs, neutralization and effector functions contributed to nHSV-1 protection. In contrast, effector functions alone were sufficient to protect against nHSV-2, exposing a functional dichotomy between virus types consistent with vaccine trial results. Effector functions are therefore crucial for protection by these gD-specific mAbs, informing effective Ab and vaccine design and demonstrating the potential of polyfunctional Abs as therapeutics for nHSV infections.

Antibody agonists trigger immune receptor signaling through local exclusion of receptor-type protein tyrosine phosphatases

Antibodies can block immune receptor engagement or trigger the receptor machinery to initiate signaling. We hypothesized that antibody agonists trigger signaling by sterically excluding large receptor-type protein tyrosine phosphatases (RPTPs) such as CD45 from sites of receptor engagement. An agonist targeting the costimulatory receptor CD28 produced signals that depended on antibody immobilization and were sensitive to the sizes of the receptor, the RPTPs, and the antibody itself. Although both the agonist and a non-agonistic anti-CD28 antibody locally excluded CD45, the agonistic antibody was more effective. An anti-PD-1 antibody that bound membrane proximally excluded CD45, triggered Src homology 2 domain-containing phosphatase 2 recruitment, and suppressed systemic lupus erythematosus and delayed-type hypersensitivity in experimental models. Paradoxically, nivolumab and pembrolizumab, anti-PD-1-blocking antibodies used clinically, also excluded CD45 and were agonistic in certain settings. Reducing these agonistic effects using antibody engineering improved PD-1 blockade. These findings establish a framework for developing new and improved therapies for autoimmunity and cancer.

An integrated signaling threshold initiates IgG response towards virus-like immunogens

Class-switched neutralizing antibody (nAb) production is rapidly induced upon many viral infections. However, due to the presence of multiple components in typical virions, the precise biochemical and biophysical signals from viral infections that initiate nAb responses remain inadequately defined. Using a reductionist system of synthetic virus-like structures (SVLS) containing minimal, highly purified biochemical components commonly found in enveloped viruses, here we show that a foreign protein on a virion-sized liposome can serve as a stand-alone danger signal to initiate class-switched nAb responses in the absence of cognate T cell help or Toll-like receptor signaling but requires CD19, the antigen (Ag) coreceptor on B cells. Introduction of internal nucleic acids (iNAs) obviates the need for CD19, lowers the epitope density (ED) required to elicit the Ab response and transforms these structures into highly potent immunogens that rival conventional virus-like particles in their ability to elicit strong Ag-specific IgG. As early as day 5 after immunization, structures harbouring iNAs and decorated with just a few molecules of surface Ag at doses as low as 100 ng induced all IgG subclasses of Ab known in mice and reproduced the IgG2a/2c restriction that has been long observed in live viral infections. These findings reveal a shared mechanism for nAb response upon viral infection. High ED is capable but not necessary for driving Ab secretion in vivo . Instead, even a few molecules of surface Ag, when combined with nucleic acids within these structures, can trigger strong antiviral IgG production. As a result, the signaling threshold for the induction of neutralizing IgG is set by dual signals originating from both ED on the surface and the presence of iNAs within viral particulate immunogens.

One-sentence summary

Reconstitution of minimal viral signals necessary to initiate antiviral IgG.

Therapeutic efficacy of a potent anti-Venezuelan equine encephalitis virus antibody is contingent on Fc effector function

The development of specific, safe, and potent monoclonal antibodies (Abs) has led to novel therapeutic options for infectious disease. In addition to preventing viral infection through neutralization, Abs can clear infected cells and induce immunomodulatory functions through engagement of their crystallizable fragment (Fc) with complement proteins and Fc receptors on immune cells. Little is known about the role of Fc effector functions of neutralizing Abs in the context of encephalitic alphavirus infection. To determine the role of Fc effector function in therapeutic efficacy against Venezuelan equine encephalitis virus (VEEV), we compared the potently neutralizing anti-VEEV human IgG F5 (hF5) Ab with intact Fc function (hF5-WT) or containing the loss of function Fc mutations L234A and L235A (hF5-LALA) in the context of VEEV infection. We observed significantly reduced binding to complement and Fc receptors, as well as differential in vitro kinetics of Fc-mediated cytotoxicity for hF5-LALA compared to hF5-WT. The in vivo efficacy of hF5-LALA was comparable to hF5-WT at -24 and + 24 h post infection, with both Abs providing high levels of protection. However, when hF5-WT and hF5-LALA were administered + 48 h post infection, there was a significant decrease in the therapeutic efficacy of hF5-LALA. Together these results demonstrate that optimal therapeutic Ab treatment of VEEV, and possibly other encephalitic alphaviruses, requires neutralization paired with engagement of immune effectors via the Fc region.

Fcγ receptors and immunomodulatory antibodies in cancer

The discovery of both cytotoxic T lymphocyte-associated antigen 4 (CTLA4) and programmed cell death protein 1 (PD1) as negative regulators of antitumour immunity led to the development of numerous immunomodulatory antibodies as cancer treatments. Preclinical studies have demonstrated that the efficacy of immunoglobulin G (IgG)-based therapies depends not only on their ability to block or engage their targets but also on the antibody's constant region (Fc) and its interactions with Fcγ receptors (FcγRs). Fc-FcγR interactions are essential for the activity of tumour-targeting antibodies, such as rituximab, trastuzumab and cetuximab, where the killing of tumour cells occurs at least in part due to these mechanisms. However, our understanding of these interactions in the context of immunomodulatory antibodies designed to boost antitumour immunity remains less explored. In this Review, we discuss our current understanding of the contribution of FcγRs to the in vivo activity of immunomodulatory antibodies and the challenges of translating results from preclinical models into the clinic. In addition, we review the impact of genetic variability of human FcγRs on the activity of therapeutic antibodies and how antibody engineering is being utilized to develop the next generation of cancer immunotherapies.

Exogenous l-fucose attenuates neuroinflammation induced by lipopolysaccharide

α1,6-Fucosyltransferase (Fut8) catalyzes the transfer of fucose to the innermost GlcNAc residue of N-glycan to form core fucosylation. Our previous studies showed that lipopolysaccharide (LPS) treatment highly induced neuroinflammation in Fut8 homozygous KO (Fut8-/-) or heterozygous KO (Fut8+/-) mice, compared with the WT (Fut8+/+) mice. To understand the underlying mechanism, we utilized a sensitive inflammation-monitoring mouse system that contains the human interleukin-6 (hIL6) bacterial artificial chromosome transgene modified with luciferase (Luc) reporter cassette. We successfully detected LPS-induced neuroinflammation in the central nervous system by exploiting this bacterial artificial chromosome transgenic monitoring system. Then we examined the effects of l-fucose on neuroinflammation in the Fut8+/- mice. The lectin blot and mass spectrometry analysis showed that l-fucose preadministration increased the core fucosylation levels in the Fut8+/- mice. Notably, exogenous l-fucose attenuated the LPS-induced IL-6 mRNA and Luc mRNA expression in the cerebral tissues, confirmed using the hIL6-Luc bioluminescence imaging system. The activation of microglial cells, which provoke neuroinflammatory responses upon LPS stimulation, was inhibited by l-fucose preadministration. l-Fucose also suppressed the downstream intracellular signaling of IL-6, such as the phosphorylation levels of JAK2 (Janus kinase 2), Akt (protein kinase B), and STAT3 (signal transducer and activator of transcription 3). l-Fucose administration increased gp130 core fucosylation levels and decreased the association of gp130 with the IL-6 receptor in Fut8+/- mice, which was further confirmed in BV-2 cells. These results indicate that l-fucose administration ameliorates the LPS-induced neuroinflammation in the Fut8+/- mice, suggesting that core fucosylation plays a vital role in anti-inflammation and that l-fucose is a potential prophylactic compound against neuroinflammation.

Co-adjuvanting DDA/TDB liposomes with a TLR7 agonist allows for IgG2a/c class-switching in the absence of Th1 cells

Class-switching to IgG2a/c in mice is a hallmark response to intracellular pathogens. T cells can promote class-switching and the predominant pathway for induction of IgG2a/c antibody responses has been suggested to be via stimulation from Th1 cells. We previously formulated CAF®01 (cationic liposomes containing dimethyldioctadecylammonium bromide (DDA) and Trehalose-6,6-dibehenate (TDB)) with the lipidated TLR7/8 agonist 3M-052 (DDA/TDB/3M-052), which promoted robust Th1 immunity in newborn mice. When testing this adjuvant in adult mice using the recombinant Chlamydia trachomatis (C.t.) vaccine antigen CTH522, it similarly enhanced IgG2a/c responses compared to DDA/TDB, but surprisingly reduced the magnitude of the IFN-γ+Th1 response in a TLR7 agonist dose-dependent manner. Single-cell RNA-sequencing revealed that DDA/TDB/3M-052 liposomes initiated early transcription of class-switch regulating genes directly in pre-germinal center B cells. Mixed bone marrow chimeras further demonstrated that this adjuvant did not require Th1 cells for IgG2a/c switching, but rather facilitated TLR7-dependent T-bet programming directly in B cells. This study underlines that adjuvant-directed IgG2a/c class-switching in vivo can occur in the absence of T-cell help, via direct activation of TLR7 on B cells and positions DDA/TDB/3M-052 as a powerful adjuvant capable of eliciting type I-like immunity in B cells without strong induction of Th1 responses.

CpG ODN enhances the efficacy of F protein vaccine against respiratory syncytial virus infection in the upper respiratory tract via CD4+ T cells

Respiratory syncytial virus (RSV) is a leading cause of severe respiratory illness worldwide, particularly in infants and older adults. Vaccines targeting the fusion glycoprotein (F protein) -one of the surface antigens of RSV- are highly effective in preventing RSV-associated severe lower respiratory tract disease. However, the efficacy of these vaccines against upper respiratory tract challenge needs improvement. Here, we aimed to examine the efficacy of F protein vaccines with or without CpG oligodeoxynucleotide (CpG ODN) as an adjuvant in the upper and lower respiratory tracts in mice. F + CpG ODN induced higher levels of F-specific IgG than that induced by F alone; however, levels of neutralizing antibodies did not increase compared to those induced by F alone. F + CpG ODN induced T helper 1 (Th1) cells while F alone induced T helper 2 (Th2) cells. Moreover, F + CpG ODN improved the protection against RSV challenge in the upper respiratory tract compared to F alone, which was largely dependent on CD4+ T cells. Meanwhile, both F + CpG ODN and F alone protected the lower respiratory tract. In conclusion, we demonstrated that induction of F-specific Th1 cells is an effective strategy to prevent RSV challenge in the upper respiratory tract in F protein vaccines. These data support the development of novel F protein vaccines.

The antitumor activities of anti-CD47 antibodies require Fc-FcγR interactions

While anti-CD47 antibodies hold promise for cancer immunotherapy, early-phase clinical trials have shown limited clinical benefit, suggesting that CD47 blockade alone might be insufficient for effective tumor control. Here, we investigate the contributions of the Fc domain of anti-CD47 antibodies required for optimal in vivo antitumor activity across multiple species-matched models, providing insights into the mechanisms behind the efficacy of this emerging class of therapeutic antibodies. Using a mouse model humanized for CD47, SIRPα, and FcγRs, we demonstrate that local administration of Fc-engineered anti-CD47 antibodies with enhanced binding to activating FcγRs promotes tumor infiltration of macrophages and antigen-specific T cells, while depleting regulatory T cells. These effects result in improved long-term systemic antitumor immunity and minimal on-target off-tumor toxicity. Our results highlight the importance of Fc optimization in the development of effective anti-CD47 therapies and provide an attractive strategy to enhance the activity of this promising immunotherapy.

Systematic evaluation of AML-associated antigens identifies anti-U5 SNRNP200 therapeutic antibodies for the treatment of acute myeloid leukemia

Despite recent advances in the treatment of acute myeloid leukemia (AML), there has been limited success in targeting surface antigens in AML, in part due to shared expression across malignant and normal cells. Here, high-density immunophenotyping of AML coupled with proteogenomics identified unique expression of a variety of antigens, including the RNA helicase U5 snRNP200, on the surface of AML cells but not on normal hematopoietic precursors and skewed Fc receptor distribution in the AML immune microenvironment. Cell membrane localization of U5 snRNP200 was linked to surface expression of the Fcγ receptor IIIA (FcγIIIA, also known as CD32A) and correlated with expression of interferon-regulated immune response genes. Anti-U5 snRNP200 antibodies engaging activating Fcγ receptors were efficacious across immunocompetent AML models and were augmented by combination with azacitidine. These data provide a roadmap of AML-associated antigens with Fc receptor distribution in AML and highlight the potential for targeting the AML cell surface using Fc-optimized therapeutics.

Inactivated Recombinant Rabies Virus Displaying the Nipah Virus Envelope Glycoproteins Induces Systemic Immune Responses in Mice

Nipah virus (NiV) causes severe, lethal encephalitis in humans and pigs. However, there is no licensed vaccine available to prevent NiV infection. In this study, we used the reverse genetic system based on the attenuated rabies virus strain SRV9 to construct two recombinant viruses, rSRV9-NiV-F and rSRV9-NiV-G, which displayed the NiV envelope glycoproteins F and G, respectively. Following three immunizations in BALB/c mice, the inactivated rSRV9-NiV-F and rSRV9-NiV-G alone or in combination, mixed with the adjuvants ISA 201 VG and poly (I:C), were able to induce the antigen-specific cellular and Th1-biased humoral immune responses. The specific antibodies against rSRV9-NiV-F and rSRV9-NiV-G had reactivity with two constructed bacterial-like particles displaying the F and G antigens of NiV. These data demonstrate that rSRV9-NiV-F or rSRV9-NiV-G has the potential to be developed into a promising vaccine candidate against NiV infection.

Human neutrophil Fc gamma receptors: different buttons for different responses

Neutrophils are fundamental cells in host defense. These leukocytes are quickly recruited from the blood to sites of infection or tissue damage. At these sites, neutrophils initiate several innate immune responses, including phagocytosis, production of reactive oxygen species, degranulation to release proteases and other antimicrobial compounds, production of inflammatory mediators, and formation of neutrophil extracellular traps. In addition to their role in innate immunity, neutrophils are now recognized as cells that also regulate adaptive immunity, via interaction with dendritic cells and lymphocytes. Neutrophils also respond to adaptive immunity by interacting with antibody molecules. Indeed, antibody molecules allow neutrophils to have antigen-specific responses. Neutrophils express different receptors for antibodies. The receptors for immunoglobulin G molecules are known as Fcγ receptors. Upon Fcγ receptor aggregation on the cell membrane, these receptors trigger distinct signal transduction cascades that activate particular cellular responses. In this review, we describe the major Fcγ receptors expressed on human neutrophils and discuss how each Fcγ receptor activates a choice of signaling pathways to stimulate particular neutrophil responses.

How B cells drive T-cell responses: A key role for cross-presentation of antibody-targeted antigens

In this review we discuss an underexposed mechanism in the adaptive immune system where B cell and T cell immunity collaborate. The main function of B cell immunity is the generation of antibodies which are well known for their high affinity and antigen-specificity. Antibodies can bind antigens in soluble form making so-called immune complexes (ICs) or can opsonize antigen-exposing cells or particles for degradation. This leads to well-known effector mechanisms complement activation, antibody-dependent cytotoxicity and phagocytosis. What is less realized is that antibodies can play an important role in the targeting of antigen to dendritic cells (DCs) and thereby can drive T cell immunity. Here we summarize the studies that described this highly efficient process of antibody-mediated antigen uptake in DCs in vitro and in vivo. Only very low doses of antigen can be captured by circulating antibodies and subsequently trapped by DCs in vivo. We studied the handling of these ICs by DCs in subcellular detail. Upon immune complex engulfment DCs can sustain MHC class I and II antigen presentation for many days. Cell biological analysis showed that this function is causally related to intracellular antigen-storage compartments which are functional endolysosomal organelles present in DCs. We speculate that this function is immunologically very important as DCs require time to migrate from the site of infection to the draining lymph nodes to activate T cells. The implications of these findings and the consequences for the immune system, immunotherapy with tumor-specific antibodies and novel vaccination strategies are discussed.

An FcRn-targeted mucosal vaccine against SARS-CoV-2 infection and transmission

SARS-CoV-2 is primarily transmitted through droplets and airborne aerosols, and in order to prevent infection and reduce viral spread vaccines should elicit protective immunity in the airways. The neonatal Fc receptor (FcRn) transfers IgG across epithelial barriers and can enhance mucosal delivery of antigens. Here we explore FcRn-mediated respiratory delivery of SARS-CoV-2 spike (S). A monomeric IgG Fc was fused to a stabilized spike; the resulting S-Fc bound to S-specific antibodies and FcRn. Intranasal immunization of mice with S-Fc and CpG significantly induced antibody responses compared to the vaccination with S alone or PBS. Furthermore, we intranasally immunized mice or hamsters with S-Fc. A significant reduction of virus replication in nasal turbinate, lung, and brain was observed following nasal challenges with SARS-CoV-2 and its variants. Intranasal immunization also significantly reduced viral airborne transmission in hamsters. Nasal IgA, neutralizing antibodies, lung-resident memory T cells, and bone-marrow S-specific plasma cells mediated protection. Hence, FcRn delivers an S-Fc antigen effectively into the airway and induces protection against SARS-CoV-2 infection and transmission.

Features and protective efficacy of human mAbs targeting Mycobacterium tuberculosis arabinomannan

A better understanding of the epitopes most relevant for antibody-mediated protection against tuberculosis (TB) remains a major knowledge gap. We have shown that human polyclonal IgG against the Mycobacterium tuberculosis (M. tuberculosis) surface glycan arabinomannan (AM) and related lipoarabinomannan (LAM) is protective against TB. To investigate the impact of AM epitope recognition and Fcγ receptor (FcγR) binding on antibody functions against M. tuberculosis, we isolated a high-affinity human monoclonal antibody (mAb; P1AM25) against AM and showed its binding to oligosaccharide (OS) motifs we previously found to be associated with in vitro functions of human polyclonal anti-AM IgG. Human IgG1 P1AM25, but not 2 other high-affinity human IgG1 anti-AM mAbs reactive with different AM OS motifs, enhanced M. tuberculosis phagocytosis by macrophages and reduced intracellular growth in an FcγR-dependent manner. P1AM25 in murine IgG2a, but neither murine IgG1 nor a non-FcγR-binding IgG, given intraperitoneally prior to and after aerosolized M. tuberculosis infection, was protective in C57BL/6 mice. Moreover, we demonstrated the protective efficacy of human IgG1 P1AM25 in passive transfer with M. tuberculosis-infected FcγR-humanized mice. These data enhance our knowledge of the important interplay between both antibody epitope specificity and Fc effector functions in the defense against M. tuberculosis and could inform development of vaccines against TB.

Systems serology in cystic fibrosis: Anti-Pseudomonas IgG1 responses and reduced lung function

Nearly one-half of patients with cystic fibrosis (CF) carry the homozygous F508del mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene but exhibit variable lung function phenotypes. How adaptive immunity influences their lung function remains unclear, particularly the serological antibody responses to antigens from mucoid Pseudomonas in sera from patients with CF with varying lung function. Sera from patients with CF with reduced lung function show higher anti-outer membrane protein I (OprI) immunoglobulin G1 (IgG1) titers and greater antibody-mediated complement deposition. Induction of anti-OprI antibody isotypes with complement activity enhances lung inflammation in preclinical mouse models. This enhanced inflammation is absent in immunized Rag2-/- mice and is transferrable to unimmunized mice through sera. In a CF cohort undergoing treatment with elexacaftor-tezacaftor-ivacaftor, the declination in anti-OprI IgG1 titers is associated with lung function improvement and reduced hospitalizations. These findings suggest that antibody responses to specific Pseudomonas aeruginosa (PA) antigens worsen lung function in patients with CF.

Cellular surface plasmon resonance-based detection of anti-HPA-1a antibody glycosylation in fetal and neonatal alloimmune thrombocytopenia

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) can occur due to maternal IgG antibodies targeting platelet antigens, causing life-threatening bleeding in the neonate. However, the disease manifests itself in only a fraction of pregnancies, most commonly with anti-HPA-1a antibodies. We found that in particular, the core fucosylation in the IgG-Fc tail is highly variable in anti-HPA-1a IgG, which strongly influences the binding to leukocyte IgG-Fc receptors IIIa/b (FcγRIIIa/b). Currently, gold-standard IgG-glycoanalytics rely on complicated methods (e.g., mass spectrometry (MS)) that are not suited for diagnostic purposes. Our aim was to provide a simplified method to quantify the biological activity of IgG antibodies targeting cells. We developed a cellular surface plasmon resonance imaging (cSPRi) technique based on FcγRIII-binding to IgG-opsonized cells and compared the results with MS. The strength of platelet binding to FcγR was monitored under flow using both WT FcγRIIIa (sensitive to Fc glycosylation status) and mutant FcγRIIIa-N162A (insensitive to Fc glycosylation status). The quality of the anti-HPA-1a glycosylation was monitored as the ratio of binding signals from the WT versus FcγRIIIa-N162A, using glycoengineered recombinant anti-platelet HPA-1a as a standard. The method was validated with 143 plasma samples with anti-HPA-1a antibodies analyzed by MS with known clinical outcomes and tested for validation of the method. The ratio of patient signal from the WT versus FcγRIIIa-N162A correlated with the fucosylation of the HPA-1a antibodies measured by MS (r=-0.52). Significantly, FNAIT disease severity based on Buchanan bleeding score was similarly discriminated against by MS and cSPRi. In conclusion, the use of IgG receptors, in this case, FcγRIIIa, on SPR chips can yield quantitative and qualitative information on platelet-bound anti-HPA-1a antibodies. Using opsonized cells in this manner circumvents the need for purification of specific antibodies and laborious MS analysis to obtain qualitative antibody traits such as IgG fucosylation, for which no clinical test is currently available.

Antibody-mediated phagocytosis in cancer immunotherapy

Unconjugated monoclonal antibodies (mAb) have revolutionized the treatment of many types of cancer. Some of these mAbs promote the clearance of malignant cells via direct cytotoxic effects. More recently, antibody-dependent cellular phagocytosis (ADCP) has been appreciated as a major mechanism of action for a number of widely-used mAbs, including anti-CD20 (rituximab, obinutuzumab), anti-HER2 (trazituzumab), and anti-CD38 (daratumumab). However, as a monotherapy these ADCP-inducing mAbs produce insufficient levels of cytotoxicity in vivo and are not curative. As a result, these mAbs are most effectively used in combination therapies. The efficacy of these mAbs is further hampered by the apparent development of drug resistance by many patients. Here we will explore the role of ADCP in cancer immunotherapy and discuss the key factors that could limit the efficacy of ADCP-inducing mAbs in vivo. Finally, we will discuss current insights and approaches being applied to overcome these limitations.

Modulating antibody effector functions by Fc glycoengineering

Antibody based drugs, including IgG monoclonal antibodies, are an expanding class of therapeutics widely employed to treat cancer, autoimmune and infectious diseases. IgG antibodies have a conserved N-glycosylation site at Asn297 that bears complex type N-glycans which, along with other less conserved N- and O-glycosylation sites, fine-tune effector functions, complement activation, and half-life of antibodies. Fucosylation, galactosylation, sialylation, bisection and mannosylation all generate glycoforms that interact in a specific manner with different cellular antibody receptors and are linked to a distinct functional profile. Antibodies, including those employed in clinical settings, are generated with a mixture of glycoforms attached to them, which has an impact on their efficacy, stability and effector functions. It is therefore of great interest to produce antibodies containing only tailored glycoforms with specific effects associated with them. To this end, several antibody engineering strategies have been developed, including the usage of engineered mammalian cell lines, in vitro and in vivo glycoengineering.

Antibody effector functions are required for broad and potent protection of neonates from herpes simplex virus infection

The failure of multiple herpes simplex virus (HSV) vaccine candidates that induce neutralizing antibody responses raises the hypothesis that other activities, such as Fc domain-dependent effector functions, may be critical for protection. While neonatal HSV (nHSV) infection result in mortality and lifelong neurological morbidity in humans, it is uncommon among neonates with a seropositive birthing parent, suggesting the potential efficacy of antibody-based therapeutics to protect neonates. We therefore investigated the mechanisms of monoclonal antibody (mAb)-mediated protection in a mouse model of nHSV infection. Both neutralization and effector functions contributed to robust protection against nHSV-1. In contrast, effector functions alone were sufficient to protect against nHSV-2, exposing a functional dichotomy between virus types that is consistent with vaccine trial results. Together, these results emphasize that effector functions are crucial for optimal mAb-mediated protection, informing effective Ab and vaccine design, and demonstrating the potential of polyfunctional Abs as potent therapeutics for nHSV infections.