FcγR dependent mechanisms of cytotoxic, agonistic, and neutralizing antibody activities

Platelet FcRγ inhibits tumor metastasis by preventing the colonization of circulating tumor cells

Fc receptor γ subunit (FcRγ) activation plays a crucial role in cancer carcinogenesis. Here, we aimed to uncover the impact of FcRγ on circulating tumor cells (CTC) colonization and the underlying mechanism. FcRγ deficient (FcRγ-/-) mice were used to investigate the functional effects of FcRγ in cancer metastasis, and the results demonstrated that FcRγ deficiency significantly promotes metastasis. The tumor metastasis effect, antiplatelet, platelet or neutrophil infusion experiments were conducted with FcRγ deficient (FcRγ-/-) mice and wild type mice (WT), bearing B16F10 or LCC tumor cells. Blood routine test, flow cytometry, immunofluorescent staining and in vivo image were applied for analysis. Platelet adhesion and neutrophil chemotaxis were analyzed by flow cytometry and ELISA in vitro. Platelet adoptive model was used for mimicing early colonization stage. Our results indicated FcRγ deficiency significantly promoted tumor metastasis accompanied with increased number of platelet and neutrophil in the lung. Further investigation showed that FcRγ-/- platelet infusion, rather than FcRγ-/- neutrophils, promoted CTC colonization. While platelet inhibitor Aspirin abrogated the platelet-mediated infiltration of neutrophil in the lung. Mechanistically, platelet FcRγ deficiency facilitated the adhesion of platelets and cancer cells and increased secretion of CXCL5 and CXCL7 which triggered the platelet-induced neutrophil recruitment. In sum, our study indicates that FcRγ is a restrainer in controlling cancer metastasis through regulating the adhesion of platelets and cancer cells and recruiting more neutrophils, which provides a potential target for anti-metastatic therapies. The level of FcRγ expression in platelets could act as a novel biomarker for cancer metastasis.

Fc-Afucosylation of VAR2CSA-Specific Immunoglobulin G and Clinical Immunity to Placental Plasmodium falciparum Malaria

BACKGROUND

Acquired immunity to Plasmodium falciparum malaria is mainly mediated by immunoglobulin G (IgG) targeting erythrocyte membrane protein 1 (PfEMP1). These adhesins mediate infected erythrocyte (IE) sequestration, protecting IEs from splenic destruction. PfEMP1-specific IgG is therefore thought to protect mainly by inhibiting IE sequestration. VAR2CSA-type PfEMP1 mediates placental IE sequestration, putting pregnant women exposed to P falciparum parasites at risk of placental malaria (PM).

METHODS

Levels and Fc-afucosylation of VAR2CSA-specific plasma IgG were measured by a modified enzyme-linked immunosorbent assay (FEASI). We also measured the ability of the IgG to inhibit IE adhesion and to induce natural killer (NK) cell degranulation. The results were related to parity and clinical pregnancy outcomes.

RESULTS

Parity was positively correlated with levels and Fc-afucosylation of VAR2CSA-specific IgG, and with birth weight and plasma IgG inhibition of IE adhesion in vitro. Fc-afucosylation of VAR2CSA-specific IgG increased NK-cell degranulation. Women with Fc-afucosylated VAR2CSA-specific IgG had a reduced risk of delivering a low birth weight (LBW) baby, but not of PM or anemia.

CONCLUSIONS

Fc-afucosylated VAR2CSA-specific IgG effectively induced NK-cell degranulation and was associated with protection against LBW, independent of IgG levels. Our study has implications for the development of VAR2CSA-based subunit vaccines, which exclusively induce Fc-fucosylated IgG.

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.

Sequence variants influencing the regulation of serum IgG subclass levels

Immunoglobulin G (IgG) is the main isotype of antibody in human blood. IgG consists of four subclasses (IgG1 to IgG4), encoded by separate constant region genes within the Ig heavy chain locus (IGH). Here, we report a genome-wide association study on blood IgG subclass levels. Across 4334 adults and 4571 individuals under 18 years, we discover ten new and identify four known variants at five loci influencing IgG subclass levels. These variants also affect the risk of asthma, autoimmune diseases, and blood traits. Seven variants map to the IGH locus, three to the Fcγ receptor (FCGR) locus, and two to the human leukocyte antigen (HLA) region, affecting the levels of all IgG subclasses. The most significant associations are observed between the G1m (f), G2m(n) and G3m(b*) allotypes, and IgG1, IgG2 and IgG3, respectively. Additionally, we describe selective associations with IgG4 at 16p11.2 (ITGAX) and 17q21.1 (IKZF3, ZPBP2, GSDMB, ORMDL3). Interestingly, the latter coincides with a highly pleiotropic signal where the allele associated with lower IgG4 levels protects against childhood asthma but predisposes to inflammatory bowel disease. Our results provide insight into the regulation of antibody-mediated immunity that can potentially be useful in the development of antibody based therapeutics.

NK Cell Degranulation Triggered by Rituximab Identifies Potential Markers of Subpopulations with Enhanced Cytotoxicity toward Malignant B Cells

A promising strategy in cancer immunotherapy is to restore or enhance the cytotoxicity of NK cells, among others, by activating the mechanism of antibody-dependent cellular cytotoxicity (ADCC). Monoclonal antibodies targeting tumor antigens, such as rituximab (targeting CD20), induce NK cell-mediated ADCC and have been used to treat B cell malignancies, such as non-Hodgkin lymphoma, but not always successfully. The aim of this study was to analyze the gene expression profile of the NK cells involved in the cytolytic response stimulated by rituximab. NK cells were co-cultured with rituximab-opsonized Raji cells. Sorting into responder and non-responder groups was based on the presence of CD107a, which is a degranulation marker. RNA-seq results showed that the KIT and TNFSF4 genes were strongly down-regulated in the degranulating population of NK cells (responders); this was further confirmed by qRT-PCR. Both genes encode surface proteins with cellular signaling abilities, namely c-KIT and the OX40 ligand. Consistent with our findings, c-KIT was previously reported to correlate inversely with cytokine production by activated NK cells. The significance of these findings for cancer immunotherapy seems essential, as the pharmacological inhibition of c-KIT and OX40L, or gene ablation, could be further tested for the enhancement of the anti-tumor activity of NK cells in response to rituximab.

Affinity-Resolved Size Exclusion Chromatography Coupled to Mass Spectrometry: A Novel Tool to Study the Attribute-and-Function Relationship in Therapeutic Monoclonal Antibodies

Assessment of critical quality attributes (CQAs) is an important aspect during the development of therapeutic monoclonal antibodies (mAbs). Attributes that affect either the target binding or Fc receptor engagement may have direct impacts on the drug safety and efficacy and thus are considered as CQAs. Native size exclusion chromatography (SEC)-based competitive binding assay has recently been reported and demonstrated significant benefits compared to conventional approaches for CQA identification, owing to its faster turn-around and higher multiplexity. Expanding on the similar concept, we report the development of a novel affinity-resolved size exclusion chromatography-mass spectrometry (AR-SEC-MS) method for rapid CQA evaluation in therapeutic mAbs. This method features wide applicability, fast turn-around, high multiplexity, and easy implementation. Using the well-studied Fc gamma receptor III-A (FcγRIIIa) and Fc interaction as a model system, the effectiveness of this method in studying the attribute-and-function relationship was demonstrated. Further, two case studies were detailed to showcase the application of this method in assessing CQAs related to antibody target binding, which included unusual N-linked glycosylation in a bispecific antibody and Met oxidation in a monospecific antibody, both occurring within the complementarity-determining regions (CDRs).

Influence of AAV vector tropism on long-term expression and Fc-γ receptor binding of an antibody targeting SARS-CoV-2

Long-acting passive immunization strategies are needed to protect immunosuppressed vulnerable groups from infectious diseases. To further explore this concept for COVID-19, we constructed Adeno-associated viral (AAV) vectors encoding the human variable regions of the SARS-CoV-2 neutralizing antibody, TRES6, fused to murine constant regions. An optimized vector construct was packaged in hepatotropic (AAV8) or myotropic (AAVMYO) AAV capsids and injected intravenously into syngeneic TRIANNI-mice. The highest TRES6 serum concentrations (511 µg/ml) were detected 24 weeks after injection of the myotropic vector particles and mean TRES6 serum concentrations remained above 100 µg/ml for at least one year. Anti-drug antibodies or TRES6-specific T cells were not detectable. After injection of the AAV8 particles, vector mRNA was detected in the liver, while the AAVMYO particles led to high vector mRNA levels in the heart and skeletal muscle. The analysis of the Fc-glycosylation pattern of the TRES6 serum antibodies revealed critical differences between the capsids that coincided with different binding activities to murine Fc-γ-receptors. Concomitantly, the vector-based immune prophylaxis led to protection against SARS-CoV-2 infection in K18-hACE2 mice. High and long-lasting expression levels, absence of anti-drug antibodies and favourable Fc-γ-receptor binding activities warrant further exploration of myotropic AAV vector-based delivery of antibodies and other biologicals.

Coffee Ring Effect Enhanced Surface Plasmon Resonance Imaging Biosensor via 2-λ Fitting Detection Method

SPR biosensors have been extensively used for investigating protein-protein interactions. However, in conventional surface plasmon resonance (SPR) biosensors, detection is limited by the Brownian-motion-governed diffusion process of sample molecules in the sensor chip, which makes it challenging to detect biomolecule interactions at ultra-low concentrations. Here, we propose a highly sensitive SPR imaging biosensor which exploits the coffee ring effect (CRE) for in situ enrichment of molecules on the sensing surface. In addition, we designed a wavelength modulation system utilizing two LEDs to reduce the system cost and enhance the detection speed. Furthermore, a detection limit of 213 fM is achieved, which amounts to an approximately 365 times improvement compared to traditional SPR biosensors. With further development, we believe that this SPR imaging system with high sensitivity, less sample consumption, and faster detection speed can be readily applied to ultra-low-concentration molecular detection and interaction analysis.

IgG is an aging factor that drives adipose tissue fibrosis and metabolic decline

Aging is underpinned by pronounced metabolic decline; however, the drivers remain obscure. Here, we report that IgG accumulates during aging, particularly in white adipose tissue (WAT), to impair adipose tissue function and metabolic health. Caloric restriction (CR) decreases IgG accumulation in WAT, whereas replenishing IgG counteracts CR's metabolic benefits. IgG activates macrophages via Ras signaling and consequently induces fibrosis in WAT through the TGF-β/SMAD pathway. Consistently, B cell null mice are protected from aging-associated WAT fibrosis, inflammation, and insulin resistance, unless exposed to IgG. Conditional ablation of the IgG recycling receptor, neonatal Fc receptor (FcRn), in macrophages prevents IgG accumulation in aging, resulting in prolonged healthspan and lifespan. Further, targeting FcRn by antisense oligonucleotide restores WAT integrity and metabolic health in aged mice. These findings pinpoint IgG as a hidden culprit in aging and enlighten a novel strategy to rejuvenate metabolic health.

Human Tumor-Associated Macrophages and Neutrophils Regulate Antitumor Antibody Efficacy through Lethal and Sublethal Trogocytosis

The clinical benefits of tumor-targeting antibodies (tAb) are modest in solid human tumors. The efficacy of many tAbs is dependent on Fc receptor (FcR)-expressing leukocytes that bind Fc fragments of tAb. Tumor-associated macrophages (TAM) and neutrophils (TAN) represent the majority of FcR+ effectors in solid tumors. A better understanding of the mechanisms by which TAMs and TANs regulate tAb response could help improve the efficacy of cancer treatments. Here, we found that myeloid effectors interacting with tAb-opsonized lung cancer cells used antibody-dependent trogocytosis (ADT) but not antibody-dependent phagocytosis. During this process, myeloid cells "nibbled off" tumor cell fragments containing tAb/targeted antigen (tAg) complexes. ADT was only tumoricidal when the tumor cells expressed high levels of tAg and the effectors were present at high effector-to-tumor ratios. If either of these conditions were not met, which is typical for solid tumors, ADT was sublethal. Sublethal ADT, mainly mediated by CD32hiCD64hi TAM, led to two outcomes: (i) removal of surface tAg/tAb complexes from the tumor that facilitated tumor cell escape from the tumoricidal effects of tAb; and (ii) acquisition of bystander tAgs by TAM with subsequent cross-presentation and stimulation of tumor-specific T-cell responses. CD89hiCD32loCD64lo peripheral blood neutrophils (PBN) and TAN stimulated tumor cell growth in the presence of the IgG1 anti-EGFR Ab cetuximab; however, IgA anti-EGFR Abs triggered the tumoricidal activity of PBN and negated the stimulatory effect of TAN. Overall, this study provides insights into the mechanisms by which myeloid effectors mediate tumor cell killing or resistance during tAb therapy.

SIGNIFICANCE

The elucidation of the conditions and mechanisms by which human FcR+ myeloid effectors mediate cancer cell resistance and killing during antibody treatment could help develop improved strategies for treating solid tumors.

Phenotyping of Macrophages in Human Immune System Mice

Human immune system mice, also referred to as humanized mice, are a major research tool for the in vivo study of human immune system function. Upon reconstitution with human hematopoietic stem cells, all major human leukocyte populations develop in immunodeficient mice and can be detected in peripheral blood as well as in lymphatic and nonlymphatic tissue. This includes human macrophages that are intrinsically difficult to study from humans due to their organ-resident nature. In the following chapter, we provide a detailed protocol for generation of human immune system mice. We suggest that these mice are a suitable model to study human macrophage function in vivo.

Analyzing Fcγ-Receptor Interactions on Monocytes with the Proximity Ligation Assay (PLA)

Proximity ligation assays (PLA) enable the detection and characterization of protein interactions independent of protein abundance or genetic modifications. This technique exploits both antibody and DNA-binding features, providing high selectivity and sensitivity for protein recognition and visualization of single-protein molecules with high spatial accuracy. Here, we describe the general procedure for a direct PLA on splenic monocytes to analyze FcγRIIb homodimerization. However, this method can be applied to other cells and receptors of interest.

Immunotherapy targeting isoDGR-protein damage extends lifespan in a mouse model of protein deamidation

Aging results from the accumulation of molecular damage that impairs normal biochemical processes. We previously reported that age-linked damage to amino acid sequence NGR (Asn-Gly-Arg) results in "gain-of-function" conformational switching to isoDGR (isoAsp-Gly-Arg). This integrin-binding motif activates leukocytes and promotes chronic inflammation, which are characteristic features of age-linked cardiovascular disorders. We now report that anti-isoDGR immunotherapy mitigates lifespan reduction of Pcmt1-/- mouse. We observed extensive accumulation of isoDGR and inflammatory cytokine expression in multiple tissues from Pcmt1-/- and naturally aged WT animals, which could also be induced via injection of isoDGR-modified plasma proteins or synthetic peptides into young WT animals. However, weekly injection of anti-isoDGR mAb (1 mg/kg) was sufficient to significantly reduce isoDGR-protein levels in body tissues, decreased pro-inflammatory cytokine concentrations in blood plasma, improved cognition/coordination metrics, and extended the average lifespan of Pcmt1-/- mice. Mechanistically, isoDGR-mAb mediated immune clearance of damaged isoDGR-proteins via antibody-dependent cellular phagocytosis (ADCP). These results indicate that immunotherapy targeting age-linked protein damage may represent an effective intervention strategy in a range of human degenerative disorders.

Non-neutralizing monoclonal antibody targeting VP2 EF loop of Coxsackievirus A16 can protect mice from lethal attack via Fc-dependent effector mechanism

Coxsackievirus A16 (CA16), a main causative agent of hand, foot, and mouth disease (HFMD), has become a serious public health concern in the Asia-Pacific region. Here, we generated an anti-CA16 monoclonal antibody, DMA2017, derived from an epidemic strain CA16. Surprisingly, although DMA2017 could not neutralize the original and circulating CA16 strains in vitro, the passive transfer of DMA2017 (10 μg/g) could protect suckling mice from a lethal challenge with CA16 in vivo. Then, we confirmed the protective effect of DMA2017 relies on the Fc-dependent effector functions, such as antibody-dependent cellular cytotoxicity (ADCC). The linear epitope of DMA2017 was mapped by phage display technique to a conserved patch spanning residues 143-148 (NSHPPY) of the VP2 EF-loop of CA16. DMA2017 could inhibit the binding of the antibodies present in the sera of naturally infected children to CA16, indicating that the epitope of DMA2017 is immunodominant for CA16. Our results confirm, for the first time, that a potential preventive and therapeutic effect could be mediated by a non-neutralizing antibody elicited against CA16. These findings bring a hitherto understudied protective role of non-neutralizing antibodies during viral infections into the spotlight and provide a new perspective on the design and evaluation of CA16 vaccines.

Detection of Antibody-Dependent Cell-Mediated Cytotoxicity-Supporting Antibodies by NK-92-CD16A Cell Externalization of CD107a: Recognition of Antibody Afucosylation and Assay Optimization

Antibody-dependent cell-mediated cytotoxicity (ADCC) by natural killer (NK) lymphocytes eliminates cells infected with viruses. Anti-viral ADCC requires three components: (1) antibody; (2) effector lymphocytes with the Fc-IgG receptor CD16A; and (3) viral proteins in infected cell membranes. Fc-afucosylated antibodies bind with greater affinity to CD16A than fucosylated antibodies; individuals' variation in afucosylation contributes to differences in ADCC. Current assays for afucosylated antibodies involve expensive methods. We report an improved bioassay for antibodies that supports ADCC, which encompasses afucosylation. This assay utilizes the externalization of CD107a by NK-92-CD16A cells after antibody recognition. We used anti-CD20 monoclonal antibodies, GA101 WT or glycoengineered (GE), 10% or ~50% afucosylated, and CD20-positive Raji target cells. CD107a increased detection 7-fold compared to flow cytometry to detect Raji-bound antibodies. WT and GE antibody effective concentrations (EC50s) for CD107a externalization differed by 20-fold, with afucosylated GA101-GE more detectable. The EC50s for CD107a externalization vs. 51Cr cell death were similar for NK-92-CD16A and blood NK cells. Notably, the % CD107a-positive cells were negatively correlated with dead Raji cells and were nearly undetectable at high NK:Raji ratios required for cytotoxicity. This bioassay is very sensitive and adaptable to assess anti-viral antibodies but unsuitable as a surrogate assay to monitor cell death after ADCC.

Comparative Analysis of Fcγ and Complement Receptors Presence on Monocytes in Pulmonary Sarcoidosis and Tuberculosis

Sarcoidosis (SA) is a granulomatous disorder, which mostly affects the lungs. Its clinical characteristics resemble tuberculosis (TB), but its treatment is different. The etiology of SA is unknown; however, mycobacterial antigens were proposed as environmental factors in its development. Due to previously revealed immunocomplexemia with mycobacterial antigens in the blood of our SA but not TB patients, and in the search for biomarkers for differential diagnosis of the two disorders, we studied the phagocytic activity of monocytes from both patients' groups with flow cytometry. With the use of this method, we also analyzed the occurrence of receptors for IgG (FcγR) and complement components (CR) at the surface of these monocytes, responsible for phagocytosis of immunocomplexes. We revealed a higher phagocytic activity of monocytes in both disorders, but an increased frequency of monocytes with FcγRIII (CD16) and decreased with CR1 (CD35) receptor in the blood of SA vs. TB patients. With regard to our other genetic study on FcγRIII variants in SA and TB, this may account for the decreased clearance of immunocomplexes and different immune responses in the two diseases. Thus, the presented analysis not only sheds light on the pathomechanisms of SA and TB but may also support their differential diagnosis.

Clinical impact of anti-inflammatory microglia and macrophage phenotypes at glioblastoma margins

Glioblastoma is a devastating brain cancer for which effective treatments are required. Tumour-associated microglia and macrophages promote glioblastoma growth in an immune-suppressed microenvironment. Most recurrences occur at the invasive margin of the surrounding brain, yet the relationships between microglia/macrophage phenotypes, T cells and programmed death-ligand 1 (an immune checkpoint) across human glioblastoma regions are understudied. In this study, we performed a quantitative immunohistochemical analysis of 15 markers of microglia/macrophage phenotypes (including anti-inflammatory markers triggering receptor expressed on myeloid cells 2 and CD163, and the low-affinity-activating receptor CD32a), T cells, natural killer cells and programmed death-ligand 1, in 59 human IDH1-wild-type glioblastoma multi-regional samples (n = 177; 1 sample at tumour core, 2 samples at the margins: the infiltrating zone and leading edge). Assessment was made for the prognostic value of markers; the results were validated in an independent cohort. Microglia/macrophage motility and activation (Iba1, CD68), programmed death-ligand 1 and CD4+ T cells were reduced, and homeostatic microglia (P2RY12) were increased in the invasive margins compared with the tumour core. There were significant positive correlations between microglia/macrophage markers CD68 (phagocytic)/triggering receptor expressed on myeloid cells 2 (anti-inflammatory) and CD8+ T cells in the invasive margins but not in the tumour core (P < 0.01). Programmed death-ligand 1 expression was associated with microglia/macrophage markers (including anti-inflammatory) CD68, CD163, CD32a and triggering receptor expressed on myeloid cells 2, only in the leading edge of glioblastomas (P < 0.01). Similarly, there was a positive correlation between programmed death-ligand 1 expression and CD8+ T-cell infiltration in the leading edge (P < 0.001). There was no relationship between CD64 (a receptor for autoreactive T-cell responses) and CD8+/CD4+ T cells, or between the microglia/macrophage antigen presentation marker HLA-DR and microglial motility (Iba1) in the tumour margins. Natural killer cell infiltration (CD335+) correlated with CD8+ T cells and with CD68/CD163/triggering receptor expressed on myeloid cells 2 anti-inflammatory microglia/macrophages at the leading edge. In an independent large glioblastoma cohort with transcriptomic data, positive correlations between anti-inflammatory microglia/macrophage markers (triggering receptor expressed on myeloid cells 2, CD163 and CD32a) and CD4+/CD8+/programmed death-ligand 1 RNA expression were validated (P < 0.001). Finally, multivariate analysis showed that high triggering receptor expressed on myeloid cells 2, programmed death-ligand 1 and CD32a expression at the leading edge were significantly associated with poorer overall patient survival (hazard ratio = 2.05, 3.42 and 2.11, respectively), independent of clinical variables. In conclusion, anti-inflammatory microglia/macrophages, CD8+ T cells and programmed death-ligand 1 are correlated in the invasive margins of glioblastoma, consistent with immune-suppressive interactions. High triggering receptor expressed on myeloid cells 2, programmed death-ligand 1 and CD32a expression at the human glioblastoma leading edge are predictors of poorer overall survival. Given substantial interest in targeting microglia/macrophages, together with immune checkpoint inhibitors in cancer, these data have major clinical implications.

Comparative Analysis of FCGR Gene Polymorphism in Pulmonary Sarcoidosis and Tuberculosis

The clinical outcome of sarcoidosis (SA) is very similar to tuberculosis (TB); however, they are treated differently and should not be confused. In search for their biomarkers, we have previously revealed changes in the phagocytic activity of monocytes in sarcoidosis and tuberculosis. On these monocytes we found a higher expression of receptors for the Fc fragment of immunoglobulin G (FcγR) in SA and TB patients vs. healthy controls. FcγRs are responsible for the binding of immune complexes (ICs) to initiate an (auto)immune response and for ICs clearance. Surprisingly, our SA patients had a high blood level of ICs, despite the abundant presence of FcγRs. It pointed to FcγR disfunction, presumably caused by the polymorphism of their (FCGR) genes. Therefore, we present here an analysis of the occurrence of FCGR2A, FCGR2B, FCGR2C, FCGR3A and FCGR3B variants in Caucasian SA and TB patients, and healthy individuals with the use of polymerase chain reaction (PCR) and real-time PCR. The presented data point to a possibility of supporting the differential diagnosis of SA and TB by analyzing FCGR2C, FCGR3A and FCGR3B polymorphism, while for severe stages of SA also by studying FCGR2A variants. Additionally, the genotyping of FCGR2A and FCGR3B might serve as a marker of SA progression.

Cancer immunotherapies: A hope for the uncurable?

The use of cancer immunotherapies is not novel but has been used over the decades in the clinic. Only recently have we found the true potential of stimulating an anti-tumor response after the breakthrough of checkpoint inhibitors. Cancer immunotherapies have become the first line treatment for many malignancies at various stages. Nevertheless, the clinical results in terms of overall survival and progression free survival were not as anticipated. Majority of cancer patients do not respond to immunotherapies and the reasons differ. Hence, further improvements for cancer immunotherapies are crucially needed. In the review, we will discuss various forms of cancer immunotherapies that are being tested or already in the clinic. Moreover, we also highlight future directions to improve such therapies.

Advances in antibody-based therapy in oncology

Monoclonal antibodies are a growing class of targeted cancer therapeutics, characterized by exquisite specificity, long serum half-life, high affinity and immune effector functions. In this review, we outline key advances in the field with a particular focus on recent and emerging classes of engineered antibody therapeutic candidates, discuss molecular structure and mechanisms of action and provide updates on clinical development and practice.

A pH-dependent anti-CD47 antibody that selectively targets solid tumors and improves therapeutic efficacy and safety

BACKGROUND

The antiphagocytic molecule CD47 is overexpressed in a wide variety of cancer cells, and antibodies targeting CD47 for cancer therapies are currently under intensive investigation. However, owing to the ubiquitous expression of CD47 on healthy cells, anti-CD47 therapies often achieve only weak therapeutic benefits and can induce severe side effects. Here, we report the generation of a pH-dependent anti-CD47 antibody (BC31M4) which selectively binds to tumors under the acidic solid tumor microenvironment.

METHODS

BC31M4 was generated using antibody phage display and a pH-dependent selection strategy. The pH-dependent binding and blocking activities of BC31M4 were verified using in vitro assays, and the structural basis of the pH-dependent binding property was characterized. BC31M4's antitumor effect was confirmed by both phagocytosis assays and studies in xenograft models. The tumor selectivity, mechanism of action, PK properties, side effects, and therapeutic efficacy were further evaluated in humanized (hCD47 and its receptor hSIRPα) immunocompetent syngeneic mouse models.

RESULTS

The crystal structure reveals that two histidines locate within the CDRs of the light chain directly contribute to the pH-dependent binding of BC31M4. BC31M4 promotes macrophage phagocytosis of tumor cells more potently at acidic-pH than at physiological-pH. Our hCD47/hSIRPα humanized syngeneic mouse model results demonstrated that BC31M4 selectively accumulates in tumors but not in normal tissues. BC31M4 causes minimal side effects and exhibits superior PK properties as compared to the other examined anti-CD47 antibodies. When combined with adoptive T cell transfer, BC31M4 efficiently promotes adaptive immune responses against tumors and also induces immune memory. Moreover, we show that BC31M4's antitumor effects rely on an Fc that mediates strong effector functions.

CONCLUSIONS

Our study illustrates that the development of a tumor-selective, pH-dependent anti-CD47 antibody safely confers strong therapeutic effects against solid tumors, thus providing a promising therapeutic strategy to overcome the challenges of anti-CD47 therapy.

An anti-CD98 antibody displaying pH-dependent Fc-mediated tumour-specific activity against multiple cancers in CD98-humanized mice

The cell-surface glycoprotein CD98-a subunit of the LAT1/CD98 amino acid transporter-is an attractive target for cancer immunotherapies, but its widespread expression has hampered the development of CD98-targeting antibody therapeutics. Here we report that an anti-CD98 antibody, identified via the screening of phage-display libraries of CD98 single-chain variable fragments with mutated complementarity-determining regions, preserves the physiological function of CD98 and elicits broad-spectrum crystallizable-fragment (Fc)-mediated anti-tumour activity (requiring Fcγ receptors for immunoglobulins, macrophages, dendritic cells and CD8⁺ T cells, as well as other components of the innate and adaptive immune systems) in multiple xenograft and syngeneic tumour models established in CD98-humanized mice. We also show that a variant of the anti-CD98 antibody with pH-dependent binding, generated by solving the structure of the antibody-CD98 complex, displayed enhanced tumour-specific activity and pharmacokinetics. pH-dependent antibody variants targeting widely expressed antigens may lead to superior therapeutic outcomes.

FcγRs and Their Relevance for the Activity of Anti-CD40 Antibodies

Inhibitory targeting of the CD40L-CD40 system is a promising therapeutic option in the field of organ transplantation and is also attractive in the treatment of autoimmune diseases. After early complex results with neutralizing CD40L antibodies, it turned out that lack of Fcγ receptor (FcγR)-binding is the crucial factor for the development of safe inhibitory antibodies targeting CD40L or CD40. Indeed, in recent years, blocking CD40 antibodies not interacting with FcγRs, has proven to be well tolerated in clinical studies and has shown initial clinical efficacy. Stimulation of CD40 is also of considerable therapeutic interest, especially in cancer immunotherapy. CD40 can be robustly activated by genetically engineered variants of soluble CD40L but also by anti-CD40 antibodies. However, the development of CD40L-based agonists is biotechnologically and pharmacokinetically challenging, and anti-CD40 antibodies typically display only strong agonism in complex with FcγRs or upon secondary crosslinking. The latter, however, typically results in poorly developable mixtures of molecule species of varying stoichiometry and FcγR-binding by anti-CD40 antibodies can elicit unwanted side effects such as antibody-dependent cellular cytotoxicity (ADCC) or antibody-dependent cellular phagocytosis (ADCP) of CD40 expressing immune cells. Here, we summarize and compare strategies to overcome the unwanted target cell-destroying activity of anti-CD40-FcγR complexes, especially the use of FcγR type-specific mutants and the FcγR-independent cell surface anchoring of bispecific anti-CD40 fusion proteins. Especially, we discuss the therapeutic potential of these strategies in view of the emerging evidence for the dose-limiting activities of systemic CD40 engagement.

Cyclophosphamide depletes tumor infiltrating T regulatory cells and combined with anti-PD-1 therapy improves survival in murine neuroblastoma

The outcome for children with high-risk neuroblastoma is poor despite intensive multi-modal treatment protocols. Toxicity from current treatments is significant, and novel approaches are needed to improve outcome. Cyclophosphamide (CPM) is a key component of current chemotherapy regimens and is known to have immunomodulatory effects. However, this has not been investigated in the context of tumor infiltrating lymphocytes in neuroblastoma. Using murine models of neuroblastoma, the immunomodulatory effects of low-dose CPM were investigated using detailed immunophenotyping. We demonstrated that CPM resulted in a specific depletion of intratumoral T regulatory cells by apoptosis, and when combined with anti-PD-1 antibody therapy, this resulted in improved therapeutic efficacy. CPM combined with anti-PD-1 therapy was demonstrated to be an effective combinational therapy, with metronomic CPM found to be more effective than single dosing in more resistant tumor models. Overall, this pre-clinical data strongly support clinical evaluation of such combination strategies in neuroblastoma.

Role of N-Glycosylation in FcγRIIIa interaction with IgG

Immunoglobulins G (IgG) and their Fc gamma receptors (FcγRs) play important roles in our immune system. The conserved N-glycan in the Fc region of IgG1 impacts interaction of IgG with FcγRs and the resulting effector functions, which has led to the design of antibody therapeutics with greatly improved antibody-dependent cell cytotoxicity (ADCC) activities. Studies have suggested that also N-glycosylation of the FcγRIII affects receptor interactions with IgG, but detailed studies of the interaction of IgG1 and FcγRIIIa with distinct N-glycans have been hindered by the natural heterogeneity in N-glycosylation. In this study, we employed comprehensive genetic engineering of the N-glycosylation capacities in mammalian cell lines to express IgG1 and FcγRIIIa with different N-glycan structures to more generally explore the role of N-glycosylation in IgG1:FcγRIIIa binding interactions. We included FcγRIIIa variants of both the 158F and 158V allotypes and investigated the key N-glycan features that affected binding affinity. Our study confirms that afucosylated IgG1 has the highest binding affinity to oligomannose FcγRIIIa, a glycan structure commonly found on Asn162 on FcγRIIIa expressed by NK cells but not monocytes or recombinantly expressed FcγRIIIa.

Utility of SPR technology in biotherapeutic development: Qualification for intended use

Surface plasmon resonance (SPR) analysis provides important binding characteristic information for an antibody to its binding partner, such as binding specificity and affinity (K_D). In recent years, SPR has been increasingly used in biosimilar development as part of the comparative analytical similarity assessment. Although there is no systematic study describing how to qualify SPR assays, there are various SPR result types (outputs) that have been used for assay qualification in publicly available regulatory documents. The mixed usage of SPR output can cause confusion and can be misleading when comparing binding attributes among antibody molecules. In this report, using a recombinant huIgG1 (mAb 1) antibody as an example, we performed assay qualification strictly based on the nature of the biomolecular interaction. We recommend that K_D should be used as the output of assay qualification when the K_D can be measured accurately by SPR. When K_D cannot be accurately determined in a SPR setting, sensorgram comparison and Parallel Line Analysis (PLA) can be used to qualify the assay. We emphasize the importance of setting up appropriate SPR assay conditions for target and/or Fc receptor interactions to ensure the assay qualification parameters, such as accuracy and repeatability, to meet the criteria acceptable for regulatory filings. With increasing numbers of biotherapeutics being developed, the methods and guidelines provided here can help to align SPR application between the drug development industry and regulatory authorities which will benefit the scientific communities involved in biotherapeutic drug development.

An exploration of how broadly neutralizing antibodies might induce HIV remission: the 'vaccinal' effect

PURPOSE OF REVIEW

Broadly neutralizing antibodies (bNAbs) are a potential new therapeutic strategy to treat HIV infection. This review explores possible mechanisms of action of bNAbs and summarizes the current evidence supporting their immunomodulatory properties, which might lead to sustained virological remission - the 'vaccinal effect'.

RECENT FINDINGS

Antiretroviral therapy (ART) is required to confer lasting HIV suppression; stopping ART almost invariably leads to HIV recrudescence from a persistent pool of virally infected cells - the HIV reservoir. HIV-specific broadly neutralizing antibodies (bNAbs) may confer viral control after ART cessation predominantly through blockade of viral entry into uninfected target cells. In some human and animal studies, HIV bNAbs also conferred lasting viral suppression after therapeutic bNAb plasma levels had declined. Immune-modulatory mechanisms have been postulated to underlie this observation - the 'vaccinal effect'. Hypothesized mechanisms include the formation of immune complexes between bNAbs and HIV envelope protein, thereby enhancing antigen presentation and uptake by immune cells, with boosted adaptive immune responses subsequently controlling the HIV reservoir.

SUMMARY

There is emerging evidence for potent antiviral efficacy of bNAb therapy. Whether bNAbs can induce sustained viral suppression after dropping below therapeutic levels remains controversial. Mechanistic data from on-going and future clinical trials will help answer these questions.

Antigen improves binding of IgGs to FcγRs in SPR analysis

FcγR binding characterization is one of the critical attributes during the development of therapeutic antibodies. Here, we report a novel assay format to characterize IgG-FcγR interaction in the presence of antigen using Surface plasmon resonance (SPR). The new assay format was developed by creating stable antigen/antibody immunocomplexes on a sensor chip surface before injection of FcγRs. In this assay format, binding activity of both huIgG1 (including IgG1 Fc fusion Protein) and huIgG2 increased significantly to most activating human FcγRs, especially to FcγRI, FcγRIIa-131H and FcγRIIIa-158F. To our knowledge, this study provides the first set of evidence using a biophysical method to demonstrate antigen binding facilitating IgG-FcγR interaction, especially for huIgG2 where previous studies did not indicate its binding to human FcγRI or FcγRIIIa-158F. Although further studies are needed to investigate the correlation of the binding data with effector function data in vivo, our results suggest that it may be useful to evaluate the IgG-FcγR interaction in the presence of antigen to help design safer and more effective biotherapeutics.

Antibody bivalency improves antiviral efficacy by inhibiting virion release independently of Fc gamma receptors

Across the animal kingdom, multivalency discriminates antibodies from all other immunoglobulin superfamily members. The evolutionary forces conserving multivalency above other structural hallmarks of antibodies remain, however, incompletely defined. Here, we engineer monovalent either Fc-competent or -deficient antibody formats to investigate mechanisms of protection of neutralizing antibodies (nAbs) and non-neutralizing antibodies (nnAbs) in virus-infected mice. Antibody bivalency enables the tethering of virions to the infected cell surface, inhibits the release of virions in cell culture, and suppresses viral loads in vivo independently of Fc gamma receptor (FcγR) interactions. In return, monovalent antibody formats either do not inhibit virion release and fail to protect in vivo or their protective efficacy is largely FcγR dependent. Protection in mice correlates with virus-release-inhibiting activity of nAb and nnAb rather than with their neutralizing capacity. These observations provide mechanistic insights into the evolutionary conservation of antibody bivalency and help refining correlates of nnAb protection for vaccine development.

Epidermal Growth Factor Receptor as Target for Perioperative Elimination of Circulating Colorectal Cancer Cells

Surgical resection of the tumor is the primary treatment of colorectal cancer patients. However, we previously demonstrated that abdominal surgery promotes the adherence of circulating tumor cells (CTC) in the liver and subsequent liver metastasis development. Importantly, preoperative treatment with specific tumor-targeting monoclonal antibodies (mAb) prevented surgery-induced liver metastasis development in rats. This study investigated whether the epidermal growth factor receptor (EGFR) represents a suitable target for preoperative antibody treatment of colorectal cancer patients undergoing surgery. The majority of patients with resectable colorectal liver metastases were shown to have EGFR + CTCs. Three different anti-EGFR mAbs (cetuximab, zalutumumab, and panitumumab) were equally efficient in the opsonization of tumor cell lines. Additionally, all three mAbs induced antibody-dependent cellular phagocytosis (ADCP) of tumor cells by macrophages at low antibody concentrations in vitro, independent of mutations in EGFR signaling pathways. The plasma of cetuximab-treated patients efficiently opsonized tumor cells ex vivo and induced phagocytosis. Furthermore, neither proliferation nor migration of epithelial cells was affected in vitro, supporting that wound healing will not be hampered by treatment with low anti-EGFR mAb concentrations. These data support the use of a low dose of anti-EGFR mAbs prior to resection of the tumor to eliminate CTCs without interfering with the healing of the anastomosis. Ultimately, this may reduce the risk of metastasis development, consequently improving long-term patient outcome significantly.

Non-targeted characterization of attributes affecting antibody-FcγRIIIa V158 (CD16a) binding via online affinity chromatography-mass spectrometry

Antibodies facilitate targeted cell killing by engaging with immune cells such as natural killer cells through weak binding interactions with Fcγ receptors on the cell surface. Here, we evaluate the binding affinity of the receptor FcγRIIIa V158 (CD16a) for several therapeutic antibody classes, isoforms, and Fc-fusion proteins using an immobilized receptor affinity liquid chromatography (LC) approach coupled with online mass spectrometry (MS) detection. Aglycosylated FcγRIIIa was used in the affinity chromatography and compared with published affinities using glycosylated receptors. Affinity LC-MS differentiated the IgG1 antibodies primarily according to their Fc glycosylation patterns, with highly galactosylated species having greater affinity for the immobilized receptors and thus eluting later from the column (M5< G0F < G0 afucosylated ≅ G1F < G2F). Sialylated species bound weaker to their asialylated counterparts as reported previously. High mannose glycoforms bound weaker than G0F, contrary to previously published studies using glycosylated receptors. Also, increased receptor binding affinity associated with afucosylated antibodies was not observed with the aglycosylated FcγRIIIa. This apparent difference from previous findings highlighted the importance of the glycans on the receptors for mediating stronger binding interactions. Characterization of temperature-stressed samples by LC-MS peptide mapping revealed over 200 chemical and post-translational modifications, but only the Fc glycans, deamidation of EU N325, and an unknown modification to either proline or cysteine residues of the hinge region were found to have a statistically significant impact on binding.

Abbreviations: Antibody-dependent cell-mediated cytotoxicity (ADCC), chimeric antigen receptor (CAR), Chinese hamster ovary (CHO), dithiothreitol (DTT), electrospray ionization (ESI), hydrogen-deuterium exchange (HDX), filter aided-sample preparation (FASP), Fcγ receptor (FcγR), fragment crystallizable (Fc), high-pressure liquid chromatography (HPLC), immunoglobulin G (IgG), liquid chromatography (LC), monoclonal antibody (mAb), mass spectrometry (MS), natural killer (NK), N-glycolylneuraminic acid (NGNA), N-acetylneuraminic acid (NANA), principal component analysis (PCA), surface plasmon resonance (SPR), trifluoroacetic acid (TFA), and extracted mass chromatogram (XMC).

Anti-SARS-CoV-2 antibodies elicited by COVID-19 mRNA vaccine exhibit a unique glycosylation pattern

Messenger RNA-based vaccines against COVID-19 induce a robust anti-SARS-CoV-2 antibody response with potent viral neutralization activity. Antibody effector functions are determined by their constant region subclasses and by their glycosylation patterns, but their role in vaccine efficacy is unclear. Moreover, whether vaccination induces antibodies similar to those in patients with COVID-19 remains unknown. We analyze BNT162b2 vaccine-induced IgG subclass distribution and Fc glycosylation patterns and their potential to drive effector function via Fcγ receptors and complement pathways. We identify unique and dynamic pro-inflammatory Fc compositions that are distinct from those in patients with COVID-19 and convalescents. Vaccine-induced anti-Spike IgG is characterized by distinct Fab- and Fc-mediated functions between different age groups and in comparison to antibodies generated during natural viral infection. These data highlight the heterogeneity of Fc responses to SARS-CoV-2 infection and vaccination and suggest that they support long-lasting protection differently.

circRNAs: Insight Into Their Role in Tumor-Associated Macrophages

Currently, it is well known that the tumor microenvironment not only provides energy support for tumor growth but also regulates tumor signaling pathways and promotes the proliferation, invasion, metastasis, and drug resistance of tumor cells. The tumor microenvironment, especially the function and mechanism of tumor-associated macrophages (TAMs), has attracted great attention. TAMs are the most common immune cells in the tumor microenvironment and play a vital role in the occurrence and development of tumors. circular RNA (circRNA) is a unique, widespread, and stable form of non-coding RNA (ncRNA), but little is known about the role of circRNAs in TAMs or how TAMs affect circRNAs. In this review, we summarize the specific manifestations of circRNAs that affect the tumor-associated macrophages and play a significant role in tumor progression. This review helps improve our understanding of the association between circRNAs and TAMs, thereby promoting the development and progress of potential clinical targeted therapies.

Investigation of the causal relationships between human IgG N-glycosylation and twelve common diseases associated with changes in the IgG N-glycome

Changes in the N-glycosylation of immunoglobulin G (IgG) are often observed in pathological states, such as autoimmune, inflammatory, neurodegenerative, cardiovascular diseases and some types of cancer. However, in most cases it is not clear if the disease onset causes these changes, or if the changes in IgG N-glycosylation are among the risk factors for the diseases. The aim of this study was to investigate the casual relationships between IgG N-glycosylation traits and 12 diseases, in which the alterations of IgG N-glycome were previously reported, using Two Sample Mendelian Randomization (MR) approach. We have performed Two Sample MR using publicly available summary statistics of genome-wide association studies of IgG N-glycosylation and disease risks. Our results indicate positive causal effect of systemic lupus erythematosus (SLE) on the abundance of N-glycans with bisecting N-acetylglucosamine in the total IgG N-glycome. Therefore, we suggest regarding this IgG glycosylation trait as a biomarker of SLE. We also emphasize the need for more powerful GWAS studies of IgG N-glycosylation to further elucidate the causal effect of IgG N-glycome on the diseases.

Fc Binding by FcγRIIa Is Essential for Cellular Activation by the Anti-FcγRIIa mAbs 8.26 and 8.2

FcγR activity underpins the role of antibodies in both protective immunity and auto-immunity and importantly, the therapeutic activity of many monoclonal antibody therapies. Some monoclonal anti-FcγR antibodies activate their receptors, but the properties required for cell activation are not well defined. Here we examined activation of the most widely expressed human FcγR; FcγRIIa, by two non-blocking, mAbs, 8.26 and 8.2. Crosslinking of FcγRIIa by the mAb F(ab’)₂ regions alone was insufficient for activation, indicating activation also required receptor engagement by the Fc region. Similarly, when mutant receptors were inactivated in the Fc binding site, so that intact mAb was only able to engage receptors via its two Fab regions, again activation did not occur. Mutation of FcγRIIa in the epitope recognized by the agonist mAbs, completely abrogated the activity of mAb 8.26, but mAb 8.2 activity was only partially inhibited indicating differences in receptor recognition by these mAbs. FcγRIIa inactivated in the Fc binding site was next co-expressed with the FcγRIIa mutated in the epitope recognized by the Fab so that each mAb 8.26 molecule can contribute only three interactions, each with separate receptors, one via the Fc and two via the Fab regions. When the Fab and Fc binding were thus segregated onto different receptor molecules receptor activation by intact mAb did not occur. Thus, receptor activation requires mAb 8.26 Fab and Fc interaction simultaneously with the same receptor molecules. Establishing the molecular nature of FcγR engagement required for cell activation may inform the optimal design of therapeutic mAbs.

There Is Strength in Numbers: Quantitation of Fc Gamma Receptors on Murine Tissue-Resident Macrophages

Many of the effector functions of antibodies rely on the binding of antibodies/immune complexes to cellular Fcγ receptors (FcγRs). Since the majority of innate immune effector cells express both activating and inhibitory Fc receptors, the outcome of the binding of immune complexes to cells of a given population is influenced by the relative affinities of the respective IgG subclasses to these receptors, as well as by the numbers of activating and inhibitory FcγRs on the cell surface. A group of immune cells that has come into focus more recently is the various subsets of tissue-resident macrophages. The central functions of FcγRs on tissue macrophages include the clearance of opsonized pathogens, the removal of small immune complexes from the circulation and the depletion of antibody-opsonized cells in the therapy of autoimmunity and cancer. Despite these essential functions of FcγRs on tissue-resident macrophages, an in-depth quantification of FcγRs is lacking. Thus, the aim of our current study was to quantify the various Fcγ receptors on macrophages in murine liver, lung, kidney, brain, skin and spleen. Our study identified a pronounced heterogeneity between FcγR expression patterns of the different tissue macrophages, which may reflect their specialized functions within their unique niches in different organ environments.

Immune environment of the brain in schizophrenia and during the psychotic episode: A human post-mortem study

A causal relationship between immune dysregulation and schizophrenia has been supported by genome-wide association studies and epidemiological evidence. It remains unclear to what extent the brain immune environment is implicated in this hypothesis. We investigated the immunophenotype of microglia and the presence of perivascular macrophages and T lymphocytes in post-mortem brain tissue. Dorsal prefrontal cortex of 40 controls (22F:18M) and 37 (10F:27M) schizophrenia cases, of whom 16 had active psychotic symptoms at the time of death, was immunostained for seven markers of microglia (CD16, CD32a, CD64, CD68, HLA-DR, Iba1 and P2RY12), two markers for perivascular macrophages (CD163 and CD206) and T-lymphocytes (CD3). Automated quantification was blinded to the case designation and performed separately on the grey and white matter. 3D reconstruction of Iba1-positive microglia was performed in selected cases. An increased cortical expression of microglial Fcγ receptors (CD64 F = 7.92, p = 0.007; CD64/HLA-DR ratio F = 5.02, p = 0.029) highlights the importance of communication between the central and peripheral immune systems in schizophrenia. Patients in whom psychotic symptoms were present at death demonstrated an age-dependent increase of Iba1 and increased CD64/HLA-DR ratios relative to patients without psychotic symptoms. Microglia in schizophrenia demonstrated a primed/reactive morphology. A potential role for T-lymphocytes was observed, but we did not confirm the presence of recruited macrophages in the brains of schizophrenia patients. Taking in account the limitations of a post-mortem study, our findings support the hypothesis of an alteration of the brain immune environment in schizophrenia, with symptomatic state- and age-dependent effects.

Contribution to HIV Prevention and Treatment by Antibody-Mediated Effector Function and Advances in Broadly Neutralizing Antibody Delivery by Vectored Immunoprophylaxis

HIV-1 broadly neutralizing antibodies (bNAbs) targeting the viral envelope have shown significant promise in both HIV prevention and viral clearance, including pivotal results against sensitive strains in the recent Antibody Mediated Prevention (AMP) trial. Studies of bNAb passive transfer in infected patients have demonstrated transient reduction of viral load at high concentrations that rebounds as bNAb is cleared from circulation. While neutralization is a crucial component of therapeutic efficacy, numerous studies have demonstrated that bNAbs can also mediate effector functions, such as antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and antibody-dependent complement deposition (ADCD). These functions have been shown to contribute towards protection in several models of HIV acquisition and in viral clearance during chronic infection, however the role of target epitope in facilitating these functions, as well as the contribution of individual innate functions in protection and viral clearance remain areas of active investigation. Despite their potential, the transient nature of antibody passive transfer limits the widespread use of bNAbs. To overcome this, we and others have demonstrated vectored antibody delivery capable of yielding long-lasting expression of bNAbs in vivo. Two clinical trials have shown that adeno-associated virus (AAV) delivery of bNAbs is safe and capable of sustained bNAb expression for over 18 months following a single intramuscular administration. Here, we review key concepts of effector functions mediated by bNAbs against HIV infection and the potential for vectored immunoprophylaxis as a means of producing bNAbs in patients.

Influenza hemagglutinin-specific IgA Fc-effector functionality is restricted to stalk epitopes

In this study, we utilized a panel of human immunoglobulin (Ig) IgA monoclonal antibodies isolated from the plasmablasts of eight donors after 2014/2015 influenza virus vaccination (Fluarix) to study the binding and functional specificities of this isotype. In this cohort, isolated IgA monoclonal antibodies were primarily elicited against the hemagglutinin protein of the H1N1 component of the vaccine. To compare effector functionalities, an H1-specific subset of antibodies targeting distinct epitopes were expressed as monomeric, dimeric, or secretory IgA, as well as in an IgG1 backbone. When expressed with an IgG Fc domain, all antibodies elicited Fc-effector activity in a primary polymorphonuclear cell-based assay which differs from previous observations that found only stalk-specific antibodies activate the low-affinity FcγRIIIa. However, when expressed with IgA Fc domains, only antibodies targeting the stalk domain showed Fc-effector activity in line with these previous findings. To identify the cause of this discrepancy, we then confirmed that IgG signaling through the high-affinity FcγI receptor was not restricted to stalk epitopes. Since no corresponding high-affinity Fcα receptor exists, the IgA repertoire may therefore be limited to stalk-specific epitopes in the context of Fc receptor signaling.

Role of CGRP pathway polymorphisms in migraine: a systematic review and impact on CGRP mAbs migraine therapy

Background

the interest of clinical reaseach in polymorphisms and epigenetics in migraine has been growing over the years. Due to the new era of preventative migraine treatment opened by monoclonal antibodies (mAbs) targeting the signaling of the calcitonin-gene related peptide (CGRP), the present systematic review aims at identifying genetic variants occurring along the CGRP pathway and at verifying whether these can affect the clinical features and the course of disease and the responsiveness of patients to therapy.

Methods

the literature search has been conducted consulting the most relevant scientific databases, i.e. PubMed/MEDLINE, Scopus, Web of Science, the Human Genome Epidemiology (HuGE) Published Literature database (Public Health Genomics Knowledge Base) and Clinicaltrials.gov from database inception until April 1, 2021. The process of identification and selection of the studies included in the analysis has followed the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) criteria for systematic reviews and meta-analyses and the guidance from the Human Genome Epidemiology Network for reporting gene-disease associations.

Results

the search has retrieved 800 results, among which only 7 studies have met the eligibility criteria for inclusion in the analysis. The latter are case-control studies of genetic association and an exploratory analysis and two polymorphisms have been detected as the most recurring: the rs3781719 (T > C) of the CALC A gene encoding CGRP and the rs7590387 of the gene encoding the receptor activity-modifying protein (RAMP) 1 (C > G). Only one study assessing the methylation pattern with regard to CGRP pathway has been found from the search. No genetic association studies investigating the possible effect of genetic variants affecting CGRP signaling on the responsiveness to the most recent pharmacological approaches, i.e. anti-CGRP(R) mAbs, gepants and ditans, have been published. According to the Human Genome Epidemiology (HuGE) systematic reviews and meta-analyses risk-of-bias score for genetic association studies, the heterogeneity between and across studies and the small sample size do not allow to draw conclusions and prompt future studies.

Conclusions

adequately powered, good quality genetic association studies are needed to understand the impact of genetic variants affecting the pathway of CGRP on migraine susceptibility and clinical manifestation and to predict the response to therapy in terms of efficacy and safety.

Factor VIII-Fc Activates Natural Killer Cells via Fc-Mediated Interactions With CD16

The most challenging complication associated with Factor VIII (FVIII) replacement therapy is the development of neutralizing anti-drug antibodies, or inhibitors, which occur in 23-35% of severe (FVIII level <1%) hemophilia A (HA) patients and are a serious hindrance to effective management of HA. Consequently, strategies that can either prevent anti-FVIII inhibitors from developing or "tolerize" individuals who develop such antibodies represent a clinically important unmet need. One intervention for patients with high-titer inhibitors is immune tolerance induction (ITI) therapy. Although ITI therapy is the only clinically proven strategy to eradicate anti-FVIII inhibitors, mechanisms of inhibitor reduction remain unknown. Factor VIII Fc-fusion (rFVIIIFc) is an enhanced half-life antihemophilic factor used in replacement therapy for HA. Fc-fusion is a successful protein bio-engineering platform technology. In addition to enhancement of plasma half-life via neonatal Fc receptor (FcRn) binding, other Fc-mediated interactions, including engagement with Fc gamma receptors (FcγR), may have immunological consequences. Several case reports and retrospective analyses suggest that rFVIIIFc offers superior outcomes with respect to ITI compared to other FVIII products. Previously we and others demonstrated rFVIIIFc interactions with activating FcγRIIIA/CD16. Here, we investigated if rFVIIIFc activates natural killer (NK) cells via CD16. We demonstrated rFVIIIFc signaling via CD16 independent of Von Willebrand Factor (VWF):FVIII complex formation. We established that rFVIIIFc potently activated NK cells in a CD16-dependent fashion resulting in IFNγ secretion and cytolytic perforin and granzyme B release. We also demonstrated an association between rFVIIIFc-mediated NK cell IFNγ secretion levels and the high-affinity (158V) CD16 genotype. Furthermore, we show that rFVIIIFc-activated CD16⁺ NK cells were able to lyse a B-cell clone (BO2C11) bearing an anti-FVIII B-cell receptor in an antibody-dependent cellular cytotoxicity (ADCC) assay. These in vitro findings provide an underlying molecular mechanism that may help explain clinical case reports and retrospective studies suggesting rFVIIIFc may be more effective in tolerizing HA patients with anti-FVIII inhibitors compared to FVIII not linked to Fc. Our in vitro findings suggest a potential use of Fc-fusion proteins acting via NK cells to target antigen-specific B-cells, in the management of unwanted immune responses directed against immunogenic self-antigens or therapeutic protein products.

Requirement of Fc-Fc Gamma Receptor Interaction for Antibody-Based Protection against Emerging Virus Infections

Identification of therapeutics against emerging and re-emerging viruses remains a continued priority that is only reinforced by the recent SARS-CoV-2 pandemic. Advances in monoclonal antibody (mAb) isolation, characterization, and production make it a viable option for rapid treatment development. While mAbs are traditionally screened and selected based on potency of neutralization in vitro, it is clear that additional factors contribute to the in vivo efficacy of a mAb beyond viral neutralization. These factors include interactions with Fc receptors (FcRs) and complement that can enhance neutralization, clearance of infected cells, opsonization of virions, and modulation of the innate and adaptive immune response. In this review, we discuss recent studies, primarily using mouse models, that identified a role for Fc-FcγR interactions for optimal antibody-based protection against emerging and re-emerging virus infections.

Afucosylated IgG Targets FcγRIV for Enhanced Tumor Therapy in Mice

Simple Summary

Cancer treatments are increasingly based on therapeutic antibodies to clear tumors. While in vivo mouse models are useful to predict effectiveness of human antibodies it is not completely clear how useful these models are to test antibodies engineered with enhanced effector functions designed for humans. One of the changes considered for many new antibody-based drugs is the removal of fucose (resulting in afucosylated IgG) which enhances IgG-Fc receptor (FcγR) mediated effector functions in humans through FcγRIIIa. Here we show that afucosylated human IgG1 also have enhanced effector functions against peritoneal metastasis of melanoma cells in mice through the evolutionary related mouse FcγRIV. This shows that afucosylated human IgG is functionally recognized across species and shows that mouse tumor models can be used to assess the therapeutic potential of afucosylated IgG1.

Abstract

Promising strategies for maximizing IgG effector functions rely on the introduction of natural and non-immunogenic modifications. The Fc domain of IgG antibodies contains an N-linked oligosaccharide at position 297. Human IgG antibodies lacking the core fucose in this glycan have enhanced binding to human (FcγR) IIIa/b, resulting in enhanced antibody dependent cell cytotoxicity and phagocytosis through these receptors. However, it is not yet clear if glycan-enhancing modifications of human IgG translate into more effective treatment in mouse models. We generated humanized hIgG1-TA99 antibodies with and without core-fucose. C57Bl/6 mice that were injected intraperitoneally with B16F10-gp75 mouse melanoma developed significantly less metastasis outgrowth after treatment with afucosylated hIgG1-TA99 compared to mice treated with wildtype hhIgG1-TA99. Afucosylated human IgG1 showed stronger interaction with the murine FcγRIV, the mouse orthologue of human FcγRIIIa, indicating that this glycan change is functionally conserved between the species. In agreement with this, no significant differences were observed in tumor outgrowth in FcγRIV^-/- mice treated with human hIgG1-TA99 with or without the core fucose. These results confirm the potential of using afucosylated therapeutic IgG to increase their efficacy. Moreover, we show that afucosylated human IgG1 antibodies act across species, supporting that mouse models can be suitable to test afucosylated antibodies.

Physiological and Pathological Inflammation Induced by Antibodies and Pentraxins

Macrophages play a key role in induction of inflammatory responses. These inflammatory responses are mostly considered to be instigated by activation of pattern recognition receptors (PRRs) or cytokine receptors. However, recently it has become clear that also antibodies and pentraxins, which can both activate Fc receptors (FcRs), induce very powerful inflammatory responses by macrophages that can even be an order of magnitude greater than PRRs. While the physiological function of this antibody-dependent inflammation (ADI) is to counteract infections, undesired activation or over-activation of this mechanism will lead to pathology, as observed in a variety of disorders, including viral infections such as COVID-19, chronic inflammatory disorders such as Crohn's disease, and autoimmune diseases such as rheumatoid arthritis. In this review we discuss how physiological ADI provides host defense by inducing pathogen-specific immunity, and how erroneous activation of this mechanism leads to pathology. Moreover, we will provide an overview of the currently known signaling and metabolic pathways that underlie ADI, and how these can be targeted to counteract pathological inflammation.

Protective impact of Spirulina platensis against γ-irradiation and thioacetamide-induced nephrotoxicity in rats mediated by regulation of micro-RNA 1 and micro-RNA 146a

Chronic kidney disease develops popular and medical health problems, especially in developing countries. The objective of this study is to investigate the protective mechanism of Spirulina platensis against γ-irradiation (R) and/or thioacetamide (TAA)-induced nephrotoxicity in rats. Rats intoxicated with R or TAA showed alterations in kidney function markers (urea, creatinine, albumin, and total protein contents), oxidative stress markers (malondialdehyde, reduced glutathione), antioxidant enzymes (superoxide dismutase, catalase), and several inflammatory markers (including, the high-sensitivity C-reactive protein, hypoxia-inducible factor-1 alpha, tumor necrosis factor-alpha, interferon-gamma, some interleukins, and nuclear factor-kappa B). Rats also acquired apoptosis, evinced by high caspase-3 efficacy. This nephrotoxicity mediated by upregulation of the messenger RNA (mRNA) gene expression of the autophagy markers: Beclin-1, microtubule-associated protein LC3, p62 binding protein, immunoglobulin G receptor Fcγ receptor (FcγR), micro-RNA-1 (miR-1), protein expression of phospho-adenosine monophosphate-activated protein kinase, and phospho-mammalian target of rapamycin, along with downregulation of miR-146a mRNA gene expression and alteration of calcium and iron levels. The combined treatment R/TAA enhanced the observed oxidative stress, inflammation, apoptosis, and autophagy that mediated by higher upregulation of miR-1 and downregulation of miR-146a mRNA gene expression. Spirulina platensis administration exhibited a nephroprotective impact on R, TAA, and R/TAA toxicities via regulating miR-1 and miR-146a mRNA gene expression that monitored adenosine monophosphate-activated protein kinase/mammalian target of rapamycin signaling.

Improved HIV-positive infant survival is correlated with high levels of HIV-specific ADCC activity in multiple cohorts

Defining immune responses that protect humans against diverse HIV strains has been elusive. Studying correlates of protection from mother-to-child transmission provides a benchmark for HIV vaccine protection because passively transferred HIV antibodies are present during infant exposure to HIV through breast milk. A previous study by our group illustrated that passively acquired antibody-dependent cellular cytotoxicity (ADCC) activity is associated with improved infant survival whereas neutralization is not. Here, we show, in another cohort and with two effector measures, that passively acquired ADCC antibodies correlate with infant survival. In combined analyses of data from both cohorts, there are highly statistically significant associations between higher infant survival and passively acquired ADCC levels (p = 0.029) as well as dimeric FcγRIIa (p = 0.002) or dimeric FcγRIIIa binding (p < 0.001). These results suggest that natural killer (NK) cell- and monocyte antibody-mediated effector functions may contribute to the observed survival benefit and support a role of pre-existing ADCC-mediating antibodies in clinical outcome.

Matrix Protein 2 Extracellular Domain-Specific Monoclonal Antibodies Are an Effective and Potentially Universal Treatment for Influenza A

Influenza virus infection causes significant morbidity and mortality worldwide. Humans fail to make a universally protective memory immune response to influenza A. Hemagglutinin and Neuraminidase undergo antigenic drift and shift, resulting in new influenza A strains to which humans are naive. Seasonal vaccines are often ineffective and escape mutants have been reported to all treatments for influenza A. In the absence of a universal influenza A vaccine or treatment, influenza A will remain a significant threat to human health. The extracellular domain of the M2-ion channel (M2e) is an ideal antigenic target for a universal therapeutic agent, as it is highly conserved across influenza A serotypes, has a low mutation rate, and is essential for viral entry and replication. Previous M2e-specific monoclonal antibodies (M2e-MAbs) show protective potential against influenza A, however, they are either strain specific or have limited efficacy. We generated seven murine M2e-MAbs and utilized in vitro and in vivo assays to validate the specificity of our novel M2e-MAbs and to explore the universality of their protective potential. Our data shows our M2e-MAbs bind to M2e peptide, HEK cells expressing the M2 channel, as well as, influenza virions and MDCK-ATL cells infected with influenza viruses of multiple serotypes. Our antibodies significantly protect highly influenza A virus susceptible BALB/c mice from lethal challenge with H1N1 A/PR/8/34, pH1N1 A/CA/07/2009, H5N1 A/Vietnam/1203/2004, and H7N9 A/Anhui/1/2013 by improving survival rates and weight loss. Based on these results, at least four of our seven M2e-MAbs show strong potential as universal influenza A treatments.IMPORTANCE Despite a seasonal vaccine and multiple therapeutic treatments, Influenza A remains a significant threat to human health. The biggest obstacle is producing a vaccine or treatment for influenza A is their universality or efficacy against not only seasonal variances in the influenza virus, but also against all human, avian, and swine serotypes and, therefore, potential pandemic strains. M2e has huge potential as a target for a vaccine or treatment against influenza A. It is the most conserved external protein on the virus. Antibodies against M2e have made it to clinical trials, but not succeeded. Here, we describe novel M2e antibodies produced in mice that are not only protective at low doses, but that we extensively test to determine their universality and found to be cross protective against all strains tested. Additionally, our work begins to elucidate the critical role of isotype for an influenza A monoclonal antibody therapeutic.

Imaging the mechanisms of anti-CD20 therapy in vivo uncovers spatiotemporal bottlenecks in antibody-dependent phagocytosis

Anti-CD20 antibody (mAb) represents an effective strategy for the treatment of B cell malignancies, possibly involving complement activity, antibody-dependent cellular cytotoxicity and phagocytosis (ADP). While ADP by Kupffer cells deplete circulating tumors, mechanisms targeting non-circulating tumors remain unclear. Using intravital imaging in a model of B cell lymphoma, we establish here the dominance and limitations of ADP in the bone marrow (BM). We found that tumor cells were stably residing in the BM with little evidence for recirculation. To elucidate the mechanism of depletion, we designed a dual fluorescent reporter to visualize phagocytosis and apoptosis. ADP by BM-associated macrophages was the primary mode of tumor elimination but was no longer active after one hour, resulting in partial depletion. Moreover, macrophages were present at low density in tumor-rich regions, targeting only neighboring tumors. Overcoming spatiotemporal bottlenecks in tumor-targeting Ab therapy thus represents a critical path towards the design of optimized therapies.