Cross-reactivity of mouse IgG subclasses to human Fc gamma receptors: Antibody deglycosylation only eliminates IgG2b binding

Identification of isoaspartate-modified transthyretin as potential target for selective immunotherapy of transthyretin amyloidosis

BACKGROUND

Numerous studies suggest a progressive accumulation of post-translationally modified peptides within amyloid fibrils, including isoaspartate (isoD) modifications. Here, we generated and characterised novel monoclonal antibodies targeting isoD-modified transthyretin (TTR). The antibodies were used to investigate the presence of isoD-modified TTR in deposits from transthyretin amyloidosis patients and to mediate antibody-dependent phagocytosis of TTR fibrils.

METHODS

Monoclonal antibodies were generated by immunisation of mice using an isoD-modified peptide and subsequent hybridoma generation. The antibodies were characterised in terms of affinity and specificity to isoD-modified TTR using surface plasmon resonance, transmission electron microscopy and immunohistochemical staining of human cardiac tissue. The potential to elicit antibody-dependent phagocytosis of TTR fibrils was assessed using THP-1 cells.

RESULTS

We developed two mouse monoclonal antibodies, 2F2 and 4D4, with high nanomolar affinity for isoD-modified TTR and strong selectivity over the unmodified epitope. Both antibodies show presence of isoD-modified TTR in human cardiac tissue, but not in freshly purified recombinant TTR, suggesting isoD modification only present in aged fibrillar deposits. Likewise, the antibodies only facilitated phagocytosis of TTR fibrils and not TTR monomers by THP-1 cells.

CONCLUSIONS

These antibodies label aged, non-native TTR deposits, leaving native TTR unattended and thereby potentially enabling new therapeutic approaches.

Combining Cellular Immunization and Phage Display Screening Results in Novel, FcγRI-Specific Antibodies

Antibodies that specifically bind to individual human fragment crystallizable γ receptors (FcγRs) are of interest as research tools in studying immune cell functions, as well as components in bispecific antibodies for immune cell engagement in cancer therapy. Monoclonal antibodies for human low-affinity FcγRs have been successfully generated by hybridoma technology and are widely used in pre-clinical research. However, the generation of monoclonal antibodies by hybridoma technology that specifically bind to the high-affinity receptor FcγRI is challenging. Monomeric mouse IgG2a, IgG2b, and IgG3 bind human FcγRI with high affinity via the Fc part, leading to an Fc-mediated rather than a fragment for antigen binding (Fab)-mediated selection of monoclonal antibodies. Blocking the Fc-binding site of FcγRI with an excess of human IgG or Fc during screening decreases the risk of Fc-mediated interactions but can also block the potential epitopes of new antibody candidates. Therefore, we replaced hybridoma technology with phage display of a single-chain fragment variable (scFv) antibody library that was generated from mice immunized with FcγRI-positive cells and screened it with a cellular panning approach assisted by next-generation sequencing (NGS). Seven new FcγRI-specific antibody sequences were selected with this methodology, which were produced as Fc-silent antibodies showing FcγRI-restricted specificity.

Development and Validation of a Cell-Based Binding Neutralizing Antibody Assay for an Antibody-Drug Conjugate

The utilization of antibody-drug conjugates (ADCs) has gained considerable attention in the field of targeted cancer therapy due to their ability to synergistically combine the specificity of monoclonal antibodies (mAbs) and the potency of small molecular drugs. However, the immunogenic nature of the antibody component within ADCs warrants the need for robust immunogenicity testing, including a neutralizing antibody (NAb) assay. Since the mechanism of action (MOA) of the ADC is to first bind to the target cells and then release the payload intracellularly to kill the cells, the most relevant NAb assay format would be a cell-based killing assay. However, in this paper, we present a case where a cell-based killing assay could not be developed after multiple cell lines and NAb-positive controls (PC) had been tested. Surprisingly, contrary to our expectations, all NAb PCs tested exhibited an increased killing effect on the target cells, instead of the expected protective response. This unexpected phenomenon most likely is due to the non-specific internalization of drug/NAb complexes via FcγRs, as an excessive amount of human IgG1 and mouse IgG2a, but not mouse IgG1, greatly inhibited drug or drug/NAb complexes induced cell death. To overcome this obstacle, we implemented a novel cell-based binding assay utilizing the Meso Scale Discovery (MSD) platform. We also propose that an in vitro cell killing NAb assay is limited to at best monitoring the target binding and internalization induced cell death, but not by-stander killing induced by prematurely released or dead-cell released payload, hence cannot really mimic the in vivo MOA of ADC.

Dissecting the Ability of Siglecs To Antagonize Fcγ Receptors

Fcγ receptors (FcγRs) play key roles in the effector function of IgG, but their inappropriate activation plays a role in several disease etiologies. Therefore, it is critical to better understand how FcγRs are regulated. Numerous studies suggest that sialic acid-binding immunoglobulin-type lectins (Siglecs), a family of immunomodulatory receptors, modulate FcγR activity; however, it is unclear of the circumstances in which Siglecs can antagonize FcγRs and which Siglecs have this ability. Using liposomes displaying selective ligands to coengage FcγRs with a specific Siglec, we explore the ability of Siglec-3, Siglec-5, Siglec-7, and Siglec-9 to antagonize signaling downstream of FcγRs. We demonstrate that Siglec-3 and Siglec-9 can fully inhibit FcγR activation in U937 cells when coengaged with FcγRs. Cells expressing Siglec mutants reveal differential roles for the immunomodulatory tyrosine-based inhibitory motif (ITIM) and immunomodulatory tyrosine-based switch motif (ITSM) in this inhibition. Imaging flow cytometry enabled visualization of SHP-1 recruitment to Siglec-3 in an ITIM-dependent manner, while SHP-2 recruitment is more ITSM-dependent. Conversely, both cytosolic motifs of Siglec-9 contribute to SHP-1/2 recruitment. Siglec-7 poorly antagonizes FcγR activation for two reasons: masking by cis ligands and differences in its ITIM and ITSM. A chimera of the Siglec-3 extracellular domains and Siglec-5 cytosolic tail strongly inhibits FcγR when coengaged, providing evidence that Siglec-5 is more like Siglec-3 and Siglec-9 in its ability to antagonize FcγRs. Additionally, Siglec-3 and Siglec-9 inhibited FcγRs when coengaged by cells displaying ligands for both the Siglec and FcγRs. These results suggest a role for Siglecs in mediating FcγR inhibition in the context of an immunological synapse, which has important relevance to the effectiveness of immunotherapies.

Streptavidin-drug conjugates streamline optimization of antibody-based conditioning for hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) conditioning using antibody-drug conjugates (ADC) is a promising alternative to conventional chemotherapy- and irradiation-based conditioning regimens. The drug payload bound to an ADC is a key contributor to its efficacy and potential toxicities; however, a comparison of HSCT conditioning ADCs produced with different toxic payloads has not been performed. Indeed, ADC optimization studies in general are hampered by the inability to produce and screen multiple combinations of antibody and drug payload in a rapid, cost-effective manner. Herein, we used Click chemistry to covalently conjugate four different small molecule payloads to streptavidin; these streptavidin-drug conjugates can then be joined to any biotinylated antibody to produce stable, indirectly conjugated ADCs. Evaluating CD45-targeted ADCs produced with this system, we found the pyrrolobenzodiazepine (PBD) dimer SGD-1882 was the most effective payload for targeting mouse and human hematopoietic stem cells (HSCs) and acute myeloid leukemia cells. In murine syngeneic HSCT studies, a single dose of CD45-PBD enabled near-complete conversion to donor hematopoiesis. Finally, human CD45-PBD provided significant antitumor benefit in a patient-derived xenograft model of acute myeloid leukemia. As our streptavidin-drug conjugates were generated in-house with readily accessible equipment, reagents, and routine molecular biology techniques, we anticipate this flexible platform will facilitate the evaluation and optimization of ADCs for myriad targeting applications.

Complement activation drives antibody-mediated transfusion-related acute lung injury via macrophage trafficking and formation of NETs

ABSTRACT

Transfusion-related acute lung injury (TRALI) is one of the leading causes of transfusion-related fatalities and, to date, is without available therapies. Here, we investigated the role of the complement system in TRALI. Murine anti-major histocompatibility complex class I antibodies were used in TRALI mouse models, in combination with analyses of plasma samples from patients with TRALI. We found that in vitro complement activation was related to in vivo antibody-mediated TRALI induction, which was correlated with increased macrophage trafficking from the lungs to the blood in a fragment crystallizable region (Fc)-dependent manner and that this was dependent on C5. Human immunoglobulin G 1 variants of the murine TRALI-inducing antibody 34-1-2S, either unable to activate complement and/or bind to Fcγ receptors (FcγRs), revealed an essential role for the complement system, but not for FcγRs, in the onset of 34-1-2S-mediated TRALI in mice. In addition, we found high levels of complement activation in the plasma of patients with TRALI (n = 53), which correlated with elevated neutrophil extracellular trap (NET) markers. In vitro we found that NETs could be formed in a murine, 2-hit model, mimicking TRALI with lipopolysaccharide and C5a stimulation. Collectively, this reveals a critical role of Fc-mediated complement activation in TRALI, with a direct relation to macrophage trafficking from the lungs to the blood and an association with NET formation, suggesting that targeting the complement system may be an attractive therapeutic approach for combating TRALI.

Trivalent nanobody-based ligands mediate powerful activation of GPVI, CLEC-2, and PEAR1 in human platelets whereas FcγRIIA requires a tetravalent ligand

BACKGROUND

Clustering of the receptors glycoprotein receptor VI (GPVI), C-type lectin-like receptor 2 (CLEC-2), low-affinity immunoglobulin γ Fc region receptor II-a (FcγRIIA), and platelet endothelial aggregation receptor 1 (PEAR1) leads to powerful activation of platelets through phosphorylation of tyrosine in their cytosolic tails and initiation of downstream signaling cascades. GPVI, CLEC-2, and FcγRIIA signal through YxxL motifs that activate Syk. PEAR1 signals through a YxxM motif that activates phosphoinositide 3-kinase. Current ligands for these receptors have an undefined valency and show significant batch variation and, for some, uncertain specificity.

OBJECTIVES

We have raised nanobodies against each of these receptors and multimerized them to identify the minimum number of epitopes to achieve robust activation of human platelets.

METHODS

Divalent and trivalent nanobodies were generated using a flexible glycine-serine linker. Tetravalent nanobodies utilize a mouse Fc domain (IgG2a, which does not bind to FcγRIIA) to dimerize the divalent nanobody. Ligand affinity measurements were determined by surface plasmon resonance. Platelet aggregation, adenosine triphosphate secretion, and protein phosphorylation were analyzed using standardized methods.

RESULTS

Multimerization of the nanobodies led to a stepwise increase in affinity with divalent and higher-order nanobody oligomers having sub-nanomolar affinity. The trivalent nanobodies to GPVI, CLEC-2, and PEAR1 stimulated powerful and robust platelet aggregation, secretion, and protein phosphorylation at low nanomolar concentrations. A tetravalent nanobody was required to activate FcγRIIA with the concentration-response relationship showing a greater variability and reduced sensitivity compared with the other nanobody-based ligands, despite a sub-nanomolar binding affinity.

CONCLUSION

The multivalent nanobodies represent a series of standardized, potent agonists for platelet glycoprotein receptors. They have applications as research tools and in clinical assays.

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.

Site-Specific Antibody Conjugation Using Modified Bisected N-Glycans: Method Development and Potential toward Tunable Effector Function

Antibody-drug conjugates (ADCs) have garnered worldwide attention for disease treatment, as they possess high target specificity, a long half-life, and outstanding potency to kill or modulate the functions of targets. FDA approval of multiple ADCs for cancer therapy has generated a strong desire for novel conjugation strategies with high biocompatibility and controllable bioproperties. Herein, we present a bisecting glycan-bridged conjugation strategy that enables site-specific conjugation without the need for the oligosaccharide synthesis and genetic engineering of antibodies. Application of this method is demonstrated by conjugation of anti-HER2 human and mouse IgGs with a cytotoxic drug, monomethyl auristatin E. The glycan bridge showed outstanding stability, and the resulting ADCs eliminated HER2-expressing cancer cells effectively. Moreover, our strategy preserves the feasibility of glycan structure remodeling to fine-tune the immunogenicity and pharmacokinetic properties of ADCs through glycoengineering.

Oral Immunization with rVSV Bivalent Vaccine Elicits Protective Immune Responses, Including ADCC, against Both SARS-CoV-2 and Influenza A Viruses

COVID-19 and influenza both cause enormous disease burdens, and vaccines are the primary measures for their control. Since these viral diseases are transmitted through the mucosal surface of the respiratory tract, developing an effective and convenient mucosal vaccine should be a high priority. We previously reported a recombinant vesicular stomatitis virus (rVSV)-based bivalent vaccine (v-EM2/SPΔC1Delta) that protects animals from both SARS-CoV-2 and influenza viruses via intramuscular and intranasal immunization. Here, we further investigated the immune response induced by oral immunization with this vaccine and its protective efficacy in mice. The results demonstrated that the oral delivery, like the intranasal route, elicited strong and protective systemic immune responses against SARS-CoV-2 and influenza A virus. This included high levels of neutralizing antibodies (NAbs) against SARS-CoV-2, as well as strong anti-SARS-CoV-2 spike protein (SP) antibody-dependent cellular cytotoxicity (ADCC) and anti-influenza M2 ADCC responses in mice sera. Furthermore, it provided efficient protection against challenge with influenza H1N1 virus in a mouse model, with a 100% survival rate and a significantly low lung viral load of influenza virus. All these findings provide substantial evidence for the effectiveness of oral immunization with the rVSV bivalent vaccine.

FcγRIIA-specific DARPins as novel tools in blood cell analysis and platelet aggregation

Fc receptors are involved in a variety of physiologically and disease-relevant responses. Among them, FcγRIIA (CD32a) is known for its activating functions in pathogen recognition and platelet biology, and, as potential marker of T lymphocytes latently infected with HIV-1. The latter has not been without controversy due to technical challenges complicated by T-B cell conjugates and trogocytosis as well as a lack of antibodies distinguishing between the closely related isoforms of FcγRII. To generate high-affinity binders specific for FcγRIIA, libraries of designed ankyrin repeat proteins (DARPins) were screened for binding to its extracellular domains by ribosomal display. Counterselection against FcγRIIB eliminated binders cross-reacting with both isoforms. The identified DARPins bound FcγRIIA with no detectable binding for FcγRIIB. Their affinities for FcγRIIA were in the low nanomolar range and could be enhanced by cleavage of the His-tag and dimerization. Interestingly, complex formation between DARPin and FcγRIIA followed a two-state reaction model, and discrimination from FcγRIIB was based on a single amino acid residue. In flow cytometry, DARPin F11 detected FcγRIIA+ cells even when they made up less than 1% of the cell population. Image stream analysis of primary human blood cells confirmed that F11 caused dim but reliable cell surface staining of a small subpopulation of T lymphocytes. When incubated with platelets, F11 inhibited their aggregation equally efficient as antibodies unable to discriminate between both FcγRII isoforms. The selected DARPins are unique novel tools for platelet aggregation studies as well as the role of FcγRIIA for the latent HIV-1 reservoir.

THP-1 cells transduced with CD16A utilize Fcγ receptor I and III in the phagocytosis of IgG-sensitized human erythrocytes and platelets

Fc gamma receptors (FcγRs) are critical effector receptors for immunoglobulin G (IgG) antibodies. On macrophages, FcγRs mediate multiple effector functions, including phagocytosis, but the individual contribution of specific FcγRs to phagocytosis has not been fully characterized. Primary human macrophage populations, such as splenic macrophages, can express FcγRI, FcγRIIA, and FcγRIIIA. However, there is currently no widely available monocyte or macrophage cell line expressing all these receptors. Common sources of monocytes for differentiation into macrophages, such as human peripheral blood monocytes and the monocytic leukemia cell line THP-1, generally lack the expression of FcγRIIIA (CD16A). Here, we utilized a lentiviral system to generate THP-1 cells stably expressing human FcγRIIIA (CD16F158). THP-1-CD16A cells treated with phorbol 12-myristate 13-acetate for 24 hours phagocytosed anti-D-opsonized human red blood cells primarily utilizing FcγRI with a lesser but significant contribution of IIIA while phagocytosis of antibody-opsonized human platelets equally utilized FcγRI and Fcγ IIIA. Despite the well-known ability of FcγRIIA to bind IgG in cell free systems, this receptor did not appear to be involved in either RBC or platelet phagocytosis. These transgenic cells may constitute a valuable tool for studying macrophage FcγR utilization and function.

CD16+ fibroblasts foster a trastuzumab-refractory microenvironment that is reversed by VAV2 inhibition

The leukocyte Fcγ receptor (FcγR)-mediated response is important for the efficacy of therapeutic antibodies; however, little is known about the role of FcγRs in other cell types. Here we identify a subset of fibroblasts in human breast cancer that express CD16 (FcγRIII). An abundance of these cells in HER2⁺ breast cancer patients is associated with poor prognosis and response to trastuzumab. Functionally, upon trastuzumab stimulation, CD16⁺ fibroblasts reduce drug delivery by enhancing extracellular matrix stiffness. Interaction between trastuzumab and CD16 activates the intracellular SYK-VAV2-RhoA-ROCK-MLC2-MRTF-A pathway, leading to elevated contractile force and matrix production. Targeting of a Rho family guanine nucleotide exchange factor, VAV2, which is indispensable for the function of CD16 in fibroblasts rather than leukocytes, reverses desmoplasia provoked by CD16⁺ fibroblasts. Collectively, our study reveals a role for the fibroblast FcγR in drug resistance, and suggests that VAV2 is an attractive target to augment the effects of antibody treatments.

Prevention and Therapy of Metastatic HER-2+ Mammary Carcinoma with a Human Candidate HER-2 Virus-like Particle Vaccine

Vaccines are a promising therapeutic alternative to monoclonal antibodies against HER-2+ breast cancer. We present the preclinical activity of an ES2B-C001, a VLP-based vaccine being developed for human breast cancer therapy. FVB mice challenged with HER-2+ mammary carcinoma cells QD developed progressive tumors, whereas all mice vaccinated with ES2B-C001+Montanide ISA 51, and 70% of mice vaccinated without adjuvant, remained tumor-free. ES2B-C001 completely inhibited lung metastases in mice challenged intravenously. HER-2 transgenic Delta16 mice developed mammary carcinomas by 4−8 months of age; two administrations of ES2B-C001+Montanide prevented tumor onset for >1 year. Young Delta16 mice challenged intravenously with QD cells developed a mean of 68 lung nodules in 13 weeks, whereas all mice vaccinated with ES2B-C001+Montanide, and 73% of mice vaccinated without adjuvant, remained metastasis-free. ES2B-C001 in adjuvant elicited strong anti-HER-2 antibody responses comprising all Ig isotypes; titers ranging from 1−10 mg/mL persisted for many months. Antibodies inhibited the 3D growth of human HER-2+ trastuzumab-sensitive and -resistant breast cancer cells. Vaccination did not induce cytokine storms; however, it increased the ELISpot frequency of IFN-γ secreting HER-2-specific splenocytes. ES2B-C001 is a promising candidate vaccine for the therapy of tumors expressing HER-2. Preclinical results warrant further development towards human clinical studies.

Phagocytosis of platelets opsonized with differently glycosylated anti-HLA hIgG1 by monocyte-derived macrophages

Immune-mediated platelet refractoriness (PR) remains a significant problem in the setting of platelet transfusion and is predominantly caused by the presence of alloantibodies directed against class I human leukocyte antigens (HLA). Opsonization of donor platelets with these alloantibodies can result in rapid clearance after transfusion via multiple mechanisms, including antibody dependent cellular phagocytosis (ADCP). Interestingly, not all alloimmunized patients develop PR to unmatched platelet transfusions, suggesting variation in HLA-specific IgG responses between patients. Previously, we observed that the glycosylation profile of anti-HLA antibodies was highly variable between PR patients, especially with respect to Fc galactosylation, sialylation and fucosylation. In the current study, we investigated the effect of different Fc glycosylation patterns, with known effects on complement deposition and FcγR binding, on phagocytosis of opsonized platelets by monocyte-derived human macrophages. We found that the phagocytosis of antibody- and complement-opsonized platelets, by monocyte derived M1 macrophages, was unaffected by these qualitative IgG-glycan differences.

Single domain antibodies targeting pathological tau protein: Influence of four IgG subclasses on efficacy and toxicity

BACKGROUND

Eleven tau immunoglobulin G (IgG) antibodies have entered clinical trials to treat tauopathies, including Alzheimer's disease, but it is unclear which IgG subclass/subtype has the ideal efficacy and safety profile. Only two subtypes, with or without effector function, have been examined in the clinic and not for the same tau antibody. The few preclinical studies on this topic have only compared two subtypes of one antibody each and have yielded conflicting results.

METHODS

We selected two single domain antibodies (sdAbs) derived from a llama immunized with tau proteins and utilized them to generate an array of Fc-(sdAb)2 subclasses containing identical tau binding domains but differing Fc region. Unmodified sdAbs and their IgG subclasses were tested for efficacy in primary cultures and in vivo microdialysis using JNPL3 tauopathy mice.

FINDINGS

Unmodified sdAbs were non-toxic, blocked tau toxicity and promoted tau clearance. However, the efficacy/safety profile of their Fc-(sdAb)2 subclasses varied greatly within and between sdAbs. For one of them, all its subtypes were non-toxic, only those with effector function cleared tau, and were more effective in vivo than unmodified sdAb. For the other sdAb, all its subtypes were toxic in tauopathy cultures but not in wild-type cells, suggesting that bivalent binding of its tau epitope stabilizes a toxic conformation of tau, with major implications for tau pathogenesis. Likewise, its subclasses were less effective than the unmodified sdAb in clearing tau in vivo.

INTERPRETATION

These findings indicate that tau antibodies with effector function are safe and better at clearing pathological tau than effectorless antibodies, Furthermore, tau antibodies can provide a valuable insight into tau pathogenesis, and some may aggravate it.

FUNDING

Funding for these studies was provided by the National Institute of Health (R01 AG032611, R01 NS077239, RF1 NS120488, R21 AG 069475, R21 AG 058282, T32AG052909), and the NYU Alzheimer's Disease Center Pilot Grant Program (via P30 AG008051).

The CD3ζ adaptor structure determines functional differences between human and mouse CD16 Fc receptor signaling

Natural killer (NK) cells can detect antibody-coated cells through recognition by the CD16 Fc receptor. The importance of CD16 in human NK cell biology has long been appreciated, but how CD16 functions in mouse NK cells remains poorly understood. Here, we report drastic differences between human and mouse CD16 functions in NK cells. We demonstrate that one of the adaptor molecules that CD16 associates with and signals through, CD3ζ, plays a critical role in these functional differences. Using a systematic approach, we demonstrate that residues in the transmembrane domain of the mouse CD3ζ molecule prevent efficient complex formation with mouse CD16, thereby dampening receptor function. Mutating these residues in mouse CD3ζ to those encoded by human CD3ζ resulted in rescue of CD16 receptor function. We reveal that the mouse CD3ζ transmembrane domain adopts a tightly packed confirmation, preventing association with CD16, whereas human CD3ζ adopts a versatile configuration that accommodates receptor assembly.

Specificity of mouse and human Fcgamma receptors and their polymorphic variants for IgG subclasses of different species

Immunoglobulin G (IgG) is the predominant antibody class generated during infections and used for the generation of therapeutic antibodies. Antibodies are mainly characterized in or generated from animal models that support particular infections, respond to particular antigens or allow the generation of hybridomas. Due to the availability of numerous transgenic mouse models and the ease of performing bioassays with human blood cells in vitro, most antibodies from species other than mice and humans are tested in vitro using human cells and/or in vivo using mice. In this process, it is expected, but not yet systematically documented, that IgG from these species interact with human or mouse IgG receptors (FcγRs). In this study, we undertook a systematic assessment of binding specificities of IgG from various species to the families of mouse and human FcγRs, including their polymorphic variants. Our results document the specific binding patterns for each of these IgG (sub)classes, reveal possible caveats of antibody-based immunoassays, and will be a useful reference for the transition from one animal model to preclinical mouse models or human cell-based bioassays. This article is protected by copyright. All rights reserved.

Genome-wide CRISPR screens reveal a specific ligand for the glycan-binding immune checkpoint receptor Siglec-7

Glyco-immune checkpoint receptors, molecules that inhibit immune cell activity following binding to glycosylated cell-surface antigens, are emerging as attractive targets for cancer immunotherapy. Defining biologically relevant ligands that bind and activate such receptors, however, has historically been a significant challenge. Here, we present a CRISPRi genomic screening strategy that allowed unbiased identification of the key genes required for cell-surface presentation of glycan ligands on leukemia cells that bind the glyco-immune checkpoint receptors Siglec-7 and Siglec-9. This approach revealed a selective interaction between Siglec-7 and the mucin-type glycoprotein CD43. Further work identified a specific N-terminal glycopeptide region of CD43 containing clusters of disialylated O-glycan tetrasaccharides that form specific Siglec-7 binding motifs. Knockout or blockade of CD43 in leukemia cells relieves Siglec-7-mediated inhibition of immune killing activity. This work identifies a potential target for immune checkpoint blockade therapy and represents a generalizable approach to dissection of glycan-receptor interactions in living cells.

Erroneous expression of NKG2D on granulocytes detected by phycoerythrin-conjugated clone 149810 antibody

BACKGROUND

The activating Natural killer group 2 member D (NKG2D) receptor is typically expressed on NK cells, CD8 T lymphocytes, γδ T cells and small subsets of CD4 T lymphocytes. During the course of an extensive flow cytometry phenotyping of immune cells in the peripheral blood of patients with glioblastoma multiforme (GBM) we noticed an unexpected expression of NKG2D receptor on granulocytes using the phycoerythrin (PE)-conjugated clone 149810 antibody.

METHODS

Peripheral blood samples from 35 patients with GBM and 22 age-matched healthy control (HC) donors were analyzed using flow cytometry, imaging cytometry and real-time quantitative reverse transcription PCR to validate the observed expression of NKG2D receptor on myeloid cells.

RESULTS

Reactivity with PE-149810 was mostly observed on granulocytes from GBM patients on dexamethasone treatment where it correlated with inferior survival rates. Surprisingly, such NKG2D expression on granulocytes was not observed using the allophycocyanin (APC)-conjugate of the same clone 149810 antibody or an indirect staining procedure with unconjugated clone 149810 antibody. Moreover, the PE-conjugate of a different anti-NKG2D clone (1D11) also did not stain granulocytes. Imaging cytometry indicated cell surface and intracellular localization of PE-149810 but not of PE-1D11 in granulocytes.

CONCLUSION

Our results uncover an erroneous and false positive reactivity of PE-labeled (but not of APC-labeled or unconjugated) anti-NKG2D antibody 149810 on granulocytes from dexamethasone-treated GBM patients and raise a note of caution for studies of NKG2D expression on non-lymphoid cells.