Receptor Cross-linking Research Articles

Evaluation of a Novel Detection Method for Allergen-Specific IgE Antibodies with IgE Receptor Crosslinking Using Rat Food Allergy Model.

The specific detection of serum IgE antibodies specific to allergens (sIgE Abs) that can crosslink the plural high-affinity IgE receptor (FcεRIα) molecules on the surface of mast cells or basophils with a multivalent allergen can reduce the false-positive diagnoses observed in chemiluminescent and fluorescence enzyme immunoassays for type-I allergic patients. In this study, we detected sIgE Abs to the egg-allergen ovalbumin (OVA) and the wheat-allergen gluten in the sera of rats sensitized with each allergen using an amplified luminescence proximity homogeneous assay by crosslinking (AlphaCL). OVA and gluten were reacted with each sIgE Ab in the sera. Then, acceptor and donor beads labeled with the human FcεRIα were added to the reacted solution. The luminescence intensity for anti-OVA IgE Abs in the sera with the removal of IgG Abs was observed in five of seven (71.4%) of the sensitized rats, whereas no signals were observed in any of the unsensitized rats. The AlphaCL could also detect anti-gluten sIgE Abs in the sera of sensitized rats, but not of unsensitized rats. In conclusion, we successfully detected sIgE Abs in the sera of rats sensitized to two allergens using the AlphaCL. This detection method has the potential to be used as a new diagnostic tool for type-I allergic patients.

Control of germinal center B cell survival and IgE production by an adaptor molecule containing PH and SH2 domains, Aps/Sh2b2

The germinal centers (GCs) are structure found within secondary lymphoid organs and are important for the antibody-producing response against foreign antigens. In GCs, antigen-specific B cells proliferate intensely, inducing immunoglobulin class switching. Recent studies have shown that GCs are also an important site for class switching to IgE, which is implicated in allergy. However, the mechanisms by which IgE production is regulated in GCs remain unclear. Here, we found impairment in IgE-specific production and a reduction of GC B cells after immunization in mice deficient in the Aps/Sh2b2 gene encoding the Lnk/Sh2b family adaptor protein Aps. GC B cells express higher levels of the Aps gene than non-GC B cells, and cell death of Aps-/- GC B cells is enhanced compared to wild-type GC B cells. An in vitro culture system with purified Aps-/- B cells induced the same level of IgE production and frequencies of IgE+ B cells as wild-type B cells. We found that Aps deficiency in B cells resulted in augmented depletion of IgE+ blasts by B cell receptor crosslinking with anti-CD79b antibodies compared to wild-type IgE+ cells. These results suggest that Aps regulates IgE production by controlling the survival of GC B cells and IgE+ plasma cells and may serve as a potential therapeutic target to control IgE production.

Extracellular vesicle surface display enhances the therapeutic efficacy and safety profile of cancer immunotherapy

Immunotherapy has emerged as a mainstay in cancer therapy, yet its efficacy is constrained by the risk of immune-related adverse events. In this study, we present a nanoparticle-based delivery system that enhances the therapeutic efficacy of immunomodulatory ligands while concurrently limiting systemic toxicity. We demonstrate that extracellular vesicles (EVs), lipid bilayer enclosed particles released by cells, can be efficiently engineered via iEDDA-mediated conjugation to display multiple immunomodulatory ligands on their surface. Display of immunomodulatory ligands on the EV surface conferred substantial enhancements in signaling efficacy, particularly for tumor necrosis factor receptor superfamily (TNFRSF) agonists, where EV surface display served as an alternative FcγR-independent approach to induce ligand multimerization and efficient receptor crosslinking. EVs displaying a complementary combination of immunotherapeutic ligands were able to shift the tumor immune milieu towards an anti-tumorigenic phenotype and significantly suppress tumor burden and increase survival in multiple models of metastatic cancer to a greater extent than an equivalent dose of free ligands. In summary, we present an EV-based delivery platform for cancer immunotherapeutic ligands that facilitates superior anti-tumor responses at significantly lower doses with less side-effects than is possible with conventional delivery approaches.

Surface charge, but not size, of liposomes is involved in the suppression of rat basophilic leukemia (RBL-2H3) cell degranulation mediated by Akt phosphorylation.

Cationic liposomes composed of cholesteryl-3β-carboxyamidoethylene-N-hydroxyethylamine (OH-chol) and 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) inhibit mast cell degranulation mediated via crosslinking of high-affinity IgE receptors (FcεRI). Although the inhibitory efficiency of mast cell degranulation is altered by modifying the ratio of OH-chol and DOPE in cationic liposomes, the manner in which physicochemical properties, such as surface charge and size, influence suppression is not clear. We observed that positive surface charge, but not the size, of liposomes plays a role in suppressing rat basophilic leukemia (RBL-2H3) cell activation. Pretreatment with middle-ratio OH-chol liposomes (zeta potential, 62.2 ± 0.5 mV; diameter, 325.4 ± 7.3 nm) exhibited a larger suppression of RBL-2H3 cell degranulation evoked by FcεRI crosslinking compared with that by low-ratio OH-chol liposomes (zeta potential, 48.6 ± 1.9 mV; diameter, 344.4 ± 25.0 nm), although both liposomes were similarly attached to RBL-2H3 cells. Preparation of middle-ratio OH-chol liposomes, classified roughly by size using an extrusion method, revealed that the liposomal size did not affect the inhibitory efficiency of RBL-2H3 cell activation. Mechanistically, we found that middle-ratio OH-chol liposomes increased the inhibition of antigen-induced Akt phosphorylation compared to low-ratio OH-chol liposomes. We measured the phosphorylation of linker for activation of T cells (LAT) and paxillin, which are important proteins in FcεRI- and focal adhesions (FAs)-mediated signaling, respectively. Middle ratio OH-chol liposomes significantly suppressed antigen-induced paxillin phosphorylation, but did not affect LAT phosphorylation, suggesting that middle-ratio OH-chol liposomes attached to RBL-2H3 cells suppress the degranulation by impairing FA-mediated Akt phosphorylation evoked by FcεRI crosslinking.

Human serum albumin-based drug-free macromolecular therapeutics induce apoptosis in chronic lymphocytic leukemia patient cells by crosslinking of CD20 and/or CD38 receptors.

This study explores the efficacy of human serum albumin (HSA)-based Drug-Free Macromolecular Therapeutics (DFMT) in treating Chronic Lymphocytic Leukemia (CLL), a prevalent adult leukemia subtype. DFMT, a novel strategy, employs biomimetic crosslinking of CD20 and CD38 receptors on malignant B cells without the need for low molecular weight drugs. Apoptosis is initiated via a two-step process: i) Recognition of a bispecific engager, Fab' fragment conjugated with morpholino oligonucleotide (Fab'-MORF1), by a cell surface antigen; followed by ii) crosslinking of the MORF1-decorated cells with a multivalent effector, HSA holding multiple copies of complementary MORF2, HSA-(MORF2)x. Herein we evaluated the efficacy of HSA-based DFMT in the treatment of 56 samples isolated from patients diagnosed with CLL. Fab' fragments from Obinutuzumab (OBN) and Isatuximab (ISA) were employed in the synthesis of anti-CD20 (Fab'OBN-MORF1) and anti-CD38 (Fab'ISA-MORF1) bispecific engagers. The efficacy of DFMT was significantly influenced by the expression levels of CD20 and CD38 receptors. Dual-targeting DFMT strategies (CD20 + CD38) were more effective than single-target approaches, particularly in samples with elevated receptor expression. Pretreatment of patient cells with gemcitabine or ricolinostat markedly increased cell surface CD20 and CD38 expression, respectively. Apoptosis was effectively initiated in 62.5% of CD20-targeted samples and in 42.9% of CD38-targeted samples. Our findings demonstrate DFMT's potential in personalized CLL therapy. Further research is needed to validate these outcomes in a larger number of patient samples and to explore DFMT's applicability to other malignancies.

The diverse dependence of galectin-1 and -8 on multivalency for the modulation of FGFR1 endocytosis

Fibroblast growth factor receptor 1 (FGFR1) is a N-glycosylated cell surface receptor tyrosine kinase, which upon recognition of specific extracellular ligands, fibroblast growth factors (FGFs), initiates an intracellular signaling. FGFR1 signaling ensures homeostasis of cells by fine-tuning essential cellular processes, like differentiation, division, motility and death. FGFR1 activity is coordinated at multiple steps and unbalanced FGFR1 signaling contributes to developmental diseases and cancers. One of the crucial control mechanisms over FGFR1 signaling is receptor endocytosis, which allows for rapid targeting of FGF-activated FGFR1 to lysosomes for degradation and the signal termination. We have recently demonstrated that N-glycans of FGFR1 are recognized by a precise set of extracellular galectins, secreted and intracellular multivalent lectins implicated in a plethora of cellular processes and altered in immune responses and cancers. Specific galectins trigger FGFR1 clustering, resulting in activation of the receptor and in initiation of intracellular signaling cascades that shape the cell physiology. Although some of galectin family members emerged recently as key players in the clathrin-independent endocytosis of specific cargoes, their impact on endocytosis of FGFR1 was largely unknown.Here we assessed the contribution of extracellular galectins to the cellular uptake of FGFR1. We demonstrate that only galectin-1 induces internalization of FGFR1, whereas the majority of galectins predominantly inhibit endocytosis of the receptor. We focused on three representative galectins: galectin-1, -7 and -8 and we demonstrate that although all these galectins directly activate FGFR1 by the receptor crosslinking mechanism, they exert different effects on FGFR1 endocytosis. Galectin-1-mediated internalization of FGFR1 doesn’t require galectin-1 multivalency and occurs via clathrin-mediated endocytosis, resembling in this way the uptake of FGF/FGFR1 complex. In contrast galectin-7 and -8 impede FGFR1 endocytosis, causing stabilization of the receptor on the cell surface and prolonged propagation of the signals. Furthermore, using protein engineering approaches we demonstrate that it is possible to modulate or even fully reverse the endocytic potential of galectins.

PD-1 endocytosis unleashes the cytolytic potential of check-point blockade in tumor immunity

Abstract PD-1 immune checkpoint blockade (ICB) has revolutionized cancer treatment. Present models indicate that anti-PD-1 operates by preventing PD-1 from binding to its ligand PD-L1. Surprisingly, ICB-mediated internalization of PD-1 and its importance have not been fully explored. Here, we demonstrate that PD-1 internalization is associated with increased cytolytic activity during cancer immunotherapy. Anti-hPD-1 and -mPD-1 antibodies induced internalization of PD-1 generating a PD-1int subset, resistant to further internalization. Moreover, anti-PD-1 downregulation was more effective in CD8+ T cells than CD4+ T cells. ICB also induced PD-1 degradation in a proteosome-dependent manner. Interestingly, Nivolumab outperformed Pembrolizumab with both antibodies exhibiting distinct effects on CD8+ effector and effector memory T-cells. Importantly, PD-1 downregulation was dependent on receptor crosslinking by bivalent but not monovalent antibodies. Consistent with this, B16-PD-L1+ tumor-bearing mice treated with bivalent antibodies showed better anti-tumor response relative to monovalent antibodies. While mono and bivalent blockade increased granzyme B expression, only bivalent antibody induced perforin in CD8+ T-cells. Our findings unveil a mechanism beyond steric blockade and underscore the significance of PD-1 endocytosis in optimizing checkpoint blockade. Targeting PD-1 internalization holds promise for enhancing anti-tumor immunity and improving the efficacy of PD-1 ICB.

Lrba-/- murine B cells show NF-κB overactivation and altered BCR signaling.

Abstract Lipopolysaccharide-Responsive Beige-like anchor (LRBA) is a scaffolding protein whose deficiency is associated with an inborn error of immunity error like common variable immunodeficiency. Patients with LRBA deficiency have a heterogeneous clinical presentation including hypogammaglobulinemia, reduction of B and T regulatory cells, recurrent infections, and autoimmune diseases. Functions of Lrba on T regulatory cells have been described, however, function on B cells remains unknown. This work aims to identify the function of Lrba in B-cell receptor (BCR) signaling. Lrba-deficient mice (Lrba-/-) have a higher number of Transitional 1 B cells in the spleen. Flow cytometry assays showed reduced B cell proliferation and an increased cell death, in response to B-cell Receptor (BCR) crosslinking. Immunoblot and confocal microscopy revealed an increased activation of p50, p65, and IκBα (components of the canonical pathway of NF-κB) in Lrba-/- B cells under basal conditions with a subsequent reduced response after BCR crosslinking. Co-immunoprecipitation assays suggest an interaction between Lrba and components of BCR signaling such as PLC-γ2 and p65. The activated phenotype of Lrba-/- B cells as well as the interaction with p65 and PLC-γ2 indicates that Lrba is involved in the regulation of NF-κB activation driven by BCR signaling, which finally impacts on survival of B cells.

Abstract LT08: Extracellular Vesicle Surface Display Enhances the Therapeutic Efficacy and Safety Profile of Cancer Immunotherapy

Abstract As our understanding of the complex interactions between the immune system and cancer has progressed, so has the identification of novel targets and ligands that can modulate effective anti-cancer immune responses. While immunotherapy has emerged as a mainstay in cancer therapy, its efficacy has been limited by the potential for off-target toxicity against normal body cells. In this study, we present a nanoparticle-based delivery system that enhances the signaling efficacy of immunomodulatory ligands while concurrently limiting systemic toxicity. We demonstrate that extracellular vesicles (EVs), lipid bilayer enclosed nanoparticles released by cells, can be efficiently engineered to display multiple immunomodulatory ligands on their surface. Display of immunomodulatory ligands such as agonistic CD137 and CD40 antibodies on the EV surface significantly enhanced their therapeutic efficacy over equivalent doses of free ligands by inducing ligand multimerization, efficient receptor crosslinking and the formation of immune synapses. EVs conjugated with a complementary combination of immune stimulatory ligands and immune checkpoint inhibitors were able to shift the tumor immune milieu towards an anti-tumorigenic phenotype in a lung metastatic melanoma allograft and suppress tumor progression to a greater extent than an equivalent dose of free ligands. We also demonstrate the ability of EVs to co-deliver intraluminally loaded TLR agonists which synergize with surface displayed agonistic CD40 antibodies to induce effective anti-tumor responses and tumor regression in a metastatic autochthonous cell-derived model of PDAC. Remarkably, we also observed that EV-associated immunotherapeutics were limited in their biodistribution to the tumor microenvironment, resulting in significantly lower off-target toxicity than treatment with free ligands. In summary, we present an EV-based delivery approach that allows the use of potent cancer immunotherapy combinations to achieve superior anti-tumor responses at significantly lower doses with less side-effects than is possible with conventional administration methods for cancer immunotherapy. Citation Format: Migara Kavishka Jayasinghe, Dawn Liu Xiao Tian, Yock Sin Lay, Chang Yu Lee, Brendon Zhi Jie Yeo, Dong Van Hoang, Rebecca Carissa Prajogo, Boya Peng, Thach Tuan Pham, Minh Thi Nguyet Le. Extracellular Vesicle Surface Display Enhances the Therapeutic Efficacy and Safety Profile of Cancer Immunotherapy [abstract]. In: Proceedings of Frontiers in Cancer Science; 2023 Nov 6-8; Singapore. Philadelphia (PA): AACR; Cancer Res 2024;84(8_Suppl):Abstract nr LT08.

Mast Cells are Dependent on Glucose Transporter 1 (GLUT1) and GLUT3 for IgE-mediated Activation

Mast cells (MCs) are known to have a pathological impact in a variety of settings, in particular in allergic conditions. There is also limited evidence implicating MCs in diabetes, raising the possibility that MC function may be influenced by alterations in glucose levels. However, it is not known whether MCs are directly affected by elevated glucose concentrations. Moreover, it is not known which glucose transporters that are expressed by MCs, and whether MCs are dependent on glucose transporters for activation. Here we addressed these issues. We show that MCs express high levels of both glucose transporter 1 (GLUT1/Slc2A1) and GLUT3 (Slc2A3). Further, we show that the inhibition of either GLUT1 or GLUT3 dampens both MC degranulation and cytokine induction in response to IgE receptor crosslinking, and that combined GLUT1 and GLUT3 inhibition causes an even more pronounced inhibition of these parameters. In contrast, the inhibition of GLUT1 or GLUT3, or combined GLUT1 and GLUT3 inhibition, had less impact on the ability of the MCs to respond to activation via compound 48/80. Elevated glucose concentrations did not affect MC viability, and had no stimulatory effect on MC responses to either IgE receptor crosslinking or compound 48/80. Altogether, these findings reveal that MCs are strongly dependent on glucose transport via GLUT1 and/or GLUT3 for optimal responses towards IgE-mediated activation, whereas MC functionality is minimally affected by elevated glucose levels. Based on these findings, antagonists of GLUT1 and GLUT3 may be considered for therapeutic intervention in allergic conditions.

Isotype switching in human memory B cells sets intrinsic antigen-affinity thresholds that dictate antigen-driven fates

Memory B cells (MBCs) play a critical role in protection against homologous and variant pathogen challenge by either differentiating to plasma cells (PCs) or to germinal center (GC) B cells. The human MBC compartment contains both switched IgG+ and unswitched IgM+ MBCs; however, whether these MBC subpopulations are equivalent in their response to B cell receptor cross-linking and their resulting fates is incompletely understood. Here, we show that IgG+ and IgM+ MBCs can be distinguished based on their response to κ-specific monoclonal antibodies of differing affinities. IgG+ MBCs responded only to high-affinity anti-κ and differentiated almost exclusively toward PC fates. In contrast, IgM+ MBCs were eliminated by apoptosis by high-affinity anti-κ but responded to low-affinity anti-κ by differentiating toward GC B cell fates. These results suggest that IgG+ and IgM+ MBCs may play distinct yet complementary roles in response to pathogen challenge ensuring the immediate production of high-affinity antibodies to homologous and closely related challenges and the generation of variant-specific MBCs through GC reactions.

TGFβ prevents IgE-mediated allergic disease by restraining T follicular helper 2 differentiation.

Allergic diseases are common, affecting more than 20% of the population. Genetic variants in the TGFβ pathway are strongly associated with atopy. To interrogate the mechanisms underlying this association, we examined patients and mice with Loeys-Dietz syndrome (LDS) who harbor missense mutations in the kinase domain of TGFΒR1/2. We demonstrate that LDS mutations lead to reduced TGFβ signaling and elevated total and allergen-specific IgE, despite the presence of wild-type T regulatory cells in a chimera model. Germinal center activity was enhanced in LDS and characterized by a selective increase in type 2 follicular helper T cells (TFH2). Expression of Pik3cg was increased in LDS TFH cells and associated with reduced levels of the transcriptional repressor SnoN. PI3Kγ/mTOR signaling in LDS naïve CD4+ T cells was elevated after T cell receptor cross-linking, and pharmacologic inhibition of PI3Kγ or mTOR prevented exaggerated TFH2 and antigen-specific IgE responses after oral antigen exposure in an adoptive transfer model. Naïve CD4+ T cells from nonsyndromic allergic individuals also displayed decreased TGFβ signaling, suggesting that our mechanistic discoveries may be broadly relevant to allergic patients in general. Thus, TGFβ plays a conserved, T cell-intrinsic, and nonredundant role in restraining TFH2 development via the PI3Kγ/mTOR pathway and thereby protects against allergic disease.

Tripodal receptor cross-linked polymer as a promising adsorbent for iodine vapor capture and adsorption from water

A cross-linked tripodal receptor polymer was synthesized using a Friedel-Crafts polymerization reaction which showed an iodine vapor capture capacity of 2.47 g g−1 at 80 °C with remarkable iodine adsorption per unit BET surface area of 86 wt/(m2/g). UV–Vis spectral analysis confirmed that the polymer adsorbent rapidly adsorbs iodine from water. Importantly, the polymer exhibited reversible iodine adsorption allowing the polymer to be reused several times without losing the adsorption efficiency. We also investigated the adsorption capability of the synthesized polymer TPP as a filtration material for practical applications. Through dynamic adsorption experiments using a syringe pump setup, we demonstrated that a mere 40 mg of the TPP polymer effectively purifies 20 ml of a 2.5 mM aqueous iodine solution. Our findings underscore the exceptional adsorption efficiency of the TPP polymer, as evidenced by the successful removal of iodine molecules from the solution. These results not only highlight the potential of the TPP polymer for its utility in environmental remediation applications particularly for the treatment of effluents from nuclear reactors.

Hem1 inborn errors of immunity: waving goodbye to coordinated immunity in mice and humans.

Inborn errors of immunity (IEI) are a group of diseases in humans that typically present as increased susceptibility to infections, autoimmunity, hyperinflammation, allergy, and in some cases malignancy. Among newly identified genes linked to IEIs include 3 independent reports of 9 individuals from 7 independent kindreds with severe primary immunodeficiency disease (PID) and autoimmunity due to loss-of-function mutations in the NCKAP1L gene encoding Hematopoietic protein 1 (HEM1). HEM1 is a hematopoietic cell specific component of the WASp family verprolin homologous (WAVE) regulatory complex (WRC), which acts downstream of multiple immune receptors to stimulate actin nucleation and polymerization of filamentous actin (F-actin). The polymerization and branching of F-actin is critical for creating force-generating cytoskeletal structures which drive most active cellular processes including migration, adhesion, immune synapse formation, and phagocytosis. Branched actin networks at the cell cortex have also been implicated in acting as a barrier to regulate inappropriate vesicle (e.g. cytokine) secretion and spontaneous antigen receptor crosslinking. Given the importance of the actin cytoskeleton in most or all hematopoietic cells, it is not surprising that HEM1 deficient children present with a complex clinical picture that involves overlapping features of immunodeficiency and autoimmunity. In this review, we will provide an overview of what is known about the molecular and cellular functions of HEM1 and the WRC in immune and other cells. We will describe the common clinicopathological features and immunophenotypes of HEM1 deficiency in humans and provide detailed comparative descriptions of what has been learned about Hem1 disruption using constitutive and immune cell-specific mouse knockout models. Finally, we discuss future perspectives and important areas for investigation regarding HEM1 and the WRC.

Improving Intracellular Delivery of an Antibody-Drug Conjugate Targeting Carcinoembryonic Antigen Increases Efficacy at Clinically Relevant Doses In Vivo.

Solid tumor antibody-drug conjugates (ADC) have experienced more clinical success in the last 5 years than the previous 18-year span since the first ADC approval in 2000. While recent advances in protein engineering, linker design, and payload variations have played a role in this success, high expression and readily internalized targets have also been crucial to solid tumor therapy. However, these factors are also paradoxically connected to poor tissue penetration and lower efficacy. Previous work shows that potent ADCs can benefit from slower internalization under subsaturating doses to improve tissue penetration and increase tumor response. In contrast, faster internalization is predicted to increase efficacy under higher, tumor saturating doses. In this work, the intracellular delivery of SN-38 conjugated to an anti-carcinoembryonic antigen (anti-CEA) antibody (Ab) is increased by coadministering a noncompeting (cross-linking) anti-CEA Ab to improve efficacy in a colorectal carcinoma animal model. The SN-38 payload enables broad tumor saturation with clinically-tolerable doses, and under these saturating conditions, using a second CEA receptor cross-linking Ab yields faster internalization, which increases tumor killing efficacy. Our spheroid results show indirect bystander killing can also occur, but the more efficient direct cell killing from targeted intracellular payload release drives a greater tumor response. These results provide a strategy to increase therapeutic effectiveness with improved intracellular delivery under tumor saturating doses with the potential to expand the ADC target repertoire.

Development of a Cytotoxic Antibody-Drug Conjugate Targeting Membrane Immunoglobulin E-Positive Cells.

High numbers of membrane immunoglobulin E (IgE)-positive cells are characteristic of allergic conditions, atopic dermatitis, or IgE myeloma. Antibodies targeting the extracellular membrane-proximal domain of the membranous IgE-B-cell receptor (BCR) fragment can be used for specific depletion of IgE-BCR-positive cells. In this study, we derivatized such an antibody with a toxin and developed an antibody-drug conjugate (ADC) that showed strong cytotoxicity for an IgE-positive target cell line. Site-specific conjugation with maleimidocaproyl-valine-citrulline-p-aminobenzoyloxycarbonyl-monomethyl-auristatin E via a newly introduced single cysteine residue was used to prepare a compound with a drug-antibody ratio of 2 and favorable biophysical properties. The antibody was rapidly taken up by the target cells, showing almost complete internalization after 4 h of treatment. Its cytotoxic effect was potentiated upon cross-linking mediated by an anti-human IgG F(ab')2 fragment. Because of its fast internalization and strict target specificity, this antibody-drug conjugate presents a valuable starting point for the further development of an anti-IgE cell-depleting agent, operating by the combined action of receptor cross-linking and toxin-mediated cytotoxicity.

Degranulation of human mast cells: modulation by P2 receptors' agonists.

Since the late 1970s, there has been an alarming increase in the incidence of asthma and its morbidity and mortality. Acute obstruction and inflammation of allergic asthmatic airways are frequently caused by inhalation of exogenous substances such as allergens cross-linking IgE receptors expressed on the surface of the human lung mast cells (HLMC). The degree of constriction of human airways produced by identical amounts of inhaled allergens may vary from day to day and even hour to hour. Endogenous factors in the human mast cell (HMC)'s microenvironment during allergen exposure may markedly modulate the degranulation response. An increase in allergic responsiveness may significantly enhance bronchoconstriction and breathlessness. This review focuses on the role that the ubiquitous endogenous purine nucleotide, extracellular adenosine 5'-triphosphate (ATP), which is a component of the damage-associated molecular patterns, plays in mast cells' physiology. ATP activates P2 purinergic cell-surface receptors (P2R) to trigger signaling cascades resulting in heightened inflammatory responses. ATP is the most potent enhancer of IgE-mediated HLMC degranulation described to date. Current knowledge of ATP as it relates to targeted receptor(s) on HMC along with most recent studies exploring HMC post-receptor activation pathways are discussed. In addition, the reviewed studies may explain why brief, minimal exposures to allergens (e.g., dust, cat, mouse, and grass) can unpredictably lead to intense clinical reactions. Furthermore, potential therapeutic approaches targeting ATP-related enhancement of allergic reactions are presented.

Molecular basis for potent B cell responses to antigen displayed on particles of viral size.

Multivalent viral epitopes induce rapid, robust and T cell-independent humoral immune responses, but the biochemical basis for such potency remains incompletely understood. We take advantage of a set of liposomes of viral size engineered to display affinity mutants of the model antigen (Ag) hen egg lysozyme. Particulate Ag induces potent 'all-or-none' B cell responses that are density dependent but affinity independent. Unlike soluble Ag, particulate Ag induces signal amplification downstream of the B cell receptor by selectively evading LYN-dependent inhibitory pathways and maximally activates NF-κB in a manner that mimics T cell help. Such signaling induces MYC expression and enables even low doses of particulate Ag to trigger robust B cell proliferation in vivo in the absence of adjuvant. We uncover a molecular basis for highly sensitive B cell responses to viral Ag display that is independent of encapsulated nucleic acids and is not merely accounted for by avidity and B cell receptor cross-linking.

PRELIMINARY SAFETY, EFFICACY AND PHARMACOKINETICS (PK) RESULTS OF KN026 (A HER2 BISPECIFIC ANTIBODY) MONOTHERAPY IN ADVANCED SOLID TUMOR PATIENTS WITH HER2 EXPRESSION

Abstract Background KN026 is a novel bispecific antibody and simultaneously binds to two distinct HER2 epitopes which are the same domains as trastuzumab (ECD4) and pertuzumab (ECD2). It showed higher maximal binding than monospecific HER2 antibodies and favors that crosslinking of HER2 receptors could enhance the receptors internalization in preclinical studies. KN026 significantly inhibited the growth of human cancer cell lines and demonstrated obviously antitumor activity against different xenografts models. The encouraging efficacy and manageable safety of KN026 were reported in Chinese cancer patients (pts) with HER2 expression and ph3 study is ongoing in gastric cancer (NCT05427383). Methods The late line solid tumor pts with HER2 expression who were refractory to or ineligible for standard therapy were recruited in this phase I dose-escalation study in US (NCT03847168). All pts intravenously received KN026 monotherapy at ascending dose of 10 mg/kg (QW), 20 mg/kg (Q2W) or 30 mg/kg (Q3W). Dose escalation followed standard “3 + 3” design. Expansion was determined by Safety Monitoring Committee (SMC). The primary objectives were to evaluate safety and tolerability of KN026 and determine the MTD and/or RP2D. Safety was evaluated according to CTCAE v 5.0, and efficacy was assessed by RECIST 1.1. Results A total of 22 pts with median 4 lines prior treatment were enrolled, including 5 breast cancer pts, 3 gastric or gastroesophageal junction cancer pts and 14 other solid tumor pts. 21 pts were included in the efficacy analysis. The median age was 57.0 (47-79), with 8 males and 14 females and most of pts were Caucasian (72.7%). 3, 10 (7 at expansion phase), and 9 (6 at expansion phase) pts were treated at 10mg/kg, 20mg/kg, 30mg/kg, respectively. No dose-limiting toxicities (DLTs) were observed and MTD wasn’t reached. 20 pts (90.9%) occurred TRAEs and the common (≥20%) TRAEs were diarrhea (45.5%), fatigue (40.9%), chills (36.4%) and nausea (27.3%). Most of TRAE were Gr 1-2, and only 3 pts (13.6%) experienced ≥ Gr3 TRAE (anemia, fatigue and pneumonitis) without treatment discontinuation and death caused by KN026. 4 of 21 pts (1 at 10mg/kg, 2 at 20 mg/kg, 1 at 30mg/kg) achieved objective response (ORR 19.0%, 95% CI: 5.5, 41.9), and DCR was 61.9% (95% CI: 38.4, 81.9). The exposure of KN026 and T1/2 increased with dose escalation. Accumulation ratio of Cmax and AUC was 1.18-1.42 and 1.14-1.71. The concentration of Ctrough was over 20μM at all dose levels. There was only one positive ADA sample in 20 mg/kg group in C1D1. And the RP2D was 20mg/kg Q2W or 30mg/kg Q3W. Conclusion KN026 was well tolerated and showed the promising anti-tumor activity in US pts with HER2 expression. Besides, KN026 has well pharmacokinetic profile and favorable immunogenicity.

Effects of IL-9 on TRAF3-deficient B cell activation

Abstract The pleiotropic cytokine interleukin-9 (IL-9) signals to target cells by binding to a heterodimeric receptor consisting of the IL-9 receptor (IL-9R) and the common subunit γ chain. In the present study, we found that the expression of IL-9R was strikingly up-regulated in mouse naïve follicular B cells genetically deficient in TRAF3, a critical regulator of B cell survival and function. The highly up-regulated IL-9R on Traf3 −/−follicular B cells conferred responsiveness to IL-9, including IgM production and STAT3 phosphorylation. Interestingly, IL-9 significantly enhanced class switch recombination to IgG1 induced by B cell antigen receptor crosslinking plus IL-4 in Traf3 −/−B cells but not in wild type B cells. Blocking the JAK-STAT3 pathway abrogated the effects of IL-9 on Traf3 −/−B cells. Our study thus revealed a novel pathway that TRAF3 suppresses B cell activation and Ig isotype switching by inhibiting IL-9R-JAK-STAT3 signaling. Our findings provide new insights into the TRAF3-IL-9R axis in B cell function and have significant implications for the understanding and treatment of a variety of human diseases involving aberrant B cell activation. This study was supported by the National Institutes of Health grants R01 CA158402 (P. Xie) and R21 AI128264 (P. Xie), the Department of Defense grant W81XWH-13-1-0242 (P. Xie), and a Busch Biomedical Grant (P. Xie). FACS analyses were supported by the Flow Cytometry Core Facility with funding from NCI-CCSG P30CA072720.