Antibody-dependent Cellular Phagocytosis Research Articles

A platform for mapping reactive cysteines within the immunopeptidome

The major histocompatibility complex class I antigen presentation pathways play pivotal roles in orchestrating immune responses. Recent studies have begun to explore the therapeutic potential of cysteines within the immunopeptidome, such as the use of covalent ligands to generate haptenated peptide neoepitopes for immunotherapy. In this work, we report a platform for mapping reactive cysteines on MHC-I-bound peptide antigens. We develop cell-impermeable sulfonated maleimide probes capable of capturing reactive cysteines on these antigens. Using these probes in chemoproteomic experiments, we discover that cysteines on MHC-I-bound antigens exhibit various degrees of reactivity. Moreover, interferon-gamma stimulation enhances the reactivity of cysteines at position 8 of 9-mer MHC-I-bound antigens. Finally, we demonstrate that targeting reactive cysteines on MHC-I-bound antigens with a maleimide-conjugated Fc-binding cyclic peptide contributes to the induction of antibody-dependent cellular phagocytosis.

Nonclinical Similarity of the Biosimilar Candidate ABP 938 with Aflibercept Reference Product.

ABP 938 is being developed as a biosimilar to Eylea® (aflibercept reference product [RP]), an anti-vascular endothelial growth factor (VEGF) drug used in the management of retinal diseases. Previously, a comparative analytical similarity assessment demonstrated that ABP 938 and aflibercept RP have the same amino acid sequence and exhibit similar higher-order structure and biological activity. The nonclinical studies described here were designed to assess the in vitro pharmacology and the in vivo pharmacokinetics (PK), toxicokinetics (TK), and safety profiles of ABP 938 compared to aflibercept RP. In vitro target-binding kinetics and affinity for VEGF-A and placental growth factor (PIGF) isoforms were evaluated using surface plasmon resonance (SPR). Effector functions were assessed by cell-based assays. PK was evaluated in a nonterminal intravitreal (IVT) ocular distribution study in rabbits. Safety was assessed in a 1-month IVT study in cynomolgus monkeys. SPR results demonstrated that ABP 938 is similar to aflibercept RP in binding kinetics and affinity for VEGF-A111, VEGF-A121, VEGF-A165, VEGF-A189, PlGF-1, and PlGF-2 isoforms. No antibody-dependent cellular cytotoxicity, antibody-dependent cellular phagocytosis, or complement-dependent cytotoxicity was observed with ABP 938 and aflibercept RP. Results from thenonterminal ocular distribution study in rabbits indicated that there were no meaningful differences in the distribution kinetics between intravitreally injected ABP 938 and aflibercept RP. Additionally, there was no evidence of ocular or systemic toxicity associated with IVT administration of ABP 938 in a repeat-dose, 1-month toxicology study in cynomolgus monkeys; toxicokinetic and toxicology profiles were similar to aflibercept RP. This integrated assessment of results from the in vitro pharmacology assessment and in vivo PK and TK/toxicology profiles formed the nonclinical portion of the totality of evidence demonstrating ABP938 is a biosimilar to aflibercept RP.

Enterovirus Antibodies: Friends and Foes.

Enteroviruses (EV) initiate replication by binding to their cellular receptors, leading to the uncoating and release of the viral genome into the cytosol of the host cell. Neutralising antibodies (NAbs) binding to epitopes on enteroviral capsid proteins can inhibit this infectious process through several mechanisms of neutralisation in vitro. Fc-mediated antibody effector functions such as antibody-dependent cell-mediated cytotoxicity and antibody-dependent cellular phagocytosis have also been described for some EV. However, antibody binding to virions does not always result in viral neutralisation. Non-neutralising antibodies, or sub-neutralising concentrations of antibodies, can enhance infection of viruses, leading to more severe pathologies. This phenomenon, known as antibody-dependent enhancement (ADE) of infection, has been described in vitro and/or in vivo for EV including poliovirus, coxsackievirus B and EV-A71. It has been shown that ADE of EV infection is mediated by FcγRs expressed by monocytes, macrophages, B lymphocytes and granulocytes. Antibodies play a crucial role in the diagnosis and monitoring of infections. They are valuable markers that have been used to establish a link between enteroviral infection and chronic diseases such as type 1 diabetes. Monoclonal and polyclonal antibodies targeting enteroviral proteins have been developed and shown to be effective to prevent or combat EV infections in vitro and in vivo. In addition, vaccines are under development, and clinical trials of vaccines are underway or have been completed, providing hope for the prevention of diseases due to EV. However, the ADE of the infection should be considered in the development of anti-EV antibodies or safe vaccines.

Potent broadly neutralizing antibodies mediate efficient antibody-dependent phagocytosis of HIV-infected cells.

Antibody-dependent cellular phagocytosis (ADCP) has been implicated in protection against HIV-1. However, methods for measuring ADCP currently rely on the phagocytosis of gp120- or gp41-coated beads that do not reflect physiologically relevant conformations of the viral envelope glycoprotein or the size of a virus-infected cell. We therefore developed a novel approach for measuring ADCP of HIV-infected cells expressing natural conformations of Env. A monocytic cell line (THP-1 cells) or primary human monocytes were incubated with a CD4+ T cell line that expresses eGFP upon HIV-1 infection in the presence of antibodies and ADCP was measured as the accumulation of eGFP+ material by flow cytometry. The internalization of HIV-infected cells by monocytes was confirmed visually by image-capture flow cytometry. Cytoskeletal remodeling, pseudopod formation and phagocytosis were also observed by confocal microscopy. We found that potent broadly neutralizing antibodies (bnAbs), but not non-neutralizing antibodies (nnAbs), mediate efficient phagocytosis of cells infected with either primary or lab-adapted HIV-1. A nnAb to a CD4-inducible epitope of gp120 (A32) failed to enable ADCP of HIV-infected cells but mediated efficient phagocytosis of gp120-coated beads. Conversely, a bnAb specific to intact Env trimers (PGT145) mediated potent ADCP of HIV-infected cells but did not facilitate the uptake of gp120-coated beads. These results underscore the importance of measuring ADCP of HIV-infected cells expressing physiologically relevant conformations of Env and show that most antibodies that are capable of binding to Env trimers on virions to neutralize virus infectivity are also capable of binding to Env on the surface of virus-infected cells to mediate ADCP.

Novel recombinant vaccinia virus-vectored vaccine affords complete protection against homologous Borrelia burgdorferi infection in mice

ABSTRACT The rising prevalence of Lyme disease (LD) in North America and Europe has emerged as a pressing public health concern. Despite the availability of veterinary LD vaccines, no vaccine is currently available for human use. Outer surface protein C (OspC) found on the outer membrane of the causative agent, Borrelia burgdorferi, has been identified as a promising target for LD vaccine development due to its sustained expression during mammalian infection. However, the efficacy and immunological mechanisms of LD vaccines solely targeting OspC are not well characterized. In this study, we developed an attenuated Vaccinia virus (VV) vectored vaccine encoding type A OspC (VV-OspC-A). Two doses of the VV-OspC-A vaccine conferred complete protection against homologous B. burgdorferi challenge in mice. Furthermore, the candidate vaccine also prevented the development of carditis and lymph node hyperplasia associated with LD. When investigating the humoral immune response to vaccination, VV-OspC-A was found to induce a robust antibody response predominated by the IgG2a subtype, indicating a Th1-bias. Using a novel quantitative flow cytometry assay, we also determined that elicited antibodies were capable of inducing antibody-dependent cellular phagocytosis in vitro. Finally, we demonstrated that VV-OspC-A vaccination generated a strong antigen-specific CD4+ T-cell response characterized by the secretion of numerous cytokines upon stimulation of splenocytes with OspC peptides. This study suggests a promising avenue for LD vaccine development utilizing viral vectors targeting OspC and provides insights into the immunological mechanisms that confer protection against B. burgdorferi infection.

Antibody-mediated cellular responses are dysregulated in Multisystem Inflammatory Syndrome in Children (MIS-C)

Abstract Background Multisystem Inflammatory Syndrome in Children (MIS-C) is a rare and severe complication of SARS-CoV-2 infection that is characterized by multi-organ involvement and substantial inflammation. The immunological responses in MIS-C are not fully known. Antibody-mediated viral clearance in which innate immune cells interact with antibodies via their Fc receptors to remove the virus is an important mechanism for reducing SARS-CoV-2 viral load. However, little is known about how antibody-mediated cellular responses in MIS-C compared to acute COVID-19 infection and direct testing of cellular function ex vivo to understand the aberrant immune response in MIS-C is limited. Therefore, we focused on the antibody-mediated cellular responses in MIS-C relative to children and adults that had acute COVID-19 infection with spectrum of symptoms. We hypothesized that cells that bind antibodies to help clear the virus are dysfunctional in MIS-C patients, preventing the virus from being fully cleared. Methods We collected samples from MIS-C children along with pediatric and adult subjects with a clinical spectrum of COVID-19 symptoms and uninfected controls. Through these controls, we can compare Fc-mediated antibody functions between ages and clinical symptoms. We utilized high dimension flow cytometry to assess phenotype and function of innate immune cells that bind to antibodies and sequencing to study Fc receptor genetic. This data was then correlated with matched clinical data. Results Monocytes in MIS-C were hyperfunctional for antibody-dependent cellular phagocytosis and production of proinflammatory cytokines. In contrast, natural killer (NK) cells in MIS-C were hypofunctional for antibody-dependent cellular cytotoxicity and cytokine production. To provide some preliminary insight into mechanism, we show multiple ways leading to decreased cytotoxicity for NK cells, including phenotypic exhaustion of NK cells, variants in CD16 (NK cell Fc receptor) genetics that reduce Fc binding to IgG, and cytokine-induced associations. Using a novel anti-CD16 novel bispecific reagent that we developed, we could rescue the hypofunctional antibody-mediated NK cell function in MIS-C to the same levels as control. Conclusion Together, our results reveal dysregulation in antibody-mediated responses that are unique to MIS-C and may contribute to the immune pathology of this disease. Specifically, we find that monocytes are hyperfunctional with NK cells are hypofunctional. In the case of the MIS-C antibody-mediated response, while it is likely that multiple pathogenetic mechanisms contribute to MIS-C, our data suggest an imbalance of the antibody-mediated cellular response as a mechanistic correlate of this rare, but life-threatening outcome of SARS-COV-2 in children. Our results highlight that targeted therapies to reduce viral burden and/or boost NK cells responses while decreasing cytokine levels may be effective in preventing MIS-C.

Preventative Cancer Vaccine-Elicited Human Anti-MUC1 Antibodies Have Multiple Effector Functions.

Mucin-1 (MUC1) is a transmembrane glycoprotein that is overexpressed and hypoglycosylated in premalignant and malignant epithelial cells compared to normal cells, creating a target antigen for humoral and cellular immunity. Healthy individuals with a history of advanced colonic adenomas and at high risk for colon cancer were enrolled in a clinical trial to evaluate the feasibility of using a MUC1 peptide vaccine to prevent colon cancer. Anti-MUC1 antibodies elicited by this vaccine were cloned using peripheral blood B cells and sera collected two weeks after a one-year booster. Twelve of these fully human monoclonal antibodies (mAb) were tested for binding to MUC1+ target cells, and three with the highest binding were further evaluated for various effector functions important for tumor rejection. Immune cells were incubated together with target cells expressing variations in the number, distance, and membrane anchoring properties of the MUC1 epitope in the presence of each mAb. All three mAbs mediated antibody-dependent cytokine release (ADCR), antibody-dependent cellular cytotoxicity (ADCC), and antibody-dependent cellular phagocytosis (ADCP). Two also mediated antibody-dependent trogocytosis/trogoptosis (ADCT). None were capable of complement-dependent cytotoxicity (CDC). ADCP and ADCT functions were more efficient when antibodies bound epitopes proximal to and anchored to the membrane, providing insight for future therapeutic antibody validation strategies.

Cutting-edge approaches to B-cell depletion in autoimmune diseases.

B-cell depletion therapy (BCDT) has been employed to treat autoimmune disease for ~20 years. Immunoglobulin G1 (IgG1) monoclonal antibodies targeting CD20 and utilizing effector function (eg, antibody-dependent cellular cytotoxicity, complement-dependent cytotoxicity, antibody-dependent cellular phagocytosis) to eliminate B cells have historically been the predominant therapeutic approaches. More recently, diverse BCDT approaches targeting a variety of B-cell surface antigens have been developed for use in hematologic malignancies, including effector-function-enhanced monoclonal antibodies, chimeric antigen receptor T-cell (CAR-T) treatment, and bispecific T-cell engagers (TCEs). The latter category of antibodies employs CD3 engagement to augment the killing of target cells. Given the improvement in B-cell depletion observed with CAR-T and TCEs compared with conventional monospecific antibodies for treatment of hematologic malignancies and the recent case reports demonstrating therapeutic benefit of CAR-T in autoimmune disease, there is potential for these mechanisms to be effective for B-cell-mediated autoimmune disease. In this review, we discuss the various BCDTs that are being developed in autoimmune diseases, describing the molecule designs, depletion mechanisms, and potential advantages and disadvantages of each approach as they pertain to safety, efficacy, and patient experience. Additionally, recent advances and strategies with TCEs are presented to help broaden understanding of the potential for bispecific antibodies to safely and effectively engage T cells for deep B-cell depletion in autoimmune diseases.

Using IMGT unique numbering for IG allotypes and Fc-engineered variants of effector properties and half-life of therapeutic antibodies.

Therapeutic monoclonal antibodies (mAb) are usually of the IgG1, IgG2, and IgG4 classes, and their heavy chains may be modified by amino acid (aa) changes involved in antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), complement-dependent cytotoxicity (CDC), and/or half-life. Allotypes and Fc-engineered variants are classified using IMGT/HGNC gene nomenclature (e.g., Homo sapiens IGHG1). Allotype names follow the WHO/IMGT nomenclature. IMGT-engineered variant names use the IMGT nomenclature (e.g., Homsap G1v1), which comprises species and gene name (both abbreviated) followed by the letter v (for variant) and a number. Both allotypes and engineered variants are defined by their aa changes and positions, based on the IMGT unique numbering for C domain, identified in sequence motifs, referred to as IMGT topological motifs, as their limits and length are standardized and correspond to a structural feature (e.g., strand or loop). One hundred twenty-six variants are displayed with their type, IMGT numbering, Eu-IMGT positions, motifs before and after changes, and their property and function (effector and half-life). Three motifs characterize effector variants, CH2 1.6-3, 23-BC-41, and the FG loop, whereas three different motifs characterize half-life variants, two on CH2 13-AB-18 and 89-96 with H93, and one on CH3 the FG loop with H115.

Preclinical comparison of prolgolimab, pembrolizumab and nivolumab

Prolgolimab is a recombinant IgG1-based anti-PD-1 antibody, whose properties were improved by the introduction of the LALA mutation, and which has demonstrated high efficacy in patients with metastatic melanoma. This paper presents the results of comparative preclinical studies of antigen-binding and effector functions involving prolgolimab and conventional IgG4 antibodies, nivolumab and pembrolizumab. None of the studied antibodies had undesirable antibody-dependent cellular cytotoxicity activity. Prolgolimab has shown higher PD-1 receptor occupancy and T-cell activation, but lower propensity to activate antibody-dependent cellular phagocytosis as compared to nivolumab and pembrolizumab. An in vivo study in mice inoculated with CT26.wt cancer cells showed that tumor growth inhibition was 16% for pembrolizumab and 56% for prolgolimab. This study warrants clinical comparison of IgG1- and IgG4-based anti-PD-1 antibodies.

The relevance of tumor target expression levels on IgA-mediated cytotoxicity in cancer immunotherapy

Recent advances in cancer immunotherapy, particularly the success of immune checkpoint inhibitors, have reignited interest in targeted monoclonal antibodies for immunotherapy. Antibody therapies aim to minimize on-target, off-tumor toxicity by targeting antigens overexpressed on tumor cells but not on healthy cells. Despite considerable efforts, some therapeutic antibodies have been linked to dose-limiting side effects. Our hypothesis suggests that the efficacy of IgG leads to a lower target expression threshold for tumor cell killing, contributing to these side effects. Earlier, therapeutic IgG antibodies were reformatted into the IgA isotype. Unlike IgG, which primarily engages Fc gamma receptors (FcγR) to induce antibody-dependent cellular cytotoxicity (ADCC) by NK cells and antibody-dependent cellular phagocytosis (ADCP) by monocytes/macrophages, IgA antibodies activate neutrophils through the Fc alpha receptor I (CD89, FcαRI). In previous studies, it appeared that IgA may require a higher target expression threshold for effective killing, and we aimed to investigate this in our current study. Moreover, we investigated how blocking the myeloid checkpoint CD47/SIRPα axis affect the target expression threshold. Using a tetracycline-inducible expression system, we regulated target expression in different cell lines. Our findings from ADCC assays indicate that IgA-mediated PMN ADCC requires a higher antigen expression level than IgG-mediated PBMC ADCC. Furthermore, blocking CD47 enhanced IgA-mediated ADCC, lowering the antigen threshold. Validated in two in vivo models, our results show that IgA significantly reduces tumor growth in high-antigen-expressing tumors without affecting low-antigen-expressing healthy tissues. This suggests IgA-based immunotherapy could potentially minimize on-target, off-tumor side effects, improving treatment efficacy and patient safety.

Monoclonal Antibodies for the Treatment of Ocular Diseases

Monoclonal antibodies (mAbs) have revolutionized the landscape of cancer therapy, offering unprecedented specificity and diverse mechanisms to combat malignant cells. These biologic agents have emerged as a cornerstone in targeted cancer treatment, binding to specific antigens on cancer cells and exerting their therapeutic effects through various mechanisms, including inhibition of signaling pathways, antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and antibody-dependent cellular phagocytosis (ADCP). The unique ability of mAbs to engage the immune system and directly interfere with cancer cell function has significantly enhanced the therapeutic armamentarium against a broad spectrum of malignancies. mAbs were initially studied in oncology; however, today, treatments have been developed for eye diseases. This review discusses the current applications of mAbs for the treatment of ocular diseases, discussing the specificity and the variety of mechanisms by which these molecules exhibit their therapeutic effects. The benefits, drawbacks, effectiveness, and risks associated with using mAbs in ophthalmology are highlighted, focusing on the most relevant ocular diseases and mAbs currently in use. Technological advances have led to in vitro production methods and recombinant engineering techniques, allowing the development of chimeric, humanized, and fully human mAbs. Nowadays, many humanized mAbs have several applications, e.g., for the treatment of age-related macular disease, diabetic retinopathy, and uveitis, while studies about new applications of mAbs, such as for SARS-CoV-2 infection, are also currently ongoing to seek more efficient and safe approaches to treat this new ocular disease.

Functional comparison of Fc-engineering strategies to improve anti-HIV-1 antibody effector functions

Substantial reduction of the intact proviral reservoir is essential towards HIV-1 cure. In vivo administration of broadly neutralizing antibodies (bNAbs) targeting the HIV-1 envelope glycoprotein (Env) trimer can decrease the viral reservoir, through Fc-mediated killing of infected cells. In this study, we compared three commonly used antibody engineering strategies to enhance Fc-mediated effector functions: (i) glyco-engineering, (ii) protein engineering, and (iii) subclass/hinge modifications in a panel of anti-HIV-1 antibodies. We found that antibody-dependent cellular phagocytosis (ADCP) was improved by elongating the hinge domain and switching to an IgG3 constant domain. In addition, potent NK cell activation and ADCC activity was observed for afucosylated antibodies and antibodies bearing the GASDALIE mutations. The combination of these engineering strategies further increased NK cell activation and induced antibody dependent cytotoxicity (ADCC) of infected cells at low antibody concentrations. The bNAb N6 was most effective at killing HIV-1 infected cells, likely due to its high affinity and optimal angle of approach. Overall, the findings of this study are applicable to other antibody formats, and can aid the development of effective immunotherapies and antibody-based treatments for HIV-1 cure strategies.

Discovery and characterization of a pan-betacoronavirus S2-binding antibody

The continued emergence of deadly human coronaviruses from animal reservoirs highlights the need for pan-coronavirus interventions for effective pandemic preparedness. Here, using linking B cell receptor to antigen specificity through sequencing (LIBRA-seq), we report a panel of 50 coronavirus antibodies isolated from human B cells. Of these, 54043-5 was shown to bind the S2 subunit of spike proteins from alpha-, beta-, and deltacoronaviruses. A cryoelectron microscopy (cryo-EM) structure of 54043-5 bound to the prefusion S2 subunit of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike defined an epitope at the apex of S2 that is highly conserved among betacoronaviruses. Although non-neutralizing, 54043-5 induced Fc-dependent antiviral responses invitro, including antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). In murine SARS-CoV-2 challenge studies, protection against disease was observed after introduction of Leu234Ala, Leu235Ala, and Pro329Gly (LALA-PG) substitutions in the Fc region of 54043-5. Together, these data provide new insights into the protective mechanisms of non-neutralizing antibodies and define a broadly conserved epitope within the S2 subunit.

Enhancing Fc-mediated effector functions of monoclonal antibodies: The example of HexaBodies.

Since the approval of the CD20-targeting monoclonal antibody (mAb) rituximab for the treatment of lymphoma in 1997, mAb therapy has significantly transformed cancer treatment. With over 90 FDA-approved mAbs for the treatment of various hematological and solid cancers, modern cancer treatment relies heavily on these therapies. The overwhelming success of mAbs as cancer therapeutics is attributed to their broad applicability, high safety profile, and precise targeting of cancer-associated surface antigens. Furthermore, mAbs can induce various anti-tumor cytotoxic effector mechanisms including antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and complement-dependent cytotoxicity (CDC), all of which are mediated via their fragment crystallizable (Fc) domain. Over the past decades, these effector mechanisms have been substantially improved through Fc domain engineering. In this review, we will outline the different approaches to enhance Fc effector functions via Fc engineering of mAbs, with a specific emphasis on the so-called "HexaBody" technology, which is designed to enhance the hexamerization of mAbs on the target cell surface, thereby inducing greater complement activation, CDC, and receptor clustering. The review will summarize the development, preclinical, and clinical testing of several HexaBodies designed for the treatment of B-cell malignancies, as well as the potential use of the HexaBody technology beyond Fc-mediated effector functions.

Neoadjuvant androgen deprivation therapy with or without Fc-enhanced non-fucosylated anti-CTLA-4 (BMS-986218) in high risk localized prostate cancer: a randomized phase 1 trial.

Men with high-risk localized prostate cancer exhibit high rates of post-surgical recurrence. In these patients, androgen deprivation therapy (ADT) is immunomodulatory, however increased infiltration of regulatory T cells (Tregs) may limit the antitumor immune effects of ADT. We designed a neoadjuvant clinical trial to test whether BMS-986218 - a next-generation non-fucosylated anti-CTLA-4 antibody engineered for enhanced antibody-dependent cellular cytotoxicity or phagocytosis (ADCC/P) - depletes intratumoral Tregs and augments the response to ADT. In this single-center, two-arm, open-label study, 24 men with high-risk localized prostate cancer were randomized to receive a single dose of ADT with or without two pre-operative doses of BMS-986218 (anti-CTLA4-NF) prior to radical prostatectomy. Treatment was well tolerated and feasible in the neoadjuvant setting. A secondary clinical outcome was the rate of disease recurrence, which was lower than predicted in both arms. Mechanistically, anti-CTLA4-NF reduced ADT-induced Treg accumulation through engagement of CD16a/FCGR3A on tumor macrophages, and depth of Treg depletion was quantitatively associated with clinical outcome. Increased intratumoral dendritic cell (DC) frequencies also associated with lack of recurrence, and pre-clinical data suggest ADCC/P-competent anti-CTLA-4 antibodies elicit activation and expansion of tumor DCs. Patients receiving anti-CTLA4-NF also exhibited phenotypic signatures of enhanced antitumor T cell priming. In total, this study provides the first-in-human evidence of Treg depletion by glycoengineered antibodies targeting CTLA-4 in humans and their potential in combination with ADT in prostate cancer patients with high-risk of recurrence.

A genetically engineered mouse/human chimeric antibody targeting CD99 enhances antibody-dependent cellular phagocytosis against human mantle cell lymphoma Z138 cells

Background: Mantle cell lymphoma (MCL) is an aggressive form of B-cell nonHodgkin lymphoma. The elimination of MCL cells via phagocytosis is essential for cancer eradication. Therefore, discovering novel targeted antibodies that can induce phagocytosis is needed. We have demonstrated that our in-houseproduced mouse anti-CD99 mAb clone MT99/3 could induce potent anticancer activities against MCL cell lines in both in vitro and in vivo mouse xenograft models. Nevertheless, for use in humans, the mouse mAb needs to be transformed into a mouse/human chimeric mAb that contains a human Fc region to activate human immune effector functions, especially macrophage-mediated phagocytosis. Antibody-dependent cellular phagocytosis (ADCP) mediated by mouse/human chimeric mAb MT99/3 against MCL has not been previously reported. Objective: This study aimed to genetically engineer a mouse/human chimeric antibody against human CD99 derived from mouse mAb MT99/3 and to evaluate its effect in mediating the ADCP mechanism for eradicating MCL cells in vitro using monocyte-derived macrophages. Materials and methods: The expression plasmid to produce chimeric anti-CD99 antibody, ChAbMT99/3, was constructed by fusing the variable domains of mouse mAb MT99/3 with the constant domains of human IgG1 and the constant domains of kappa light chain. ChAbMT99/3 was expressed in the stable human expression system based on HEK293T cells. ChAbMT99/3 was purified from the culture supernatant of ChAbMT99/3-expressing HEK293T cells using Protein G chromatography. The purity and structure of ChAbMT99/3 were verified by SDS-PAGE and western blotting. The binding specificity and activity were determined by staining with cells expressing recombinant and native human CD99. The anticancer activity of ChAbMT99/3 in mediating the ADCP mechanism against MCL cell line Z138 using human monocytederived macrophages was evaluated. Results: We successfully constructed the plasmid to produce ChAbMT99/3. Human HEK293T cells stably expressing ChAbMT99/3 were established. The ChAbMT99/3- expressing HEK293T cells could secrete ChAbMT99/3 into the culture supernatant. The high purity and complete IgG structure of ChAbMT99/3 were obtained from the purification process. Crucially, this chimeric antibody retained its binding reactivity to recombinant and native human CD99. In addition, the produced ChAbMT99/3, upon binding to MCL cells, significantly enhanced ADCP against MCL cell line Z138 in a dose-dependent manner. Conclusion: The production of a mouse/human chimeric antibody against human CD99 derived from mouse mAb MT99/3 was successful. The engineered antibody could mediate ADCP activity against MCL cells. The produced ChAbMT99/3 might be a promising therapeutic candidate for MCL treatment.

Trogocytosis: A potential pathogenic mechanism in immune thrombocytopenia leading to impaired megakaryocyte maturation and reduced platelet production

Immune thrombocytopenia (ITP) is an autoimmune disease due to increased peripheral platelets destruction and inappropriate bone marrow production of platelets by megakaryocytes (MKs). The pathophysiology of ITP is complex and multifactorial, which remains not fully understood. However, the production of antiplatelet autoantibodies and the destruction of antibody-coated platelets through antibody-dependent cellular phagocytosis by macrophages (Mθ) expressing Fc gamma receptor (FcγR) are regarded as the key mechanisms. Glycoprotein (GP) Ⅱb/Ⅲa is the main target of antiplatelet antibodies leading to platelet phagocytosis by splenic Mθ, through interactions with FcγR. As GPⅡb/Ⅲa is normally expressed both on platelets and the MKs from which they are derived, we inferred that partial phagocytosis (definitely trogocytosis) of MKs by bone marrow Mθ might exist, leading to the increased amount of granular MKs (or non-platelets-producing MKs) in ITP. And we further hypothesized that the “bitten” MKs cannot sustain their normal function of maturation. Such trogocytosis mechanism may shed new light on the understanding of morphology alterations, maturation defects and decreased platelets production of MKs in ITP, and provide appealing implications in therapeutic modifications targeting the interplay of MKs and Mθ in bone marrow.

Safety and activity of lenalidomide in combination with obinutuzumab in patients with relapsed indolent non-Hodgkin lymphoma: a single group, open-label, phase 1/2 trial

Rituximab and lenalidomide is a preferred option for relapsed indolent B cell non-Hodgkin lymphoma. Obinutuzumab may be a superior combination partner with lenalidomide given enhanced antibody dependent cellular cytotoxicity and phagocytosis compared to rituximab. Our aim was to determine the recommended phase 2 dose, safety, and activity of lenalidomide in combination with fixed dose of obinutuzumab in relapsed and refractory indolent B cell non-Hodgkin lymphoma. In this single-arm, open-label, phase 1/2 trial, we enrolled patients with relapsed or refractory WHO Grade 1-3A follicular lymphoma, marginal zone lymphoma and small lymphocytic lymphoma and adequate performance status (ECOG 0-2) at the MD Anderson Cancer Center. We excluded patients with evidence of ongoing transformation to aggressive lymphoma. During phase 1, 1000mg intravenous obinutuzumab was administered with three predefined levels of oral lenalidomide in a 3+3 dose escalation design to establish lenalidomide 20mg as the recommended phase 2 dose. During phase 2, patients received induction therapy with six 28-day cycles of lenalidomide 20mg with intravenous obinutuzumab 1000mg. In accordance with our prior experience with lenalidomide plus rituximab, patients who were responding to the combination could receive up to 6 additional cycles (up to 12 cycles in total) of combination therapy. Dosing of obinutuzumab was continued in all responding patients after cycle 6 every 2 months for a total of 30 months from the start of therapy. The decision of number of cycles of combination therapy beyond 6 was at discretion of the investigator and was included to allow individualisation of therapy to maximise response while minimising exposure. The co-primary objectives were to evaluate the safety and overall response, defined as the proportion of patients who achieved a complete or partial response in relapsed and refractory indolent non-Hodgkin lymphoma at the end of induction therapy, according to Cheson and colleagues (2007 criteria). The secondary endpoints were complete response after induction therapy and time to event endpoints including time to progression, progression free survival, and overall survival. Analyses were intent to treat in the efficacy cohort and per-treated in the safety population in all patients who received at least one dose of either investigational agent. This trial is registered with ClinicalTrials.gov, NCT01995669. Between June 03, 2014, and 07 March 2019, we completed planned enrolment, and 66 patients started therapy including 9 patients in phase 1 and 57 patients in phase 2. All patients were evaluated for safety and the 60 patients treated at the recommended phase 2 dose of lenalidomide 20mg were evaluable for activity. Grade 3-4 haematological toxicities included neutropenia 21% (14/66) and thrombocytopenia 11% (7/66) with no cases of febrile neutropenia. Grade 3-4 non-haematological toxicities included lung infection 8% (5/66), fatigue 8% (5/66) and rash 6% (4/66). By Cheson 2007 criteria, 90% (54/60, 95% CI: 79-96) achieved an overall response at the end of induction meeting the prespecified activity endpoint. Complete responses were seen in 33% (20/60, 95% CI: 22-47) at the end of induction. Median progression free survival, time to progression and overall survival have not been reached after median follow-up of 41.7 months. Estimated 4-year progression free survival rates were 55% (95% CI: 42-73), time to progression of 56% (95% CI: 43-74) and overall survival of 84% (95% CI: 74-95). Our findings suggest that oral lenalidomide with obinutuzumab is safe and highly active in patients with relapsed and refractory indolent B cell non-Hodgkin lymphoma and is associated with prolonged remission duration. The study is limited by the lack of a control arm leading to cross-trial comparisons to evaluate activity. Future randomised trials comparing this regime to rituximab and lenalidomide are warranted. Genentech and an MD Anderson Core grant.

Enhancing Neutrophil Cytotoxicity of a Panel of Clinical EGFR Antibodies by Fc Engineering to IgA3.0.

EGFR plays an essential role in cellular signaling pathways that regulate cell growth, proliferation, and survival and is often dysregulated in cancer. Several monoclonal IgG antibodies have been clinically tested over the years, which exert their function via blocking the ligand binding domain (thereby inhibiting downstream signaling) and inducing Fc-related effector functions, such as antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). However, these IgG antibodies do not optimally recruit neutrophils, which are the most abundant white blood cell population in humans. Therefore, we reformatted six therapeutic EGFR antibodies (cetuximab, panitumumab, nimotuzumab, necitumumab, zalutumumab, and matuzumab) into the IgA3.0 format, which is an IgA2 isotype adapted for clinical application. Reformatting these antibodies preserved Fab-mediated functions such as EGFR binding, growth inhibition, and ligand blockade. In addition, whole leukocyte ADCC was significantly increased when using this panel of IgA3.0 antibodies compared with their respective IgG counterparts, with no major differences between IgA3.0 antibodies. In vivo, IgA3.0 matuzumab outperformed the other antibodies, resulting in the strongest suppression of tumor outgrowth in a long intraperitoneal model. We showed that neutrophils are important for the suppression of tumor outgrowth. IgA3.0 matuzumab exhibited reduced receptor internalization compared with the other antibodies, possibly accounting for its superior in vivo Fc-mediated tumor cell killing efficacy. In conclusion, reformatting EGFR antibodies into an IgA3.0 format increased Fc-mediated killing while retaining Fab-mediated functions and could therefore be a good alternative for the currently available antibody therapies.