A new class of bispecific antibodies to redirect T cells for cancer immunotherapy

The Evolving Role of Bispecific Antibodies in Diffuse Large B-Cell Lymphoma

The advent of targeted therapies such as monoclonal antibodies, adoptive T-cell therapies, and antibody-drug conjugates (ADCs) dramatically changed the treatment landscape of diffuse large B-cell lymphoma (DLBCL) over the last two decades. Rituximab was the first one approved. Chimeric antigen receptor T-cells are currently approved as second-line treatment in patients with DLBCL refractory to first-line chemo-immunotherapy. Polatuzumab, a CD79b-targeting ADC, is approved as first-line treatment in high-risk patients in combination with chemo-immunotherapy. Bispecific antibodies (BsAbs) are a novel category of drugs that are also changing the treatment paradigm of patients with DLBCL. They are engineered to bind to two different targets at the same time. To date, two BsAbs (glofitamab and epcoritamab) are approved as monotherapy in third-line treatment in DLBCL. Combination strategies with chemotherapy, immunotherapy, and ADCs are currently under investigation with encouraging results in first-line or subsequent lines of treatment. In the following review, we focus on the structure of BsAbs, the mechanism of action, clinical efficacy, and the mechanisms of resistance to BsAbs.

A Novel bispecific T-cell engager (BiTE) targeting CD22 and CD3 has both in vitro and in vivo activity and synergizes with blinatumomab in an acute lymphoblastic leukemia (ALL) tumor model

Immunotherapy has revolutionized cancer therapy. Two recently FDA-approved immunotherapies for B-cell malignancies target CD19, in the form of a Bispecific T-Cell Engager (BiTE) antibody construct or chimeric antigen receptor T (CAR-T) cells. Blinatumomab, an FDA-approved BiTE, binds to CD19 on B cells and to CD3 on T cells, mediating effector-target cell contact and T-cell activation that results in effective elimination of target B cells. Although CD19 is expressed by essentially all B-cell malignancies at clinical presentation, relapses with loss or reduction in CD19 surface expression are increasingly recognized as a cause of treatment failure. Therefore, there is a clear need to develop therapeutics for alternate targets. We have developed a novel BiTE consisting of humanized anti-CD22 and anti-CD3 single chain variable fragments. Target binding of the anti-CD22 and anti-CD3 moieties was confirmed by flow cytometry. CD22-BiTE promoted in vitro cell-mediated cytotoxicity in a dose and effector: target (E:T)-dependent fashion. Additionally, in an established acute lymphoblastic leukemia (ALL) xenograft mouse model, CD22-BiTE demonstrated tumor growth inhibition, comparable to blinatumomab. Further, the combination of blinatumomab and CD22-BiTE yielded increased efficacy in vivo when compared to the single agents. In conclusion, we report here the development of a new BiTE with cytotoxic activity against CD22+ cells which could represent an alternate or complementary therapeutic option for B-cell malignancies.

A literature review of the promising future of TROP2: a potential drug therapy target

Background and Objective

Previous studies have demonstrated that the oncogene trophoblast cell surface antigen 2 (TROP2) has great application prospects as a therapeutic target. However, few literature reviews have systematically summarized and evaluated its role in cancer therapy. This study aims to summarize the molecular structure, functions, signal transduction pathways, and prognostic value of TROP2, and explore therapeutic agents that target TROP2.

Methods

A total of 1,376 published literatures from PubMed and 614 published literatures from EMBASE were retrieved by searching "TROP2" or "Trophoblast cell surface antigen 2". The search was conducted on December 12, 2020, and updated on November 20, 2022. The cBioportal and GEPIA (Gene Expression Profiling Interactive Analysis) databases were used to analyze the expression, mutation, and prognostic value of TROP2 in different types of cancer.

Key Content and Findings

TROP2 is overexpressed in different tumor tissues and plays roles in cell proliferation, invasion, migration, apoptosis, and treatment resistance by binding to or interacting with several molecules. As a therapeutic target, TROP2 is particularly suitable for antibody-based therapies. Monoclonal antibodies, bispecific antibodies, antibody-drug conjugates (ADCs), virus-like particles, and antibody drugs in combination with traditional chemotherapy, immunotherapy, radioimmunotherapy, photoimmunotherapy, and nanoparticles that target TROP2 have thus far been rapidly developed. For example, sacituzumab govitecan (IMMU-132), a TROP2-targeting ADC, was granted accelerated approval for the treatment of metastatic triple-negative breast cancer (TNBC). Anti-TROP2 antibody-conjugated nanoparticles (ST-NPs) are a promising vehicle for delivering doxorubicin in targeted TNBC therapy.

Conclusions

The availability of TROP2-targeting ADCs makes TROP2 an accessible and promising therapeutic target for advanced metastatic cancers. The present review describes the important role of TROP2 in tumorigenesis and its potential applications as a promising biomarker and therapeutic target that is capable of reversing resistance.

Antibody-based therapy for acute myeloid leukemia: a review of phase 2 and 3 trials

INTRODUCTION

Despite recent advances in the treatment of adult acute myeloid leukemia (AML), the clinical outcome of patients continues to be unsatisfactory especially among older patients, those with a high-risk profile, and in the relapsed/refractory setting. For this reason, recent clinical trials have explored novel therapeutic agents either used alone or in combination with intensive chemotherapy or low-intensity treatments.

AREAS COVERED

The current paper reviews the clinical development of monoclonal antibody-based therapies in AML, their current status and phases 2 and 3 prospective trials.

EXPERT OPINION

Monoclonal antibody-based therapies demonstrated efficacy and tolerability in several clinical trials, especially when used in combination either with '3+7' chemotherapy or with low-intensity treatments. Additional studies are needed to determine new antigens for antibody-based therapies that target leukemia stem cells and spare normal hematopoiesis. Phase 2 and 3 additional clinical trial data are needed to assess the promise of first trials, especially regarding chimeric antigen receptor T cells redirected against myeloid antigens and immune checkpoint inhibitor therapies.

An Update on Immune Based Therapies in Acute Myeloid Leukemia: 2021 and Beyond!

Despite advances in the treatment of acute myeloid leukemia (AML), relapse is still widely observed and represents the major cause of death among patients with AML. Treatment options in the relapse setting are limited, still relying predominantly on allogeneic hematopoietic stem cell transplantation (allo-HSCT) and cytotoxic chemotherapy, with poor outcomes. Novel targeted and venetoclax-based combinations are being investigated and have shown encouraging results. Immune checkpoint inhibitors in combination with low-intensity chemotherapy demonstrated encouraging response rates and survival among patients with relapsed and/or refractory (R/R) AML, especially in the pre- and post-allo-HSCT setting. Blocking the CD47/SIRPα pathway is another strategy that showed robust anti-leukemic activity, with a response rate of around 70% and an encouraging median overall survival in patients with newly diagnosed, higher-risk myelodysplastic syndrome and patients with AML with a TP53 mutation. One approach that was proven to be very effective in the relapsed setting of lymphoid malignancies is chimeric antigen receptor (CAR) T cells. It relies on the infusion of genetically engineered T cells capable of recognizing specific epitopes on the surface of leukemia cells. In AML, different CAR constructs with different target antigens have been evaluated and demonstrated safety and feasibility in the R/R setting. However, the difficulty of potently targeting leukemic blasts in AML while sparing normal cells represents a major limitation to their use, and strategies are being tested to overcome this obstacle. A different approach is based on endogenously redirecting the patient's system cells to target and destroy leukemic cells via bispecific T-cell engagers (BiTEs) or dual antigen receptor targeting (DARTs). Early results have demonstrated the safety and feasibility of these agents, and research is ongoing to develop BiTEs with longer half-life, allowing for less frequent administration schedules and developing them in earlier and lower disease burden settings.

Immunotherapy in Acute Myeloid Leukemia: Where We Stand

In the past few years, our improved knowledge of acute myeloid leukemia (AML) pathogenesis has led to the accelerated discovery of new drugs and the development of innovative therapeutic approaches. The role of the immune system in AML development, growth and recurrence has gained increasing interest. A better understanding of immunological escape and systemic tolerance induced by AML blasts has been achieved. The extraordinary successes of immune therapies that harness the power of T cells in solid tumors and certain hematological malignancies have provided new stimuli in this area of research. Accordingly, major efforts have been made to develop immune therapies for the treatment of AML patients. The persistence of leukemia stem cells, representing the most relevant cause of relapse, even after allogeneic stem cell transplant (allo-SCT), remains a major hurdle in the path to cure for AML patients. Several clinical trials with immune-based therapies are currently ongoing in the frontline, relapsed/refractory, post-allo-SCT and minimal residual disease/maintenance setting, with the aim to improve survival of AML patients. This review summarizes the available data with immune-based therapeutic modalities such as monoclonal antibodies (naked and conjugated), T cell engagers, adoptive T-cell therapy, adoptive-NK therapy, checkpoint blockade via PD-1/PD-L1, CTLA4, TIM3 and macrophage checkpoint blockade via the CD47/SIRPa axis, and leukemia vaccines. Combining clinical results with biological immunological findings, possibly coupled with the discovery of biomarkers predictive for response, will hopefully allow us to determine the best approaches to immunotherapy in AML.

Development of an antibody-like T-cell engager based on VH-VL heterodimer formation and its application in cancer therapy

Following the clinical success of immunotherapeutic antibodies, bispecific antibodies for cytotoxic effector cell redirection, tumor-targeted immunomodulation and dual immunomodulation, have received particular attentions. Here, we developed a novel bispecific antibody platform, termed Antibody-Like Cell Engager (ALiCE), wherein the Fc domain of each heavy chain of immunoglobulin G (IgG) is replaced by the VH and VL domains of an IgG specific to a second antigen while retaining the N-terminal Fab of the parent antibody. Because of specific interactions between the substituted VH and VL domains, the C-terminal stem Fv enables ALiCE to assemble autonomously into hetero-tetramers, thus simultaneously binding to two distinct antigens but with different avidities. This design strategy was used to generate ACE-05 (two anti-PD-L1 Fab × anti-CD3 Fv) and ACE-31 (two anti-CD3 Fab × anti-PD-L1 Fv), both of which bound PD-L1 and CD3. However, ACE-05 was more effective than ACE-31 in reducing off-target toxicity caused by the indiscriminate activation of T cells. Moreover, in cell-based assays and PBMC-reconstituted humanized mice harboring human non-small-cell lung cancer tumors, ACE-05 showed marked antitumor efficacy, causing complete tumor regression at a dose of 0.05 mg/kg body weight. The dual roles of ACE-05 in immune checkpoint inhibition and T-cell redirection, coupled with reduced off-target toxicity, suggest that ACE-05 may be a promising anti-cancer therapeutic agent. Moreover, the bispecific ALiCE platform can be further used for tumor-targeted or multiple immunomodulation applications.

Biology drives the discovery of bispecific antibodies as innovative therapeutics

A bispecific antibody (bsAb) is able to bind two different targets or two distinct epitopes on the same target. Broadly speaking, bsAbs can include any single molecule entity containing dual specificities with at least one being antigen-binding antibody domain. Besides additive effect or synergistic effect, the most fascinating applications of bsAbs are to enable novel and often therapeutically important concepts otherwise impossible by using monoclonal antibodies alone or their combination. This so-called obligate bsAbs could open up completely new avenue for developing novel therapeutics. With evolving understanding of structural architecture of various natural or engineered antigen-binding immunoglobulin domains and the connection of different domains of an immunoglobulin molecule, and with greatly improved understanding of molecular mechanisms of many biological processes, the landscape of therapeutic bsAbs has significantly changed in recent years. As of September 2019, over 110 bsAbs are under active clinical development, and near 180 in preclinical development. In this review article, we introduce a system that classifies bsAb formats into 30 categories based on their antigen-binding domains and the presence or absence of Fc domain. We further review the biology applications of approximately 290 bsAbs currently in preclinical and clinical development, with the attempt to illustrate the principle of selecting a bispecific format to meet biology needs and selecting a bispecific molecule as a clinical development candidate by 6 critical criteria. Given the novel mechanisms of many bsAbs, the potential unknown safety risk and risk/benefit should be evaluated carefully during preclinical and clinical development stages. Nevertheless we are optimistic that next decade will witness clinical success of bsAbs or multispecific antibodies employing some novel mechanisms of action and deliver the promise as next wave of antibody-based therapeutics.

A bispecific broadly neutralizing antibody against enterovirus 71 and coxsackievirus A16 with therapeutic potential

Enterovirus 71 (EV71) and coxsackievirus A16 (CA16) are the major pathogens of hand, foot and mouth disease (HFMD), which affects children worldwide and is often associated with neurological complications. At present, there is no vaccine or cure available for simultaneous EV71 and CA16 infection, posing a great need to develop novel strategies for the treatment of this disease. Here, we engineered four bispecific antibodies using variable fragments of monoclonal antibodies (mAbs) from EV71- and CA16-specific neutralizing antibodies. The engineered bispecific antibody Bs(scFv)4-IgG-1 exhibits remarkable cross-reactivity against EV71 and CA16 and has a more potent cross-neutralization than its parental antibodies. Furthermore, we showed that Bs(scFv)4-IgG-1 conferred 100% therapeutic efficacy against single or mixed EV71 and CA16 infections in mice. Our study provides important insights into bispecific antibody engineering against enterovirus and will inform new curative treatment options for HFMD.

Profiling targetable immune checkpoints in osteosarcoma

Osteosarcomas are aggressive bone tumors for which therapeutic advances have not improved over several decades. Unlike most pediatric tumors, the osteosarcoma genome is remarkably unstable, characterized by numerous copy number alterations and chromosomal structural aberrations. In this study, we asked if the targetable immune checkpoints CD274 (PD-L1), PDCD1LG2 (PD-L2), CD276 (B7-H3) and IDO1 are impacted by copy number alterations in osteosarcoma. Of the 215 osteosarcoma samples investigated, PD-L1/PD-L2, B7-H3 and IDO1 were independently gained at frequencies of approximately 8-9%, with a cumulative frequency of approximately 24%. RNA sequencing data from two independent cohorts revealed that B7-H3 is the most highly expressed immune checkpoint gene among the four investigated. We also show that IDO1 is preferentially expressed in pediatric solid tumors and that increased protein expression of B7-H3 and IDO1 are significantly associated with inferior survival in patient samples. Using human osteosarcoma cell lines, we demonstrate that IDO1 is gained in MG63 and G292 cells and that the IDO1 inhibitor, epacadostat, inhibits the enzymatic activity of IDO1 in a dose-dependent manner in these cells. Together, these data reveal the genomic and transcriptomic profiles of PD-L1, PD-L2, B7-H3 and IDO1 in osteosarcoma and identifies a potential context for targeted immunotherapeutic intervention in a subset of patients.

Design Principles for Bispecific IgGs, Opportunities and Pitfalls of Artificial Disulfide Bonds

Bispecific antibodies (bsAbs) are antibodies with two binding sites directed at different antigens, enabling therapeutic strategies not achievable with conventional monoclonal antibodies (mAbs). Since bispecific antibodies are regarded as promising therapeutic agents, many different bispecific design modalities have been evaluated, but as many of them are small recombinant fragments, their utility could be limited. For some therapeutic applications, full-size IgGs may be the optimal format. Two challenges should be met to make bispecific IgGs; one is that each heavy chain will only pair with the heavy chain of the second specificity and that homodimerization be prevented. The second is that each heavy chain will only pair with the light chain of its own specificity and not with the light chain of the second specificity. The first solution to the first criterion (knobs into holes, KIH) was presented in 1996 by Paul Carter's group from Genentech. Additional solutions were presented later on. However, until recently, out of >120 published bsAb formats, only a handful of solutions for the second criterion that make it possible to produce a bispecific IgG by a single expressing cell were suggested. We present a solution for the second challenge-correct pairing of heavy and light chains of bispecific IgGs; an engineered (artificial) disulfide bond between the antibodies' variable domains that asymmetrically replaces the natural disulfide bond between CH1 and CL. We name antibodies produced according to this design "BIClonals". Bispecific IgGs where the artificial disulfide bond is placed in the CH1-CL interface are also presented. Briefly, we found that an artificial disulfide bond between VH position 44 to VL position 100 provides for effective and correct H-L chain pairing while also preventing the formation of wrong H-L chain pairs. When the artificial disulfide bond links the CH1 with the CL domain, effective H-L chain pairing also occurs, but in some cases, wrong H-L pairing is not totally prevented. We conclude that H-L chain pairing seems to be driven by VH-VL interfacial interactions that differ between different antibodies, hence, there is no single optimal solution for effective and precise assembly of bispecific IgGs, making it necessary to carefully evaluate the optimal solution for each new antibody.

The emergence of trophoblast cell-surface antigen 2 (TROP-2) as a novel cancer target

TROP-2 is a glycoprotein first described as a surface marker of trophoblast cells, but subsequently shown to be increased in many solid cancers, with lower expression in certain normal tissues. It regulates cancer growth, invasion and spread by several signaling pathways, and has a role in stem cell biology and other diseases. This review summarizes TROP-2's properties, especially in cancer, and particularly its role as a target for antibody-drug conjugates (ADC) or immunotherapy. When the irinotecan metabolite, SN-38, is conjugated to a humanized anti-TROP-2 antibody (sacituzumab govitecan), it shows potent broad anticancer activity in human cancer xenografts and in patients with advanced triple-negative breast, non-small cell and small-cell lung, as well as urothelial cancers.

Challenges and Perspectives for Immunotherapy in Adenocarcinoma of the Pancreas: The Cancer Immunity Cycle

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease with a devastating 5-year overall survival of only approximately 7%. Although just 4% of all malignant diseases are accounted to PDAC, it will become the second leading cause of cancer-related deaths before 2030. Immunotherapy has proven to be a promising therapeutic option in various malignancies such as melanoma, non-small cell lung cancer (NSCLC), microsatellite instability-high gastrointestinal cancer, urinary tract cancer, kidney cancer, and others. In this review, we summarize recent findings about immunological aspects of PDAC with the focus on the proposed model of the "cancer immunity cycle". By this model, a deeper understanding of the underlying mechanism in achieving a T-cell response against cancer cells is provided. There is currently great interest in the field around designing novel immunotherapy combination studies for PDAC based on a sound understanding of the underlying immunobiology.

T cell engaging bispecific antibody (T-BsAb): From technology to therapeutics

Harnessing the power of the human immune system to treat cancer is the essence of immunotherapy. Monoclonal antibodies engage the innate immune system to destroy targeted cells. For the last 30years, antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity have been the main mechanisms of anti-tumor action of unconjugated antibody drugs. Efforts to exploit the potentials of other immune cells, in particular T cells, culminated in the recent approval of two T cell engaging bispecific antibody (T-BsAb) drugs, thereby stimulating new efforts to accelerate similar platforms through preclinical and clinical trials. In this review, we have compiled the worldwide effort in exploring T cell engaging bispecific antibodies. Our special emphasis is on the lessons learned, with the hope to derive insights in this fast evolving field with tremendous clinical potential.

Single domain based bispecific antibody, Muc1-Bi-1, and its humanized form, Muc1-Bi-2, induce potent cancer cell killing in muc1 positive tumor cells

Muc1 is one of the most studied tumor antigens. However, antibodies or antibody-toxin conjugates against Muc1 have not shown significant efficacy for tumors with Muc1 overexpression. In this study, we employed bispecific antibody approach to target Muc1 positive tumor cells. A novel bispecific antibody, Muc1-Bi-1, was constructed by linking single domain antibodies, anti-Muc1-VHH and anti-CD16-VHH. Muc1-Bi-2, the humanized form of Muc1-Bi-1, was also constructed by grafting. Both Muc1-Bi bispecific antibodies can be efficiently expressed and purified from bacteria. In vitro, the Muc1-Bi bispecific antibodies can recruit Natural Killer (NK) cells to drive potent and specific cell killing of Muc1-overexpressing tumor cells. In xenograft model, the Muc1-Bi bispecific antibodies can suppress tumor growth in the presence of human peripheral blood mononuclear cells (PBMC). These data suggested that the single domain based Muc1-Bi may provide a valid strategy for targeting tumors with Muc1 overexpression.

Bispecific antibodies: design, therapy, perspectives

Antibodies (Abs) containing two different antigen-binding sites in one molecule are called bispecific. Bispecific Abs (BsAbs) were first described in the 1960s, the first monoclonal BsAbs were generated in the 1980s by hybridoma technology, and the first article describing the therapeutic use of BsAbs was published in 1992, but the number of papers devoted to BsAbs has increased significantly in the last 10 years. Particular interest in BsAbs is due to their therapeutic use. In the last decade, two BsAbs - catumaxomab in 2009 and blinatumomab in 2014, were approved for therapeutic use. Papers published in recent years have been devoted to various methods of BsAb generation by genetic engineering and chemical conjugation, and describe preclinical and clinical trials of these drugs in a variety of diseases. This review considers diverse BsAb-production methods, describes features of therapeutic BsAbs approved for medical use, and summarizes the prospects of practical application of promising new BsAbs.

The making of bispecific antibodies

During the past two decades we have seen a phenomenal evolution of bispecific antibodies for therapeutic applications. The 'zoo' of bispecific antibodies is populated by many different species, comprising around 100 different formats, including small molecules composed solely of the antigen-binding sites of two antibodies, molecules with an IgG structure, and large complex molecules composed of different antigen-binding moieties often combined with dimerization modules. The application of sophisticated molecular design and genetic engineering has solved many of the technical problems associated with the formation of bispecific antibodies such as stability, solubility and other parameters that confer drug properties. These parameters may be summarized under the term 'developability'. In addition, different 'target product profiles', i.e., desired features of the bispecific antibody to be generated, mandates the need for access to a diverse panel of formats. These may vary in size, arrangement, valencies, flexibility and geometry of their binding modules, as well as in their distribution and pharmacokinetic properties. There is not 'one best format' for generating bispecific antibodies, and no single format is suitable for all, or even most of, the desired applications. Instead, the bispecific formats collectively serve as a valuable source of diversity that can be applied to the development of therapeutics for various indications. Here, a comprehensive overview of the different bispecific antibody formats is provided.

ATTACK, a novel bispecific T cell-recruiting antibody with trivalent EGFR binding and monovalent CD3 binding for cancer immunotherapy

The redirection of T cell activity using bispecific antibodies is one of the most promising cancer immunotherapy approaches currently in development, but it is limited by cytokine storm-related toxicities, as well as the pharmacokinetics and tumor-penetrating capabilities of current bispecific antibody formats. Here, we have engineered the ATTACK (Asymmetric Tandem Trimerbody for T cell Activation and Cancer Killing), a novel T cell-recruiting bispecific antibody which combines three EGFR-binding single-domain antibodies (V_HH; clone EgA1) with a single CD3-binding single-chain variable fragment (scFv; clone OKT3) in an intermediate molecular weight package. The two specificities are oriented in opposite directions in order to simultaneously engage cancer cells and T cell effectors, and thereby promote immunological synapse formation. EgA1 ATTACK was expressed as a homogenous, non-aggregating, soluble protein by mammalian cells and demonstrated an enhanced binding to EGFR, but not CD3, when compared to the previously characterized tandem bispecific antibody which has one EgA1 V_HH and one OKT3 scFv per molecule. EgA1 ATTACK induced synapse formation and early signaling pathways downstream of TCR engagement at lower concentrations than the tandem V_HH-scFv bispecific antibody. Furthermore, it demonstrated extremely potent, dose-dependent cytotoxicity when retargeting human T cells towards EGFR-expressing cells, with an efficacy over 15-fold higher than that of the tandem V_HH-scFv bispecific antibody. These results suggest that the ATTACK is an ideal format for the development of the next-generation of T cell-redirecting bispecific antibodies.

Combination Therapy with Bispecific Antibodies and PD-1 Blockade Enhances the Antitumor Potency of T Cells

The DOCK-AND-LOCK (DNL) method is a platform technology that combines recombinant engineering and site-specific conjugation to create multispecific, multivalent antibodies of defined composition with retained bioactivity. We have applied DNL to generate a novel class of trivalent bispecific antibodies (bsAb), each comprising an anti-CD3 scFv covalently conjugated to a stabilized dimer of different antitumor Fabs. Here, we report the further characterization of two such constructs, (E1)-3s and (14)-3s, which activate T cells and target Trop-2- and CEACAM5-expressing cancer cells, respectively. (E1)-3s and (14)-3s, in the presence of human T cells, killed target cells grown as monolayers at subnanomolar concentrations, with a similar potency observed for drug-resistant cells. Antitumor efficacy was demonstrated for (E1)-3s coadministered with human peripheral blood mononuclear cells (PBMC) in NOD/SCID mice harboring xenografts of MDA-MB-231, a triple-negative breast cancer line constitutively expressing Trop-2 and PD-L1. Growth inhibition was observed following treatment with (E1)-3s or (14)-3s combined with human PBMC in 3D spheroids generated from target cell lines to mimic the in vivo behavior and microenvironment of these tumors. Moreover, addition of an antagonistic anti-PD-1 antibody increased cell death in 3D spheroids and extended survival of MDA-MB-231-bearing mice. These preclinical results emphasize the potential of combining T-cell-redirecting bsAbs with antagonists or agonists that mitigate T-cell inhibition within the tumor microenvironment to improve immunotherapy of solid cancers in patients. They also support the use of 3D spheroids as a predictive alternative to in vivo models for evaluating T-cell functions. Cancer Res; 77(19); 5384-94. ©2017 AACR.

Construction and functional analysis of an anti-human cervical carcinoma/anti-human CD3 single-chain bispecific antibody

The aim of the present study was to construct a single-chain bispecific antibody (scBsAb) against cervical carcinoma and to investigate its biological activities. The scBsAb was constructed using a genetic cloning technique and antigen binding activities were detected by ELISA. The iodogen method was used to analyze the pharmacokinetics. The Rosette formation test was used to detect the binding ability between peripheral blood lymphocytes (PBLs) and Cs1213 cervical cancer cells. In addition, the MTT method was performed to detect the killing effect of PBLs. The molecular weight of the scBsAb was ~60 kDa. The antigen binding activities of scBsAbs were compared with the anti‑human cervical carcinoma antibody single‑chain Fv fragment (CSAs‑1 scFv) and anti‑cluster of differentiation (CD)3 scFv (P>0.05). In addition, a pharmacokinetics assay demonstrated that compared with the two corresponding scFvs, scBsAbs exhibited a significantly prolonged retention time in the body (P<0.01). In addition, the number of rosettes formed by PBLs and Cs1213 cells in the scBsAb group was markedly greater than that in the scFv groups or the RPMI‑1640 group (P<0.05 and P<0.01, respectively). The killing activity of PBLs against scBsAb‑mediated Cs1213 cells was significantly greater than that mediated by the other antibodies (P<0.05). When the concentration of scBsAb was 40 µg/ml, the killing rate was 64.5%. Thus, anti‑human cervical carcinoma/anti‑CD3 scBsAbs may possess two types of antigen binding activity, prolong the duration in vivo and improve the killing activity of PBLs against cancer cells.

"NextGen" Biologics: Bispecific Antibodies and Emerging Clinical Results

INTRODUCTION

Bispecific antibodies (BsAb) are emerging as a novel approach for dual targeting strategies. Two bispecific antibodies are approved for therapy and >30 are in clinical development. The first generation of BsAb were produced by chemical cross-linking or hybridoma technology; with the recent advent of genetic and protein engineering technologies numerous formats of bispecific antibodies have emerged using either the fragments of IgG or whole IgG molecules. Further areas of development include dual blockade of different disease pathways, diagnosis and imaging.

AREAS COVERED

Biologics, including bi- or multi-specific antibodies and T cell-based approaches are rapidly changing the landscape of cancer therapeutics. New engineering platforms for bi- or multi-specific antibodies and scaffolds offer improved efficacy and reduced toxicities over IgG-based monoclonal antibodies. Preclinical and clinical studies using different formats of BsAbs are described in this review using PubMed as a literature search tool.

EXPERT OPINION

A comprehensive presentation of preclinical data and clinical trials evaluating the various formats of BsAbs indicate their safety and efficacy. However, a vast opportunity to fine tune physical properties and functional activity of biologics to improve the stability, engagement of cytotoxic CD8 T cells and multi-antigen targeting strategy through protein engineering holds a greater therapeutic potential.

Antibody Therapeutics in Oncology

One of the newer classes of targeted cancer therapeutics is monoclonal antibodies. Monoclonal antibody therapeutics are a successful and rapidly expanding drug class due to their high specificity, activity, favourable pharmacokinetics, and standardized manufacturing processes. Antibodies are capable of recruiting the immune system to attack cancer cells through complement-dependent cytotoxicity or antibody dependent cellular cytotoxicity. In an ideal scenario the initial tumor cell destruction induced by administration of a therapeutic antibody can result in uptake of tumor associated antigens by antigen-presenting cells, establishing a prolonged memory effect. Mechanisms of direct tumor cell killing by antibodies include antibody recognition of cell surface bound enzymes to neutralize enzyme activity and signaling, or induction of receptor agonist or antagonist activity. Both approaches result in cellular apoptosis. In another and very direct approach, antibodies are used to deliver drugs to target cells and cause cell death. Such antibody drug conjugates (ADCs) direct cytotoxic compounds to tumor cells, after selective binding to cell surface antigens, internalization, and intracellular drug release. Efficacy and safety of ADCs for cancer therapy has recently been greatly advanced based on innovative approaches for site-specific drug conjugation to the antibody structure. This technology enabled rational optimization of function and pharmacokinetics of the resulting conjugates, and is now beginning to yield therapeutics with defined, uniform molecular characteristics, and unprecedented promise to advance cancer treatment.

Taking up Cancer Immunotherapy Challenges: Bispecific Antibodies, the Path Forward?

As evidenced by the recent approvals of Removab (EU, Trion Pharma) in 2009 and of Blincyto (US, Amgen) in 2014, the high potential of bispecific antibodies in the field of immuno-oncology is eliciting a renewed interest from pharmaceutical companies. Supported by rapid advances in antibody engineering and the development of several technological platforms such as Triomab or bispecific T cell engagers (BiTEs), the “bispecifics” market has increased significantly over the past decade and may occupy a pivotal space in the future. Over 30 bispecific molecules are currently in different stages of clinical trials and more than 70 in preclinical phase. This review focuses on the clinical potential of bispecific antibodies as immune effector cell engagers in the onco-immunotherapy field. We summarize current strategies targeting various immune cells and their clinical interests. Furthermore, perspectives of bispecific antibodies in future clinical developments are addressed.

Human derived dimerization tag enhances tumor killing potency of a T-cell engaging bispecific antibody

Bispecific antibodies (BsAbs) have proven highly efficient T cell recruiters for cancer immunotherapy by virtue of one tumor antigen-reactive single chain variable fragment (scFv) and another that binds CD3. In order to enhance the antitumor potency of these tandem scFv BsAbs (tsc-BsAbs), we exploited the dimerization domain of the human transcription factor HNF1α to enhance the avidity of a tsc-BsAb to the tumor antigen disialoganglioside GD2 while maintaining functional monovalency to CD3 to limit potential toxicity. The dimeric tsc-BsAb showed increased avidity to GD2, enhanced T cell mediated killing of neuroblastoma and melanoma cell lines in vitro (32–37 fold), exhibited a near 4-fold improvement in serum half-life, and enhanced tumor ablation in mouse xenograft models. We propose that the use of this HNF1α-derived dimerization tag may be a novel and effective strategy to increase the potency of T-cell engaging antibodies for clinical cancer immunotherapy.

The coming of age of engineered multivalent antibodies

The development of monoclonal antibody (mAb) technology has had a profound impact on medicine. The therapeutic use of first-generation mAb achieved considerable success in the treatment of major diseases, including cancer, inflammation, autoimmune, cardiovascular, and infectious diseases. Next-generation antibodies have been engineered to further increase potency, improve the safety profile and acquire non-natural properties, and constitute a thriving area of mAb research and development. Currently, a variety of alternative antibody formats with modified architectures have been generated and are moving fast into the clinic. In fact, the bispecific antibody blinatumomab was the first in its class to be approved by the US Food and Drug Administration (FDA) as recently as December 2014. Here, we outline the fundamental strategies used for designing the next generation of therapeutic antibodies, as well as the most relevant results obtained in preclinical studies and clinical trials.

New Horizons in Therapeutic Antibody Discovery

Antibody drugs have become an increasingly significant component of the therapeutic landscape. Their success has been driven by some of their unique properties, in particular their very high specificity and selectivity, in contrast to the off-target liabilities of small molecules (SMs). Antibodies can bring additional functionality to the table with their ability to interact with the immune system, and this can be further manipulated with advances in antibody engineering. This review summarizes what antibody therapeutics have achieved to date and what opportunities and challenges lie ahead. The target landscape for large molecules (LMs) versus SMs and some of the challenges for antibody drug development are discussed. Effective penetration of membrane barriers and intracellular targeting is one challenge, particularly across the highly resistant blood-brain barrier. The expanding pipeline of antibody-drug conjugates offers the potential to combine SM and LM modalities in a variety of creative ways, and antibodies also offer exciting potential to build bi- and multispecific molecules. The ability to pursue more challenging targets can also be further exploited but highlights the need for earlier screening in functional cell-based assays. I discuss how this might be addressed given the practical constraints imposed by high-throughput screening sample type and process differences in antibody primary screening.

Immune-based therapies in pancreatic and colorectal cancers and biomarkers of responsiveness

Immune-based strategies are the most promising treatments to improve cancer disease control. Early clinical trials are ongoing to test the safety and feasibility of immune-based therapies for gastrointestinal cancers. However, to date, immunotherapy has been only an experimental option for these diseases and a better understanding of their molecular, cellular, structural and clinical dissimilarities is crucial in the generation of tailored immunotherapeutic treatments. In this review, we will summarize the key mechanisms that regulate the action of immune system in cancer and the different immune-based approaches aimed at improving disease control in patients with advanced disease. We will then move on to discussing the current immunotherapeutic approaches in two types of gastrointestinal (colo-rectal and pancreatic) cancers, whose immune microenvironment has been lately object of intense analyses and has emerged as an important determinant of clinical outcome.