Bispecific antibody platforms for cancer immunotherapy

Expanding horizons in cancer therapy by immunoconjugates targeting tumor microenvironments

Immunoconjugates are promising molecules combining antibodies with different agents, such as toxins, drugs, radionuclides, or cytokines that primarily aim to target tumor cells. However, tumor microenvironment (TME), which comprises a complex network of various cells and molecular cues guiding tumor growth and progression, remains a major challenge for effective cancer therapy. Our review underscores the pivotal role of TME in cancer therapy with immunoconjugates, examining the intricate interactions with TME and recent advancements in TME-targeted immunoconjugates. We explore strategies for targeting TME components, utilizing diverse antibodies such as neutralizing, immunomodulatory, immune checkpoint inhibitors, immunostimulatory, and bispecific antibodies. Additionally, we discuss different immunoconjugates, elucidating their mechanisms of action, advantages, limitations, and applications in cancer immunotherapy. Furthermore, we highlight emerging technologies enhancing the safety and efficacy of immunoconjugates, such as antibody engineering, combination therapies, and nanotechnology. Finally, we summarize current advancements, perspectives, and future developments of TME-targeted immunoconjugates.

Bispecific antibody targeting TGF-β and PD-L1 for synergistic cancer immunotherapy

The PD-1/PD-L1 signaling pathway plays a crucial role in cancer immune evasion, and the use of anti-PD-1/PD-L1 antibodies represents a significant milestone in cancer immunotherapy. However, the low response rate observed in unselected patients and the development of therapeutic resistance remain major obstacles to their clinical application. Accumulating studies showed that overexpressed TGF-β is another immunosuppressive factor apart from traditional immune checkpoints. Actually, the effects of PD-1 and TGF-β pathways are independent and interactive, which work together contributing to the immune evasion of cancer cell. It has been verified that blocking TGF-β and PD-L1 simultaneously could enhance the efficacy of PD-L1 monoclonal antibody and overcome its treatment resistance. Based on the bispecific antibody or fusion protein technology, multiple bispecific and bifunctional antibodies have been developed. In the preclinical and clinical studies, these updated antibodies exhibited potent anti-tumor activity, superior to anti-PD-1/PD-L1 monotherapies. In the review, we summarized the advances of bispecific antibodies targeting TGF-β and PD-L1 in cancer immunotherapy. We believe these next-generation immune checkpoint inhibitors would substantially alter the cancer treatment paradigm, especially in anti-PD-1/PD-L1-resistant patients.

Bispecific Antibodies: A Novel Approach for the Treatment of Solid Tumors

Advancement in sequencing technologies allows for the identification of molecular pathways involved in tumor progression and treatment resistance. Implementation of novel agents targeting these pathways, defined as targeted therapy, significantly improves the prognosis of cancer patients. Targeted therapy also includes the use of monoclonal antibodies (mAbs). These drugs recognize specific oncogenic proteins expressed in cancer cells. However, as with many other types of targeting agents, mAb-based therapy usually fails in the long-term control of cancer progression due to the development of resistance. In many cases, resistance is caused by the activation of alternative pathways involved in cancer progression and the development of immune evasion mechanisms. To overcome this off-target resistance, bispecific antibodies (bsAbs) were developed to simultaneously target differential oncogenic pathway components, tumor-associated antigens (TAA) and immune regulatory molecules. As a result, in the last few years, several bsAbs have been tested or are being tested in cancer patients. A few of them are currently approved for the treatment of some hematologic malignancies but no bsAbs are approved in solid tumors. In this review, we will provide an overview of the state-of-the-art of bsAbs for the treatment of solid malignancies outlining their classification, design, main technologies utilized for production, mechanisms of action, updated clinical evidence and potential limitations.

Recent advances and challenges of bispecific antibodies in solid tumors

Cancer immunotherapy has made remarkable progress in the past decade. Bispecific antibodies (BsAbs) have acquired much attention as the next generation strategy of antibody-target cancer immunotherapy, which overwhelmingly focus on T cell recruitment and dual receptors blockade. So far, BsAb drugs have been proved clinically effective and approved for the treatment of hematologic malignancies, but no BsAb have been approved in solid tumors. Numerous designed BsAb drugs for solid tumors are now undergoing evaluation in clinical trials. In this review, we will introduce the formats of bispecific antibodies, and then update the latest preclinical studies and clinical trials in solid tumors of BsAbs targeting EpCAM, CEA, PMSA, ErbB family, and so on. Finally, we discuss the BsAb-related adverse effects and the alternative strategy for future study.

A new approach to produce IgG4-like bispecific antibodies

While achieving rapid developments in recent years, bispecific antibodies are still difficult to design and manufacture, due to mispair of both heavy and light chains. Here we report a novel technology to make bispecific molecules. The knob-into-hole method was used to pair two distinct heavy chains as a heterodimer. IgG₄ S228P CH1-CL interface was then partially replaced by T-cell receptor α/β constant domain to increase the efficiency of cognate heavy and light chain pairing. Following expression and purification, the bispecific antibody interface exchange was confirmed by Western blotting and LC–MS/MS. To ensure its validity, we combined a monovalent bispecific antibody against PD-1 (sequence from Pembrolizumab) and LAG3 (sequence from Relatlimab). The results showed that the molecule could be assembled correctly at a ratio of 95% in cells. In vitro functional assay demonstrated that the purified bispecific antibody exhibits an enhanced agonist activity compared to that of the parental antibodies. Low immunogenicity was predicted by an open-access software and ADA test.

Elimination of SHIV Infected Cells by Combinations of Bispecific HIVxCD3 DART® Molecules

Bispecific HIVxCD3 DART molecules that co-engage the viral envelope glycoprotein (Env) on HIV-1-infected cells and the CD3 receptor on CD3+ T cells are designed to mediate the cytolysis of HIV-1-infected, Env-expressing cells. Using a novel ex vivo system with cells from rhesus macaques (RMs) infected with a chimeric Simian-Human Immunodeficiency Virus (SHIV) CH505 and maintained on ART, we tested the ability of HIVxCD3 DART molecules to mediate elimination of in vitro-reactivated CD4+ T cells in the absence or presence of autologous CD8+ T cells. HIVxCD3 DART molecules with the anti-HIV-1 Env specificities of A32 or 7B2 (non-neutralizing antibodies) or PGT145 (broadly neutralizing antibody) were evaluated individually or combined. DART molecule-mediated antiviral activity increased significantly in the presence of autologous CD8+ T cells. In this ex vivo system, the PGT145 DART molecule was more active than the 7B2 DART molecule, which was more active than the A32 DART molecule. A triple combination of the DART molecules exceeded the activity of the individual PGT145 DART molecule. Modified quantitative virus outgrowth assays confirmed the ability of the DART molecules to redirect RM CD3+ T cells to eliminate SHIV-infected RM CD4+ T cells as demonstrated by the decreased propagation of in vitro infection by the infected cells pre-incubated with DART molecules in presence of effector CD8+ T cells. While mediating cytotoxic activity, DART molecules did not increase proinflammatory cytokine production. In summary, combination of HIVxCD3 DART molecules that have broadly-neutralizing and non-neutralizing anti-HIV-1 Env specificities can leverage the host immune system for treatment of HIV-1 infection but will require appropriate reactivation of the latent reservoir.

Preclinical Evaluation of 89Zr-Df-IAB22M2C PET as an Imaging Biomarker for the Development of the GUCY2C-CD3 Bispecific PF-07062119 as a T Cell Engaging Therapy

Purpose

A sensitive and specific imaging biomarker to monitor immune activation and quantify pharmacodynamic responses would be useful for development of immunomodulating anti-cancer agents. PF-07062119 is a T cell engaging bispecific antibody that binds to CD3 and guanylyl cyclase C, a protein that is over-expressed by colorectal cancers. Here, we used ⁸⁹Zr-Df-IAB22M2C (⁸⁹Zr-Df-Crefmirlimab), a human CD8-specific minibody to monitor CD8+ T cell infiltration into tumors by positron emission tomography. We investigated the ability of ⁸⁹Zr-Df-IAB22M2C to track anti-tumor activity induced by PF-07062119 in a human CRC adoptive transfer mouse model (with injected activated/expanded human T cells), as well as the correlation of tumor radiotracer uptake with CD8+ immunohistochemical staining.

Procedures

NOD SCID gamma mice bearing human CRC LS1034 tumors were treated with four different doses of PF-07062119, or a non-targeted CD3 BsAb control, and imaged with ⁸⁹Zr-Df-IAB22M2C PET at days 4 and 9. Following PET/CT imaging, mice were euthanized and dissected for ex vivo distribution analysis of ⁸⁹Zr-Df-IAB22M2C in tissues on days 4 and 9, with additional data collected on day 6 (supplementary). Data were analyzed and reported as standard uptake value and %ID/g for in vivo imaging and ex vivo tissue distribution. In addition, tumor tissues were evaluated by immunohistochemistry for CD8+ T cells.

Results

The results demonstrated substantial mean uptake of ⁸⁹Zr-Df-IAB22M2C (%ID/g) in PF-07062119-treated tumors, with significant increases in comparison to non-targeted BsAb-treated controls, as well as PF-07062119 dose-dependent responses over time of treatment. A moderate correlation was observed between tumor tissue radioactivity uptake and CD8+ cell density, demonstrating the value of the imaging agent for non-invasive assessment of intra-tumoral CD8+ T cells and the mechanism of action for PF-07062119.

Conclusion

Immune-imaging technologies for quantitative cellular measures would be a valuable biomarker in immunotherapeutic clinical development. We demonstrated a qualification of ⁸⁹Zr-IAB22M2C PET to evaluate PD responses (mice) to a novel immunotherapeutic.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11307-021-01621-0.

HDP-101, an Anti-BCMA Antibody-Drug Conjugate, Safely Delivers Amanitin to Induce Cell Death in Proliferating and Resting Multiple Myeloma Cells

Despite major treatment advances in recent years, patients with multiple myeloma inevitably relapse. The RNA polymerase II complex has been identified as a promising therapeutic target in both proliferating and dormant cancer cells. Alpha-amanitin, a toxin so far without clinical application due to high liver toxicity, specifically inhibits this complex. Here, we describe the development of HDP-101, an anti-B-cell maturation antigen (BCMA) antibody conjugated with an amanitin derivative. HDP-101 displayed high efficacy against both proliferating and resting myeloma cells in vitro, sparing BCMA-negative cells. In subcutaneous and disseminated murine xenograft models, HDP-101 induced tumor regression at low doses, including durable complete remissions after a single intravenous dose. In cynomolgus monkeys, HDP-101 was well tolerated with a promising therapeutic index. In conclusion, HDP-101 safely and selectively delivers amanitin to myeloma cells and provides a novel therapeutic approach to overcome drug resistance in this disease.

Engineering antibody-based molecules for HIV treatment and cure

PURPOSE OF REVIEW

Immunotherapy strategies alternative to current antiretroviral therapies will need to address viral diversity while increasing the immune system's ability to efficiently target the latent virus reservoir. Antibody-based molecules can be designed based on broadly neutralizing and non-neutralizing antibodies that target free virions and infected cells. These multispecific molecules, either by IgG-like or non-IgG-like in structure, aim to target several independent HIV-1 epitopes and/or engage effector cells to eliminate the replicating virus and infected cells. This detailed review is intended to stimulate discussion on future requirements for novel immunotherapeutic molecules.

RECENT FINDINGS

Bispecific and trispecific antibodies are engineered as a single molecules to target two or more independent epitopes on the HIV-1 envelope (Env). These antibody-based molecules have increased avidity for Env, leading to improved neutralization potency and breadth compared with single parental antibodies. Furthermore, bispecific and trispecific antibodies that engage cellular receptors with one arm of the molecule help concentrate inhibitory molecules to the sites of potential infection and facilitate engagement of immune effector cells and Env-expressing target cells for their elimination.

SUMMARY

Recently engineered antibody-based molecules of different sizes and structures show promise in vitro or in vivo and are encouraging candidates for HIV treatment.

Impact and Intricacies of Bone Marrow Microenvironment in B-cell Lymphomas: From Biology to Therapy

Lymphoma, a group of widely prevalent hematological malignancies of lymphocyte origin, has become the focus of significant clinical research due to their high propensity for refractory/relapsed (R/R) disease, leading to poor prognostic outcomes. The complex molecular circuitry in lymphomas, especially in the aggressive phenotypes, has made it difficult to find a therapeutic option that can salvage R/R disease. Furthermore, the association of lymphomas with the Bone Marrow (BM) microenvironment has been found to portend worse outcomes in terms of heightened chances of relapse and acquired resistance to chemotherapy. This review assesses the current therapy options in three distinct types of lymphomas: diffuse large B-cell lymphoma, follicular lymphoma and mantle cell lymphoma. It also explores the role of the BM tumor microenvironment as a secure 'niche' for lymphoma cells to grow, proliferate and survive. It further evaluates potential mechanisms through which the tumor cells can establish molecular connections with the BM cells to provide pro-tumor benefits, and discusses putative therapeutic strategies for disrupting the BM-lymphoma cell communication.

Tumor immune microenvironment modulation-based drug delivery strategies for cancer immunotherapy

The past years have witnessed promising clinical feedback for anti-cancer immunotherapies, which have become one of the hot research topics; however, they are limited by poor delivery kinetics, narrow patient response profiles, and systemic side effects. To the best of our knowledge, the development of cancer is highly associated with the immune system, especially the tumor immune microenvironment (TIME). Based on the comprehensive understanding of the complexity and diversity of TIME, drug delivery strategies focused on the modulation of TIME can be of great significance for directing and improving cancer immunotherapy. This review highlights the TIME modulation in cancer immunotherapy and summarizes the versatile TIME modulation-based cancer immunotherapeutic strategies, medicative principles and accessory biotechniques for further clinical transformation. Remarkably, the recent advances of cancer immunotherapeutic drug delivery systems and future prospects of TIME modulation-based drug delivery systems for much more controlled and precise cancer immunotherapy will be emphatically discussed.

Overview of Targeted Drugs for Mature B-Cell Non-hodgkin Lymphomas

The improved knowledge of pathogenetic mechanisms underlying lymphomagenesis and the discovery of the critical role of tumor microenvironments have enabled the design of new drugs against cell targets and pathways. The Food and Drug Administration (FDA) has approved several monoclonal antibodies (mAbs) and small molecule inhibitors (SMIs) for targeted therapy in hematology. This review focuses on the efficacy results of the currently available targeted agents and recaps the main ongoing trials in the setting of mature B-Cell non-Hodgkin lymphomas. The objective is to summarize the different classes of novel agents approved for mature B-cell lymphomas, to describe in synoptic tables the results they achieved and, finally, to draw future scenarios as we glimpse through the ongoing clinical trials. Characteristics and therapeutic efficacy are summarized for the currently approved mAbs [i.e., anti-Cluster of differentiation (CD) mAbs, immune checkpoint inhibitors, chimeric antigen receptor (CAR) T-cell therapy, and bispecific antibodies] as well as for SMIs i.e., inhibitors of B-cell receptor signaling, proteasome, mTOR BCL-2 HDAC pathways. The biological disease profiling of B-cell lymphoma subtypes may foster the discovery of innovative drug strategies for improving survival outcome in lymphoid neoplasms, as well as the trade-offs between efficacy and toxicity. The hope for clinical advantages should carefully be coupled with mindful awareness of the potential pitfalls and the occurrence of uneven, sometimes severe, toxicities.

A Translational Quantitative Systems Pharmacology Model for CD3 Bispecific Molecules: Application to Quantify T Cell-Mediated Tumor Cell Killing by P-Cadherin LP DART®

CD3 bispecific antibody constructs recruit cytolytic T cells to kill tumor cells, offering a potent approach to treat cancer. T cell activation is driven by the formation of a trimolecular complex (trimer) between drugs, T cells, and tumor cells, mimicking an immune synapse. A translational quantitative systems pharmacology (QSP) model is proposed for CD3 bispecific molecules capable of predicting trimer concentration and linking it to tumor cell killing. The model was used to quantify the pharmacokinetic (PK)/pharmacodynamic (PD) relationship of a CD3 bispecific targeting P-cadherin (PF-06671008). It describes the disposition of PF-06671008 in the central compartment and tumor in mouse xenograft models, including binding to target and T cells in the tumor to form the trimer. The model incorporates T cell distribution to the tumor, proliferation, and contraction. PK/PD parameters were estimated for PF-06671008 and a tumor stasis concentration (TSC) was calculated as an estimate of minimum efficacious trimer concentration. TSC values ranged from 0.0092 to 0.064 pM across mouse tumor models. The model was translated to the clinic and used to predict the disposition of PF-06671008 in patients, including the impact of binding to soluble P-cadherin. The predicted terminal half-life of PF-06671008 in the clinic was approximately 1 day, and P-cadherin expression and number of T cells in the tumor were shown to be sensitive parameters impacting clinical efficacy. A translational QSP model is presented for CD3 bispecific molecules, which integrates in silico, in vitro and in vivo data in a mechanistic framework, to quantify and predict efficacy across species.

A review of bispecific antibodies and antibody constructs in oncology and clinical challenges

Bispecific antibodies (bsAbs) are antibodies that bind two distinct epitopes to cancer.. For use in oncology, one bsAb has been approved and 57 bsAbs are in clinical trials, none of which has reached phase 3. These bsAbs show great variability in design and mechanism of action. The various designs are often linked to the mechanisms of actions. The majority of bsAbs engage immune cells to destroy tumor cells. However, some bsAbs are also used to deliver payloads to tumors or to block tumor signaling pathways. This review provides insight into the choice of construct for bsAbs, summarizes the clinical development of bsAbs in oncology and identifies subsequent challenges.

Enhancing bioactivity, physicochemical, and pharmacokinetic properties of a nano-sized, anti-VEGFR2 Adnectin, through PASylation technology

The crucial role of VEGF receptor 2 (VEGFR2) signaling in the angiogenesis and metastasis of solid tumors has prompted the development of inhibitors with minimal bystander effects. Recently, Adnectin C has attracted attention for cancer treatment. To overcome the problematic properties of Adnectin, a novel form of Adnectin C has been designed by its fusion to a biodegradable polymeric peptide containing Pro/Ala/Ser (PAS) repetitive residues. E. coli-expressed recombinant fused and unfused proteins were compared in terms of bioactivity, physicochemical, and pharmacokinetic properties using standard methods. Dynamic light scattering (DLS) analysis of PASylated adnectin C revealed an approximate 2-fold increase in particle size with a slight change in the net charge. Additionally, fusion of the PAS sequence improved its stability against the growth of thermo-induced aggregated forms. The high receptor-binding and improved binding kinetic parameters of PASylated Adnectin C was confirmed by ELISA and surface plasmon resonance assays, respectively. Pharmacokinetic studies showed a noticeable increase in the terminal half-life of Adnectin C-PAS#1(200) by a factor of 4.57 after single dose by intravenous injection into female BALB/c mice. The results suggest that PASylation could offer a superior delivery strategy for developing Adnectin-derived drugs with improved patient compliance.

Immunoglobulin Gamma-Like Therapeutic Bispecific Antibody Formats for Tumor Therapy

Bispecific antibodies (BsAbs) are a sort of dual functional proteins with specific binding to two distinct targets, which have become a focus of interest in antibody engineering and drug development research and have a promising future for wide applications in cancer immunotherapy and autoimmune disease. The key of clinical application and commercial-scale manufacturing of BsAbs is the amenability to assembly and purification of desired heterodimers. Advances in genetic engineering technology had resulted in the development of diverse BsAbs. Multiple recombinant strategies have been used to solve the mispairing problem between light and heavy chains, as well as to enforce accurate dimerization of heterologous heavy chains. There are 23 platforms available to generate 62 BsAbs which can be further divided into IgG-like ones and fragment-based ones, and more than 50 molecules are undergoing clinical trials currently. BsAbs with IgG-like architecture exhibit superior advantages in structure (similar to natural antibodies), pharmacokinetics, half-life, FcR-mediated function, and biological activity. This review considers various IgG-like BsAb generation approaches, summarizes the clinical applications of promising new BsAbs, and describes the mechanism of BsAbs in tumor therapy.

Site-specific PEGylation of an anti-CEA/CD3 bispecific antibody improves its antitumor efficacy

Introduction

Bispecific antibodies that engage immune cells to kill cancer cells are actively pursued in cancer immunotherapy. Different types of bispecific antibodies, including single-chain fragments, Fab fragments, nanobodies, and immunoglobulin Gs (IgGs), have been studied. However, the low molecular weight of bispecific antibodies with single-chain or Fab fragments generally leads to their rapid clearance in vivo, which limits the therapeutic potential of these bispecific antibodies.

Materials and methods

In this study, we used a site-specific PEGylation strategy to modify the bispecific single-domain antibody-linked Fab (S-Fab), which was designed by linking an anticarcinoembryonic antigen (anti-CEA) nanobody with an anti-CD3 Fab.

Results

The half-life (t_1/2) of PEGylated S-Fab (polyethylene glycol-S-Fab) was increased 12-fold in vivo with a slightly decreased tumor cell cytotoxicity in vitro as well as more potent tumor growth inhibition in vivo compared to S-Fab.

Conclusion

This study demonstrated that PEGylation is an effective approach to enhance the antitumor efficacy of bispecific antibodies.

CD47 is a novel potent immunotherapy target in human malignancies: current studies and future promises

Recently, many immunosuppressive checkpoints such as PD-L1, CTLA-4 and CD47, were identified in succession and serve as potential immunotherapy targets in human cancers. Among them, CD47, a 'marker-of-self' protein that is overexpressed broadly across tumor types, is emerging as a novel potent macrophage immune checkpoint for cancer immunotherapy. In this review, we highlight the prominent role of CD47 as a 'don't-eat-me' signal that inhibits macrophage phagocytosis for immune evasion of a tumor and presents the opportunities and challenges for CD47 inhibitors both as monotherapy and in combination treatments for hematological cancers and solid tumors; some of these agents are currently in clinical trials.

Recombinant Antibody Fragments for Neurodegenerative Diseases

BACKGROUND

Recombinant antibody fragments are promising alternatives to full-length immunoglobulins and offer important advantages compared with conventional monoclonal antibodies: extreme specificity, higher affinity, superior stability and solubility, reduced immunogenicity as well as easy and inexpensive large-scale production.

OBJECTIVE

In this article we will review and discuss recombinant antibodies that are being evaluated for neurodegenerative diseases in pre-clinical models and in clinical studies and will summarize new strategies that are being developed to optimize their stability, specificity and potency for advancing their use.

METHODS

Articles describing recombinant antibody fragments used for neurological diseases were selected (PubMed) and evaluated for their significance.

RESULTS

Different antibody formats such as single-chain fragment variable (scFv), single-domain antibody fragments (VHHs or sdAbs), bispecific antibodies (bsAbs), intrabodies and nanobodies, are currently being studied in pre-clinical models of cancer as well as infectious and autoimmune diseases and many of them are being tested as therapeutics in clinical trials. Immunotherapy approaches have shown therapeutic efficacy in several animal models of Alzheimer´s disease (AD), Parkinson disease (PD), dementia with Lewy bodies (DLB), frontotemporal dementia (FTD), Huntington disease (HD), transmissible spongiform encephalopathies (TSEs) and multiple sclerosis (MS). It has been demonstrated that recombinant antibody fragments may neutralize toxic extra- and intracellular misfolded proteins involved in the pathogenesis of AD, PD, DLB, FTD, HD or TSEs and may target toxic immune cells participating in the pathogenesis of MS.

CONCLUSION

Recombinant antibody fragments represent a promising tool for the development of antibody-based immunotherapeutics for neurodegenerative diseases.

Human Tumor Antigens Yesterday, Today, and Tomorrow

The question of whether human tumors express antigens that can be recognized by the immune system has been answered with a resounding YES. Most were identified through spontaneous antitumor humoral and cellular immune responses found in cancer patients and include peptides, glycopeptides, phosphopeptides, viral peptides, and peptides resulting from common mutations in oncogenes and tumor-suppressor genes, or common gene fusion events. Many have been extensively tested as candidates for anticancer vaccines. More recently, attention has been focused on the potentially large number of unique tumor antigens, mutated neoantigens, that are the predicted products of the numerous mutations revealed by exome sequencing of primary tumors. Only a few have been confirmed as targets of spontaneous immunity and immunosurveillance, and even fewer have been tested in preclinical and clinical settings. The field has been divided for a long time on the relative importance of shared versus mutated antigens in tumor surveillance and as candidates for vaccines. This question will eventually need to be answered in a head to head comparison in well-designed clinical trials. One advantage that shared antigens have over mutated antigens is their potential to be used in vaccines for primary cancer prevention. Cancer Immunol Res; 5(5); 347-54. ©2017 AACR.

A CD3-bispecific molecule targeting P-cadherin demonstrates T cell-mediated regression of established solid tumors in mice

Strong evidence exists supporting the important role T cells play in the immune response against tumors. Still, the ability to initiate tumor-specific immune responses remains a challenge. Recent clinical trials suggest that bispecific antibody-mediated retargeted T cells are a promising therapeutic approach to eliminate hematopoietic tumors. However, this approach has not been validated in solid tumors. PF-06671008 is a dual-affinity retargeting (DART®)-bispecific protein engineered with enhanced pharmacokinetic properties to extend in vivo half-life, and designed to engage and activate endogenous polyclonal T cell populations via the CD3 complex in the presence of solid tumors expressing P-cadherin. This bispecific molecule elicited potent P-cadherin expression-dependent cytotoxic T cell activity across a range of tumor indications in vitro, and in vivo in tumor-bearing mice. Regression of established tumors in vivo was observed in both cell line and patient-derived xenograft models engrafted with circulating human T lymphocytes. Measurement of in vivo pharmacodynamic markers demonstrates PF-06671008-mediated T cell activation, infiltration and killing as the mechanism of tumor inhibition.

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.

Immunotherapy for breast cancer: past, present, and future

Immunotherapy has shown promise in many solid tumors including melanoma and non-small cell lung cancer with an evolving role in breast cancer. Immunotherapy encompasses a wide range of therapies including immune checkpoint inhibition, monoclonal antibodies, bispecific antibodies, vaccinations, antibody-drug conjugates, and identifying other emerging interventions targeting the tumor microenvironment. Increasing efficacy of these treatments in breast cancer patients requires identification of better biomarkers to guide patient selection; recognizing when to initiate these therapies in multi-modality treatment plans; establishing novel assays to monitor immune-mediated responses; and creating combined systemic therapy options incorporating conventional treatments such as chemotherapy and endocrine therapy. This review will focus on the current role and future directions of many of these immunotherapies in breast cancer, as well as highlighting clinical trials that are investigating several of these active issues.

A bispecific nanobody approach to leverage the potent and widely applicable tumor cytolytic capacity of Vγ9Vδ2-T cells

Though Vγ9Vδ2-T cells constitute only a small fraction of the total T cell population in human peripheral blood, they play a vital role in tumor defense and are therefore of major interest to explore for cancer immunotherapy. Vγ9Vδ2-T cell-based cancer immunotherapeutic approaches developed so far have been generally well tolerated and were able to induce significant clinical responses. However, overall results were inconsistent, possibly due to the fact that these strategies induced systemic activation of Vγ9Vδ2-T cells without preferential accumulation and targeted activation in the tumor. Here we show that a novel bispecific nanobody-based construct targeting both Vγ9Vδ2-T cells and EGFR induced potent Vγ9Vδ2-T cell activation and subsequent tumor cell lysis both in vitro and in an in vivo mouse xenograft model. Tumor cell lysis was independent of KRAS and BRAF tumor mutation status and common Vγ9Vδ2-T cell receptor sequence variations. In combination with the conserved monomorphic nature of the Vγ9Vδ2-TCR and the facile replacement of the tumor-specific nanobody, this immunotherapeutic approach can be applied to a large group of cancer patients.

Antibody or Antibody Fragments: Implications for Molecular Imaging and Targeted Therapy of Solid Tumors

The use of antibody-based therapeutics has proven very promising for clinical applications in cancer patients, with multiple examples of antibodies and antibody–drug conjugates successfully applied for the treatment of solid tumors and lymphomas. Given reported recurrence rates, improvements are clearly still necessary. A major factor limiting the efficacy of antibody-targeted cancer therapies may be the incomplete penetration of the antibody or antibody–drug conjugate into the tumor. Incomplete tumor penetration also affects the outcome of molecular imaging, when using such targeting agents. From the injection site until they arrive inside the tumor, targeting molecules are faced with several barriers that impact intratumoral distribution. The primary means of antibody transport inside tumors is based on diffusion. The diffusive penetration inside the tumor is influenced by both antibody properties, such as size and binding affinity, as well as tumor properties, such as microenvironment, vascularization, and targeted antigen availability. Engineering smaller antibody fragments has shown to improve the rate of tumor uptake and intratumoral distribution. However, it is often accompanied by more rapid clearance from the body and in several cases also by inherent destabilization and reduction of the binding affinity of the antibody. In this perspective, we discuss different cancer targeting approaches based on antibodies or their fragments. We carefully consider how their size and binding properties influence their intratumoral uptake and distribution, and how this may affect cancer imaging and therapy of solid tumors.

Blinatumomab, a Bispecific T-cell Engager (BiTE(®)) for CD-19 Targeted Cancer Immunotherapy: Clinical Pharmacology and Its Implications

BACKGROUND AND OBJECTIVES

Blinatumomab is a bispecific T-cell engager (BiTE(®)) antibody construct that transiently links CD19-positive B cells to CD3-positive T cells, resulting in induction of T-cell-mediated serial lysis of B cells and concomitant T-cell proliferation. Blinatumomab showed anti-leukemia activity in clinical trials and was approved by the US Food and Drug Administration for the treatment of Philadelphia chromosome-negative relapsed/refractory B-cell precursor acute lymphoblastic leukemia (r/r ALL). The objectives of this work were to characterize blinatumomab pharmacokinetics and pharmacodynamics and to evaluate dosing regimens.

METHODS

Data from six phase I and II trials in patients with r/r ALL, minimal residual disease-positive ALL, and non-Hodgkin's lymphoma (NHL) were analyzed. Blinatumomab pharmacokinetics was characterized by non-compartmental and population pharmacokinetic analyses and pharmacodynamics was described graphically.

RESULTS

Blinatumomab exhibited linear pharmacokinetics under continuous intravenous infusion for 4-8 weeks per cycle over a dose range of 5-90 µg/m(2)/day, without target-mediated disposition. Estimated mean (standard deviation) volume of distribution, clearance, and elimination half-life were 4.52 (2.89) L, 2.72 (2.71) L/h, and 2.11 (1.42) h, respectively. Pharmacokinetics was similar in patients with ALL and NHL and was not affected by patient demographics, supporting fixed dosing in adults. Although creatinine clearance was a significant covariate of drug clearance, no dose adjustment was required in patients with mild or moderate renal impairment. Incidence of neutralizing antidrug antibodies was <1 %. Blinatumomab pharmacodynamics featured T-cell redistribution and activation, B-cell depletion, and transient dose-dependent cytokine elevation. Blinatumomab did not affect cytochrome P450 enzymes directly; cytokines may trigger transient cytochrome P450 suppression with low potential for inducing drug interactions.

CONCLUSIONS

Blinatumomab has unique pharmacokinetic and immunological features that require indication-dependent dosing regimens. Stepped dosing is required to achieve adequate efficacy and minimize cytokine release in diseases with high tumor burden.

Checkpoint Inhibitors and Other Immune Therapies for Hodgkin and Non-Hodgkin Lymphoma

OPINION STATEMENT

Treatment for relapsed/refractory (R/R) Hodgkin and non-Hodgkin lymphoma remains challenging. The introduction of rituximab to B cell non-Hodgkin lymphoma (B-NHL) treatment significantly improved patients' response rate and survival; however, approximately one third of patients with diffuse large B cell lymphoma, the most common B-NHL subtype, still have a relapse or become refractory after first-line therapy. More recently, antibody therapies and small-molecule inhibitors were approved for treating R/R lymphomas; these agents include brentuximab vedotin, ibrutinib, and idelalisib. Immune checkpoint inhibitors and other immune therapies are emerging treatments currently being evaluated in various clinical trials for their efficacy against lymphoid malignancies. Striking results from these treatment modalities have been observed in solid tumors, and evidence is accumulating to support their use in various lymphomas. The most exciting results from immune checkpoint inhibitor therapy have been seen in patients with R/R Hodgkin lymphoma, in whom the overall response rate has reached 60-80 %. Results in NHL are more similar to those seen in other solid malignancies, ranging between 20 and 40 %, depending on the histology. Formal approval of these drugs is being awaited, as are the results of combination therapy with checkpoint inhibitors and other treatment modalities, including conventional chemotherapy, small-molecule inhibitors, and other immune therapies. Although response rates have been promising, attention must be paid to the management of unique immune-related adverse events, which warrant close monitoring in some cases. Identification of biomarkers that predict response or severe adverse events using either the tumor specimen or peripheral blood would aid in selecting patients suited for these types of treatment as well as determining the ideal sequence of treatment within the realm of immune therapies.

BiHC, a T-Cell-Engaging Bispecific Recombinant Antibody, Has Potent Cytotoxic Activity Against Her2 Tumor Cells

Among different cancer immunotherapy approaches, bispecific antibodies (BsAbs) are of great interest due to their ability to recruit immune cells to kill tumor cells directly. Various BsAbs against Her2 tumor cells have been proposed with potent cytotoxic activities. However, most of these formats require extensive processing to obtain heterodimeric bispecific antibodies. In this study, we describe a bispecific antibody, BiHC (bispecific Her2-CD3 antibody), constructed with a single-domain anti-Her2 and a single-chain Fv (variable fragment) of anti-CD3 in an IgG-like format. In contrast to most IgG-like BsAbs, the two arms in BiHC have different molecular weights, making it easier to separate hetero- or homodimers. BiHC can be expressed in Escherichia coli and purified via Protein A affinity chromatography. The purified BiHC can recruit T cells and induce specific cytotoxicity of Her2-expressing tumor cells in vitro. The BiHC can also efficiently inhibit the tumor growth in vivo. Thus, BiHC is a promising candidate for the treatment of Her2-positive cancers.

Generation and characterization of CD1d-specific single-domain antibodies with distinct functional features

Ligation of the CD1d antigen-presenting molecule by monoclonal antibodies (mAbs) can trigger important biological functions. For therapeutic purposes camelid-derived variable domain of heavy-chain-only antibodies (VHH) have multiple advantages over mAbs because they are small, stable and have low immunogenicity. Here, we generated 21 human CD1d-specific VHH by immunizing Lama glama and subsequent phage display. Two clones induced maturation of dendritic cells, one clone induced early apoptosis in CD1d-expressing B lymphoblasts and multiple myeloma cells, and another clone blocked recognition of glycolipid-loaded CD1d by CD1d-restricted invariant natural killer T (iNKT) cells. In contrast to reported CD1d-specific mAbs, these CD1d-specific VHH have the unique characteristic that they induce specific and well-defined biological effects. This feature, combined with the above-indicated general advantages of VHH, make the CD1d-specific VHH generated here unique and useful tools to exploit both CD1d ligation as well as disruption of CD1d-iNKT interactions in the treatment of cancer or inflammatory disorders.

Antibodies Create Killer Bonds in Myeloma

In this issue of Cancer Cell, Li et al. and Seckinger et al. describe promising results of two T-cell-dependent bi-specific antibodies for the treatment of multiple myeloma: one targets FcRH5 expressed on B cells, whereas the other targets the B cell maturation antigen expressed on plasma cells.

Target Expression, Generation, Preclinical Activity, and Pharmacokinetics of the BCMA-T Cell Bispecific Antibody EM801 for Multiple Myeloma Treatment

We identified B cell maturation antigen (BCMA) as a potential therapeutic target in 778 newly diagnosed and relapsed myeloma patients. We constructed an IgG-based BCMA-T cell bispecific antibody (EM801) and showed that it increased CD3⁺ T cell/myeloma cell crosslinking, followed by CD4⁺/CD8⁺ T cell activation, and secretion of interferon-γ, granzyme B, and perforin. This effect is CD4 and CD8 T cell mediated. EM801 induced, at nanomolar concentrations, myeloma cell death by autologous T cells in 34 of 43 bone marrow aspirates, including those from high-risk patients and patients after multiple lines of treatment, tumor regression in six of nine mice in a myeloma xenograft model, and depletion of BCMA⁺ cells in cynomolgus monkeys. Pharmacokinetics and pharmacodynamics indicate weekly intravenous/subcutaneous administration.

Beyond checkpoint inhibition - Immunotherapeutical strategies in combination with radiation

The revival of cancer immunotherapy has taken place with the clinical success of immune checkpoint inhibition. However, the spectrum of immunotherapeutic approaches is much broader encompassing T cell engaging strategies, tumour-specific vaccination, antibodies or immunocytokines. This review focuses on the immunological effects of irradiation and the evidence available on combination strategies with immunotherapy. The available data suggest great potential of combined treatments, yet also poses questions about dose, fractionation, timing and most promising multimodal strategies.

Prevention of Vγ9Vδ2 T Cell Activation by a Vγ9Vδ2 TCR Nanobody

Vγ9Vδ2 T cell activation plays an important role in antitumor and antimicrobial immune responses. However, there are conditions in which Vγ9Vδ2 T cell activation can be considered inappropriate for the host. Patients treated with aminobisphosphonates for hypercalcemia or metastatic bone disease often present with a debilitating acute phase response as a result of Vγ9Vδ2 T cell activation. To date, no agents are available that can clinically inhibit Vγ9Vδ2 T cell activation. In this study, we describe the identification of a single domain Ab fragment directed to the TCR of Vγ9Vδ2 T cells with neutralizing properties. This variable domain of an H chain-only Ab (VHH or nanobody) significantly inhibited both phosphoantigen-dependent and -independent activation of Vγ9Vδ2 T cells and, importantly, strongly reduced the production of inflammatory cytokines upon stimulation with aminobisphosphonate-treated cells. Additionally, in silico modeling suggests that the neutralizing VHH binds the same residues on the Vγ9Vδ2 TCR as the Vγ9Vδ2 T cell Ag-presenting transmembrane protein butyrophilin 3A1, providing information on critical residues involved in this interaction. The neutralizing Vγ9Vδ2 TCR VHH identified in this study might provide a novel approach to inhibit the unintentional Vγ9Vδ2 T cell activation as a consequence of aminobisphosphonate administration.

Emerging concepts of T cell metabolism as a target of immunotherapy

T cells have a pivotal protective role in defense against infection and cancer but also are instrumental in the development of many autoimmune diseases. The regulation of nutrient uptake and utilization in T cells is critically important for the control of their differentiation, and manipulating metabolic pathways in these cells can alter their function and longevity. While the importance of T cell metabolic remodeling in different physiological settings is not fully understood, there is a growing realization that inappropriate metabolic remodeling underlies many aberrant immune responses and that manipulating cellular metabolism can beneficially enhance or temper immunity. Here we comment on the basic metabolic pathways in T cells, followed by a discussion on up-to-date findings about the relationship between metabolism and T cell function and longevity. Furthermore, we expand on potential approaches and applications in which T cells might be manipulated by the reprogramming of metabolic pathways for therapeutic purposes.

Highly specific and potently activating Vγ9Vδ2-T cell specific nanobodies for diagnostic and therapeutic applications

Vγ9Vδ2-T cells constitute the predominant subset of γδ-T cells in human peripheral blood and have been shown to play an important role in antimicrobial and antitumor immune responses. Several efforts have been initiated to exploit these cells for cancer immunotherapy, e.g. by using phosphoantigens, adoptive cell transfer, and by a bispecific monoclonal antibody based approach. Here, we report the generation of a novel set of Vγ9Vδ2-T cell specific VHH (or nanobody). VHH have several advantages compared to conventional antibodies related to their small size, stability, ease of generating multispecific molecules and low immunogenicity. With high specificity and affinity, the anti-Vγ9Vδ2-T cell receptor VHHs are shown to be useful for FACS, MACS and immunocytochemistry. In addition, some VHH were found to specifically activate Vγ9Vδ2-T cells. Besides being of possible immunotherapeutic value, these single domain antibodies will be of great value in the further study of this important immune effector cell subset.

Designing multivalent proteins based on natural killer cell receptors and their ligands as immunotherapy for cancer

INTRODUCTION

Natural killer (NK) cells are an important component of the innate immune system that play a key role in host immunity against cancer. NK cell recognition and activation is based on cell surface receptors recognizing specific ligands that are expressed on many types of tumor cells. Some of these receptors are capable of activating NK cell function while other receptors inhibit NK cell function. Therapeutic approaches to treat cancer have been developed based on preventing NK cell inhibition or using NK cell receptors and their ligands to activate NK cells or T cells to destroy tumor cells.

AREAS COVERED

This article describes the various strategies for targeting NK cell receptors and NK cell receptor ligands using multivalent proteins to activate immunity against cancer.

EXPERT OPINION

NK cell receptors work in synergy to activate NK cell effector responses. Effective anti-cancer strategies will need to not only kill tumor cells but must also lead to the destruction of the tumor microenvironment. Immunotherapy based on NK cells and their receptors has the capacity to accomplish this through triggering lymphocyte cytotoxicity and cytokine production.

The Evolution of T-cell Therapies for Solid Malignancies

Primary resistant, recurrent, and relapsed solid tumors are often nonresponsive to conventional antineoplastic therapies. Moreover, in responsive tumors, the therapeutic-to-toxic range of these interventions remains quite narrow, such that side effects of therapy are substantial. Targeted therapies, such as adoptive T-cell transfer, not only spare normal tissues but also use alternative killing mechanisms to which the tumor cells are usually not immune. Adoptive T-cell transfer for solid tumors faces unique challenges because of the inherent heterogeneity of tumor parenchyma, the complexity of the tumor microenvironment, and tumor occurrence in areas with limited therapeutic accessibility. In this review, we examine the recent evolution of various T-cell-based immunotherapeutics, the mechanisms of action behind their antitumor activity, their increasing complexity, and the prospect of building on previous successes in the treatment of solid tumors.

Antibody Production in Plants and Green Algae

Monoclonal antibodies (mAbs) have a wide range of modern applications, including research, diagnostic, therapeutic, and industrial uses. Market demand for mAbs is high and continues to grow. Although mammalian systems, which currently dominate the biomanufacturing industry, produce effective and safe recombinant mAbs, they have a limited manufacturing capacity and high costs. Bacteria, yeast, and insect cell systems are highly scalable and cost effective but vary in their ability to produce appropriate posttranslationally modified mAbs. Plants and green algae are emerging as promising production platforms because of their time and cost efficiencies, scalability, lack of mammalian pathogens, and eukaryotic posttranslational protein modification machinery. So far, plant- and algae-derived mAbs have been produced predominantly as candidate therapeutics for infectious diseases and cancer. These candidates have been extensively evaluated in animal models, and some have shown efficacy in clinical trials. Here, we review ongoing efforts to advance the production of mAbs in plants and algae.

Development of PF-06671008, a Highly Potent Anti-P-cadherin/Anti-CD3 Bispecific DART Molecule with Extended Half-Life for the Treatment of Cancer

Bispecific antibodies offer a promising approach for the treatment of cancer but can be challenging to engineer and manufacture. Here we report the development of PF-06671008, an extended-half-life dual-affinity re-targeting (DART®) bispecific molecule against P-cadherin and CD3 that demonstrates antibody-like properties. Using phage display, we identified anti-P-cadherin single chain Fv (scFv) that were subsequently affinity-optimized to picomolar affinity using stringent phage selection strategies, resulting in low picomolar potency in cytotoxic T lymphocyte (CTL) killing assays in the DART format. The crystal structure of this disulfide-constrained diabody shows that it forms a novel compact structure with the two antigen binding sites separated from each other by approximately 30 Å and facing approximately 90° apart. We show here that introduction of the human Fc domain in PF-06671008 has produced a molecule with an extended half-life (-4.4 days in human FcRn knock-in mice), high stability (Tm1 > 68 °C), high expression (>1 g/L), and robust purification properties (highly pure heterodimer), all with minimal impact on potency. Finally, we demonstrate in vivo anti-tumor efficacy in a human colorectal/human peripheral blood mononuclear cell (PBMC) co-mix xenograft mouse model. These results suggest PF-06671008 is a promising new bispecific for the treatment of patients with solid tumors expressing P-cadherin.

Challenges of phase 1 clinical trials evaluating immune checkpoint-targeted antibodies

BACKGROUND

Immunostimulatory monoclonal antibodies (imAbs) targeting immune checkpoint molecules are revolutionizing oncology not only regarding cancer therapeutics and clinical care, but also from a drug development point of view. A handful of first-generation molecules have been approved so far based on their tremendous efficacy, after an expedited development phase that has challenged most paradigms established in the era of conventional cytotoxic therapy and to some extent molecularly targeted agents. A huge wave of second-generation imAbs is just entering into phase 1 trials now, in monotherapy or in combination. In order to maximize their chances of success in early phase trials, and eventually for patients' benefit, their clinical development has to benefit from lessons learnt from previous imAbs phase 1 trials.

MATERIALS AND METHODS

We reviewed the early clinical development of anti-cytotoxic T-lymphocyte antigen 4 and anti-programmed death-1 receptor/ligand. Particularities of each agent, including safety, dose--toxicity and dose--efficacy relationships, scheduling, pharmacokinetics (PK), pharmacodynamics (PD), trial design, biomarkers, response assessment and overall drug development strategies, are described and challenged.

RESULTS

As opposed to conventional cytotoxic agents, dose of imAbs is not linearly associated with efficacy and toxicity. Therefore, the definition of a minimal immunologically active dose could be proposed. Traditional patient eligibility criteria might also be revisited as the toxicity profile and mechanism of toxicity--immune-related adverse events--are mostly known and their physiopathology somehow less unexpected than with molecularly targeted small molecules. Most challenging are the comprehensive investigation of complex PK and PD characteristics as well as the definition of patient selection biomarkers. Finally, the early focus on efficacy (and not only dose confirmation) in expansion cohorts challenges the traditional phase 1/2/3 drug development process.

CONCLUSION

Several drug development paradigms have been challenged by imAbs. Here, we discuss novel approaches for an efficient and successful drug development of these agents.

Clinical pharmacology of bispecific antibody constructs

The confluence of rapid scientific advancements especially in protein engineering and recombinant technology, unmet medical needs, and commercial incentives have led to the development of the next generation of therapeutic proteins. Bispecific antibody constructs are one of the novel strategies that is being pursued, combining the ability to bind simultaneously to two distinct targets and the advantages of purpose-designed and optimized antibody-based scaffolds. Their pharmacokinetic and pharmacodynamic properties, including their immunogenic potential, are closely related to their structural features and ability to interact with disposition mechanisms of immunoglobulin molecules. Catumaxomab and blinatumomab are bispecific constructs that are approved for clinical use and have provided clinical pharmacology data for this novel class of therapeutics. This knowledgebase on the clinical behavior of bispecific therapeutic proteins is poised to rapidly evolve over the next few years with many development programs having entered the clinical development stage.

Cancer immunotherapy in veterinary medicine: Current options and new developments

Excitement in the field of tumor immunotherapy is being driven by several remarkable breakthroughs in recent years. This review will cover recent advances in cancer immunotherapy, including the use of T cell checkpoint inhibitors, engineered T cells, cancer vaccines, and anti-B cell and T cell antibodies. Inhibition of T cell checkpoint molecules such as PD-1 and CTLA-4 using monoclonal antibodies has achieved notable success against advanced tumors in humans, including melanoma, renal cell carcinoma, and non-small cell lung cancer. Therapy with engineered T cells has also demonstrated remarkable tumor control and regression in human trials. Autologous cancer vaccines have recently demonstrated impressive prolongation of disease-free intervals and survival times in dogs with lymphoma. In addition, caninized monoclonal antibodies targeting CD20 and CD52 just recently received either full (CD20) or conditional (CD52) licensing by the United States Department of Agriculture for clinical use in the treatment of canine B-cell and T-cell lymphomas, respectively. Thus, immunotherapy for cancer is rapidly moving to the forefront of cancer treatment options in veterinary medicine as well as human medicine.