Requisite considerations for successful adoptive immunotherapy with engineered T-lymphocytes using tumor antigen-specific T-cell receptor gene transfer

Introduction: Although engineered T-cell-based antitumor immunotherapy using tumor-antigen-specific T-cell receptor (TCR) gene transfer is undoubtedly a promising strategy, a number of studies have revealed that it has several drawbacks.

Areas covered: This review covers selected articles detailing recent progress in this field, not only for solid tumors, but also for leukemias. In terms of achieving uniform therapeutic quality of TCR gene-modified T cells as an ‘off-the-shelf’ product, the authors abstract and discuss the requisite conditions for successful outcome, including: i) the optimal target choice reflecting the specificity of the introduced TCR, ii) the quality and quantity of expressed TCRs in gene-modified T cells, and additional genetic modification reflecting enhanced antitumor functionality, and iii) ‘on-’ and ‘off-target’ adverse events caused by the quality of the introduced TCRs and other adverse events related to genetic modification itself. Readers will be able to readily abstract recent advances in TCR gene-transferred T-cell therapy, centering notably on efforts to obtain uniformity in the therapeutic functionality of engineered T cells

Expert opinion: Harmonizing the functionality and target specificity of TCR will allow the establishment of clinically useful adoptive immunotherapy in the near future.     

Antibody therapeutics for treating prostate cancer: where are we now and what comes next?

Introduction: Progress in the understanding of molecular events of carcinogenesis and cancer evolution as well as the identification of tumor antigens has led to the development of different targeted therapeutic approaches, including the use of monoclonal antibodies (mAbs). Prostate cancer (PC) is highly amenable to mAb targeting given the existence of prostate-specific targets and the natural history and localization of metastatic disease.

Areas covered: Several aspects of the PC phenotype, including growth factors, angiogenesis mediators, bone microenvironment signals, and immune evasion pathways, have become areas of ongoing investigation in terms of mAb targeting. These are reviewed. The greatest success so far has been the development of mAbs against prostate-specific tumor antigen (PSMA), which opened an opportunity to improve diagnostic accuracy and simultaneously target metastatic disease.

Expert opinion: As mAb use in PC continues to evolve, more accurate imaging of the extent of disease and more effective mAb therapies (naked or conjugated with drugs, toxins or radioactive molecules) are emerging. In addition, the combination of mAbs with other treatment modalities is expected to further improve responses and overall survival. Identification of validated biomarkers is necessary for better recognition of patient subgroups who will derive the greatest benefit from mAb therapy.     

Monoclonal antibodies for the treatment of osteoarthritis

ABSTRACT

Introduction: Osteoarthritis (OA) is a multifactorial chronic joint disease, and so far, there are no approved disease-modifying anti-OA drugs (DMOADs). There is an urgent need to develop therapies for different phenotypes of OA. Monoclonal antibodies (mAb) may slow structural progression, control inflammation and relieve pain, and thus have the potential to be DMOADs.

Areas covered: In this review, the authors searched the literature on PubMed, EMBASE and the Cochrane Library using keywords, including mAbs, biological agents, OA and osteoarthritis, electronically up to May 2016. They also included abstracts of international conferences. Furthermore, they reviewed experimental and clinical studies of various mAbs targeting different pathological mechanisms of OA, including ADAMTS, Interleukine-1, tumour necrosis factor, never growth factor and vascular endothelial growth factor.

Expert opinion: MAbs for the treatment of OA are under intense investigation and the results for some mAbs (e.g., anti-nerve growth factor mAbs, anti- vascular endothelial growth factor mAbs) are promising. The authors believe that mAb therapy can be a targeted therapeutic approach for the treatment of OA. Future clinical trials are required to evaluate the therapeutic efficacy of these agents by the appropriate selection of specific phenotype for targeted therapy based on the mechanism of drug action.     

Monoclonal antibodies in neuroinflammatory diseases

Introduction: Monoclonal antibodies (mAbs) represent an emerging and rapidly growing field of therapy in neuroinflammatory diseases. Adhesion molecule blockade by natalizumab represents the first approved mAb therapy in neurology, approved for therapy of highly active multiple sclerosis (MS). Removal of immune cells by anti-CD52 mAb alemtuzumab or anti-CD20 mAb rituximab are other prime examples with existing positive Phase II and Phase III trials. MS clearly represents the neuroinflammatory disease entity with the largest body of evidence. However, some of these approaches are currently investigated or translated for use in other, rare neuroinflammatory diseases, such as neuromyelitis optica (NMO), inflammatory neuropathies and (neuro)-muscular disorders.

Areas covered: This review will highlight the most relevant therapeutic approaches involving mAbs in the field of neuroinflammatory diseases as published in peer-reviewed journals and presented on international meetings.

Expert opinion: There is continuously growing evidence on the therapeutic relevance of mAbs in neuroinflammatory disorders. In MS meanwhile several studies have provided evidence for efficacy: In addition to natalizumab, approved in 2006, several other candidates are under development, the most eminent examples with the most advanced study programs being anti-CD52 alemtuzumab, anti-CD20 principles and anti-CD25 daclizumab. Other intriguing candidates are anti-IL-17 strategies, and interference with the complement pathway, partly also developed for other neuroinflammatory disorders.     

Monoclonal antibodies for renal diseases: current concepts and ongoing treatments

Introduction: In recent years, technological innovations in the field of molecular biology have provided new therapeutic options. In particular, human monoclonal antibodies (mAbs), initially used in the treatment of malignancies, have become a therapeutic tool for many other diseases. Most of the application of mAbs revealed encouraging findings to treat patients with immune-mediated glomerular diseases, for whom the standard protocols based on corticosteroids and non-specific immunosuppressants with heavy side effects have for decades been the only therapies.

Area covered: Rituximab, an mAb directed against a specific antigen expressed on B lymphocytes, CD20 antigen, inducing a premature cell apoptosis became very important in the treatment of membranous glomerulonephritis, steroid-resistant nephrotic syndromes and membranoproliferative glomerulonephritis (MPGN). Another important mAb, eculizumab, is used successfully for treatment of atypical hemolytic uremic syndrome, C3 nephropathy and MPGN. Many other mAbs are now under premarketing investigation, such as adalimumab, daclizumab, fresolimumab, belimumab, tocilizumab, although some of these mAbs are already approved for different medical applications.

Expert opinion: The availability of novel mAb may therefore constitute the basis for a revolution in the treatment of immune-mediated renal diseases. However, the cost for this therapy remains very high and represents a barrier for its widespread use.     

From therapeutic antibodies to chimeric antigen receptors (CARs): making better CARs based on antigen-binding domain

ABSTRACT

Introduction: A variety of approaches are being pursued to improve the safety and antitumor potency of chimeric antigen receptor (CAR) T-cell therapy. However, most engineering efforts have thus far been focused on its intracellular signaling domain, while its extracellular antigen-binding domain has received less attention.

Areas covered: Herein, the authors summarize the current knowledge of CAR T-cell therapy. Accordingly, they focus on its antigen-binding domain, discuss key considerations for selecting an optimal single-chain variable fragment (scFv) when designing a CAR, and suggest potential directions aimed at developing the next-generation CARs.

Expert opinion: The extracellular region of CARs can play a decisive role in their safety and efficacy. Instead of directly translating an available therapeutic mAb to a scFv-based CAR construct, the authors suggest that various CAR-displayed scFvs with different affinity, specificity and binding epitopes against an individual target molecule should be generated and evaluated side-by-side. Incorporating new antibody formats that possess characteristics superior to those of scFvs may be one way to engineer safer and more effective CARs. The authors expect that further CAR engineering will enable us to target more antigens involved in hematological and solid malignancies with minimal side effects to serve unmet clinical needs.     

The use of monoclonal antibodies for the treatment of graft-versus-host disease following allogeneic stem cell transplantation

Introduction: Graft-versus-host disease (GVHD) remains the leading cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HSCT). Steroids along with calcineurin inhibitors remain the standard initial therapy, however, less than half of the patients completely respond and there is no uniformly accepted therapy for patients with steroid-resistant GVHD.

Areas covered: This paper reviews the current role and ongoing development of mAbs in the treatment of GVHD. Various mAbs to cell surface antigens on GVHD effector cells have been investigated for the treatment of acute GVHD: these include anti-TNF-α antibodies, IL-2 receptor antagonists, anti-CD3 and anti-CD52 mAbs, while anti-CD20 mAb has been extensively investigated in the setting of chronic GVHD. Overall, response rates have been reported to be greater than 60%, although it should be emphasized that the long-term survival still remains suboptimal, mainly due to the detrimental side effects of infectious complications, progressive GVHD and relapse of underlying malignancy.

Expert opinion: Future challenges will include more appropriate definition of these agents in the therapeutic scenario of GVHD. Combinations of mAbs or mAb combined with newer immunosuppressive drugs might potentially achieve greater success, especially if used early in the disease process.     

Humoral immunotherapy of multiple myeloma: perspectives and perplexities

Importance of the field: Multiple myeloma (MM) is a hematological malignancy still remaining incurable despite the various therapies available, mainly because of the high fraction of refractory/relapsing cases. Therefore, the development of novel therapeutic approaches is urgently needed to overcome conventional treatment resistance.

Areas covered in this review: In the era of targeted therapies, treatments combining a high specificity for neoplastic cells and the capability to interfere with environmental signals should be regarded as the weapons of choice. Monoclonal antibody (mAb)-based humoral immunotherapy could satisfy both these requirements when applied to MM. Indeed, many of the molecules expressed on MM cells, such as CD38, CD40, CD49d, CD138 and CD162 are involved in the adhesive dynamics regulating the crosstalk between MM and the BM-microenvironment.

What the reader will gain: In this study we review those MM-associated molecules that have shown promising antitumor effects as targets of specific mAbs in preclinical settings, thus deserving to be considered for clinical investigation.

Take home message: mAbs directed against MM-associated adhesion markers should be taken into account in clinical practice, since they could possibly represent the best available combination of tumor cytotoxicity, environmental signal deprivation and immune system redirection.     

T cell receptor (TCR) gene therapy to treat melanoma: lessons from clinical and preclinical studies

Importance of the field: Adoptive T cell therapy (ACT) with tumour infiltrating lymphocytes is currently the best treatment option for metastatic melanoma. Despite its clinical successes, ACT has limitations in availability and generation of therapeutic T cells for a larger group of patients. Introduction of tumour-specific T cell receptors into T cells, termed TCR gene therapy, can provide an alternative for ACT that is more widely applicable and might be extended to other types of cancer.

Areas covered in this review: The current status of TCR gene therapy studies including clinical challenges, such as on-target toxicity, compromised anti-tumour T cell responses, compromised T cell persistence and potential immunogenicity of receptor transgenes. Strategies to address these challenges are covered.

What the reader will gain: A listing and discussion of strategies that aim at improving the efficacy and safety of TCR gene therapy. Such strategies address antigen choice, TCR mis-pairing, functional avidity and persistence of T cells, immune responses towards receptor transgenes, and combination of ACT with other therapies.

Take home message: To ensure further clinical development of TCR gene therapy, it is necessary to choose safe T cell target antigens, and implement (combinations of) strategies that enhance the correct pairing of TCR transgenes and the functional avidity and persistence of T cells.     

Ofatumumab,a human anti-CD20 monoclonal antibody

Importance of the field: Since relapse of chronic lymphocytic leukemia (CLL), and refractoriness to treatment following relapse, is inevitable after initial treatment, development of novel treatment strategies is necessary.

Areas covered in this review: CD20 as a therapeutic target for CLL, successes and limitations of current anti-CD20 monoclonal antibody (mAb) therapy, and implications of preclinical and clinical developments of novel alternatives, including ofatumumab, that may enhance anti-CD20 mAb therapy are reviewed. The literature reviewed encompasses papers and congress abstracts from the past 13 years.

What the reader will gain: While rituximab combined with chemotherapy has considerably improved outcomes for some but not all CLL patients, single-agent use is limited in relapsed/refractory CLL. Novel anti-CD20 mAbs in development, such as ofatumumab, may bypass some limitations by virtue of alternative epitope binding and modified effector functions. Ofatumumab induces significant complement-dependent cell lysis in vitro, particularly in cells with low CD20 expression. The FDA recently approved ofatumumab for treatment of CLL refractory to fludarabine and alemtuzumab.

Take home message: CD20-targetting chemoimmunotherapeutic options have advanced treatment of CLL. Results for single-agent ofatumumab and other new CD20 mAbs, in different lines of therapy and in combination with chemotherapy, will guide optimal use of these alternative therapies for B-cell malignancies.     

Tolerance to rat monoclonal antibodies. Implications for serotherapy

The antiglobulin response is a major complication of mAb therapy. It has been suggested that, in clinical practice, this might be avoided by using human or chimeric mAbs, or by prior induction of tolerance to the therapeutic mAb. In this study, we show that it is possible to induce tolerance in mice to the constant regions of rat IgG2b mAbs by both classical deaggregation methods and by anti-L3T4 mAb therapy. Mice tolerant to IgG2b constant region determinants failed to make an antiglobulin response when immunized with a number of mAbs of the same isotype that had no binding specificity for mouse cells, but produced vigorous antiidiotypic responses to cell-binding mAbs. Binding of antibodies to hemopoietic cells rends their idiotypic determinants major immunogens even in the presence of tolerance to constant region epitopes. These findings suggest that the use of human or chimeric mAbs will not be sufficient to eliminate the antiglobulin response, and that additional methods need to be investigated.     

Enhanced T cell receptor gene therapy for cancer

Importance of the field: Adoptive therapy with T cell receptor- (TCR-) redirected T cells has shown efficacy in mouse tumor models and first responses in cancer patients. One prerequisite to elicit effective anti-tumor reactivity is the transfer of high-avidity T cells. Their generation, however, faces several technical difficulties. Target antigens are often expressed at low levels and their recognition requires the use of high-affine receptors. Yet, mainly low-affine TCRs have been isolated from tumor-infiltrating lymphocytes. Furthermore, upon transfer into a T cell the introduced receptor has to compete with the endogenous TCR.

Areas covered in this review: This review discusses how the functional avidity of TCR-modified T cells can be enhanced by i) increasing the amount of introduced TCR heterodimers on the cell surface; and ii) generating receptors with high affinity. Risks of TCR gene therapy and possible safety mechanisms are discussed.

What the reader will gain: The reader will gain an overview of the technical developments in TCR and T cell engineering.

Take home message: Despite technical obstacles, many advances have been made in the generation of high-avidity T cells expressing enhanced TCRs. Mouse studies and clinical trials will evaluate the effect of these improvements.     

Protective and nonprotective monoclonal antibodies to Cryptococcus neoformans originating from one B cell

Two immunoglobulin M monoclonal antibodies (mAbs) derived from the same B cell recognize different epitopes on the capsular polysaccharide of the pathogenic yeast, Cryptococcus neoformans. Their respective epitopes are located in spatially distinct regions of the capsule. Passive administration of one mAb prolonged survival whereas the other mAb did not. The results indicate that specificity is an important determinant of antibody efficacy against C. neoformans and that somatic mutations occurring during the antibody response can affect the protective efficacy of antibodies to C. neoformans.     

Anti-CD20 monoclonal antibodies in chronic lymphocytic leukemia

Introduction: The last decade has witnesd immense progress in the treatment of chronic lymphocytic leukemia (CLL). Chemoimmunotherapy (CIT) combining rituximab and fludarabine with cyclophosphamide (FCR) in the frontline setting has clearly been shown to improve outcomes in patients with CLL. Building on the success achieved with rituximab, other anti-CD20 monoclonal antibodies (mAbs) are being investigated. Novel bioengineering techniques have helped in the development of anti-CD20 mAbs. One antibody, ofatumumab, was recently approved for the treatment of refractory CLL. A type II anti-CD20 mAb, GA-101 (obinutuzumab), is currently in clinical trials. This short review focuses on ongoing clinical trials of anti-CD20 mAbs in CLL.

Areas covered: Literature search was performed using PubMed (www.clinicaltrials.gov (till August 2012)), and recent American Society of Clinical Oncology (ASCO), American Society of Hematology (ASH), European Hematology association (EHA), International workshop on CLL (iwCLL) abstracts, using the primary search terms ‘anti-CD20 monoclonal antibody' with/without CLL. Articles were chosen on the basis of relevance of anti-CD20 mAbs to CLL therapy.

Expert opinion: Rituximab, the prototype anti-CD20 mAb, forms the core of CIT in CLL. The success of rituximab and ofatumumab has led investigators to evaluate other anti-CD20 mAbs in the treatment of CLL.     

Predominant expression of a T cell receptor V beta gene subfamily in autoimmune encephalomyelitis

TCR beta chain gene expression of individual T cell clones that share the same MHC class II restriction and similar fine specificity for the encephalitogenic NH2 terminus of the autoantigen myelin basic protein (MBP) has been examined. TCR V beta expression was examined by FACS analysis with mAbs specific for the V beta 8 subfamily of TCR beta chain genes. 14 of 18 (78%) NH2-terminal MBP-specific clones examined express a member of the TCR V beta 8 subfamily. Southern analysis was used to identify which member(s) of the TCR V beta 8 subfamily is expressed by these clones. Each of four clones examined uses V beta 8.2, though two different V beta 8.2-J beta 2 combinations were identified. Our findings indicate that there is restricted TCR V beta usage in the autoimmune T cell response to the dominant encephalitogenic NH2-terminal epitope of the MBP. The use of an mAb to the antigen-specific TCR in the prevention of T cell-mediated autoimmune disease has been investigated. Our results demonstrate that in vivo administration of a TCR V beta 8-specific mAb prevents induction of autoimmune encephalomyelitis.     

Monoclonal antibodies to two epitopes of beta-human chorionic gonadotropin for the treatment of cancer

Human chorionic gonadotropin (hCG) is expressed by many histological types of cancer and may play an important role in tumor maintenance and progression. Vaccination of patients with the therapeutic peptide Avicine (CTP37; AVI BioPharma Inc/SuperGen Inc), that contains 37 amino acids from the carboxyl terminus (CTP37; AVI BioPharma Inc/SuperGen Inc) of hCG, can result in two distinct antibody responses to separate epitopes within the peptide. Colorectal cancer patients who develop both anti-hCG responses show a significant improvement in median survival time. These observations provide a compelling rationale for the development of two human monoclonal antibodies (mAbs), one for each of the epitopes within the 37 amino acid peptide region of hCG. Two such human mAbs, both exhibiting a high degree of specificity and affinity have been prepared using XenoMouse technology. These mAbs may prove useful in multiple clinical settings for the treatment of various cancers. Treatment options may include passive immunotherapy with both mAbs, mixed passive supplement to active specific immunotherapy with Avicine and conjugation of the mAbs with radioisotopes or cytotoxic drugs. The requirement for dual mAb therapy is consistent with current trends in the development of complex, non-toxic therapies for cancer.     

Bococizumab for the treatment of hypercholesterolaemia

Introduction: Low-density lipoprotein cholesterol (LDL-C) remains a well-established risk factor for cardiovascular disease (CVD). LDL-C levels are considered primary targets of therapy. A new series of systemic biomolecules, the monoclonal antibodies (mAbs) of proprotein convertase subtilisin/kexin type 9 (PCSK9), have a higher activity in reducing LDL-C.

Areas covered: The authors critically review the current evidence on the efficacy and safety of bococizumab, a humanized mAb against PCSK9, which was surprisingly discontinued in November 2016. The pharmacokinetic profile and the biological features of bococizumab vs others mAbs are also discussed. As of now, in adjunct to diet, alirocumab and evolocumab are the only approved PCSK9 mAbs for the treatment of adult patients with severe clinical atherosclerotic CVD already at maximally-tolerated statin therapy and require additional LDL-C lowering.

Expert opinion: Although discontinued, data from a phase 2b trial show the effectiveness of bococizumab in lowering LDL-C in a similar way to the two available PCSK9 antagonists. However, some peculiar biological characteristics of bococizumab may explain the attenuation of LDL-C lowering over time, as well as a higher rate of immunogenicity and of injection-site reactions.     

Cancer–germline antigen vaccines and epigenetic enhancers: future strategies for cancer treatment

Importance of the field: Immunotherapy holds great potential for disseminated cancer, and cancer–germline (CG) antigens are among the most promising tumor targets. They are widely expressed in different cancer types and are essentially tumor-specific, since their expression in normal tissues is largely restricted to immune-privileged sites. Although the therapeutic potential of these antigens may be compromised by their highly heterogeneous expression in many tumors and low frequency in some cancers, recent developments suggest that tumor-cell-selective enhancement of CG antigen gene expression can be achieved using epigenetic modifiers.

Areas covered in this review: We provide an overview of the potential of CG antigens as targets for cancer immunotherapy, including advantages and disadvantages. We also discuss the current state of development of CG antigen vaccines, and the potential synergistic effect of combining CG antigen immunotherapeutic strategies with epigenetic modifiers.

What the reader will gain: The reader will gain an overview of the past, present and future role of CG antigens in cancer immunotherapy.

Take home message: Chemoimmunotherapy using epigenetic drugs and CG antigen vaccines may be a useful approach for treating cancer.     

Treating hematological malignancies with cell therapy: where are we now?

Introduction: Adoptive cell therapy (ACT) is becoming an increasingly successful and widespread form of treatment for different types of cancer. Compared to chemotherapy or monoclonal antibodies, ACT is an active biological strategy, with infused immune cells featuring dynamic migration, expansion and long-term persistence properties. ACT in hematological malignancies offered the initial proof of principle of the feasibility for this innovative ‘live-drug’.

Areas covered: In this review, the authors summarize the clinical results achieved with two specific strategies in hematological malignancies: chimeric antigen receptor (CAR) and T cell receptor (transgenic TCR) redirected T cells. Moreover, they discuss the recent pre-clinical studies aimed at increasing the feasibility, safety and efficacy of ACT.

Expert opinion: ACT can promote cancer regression in patients with leukemia, lymphoma and multiple myeloma. Nevertheless, more precise targeting of tumor cells and containment of side effects are needed. Overcoming tumor-associated immunosuppressive mechanisms and preventing tumor escape are also emerging as critical barriers. Finally, simplification in the manufacturing procedures should promote wider application of these technologies outside academic centers. Although the enthusiasm for ACT-based therapies is high, comprehensive and systematic clinical studies are required to advance the field.     

Shark variable new antigen receptor biologics – a novel technology platform for therapeutic drug development

Introduction: Biologics drugs have succeeded in achieving a commercial dominance in the global market for new therapies and large pharmaceutical companies' interest remains strong through a continued commitment to pipeline development. It is not surprising, therefore, that next-generation biologics, particularly antibody-like scaffolds that offer many of the advantages of the original biologic drugs but in simplified formats, have entered the clinic as competing substitute therapeutic products, to capture market share.

Areas covered: Specifically, this paper will position shark-derived variable new antigen receptors (VNARs) within an overview of the existing biologics landscape including the growth, diversity and success to date of alternative scaffolds. The intention is not to provide a comprehensive review of biologics as a whole but to discuss the main competing single-domain technologies and the exciting therapeutic potential of VNAR domains as clinical candidates within this context.

Expert opinion: The inherent ability to specifically bind target and intervene in disease-related biological processes, while reducing off-site toxicity, makes mAbs an effective, potent and now proven class of therapeutics. There are, however, limitations to these ‘magic bullets’. Their size and complexity can restrict their utility in certain diseases types and disease locations. In contrast, a number of so-called alternative scaffolds, derived from both immunoglobulin- and non-immunoglobulin-based sources have been developed with real potential to overcome many of the shortcomings documented for mAb treatments. Unlike competing approaches such as Darpins and Affibodies, we now know that shark VNAR domains (like camel VHH nanobody domains), are an integral part of the adaptive immune system of these animals and have evolved naturally (but from very different starting molecules) to exhibit high affinity and selectivity for target. In addition, and again influenced by the environment in which they have evolved naturally, their small size, simple architecture, high solubility and stability, deliver additional flexibility compared to classical antibodies (and many non-natural alternative scaffolds), thereby providing an attractive basis for particular clinical indications where these attributes may offer advantages.