TCR transgenes and transgene cassettes for TCR gene therapy: status in 2008

Modifications to rhesus macaque TCR constant regions improve TCR cell surface expression

T cell immunotherapy success is dependent on effective levels of antigen receptor expressed at the surface of engineered cells. Efforts to optimize surface expression in T cell receptor (TCR)-based therapeutic approaches include optimization of cellular engineering methods and coding sequences, and reducing the likelihood of exogenous TCR α and β chains mispairing with the endogenous TCR chains. Approaches to promote correct human TCR chain pairing include constant region mutations to create an additional disulfide bond between the two chains, full murinization of the constant region of the TCR α and β sequences, and a minimal set of murine mutations to the TCR α and β constant regions. Preclinical animal models are valuable tools to optimize engineering designs and methods, and to evaluate the potential for off-target tissue injury. To further develop rhesus macaque models for TCR based cellular immunotherapy, we tested methods for improving cell surface expression of rhesus macaque TCR in rhesus macaque primary cells by generating five alternative TCRαβ constant region constructs in the context of a SIV Gag-specific TCR: 1. human codon optimized rhesus macaque (RH); 2. RH TCR with an additional disulfide linkage; 3. rhesus macaque constant sequences with minimal murine amino acid substitutions; 4. murinized constant sequences; and 5. murinized constant sequences with a portion of the exposed FG loop in the β constant sequence replaced with rhesus macaque sequence to reduce potential immunogencity. Murinization or mutation of a minimal set of amino acids to the corresponding murine sequence of the constant region resulted in the greatest increase in rhesus macaque TCR surface expression relative to wild type. All novel TCR constructs retained the ability to induce production of cytokines in response to cognate peptide antigen specific stimulation. This work can inform the design of TCRs selected for use in rhesus macaque models of TCR-based cellular immunotherapy.

Engineered Treg cells: The heir to the throne of immunotherapy

Recently, increased interest in the use of Tregs as adoptive cell therapy for the treatment of autoimmune diseases and transplant rejection had led to several advances in the field. However, Treg cell therapies, while constantly advancing, indiscriminately suppress the immune system without the permanent stabilization of certain diseases. Genetically modified Tregs hold great promise towards solving these problems, but, challenges in identifying the most potent Treg subtype, accompanied by the ambiguity involved in identifying the optimal Treg source, along with its expansion and engineering in a clinical-grade setting remain paramount. This review highlights the recent advances in methodologies for the development of genetically engineered Treg cell-based treatments for autoimmune, inflammatory diseases, and organ rejection. Additionally, it provides a systematized guide to all the recent progress in the field and informs the readers of the feasibility and safety of engineered adoptive Treg cell therapy, with the aim to provide a framework for researchers involved in the development of engineered Tregs.

Genetic Strategies to Study T Cell Development

Genetics approaches have been instrumental to deciphering T cell development in the thymus, including gene disruption by homologous recombination and more recently Crispr-based gene editing and transgenic gene expression, especially of specific T cell antigen receptors (TCR). This brief chapter describes commonly used tools and strategies to modify the genome of thymocytes, including mouse strains with lineage- and stage-specific expression of the Cre recombinase used for conditional allele inactivation or expressing unique antigen receptor specificities.

Adoptive T-cell Immunotherapy: Perfecting Self-Defenses

As an important part of the immune system, T lymphocytes exhibit undoubtedly an important role in targeting and eradicating cancer. However, despite these characteristics, their natural antitumor response may be insufficient. Numerous clinical trials in terminally ill cancer patients testing the design of novel and efficient immunotherapeutic approaches based on the adoptive transfer of autologous tumor-specific T lymphocytes have shown encouraging results. Moreover, this also led to the approval of engineered T-cell therapies in patients. Herein, we will expand on the development and the use of such strategies using tumor-infiltrating lymphocytes or genetically engineered T-cells. We will also comment on the requirements and potential hurdles encountered when elaborating and implementing such treatments as well as the exciting prospects for this kind of emerging personalized medicine therapy.

Retroviral gene therapy in Germany with a view on previous experience and future perspectives

Gene therapy can be used to restore cell function in monogenic disorders or to endow cells with new capabilities, such as improved killing of cancer cells, expression of suicide genes for controlled elimination of cell populations, or protection against chemotherapy or viral infection. While gene therapies were originally most often used to treat monogenic diseases and to improve hematopoietic stem cell transplantation outcome, the advent of genetically modified immune cell therapies, such as chimeric antigen receptor modified T cells, has contributed to the increased numbers of patients treated with gene and cell therapies. The advancement of gene therapy with integrating retroviral vectors continues to depend upon world-wide efforts. As the topic of this special issue is "Spotlight on Germany," the goal of this review is to provide an overview of contributions to this field made by German clinical and research institutions. Research groups in Germany made, and continue to make, important contributions to the development of gene therapy, including design of vectors and transduction protocols for improved cell modification, methods to assess gene therapy vector efficacy and safety (e.g., clonal imbalance, insertion sites), as well as in the design and conduction of clinical gene therapy trials.

Human immunology and immunotherapy: main achievements and challenges

The immune system is a fascinating world of cells, soluble factors, interacting cells, and tissues, all of which are interconnected. The highly complex nature of the immune system makes it difficult to view it as a whole, but researchers are now trying to put all the pieces of the puzzle together to obtain a more complete picture. The development of new specialized equipment and immunological techniques, genetic approaches, animal models, and a long list of monoclonal antibodies, among many other factors, are improving our knowledge of this sophisticated system. The different types of cell subsets, soluble factors, membrane molecules, and cell functionalities are some aspects that we are starting to understand, together with their roles in health, aging, and illness. This knowledge is filling many of the gaps, and in some cases, it has led to changes in our previous assumptions; e.g., adaptive immune cells were previously thought to be unique memory cells until trained innate immunity was observed, and several innate immune cells with features similar to those of cytokine-secreting T cells have been discovered. Moreover, we have improved our knowledge not only regarding immune-mediated illnesses and how the immune system works and interacts with other systems and components (such as the microbiome) but also in terms of ways to manipulate this system through immunotherapy. The development of different types of immunotherapies, including vaccines (prophylactic and therapeutic), and the use of pathogens, monoclonal antibodies, recombinant proteins, cytokines, and cellular immunotherapies, are changing the way in which we approach many diseases, especially cancer.

Sarcoma Tumor Microenvironment

Components of the tumor microenvironment (TME) are known to play an essential role during malignant progression, but often in a context-dependent manner. In bone and soft tissue sarcomas, disease-regulatory activities in the TME remain largely uncharacterized. This chapter introduces the cellular, structural, and chemical composition of the sarcoma TME from a pathobiological and therapeutic perspective.Sarcomas are malignant tumors with diverse features when it comes to primary tumor appearance, metastatic potential, and response to treatment. Many of the classic subtypes are mainly composed of malignant cells and are therefore assumed to be committed to autocrine signaling. Some of the tumors are infiltrated by immune cells and contain necrotic areas or excessive amounts of extracellular matrix (ECM) that regulates tissue stiffness and interstitial fluid pressure. Vascular invasion and blood vessel characteristics can in some instances be considered in the prognostic setting.Further insights into the disease-regulatory activities of the sarcoma TME will provide essential knowledge on how to develop successful combination treatments targeting not only malignant cells, but also their routes of nutrition and ability to shield themselves toward existing therapy.

Next-generation regulatory T cell therapy

Regulatory T cells (Treg cells) are a small subset of immune cells that are dedicated to curbing excessive immune activation and maintaining immune homeostasis. Accordingly, deficiencies in Treg cell development or function result in uncontrolled immune responses and tissue destruction and can lead to inflammatory disorders such as graft-versus-host disease, transplant rejection and autoimmune diseases. As Treg cells deploy more than a dozen molecular mechanisms to suppress immune responses, they have potential as multifaceted adaptable smart therapeutics for treating inflammatory disorders. Indeed, early-phase clinical trials of Treg cell therapy have shown feasibility, tolerability and potential efficacy in these disease settings. In the meantime, progress in the development of chimeric antigen receptors and in genome editing (including the application of CRISPR-Cas9) over the past two decades has facilitated the genetic optimization of primary T cell therapy for cancer. These technologies are now being used to enhance the specificity and functionality of Treg cells. In this Review, we describe the key advances and prospects in designing and implementing Treg cell-based therapy in autoimmunity and transplantation.

T-cells "à la CAR-T(e)" - Genetically engineering T-cell response against cancer

The last decade will be remembered as the dawn of the immunotherapy era during which we have witnessed the approval by regulatory agencies of genetically engineered CAR T-cells and of checkpoint inhibitors for cancer treatment. Understandably, T-lymphocytes represent the essential player in these approaches. These cells can mediate impressive tumor regression in terminally-ill cancer patients. Moreover, they are amenable to genetic engineering to improve their function and specificity. In the present review, we will give an overview of the most recent developments in the field of T-cell genetic engineering including TCR-gene transfer and CAR T-cells strategies. We will also elaborate on the development of other types of genetic modifications to enhance their anti-tumor immune response such as the use of co-stimulatory chimeric receptors (CCRs) and unconventional CARs built on non-antibody molecules. Finally, we will discuss recent advances in genome editing and synthetic biology applied to T-cell engineering and comment on the next challenges ahead.

Domain-swapped T cell receptors improve the safety of TCR gene therapy

T cells engineered to express a tumor-specific αβ T cell receptor (TCR) mediate anti-tumor immunity. However, mispairing of the therapeutic αβ chains with endogenous αβ chains reduces therapeutic TCR surface expression and generates self-reactive TCRs. We report a general strategy to prevent TCR mispairing: swapping constant domains between the α and β chains of a therapeutic TCR. When paired, domain-swapped (ds)TCRs assemble with CD3, express on the cell surface, and mediate antigen-specific T cell responses. By contrast, dsTCR chains mispaired with endogenous chains cannot properly assemble with CD3 or signal, preventing autoimmunity. We validate this approach in cell-based assays and in a mouse model of TCR gene transfer-induced graft-versus-host disease. We also validate a related approach whereby replacement of αβ TCR domains with corresponding γδ TCR domains yields a functional TCR that does not mispair. This work enables the design of safer TCR gene therapies for cancer immunotherapy.

DOI:http://dx.doi.org/10.7554/eLife.19095.001

T cells enable the immune system to recognize invading microbes and diseased cells while ignoring healthy cells. The ability of a T cell to recognize a specific microbe or diseased cell is determined by two proteins that pair to form its “T cell receptor.” The paired receptors are exported to the surface of the T cell, where they bind to infected or cancerous cells. Those T cells that produce receptors that bind healthy cells are eliminated during development.

T cells can generally distinguish between the body’s own cells and the cells of invading bacteria or other microbes. However, cancer cells are more difficult to identify because they are similar to healthy cells. Efforts to develop therapies that enhance the immune system’s ability to recognize cancer cells have had only limited success. One successful approach – known as T cell receptor gene therapy – modifies T cells to destroy cancer cells by arming them with a cancer-specific T cell receptor.

This technique produces T cells possessing two T cell receptors – the cancer-specific receptor and the one it had originally – so it is possible for proteins from the two receptors to mispair. This impedes the correct pairing of the cancer-specific T cell receptor, reducing the effectiveness of the therapy. More importantly, mispaired T cell receptors may cause the immune cells to attack healthy cells in the body, leading to autoimmune disease. To make T cell receptor gene therapy safe, the cancer-specific receptor must not mispair with the resident receptor.

Here, Bethune et al. describe a new strategy to prevent T cell receptors from mispairing. The researchers altered the arrangement of particular regions in a cancer-specific T cell receptor to make a new receptor called a domain-swapped T cell receptor (dsTCR). Like normal T cell receptors, the dsTCRs were exported to the T cell surface and were able to interact with other proteins involved in immune responses. Furthermore, T cells armed with dsTCRs were able to kill cancer cells and prevent tumor growth in mice. Unlike other cancer-specific receptors, dsTCRs did not mispair with the resident T cell receptors in mouse or human cells, and did not cause autoimmune disease in mice.

The findings of Bethune et al. show that the structure of the T cell receptor is unexpectedly robust, in that it still works even if it is modified. The next step is to study dsTCRs in more detail with the aim of optimizing them so that they might be used in human clinical trials in the future.

DOI:http://dx.doi.org/10.7554/eLife.19095.002

Identification of peptide-specific TCR genes by in vitro peptide stimulation and CDR3 length polymorphism analysis

Identification of TCR genes specific for tumor-associated antigens (TAAs) is necessary for TCR gene modification of T cells, which is applied in anti-tumor adoptive T cell therapy (ACT). The usual identification methods are based on isolating single peptide-responding T cells and cloning the TCR gene by in vitro expansion or by single-cell RT-PCR. However, the long and exacting in vitro culture period and demanding operational requirements restrict the application of these methods. Immunoscope is an effective tool that profiles a repertoire of TCRs and identifies significantly expanded clones through CDR3 length analysis. In this study, a survivin-derived mutant peptide optimized for HLA-A2 binding was selected to load DCs and activate T cells. The monoclonal expansion of TCRA and TCRB genes was separately identified by Immunoscope analysis and following sequence identification, the properly paired TCR genes were transferred into T cells. Peptide recognition and cytotoxicity assays indicated that TCR-modified PBMCs could respond to both the mutant and wild type peptides and lyse target cells. These results show that combining Immunoscope with in vitro peptide stimulation provides an alternative and superior method for identifying specific TCR genes, which represents a significant advance for the application of TCR gene-modified T cells.

Asymmetry of Cell Division in CFSE-Based Lymphocyte Proliferation Analysis

Flow cytometry-based analysis of lymphocyte division using carboxyfluorescein succinimidyl ester (CFSE) dye dilution permits acquisition of data describing cellular proliferation and differentiation. For example, CFSE histogram data enable quantitative insight into cellular turnover rates by applying mathematical models and parameter estimation techniques. Several mathematical models have been developed using different types of deterministic or stochastic approaches. However, analysis of CFSE proliferation assays is based on the premise that the label is halved in the two daughter cells. Importantly, asymmetry of protein distribution in lymphocyte division is a basic biological feature of cell division with the degree of the asymmetry depending on various factors. Here, we review the recent literature on asymmetric lymphocyte division and CFSE-based lymphocyte proliferation analysis. We suggest that division- and label-structured mathematical models describing CFSE-based cell proliferation should take into account asymmetry and time-lag in cell proliferation. Utilization of improved modeling algorithms will permit straightforward quantification of essential parameters describing the performance of activated lymphocytes.

Chimeric adenoviral vector Ad5F35L containing the Ad5 natural long-shaft exhibits efficient gene transfer into human T lymphocytes

Adoptive therapy using T cells modified with tumour antigen-specific T cell receptor (TCR) genes has become a popular area of research in tumour biotherapy research. However, the efficiency of this treatment is low. To increase the efficiency of this therapy, the antigen specific TCR expression in the T cells needs to be improved. Adenoviral vector-mediated gene expression is an attractive approach to bypass the issue of TCR gene modification. The efficiency of adenovirus vector serotype 5 (Ad5) infection is low due to the absence of coxsackievirus B-adenovirus receptor (CAR) expression in T cells. In the present study, a chimeric adenoviral vector (Ad5F35L) was generated; this construct contained both the natural long-shaft of Ad5 and the Ad35 knob. A transduction study showed that the Ad5F35L vector exhibited a higher transduction efficiency in human primary T lymphocytes than the Ad5 vector and the Ad5F35S vector, which contained the Ad35 natural short-shaft and the Ad35 knob. Similar transduction efficiencies were observed for both CD4(+) T lymphocytes and CD8(+) T lymphocytes and the transfection was independent of the expression of cell surface receptors. The activation of T lymphocytes resulted in an improvement of the Ad5F35L transduction efficiency in CD4(+) T cells and a decrease in Ad5F35L transduction efficiency in CD8(+) T cells. The results demonstrate that Ad5F35L is a promising viral vector and will facilitate the clinical application of tumour antigen-specific TCR gene therapy.

Characterization of T-cell receptors directed against HLA-A*01-restricted and C*07-restricted epitopes of MAGE-A3 and MAGE-A12

The ability of T cells that have been genetically engineered to express T-cell receptors (TCRs) directed against tumor antigens to mediate tumor regression has been demonstrated in several clinical trials. These TCRs have primarily targeted HLA-A*0201-restricted TCRs, as approximately 50% of whites, who represent the predominant population of patients who develop melanomas, expresses this HLA class I allele. These therapies could be extended to additional patients through the use of TCRs that target epitopes that are presented by additional class I alleles that are prevalent in this population such as HLA-C*07 and HLA-A*01, which are expressed by approximately 50% and 30% of the patient population respectively. Therefore, 2 TCRs that recognize an epitope of MAGE-A12 in the context of HLA-C*07 and 2 TCRs that recognize an epitope of MAGE-A3 in the context of HLA-A*01 were isolated from tumor-reactive T-cell clones and cloned in a recombinant retroviral expression vector. Comparative studies indicated that one of the 2 MAGE-A3-reactive TCRs and one of the 2 MAGE-A12-reactive TCRs were superior to the additional TCRs in conferring transduced peripheral blood mononuclear cells with the capacity to recognize a broad array of antigen and MHC-positive target cells. These results provide support for the use of these TCRs in cancer adoptive immunotherapy trials.

Molecular pathways: comparing the effects of drugs and T cells to effectively target oncogenes

Mutant cancer-driving oncogenes are the best therapeutic targets, both with drugs like small-molecule inhibitors (SMI) and adoptive T-cell therapy (ATT), the most effective form of immunotherapy. Cancer cell survival often depends on oncogenes, which implies that they are homogeneously expressed by all cancer cells and are difficult to select against. Mutant oncogene-directed therapy is relatively selective, as it targets preferentially the oncogene-expressing cancer cells. Both SMI and ATT can be highly effective in relevant preclinical models as well as selected clinical situations, and both share the risk of therapy resistance, facilitated by the frequent genetic instability of cancer cells. Recently, both therapies were compared in the same experimental model targeting the same oncogene. It showed that the oncogene-inactivating drug selected resistant clones, leading eventually to tumor relapse, whereas ATT eradicated large established tumors completely. The mode of tumor destruction likely explained the different outcome with only ATT destroying the tumor vasculature. Elucidating the cellular and molecular mechanisms responsible for tumor regression and relapse will define optimal conditions for the clinic. We argue that the ideal conditions of ATT in the experimental cancer model can be translated to individuals with cancer.

Potential of human γδ T cells for immunotherapy of osteosarcoma

Recurrent or metastatic osteosarcomas remain a challenging malignancy to treat. Therefore, development and testing of novel therapeutic strategies to target these patients are needed. Adoptive cellular therapy strategies are being evaluated intensively as a novel therapeutic strategy for cancer. Unlike αβ T cells requiring antigen processing and MHC-restricted peptide displayed by antigen-presenting cells, γδ T cells exhibit the potent MHC-unrestricted lytic activity against various tumors in vitro and in vivo. The recent considerable success of γδ T cell-based immunotherapy in lung metastasis of renal cell carcinoma warrants further efforts to apply this treatment to other cancers including osteosarcoma, especially recurrent and metastatic osteosarcomas. In this review, we summarize the available evidence on γδ T cell-based immunotherapy for osteosarcoma that has been achieved to date. More importantly, we discuss potential strategies of the combination of expanded γδ T cells and bisphosphonates, and modification and expansion of αβ TCR modified γδ T cells for improving its efficacy for the treatment of osteosarcoma.

Protective capacity of virus-specific T cell receptor-transduced CD8 T cells in vivo

The transfer of T cell receptor (TCR) genes by viral vectors represents a promising technique to generate antigen-specific T cells for adoptive immunotherapy. TCR-transduced T cells specific for infectious pathogens have been described, but their protective function in vivo has not yet been examined. Here, we demonstrate that CD8 T cells transduced with the P14 TCR specific for the gp33 epitope of lymphocytic choriomeningitis virus exhibit protective activities in both viral and bacterial infection models in mice.

How (specific) would like your T-cells today? Generating T-cell therapeutic function through TCR-gene transfer

T-cells are central players in the immune response against both pathogens and cancer. Their specificity is solely dictated by the T-cell receptor (TCR) they clonally express. As such, the genetic modification of T lymphocytes using pathogen- or cancer-specific TCRs represents an appealing strategy to generate a desired immune response from peripheral blood lymphocytes. Moreover, notable objective clinical responses were observed in terminally ill cancer patients treated with TCR-gene modified cells in several clinical trials conducted recently. Nevertheless, several key aspects of this approach are the object of intensive research aimed at improving the reliability and efficacy of this strategy. Herein, we will survey recent studies in the field of TCR-gene transfer dealing with the improvement of this approach and its application for the treatment of malignant, autoimmune, and infectious diseases.

Incorporation of transmembrane hydrophobic mutations in the TCR enhance its surface expression and T cell functional avidity

TCR-gene transfer represents an effective way to redirect the specificity of T lymphocytes for therapeutic purposes. Recent successful clinical trials have underscored the potential of this approach in which efficient expression of the exogenous TCR has been directly linked to the efficacy of T cell activity. It has been also demonstrated that the TCR exhibits a lack of stability associated with the presence of positively charged residues in its transmembrane (TM) region. In this study, we designed an original approach selectively to improve exogenous TCR stability by increasing the hydrophobic nature of the TCRα TM region. Incorporation of hydrophobic residues at evolutionarily permissive positions resulted in an enhanced surface expression of the TCR chains, leading to an improved cellular avidity and anti-tumor TCR activity. Furthermore, this strategy was successfully applied to different TCRs, enabling the targeting of human tumors from different histologies. We also show that the combination of these hydrophobic mutations with another TCR-enhancing approach further improved TCR expression and function. Overall, these findings provide information regarding TCR TM composition that can be applied for the improvement of TCR-gene transfer-based treatments.

Immunology in the clinic review series; focus on cancer: double trouble for tumours: bi-functional and redirected T cells as effective cancer immunotherapies

Cancer is one of the most important pathological conditions facing mankind in the 21st century, and is likely to become the most important cause of death as improvements continue in health, diet and life expectancy. The immune response is responsible for controlling nascent cancer through immunosurveillance. If tumours escape this control, they can develop into clinical cancer. Although surgery and chemo- or radiotherapy have improved survival rates significantly, there is a drive to reharness immune responses to treat disease. As T cells are one of the key immune cells in controlling cancer, research is under way to enhance their function and improve tumour targeting. This can be achieved by transduction with tumour-specific T cell receptor (TCR) or chimaeric antigen receptors (CAR) to generate redirected T cells. Virus-specific cells can also be transduced with TCR or CAR to create bi-functional T cells with specificity for both virus and tumour. In this review we outline the development and optimization of redirected and bi-functional T cells, and outline the results from current clinical trials using these cells. From this we discuss the challenges involved in generating effective anti-tumour responses while avoiding concomitant damage to normal tissues and organs.

Redirected lysis of human melanoma cells by a MCSP/CD3-bispecific BiTE antibody that engages patient-derived T cells

Melanoma-associated chondroitin sulfate proteoglycan (MCSP; also called HMW-MAA, CSPG4, NG2, MSK16, MCSPG, MEL-CSPG, or gp240) is a well characterized melanoma cell-surface antigen. In this study, a new bispecific T-cell engaging (BiTE) antibody that binds to MCSP and human CD3 (MCSP-BiTE) was tested for its cytotoxic activity against human melanoma cell lines. When unstimulated peripheral mononuclear blood cells (PBMCs) derived from healthy donors were cocultured with melanoma cells at effector:target ratios of 1:1, 1:5, or 1:10, and treated with MCSP-BiTE antibody at doses of 10, 100, or 1000 ng/mL, all MCSP-expressing melanoma cell lines (n=23) were lysed in a dose-dependent and effector:target ratio-dependent manner, whereas there was no cytotoxic activity against MCSP-negative melanoma cell lines (n=2). To investigate whether T cells from melanoma patients could act as effector cells, we cocultured unstimulated PBMCs with allogeneic melanoma cells from 13 patients (4 stage I/II, 3 stage III, and 6 stage IV) or with autologous melanoma cells from 2 patients (stage IV). Although cytotoxic activity varied, all 15 PBMC samples mediated significant redirected lysis by the BiTE antibody. When PBMC or CD8 T cells were prestimulated by anti-CD3 antibody OKT-3 and interleukin-2, the MCSP-BiTE concentrations needed for melanoma cell lysis decreased up to 1000-fold. As MCSP is expressed on most human melanomas, immunotherapy with MCSP/CD3-bispecific antibodies merits clinical investigation.

Development and use of TCR transgenic mice for malaria immunology research

T-cell receptor transgenic mice are powerful tools to study T cell responses to malaria parasites. They allow for a population of antigen specific T cells to be monitored during developing responses to immunization or parasite infection; this makes them particularly useful to study fundamental aspects of T cell activation, differentiation, and migration in different tissue compartments. Moreover, the use of these cells allows for a thorough analysis of the mechanisms of antiparasite activity by T cells.

Genetically modulating T-cell function to target cancer

The adoptive transfer of tumor-specific T-lymphocytes holds promise for the treatment of metastatic cancer. Genetic modulation of T-lymphocytes using TCR transfer with tumor-specific TCR genes is an attractive strategy to generate anti-tumor response, especially against large solid tumors. Recently, several clinical trials have demonstrated the therapeutic potential of this approach which lead to impressive tumor regression in cancer patients. Still, several factors may hinder the clinical benefit of this approach, such as the type of cells to modulate, the vector configuration or the safety of the procedure. In the present review we will aim at giving an overview of the recent developments related to the immune modulation of the anti-tumor adaptive response using genetically engineered lymphocytes and will also elaborate the development of other genetic modifications to enhance their anti-tumor immune response.

A practical approach to T-cell receptor cloning and expression

Although cloning and expression of T-cell Receptors (TcRs) has been performed for almost two decades, these procedures are still challenging. For example, the use of T-cell clones that have undergone limited expansion as starting material to limit the loss of interesting TcRs, must be weighed against the introduction of mutations by excess PCR cycles. The recent interest in using specific TcRs for cancer immunotherapy has, however, increased the demand for practical and robust methods to rapidly clone and express TcRs. Two main technologies for TcR cloning have emerged; the use of a set of primers specifically annealing to all known TcR variable domains, and 5′-RACE amplification. We here present an improved 5′-RACE protocol that represents a fast and reliable way to identify a TcR from 10⁵ cells only, making TcR cloning feasible without a priori knowledge of the variable domain sequence. We further present a detailed procedure for the subcloning of TcRα and β chains into an expression system. We show that a recombination-based cloning protocol facilitates simple and rapid transfer of the TcR transgene into different expression systems. The presented comprehensive method can be performed in any laboratory with standard equipment and with a limited amount of starting material. We finally exemplify the straightforwardness and reliability of our procedure by cloning and expressing several MART-1-specific TcRs and demonstrating their functionality.

T-cell receptor gene therapy: critical parameters for clinical success

T-cell receptor (TCR) gene therapy aims to induce immune reactivity against tumors by introducing genes encoding a tumor-reactive TCR into patient T cells. This approach has been extensively tested in preclinical mouse models, and initial clinical trials have demonstrated the feasibility and potential of TCR gene therapy as a cancer treatment. However, data obtained from preclinical and clinical studies suggest that both the therapeutic efficacy and the safety of TCR gene therapy can be and needs to be further enhanced. This review highlights those strategies that can be followed to develop TCR gene therapy into a clinically relevant treatment option for cancer patients.

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.

T-cell engineering for cancer immunotherapy

The adoptive transfer of tumor-reactive cells is a promising approach for the treatment of melanoma and some other cancers. To remedy the difficulties associated with the isolation and expansion of tumor-reactive T cells in most cancer patients, peripheral blood T cells can be retargeted to any chosen tumor antigen by the genetic transfer of an antigen-specific receptor. The transduced receptors may be human leukocyte antigen-restricted, heterodimeric T-cell antigen receptor (TCRs), or chimeric antigen receptors (CARs), which typically recognize native cell-surface antigens. Considerable progress has been made in recent years to address the challenges posed by the transfer of either receptor type. Vector and protein modifications enable the expression of TCR chains in human T cells at functional levels and with a reduced risk of mis-pairing with endogenous TCR chains. The combinatorial inclusion of activating and costimulatory domains in CARs has dramatically enhanced the signaling properties of the chimeric receptors described over a decade ago. Based on the effective T-cell transduction and expansion procedures now available to support clinical investigation, improved designer TCRs and second generation CARs targeting an array of antigens are being evaluated in a range of hematological malignancies and solid tumors.

Targeting the epidermal growth factor receptor (HER) family by T cell receptor gene-modified T lymphocytes

Human epidermal growth factor receptor 2 (HER2) has been successfully targeted as a breast cancer-associated antigen by various strategies. HER2 is also overexpressed in other solid tumors such as stomach cancer, as well as in hematological malignancies such as acute lymphoblastic leukemia. HER2-targeted therapies are currently under clinical investigation for a panel of malignancies. In this study, we isolated the T cell receptor (TCR) genes of a HER2-reactive allo-human leukocyte antigen-A2-restricted CTL clone and introduced the TCRα- and β-chain genes into the retrovirus vector MP71. Murinization and codon optimization of the HER2-reactive TCR was required for efficient TCR expression in primary human T cells. The tumor recognition efficiency of HER2-TCR gene-modified T cells was similar to the parental CTL clone from which the TCR genes were isolated. The known cross-reactivity of the HER2-reactive TCR with HER3 and HER4 was retained when the TCR was transduced into primary T cells. Our results could contribute to the development of a TCR-based approach for the treatment of HER2-positive breast cancer, as well as of other malignancies expressing HER2, HER3, and/or HER4.

NCI First International Workshop on The Biology, Prevention and Treatment of Relapse after Allogeneic Hematopoietic Cell Transplantation: report from the committee on prevention of relapse following allogeneic cell transplantation for hematologic malignancies

Prevention of relapse after allogeneic hematopoietic stem cell transplantation is the most likely approach to improve survival of patients treated for hematologic malignancies. Herein we review the limits of currently available transplant therapies and the innovative strategies being developed to overcome resistance to therapy or to fill therapeutic modalities not currently available. These novel strategies include nonimmunologic therapies, such as targeted preparative regimens and posttransplant drug therapy, as well as immunologic interventions, including graft engineering, donor lymphocyte infusions, T cell engineering, vaccination, and dendritic cell-based approaches. Several aspects of the biology of the malignant cells as well as the host have been identified that obviate success of even these newer strategies. To maximize the potential for success, we recommend pursuing research to develop additional targeted therapies to be used in the preparative regimen or as maintenance posttransplant, better characterize the T cell and dendritic cells subsets involved in graft-versus-host disease and the graft-versus-leukemia/tumor effect, identify strategies for timing immunologic or nonimmunologic therapies to eliminate the noncycling cancer stem cell, identify more targets for immunotherapies, develop new vaccines that will not be limited by HLA, and develop methods to identify populations at very high risk for relapse to accelerate clinical development and avoid toxicity in patients not at risk for relapse.

RNA interference targeting programmed death receptor-1 improves immune functions of tumor-specific T cells

Adoptive cell transfer (ACT), either using rapidly expanded tumor infiltrating lymphocytes or T-cell receptor transduced peripheral blood lymphocytes, can be considered one of the most promising approaches in cancer immunotherapy. ACT results in the repopulation of the host with high frequencies of tumor-specific T cells; however, optimal function of these cells within the tumor micro-environment is required to reach long-term tumor clearance. We and others have shown that ongoing anti-tumor immune responses can be impaired by the expression of ligands, such as PD-L1 (B7-H1) on tumor cells. Such inhibitory molecules can affect T cells at the effector phase via their receptor PD-1. PD-L1/PD-1 interaction has indeed been shown crucial in inducing T-cell anergy and maintaining peripheral tolerance. In order to maximize anti-tumor responses, antibodies that target the PD-1/PD-L1 axis are currently in phase I/II trials. Alternatively, a more refined approach could be the selective targeting of PD-1 in tumor-specific T cells to obtain long-term resistance against PD-1-mediated inhibition. We addressed whether this goal could be achieved by means of retroviral siRNA delivery. Effective siRNA sequences resulting in the reduction of surface PD-1 expression led to improved murine as well as human T-cell immune functions in response to PD-L1 expressing melanoma cells. These data suggest that blockade of PD-1-mediated T-cell inhibition through siRNA forms a promising approach to achieve long-lasting enhancement of tumor-specific T-cell function in adoptive T-cell therapy protocols.

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-affinity 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.

Chimeric antigen receptor-engineered T cells for immunotherapy of cancer

CD4⁺ and CD8⁺ T lymphocytes are powerful components of adaptive immunity, which essentially contribute to the elimination of tumors. Due to their cytotoxic capacity, T cells emerged as attractive candidates for specific immunotherapy of cancer. A promising approach is the genetic modification of T cells with chimeric antigen receptors (CARs). First generation CARs consist of a binding moiety specifically recognizing a tumor cell surface antigen and a lymphocyte activating signaling chain. The CAR-mediated recognition induces cytokine production and tumor-directed cytotoxicity of T cells. Second and third generation CARs include signal sequences from various costimulatory molecules resulting in enhanced T-cell persistence and sustained antitumor reaction. Clinical trials revealed that the adoptive transfer of T cells engineered with first generation CARs represents a feasible concept for the induction of clinical responses in some tumor patients. However, further improvement is required, which may be achieved by second or third generation CAR-engrafted T cells.

Minimal amino acid exchange in human TCR constant regions fosters improved function of TCR gene-modified T cells

TCR gene therapy using adoptive transfer of TCR gene-modified T cells is a new strategy for treatment of cancer. One critical prerequisite for TCR gene therapy is sufficient expression of transferred TCRs. Several strategies to achieve optimal expression were developed, including "murinization," which replaces the human TCRalpha and TCRbeta constant regions by their murine counterparts. Using a series of mouse-human hybrid constructs, we have identified nine amino acids responsible for the improved expression of murinized TCRs. Five essential amino acid exchanges were identified in the TCRbeta C region, with exchange of a glutamic acid (human) for a basic lysine (mouse) at position 18 of the C region, being most important. For the TCRalpha C region, an area of four amino acids was sufficient for improved expression. The minimally murinized TCR variants (harboring only nine residues of the mouse sequence) enhanced expression of human TCRs by supporting preferential pairing of transferred TCR chains and a more stable association with the CD3 proteins. Most important, usage of minimally murinized TCR chains improved the function of transduced primary human T cells in comparison with cells transduced with wild-type TCRs. For TCR gene therapy, the utilization of minimally instead of completely murinized constant regions dramatically reduces the number of foreign residues and thereby the risk for immunogenicity of therapeutic TCRs.

Lethal graft-versus-host disease in mouse models of T cell receptor gene therapy

The transfer of T cell receptor (TCR) genes can be used to induce immune reactivity toward defined antigens to which endogenous T cells are insufficiently reactive. This approach, which is called TCR gene therapy, is being developed to target tumors and pathogens, and its clinical testing has commenced in patients with cancer. In this study we show that lethal cytokine-driven autoimmune pathology can occur in mouse models of TCR gene therapy under conditions that closely mimic the clinical setting. We show that the pairing of introduced and endogenous TCR chains in TCR gene-modified T cells leads to the formation of self-reactive TCRs that are responsible for the observed autoimmunity. Furthermore, we demonstrate that adjustments in the design of gene therapy vectors and target T cell populations can be used to reduce the risk of TCR gene therapy-induced autoimmune pathology.

TCR mispairing in genetically modified T cells was detected by fluorescence resonance energy transfer

Adoptive transfer of T lymphocytes genetically modified with antigen-specific T cell receptor (TCR) constitutes a promising approach for the treatment of malignant tumors and virus infections. One of the challenges in this field of TCR gene therapy is TCR mispairing defining the incorrect pairing between an introduced TCR α or β chain and an endogenous TCR β or α chain, which results in diluted surface expression of the therapeutic TCR αβ. Although there is currently no clinical evidence for TCR mispairing-induced autoreactivity, the generation of autoreactive TCRs upon TCR mispairing cannot be excluded. So it is important to detect TCR mispairing to evaluate the efficiency of TCR gene therapy. Currently there is no available quantitative assay for the measurement of TCR mispairing. Fluorescence resonance energy transfer (FRET) is a powerful approach for identifying biologically relevant molecular interactions with high spatiotemporal resolution. In this study, we described the method of FRET for the measurement of TCR mispairing. It was found that the average FRET efficiency was 12.2 ± 7.5% in HeLa cells and 8.4 ± 3.3% in Jurkat cells (P = 0.026605). The reduction of FRET efficiency in lymphocytes reflected the presence of mispaired TCRs, indicating there were ~30% TCR mispairing in lymphocytes. This study provides a quantitative intracellular assay that can be used to detect TCR mispairing in genetically modified T lymphocytes.

T-cell receptor gene-modified T cells with shared renal cell carcinoma specificity for adoptive T-cell therapy

PURPOSE

Adoptive therapy with genetically engineered T cells carrying redirected antigen specificity is a new option for the treatment of cancer. This approach is not yet available for metastatic renal cell carcinoma (RCC), due to the scarcity of therapeutically useful reagents. We analyzed tumor-infiltrating lymphocytes (TIL) from RCC to identify T-cell specificities with shared tumor-specific recognition to develop T-cell receptor (TCR)-engineered T lymphocytes for adoptive therapy of RCC.

EXPERIMENTAL DESIGN

We established a T-cell clone from TIL that recognized a human leukocyte antigen (HLA)-A2-restricted tumor antigen. The TCR alpha- and beta-chain genes were isolated, modified by codon optimization and murinization, and retrovirally transduced into peripheral blood lymphocytes (PBL). A TCR-expressing indicator line (B3Z-TCR53) was established to screen for antigen prevalence in RCC, other malignancies, and normal cell counterparts.

RESULTS

TCR53-engineered PBL recapitulated the specificity of the TIL and showed tumor-specific HLA-A2-restricted effector activities (IFN-gamma, tumor necrosis factor-alpha, interleukin-2, macrophage inflammatory protein-1beta, cytotoxicity). PBL-TCR53 of healthy donors and RCC patients exhibited similar transduction efficiency, expansion, and polyfunctional profile. Using B3Z-TCR53 cells, 130 tumor and normal cells were screened and shared TCR53 peptide: MHC expression was found in >60% of RCC and 25% of tumor lines of other histology, whereas normal tissue cells were not recognized.

CONCLUSIONS

To date, TCR53 is the only TCR with shared HLA-A2-restricted recognition of RCC. It fulfills the criteria for utilization in TCR gene therapy and advances T cell-based immunotherapy to patients with RCC and other malignancies expressing the TCR ligand.

Non-MHC-dependent redirected T cells against tumor cells

Adoptive transfer of T cells with restricted tumor specificity provides a promising approach to immunotherapy of cancers. However, the isolation of autologous cytotoxic T cells that recognize tumor-associated antigens is time consuming and fails in many instances. Alternatively, gene modification with tumor antigen-specific T-cell receptors (TCR) or chimeric antigen receptors (CARs) can be used to redirect the specificity of large numbers of immune cells toward the malignant cells. Chimeric antigen receptors are composed of the single-chain variable fragment (scFv) of a tumor-recognizing antibody cloned in frame with human T-cell signaling domains (e.g., CD3zeta, CD28, OX40, 4-1BB), thus combining the specificity of antibodies with the effector functions of cytotoxic T cells. Upon antigen binding, the intracellular signaling domains of the CAR initiate cellular activation mechanisms including cytokine secretion and cytolysis of the antigen-positive target cell.In this chapter, we provide detailed protocols for large-scale ex vivo expansion of T cells and manufacturing of medium-scale batches of CAR-expressing T cells for translational research by mRNA electroporation. An anti-CD19 chimeric receptor for the targeting of leukemias and lymphomas was used as a model system. We are currently scaling up the protocols to adapt them to cGMP production of a large number of redirected T cells for clinical applications.

Treatment of lymphoma with adoptively transferred T cells

BACKGROUND

Chemotherapy-resistant lymphomas can be cured with allogeneic hematopoietic cell transplantation, demonstrating the susceptibility of these tumors to T cell mediated immune responses. However, high rates of transplant-related morbidity and mortality limit this approach. Efforts have, therefore, been made to develop alternative T cell based therapies, and there is growing evidence that adoptive therapy with T cells targeted to lymphoma-associated antigens may be a safe and effective new method for treating this group of diseases.

OBJECTIVE/METHODS

We review publications on adoptive therapy with ex vivo expanded T cells targeting viral antigens, as well as genetically modified autologous T cells, as strategies for the treatment of lymphoma, with the goal of providing an overview of these approaches.

RESULTS/CONCLUSIONS

Epstein-Barr virus specific T cell therapy is an effective and safe method of treating Epstein-Barr virus associated lymphomas; however, most lymphoma subtypes do not express EBV antigens. For these diseases, adoptive immunotherapy with genetically modified T cells expressing chimeric T cell receptors targeting lymphoma-associated antigens such as CD19 and CD20 appears to be a promising alternative. Recent innovations including enhanced co-stimulation, exogenous cytokine administration and use of memory T cells promise to overcome many of the limitations and pitfalls initially encountered with this approach.

Adoptive immunotherapy for cancer: the next generation of gene-engineered immune cells

Adoptive cellular immunotherapy involving transfer of tumor-reactive T cells has shown some notable antitumor responses in a minority of cancer patients. In particular, transfer of tumor-infiltrating lymphocytes has resulted in long-term objective responses in patients with advanced melanoma. However, the inability to isolate sufficient numbers of tumor-specific T cells from most malignancies has restricted the broad utility of this approach. An emerging approach to circumvent this limitation involves the genetic modification of effector cells with T cell receptor (TCR) transgenes or chimeric single-chain variable fragment (scFv) receptors that can specifically redirect T cells to tumor. There has been much progress in the design of TCR and scFv receptors to enhance the antigen-specific activation of effector cells and their trafficking and persistence in vivo. Considerable effort has been directed toward improving the safety of this approach and reducing the immunogenicity of the receptor. This review discusses the latest developments in the field of adoptive immunotherapy using genetically modified immune cells that have been transduced with either TCR or scFv receptor transgenes and used in preclinical and clinical settings as anticancer agents.

CMV-specific TCR-transgenic T cells for immunotherapy

Reactivation of CMV can cause severe disease after allogeneic hemopoietic stem cell transplantation. Adoptive T cell therapy was successfully used for patients who had received transplants from CMV-positive donors. However, patients with transplants from CMV-negative donors are at highest risk, and an adoptive therapy is missing because CMV-specific T cells are not available from such donors. To address this problem, we used retroviral transfer of CMV-specific TCR genes. We generated CMV-specific T cell clones of several HLA restrictions recognizing the endogenously processed Ag pp65. The genes of four TCRs were cloned and transferred to primary T cells from CMV-negative donors. These CMV-TCR-transgenic T cells displayed a broad spectrum of important effector functions (secretion of IFN-gamma and IL-2, cytotoxicity, proliferation) in response to endogenously processed pp65 and could be enriched and expanded by strictly Ag-specific stimulation. Expansion of engineered T cells was accompanied by an increase in specific effector functions, indicating that the transferred specificity is stable and fully functional. Hence, we expect these CMV-TCR-transgenic T cells to be effective in controlling acute CMV disease and establishing an antiviral memory.

The allogeneic graft-versus-cancer effect

Allogeneic haematological stem cell transplantation (HSCT) has developed into immunotherapy. Donor CD4+, CD8+ and natural killer (NK) cells have been reported to mediate graft-versus-leukaemia (GVL) effects, using Fas-dependent killing and perforin degranulation to eradicate malignant cells. Cytokines, such as interleukin-2, interferon-gamma and tumour necrosis factor-alpha potentiate the GVL effect. Post-transplant adoptive therapy of cytotoxic T-cells (CTL) against leukaemia-specific antigens, minor histocompatibility antigens, or T-cell receptor genes may constitute successful approaches to induce anti-tumour effects. Clinically, a significant GVL effect is induced by chronic rather than acute graft-versus-host disease (GVHD). An anti-tumour effect has also been reported for myeloma, lymphoma and solid tumours. Reduced intensity conditioning enables HSCT in older and disabled patients and relies on the graft-versus-tumour effect. Donor lymphocyte infusions promote the GVL effect and can be given as escalating doses with response monitored by minimal residual disease. A high CD34+ cell dose of peripheral blood stem cells increases GVL. There is a balance between effective immunosuppression, low incidence of GVHD and relapse. For instance, T-cell depletion of the graft increases the risk of relapse. This paper reviews the current knowledge in graft-versus-cancer effects. Future directions, such as immunotherapy using leukaemia-specific CTLs, allo-depleted T-cells and suicide gene manipulated T-cells, are presented.