Adoptive immunotherapy of disseminated leukemia with TCR-transduced, CD8+ T cells expressing a known endogenous TCR

Genome Editing for Engineering the Next Generation of Advanced Immune Cell Therapies

Our current genetic engineering capacity through synthetic biology and genome editing is the foundation of a revolution in biomedical science: the use of genetically programmed cells as therapeutics. The prime example of this paradigm is the adoptive transfer of genetically engineered T cells to express tumor-specific receptors, such as chimeric antigen receptors (CARs) or engineered T-cell receptors (TCR). This approach has led to unprecedented complete remission rates in patients with otherwise incurable hematological malignancies. However, this approach is still largely ineffective against solid tumors, which comprise the vast majority of neoplasms. Also, limitations associated with the autologous nature of this therapy and shared markers between cancer cells and T cells further restrict the access to these therapies. Here, we described how cutting-edge genome editing approaches have been applied to unlock the full potential of these revolutionary therapies, thereby increasing therapeutic efficacy and patient accessibility.

Leukemia's Next Top Model? Syngeneic Models to Advance Adoptive Cellular Therapy

In recent years, there has been an emphasis on harnessing the immune system for therapeutic interventions. Adoptive cell therapies (ACT) have emerged as an effective option for B-cell derived hematological malignancies. Despite remarkable successes with ACT, immune dysregulation and the leukemia microenvironment can critically alter clinical responses. Therefore, preclinical modeling can contribute to the advancement of ACT for leukemias. Human xenografts, the current mainstay of ACT in vivo models, cannot evaluate the impact of the immunosuppressive leukemia microenvironment on adoptively transferred cells. Syngeneic mouse models utilize murine tumor models and implant them into immunocompetent mice. This provides an alternative model, reducing the need for complicated breeding strategies while maintaining a matched immune system, stromal compartment, and leukemia burden. Syngeneic models that evaluate ACT have analyzed the complexity of cytotoxic T lymphocytes, T cell receptor transgenics, and chimeric antigen receptors. This review examines the immunosuppressive features of the leukemia microenvironment, discusses how preclinical modeling helps predict ACT associated toxicities and dysfunction, and explores publications that have employed syngeneic modeling in ACT studies for the improvement of therapy for leukemias.

Identification of Claudin 6-specific HLA class I- and HLA class II-restricted T cell receptors for cellular immunotherapy in ovarian cancer

Adoptive cell therapy (ACT) is one of promising immunotherapies for cancer patients by providing a large amount of cancer antigen-specific effector T cells that can be manufactured rapidly by ex vivo gene engineering. To provide antigen-specificity to patients’ autologous T cells in a short-term culture, T-cell receptors (TCRs) or chimeric antigen receptors (CARs) are transduced to bulk T cells. Because of intra- and inter-tumoral heterogeneity in tumor antigen expression, a repertoire of TCR or CAR genes targeting a wide range of tumor antigens are required for a broad and effective treatment by ACT. Here, we characterized immunogenicity of claudin 6 (CLDN6) in ovarian cancer patients and identified specific TCR genes from CD8⁺ and CD4⁺ T cells. CLDN6 protein was frequently expressed on EpCAM⁺ ovarian cancer cells but not CD45⁺ lymphocytes in tumor ascites of ovarian cancer patients. Spontaneous CLDN6-specific CD4⁺ and CD8⁺ T-cell response was detected in peripheral blood mononuclear cells (PBMCs) from 1 out of 17 ovarian cancer patients. HLA-A*02:01 (A2) and DR*04:04 (DR4)-restricted TCR genes were isolated from CLDN6-specific CD8⁺ and CD4⁺ T cells, respectively. T cells that were engineered with A2-restricted TCR gene recognized and killed A2⁺CLDN6⁺ cancer cells. DR4-restricted TCR-transduced T cells directly recognized DR4⁺CLDN6⁺-overexpressed cancer cells. Our results demonstrate that these CLDN6-specific TCR genes are useful as therapeutic genes for ACT to patients with ovarian and other solid tumors expressing CLDN6.

Detection of engineered T cells in FFPE tissue by multiplex in situ hybridization and immunohistochemistry

Identifying engineered T cells in situ is important to understand the location, persistence, and phenotype of these cells in patients after adoptive T cell therapy. While engineered cells are routinely characterized in fresh tissue or blood from patients by flow cytometry, it is difficult to distinguish them from endogenous cells in formalin-fixed, paraffin-embedded (FFPE) tissue biopsies. To overcome this limitation, we have developed a method for characterizing engineered T cells in fixed tissue using in situ hybridization (ISH) to the woodchuck hepatitis post-transcriptional regulatory element (WPRE) common in many lentiviral vectors used to transduce chimeric antigen receptor T (CAR-T) and T cell receptor T (TCR-T) cells, coupled with alternative permeabilization conditions that allows subsequent multiplex immunohistochemical (mIHC) staining within the same image. This new method provides the ability to mark the cells by ISH, and simultaneously stain for cell-associated proteins to immunophenotype CAR/TCR modified T cells within tumors, as well as assess potential roles of these cells in on-target/off-tumor toxicity in other tissue.

T-Cell Dysfunction as a Limitation of Adoptive Immunotherapy: Current Concepts and Mitigation Strategies

Simple Summary

T cells are immune cells that can be used to target infections or cancers. Adoptive T-cell immunotherapy leverages these properties and/or confers new features to T cells through ex vivo manipulations prior to their use in patients. However, as a “living drug,” the function of these cells can be hampered by several built-in physiological constraints and external factors that limit their efficacy. Manipulating T cells ex vivo can impart dysfunctional features to T cells through repeated stimulations and expansion, but it also offers many opportunities to improve the therapeutic potential of these cells, including emerging interventions to prevent or reverse T-cell dysfunction developing ex vivo or after transfer in patients. This review outlines the various forms of T-cell dysfunction, emphasizes how it affects various types of T-cell immunotherapy approaches, and describes current and anticipated strategies to limit T-cell dysfunction.

Abstract

Over the last decades, cellular immunotherapy has revealed its curative potential. However, inherent physiological characteristics of immune cells can limit the potency of this approach. Best defined in T cells, dysfunction associated with terminal differentiation, exhaustion, senescence, and activation-induced cell death, undermine adoptive cell therapies. In this review, we concentrate on how the multiple mechanisms that articulate the various forms of immune dysfunction impact cellular therapies primarily involving conventional T cells, but also other lymphoid subtypes. The repercussions of immune cell dysfunction across the full life cycle of cell therapy, from the source material, during manufacturing, and after adoptive transfer, are discussed, with an emphasis on strategies used during ex vivo manipulations to limit T-cell dysfunction. Applicable to cellular products prepared from native and unmodified immune cells, as well as genetically engineered therapeutics, the understanding and potential modulation of dysfunctional features are key to the development of improved cellular immunotherapies.

TCR Redirected T Cells for Cancer Treatment: Achievements, Hurdles, and Goals

Adoptive T cell therapy (ACT) is a rapidly evolving therapeutic approach designed to harness T cell specificity and function to fight diseases. Based on the evidence that T lymphocytes can mediate a potent anti-tumor response, initially ACT solely relied on the isolation, in vitro expansion, and infusion of tumor-infiltrating or circulating tumor-specific T cells. Although effective in a subset of cases, in the first ACT clinical trials several patients experienced disease progression, in some cases after temporary disease control. This evidence prompted researchers to improve ACT products by taking advantage of the continuously evolving gene engineering field and by improving manufacturing protocols, to enable the generation of effective and long-term persisting tumor-specific T cell products. Despite recent advances, several challenges, including prioritization of antigen targets, identification, and optimization of tumor-specific T cell receptors, in the development of tools enabling T cells to counteract the immunosuppressive tumor microenvironment, still need to be faced. This review aims at summarizing the major achievements, hurdles and possible solutions designed to improve the ACT efficacy and safety profile in the context of liquid and solid tumors.

T cell receptor gene therapy targeting WT1 prevents acute myeloid leukemia relapse post-transplant

Relapse after allogeneic hematopoietic cell transplantation (HCT) is the leading cause of death in patients with acute myeloid leukemia (AML) entering HCT with poor-risk features^1-3. When HCT does produce prolonged relapse-free survival, it commonly reflects graft-versus-leukemia effects mediated by donor T cells reactive with antigens on leukemic cells⁴. As graft T cells have not been selected for leukemia specificity and frequently recognize proteins expressed by many normal host tissues, graft-versus-leukemia effects are often accompanied by morbidity and mortality from graft-versus-host disease⁵. Thus, AML relapse risk might be more effectively reduced with T cells expressing receptors (TCRs) that target selected AML antigens⁶. We therefore isolated a high-affinity Wilms' Tumor Antigen 1-specific TCR (TCR_C4) from HLA-A2⁺ normal donor repertoires, inserted TCR_C4 into Epstein-Bar virus-specific donor CD8⁺ T cells (T_TCR-C4) to minimize graft-versus-host disease risk and enhance transferred T cell survival^7,8, and infused these cells prophylactically post-HCT into 12 patients ( NCT01640301 ). Relapse-free survival was 100% at a median of 44 months following infusion, while a concurrent comparative group of 88 patients with similar risk AML had 54% relapse-free survival (P = 0.002). T_TCR-C4 maintained TCR_C4 expression, persisted long-term and were polyfunctional. This strategy appears promising for preventing AML recurrence in individuals at increased risk of post-HCT relapse.

Antigen Targets for the Development of Immunotherapies in Leukemia

Immunotherapeutic approaches, including allogeneic stem cell transplantation and donor lymphocyte infusion, have significantly improved the prognosis of leukemia patients. Further efforts are now focusing on the development of immunotherapies that are able to target leukemic cells more specifically, comprising monoclonal antibodies, chimeric antigen receptor (CAR) T cells, and dendritic cell- or peptide-based vaccination strategies. One main prerequisite for such antigen-specific approaches is the selection of suitable target structures on leukemic cells. In general, the targets for anti-cancer immunotherapies can be divided into two groups: (1) T-cell epitopes relying on the presentation of peptides via human leukocyte antigen (HLA) molecules and (2) surface structures, which are HLA-independently expressed on cancer cells. This review discusses the most promising tumor antigens as well as the underlying discovery and selection strategies for the development of anti-leukemia immunotherapies.

T cell receptor-engineered T cells for leukemia immunotherapy

At present, refractory and relapse are major issues for leukemia therapy and a major cause of allogeneic hematopoietic stem cell transplant failure. Over the last decade, many studies have demonstrated that adoptive cancer antigen-specific T cell therapy is an effective option for leukemia therapy. Recently, T cell immunotherapy studies have mainly focused on chimeric antigen receptor- and T cell receptor-engineered T cells. Clinical trials involving chimeric antigen receptor-engineered T cells have been a major breakthrough and became a novel therapy for leukemia. As another potential therapy for leukemia, clinical application of TCR-engineered T cells remains in its infancy. This article presents a review of the current status of anti-leukemia immunotherapy using leukemia antigen-specific TCR-engineered T cells.

A biotherapy based on PSCs-in-3D spheroid-ameliorated biologics depletes in vivo cancer-sustaining stem cells

CSCs are able to survive routine anticancer procedures and peripheral-immune attack. Here we develop and detail a framework of CSC elimination governed by 3D-biologics. Pluripotent cells-engineered 3D-biologics (PMSB) and control non-3D-biologics were prepared from placenta-based somatic stem cells (PSCs) and inoculated respectively into senile hosts bearing progressive mammary, lung, colon carcinomas and melanoma. We demonstrate that PMSB evokes in vivo central-immune microenvironment with subsequent re-expression of thymosin-α1 ~ β4 in thymic cortex-medulla borderline for rapid MHC-unrestricted renewal of γδT-dominated immunocompetence. The post-renewal γδT-subsets could accurately bind and drive CSCs into apoptosis. Finally, with central/peripheral integral microenvironment renewal and TERT/Wnt/β-catenin pathway blockade, the CSC-subsets are fully depleted, leading to substantial cure of diverse tumors by PMSB inoculation (P < 0.01), yet not by non-3D-biologics. Thus, our study may contribute to open up a new avenue for tumor remission via pluripotent cells-engineered 3D-biologics addressing quick renewal of central-thymus and peripheral immune-microenvironment.

T Cells Engineered against a Native Antigen Can Surmount Immunologic and Physical Barriers to Treat Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinomas (PDAs) erect physical barriers to chemotherapy and induce multiple mechanisms of immune suppression, creating a sanctuary for unimpeded growth. We tested the ability of T cells engineered to express an affinity-enhanced T cell receptor (TCR) against a native antigen to overcome these barriers in a genetically engineered model of autochthonous PDA. Engineered T cells preferentially accumulate in PDA and induce tumor cell death and stromal remodeling. However, tumor-infiltrating T cells become progressively dysfunctional, a limitation successfully overcome by serial T cell infusions that resulted in a near-doubling of survival without overt toxicities. Similarly engineered human T cells lyse PDA cells in vitro, further supporting clinical advancement of this TCR-based strategy for the treatment of PDA.

The pharmacology of second-generation chimeric antigen receptors

Second-generation chimeric antigen receptors (CARs) retarget and reprogramme T cells to augment their antitumour efficacy. The combined activating and co-stimulatory domains incorporated in these CARs critically determine the function, differentiation, metabolism and persistence of engineered T cells. CD19-targeted CARs that incorporate CD28 or 4-1BB signalling domains are the best known to date. Both have shown remarkable complete remission rates in patients with refractory B cell malignancies. Recent data indicate that CD28-based CARs direct a brisk proliferative response and boost effector functions, whereas 4-1BB-based CARs induce a more progressive T cell accumulation that may compensate for less immediate potency. These distinct kinetic features can be exploited to further develop CAR-based T cell therapies for a variety of cancers. A new field of immunopharmacology is emerging.

In vivo imaging of T cells loaded with gold nanoparticles: a pilot study

PURPOSE

Malignant tumours develop strategies to avoid immune recognition and elimination by T cells, even in individuals with a fully functioning immune system. To explore the treatment approach of adoptive immunotherapy, we exploited T cells loaded with radiolabelled gold nanoparticles (AuNPs) to track T cells in vivo.

MATERIALS AND METHODS

Surface-modified AuNPs were radiolabelled with (111)In or (64)Cu. They were then transferred into T cells via electroporation. To evaluate the effectiveness of this process, T cells loaded with (111)In-radiolabelled AuNPs were injected directly into the right lung of nude mice for in vivo imaging by micro-SPECT/CT. T cells loaded with (64)Cu-radiolabelled AuNPs were then injected into the tail vein of nude mice and imaged by micro-PET/CT.

RESULTS

High uptake signals were observed in the right lung following the direct injection of T cells containing (111)In-labelled AuNPs. Imaging showed a marked difference in the dynamic biodistribution of T cells containing (64)Cu-labelled AuNPs when compared with (64)Cu-labelled AuNPs alone.

CONCLUSIONS

This study demonstrated the feasibility of the in vivo imaging of T cells loaded with radiolabelled AuNPs.

Re-adapting T cells for cancer therapy: from mouse models to clinical trials

Adoptive T-cell therapy involves the isolation, expansion, and reinfusion of T lymphocytes with a defined specificity and function as a means to eradicate cancer. Our research has focused on specifying the requirements for tumor eradication with antigen-specific T cells and T cells transduced to express a defined T-cell receptor (TCR) in mouse models and then translating these strategies to clinical trials. Our design of T-cell-based therapy for cancer has reflected efforts to identify the obstacles that limit sustained effector T-cell activity in mice and humans, design approaches to enhance T-cell persistence, develop methods to increase TCR affinity/T-cell functional avidity, and pursue strategies to overcome tolerance and immunosuppression. With the advent of genetic engineering, a highly functional population of T cells can now be rapidly generated and tailored for the targeted malignancy. Preclinical studies in faithful and informative mouse models, in concert with knowledge gained from analyses of successes and limitations in clinical trials, are shaping how we continue to develop, refine, and broaden the applicability of this approach for cancer therapy.

Gene-engineered T cells for cancer therapy

T cells have the capacity to eradicate diseased cells, but tumours present considerable challenges that render T cells ineffectual. Cancer cells often make themselves almost 'invisible' to the immune system, and they sculpt a microenvironment that suppresses T cell activity, survival and migration. Genetic engineering of T cells can be used therapeutically to overcome these challenges. T cells can be taken from the blood of cancer patients and then modified with genes encoding receptors that recognize cancer-specific antigens. Additional genes can be used to enable resistance to immunosuppression, to extend survival and to facilitate the penetration of engineered T cells into tumours. Using genetic modification, highly active, self-propagating 'slayers' of cancer cells can be generated.

CD8+ T-cell clones specific for the 5T4 antigen target renal cell carcinoma tumor-initiating cells in a murine xenograft model

The tumor antigen 5T4 is frequently expressed at high levels on renal cell carcinoma (RCC) and other epithelial carcinomas. Surveys of normal tissues demonstrate abundant 5T4 expression on placental trophoblast cells with limited expression elsewhere. 5T4 is the target for a therapeutic cancer vaccine (MVA-5T4) that elicits 5T4-specific serological, proliferative, and cytotoxic T lymphocyte (CTL) responses. However, the antitumor activity of 5T4-specific CTL has not been extensively characterized. CD8 T cells from HLA-A2 healthy donors (n=4) or RCC patients (n=2) were stimulated in vitro with the HLA-A2-binding nonamer peptides 5T417-25 or 5T497-105 and screened by flow cytometry with specific tetramers (TET). CD8/TET T-cell clones specific for 5T417-25 or 5T497-105 peptide were isolated from 4/6 and 1/4 donors, respectively. A subset of clones specific for 5T417-25 was cytolytic for MVA-5T4-infected HLA-A2 EBV-transformed lymphoblastoid cell line target cells and for constitutively HLA-A2-expressing and 5T4-expressing RCC tumor cell lines (including A498 RCC). In a xenoengraftment assay, the coinoculation of a representative 5T417-25-specific CTL clone with A498 RCC tumors cells into immune-deficient mice completely prevented growth of A498 tumors. Taken together, these data demonstrate high-avidity CD8 CTL able to recognize the naturally processed 5T417-25 epitope on RCC tumor cells including putative tumor-initiating cells are present in peripheral blood of both healthy donors and RCC patients. CD8T-cell immunity targeting 5T417-25 is therefore of substantial interest both as a potential target for further development of vaccination or adoptive cellular immunotherapy and for immune monitoring studies in association with nonspecific immunotherapies.

Immunotherapies in CLL

Chronic lymphocytic leukemia (CLL) is the most frequently diagnosed leukemia in the Western world, yet remains essentially incurable. Although initial chemotherapy response rates are high, patients invariably relapse and subsequently develop resistance to chemotherapy. For the moment, allogeneic hematopoietic stem cell transplant (allo-HSCT) remains the only potentially curative treatment for patients with CLL, but it is associated with high rates of treatment-related mortality. Immune-based treatment strategies to augment the cytotoxic potential of T cells offer exciting new treatment options for patients with CLL, and provide a unique and powerful spectrum of tools distinct from traditional chemotherapy. Among the most novel and promising of these approaches are chimeric antigen receptor (CAR)-based cell therapies that combine advances in genetic engineering and adoptive immunotherapy.

Abrogation of SRC homology region 2 domain-containing phosphatase 1 in tumor-specific T cells improves efficacy of adoptive immunotherapy by enhancing the effector function and accumulation of short-lived effector T cells in vivo

T cell expression of inhibitory proteins can be a critical component for the regulation of immunopathology owing to self-reactivity or potentially exuberant responses to pathogens, but it may also limit T cell responses to some malignancies, particularly if the tumor Ag being targeted is a self-protein. We found that the abrogation of Src homology region 2 domain-containing phosphatase-1 (SHP-1) in tumor-reactive CD8(+) T cells improves the therapeutic outcome of adoptive immunotherapy in a mouse model of disseminated leukemia, with benefit observed in therapy employing transfer of CD8(+) T cells alone or in the context of also providing supplemental IL-2. SHP-1(-/-) and SHP-1(+/+) effector T cells were expanded in vitro for immunotherapy. Following transfer in vivo, the SHP-1(-/-) effector T cells exhibited enhanced short-term accumulation, followed by greater contraction, and they ultimately formed similar numbers of long-lived, functional memory cells. The increased therapeutic effectiveness of SHP-1(-/-) effector cells was also observed in recipients that expressed the tumor Ag as a self-antigen in the liver, without evidence of inducing autoimmune toxicity. SHP-1(-/-) effector CD8(+) T cells expressed higher levels of eomesodermin, which correlated with enhanced lysis of tumor cells. Furthermore, reduction of SHP-1 expression in tumor-reactive effector T cells by retroviral transduction with vectors that express SHP-1-specific small interfering RNA, a translatable strategy, also exhibited enhanced antitumor activity in vivo. These studies suggest that abrogating SHP-1 in effector T cells may improve the efficacy of tumor elimination by T cell therapy without affecting the ability of the effector cells to persist and provide a long-term response.

Cellular therapies in acute lymphoblastic leukemia

ALL remains a difficult disease to treat. In the adult setting, most patients will ultimately die of their disease, whereas in the pediatric setting, relapsed and refractory disease remains a therapeutic challenge. Cellular therapy through allo-HSCT remains an option for these patients, and recent advances in alternative forms of allo-HSCT, including unrelated donor transplants, UCB transplants, and haploidentical transplants, have expanded the numbers of patients eligible for allo-HSCT but have not improved outcomes when compared with HLA-matched related allo-HSCTs. In light of this persistent failure, several novel adoptive cellular approaches are being investigated to treat patients with ALL. The use of enriched WT-1–specific donor T cells to treat patients with ALL is currently under investigation in phase I trials at several centers. Treatment of ALL with genetically modified T cells targeted to the CD19 antigen through the expression of a CD19-specific CAR also have entered phase I clinical trials at several centers. Similarly, a clinical trial treating patients with ALL with genetically modified NK cells targeted to the CD19 antigen has recently opened for accrual. Collectively, these ongoing and anticipated trials provide a promising role for adoptive cellular therapies in the treatment of ALL. What remains to be seen is whether this promise will either translate into improved outcomes for these patients or provide significant insights on which to design second-generation adoptive cell therapeutic clinical trials for ALL in the future.

Single-chain VαVβ T-cell receptors function without mispairing with endogenous TCR chains

Transduction of exogenous T-cell receptor (TCR) genes into patients' activated peripheral blood T cells is a potent strategy to generate large numbers of specific T cells for adoptive therapy of cancer and viral diseases. However, the remarkable clinical promise of this powerful approach is still being overshadowed by a serious potential consequence: mispairing of the exogenous TCR chains with endogenous TCR chains. These 'mixed' heterodimers can generate new specificities that result in graft-versus-host reactions. Engineering TCR constant regions of the exogenous chains with a cysteine promotes proper pairing and reduces the mispairing, but, as we show here, does not eliminate the formation of mixed heterodimers. By contrast, deletion of the constant regions, through use of a stabilized Vα/Vβ single-chain TCR (scTv), avoided mispairing completely. By linking a high-affinity scTv to intracellular signaling domains, such as Lck and CD28, the scTv was capable of activating functional T-cell responses in the absence of either the CD3 subunits or the co-receptors, and circumvented mispairing with endogenous TCRs. Such transduced T cells can respond to the targeted antigen independent of CD3 subunits via the introduced scTv, without the transduced T cells acquiring any new undefined and potentially dangerous specificities.

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.

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.

Rebalancing immune specificity and function in cancer by T-cell receptor gene therapy

Adoptive immunotherapy with tumor-specific T lymphocytes has demonstrated clinical benefit in some cancers, particularly melanoma. Yet isolating and expanding tumor-specific cells from patients is challenging and there is limited ability to control T-cell affinity and response characteristics. T-cell receptor (TCR) gene therapy, in which T lymphocytes for immunotherapy are redirected using an introduced rearranged TCR, has emerged as an important alternative. Successful TCR gene therapy requires consideration of a number of issues, including TCR specificity and affinity, optimal gene therapy constructs, types of T cells administered, and the survival and activity of the modified cells. In this review we highlight the rationale for and experience with TCR gene therapy as well as new approaches to enhancing it.

T cell receptor gene therapy for cancer

T cell-based adoptive immunotherapy has been shown to be a promising treatment for various types of cancer. However, adoptive T cell therapy currently requires the custom isolation and characterization of tumor-specific T cells from each patient-a process that can be not only difficult and time-consuming but also often fails to yield high-avidity T cells, which together have limited the broad application of this approach as a clinical treatment. Employing T cell receptor (TCR) gene therapy as a component of adoptive T cell therapy strategies can overcome many of these obstacles, allowing autologous T cells with a defined specificity to be generated in a much shorter time period. Initial studies using this approach have been hampered by a number of technical difficulties resulting in low TCR expression and acquisition of potentially problematic specificities due to mispairing of introduced TCR chains with endogenous TCR chains. The last several years have seen substantial progress in our understanding of the multiple facets of TCR gene therapy that will have to be properly orchestrated for this strategy to succeed. Here we outline the challenges of TCR gene therapy and the advances that have been made toward realizing the promise of this approach.

Abrogating Cbl-b in effector CD8(+) T cells improves the efficacy of adoptive therapy of leukemia in mice

The clinical use of adoptive immunotherapy with tumor-reactive T cells to treat established cancers is limited in part by the poor in vivo survival and function of the transferred T cells. Although administration of exogenous cytokines such as IL-2 can promote T cell survival, such strategies have many nonspecific activities and are often associated with toxicity. We show here that abrogating expression of Casitas B-lineage lymphoma b (Cbl-b), a negative regulator of lymphocyte activation, in tumor-reactive CD8(+) T cells expanded ex vivo increased the efficacy of adoptive immunotherapy of disseminated leukemia in mice. Mechanistically, Cbl-b abrogation bypassed the requirement for exogenous IL-2 administration for tumor eradication in vivo. In addition, CD8(+) T cells lacking Cbl-b demonstrated a lower threshold for activation, better survival following target recognition and stimulation, and enhanced proliferative responses as a result of both IL-2-dependent and -independent pathways. Importantly, siRNA knockdown of Cbl-b in human CD8(+)CD28- effector T cell clones similarly restored IL-2 production and proliferation following target recognition independent of exogenous IL-2, enhanced IFN-γ production, and increased target avidity. Thus, abrogating Cbl-b expression in effector T cells may improve the efficacy of adoptive therapy of some human malignancies.

Transduction of human T cells with a novel T-cell receptor confers anti-HCV reactivity

Hepatitis C Virus (HCV) is a major public health concern, with no effective vaccines currently available and 3% of the world's population being infected. Despite the existence of both B- and T-cell immunity in HCV-infected patients, chronic viral infection and HCV-related malignancies progress. Here we report the identification of a novel HCV TCR from an HLA-A2-restricted, HCV NS3:1073-1081-reactive CTL clone isolated from a patient with chronic HCV infection. We characterized this HCV TCR by expressing it in human T cells and analyzed the function of the resulting HCV TCR-transduced cells. Our results indicate that both the HCV TCR-transduced CD4(+) and CD8(+) T cells recognized the HCV NS3:1073-1081 peptide-loaded targets and HCV(+) hepatocellular carcinoma cells (HCC) in a polyfunctional manner with cytokine (IFN-gamma, IL-2, and TNF-alpha) production as well as cytotoxicity. Tumor cell recognition by HCV TCR transduced CD8(-) Jurkat cells and CD4(+) PBL-derived T cells indicated this TCR was CD8-independent, a property consistent with other high affinity TCRs. HCV TCR-transduced T cells may be promising for the treatment of patients with chronic HCV infections.

Application of adoptive T-cell therapy using tumor antigen-specific T-cell receptor gene transfer for the treatment of human leukemia

The last decade has seen great strides in the field of cancer immunotherapy, especially the treatment of melanoma. Beginning with the identification of cancer antigens, followed by the clinical application of anti-cancer peptide vaccination, it has now been proven that adoptive T-cell therapy (ACT) using cancer antigen-specific T cells is the most effective option. Despite the apparent clinical efficacy of ACT, the timely preparation of a sufficient number of cancer antigen-specific T cells for each patient has been recognized as its biggest limitation. Currently, therefore, attention is being focused on ACT with engineered T cells produced using cancer antigen-specific T-cell receptor (TCR) gene transfer. With regard to human leukemia, ACT using engineered T cells bearing the leukemia antigen-specific TCR gene still remains in its infancy. However, several reports have provided preclinical data on TCR gene transfer using Wilms' tumor gene product 1 (WT1), and also preclinical and clinical data on TCR gene transfer involving minor histocompatibility antigen, both of which have been suggested to provide additional clinical benefit. In this review, we examine the current status of anti-leukemia ACT with engineered T cells carrying the leukemia antigen-specific TCR gene, and discuss the existing barriers to progress in this area.

Adoptive immunotherapy for B-cell malignancies with autologous chimeric antigen receptor modified tumor targeted T cells

Chemotherapy-resistant B-cell hematologic malignancies may be cured with allogeneic hematopoietic stem cell transplantation (HSCT), demonstrating the potential susceptibility of these tumors to donor T-cell mediated immune responses. However, high rates of transplant-related morbidity and mortality limit this approach. For this reason, there is an urgent need for less-toxic forms of immune-based cellular therapy to treat these malignancies. Adoptive transfer of autologous T cells genetically modified to express chimeric antigen receptors (CARs) targeted to specific tumor-associated antigens represents an attractive means of overcoming the limitations of conventional HSCT. To this end, investigators have generated CARs targeted to various antigens expressed by B-cell malignancies, optimized the design of these CARs to enhance receptor mediated T cell signaling, and demonstrated significant anti-tumor efficacy of the resulting CAR modified T cells both in vitro and in vivo mouse tumor models. These encouraging preclinical data have justified the translation of this approach to the clinical setting with currently 12 open clinical trials and one completed clinical trial treating various B-cell malignancies utilizing CAR modified T cells targeted to either the CD19 or CD20 B-cell specific antigens.

Allogeneic haematopoietic stem cell transplantation: individualized stem cell and immune therapy of cancer

The year 2009 marked the fiftieth anniversary of the first successful allogeneic haematopoietic stem cell transplant (HSCT). The field of HSCT has pioneered some of the most exciting areas of research today. HSCT was the original stem cell therapy, the first cancer immune therapy and the earliest example of individualized cancer therapy. In this Timeline article we review the history of the development of HSCT and major advances made in the past 50 years. We highlight accomplishments made by researchers who continue to strive to improve outcomes for patients and increase the availability of this potentially life-saving therapy for patients with otherwise incurable malignancies.

Genetic redirection of T cells for cancer therapy

Adoptive immunotherapy can induce dramatic tumor regressions in patients with melanoma or viral-induced malignancies, but extending this approach to many common cancers has been hampered by a lack of naturally occurring tumor-specific T cells. In this review, we describe recent advances in the genetic modification of T cells using genes encoding cell-surface receptors specific for tumor-associated antigen. Using genetic modification, the many functional properties of T cells, including cytokine secretion and cytolytic capacity, are redirected from their endogenous specificity toward the elimination of tumor cells. Advances in gene design, vectors, and cell production are discussed, and details of the progress in clinical application of this approach are provided.