A TCR targeting the HLA-A*0201-restricted epitope of MAGE-A3 recognizes multiple epitopes of the MAGE-A antigen superfamily in several types of cancer

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.

T cell avidity and tumor immunity: problems and solutions

A potent T cell response is an important component of durable anti-tumor immunity. The quality of the T cell response can, in-part, be measured by the avidity of the T cell for its tumor antigen-expressing target. While convention suggests that raising the avidity of the responding T cells may make for a more potent anti-tumor immune response, the threshold for effective tumor immunity remains unclear, as do some of the adverse effects of an inappropriately high avidity response. In this review, we discuss the relationship between T cell avidity and anti-tumor immunity, considering both experimental model systems as well as human clinical trials.

Reassessing target antigens for adoptive T-cell therapy

Adoptive T cell therapy can target and kill widespread malignant cells thereby inducing durable clinical responses in melanoma and selected other malignances. However, many commonly targeted tumor antigens are also expressed by healthy tissues, and T cells do not distinguish between benign and malignant tissues if both express the target antigen. As such, autoimmune toxicity from T-cell-mediated destruction of normal tissue has limited the development and adoption of this otherwise promising type of cancer therapy. A review of the unique biology of T-cell therapy and of recent clinical experience compels a reassessment of target antigens that traditionally have been viewed from the perspective of weaker immunotherapeutic modalities. In selecting target antigens for adoptive T-cell therapy, expression by tumors and not by essential healthy tissues is of paramount importance. The risk of autoimmune adverse events can be further mitigated by generating antigen receptors using strategies that reduce the chance of cross-reactivity against epitopes in unintended targets. In general, a circumspect approach to target selection and thoughtful preclinical and clinical studies are pivotal to the ongoing advancement of these promising treatments.

Gene expression profiling using nanostring digital RNA counting to identify potential target antigens for melanoma immunotherapy

PURPOSE

The success of immunotherapy for the treatment of metastatic cancer is contingent on the identification of appropriate target antigens. Potential targets must be expressed on tumors but show restricted expression on normal tissues. To maximize patient eligibility, ideal target antigens should be expressed on a high percentage of tumors within a histology and, potentially, in multiple different malignancies.

DESIGN

A Nanostring probeset was designed containing 97 genes, 72 of which are considered potential candidate genes for immunotherapy. Five established melanoma cell lines, 59 resected metastatic melanoma tumors, and 31 normal tissue samples were profiled and analyzed using Nanostring technology.

RESULTS

Of the 72 potential target genes, 33 were overexpressed in more than 20% of studied melanoma tumor samples. Twenty of those genes were identified as differentially expressed between normal tissues and tumor samples by ANOVA analysis. Analysis of normal tissue gene expression identified seven genes with limited normal tissue expression that warrant further consideration as potential immunotherapy target antigens: CSAG2, MAGEA3, MAGEC2, IL13RA2, PRAME, CSPG4, and SOX10. These genes were highly overexpressed on a large percentage of the studied tumor samples, with expression in a limited number of normal tissue samples at much lower levels.

CONCLUSION

The application of Nanostring RNA counting technology was used to directly quantitate the gene expression levels of multiple potential tumor antigens. Analysis of cell lines, 59 tumors, and normal tissues identified seven potential immunotherapy targets for the treatment of melanoma that could increase the number of patients potentially eligible for adoptive immunotherapy.

Role of T cell receptor affinity in the efficacy and specificity of adoptive T cell therapies

Over the last several years, there has been considerable progress in the treatment of cancer using gene modified adoptive T cell therapies. Two approaches have been used, one involving the introduction of a conventional αβ T cell receptor (TCR) against a pepMHC cancer antigen, and the second involving introduction of a chimeric antigen receptor (CAR) consisting of a single-chain antibody as an Fv fragment linked to transmembrane and signaling domains. In this review, we focus on one aspect of TCR-mediated adoptive T cell therapies, the impact of the affinity of the αβ TCR for the pepMHC cancer antigen on both efficacy and specificity. We discuss the advantages of higher-affinity TCRs in mediating potent activity of CD4 T cells. This is balanced with the potential disadvantage of higher-affinity TCRs in mediating greater self-reactivity against a wider range of structurally similar antigenic peptides, especially in synergy with the CD8 co-receptor. Both TCR affinity and target selection will influence potential safety issues. We suggest pre-clinical strategies that might be used to examine each TCR for possible on-target and off-target side effects due to self-reactivities, and to adjust TCR affinities accordingly.

Advances in the study of HLA-restricted epitope vaccines

Vaccination is a proven strategy for protection from disease. An ideal vaccine would include antigens that elicit a safe and effective protective immune response. HLA-restricted epitope vaccines, which include T-lymphocyte epitopes restricted by HLA alleles, represent a new and promising immunization approach. In recent years, research in HLA-restricted epitope vaccines for the treatment of tumors and for the prevention of viral, bacterial, and parasite-induced infectious diseases have achieved substantial progress. Approaches for the improvement of the immunogenicity of epitope vaccines include (1) improving the accuracy of the methods used for the prediction of epitopes, (2) making use of additional HLA-restricted CD8(+) T-cell epitopes, (3) the inclusion of specific CD4(+) T-cell epitopes, (4) adding B-cell epitopes to the vaccine construction, (5) finding more effective adjuvants and delivery systems, (6) using immunogenic carrier proteins, and (7) using multiple proteins as epitopes sources. In this manuscript, we review recent research into HLA-restricted epitope vaccines.

Immunotherapeutic strategies to target prognostic and predictive markers of cancer

Throughout the last century medical advances in cancer treatment in the fields of surgery, radiation therapy and chemotherapy have greatly impacted patients' survival rates. Nevertheless, cancer remains a significant cause of mortality, with an estimated 7.6 million deaths worldwide in 2008, reflecting the inability of existing therapies to effectively cure disease. The emergence of vaccines and their successes in preventing the spread of infectious diseases has demonstrated the unique specificity and therapeutic potential of the immune system. This potential has driven the development of novel cancer immunotherapeutics. This review focuses on the current status of the use of immunologic effectors to target known biomarkers in cancer.

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.

Cancer regression and neurological toxicity following anti-MAGE-A3 TCR gene therapy

Nine cancer patients were treated with adoptive cell therapy using autologous anti-MAGE-A3 T-cell receptors (TCR)-engineered T cells. Five patients experienced clinical regression of their cancers including 2 on-going responders. Beginning 1-2 days postinfusion, 3 patients (#'s 5, 7, and 8) experienced mental status changes, and 2 patients (5 and 8) lapsed into comas and subsequently died. Magnetic resonance imagining analysis of patients 5 and 8 demonstrated periventricular leukomalacia, and examination of their brains at autopsy revealed necrotizing leukoencephalopathy with extensive white matter defects associated with infiltration of CD3(+)/CD8(+) T cells. Patient 7, developed Parkinson-like symptoms, which resolved over 4 weeks and fully recovered. Immunohistochemical staining of patient and normal brain samples demonstrated rare positively staining neurons with an antibody that recognizes multiple MAGE-A family members. The TCR used in this study recognized epitopes in MAGE-A3/A9/A12. Molecular assays of human brain samples using real-time quantitative-polymerase chain reaction, Nanostring quantitation, and deep-sequencing indicated that MAGE-A12 was expressed in human brain (and possibly MAGE-A1, MAGE-A8, and MAGE-A9). This previously unrecognized expression of MAGE-A12 in human brain was possibly the initiating event of a TCR-mediated inflammatory response that resulted in neuronal cell destruction and raises caution for clinical applications targeting MAGE-A family members with highly active immunotherapies.

T-cell receptor affinity and avidity defines antitumor response and autoimmunity in T-cell immunotherapy

T cells expressing antigen-specific T-cell receptors (TCRs) can mediate effective tumor regression, but they often also are accompanied by autoimmune responses. To determine the TCR affinity threshold defining the optimal balance between effective antitumor activity and autoimmunity in vivo, we used a unique self-antigen system comprising seven human melanoma gp100(209-217)-specific TCRs spanning physiological affinities (1-100 μM). We found that in vitro and in vivo T-cell responses are determined by TCR affinity, except in one case that was compensated by substantial CD8 involvement. Strikingly, we found that T-cell antitumor activity and autoimmunity are closely coupled but plateau at a defined TCR affinity of 10 µM, likely due to diminished contribution of TCR affinity to avidity above the threshold. Together, these results suggest that a relatively low-affinity threshold is necessary for the immune system to avoid self-damage, given the close relationship between antitumor activity and autoimmunity. The low threshold, in turn, indicates that adoptive T-cell therapy treatment strategies using in vitro-generated high-affinity TCRs do not necessarily improve efficacy.

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.

Genetically engineered T cells for the treatment of cancer

T-cell immunotherapy is a promising approach to treat disseminated cancer. However, it has been limited by the ability to isolate and expand T cells restricted to tumour-associated antigens. Using ex vivo gene transfer, T cells from patients can be genetically engineered to express a novel T cell receptor or chimeric antigen receptor to specifically recognize a tumour-associated antigen and thereby selectively kill tumour cells. Indeed, genetically engineered T cells have recently been successfully used for cancer treatment in a small number of patients. Here we review the recent progress in the field, and summarize the challenges that lie ahead and the strategies being used to overcome them.

A Promising Vector for TCR Gene Therapy: Differential Effect of siRNA, 2A Peptide, and Disulfide Bond on the Introduced TCR Expression

Adoptive immunotherapy using TCR gene-modified T-lymphocytes is an attractive strategy for targeting malignancies. However, TCR mispairings between endogenous and introduced TCR chains are a major concern, as they may induce mixed TCRs with unknown specificities and may reduce the expression of therapeutic TCRs. To overcome these problems, we have recently established a novel retroviral siTCR vector encoding small-interfering RNAs (siRNAs) to knockdown endogenous TCR genes for the efficient expression of therapeutic TCRs. In this study, to improve the efficacy of siTCR vectors, we developed 2A peptide-based siTCR vectors that could increase the expression levels of transduced TCRs compared with internal promoter-based siTCR vectors. We also evaluated the efficacy of an siTCR strategy and the addition of a new interchain disulfide bond created by cysteine modification. We found that the effect of the cysteine modification depended on TCR variations, while the siTCR strategy improved the expression of all TCRs tested. Furthermore, the combined effect of the siTCR and cysteine modification strategies was highly significant for certain TCRs. Therefore, our novel siTCR technology, in isolation or in combination with another strategy, may open the door to effective immunotherapy for cancer patients.Molecular Therapy - Nucleic Acids (2012) 1, e63. doi:10.1038/mtna.2012.52; published online 18 December 2012.

Raising the bar: the curative potential of human cancer immunotherapy

Immunotherapy with interleukin-2 can cure 5 to 10% of patients with metastatic melanoma and renal cancer. Recent adoptive cell transfer (ACT) immunotherapies have improved cure rates in metastatic melanoma to 20 to 40%. Genetic engineering of T cells to express conventional alpha/beta T cell receptors or antibody-based chimeric antigen receptors provides an opportunity to extend ACT to patients with common epithelial cancers.

Improving the efficacy and safety of engineered T cell therapy for cancer

Adoptive T-cell therapy (ACT) using tumor-infiltrating lymphocytes (TILs) is a powerful immunotherapeutics approach against metastatic melanoma. The success of TIL therapy has led to novel strategies for redirecting normal T cells to recognize tumor-associated antigens (TAAs) by genetically engineering tumor antigen-specific T cell receptors (TCRs) or chimeric antigen receptor (CAR) genes. In this manner, large numbers of antigen-specific T cells can be rapidly generated compared with the longer term expansion of TILs. Great efforts have been made to improve these approaches. Initial clinical studies have demonstrated that genetically engineered T cells can mediate tumor regression in vivo. In this review, we discuss the development of TCR and CAR gene-engineered T cells and the safety concerns surrounding the use of these T cells in patients. We highlight the importance of judicious selection of TAAs for modified T cell therapy and propose solutions for potential "on-target, off-organ" toxicity.

Targeting the MAGE A3 antigen in pancreatic cancer

Pancreatic cancer is the fourth-leading cause of death in the United States and one of the most aggressive known malignancies. New and innovative advances in treatment are desperately needed. One promising area of investigational treatment for pancreatic cancer involves the use of immunotherapy. The development of immunotherapy for pancreatic cancer has been hampered by difficulty in generating tumor-reactive lymphocytes from resected specimens and by a lack of appropriate target antigens expressed on tumor cells. Innovative strategies have been developed with the use of peripheral blood lymphocytes that are genetically engineered to express T-cell receptors targeting common tumor antigens, including cancer-testis antigens, such as the MAGE-A3 antigen. Cancer-testis antigens pose excellent targets for immunotherapy because they are expressed in cancer and in the testis, an immune-privileged site, but have limited expression in normal tissue. An additional advantage in targeting cancer-testis antigens for immunotherapy is that their expression can be selectively up-regulated in tumor cells via epigenetic regulation with chromatin remodeling agents. Current interest in targeting cancer-testis antigens in pancreatic cancer is well-founded because cancer-testis antigens have been shown to be expressed in pancreatic cancer as potential targets for therapy. In our studies, we validated the expression pattern of cancer-testis antigens in resected specimens of pancreatic cancer and tested the hypothesis that treatment of pancreatic cancer cells with chromatin remodeling agents would render them more sensitive to antigen-specific T lymphocytes. We focused predominately on the MAGE-A3 antigen because it is highly expressed in pancreatic cancer, and several immunotherapeutic strategies are in clinical trials targeting this specific antigen. The results of these studies have important translational implications and provide the rationale for combined treatment with chromatin remodeling agents and immunotherapeutic approaches for pancreatic cancer.

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.

Genetic engineering with T cell receptors

In the past two decades, human gene transfer research has been translated from a laboratory technology to clinical evaluation. The success of adoptive transfer of tumor-reactive lymphocytes to treat the patients with metastatic melanoma has led to new strategies to redirect normal T cells to recognize tumor antigens by genetic engineering with tumor antigen-specific T cell receptor (TCR) genes. This new strategy can generate large numbers of defined antigen-specific cells for therapeutic application. Much progress has been made to TCR gene transfer systems by optimizing gene expression and gene transfer protocols. Vector and protein modifications have enabled excellent expression of introduced TCR chains in human lymphocytes with reduced mis-pairing between the introduced and endogenous TCR chains. Initial clinical studies have demonstrated that TCR gene-engineered T cells could mediate tumor regression in vivo. In this review, we discuss the progress and prospects of TCR gene-engineered T cells as a therapeutic strategy for treating patients with melanoma and other cancers.

Skewed T-cell receptor beta chain variable gene (TCRBV) usage among different clinical types of patients with chronic HBV infection

This study aimed to determine the degree of clonal expansion of T cells in peripheral blood mononuclear cells (PBMCs) isolated from patients suffering from different clinical types of hepatitis B (HB) infection and to analyse the clinical relevance of the skewed T-cell receptor beta variable (TCRBV). Sera and PBMCs were collected from 90 HB patients. Gene melting spectral pattern (GMSP) analysis was used to determine the distribution and expansion of populations expressing specific TCRBV complementary determined region 3 (CDR3) genes. TCRBV genes associated with monoclonal expansion were sequenced. TCRBV families from the majority of patients (80/90) displayed skewed T-cell expansion. Furthermore, TCRBV11, BV12 and BV13.1 were more frequent than other TCRBV genes; the sequence of TCRBV11 CDR3 was expressed as 'VYNEQ' in all patients and was accompanied by the BJ2.1 fragment. In patients with chronic HB, the frequency of skewed TCRBV was inversely correlated with hepatitis B virus (HBV) DNA levels. The persistently skewed TCRBV gene families in HB patients may be associated with the development and maintenance of hepatitis. GMSP analysis of TCRBV gene families may be helpful in estimating disease status, and BV11 may be associated with HBV replication in patients with chronic HBV infection.

Trial Watch: Adoptive cell transfer immunotherapy

During the last two decades, several approaches for the activation of the immune system against cancer have been developed. These include rather unselective maneuvers such as the systemic administration of immunostimulatory agents (e.g., interleukin-2) as well as targeted interventions, encompassing highly specific monoclonal antibodies, vaccines and cell-based therapies. Among the latter, adoptive cell transfer (ACT) involves the selection of autologous lymphocytes with antitumor activity, their expansion/activation ex vivo, and their reinfusion into the patient, often in the context of lymphodepleting regimens (to minimize endogenous immunosuppression). Such autologous cells can be isolated from tumor-infiltrating lymphocytes or generated by manipulating circulating lymphocytes for the expression of tumor-specific T-cell receptors. In addition, autologous lymphocytes can be genetically engineered to prolong their in vivo persistence, to boost antitumor responses and/or to minimize side effects. ACT has recently been shown to be associated with a consistent rate of durable regressions in melanoma and renal cell carcinoma patients and holds great promises in several other oncological settings. In this Trial Watch, we will briefly review the scientific rationale behind ACT and discuss the progress of recent clinical trials evaluating the safety and effectiveness of adoptive cell transfer as an anticancer therapy.

Targeting epigenetic mediators of gene expression in thoracic malignancies

Lung and esophageal cancers and malignant pleural mesotheliomas are highly lethal neoplasms that are leading causes of cancer-related deaths worldwide. Presently, limited information is available pertaining to epigenetic mechanisms mediating initiation and progression of these neoplasms. The following presentation will focus on the potential clinical relevance of epigenomic alterations in thoracic malignancies mediated by DNA methylation, perturbations in the histone code, and polycomb group proteins, as well as ongoing translational efforts to target epigenetic regulators of gene expression for treatment of these neoplasms. This article is part of a Special Issue entitled: Chromatin in time and space.

Adoptive immunotherapy for cancer: harnessing the T cell response

Immunotherapy based on the adoptive transfer of naturally occurring or gene-engineered T cells can mediate tumour regression in patients with metastatic cancer. Here, we discuss progress in the use of adoptively transferred T cells, focusing on how they can mediate tumour cell eradication. Recent advances include more accurate targeting of antigens expressed by tumours and the associated vasculature, and the successful use of gene engineering to re-target T cells before their transfer into the patient. We also describe how new research has helped to identify the particular T cell subsets that can most effectively promote tumour eradication.

TCR gene transfer: MAGE-C2/HLA-A2 and MAGE-A3/HLA-DP4 epitopes as melanoma-specific immune targets

Adoptive therapy with TCR gene-engineered T cells provides an attractive and feasible treatment option for cancer patients. Further development of TCR gene therapy requires the implementation of T-cell target epitopes that prevent “on-target” reactivity towards healthy tissues and at the same time direct a clinically effective response towards tumor tissues. Candidate epitopes that meet these criteria are MAGE-C2_336-344/HLA-A2 (MC2/A2) and MAGE-A3_243-258/HLA-DP4 (MA3/DP4). We molecularly characterized TCRαβ genes of an MC2/A2-specific CD8 and MA3/DP4-specific CD4 T-cell clone derived from melanoma patients who responded clinically to MAGE vaccination. We identified MC2/A2 and MA3/DP4-specific TCR-Vα3/Vβ28 and TCR-Vα38/Vβ2 chains and validated these TCRs in vitro upon gene transfer into primary human T cells. The MC2 and MA3 TCR were surface-expressed and mediated CD8 T-cell functions towards melanoma cell lines and CD4 T-cell functions towards dendritic cells, respectively. We intend to start testing these MAGE-specific TCRs in phase I clinical trial.

Cell transfer immunotherapy for metastatic solid cancer--what clinicians need to know

Cancer immunotherapy using the adoptive transfer of autologous tumor-infiltrating lymphocytes results in objective cancer regression in 49-72% of patients with metastatic melanoma. In a pilot trial combining cell transfer with a maximum lymphodepleting regimen, complete durable responses were seen in 40% of patients, with complete responses ongoing beyond 3 to 7 years. Current approaches to cell transfer therapy using autologous cells genetically engineered to express conventional or chimeric T-cell receptors have mediated cancer regression in patients with metastatic melanoma, synovial sarcoma, neuroblastoma and refractory lymphoma. Adoptive cell transfer immunotherapy is a rapidly developing new approach to the therapy of metastatic cancer in humans. This Review will emphasize the current available applications of cell transfer immunotherapy for patients with cancer.

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.

Inhibition of histone lysine methylation enhances cancer-testis antigen expression in lung cancer cells: implications for adoptive immunotherapy of cancer

Cancer-testis antigens (CTA), such as NY-ESO-1, MAGE-A1, and MAGE-A3, are immunogenic proteins encoded by genes, which are normally expressed only in male germ cells but are activated by ill-defined epigenetic mechanisms in human tumors, including lung cancers. Previously, we reported induction of these CTAs in cancer cells, but not normal cells, by DNA-demethylating agents and histone deacetylase inhibitors using clinically achievable exposure conditions. In the present study, we evaluated chromatin alterations associated with repression/activation of cancer-testis genes in lung cancer cells to further develop gene-induction regimens for cancer immunotherapy. Repression of NY-ESO-1, MAGE-A1, and MAGE-A3 coincided with DNA hypermethylation, recruitment, and binding of polycomb-group proteins, and histone heterochromatin modifications within the promoters of these genes. Derepression coincided with DNA demethylation, dissociation of polycomb proteins, and presence of euchromatin marks within the respective promoters. Short hairpin RNAs were used to inhibit several histone methyltransferases (KMT) and histone demethylases (KDM) that mediate histone methylation and repress gene expression. Knockdown of KMT6, KDM1, or KDM5B markedly enhanced deoxyazacytidine (DAC)-mediated activation of these cancer-testis genes in lung cancer cells. DZNep, a pharmacologic inhibitor of KMT6 expression, recapitulated the effects of KMT6 knockdown. Following DAC-DZNep exposure, lung cancer cells were specifically recognized and lysed by allogeneic lymphocytes expressing recombinant T-cell receptors recognizing NY-ESO-1 and MAGE-A3. Combining DNA-demethylating agents with compounds, such as DZNep, that modulate histone lysine methylation may provide a novel epigenetic strategy to augment cancer-testis gene expression as an adjunct to adoptive cancer immunotherapy.

Treating cancer with genetically engineered T cells

Administration of ex vivo cultured, naturally occurring tumor-infiltrating lymphocytes (TILs) has been shown to mediate durable regression of melanoma tumors. However, the generation of TILs is not possible in all patients and there has been limited success in generating TIL in other cancers. Advances in genetic engineering have overcome these limitations by introducing tumor-antigen-targeting receptors into human T lymphocytes. Physicians can now genetically engineer lymphocytes to express highly active T-cell receptors (TCRs) or chimeric antigen receptors (CARs) targeting a variety of tumor antigens expressed in cancer patients. In this review, we discuss the development of TCR and CAR gene transfer technology and the expansion of these therapies into different cancers with the recent demonstration of the clinical efficacy of these treatments.

Is antigen specificity the key to efficient adoptive T-cell therapy?

Adoptive transfer of T cells remains a promising approach in melanoma. Initial clinical trials performed with polyclonal tumor-infiltrating lymphocyte gave limited clinical results. Nonetheless, encouraging results have been reported in adjuvant setting (stage III melanoma), and when tumor-infiltrating lymphocytes were associated with lymphodepleting regimens. Specificity of adoptive cell therapy has been achieved with the infusion of antigen specific cytotoxic T-lymphocyte clones, associated with some clinical responses. Antigen specificity can also be obtained by the allogeneic transfer of high-avidity T-cell receptors into autologous T cells. We propose an alternative strategy based on the selection of antigen-specific T cells with magnetic beads coated with HLA–peptide multimers. Future improvements of adoptive melanoma immunotherapy may be achieved by its association with other therapeutic strategies such as targeted therapy against signaling pathways.

Genetically retargeting CD8+ lymphocyte subsets for cancer immunotherapy

The extraordinary sensitivity and specificity of T cells for their cognate antigen make them a highly attractive cancer therapeutic. However, the rarity of tumor-reactive T cells in cancer patients, the difficulty isolating them in sufficient numbers for adoptive immunotherapy, and the unpredictable persistence of transferred cells have been significant obstacles to broad application. Technologies that enable genetic modification of T cells have been refined and are being used to redirect the specificity of T cells to tumor antigens. An issue the field is now grappling with is how the diverse phenotypic and functional heterogeneity in T cells that could potentially be genetically modified can be capitalized upon to enhance the efficacy, safety, and reproducibility of cancer immunotherapy.

Immunotherapy for metastatic solid cancers

After decades of research on solid tumor immunology, immunotherapy has shown effectiveness in patients with metastatic solid cancers. Immune modulators such as IL-2 and anti-CTLA-4 can mediate tumor regression in patients with metastatic melanoma and renal cancer, two tumor types that appear exceptional in their ability to spontaneously harbor endogenous antitumor immune cells. The responses can be long lasting, but the number of patients who benefit from these molecules remains limited. Combinations of these agents with cytotoxic and biologic agents are being investigated as a means to increase response rates and in an attempt to broaden application to other cancer types. Rare responses to cancer vaccines suggest that a better understanding of the underlying biology and mechanism of actions may lead to wider application in the future. The most effective form of immunotherapy thus far, capable of eradicating large tumor burdens in melanoma patients, is the ACT of TIL given to patients after lymphodepletion. As an alternative, lymphocytes engineered to recognize tumor-associated antigens can be safely infused to patients. With this approach, tumor regression is now being reported for cancers other than melanoma, but success remains constrained by the identification of antigens expressed with high specificity by cancer cells and not by normal tissues.