Identification of a Titin-derived HLA-A1-presented peptide as a cross-reactive target for engineered MAGE A3-directed T cells

Therapeutic Potential of T Cell Chimeric Antigen Receptors (CARs) in Cancer Treatment: Counteracting Off-Tumor Toxicities for Safe CAR T Cell Therapy

A chimeric antigen receptor (CAR) is a recombinant fusion protein combining an antibody-derived targeting fragment with signaling domains capable of activating T cells. Recent early-phase clinical trials have demonstrated the remarkable ability of CAR-modified T cells to eliminate B cell malignancies. This review describes the choice of target antigens and CAR manipulations to maximize antitumor specificity. Benefits and current limitations of CAR-modified T cells are discussed, with a special focus on the distribution of tumor antigens on normal tissues and the risk of on-target, off-tumor toxicities in the clinical setting. We present current methodologies for pre-evaluating these risks and review the strategies for counteracting potential off-tumor effects. Successful implementation of these approaches will improve the safety and efficacy of CAR T cell therapy and extend the range of cancer patients who may be treated.

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

INTRODUCTION

A variety of approaches are being pursued to improve the safety and antitumor potency of chimeric antigen receptor (CAR) T-cell therapy. However, most engineering efforts have thus far been focused on its intracellular signaling domain, while its extracellular antigen-binding domain has received less attention. Areas covered: Herein, the authors summarize the current knowledge of CAR T-cell therapy. Accordingly, they focus on its antigen-binding domain, discuss key considerations for selecting an optimal single-chain variable fragment (scFv) when designing a CAR, and suggest potential directions aimed at developing the next-generation CARs. Expert opinion: The extracellular region of CARs can play a decisive role in their safety and efficacy. Instead of directly translating an available therapeutic mAb to a scFv-based CAR construct, the authors suggest that various CAR-displayed scFvs with different affinity, specificity and binding epitopes against an individual target molecule should be generated and evaluated side-by-side. Incorporating new antibody formats that possess characteristics superior to those of scFvs may be one way to engineer safer and more effective CARs. The authors expect that further CAR engineering will enable us to target more antigens involved in hematological and solid malignancies with minimal side effects to serve unmet clinical needs.

Recent advances in T-cell engineering for use in immunotherapy

Adoptive T-cell therapies have shown exceptional promise in the treatment of cancer, especially B-cell malignancies. Two distinct strategies have been used to redirect the activity of ex vivo engineered T cells. In one case, the well-known ability of the T-cell receptor (TCR) to recognize a specific peptide bound to a major histocompatibility complex molecule has been exploited by introducing a TCR against a cancer-associated peptide/human leukocyte antigen complex. In the other strategy, synthetic constructs called chimeric antigen receptors (CARs) that contain antibody variable domains (single-chain fragments variable) and signaling domains have been introduced into T cells. Whereas many reviews have described these two approaches, this review focuses on a few recent advances of significant interest. The early success of CARs has been followed by questions about optimal configurations of these synthetic constructs, especially for efficacy against solid tumors. Among the many features that are important, the dimensions and stoichiometries of CAR/antigen complexes at the synapse have recently begun to be appreciated. In TCR-mediated approaches, recent evidence that mutated peptides (neoantigens) serve as targets for endogenous T-cell responses suggests that these neoantigens may also provide new opportunities for adoptive T-cell therapies with TCRs.

Toxicities Associated With Adoptive T-Cell Transfer for Cancer

This review describes the toxicities associated with the therapeutic administration of cultured immune cells for the treatment of cancer by review of the literature. The toxicities seen are of 4 types: infection associated with preparative host immunosuppression with chemotherapy prior to cell administration, acute cytokine release by the infused cells, autoimmune complications from attacking "self-antigens" also expressed by some normal tissues, and off-target toxicities where antigens, other than the intended, are attacked. Complications from immunosuppression and cytokine release are often short-lived and currently best addressed by supportive care. Autoimmunity, either "on target, off tumor" or "off target," is the result of the selection of imperfect target antigens. In some cases, this can be tolerated because the benefits outweigh the costs. In other cases, alternative target antigens must be found. New strategies targeting viral antigens for virally induced cancers and antigens encoded by tumor-specific mutations seem to have promise as safe and potentially effective targets for adoptive cell transfer.

Chimeric Antigen Receptor T-Cells: New Approaches to Improve Their Efficacy and Reduce Toxicity

The durable remission of B-cell leukemia and lymphoma following chimeric antigen receptor (CAR) T-cell therapy has brought this new form of adoptive immunotherapy to center stage with the expectation that CAR T-cell therapy may provide similar efficacy in other hematologic and solid cancers. Herein, we review recent advances in the areas of CAR design that improve CAR T-cell proliferation, engraftment, and efficacy, as well as clinical application strategies that are designed to improve clinical efficacy while reducing the risk of toxicity and broaden patient access to this promising form of cancer immunotherapy.

Lysosome-associated membrane glycoprotein 1 predicts fratricide amongst T cell receptor transgenic CD8+ T cells directed against tumor-associated antigens

AIM

Autologous as well as allogeneic CD8+ T cells transduced with tumor antigen specific T cell receptors (TCR) may cause significant tumor lysis upon adoptive transfer. Besides unpredictable life-threatening off-target effects, these TCRs may unexpectedly commit fratricide. We hypothesized lysosome-associated membrane glycoprotein 1 (LAMP1, CD107a) to be a marker for fratricide in TCR transgenic CD8+ T cells.

METHODS

We identified HLA-A*02:01/peptide-restricted T cells directed against ADRB3295. After TCR identification, we generated HLA-A*02:01/peptide restricted TCR transgenic T cells by retroviral transduction and tested T cell expansion rates as well as A*02:01/peptide recognition and ES killing in ELISpot and xCELLigence assays. Expansion arrest was analyzed via Annexin and CD107a staining. Results were compared to CHM1319-TCR transgenic T cells.

RESULTS

Beta-3-adrenergic receptor (ADRB3) as well as chondromodulin-1 (CHM1) are over-expressed in Ewing Sarcoma (ES) but not on T cells. TCR transgenic T cells demonstrated HLA-A*02:01/ADRB3295 mediated ES recognition and killing in ELISpot and xCELLigence assays. 24h after TCR transduction, CD107a expression correlated with low expansion rates due to apoptosis of ADRB3 specific T cells in contrast to CHM1 specific transgenic T cells. Amino-acid exchange scans clearly indicated the cross-reactive potential of HLA-A*02:01/ADRB3295- and HLA-A*02:01/CHM1319-TCR transgenic T cells. Comparison of peptide motive binding affinities revealed extended fratricide among ADRB3295 specific TCR transgenic T cells in contrast to CHM1319.

CONCLUSION

Amino-acid exchange scans alone predict TCR cross-reactivity with little specificity and thus require additional assessment of potentially cross-reactive HLA-A*02:01 binding candidates. CD107a positivity is a marker for fratricide of CD8+ TCR transgenic T cells.

Adoptive Cellular Therapy (ACT) for Cancer Treatment

Adoptive cellular therapy (ACT) with various lymphocytes or antigen-presenting cells is one stone in the pillar of cancer immunotherapy, which relies on the tumor-specific T cell. The transfusion of bulk T-cell population into patients is an effective treatment for regression of cancer. In this chapter, we summarize the development of various strategies in ACT for cancer immunotherapy and discuss some of the latest progress and obstacles in technical, safety, and even regulatory aspects to translate these technologies to the clinic. ACT is becoming a potentially powerful approach to cancer treatment. Further experiments and clinical trials are needed to optimize this strategy.

Planes, Trains, and Automobiles: Perspectives on CAR T Cells and Other Cellular Therapies for Hematologic Malignancies

Hematologic oncologists now have at their disposal (or a referral away) a myriad of new options to get from point A (a patient with relapsed or poor-risk disease) to point B (potential tumor eradication and long-term disease-free survival). In this perspective piece, we discuss the putative mechanisms of action and the relative strengths and weaknesses of currently available cellular therapy approaches. Notably, while many of these approaches have been published in high impact journals, with the exception of allogeneic stem cell transplantation and of checkpoint inhibitors (PD1/PDL1 or CTLA4 blockade), the published clinical trials have mostly been early phase, uncontrolled studies. Therefore, many of the new cellular therapy approaches have yet to demonstrate incontrovertible evidence of enhanced overall survival compared with controls. Nonetheless, the science behind these is sure to advance our understanding of cancer immunology and ultimately to bring us closer to our goal of curing cancer.

Targeting B-cell neoplasia with T-cell receptors recognizing a CD20-derived peptide on patient-specific HLA

T cells engineered to express chimeric antigen receptors (CARs) targeted to CD19 are effective in treatment of B-lymphoid malignancies. However, CARs recognize all CD19 positive (pos) cells, and durable responses are linked to profound depletion of normal B cells. Here, we designed a strategy to specifically target patient B cells by utilizing the fact that T-cell receptors (TCRs), in contrast to CARs, are restricted by HLA. Two TCRs recognizing a peptide from CD20 (SLFLGILSV) in the context of foreign HLA-A*02:01 (CD20p/HLA-A2) were expressed as 2A-bicistronic constructs. T cells re-directed with the A23 and A94 TCR constructs efficiently recognized malignant HLA-A2(pos) B cells endogenously expressing CD20, including patient-derived follicular lymphoma and chronic lymphocytic leukemia (CLL) cells. In contrast, a wide range of HLA-A2(pos)CD20(neg) cells representing different tissue origins, and HLA-A2(neg)CD20(pos) cells, were not recognized. Cytotoxic T cells re-directed with CD20p/HLA-A2-specific TCRs or CD19 CARs responded with similar potencies to cells endogenously expressing comparable levels of CD20 and CD19. The CD20p/HLA-A2-specific TCRs recognized CD20p bound to HLA-A2 with high functional avidity. The results show that T cells expressing CD20p/HLA-A2-specific TCRs efficiently and specifically target B cells. When used in context of an HLA-haploidentical allogeneic stem cell transplantation where the donor is HLA-A2(neg) and the patient HLA-A2(pos), these T cells would selectively kill patient-derived B cells and allow reconstitution of the B-cell compartment with HLA-A2(neg) donor cells. These results should pave the way for clinical testing of T cells genetically engineered to target malignant B cells without permanent depletion of normal B cells.

Cellular immunotherapy for malignant gliomas

INTRODUCTION

Cancer immunotherapy has made much progress in recent years. Clinical trials evaluating a variety of immunotherapeutic approaches are underway in patients with malignant gliomas. Thanks to recent advancements in cell engineering technologies, infusion of ex vivo prepared immune cells have emerged as promising strategies of cancer immunotherapy.

AREAS COVERED

Herein, the authors review recent and current studies using cellular immunotherapies for malignant gliomas. Specifically, they cover the following areas: a) cellular vaccine approaches using tumor cell-based or dendritic cell (DC)-based vaccines, and b) adoptive cell transfer (ACT) approaches, including lymphokine-activated killer (LAK) cells, γδ T cells, tumor-infiltrating lymphocytes (TIL), chimeric antigen receptor (CAR)-T cells and T-cell receptor (TCR) transduced T cells.

EXPERT OPINION

While some of the recent studies have shown promising results, the ultimate success of cellular immunotherapy in brain tumor patients would require improvements in the following areas: 1) feasibility in producing cellular therapeutics; 2) identification and characterization of targetable antigens given the paucity and heterogeneity of tumor specific antigens; 3) the development of strategies to promote effector T-cell trafficking; 4) overcoming local and systemic immune suppression, and 5) proper interpretation of imaging data for brain tumor patients receiving immunotherapy.

Kirshner J, MacDonald D, Thurston G, C. Lin H, J. Murphy A, Zhang W. In-silico discovery of cancer-specific peptide-HLA complexes for targeted therapy

BACKGROUND

Major Histocompatibility Complex (MHC) or Human Leukocyte Antigen (HLA) Class I molecules bind to peptide fragments of proteins degraded inside the cell and display them on the cell surface. We are interested in peptide-HLA complexes involving peptides that are derived from proteins specifically expressed in cancer cells. Such complexes have been shown to provide an effective means of precisely targeting cancer cells by engineered T-cells and antibodies, which would be an improvement over current chemotherapeutic agents that indiscriminately kill proliferating cells. An important concern with the targeting of peptide-HLA complexes is off-target toxicity that could occur due to the presence of complexes similar to the target complex in cells from essential, normal tissues.

RESULTS

We developed a novel computational strategy for identifying potential peptide-HLA cancer targets and evaluating the likelihood of off-target toxicity associated with these targets. Our strategy combines sequence-based and structure-based approaches in a unique way to predict potential off-targets. The focus of our work is on the complexes involving the most frequent HLA class I allele HLA-A*02:01. Using our strategy, we predicted the off-target toxicity observed in past clinical trials. We employed it to perform a first-ever comprehensive exploration of the human peptidome to identify cancer-specific targets utilizing gene expression data from TCGA (The Cancer Genome Atlas) and GTEx (Gene Tissue Expression), and structural data from PDB (Protein Data Bank). We have thus identified a list of 627 peptide-HLA complexes across various TCGA cancer types.

CONCLUSION

Peptide-HLA complexes identified using our novel strategy could enable discovery of cancer-specific targets for engineered T-cells or antibody based therapy with minimal off-target toxicity.

T cell engineering as therapy for cancer and HIV: our synthetic future

It is now well established that the immune system can control and eliminate cancer cells. Adoptive T cell transfer has the potential to overcome the significant limitations associated with vaccine-based strategies in patients who are often immune compromised. Application of the emerging discipline of synthetic biology to cancer, which combines elements of genetic engineering and molecular biology to create new biological structures with enhanced functionalities, is the subject of this overview. Various chimeric antigen receptor designs, manufacturing processes and study populations, among other variables, have been tested and reported in recent clinical trials. Many questions remain in the field of engineered T cells, but the encouraging response rates pave a wide road for future investigation into fields as diverse as cancer and chronic infections.

Targeting of HPV-16+ Epithelial Cancer Cells by TCR Gene Engineered T Cells Directed against E6

PURPOSE

The E6 and E7 oncoproteins of HPV-associated epithelial cancers are in principle ideal immunotherapeutic targets, but evidence that T cells specific for these antigens can recognize and kill HPV(+) tumor cells is limited. We sought to determine whether TCR gene engineered T cells directed against an HPV oncoprotein can successfully target HPV(+) tumor cells.

EXPERIMENTAL DESIGN

T-cell responses against the HPV-16 oncoproteins were investigated in a patient with an ongoing 22-month disease-free interval after her second resection of distant metastatic anal cancer. T cells genetically engineered to express an oncoprotein-specific TCR from this patient's tumor-infiltrating T cells were tested for specific reactivity against HPV(+) epithelial tumor cells.

RESULTS

We identified, from an excised metastatic anal cancer tumor, T cells that recognized an HLA-A*02:01-restricted epitope of HPV-16 E6. The frequency of the dominant T-cell clonotype from these cells was approximately 400-fold greater in the patient's tumor than in her peripheral blood. T cells genetically engineered to express the TCR from this clonotype displayed high avidity for an HLA-A*02:01-restricted epitope of HPV-16, and they showed specific recognition and killing of HPV-16(+) cervical, and head and neck cancer cell lines.

CONCLUSIONS

These findings demonstrate that HPV-16(+) tumors can be targeted by E6-specific TCR gene engineered T cells, and they provide the foundation for a novel cellular therapy directed against HPV-16(+) malignancies, including cervical, oropharyngeal, anal, vulvar, vaginal, and penile cancers.

Chimeric antigen receptor-modified T cells for the treatment of solid tumors: Defining the challenges and next steps

Chimeric antigen receptor (CAR) T cell therapy has shown promise in CD19 expressing hematologic malignancies, but how to translate this success to solid malignancies remains elusive. Effective translation of CAR T cells to solid tumors will require an understanding of potential therapeutic barriers, including factors that regulate CAR T cells expansion, persistence, trafficking, and fate within tumors. Herein, we describe the current state of CAR T cells in solid tumors; define key barriers to CAR T cell efficacy and mechanisms underlying these barriers, outline potential avenues for overcoming these therapeutic obstacles, and discuss the future of translating CAR T cells for the treatment of patients with solid malignancies.

A Tet-On Inducible System for Controlling CD19-Chimeric Antigen Receptor Expression upon Drug Administration

T cells genetically modified with a CD19 chimeric antigen receptor (CD19CAR) are remarkably effective against B-cell malignancies in clinical trials. However, major concerns remain regarding toxicities, such as hypogammaglobulinemia, due to B-cell aplasia or severe cytokine release syndrome after overactivation of CAR T cells. To resolve these adverse events, we aimed to develop an inducible CAR system by using a tetracycline regulation system that would be activated only in the presence of doxycycline (Dox). In this study, the second-generation CD19CAR was fused into the third-generation Tet-On vector (Tet-CD19CAR) and was retrovirally transduced into primary CD8(+) T cells. Tet-CD19CAR T cells were successfully generated and had minimal background CD19CAR expression without Dox. Tet-CD19CAR T cells in the presence of Dox were equivalently cytotoxic against CD19(+) cell lines and had equivalent cytokine production and proliferation upon CD19 stimulation, compared with conventional CD19CAR T cells. The Dox(+) Tet-CD19CAR T cells also had significant antitumor activity in a xenograft model. However, without Dox, Tet-CD19CAR T cells lost CAR expression and CAR T-cell functions in vitro and in vivo, clearly segregating the "On" and "Off" status of Tet-CD19CAR cells by Dox administration. In addition to suicide-gene technology, controlling the expression and the functions of CAR with an inducible vector is a potential solution for CAR T-cell therapy-related toxicities, and may improve the safety profile of CAR T-cell therapy. This strategy might also open the way to treat other malignancies in combination with other CAR or TCR gene-modified T cells. Cancer Immunol Res; 4(8); 658-68. ©2016 AACRSee related Spotlight by June, p. 643.

Elimination of Latently HIV-infected Cells from Antiretroviral Therapy-suppressed Subjects by Engineered Immune-mobilizing T-cell Receptors

Persistence of human immunodeficiency virus (HIV) in a latent state in long-lived CD4+ T-cells is a major barrier to eradication. Latency-reversing agents that induce direct or immune-mediated cell death upon reactivation of HIV are a possible solution. However, clearance of reactivated cells may require immunotherapeutic agents that are fine-tuned to detect viral antigens when expressed at low levels. We tested the antiviral efficacy of immune-mobilizing monoclonal T-cell receptors against viruses (ImmTAVs), bispecific molecules that redirect CD8+ T-cells to kill HIV-infected CD4+ T-cells. T-cell receptors specific for an immunodominant Gag epitope, SL9, and its escape variants were engineered to achieve supraphysiological affinity and fused to a humanised CD3-specific single chain antibody fragment. Ex vivo polyclonal CD8+ T-cells were efficiently redirected by immune-mobilising monoclonal T-cell receptors against viruses to eliminate CD4+ T-cells from human histocompatibility leukocyte antigen (HLA)-A*0201-positive antiretroviral therapy-treated patients after reactivation of inducible HIV in vitro. The efficiency of infected cell elimination correlated with HIV Gag expression. Immune-mobilising monoclonal T-cell receptors against viruses have potential as a therapy to facilitate clearance of reactivated HIV reservoir cells.

T-cell therapies for HIV: Preclinical successes and current clinical strategies

Although antiretroviral therapy (ART) has been successful in controlling HIV infection, it does not provide a permanent cure, requires lifelong treatment, and HIV-positive individuals are left with social concerns such as stigma. The recent application of T cells to treat cancer and viral reactivations post-transplant offers a potential strategy to control HIV infection. It is known that naturally occurring HIV-specific T cells can inhibit HIV initially, but this response is not sustained in the majority of people living with HIV. Genetically modifying T cells to target HIV, resist infection, and persist in the immunosuppressive environment found in chronically infected HIV-positive individuals might provide a therapeutic solution for HIV. This review focuses on successful preclinical studies and current clinical strategies using T-cell therapy to control HIV infection and mediate a functional cure solution.

Optimizing T-cell receptor gene therapy for hematologic malignancies

Recent advances in genetic engineering have enabled the delivery of clinical trials using patient T cells redirected to recognize tumor-associated antigens. The most dramatic results have been seen with T cells engineered to express a chimeric antigen receptor (CAR) specific for CD19, a differentiation antigen expressed in B cells and B lineage malignancies. We propose that antigen expression in nonmalignant cells may contribute to the efficacy of T-cell therapy by maintaining effector function and promoting memory. Although CAR recognition is limited to cell surface structures, T-cell receptors (TCRs) can recognize intracellular proteins. This not only expands the range of tumor-associated self-antigens that are amenable for T-cell therapy, but also allows TCR targeting of the cancer mutagenome. We will highlight biological bottlenecks that potentially limit mutation-specific T-cell therapy and may require high-avidity TCRs that are capable of activating effector function when the concentrations of mutant peptides are low. Unexpectedly, modified TCRs with artificially high affinities function poorly in response to low concentration of cognate peptide but pose an increased safety risk as they may respond optimally to cross-reactive peptides. Recent gene-editing tools, such as transcription activator-like effector nucleases and clustered regularly interspaced short palindromic repeats, provide a platform to delete endogenous TCR and HLA genes, which removes alloreactivity and decreases immunogenicity of third-party T cells. This represents an important step toward generic off-the-shelf T-cell products that may be used in the future for the treatment of large numbers of patients.

Toxicities of chimeric antigen receptor T cells: recognition and management

Chimeric antigen receptor (CAR) T cells can produce durable remissions in hematologic malignancies that are not responsive to standard therapies. Yet the use of CAR T cells is limited by potentially severe toxicities. Early case reports of unexpected organ damage and deaths following CAR T-cell therapy first highlighted the possible dangers of this new treatment. CAR T cells can potentially damage normal tissues by specifically targeting a tumor-associated antigen that is also expressed on those tissues. Cytokine release syndrome (CRS), a systemic inflammatory response caused by cytokines released by infused CAR T cells can lead to widespread reversible organ dysfunction. CRS is the most common type of toxicity caused by CAR T cells. Neurologic toxicity due to CAR T cells might in some cases have a different pathophysiology than CRS and requires different management. Aggressive supportive care is necessary for all patients experiencing CAR T-cell toxicities, with early intervention for hypotension and treatment of concurrent infections being essential. Interleukin-6 receptor blockade with tocilizumab remains the mainstay pharmacologic therapy for CRS, though indications for administration vary among centers. Corticosteroids should be reserved for neurologic toxicities and CRS not responsive to tocilizumab. Pharmacologic management is complicated by the risk of immunosuppressive therapy abrogating the antimalignancy activity of the CAR T cells. This review describes the toxicities caused by CAR T cells and reviews the published approaches used to manage toxicities. We present guidelines for treating patients experiencing CRS and other adverse events following CAR T-cell therapy.

Oncogenic cancer/testis antigens: prime candidates for immunotherapy

Recent developments have set the stage for immunotherapy as a supplement to conventional cancer treatment. Consequently, a significant effort is required to further improve efficacy and specificity, particularly the identification of optimal therapeutic targets for clinical testing. Cancer/testis antigens are immunogenic, highly cancer-specific, and frequently expressed in various types of cancer, which make them promising candidate targets for cancer immunotherapy, including cancer vaccination and adoptive T-cell transfer with chimeric T-cell receptors. Our current understanding of tumor immunology and immune escape suggests that targeting oncogenic antigens may be beneficial, meaning that identification of cancer/testis antigens with oncogenic properties is of high priority. Recent work from our lab and others provide evidence that many cancer/testis antigens, in fact, have oncogenic functions, including support of growth, survival and metastasis. This novel insight into the function of cancer/testis antigens has the potential to deliver more effective cancer vaccines. Moreover, immune targeting of oncogenic cancer/testis antigens in combination with conventional cytotoxic therapies or novel immunotherapies such as checkpoint blockade or adoptive transfer, represents a highly synergistic approach with the potential to improve patient survival.

Strategies to genetically engineer T cells for cancer immunotherapy

Immunotherapy is one of the most promising and innovative approaches to treat cancer, viral infections, and other immune-modulated diseases. Adoptive immunotherapy using gene-modified T cells is an exciting and rapidly evolving field. Exploiting knowledge of basic T cell biology and immune cell receptor function has fostered innovative approaches to modify immune cell function. Highly translatable clinical technologies have been developed to redirect T cell specificity by introducing designed receptors. The ability to engineer T cells to manifest desired phenotypes and functions is now a thrilling reality. In this review, we focus on outlining different varieties of genetically engineered T cells, their respective advantages and disadvantages as tools for immunotherapy, and their promise and drawbacks in the clinic.

T-cell adoptive immunotherapy using tumor-infiltrating T cells and genetically engineered TCR-T cells

Immunotherapy has received the expectation that it should contribute to the therapy of cancer patients for >100 years. At long last, recent clinical trials of immunotherapy with immune checkpoint inhibitors and adoptive cell therapy with genetically engineered T cells have reported their remarkable efficacies. Nowadays, it is expected that T-cell adoptive immunotherapy can not only control tumor progression but even cure cancer in some patients. Conversely, severe adverse events associated with efficacy have frequently been reported in clinical trials, suggesting that the assessment and control of safety will be indispensable in the future development of the therapy. New approaches in T-cell adoptive immunotherapy such as reduction of adverse events, targeting of new antigens or utilization of allogeneic cells will open a new gate for less harmful and more effective immunological treatment of cancer patients.

Toxicity and management in CAR T-cell therapy

T cells can be genetically modified to target tumors through the expression of a chimeric antigen receptor (CAR). Most notably, CAR T cells have demonstrated clinical efficacy in hematologic malignancies with more modest responses when targeting solid tumors. However, CAR T cells also have the capacity to elicit expected and unexpected toxicities including: cytokine release syndrome, neurologic toxicity, “on target/off tumor” recognition, and anaphylaxis. Theoretical toxicities including clonal expansion secondary to insertional oncogenesis, graft versus host disease, and off-target antigen recognition have not been clinically evident. Abrogating toxicity has become a critical step in the successful application of this emerging technology. To this end, we review the reported and theoretical toxicities of CAR T cells and their management.

CD4(+) and CD8(+) TCRβ repertoires possess different potentials to generate extraordinarily high-avidity T cells

Recent high throughput sequencing analysis has revealed that the TCRβ repertoire is largely different between CD8(+) and CD4(+) T cells. Here, we show that the transduction of SIG35α, the public chain-centric HLA-A*02:01(A2)/MART127-35 TCRα hemichain, conferred A2/MART127-35 reactivity to a substantial subset of both CD8(+) and CD4(+) T cells regardless of their HLA-A2 positivity. T cells individually reconstituted with SIG35α and different A2/MART127-35 TCRβ genes isolated from CD4(+) or CD8(+) T cells exhibited a wide range of avidity. Surprisingly, approximately half of the A2/MART127-35 TCRs derived from CD4(+) T cells, but none from CD8(+) T cells, were stained by A2/MART127-35 monomer and possessed broader cross-reactivity. Our results suggest that the differences in the primary structure of peripheral CD4(+) and CD8(+) TCRβ repertoire indeed result in the differences in their ability to form extraordinarily high avidity T cells which would otherwise have been deleted by central tolerance.

In situ expansion of T cells that recognize distinct self-antigens sustains autoimmunity in the CNS

Polyspecific T cells recognizing multiple distinct self-antigens have been identified in multiple sclerosis and other organ-specific autoimmune diseases, but their pathophysiological relevance remains undetermined. Using a mouse model of multiple sclerosis, we show that autoimmune encephalomyelitis induction is strictly dependent on reactivation of pathogenic T cells by a peptide (35-55) derived from myelin oligodendrocyte glycoprotein (MOG). This disease-inducing response wanes after onset. Strikingly, the progression of disease is driven by the in situ activation and expansion of a minority of MOG35-55-specific T cells that also recognize neurofilament-medium (NF-M)15-35, an intermediate filament protein expressed in neurons. This mobilization of bispecific T cells is critical for disease progression as adoptive transfer of NF-M15-35/MOG35-55 bispecific T cell lines caused full-blown disease in wild-type but not NF-M-deficient recipients. Moreover, specific tolerance through injection of NF-M15-35 peptide at the peak of disease halted experimental autoimmune encephalomyelitis progression. Our findings highlight the importance of polyspecific autoreactive T cells in the aggravation and perpetuation of central nervous system autoimmunity.

Antigen Selection for Enhanced Affinity T-Cell Receptor-Based Cancer Therapies

Evidence of adaptive immune responses in the prevention of cancer has been accumulating for decades. Spontaneous T-cell responses occur in multiple indications, bringing the study of de novo expressed cancer antigens to the fore and highlighting their potential as targets for cancer immunotherapy. Circumventing the immune-suppressive mechanisms that maintain tumor tolerance and driving an antitumor cytotoxic T-cell response in cancer patients may eradicate the tumor or block disease progression. Multiple strategies are being pursued to harness the cytotoxic potential of T cells clinically. Highly promising results are now emerging. The focus of this review is the target discovery process for cancer immune therapeutics based on affinity-matured T-cell receptors (TCRs). Target cancer antigens in the context of adoptive cell transfer technologies and soluble biologic agents are discussed. To appreciate the impact of TCR-based technology and understand the TCR discovery process, it is necessary to understand key differences between TCR-based therapy and other immunotherapy approaches. The review first summarizes key advances in the cancer immunotherapy field and then discusses the opportunities that TCR technology provides. The nature and breadth of molecular targets that are tractable to this approach are discussed, together with the challenges associated with finding them.

TCR-engineered T cells to treat tumors: Seeing but not touching?

Adoptive transfer of T cells gene-engineered with T cell receptors (TCRs) has proven its feasibility and therapeutic potential in the treatment of malignant tumors. To ensure further clinical development of TCR gene therapy, it is necessary to accurately select TCRs that demonstrate antigen-selective responses that are restricted to tumor cells and, at the same time, include strategies that restore or enhance the entry, migration and local accumulation of T cells in tumor tissues. Here, we present the current standing of TCR-engineered T cell therapy, discuss and propose procedures to select TCRs as well as strategies to sensitize the tumor to T cell trafficking, and provide a rationale for combination therapies with TCR-engineered T cells.

Which therapeutic strategy will achieve a cure for HIV-1?

Strategies to achieve a cure for HIV-1 infection can be broadly classified into three categories: eradication cure (elimination of all viral reservoirs), functional cure (immune control without reservoir eradication), or a hybrid cure (reservoir reduction with improved immune control). The many HIV-1 cure strategies being investigated include modification of host cells to resist HIV-1, engineered T cells to eliminate HIV-infected cells, broadly HIV-1 neutralizing monoclonal antibodies, and therapeutic vaccination, but the 'kick and kill' strategy to expose latent HIV-1 with latency reversing agents (LRAs) and kill the exposed cells through immune effector functions is currently the most actively pursued. It is unknown, however, whether LRAs can deplete viral reservoirs in vivo or whether current LRAs are sufficiently safe for clinical use.

The Role of Neoantigens in Naturally Occurring and Therapeutically Induced Immune Responses to Cancer

Definitive experimental evidence from mouse cancer models and strong correlative clinical data gave rise to the Cancer Immunoediting concept that explains the dual host-protective and tumor-promoting actions of immunity on developing cancers. Tumor-specific neoantigens can serve as targets of spontaneously arising adaptive immunity to cancer and thereby determine the ultimate fate of developing tumors. Tumor-specific neoantigens can also function as optimal targets of cancer immunotherapy against established tumors. These antigens are derived from nonsynonymous mutations that occur during cellular transformation and, because they are foreign to the host genome, are not subject to central tolerance. In this review, we summarize the experimental evidence indicating that cancer neoantigens are the source of both spontaneously occurring and therapeutically induced immune responses against cancer. We also review the advances in genomics, bioinformatics, and cancer immunotherapy that have facilitated identification of neoantigens and have moved personalized cancer immunotherapies into clinical trials, with the promise of providing more specific, safer, more effective, and perhaps even more generalizable treatments to cancer patients than current immunotherapies.

Chimeric Antigen Receptors Modified T-Cells for Cancer Therapy

The genetic modification and characterization of T-cells with chimeric antigen receptors (CARs) allow functionally distinct T-cell subsets to recognize specific tumor cells. The incorporation of costimulatory molecules or cytokines can enable engineered T-cells to eliminate tumor cells. CARs are generated by fusing the antigen-binding region of a monoclonal antibody (mAb) or other ligand to membrane-spanning and intracellular-signaling domains. They have recently shown clinical benefit in patients treated with CD19-directed autologous T-cells. Recent successes suggest that the modification of T-cells with CARs could be a powerful approach for developing safe and effective cancer therapeutics. Here, we briefly review early studies, consider strategies to improve the therapeutic potential and safety, and discuss the challenges and future prospects for CAR T-cells in cancer therapy.

Melanoma Immunotherapy in Mice Using Genetically Engineered Pluripotent Stem Cells

Adoptive cell transfer (ACT) of antigen (Ag)-specific CD8(+) cytotoxic T lymphocytes (CTLs) is a highly promising treatment for a variety of diseases. Naive or central memory T-cell-derived effector CTLs are optimal populations for ACT-based immunotherapy because these cells have a high proliferative potential, are less prone to apoptosis than terminally differentiated cells, and have the higher ability to respond to homeostatic cytokines. However, such ACT with T-cell persistence is often not feasible due to difficulties in obtaining sufficient cells from patients. Here we present that in vitro differentiated HSCs of engineered PSCs can develop in vivo into tumor Ag-specific naive CTLs, which efficiently suppress melanoma growth. Mouse-induced PSCs (iPSCs) were retrovirally transduced with a construct encoding chicken ovalbumin (OVA)-specific T-cell receptors (TCRs) and survival-related proteins (i.e., BCL-xL and survivin). The gene-transduced iPSCs were cultured on the delta-like ligand 1-expressing OP9 (OP9-DL1) murine stromal cells in the presence of murine recombinant cytokines (rFlt3L and rIL-7) for a week. These iPSC-derived cells were then intravenously adoptively transferred into recipient mice, followed by intraperitoneal injection with an agonist α-Notch 2 antibody and cytokines (rFlt3L and rIL-7). Two weeks later, naive OVA-specific CD8(+) T cells were observed in the mouse peripheral lymphatic system, which were responsive to OVA-specific stimulation. Moreover, the mice were resistant to the challenge of B16-OVA melanoma induction. These results indicate that genetically modified stem cells may be used for ACT-based immunotherapy or serve as potential vaccines.

New cell sources for T cell engineering and adoptive immunotherapy

The promising clinical results obtained with engineered T cells, including chimeric antigen receptor (CAR) therapy, call for further advancements to facilitate and broaden their applicability. One potentially beneficial innovation is to exploit new T cell sources that reduce the need for autologous cell manufacturing and enable cell transfer across histocompatibility barriers. Here we review emerging T cell engineering approaches that utilize alternative T cell sources, which include virus-specific or T cell receptor-less allogeneic T cells, expanded lymphoid progenitors, and induced pluripotent stem cell (iPSC)-derived T lymphocytes. The latter offer the prospect for true off-the-shelf, genetically enhanced, histocompatible cell therapy products.

Direct molecular mimicry enables off-target cardiovascular toxicity by an enhanced affinity TCR designed for cancer immunotherapy

Natural T-cell responses generally lack the potency to eradicate cancer. Enhanced affinity T-cell receptors (TCRs) provide an ideal approach to target cancer cells, with emerging clinical data showing significant promise. Nevertheless, the risk of off target reactivity remains a key concern, as exemplified in a recent clinical report describing fatal cardiac toxicity, following administration of MAGE-A3 specific TCR-engineered T-cells, mediated through cross-reactivity with an unrelated epitope from the Titin protein presented on cardiac tissue. Here, we investigated the structural mechanism enabling TCR cross-recognition of MAGE-A3 and Titin, and applied the resulting data to rationally design mutants with improved antigen discrimination, providing a proof-of-concept strategy for altering the fine specificity of a TCR towards an intended target antigen. This study represents the first example of direct molecular mimicry leading to clinically relevant fatal toxicity, mediated by a modified enhanced affinity TCR designed for cancer immunotherapy. Furthermore, these data demonstrate that self-antigens that are expressed at high levels on healthy tissue should be treated with extreme caution when designing immuno-therapeutics.

Prospects for gene-engineered T cell immunotherapy for solid cancers

Adoptive transfer of receptor-engineered T cells has produced impressive results in treating patients with B cell leukemias and lymphomas. This success has captured public imagination and driven academic and industrial researchers to develop similar 'off-the-shelf' receptors targeting shared antigens on epithelial cancers, the leading cause of cancer-related deaths. However, the successful treatment of large numbers of people with solid cancers using this strategy is unlikely to be straightforward. Receptor-engineered T cells have the potential to cause lethal toxicity from on-target recognition of normal tissues, and there is a paucity of truly tumor-specific antigens shared across tumor types. Here we offer our perspective on how expanding the use of genetically redirected T cells to treat the majority of patients with solid cancers will require major technical, manufacturing and regulatory innovations centered around the development of autologous gene therapies targeting private somatic mutations.

Transfection of Tumor-Infiltrating T Cells with mRNA Encoding CXCR2

Adoptive T-cell therapy based on the infusion of patient's own immune cells after ex vivo culturing is among the most potent forms of personalized treatment among recent clinical developments for the treatment of cancer. However, despite high rates of successful initial clinical responses, only about 20 % of patients with metastatic melanoma treated with tumor-infiltrating lymphocytes (TILs) enter complete and long-term regression, with the majority either relapsing after initial partial regression or not benefiting at all. Previous studies have shown a positive correlation between the number infused T cells migrating to the tumor and the clinical response, but also that only a small fraction of adoptively transferred T cells reach the tumor site. In this chapter, we describe a protocol for transfection of TILs with mRNA encoding the chemokine receptor CXCR2 transiently redirecting and improving TILs migration toward tumor-secreted chemokines in vitro.

Adoptive cellular therapy: a race to the finish line

Adoptive T cell transfer for cancer, chronic infection, and autoimmunity is an emerging field that shows promise in recent trials. Using the principles of synthetic biology, advances in cell culture and genetic engineering have made it possible to generate human T cells that display desired specificities and enhanced functionalities compared with the natural immune system. The prospects for widespread availability of engineered T cells have changed dramatically, given the recent entry of the pharmaceutical industry to this arena. Here, we discuss some of the challenges--such as regulatory, cost, and manufacturing--and opportunities, including personalized gene-modified T cells, that face the field of adoptive cellular therapy.

Serial Activation of the Inducible Caspase 9 Safety Switch After Human Stem Cell Transplantation

Activation of the inducible caspase 9 (iC9) safety gene by a dimerizing drug (chemical inducer of dimerization (CID) AP1903) effectively resolves the symptoms and signs of graft-versus-host disease (GvHD) in haploidentical stem cell transplant (HSCT) recipients. However, after CID treatment, 1% of iC9-T cells remain and can regrow over time; although these resurgent T cells do not cause recurrent GvHD, it remains unclear whether repeat CID treatments are a safe and feasible way to further deplete residual gene-modified T cells should any other adverse effects associated with them occur. Here, we report a patient who received an infusion of haploidentical iC9-T cells after HSCT and subsequently received three treatments with AP1903. There was a mild (grade 2) and transient pancytopenia following each AP1903 administration but no non-hematological toxicity. Ninety five percent of circulating iC9-T cells (CD3(+)CD19(+)) were eliminated after the first AP1903 treatment. Three months later, the residual cells had expanded more than eightfold and had a lower level of iC9 expression. Each repeated AP1903 administration eliminated a diminishing percentage of the residual repopulating cells, but elimination could be enhanced by T-cell activation. These data support the safety and efficiency of repeated CID treatments for persistent or recurring toxicity from T-cell therapies.

Adoptive T-cell therapies for refractory/relapsed leukemia and lymphoma: current strategies and recent advances

Despite significant advancements in the treatment and outcome of hematologic malignancies, prognosis remains poor for patients who have relapsed or refractory disease. Adoptive T-cell immunotherapy offers novel therapeutics that attempt to utilize the noted graft versus leukemia effect. While CD19 chimeric antigen receptor (CAR)-modified T cells have thus far been the most clinically successful application of adoptive T immunotherapy, further work with antigen specific T cells and CARs that recognize other targets have helped diversify the field to treat a broad spectrum of hematologic malignancies. This article will focus primarily on therapies currently in the clinical trial phase as well as current downfalls or limitations.

Identifying Individual T Cell Receptors of Optimal Avidity for Tumor Antigens

Cytotoxic T cells recognize, via their T cell receptors (TCRs), small antigenic peptides presented by the major histocompatibility complex (pMHC) on the surface of professional antigen-presenting cells and infected or malignant cells. The efficiency of T cell triggering critically depends on TCR binding to cognate pMHC, i.e., the TCR–pMHC structural avidity. The binding and kinetic attributes of this interaction are key parameters for protective T cell-mediated immunity, with stronger TCR–pMHC interactions conferring superior T cell activation and responsiveness than weaker ones. However, high-avidity TCRs are not always available, particularly among self/tumor antigen-specific T cells, most of which are eliminated by central and peripheral deletion mechanisms. Consequently, systematic assessment of T cell avidity can greatly help distinguishing protective from non-protective T cells. Here, we review novel strategies to assess TCR–pMHC interaction kinetics, enabling the identification of the functionally most-relevant T cells. We also discuss the significance of these technologies in determining which cells within a naturally occurring polyclonal tumor-specific T cell response would offer the best clinical benefit for use in adoptive therapies, with or without T cell engineering.

Engineered T cell therapies

Alongside advancements in gene therapy for inherited immune disorders, the need for effective alternative therapeutic options for other conditions has resulted in an expansion in the field of research for T cell gene therapy. T cells are easily obtained and can be induced to divide robustly ex vivo, a characteristic that allows them to be highly permissible to viral vector-mediated introduction of transgenes. Pioneering clinical trials targeting cancers and infectious diseases have provided safety and feasibility data and important information about persistence of engineered cells in vivo. Here, we review clinical experiences with γ-retroviral and lentiviral vectors and consider the potential of integrating transposon-based vectors as well as specific genome editing with designer nucleases in engineered T cell therapies.

Tolerance and efficacy of autologous or donor-derived T cells expressing CD19 chimeric antigen receptors in adult B-ALL with extramedullary leukemia

The engineering of T lymphocytes to express chimeric antigen receptors (CARs) aims to establish T cell-mediated tumor immunity rapidly. In this study, we conducted a pilot clinical trial of autologous or donor- derived T cells genetically modified to express a CAR targeting the B-cell antigen CD19 harboring 4-1BB and the CD3ζ moiety. All enrolled patients had relapsed or chemotherapy-refractory B-cell lineage acute lymphocytic leukemia (B-ALL). Of the nine patients, six had definite extramedullary involvement, and the rate of overall survival at 18 weeks was 56%. One of the two patients who received conditioning chemotherapy achieved a three-month durable complete response with partial regression of extramedullary lesions. Four of seven patients who did not receive conditioning chemotherapy achieved dramatic regression or a mixed response in the haematopoietic system and extramedullary tissues for two to nine months. Grade 2-3 graft-versus-host disease (GVHD) was observed in two patients who received substantial donor-derived anti-CD19 CART (chimeric antigen receptor-modified T) cells 3-4 weeks after cell infusions. These results show for the first time that donor-derived anti-CD19 CART cells can cause GVHD and regression of extramedullary B-ALL. This study is registered at www.clinicaltrials.gov as NCT01864889.

Dysfunction of PSA-specific CD8+ T cells in prostate cancer patients correlates with CD38 and Tim-3 expression

The efficacy of immunotherapy in cancer patients is influenced by differences in their immune status. An evaluation of immunocompetence before therapy may help to predict therapeutic success and guide the selection of appropriate regimens. We assessed the preexisting cellular immunity against prostate-specific antigen (PSA) in untreated prostate cancer patients and healthy controls through measurement of the phenotype and function of CD8(+) T cells. Our data show that the majority of healthy men possess functional PSA-specific CD8(+) T cells in contrast to cancer patients, where <50 % showed a CD8(+) T cell response. PSA146-154-specific CD8(+) T cells of these patients had a higher expression of the activation marker CD38 and the exhaustion marker Tim-3, indicating that PSA-specific cells are exhausted. The heterogeneity of the CD8(+) T cell response against PSA in prostate cancer patients may influence their response to therapy and is a factor to be taken into account while designing and selecting treatment regimens.

T-cell receptor gene therapy--ready to go viral?

T lymphocytes can be redirected to recognize a tumor target and harnessed to combat cancer by genetic introduction of T-cell receptors of a defined specificity. This approach has recently mediated encouraging clinical responses in patients with cancers previously regarded as incurable. However, despite the great promise, T-cell receptor gene therapy still faces a multitude of obstacles. Identification of epitopes that enable effective targeting of all the cells in a heterogeneous tumor while sparing normal tissues remains perhaps the most demanding challenge. Experience from clinical trials has revealed the dangers associated with T-cell receptor gene therapy and highlighted the need for reliable preclinical methods to identify potentially hazardous recognition of both intended and unintended epitopes in healthy tissues. Procedures for manufacturing large and highly potent T-cell populations can be optimized to enhance their antitumor efficacy. Here, we review the current knowledge gained from preclinical models and clinical trials using adoptive transfer of T-cell receptor-engineered T lymphocytes, discuss the major challenges involved and highlight potential strategies to increase the safety and efficacy to make T-cell receptor gene therapy a standard-of-care for large patient groups.