Multiplex Genome-Edited T-cell Manufacturing Platform for "Off-the-Shelf" Adoptive T-cell Immunotherapies

Cancer Immunotherapy: Whence and Whither

The current concepts and practice of cancer immunotherapy evolved from classical experiments that distinguished "self" from "non-self" and the finding that humoral immunity is complemented by cellular immunity. Elucidation of the biology underlying immune checkpoints and interactions between ligands and ligand receptors that govern the immune system's ability to recognize tumor cells as foreign has led to the emergence of new strategies that mobilize the immune system to reverse this apparent tolerance. Some of these approaches have led to new therapies such as the use of mAbs to interfere with the immune checkpoint. Others have exploited molecular technologies to reengineer a subset of T cells to directly engage and kill tumor cells, particularly those of B-cell malignancies. However, before immunotherapy can become a more effective method of cancer care, there are many challenges that remain to be addressed and hurdles to overcome. Included are manipulation of tumor microenvironment (TME) to enhance T effector cell infiltration and access to the tumor, augmentation of tumor MHC expression for adequate presentation of tumor associated antigens, regulation of cytokines and their potential adverse effects, and reduced risk of secondary malignancies as a consequence of mutations generated by the various forms of genetic engineering of immune cells. Despite these challenges, the future of immunotherapy as a standard anticancer therapy is encouraging. Mol Cancer Res; 15(6); 635-50. ©2017 AACR.

Integration of a CD19 CAR into the TCR Alpha Chain Locus Streamlines Production of Allogeneic Gene-Edited CAR T Cells

Adoptive cellular therapy using chimeric antigen receptor (CAR) T cell therapies have produced significant objective responses in patients with CD19⁺ hematological malignancies, including durable complete responses. Although the majority of clinical trials to date have used autologous patient cells as the starting material to generate CAR T cells, this strategy poses significant manufacturing challenges and, for some patients, may not be feasible because of their advanced disease state or difficulty with manufacturing suitable numbers of CAR T cells. Alternatively, T cells from a healthy donor can be used to produce an allogeneic CAR T therapy, provided the cells are rendered incapable of eliciting graft versus host disease (GvHD). One approach to the production of these cells is gene editing to eliminate expression of the endogenous T cell receptor (TCR). Here we report a streamlined strategy for generating allogeneic CAR T cells by targeting the insertion of a CAR transgene directly into the native TCR locus using an engineered homing endonuclease and an AAV donor template. We demonstrate that anti-CD19 CAR T cells produced in this manner do not express the endogenous TCR, exhibit potent effector functions in vitro, and mediate clearance of CD19⁺ tumors in an in vivo mouse model.

Genome-wide Specificity of Highly Efficient TALENs and CRISPR/Cas9 for T Cell Receptor Modification

In T cells with transgenic high-avidity T cell receptors (TCRs), endogenous and transferred TCR chains compete for surface expression and may pair inappropriately, potentially causing autoimmunity. To knock out endogenous TCR expression, we assembled 12 transcription activator-like effector nucleases (TALENs) and five guide RNAs (gRNAs) from the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas9) system. Using TALEN mRNA, TCR knockout was successful in up to 81% of T cells. Additionally, we were able to verify targeted gene addition of a GFP gene by homology-directed repair at the TALEN target site, using a donor suitable for replacement of the reporter transgene with therapeutic TCR chains. Remarkably, analysis of TALEN and CRISPR/Cas9 specificity using integrase-defective lentiviral vector capture revealed only one off-target site for one of the gRNAs and three off-target sites for both of the TALENs, indicating a high level of specificity. Collectively, our work shows highly efficient and specific nucleases for T cell engineering.

Chimeric Antigen Receptor T Cells and Hematopoietic Cell Transplantation: How Not to Put the CART Before the Horse

Hematopoietic cell transplantation (HCT) remains an important and potentially curative option for most hematologic malignancies. As a form of immunotherapy, allogeneic HCT (allo-HCT) offers the potential for durable remissions but is limited by transplantation- related morbidity and mortality owing to organ toxicity, infection, and graft-versus-host disease. The recent positive outcomes of chimeric antigen receptor T (CART) cell therapy in B cell malignancies may herald a paradigm shift in the management of these disorders and perhaps other hematologic malignancies as well. Clinical trials are now needed to address the relative roles of CART cells and HCT in the context of transplantation-eligible patients. In this review, we summarize the state of the art of the development of CART cell therapy for leukemia, lymphoma, and myeloma and discuss our perspective of how CART cell therapy can be applied in the context of HCT.

Engineering Therapeutic T Cells: From Synthetic Biology to Clinical Trials

Engineered T cells are currently in clinical trials to treat patients with cancer, solid organ transplants, and autoimmune diseases. However, the field is still in its infancy. The design, and manufacturing, of T cell therapies is not standardized and is performed mostly in academic settings by competing groups. Reliable methods to define dose and pharmacokinetics of T cell therapies need to be developed. As of mid-2016, there are no US Food and Drug Administration (FDA)-approved T cell therapeutics on the market, and FDA regulations are only slowly adapting to the new technologies. Further development of engineered T cell therapies requires advances in immunology, synthetic biology, manufacturing processes, and government regulation. In this review, we outline some of these challenges and discuss the contributions that pathologists can make to this emerging field.

An oxygen sensitive self-decision making engineered CAR T-cell

A key to the success of chimeric antigen receptor (CAR) T-cell based therapies greatly rely on the capacity to identify and target antigens with expression restrained to tumor cells. Here we present a strategy to generate CAR T-cells that are only effective locally (tumor tissue), potentially also increasing the choice of targetable antigens. By fusing an oxygen sensitive subdomain of HIF1α to a CAR scaffold, we generated CAR T-cells that are responsive to a hypoxic environment, a hallmark of certain tumors. Along with the development of oxygen-sensitive CAR T-cells, this work also provides a basic framework to use a multi-chain CAR as a platform to create the next generation of smarter self-decision making CAR T-cells.

Therapeutic genome editing with engineered nucleases

Targeted genome editing with designer nucleases, such as zinc finger nucleases, TALE nucleases, and CRISPR-Cas nucleases, has heralded a new era in gene therapy. Genetic disorders, which have not been amenable to conventional gene-addition-type gene therapy approaches, such as disorders with dominant inheritance or diseases caused by mutations in tightly regulated genes, can now be treated by precise genome surgery. Moreover, engineered nucleases enable novel genetic interventions to fight infectious diseases or to improve cancer immunotherapies. Here, we review the development of the different classes of programmable nucleases, discuss the challenges and improvements in translating gene editing into clinical use, and give an outlook on what applications can expect to enter the clinic in the near future.

Homology-Directed Recombination for Enhanced Engineering of Chimeric Antigen Receptor T Cells

Gene editing by homology-directed recombination (HDR) can be used to couple delivery of a therapeutic gene cassette with targeted genomic modifications to generate engineered human T cells with clinically useful profiles. Here, we explore the functionality of therapeutic cassettes delivered by these means and test the flexibility of this approach to clinically relevant alleles. Because CCR5-negative T cells are resistant to HIV-1 infection, CCR5-negative anti-CD19 chimeric antigen receptor (CAR) T cells could be used to treat patients with HIV-associated B cell malignancies. We show that targeted delivery of an anti-CD19 CAR cassette to the CCR5 locus using a recombinant AAV homology template and an engineered megaTAL nuclease results in T cells that are functionally equivalent, in both in vitro and in vivo tumor models, to CAR T cells generated by random integration using lentiviral delivery. With the goal of developing off-the-shelf CAR T cell therapies, we next targeted CARs to the T cell receptor alpha constant (TRAC) locus by HDR, producing TCR-negative anti-CD19 CAR and anti-B cell maturation antigen (BCMA) CAR T cells. These novel cell products exhibited in vitro cytolytic activity against both tumor cell lines and primary cell targets. Our combined results indicate that high-efficiency HDR delivery of therapeutic genes may provide a flexible and robust method that can extend the clinical utility of cell therapeutics.

Global Manufacturing of CAR T Cell Therapy

Immunotherapy using chimeric antigen receptor-modified T cells has demonstrated high response rates in patients with B cell malignancies, and chimeric antigen receptor T cell therapy is now being investigated in several hematologic and solid tumor types. Chimeric antigen receptor T cells are generated by removing T cells from a patient’s blood and engineering the cells to express the chimeric antigen receptor, which reprograms the T cells to target tumor cells. As chimeric antigen receptor T cell therapy moves into later-phase clinical trials and becomes an option for more patients, compliance of the chimeric antigen receptor T cell manufacturing process with global regulatory requirements becomes a topic for extensive discussion. Additionally, the challenges of taking a chimeric antigen receptor T cell manufacturing process from a single institution to a large-scale multi-site manufacturing center must be addressed. We have anticipated such concerns in our experience with the CD19 chimeric antigen receptor T cell therapy CTL019. In this review, we discuss steps involved in the cell processing of the technology, including the use of an optimal vector for consistent cell processing, along with addressing the challenges of expanding chimeric antigen receptor T cell therapy to a global patient population.

SHP-1: the next checkpoint target for cancer immunotherapy?

The immense power of the immune system is harnessed in healthy individuals by a range of negative regulatory signals and checkpoints. Manipulating these checkpoints through inhibition has resulted in striking immune-mediated clearance of otherwise untreatable tumours and metastases; unfortunately, not all patients respond to treatment with the currently available inhibitors of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1). Combinatorial studies using both anti-CTLA-4 and anti-PD-1 demonstrate synergistic effects of targeting multiple checkpoints, paving the way for other immune checkpoints to be targeted. Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP-1) is a widely expressed inhibitory protein tyrosine phosphatase (PTP). In T-cells, it is a negative regulator of antigen-dependent activation and proliferation. It is a cytosolic protein, and therefore not amenable to antibody-mediated therapies, but its role in activation and proliferation makes it an attractive target for genetic manipulation in adoptive transfer strategies, such as chimeric antigen receptor (CAR) T-cells. This review will discuss the potential value of SHP-1 inhibition in future tumour immunotherapy.

The promise of chimeric antigen receptor T cells (CARTs) in leukaemia

The success of genetically engineered T cells that express chimeric antigen receptors (CARTs) has been a momentous step forward in harnessing the potent cancer fighting abilities of the immune system. The efficacy seen in relapsed/refractory (r/r) acute lymphoblastic leukaemia (ALL), not only by inducing remission, but also in maintaining long-term disease control, has been unprecedented. While the foundation for this approach has been firmly set in place, continued development will improve the efficacy, toxicity and applicability to other malignancies of this new class of 'living drugs'. In this review, we provide a comprehensive overview of the most current clinical trial data in both acute and chronic leukaemias, and discuss some of the potential ways to enhance the activity and safety of CART therapy going forward.

Recent advances in T-cell immunotherapy for haematological malignancies

In vitro discoveries have paved the way for bench-to-bedside translation in adoptive T cell immunotherapy, resulting in remarkable clinical responses in a variety of haematological malignancies. Adoptively transferred T cells genetically modified to express CD19 CARs have shown great promise, although many unanswered questions regarding how to optimize T-cell therapies for both safety and efficacy remain. Similarly, T cells that recognize viral or tumour antigens though their native receptors have produced encouraging clinical responses. Honing manufacturing processes will increase the availability of T-cell products, while combining T-cell therapies has the ability to increase complete response rates. Lastly, innovative mechanisms to control these therapies may improve safety profiles while genome editing offers the prospect of modulating T-cell function. This review will focus on recent advances in T-cell immunotherapy, highlighting both clinical and pre-clinical advances, as well as exploring what the future holds.

Genome Editing Techniques and Their Therapeutic Applications

Fueled by advances in the field of genetics, the methods available to edit DNA sequences in living cells have continued to develop steadily. These technologies directly impact the fields of gene and cell therapy, where changes in the DNA sequence of target cells offer a route to correct genetic diseases and manipulate disorders like cancer. We review here the expanding menu of genome editing techniques and how they are being applied to therapeutic targets. The methods encompass a myriad of approaches to modify the covalent structure of DNA, including the targeted creation of double-strand breaks that can catalyze genomic changes, as well as the use of retroviruses and transposons to mediate gene addition, recombinases for sequence-specific gene addition and deletion, and base repair for direct sequence changes. The continued growth of the exciting field of genome editing is opening new possibilities for therapeutic intervention.

Recent Developments in Cellular Immunotherapy for HSCT-Associated Complications

Allogeneic hematopoietic stem cell transplantation is associated with serious complications, and improvement of the overall clinical outcome of patients with hematological malignancies is necessary. During the last decades, posttransplant donor-derived adoptive cellular immunotherapeutic strategies have been progressively developed for the treatment of graft-versus-host disease (GvHD), infectious complications, and tumor relapses. To date, the common challenge of all these cell-based approaches is their implementation for clinical application. Establishing an appropriate manufacturing process, to guarantee safe and effective therapeutics with simultaneous consideration of economic requirements is one of the most critical hurdles. In this review, we will discuss the recent scientific findings, clinical experiences, and technological advances for cell processing toward the application of mesenchymal stromal cells as a therapy for treatment of severe GvHD, virus-specific T cells for targeting life-threating infections, and of chimeric antigen receptors-engineered T cells to treat relapsed leukemia.

Multiplex Genome Editing to Generate Universal CAR T Cells Resistant to PD1 Inhibition

Purpose: Using gene-disrupted allogeneic T cells as universal effector cells provides an alternative and potentially improves current chimeric antigen receptor (CAR) T-cell therapy against cancers and infectious diseases.Experimental Design: The CRISPR/Cas9 system has recently emerged as a simple and efficient way for multiplex genome engineering. By combining lentiviral delivery of CAR and electro-transfer of Cas9 mRNA and gRNAs targeting endogenous TCR, β-2 microglobulin (B2M) and PD1 simultaneously, to generate gene-disrupted allogeneic CAR T cells deficient of TCR, HLA class I molecule and PD1.Results: The CRISPR gene-edited CAR T cells showed potent antitumor activities, both in vitro and in animal models and were as potent as non-gene-edited CAR T cells. In addition, the TCR and HLA class I double deficient T cells had reduced alloreactivity and did not cause graft-versus-host disease. Finally, simultaneous triple genome editing by adding the disruption of PD1 led to enhanced in vivo antitumor activity of the gene-disrupted CAR T cells.Conclusions: Gene-disrupted allogeneic CAR and TCR T cells could provide an alternative as a universal donor to autologous T cells, which carry difficulties and high production costs. Gene-disrupted CAR and TCR T cells with disabled checkpoint molecules may be potent effector cells against cancers and infectious diseases. Clin Cancer Res; 23(9); 2255-66. ©2016 AACR.

Non-viral delivery of genome-editing nucleases for gene therapy

Manipulating the genetic makeup of mammalian cells using programmable nuclease-based genome-editing technology has recently evolved into a powerful avenue that holds great potential for treating genetic disorders. There are four types of genome-editing nucleases, including meganucleases, zinc finger nucleases, transcription activator-like effector nucleases and clustered, regularly interspaced, short palindromic repeat-associated nucleases such as Cas9. These nucleases have been harnessed to introduce precise and specific changes of the genome sequence at virtually any genome locus of interest. The therapeutic relevance of these genome-editing technologies, however, is challenged by the safe and efficient delivery of nuclease into targeted cells. Herein, we summarize recent advances that have been made on non-viral delivery of genome-editing nucleases. In particular, we focus on non-viral delivery of Cas9/sgRNA ribonucleoproteins for genome editing. In addition, the future direction for developing non-viral delivery of programmable nucleases for genome editing is discussed.

Genetic medicines for CF: Hype versus reality

Since identification of the CFTR gene over 25 years ago, gene therapy for cystic fibrosis (CF) has been actively developed. More recently gene therapy has been joined by other forms of "genetic medicines" including mRNA delivery, as well as genome editing and mRNA repair-based strategies. Proof-of-concept that gene therapy can stabilize the progression of CF lung disease has recently been established in a Phase IIb trial. An early phase study to assess the safety and explore efficacy of CFTR mRNA repair is ongoing, while mRNA delivery and genome editing-based strategies are currently at the pre-clinical phase of development. This review has been written jointly by some of those involved in the various CF "genetic medicine" fields and will summarize the current state-of-the-art, as well as discuss future developments. Where applicable, it highlights common problems faced by each of the strategies, and also tries to highlight where a specific strategy may have an advantage on the pathway to clinical translation. We hope that this review will contribute to the ongoing discussion about the hype versus reality of genetic medicine-based treatment approaches in CF. Pediatr Pulmonol. 2016;51:S5-S17. © 2016 Wiley Periodicals, Inc.

Perspectives on the Transition From Bacterial Phytopathogen Genomics Studies to Applications Enhancing Disease Management: From Promise to Practice

The advent of genomics has advanced science into a new era, providing a plethora of "toys" for researchers in many related and disparate fields. Genomics has also spawned many new fields, including proteomics and metabolomics, furthering our ability to gain a more comprehensive view of individual organisms and of interacting organisms. Genomic information of both bacterial pathogens and their hosts has provided the critical starting point in understanding the molecular bases of how pathogens disrupt host cells to cause disease. In addition, knowledge of the complete genome sequence of the pathogen provides a potentially broad slate of targets for the development of novel virulence inhibitors that are desperately needed for disease management. Regarding plant bacterial pathogens and disease management, the potential for utilizing genomics resources in the development of durable resistance is enhanced because of developing technologies that enable targeted modification of the host. Here, we summarize the role of genomics studies in furthering efforts to manage bacterial plant diseases and highlight novel genomics-enabled strategies heading down this path.

High Efficiency CRISPR/Cas9-mediated Gene Editing in Primary Human T-cells Using Mutant Adenoviral E4orf6/E1b55k "Helper" Proteins

Many future therapeutic applications of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 and related RNA-guided nucleases are likely to require their use to promote gene targeting, thus necessitating development of methods that provide for delivery of three components-Cas9, guide RNAs and recombination templates-to primary cells rendered proficient for homology-directed repair. Here, we demonstrate an electroporation/transduction codelivery method that utilizes mRNA to express both Cas9 and mutant adenoviral E4orf6 and E1b55k helper proteins in association with adeno-associated virus (AAV) vectors expressing guide RNAs and recombination templates. By transiently enhancing target cell permissiveness to AAV transduction and gene editing efficiency, this novel approach promotes efficient gene disruption and/or gene targeting at multiple loci in primary human T-cells, illustrating its broad potential for application in translational gene editing.

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.

Engineered T cells: the promise and challenges of cancer immunotherapy

The immune system evolved to distinguish non-self from self to protect the organism. As cancer is derived from our own cells, immune responses to dysregulated cell growth present a unique challenge. This is compounded by mechanisms of immune evasion and immunosuppression that develop in the tumour microenvironment. The modern genetic toolbox enables the adoptive transfer of engineered T cells to create enhanced anticancer immune functions where natural cancer-specific immune responses have failed. Genetically engineered T cells, so-called 'living drugs', represent a new paradigm in anticancer therapy. Recent clinical trials using T cells engineered to express chimeric antigen receptors (CARs) or engineered T cell receptors (TCRs) have produced stunning results in patients with relapsed or refractory haematological malignancies. In this Review we describe some of the most recent and promising advances in engineered T cell therapy with a particular emphasis on what the next generation of T cell therapy is likely to entail.

CRISPR-Cas9 gene editing: Delivery aspects and therapeutic potential

The CRISPR-Cas9 gene editing system has taken the biomedical science field by storm, initiating rumors about future Nobel Prizes and heating up a fierce patent war, but also making significant scientific impact. The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR), together with CRISPR-associated proteins (Cas) are a part of the prokaryotic adaptive immune system and have successfully been repurposed for genome editing in mammalian cells. The CRISPR-Cas9 system has been used to correct genetic mutations and for replacing entire genes, opening up a world of possibilities for the treatment of genetic diseases. In addition, recently some new CRISPR-Cas systems have been discovered with interesting mechanistic variations. Despite these promising developments, many challenges have to be overcome before the system can be applied therapeutically in human patients and enabling delivery technology is one of the key challenges. Furthermore, the relatively high off-target effect of the system in its current form prevents it from being safely applied directly in the human body. In this review, the transformation of the CRISPR-Cas gene editing systems into a therapeutic modality will be discussed and the currently most realistic in vivo applications will be highlighted.

Gene Editing of Human Hematopoietic Stem and Progenitor Cells: Promise and Potential Hurdles

Hematopoietic stem and progenitor cells (HSPCs) have great therapeutic potential because of their ability to both self-renew and differentiate. It has been proposed that, given their unique properties, a small number of genetically modified HSPCs could accomplish lifelong, corrective reconstitution of the entire hematopoietic system in patients with various hematologic disorders. Scientists have demonstrated that gene addition therapies-targeted to HSPCs and using integrating retroviral vectors-possess clear clinical benefits in multiple diseases, among them immunodeficiencies, storage disorders, and hemoglobinopathies. Scientists attempting to develop clinically relevant gene therapy protocols have, however, encountered a number of unexpected hurdles because of their incomplete knowledge of target cells, genomic control, and gene transfer technologies. Targeted gene-editing technologies using engineered nucleases such as ZFN, TALEN, and/or CRISPR/Cas9 RGEN show great clinical promise, allowing for the site-specific correction of disease-causing mutations-a process with important applications in autosomal dominant or dominant-negative genetic disorders. The relative simplicity of the CRISPR/Cas9 system, in particular, has sparked an exponential increase in the scientific community's interest in and use of these gene-editing technologies. In this minireview, we discuss the specific applications of gene-editing technologies in human HSPCs, as informed by prior experience with gene addition strategies. HSPCs are desirable but challenging targets; the specific mechanisms these cells evolved to protect themselves from DNA damage render them potentially more susceptible to oncogenesis, especially given their ability to self-renew and their long-term proliferative potential. We further review scientists' experience with gene-editing technologies to date, focusing on strategies to move these techniques toward implementation in safe and effective clinical trials.

Chimeric Antigen Receptor T Cell Therapy Targeting CD19-Positive Leukemia and Lymphoma in the Context of Stem Cell Transplantation

Novel therapies with chimeric antigen receptor (CAR)-transduced T cells (TCs) sparked new hope for patients with relapsed or refractory CD19-positive leukemia or lymphoma even after stem cell therapies. This review focuses on CARs recognizing the B cell antigen CD19. Both retroviral and lentiviral vectors are used, encoding various anti-CD19 CAR constructs comprising costimulatory molecules such as CD28, CD137/4-1BB, and OX40 either alone (second-generation CARs) or in combination (third-generation CARs). Current, up-to-date published studies on anti-CD19 CAR therapy for acute lymphoblastic leukemia (ALL), chronic lymphocytic leukemia (CLL), and non-Hodgkin lymphoma (NHL) with observed side effects are discussed and an outlook on 58 ongoing trials is given. Clinical responses were achieved in up to 81% of ALL, 50% of CLL, and 40% of NHL patients. Factors with potential influence on the clinical outcome might be the design of the vector, the preconditioning regimen, and the number and quality of transfused CAR TCs. The applicability of clinical CAR TC therapy might include relapse after allogeneic stem cell transplantation (alloSCT), and ineligibility for or "bridging" until alloSCT. In summary, CAR therapy represents a highly promising treatment option even in heavily pretreated patients.

Purity of transferred CD8(+) T cells is crucial for safety and efficacy of combinatorial tumor immunotherapy in the absence of SHP-1

Adoptive transfer of tumor-specific cytotoxic T cells is a promising advance in cancer therapy. Similarly, checkpoint inhibition has shown striking clinical results in some patients. Here we combine adoptive cell transfer with ablation of the checkpoint protein Src homology 2-domain-containing phosphatase 1 (SHP-1, Ptpn6). Naturally occurring motheaten mice lack SHP-1 and do not survive weaning due to extensive immunopathology. To circumvent this limitation, we created a novel SHP-1^null mouse that is viable up to 12 weeks of age by knocking out IL1r1. Using this model, we demonstrate that the absence of SHP-1 augments the ability of adoptively transferred CD8⁺ T cells to control tumor growth. This therapeutic effect was only observed in situations where T-cell numbers were limited, analogous to clinical settings. However, adoptive transfer of non-CD8⁺ SHP-1^null hematopoietic cells resulted in lethal motheaten-like pathology, indicating that systemic inhibition of SHP-1 could have serious adverse effects. Despite this caveat, our findings support the development of SHP-1 inhibition strategies in human T cells to complement adoptive transfer therapies in the clinic.

Smart CARs engineered for cancer immunotherapy

PURPOSE OF REVIEW

Chimeric antigen receptors (CARs) are synthetic immunoreceptors, which can redirect T cells to selectively kill tumor cells, and as 'living drugs' have the potential to generate long-term antitumor immunity. Given their recent clinical successes for the treatment of refractory B-cell malignancies, there is a strong push toward advancing this immunotherapy to other hematological diseases and solid cancers. Here, we summarize the current state of the field, highlighting key variables for the optimal application of CAR T cells for cancer immunotherapy.

RECENT FINDINGS

Advances in CAR T-cell therapy have highlighted intrinsic CAR design and T-cell manufacturing methods as critical components for maximal therapeutic success. Similarly, addressing the unique extrinsic challenges of each tumor type, including overcoming the immunosuppressive tumor microenvironment and tumor heterogeneity, and mitigating potential toxicity, will dominate the next wave of CAR T-cell development.

SUMMARY

CAR T-cell therapeutic optimization, including intrinsic and extrinsic factors, is critical to developing effective CAR T-cell therapies for cancer. The excitement of CAR T-cell immunotherapy has just begun, and will continue with new insights revealed in laboratory research and in ongoing clinical investigations.

Gene editing and its application for hematological diseases

The use of precise, rationally designed gene-editing nucleases allows for targeted genome and transcriptome modification, and at present, four major classes of nucleases are being employed: zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), meganucleases (MNs), and clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9. Each reagent shares the ability to recognize and bind a target sequence of DNA. Depending on the properties of the reagent, the DNA can be cleaved on one or both strands, or epigenetic changes can be mediated. These novel properties can impact hematological disease by allowing for: (1) direct modification of hematopoietic stem/progenitor cells (HSPCs), (2) gene alteration of hematopoietic lineage committed terminal effectors, (3) genome engineering in non-hematopoietic cells with reprogramming to a hematopoietic phenotype, and (4) transcriptome modulation for gene regulation, modeling, and discovery.

Chimeric antigen receptors: driving immunology towards synthetic biology

The advent of second generation chimeric antigen receptors and the CD19 paradigm have ushered a new therapeutic modality in oncology. In contrast to earlier forms of adoptive cell therapy, which were based on the isolation and expansion of naturally occurring T cells, CAR therapy is based on the design and manufacture of engineered T cells with optimized properties. A new armamentarium, comprising not only CARs but also chimeric costimulatory receptors, chimeric cytokine receptors, inhibitory receptors and synthetic Notch receptors, expressed in naïve, central memory or stem cell-like memory T cells, is being developed for clinical use in a wide range of cancers. Immunological principles are thus finding a new purpose thanks to advances in genetic engineering, synthetic biology and cell manufacturing sciences.

Impact of gene editing on the study of cystic fibrosis

Cystic fibrosis (CF) is a chronic and progressive autosomal recessive disorder of secretory epithelial cells, which causes obstructions in the lung airways and pancreatic ducts of 70,000 people worldwide (for recent review see Cutting Nat Rev Genet 16(1):45-56, 2015). The finding that mutations in the CFTR gene cause CF (Kerem et al. Science 245(4922):1073-1080, 1989; Riordan et al. Science 245(4922):1066-1073, 1989; Rommens et al. Science 245(4922):1059-1065, 1989), was hailed as the very happy middle of a story whose end is a cure for a fatal disease (Koshland Science 245(4922):1029, 1989). However, despite two licensed drugs (Ramsey et al. N Engl J Med 365(18):1663-1672, 2011; Wainwright et al. N Engl J Med 373(3):220-231, 2015), and a formal demonstration that repeated administration of CFTR cDNA to patients is safe and effects a modest but significant stabilisation of disease (Alton et al. Lancet Respir Med 3(9):684-691, 2015), we are still a long way from a cure, with many patients taking over 100 tablets per day, and a mean age at death of 28 years. The aim of this review is to discuss the impact on the study of CF of gene-editing techniques as they have developed over the last 30 years, up to and including the possibility of editing as a therapeutic approach.

Clinical manufacturing of CAR T cells: foundation of a promising therapy

The treatment of cancer patients with autologous T cells expressing a chimeric antigen receptor (CAR) is one of the most promising adoptive cellular therapy approaches. Reproducible manufacturing of high-quality, clinical-grade CAR-T cell products is a prerequisite for the wide application of this technology. Product quality needs to be built-in within every step of the manufacturing process. We summarize herein the requirements and logistics to be considered, as well as the state of the art manufacturing platforms available. CAR-T cell therapy may be on the verge of becoming standard of care for a few clinical indications. Yet, many challenges pertaining to manufacturing standardization and product characterization remain to be overcome in order to achieve broad usage and eventual commercialization of this therapeutic modality.

Challenges and opportunities of allogeneic donor-derived CAR T cells

PURPOSE OF REVIEW

As T cells engineered with chimeric antigen receptors (CARs) are entering advanced phases of clinical trial testing with promising results, the potential implications of use in an allogeneic environment are emerging as an important consideration. This review discusses the use of allogeneic CAR therapy, the potential effects of T-cell receptor (TCR) signaling on CAR T-cell efficacy, and the potential for TCR elimination to generate an off-the-shelf product.

RECENT FINDINGS

The majority of preclinical and clinical data regarding allogeneic T cells are focused on safety of their use given the potential for graft-versus-host disease (GVHD) mediated by the T-cell receptor expressed with the introduced CAR. Recent clinical trials using donor-derived CAR T cells are using either rigorous patient selection or T-cell selection (such as enrichment for virus-specific T cells). Although no GVHD has been reported, the efficacy of the allogeneic CAR treatment needs to be optimized. Several preclinical models limit allogeneic CAR-driven GVHD by utilizing memory T-cell selection, virus-specific T cells, gene-editing techniques, or suicide gene engineering.

SUMMARY

In the allogeneic environment, the potential effects of TCR signaling on the efficacy of CAR could affect the clinical responses with the use of donor-derived CAR T cells. Better understanding of the functionality of donor-derived T cells for therapy is essential for the development of universal effector cells for CAR therapy.

CAR T Cell Therapy: A Game Changer in Cancer Treatment

The development of novel targeted therapies with acceptable safety profiles is critical to successful cancer outcomes with better survival rates. Immunotherapy offers promising opportunities with the potential to induce sustained remissions in patients with refractory disease. Recent dramatic clinical responses in trials with gene modified T cells expressing chimeric antigen receptors (CARs) in B-cell malignancies have generated great enthusiasm. This therapy might pave the way for a potential paradigm shift in the way we treat refractory or relapsed cancers. CARs are genetically engineered receptors that combine the specific binding domains from a tumor targeting antibody with T cell signaling domains to allow specifically targeted antibody redirected T cell activation. Despite current successes in hematological cancers, we are only in the beginning of exploring the powerful potential of CAR redirected T cells in the control and elimination of resistant, metastatic, or recurrent nonhematological cancers. This review discusses the application of the CAR T cell therapy, its challenges, and strategies for successful clinical and commercial translation.

Translational Implications for Off-the-shelf Immune Cells Expressing Chimeric Antigen Receptors

Chimeric antigen receptor (CAR) endows specificity to T-cells independent of human leukocyte antigen (HLA). This enables one immunoreceptor to directly target the same surface antigen on different subsets of tumor cells from multiple HLA-disparate recipients. Most approaches manufacture individualized CAR(+)T-cells from the recipient or HLA-compatible donor, which are revealing promising clinical results. This is the impetus to broaden the number of patients eligible to benefit from adoptive immunotherapy such as to infuse third-party donor derived CAR(+)T-cells. This will overcome issues associated with (i) time to manufacture T-cells, (ii) cost to generate one product for one patient, (iii) inability to generate a product from lymphopenic patients or patient's immune cells fail to complete the manufacturing process, and (iv) heterogeneity of T-cell products produced for or from individual recipients. Establishing a biobank of allogeneic genetically modified immune cells from healthy third-party donors, which are cryopreserved and validated in advance of administration, will facilitate the centralizing manufacturing and widespread distribution of CAR(+)T-cells to multiple points-of-care in a timely manner. To achieve this, it is necessary to engineer an effective strategy to avoid deleterious allogeneic immune responses leading to toxicity and rejection. We review the strategies to establish "off-the-shelf" donor-derived biobanks for human application of CAR(+)T-cells as a drug.

Stacking up CRISPR against RNAi for therapeutic gene inhibition

Both RNA interference (RNAi) and clustered regularly-interspaced short palindromic repeats (CRISPR) technologies allow for the sequence-specific inhibition of gene function and therefore have the potential to be used as therapeutic modalities. By judging the current public and scientific journal interest, it would seem that CRISPR, by enabling clean, durable knockouts, will dominate therapeutic gene inhibition, also at the expense of RNAi. This review aims to look behind prevailing sentiments and to more clearly define the likely scope of the therapeutic applications of the more recently developed CRISPR technology and its relative strengths and weaknesses with regards to RNAi. It is found that largely because of their broadly overlapping delivery constraints, while CRISPR presents formidable competition for DNA-directed RNAi strategies, its impact on RNAi therapeutics triggered by synthetic oligonucleotides will likely be more moderate. Instead, RNAi and genome editing, and in particular CRISPR, are poised to jointly promote a further shift toward sequence-targeted precision medicines.

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.

pEVL: A Linear Plasmid for Generating mRNA IVT Templates With Extended Encoded Poly(A) Sequences

Increasing demand for large-scale synthesis of in vitro transcribed (IVT) mRNA is being driven by the increasing use of mRNA for transient gene expression in cell engineering and therapeutic applications. An important determinant of IVT mRNA potency is the 3' polyadenosine (poly(A)) tail, the length of which correlates with translational efficiency. However, present methods for generation of IVT mRNA rely on templates derived from circular plasmids or PCR products, in which homopolymeric tracts are unstable, thus limiting encoded poly(A) tail lengths to ~120 base pairs (bp). Here, we have developed a novel method for generation of extended poly(A) tracts using a previously described linear plasmid system, pJazz. We find that linear plasmids can successfully propagate poly(A) tracts up to ~500 bp in length for IVT mRNA production. We then modified pJazz by removing extraneous restriction sites, adding a T7 promoter sequence upstream from an extended multiple cloning site, and adding a unique type-IIS restriction site downstream from the encoded poly(A) tract to facilitate generation of IVT mRNA with precisely defined encoded poly(A) tracts and 3' termini. The resulting plasmid, designated pEVL, can be used to generate IVT mRNA with consistent defined lengths and terminal residue(s).

A genome editing primer for the hematologist

Gene editing enables the site-specific modification of the genome. These technologies have rapidly advanced such that they have entered common use in experimental hematology to investigate genetic function. In addition, genome editing is becoming increasingly plausible as a treatment modality to rectify genetic blood disorders and improve cellular therapies. Genome modification typically ensues from site-specific double-strand breaks and may result in a myriad of outcomes. Even single-strand nicks and targeted biochemical modifications that do not permanently alter the DNA sequence (epigenome editing) may be powerful instruments. In this review, we examine the various technologies, describe their advantages and shortcomings for engendering useful genetic alterations, and consider future prospects for genome editing to impact hematology.

Ethical and regulatory aspects of genome editing

Gene editing is a rapidly developing area of biotechnology in which the nucleotide sequence of the genome of living cells is precisely changed. The use of genome-editing technologies to modify various types of blood cells, including hematopoietic stem cells, has emerged as an important field of therapeutic development for hematopoietic disease. Although these technologies offer the potential for generation of transformative therapies for patients suffering from myriad disorders of hematopoiesis, their application for therapeutic modification of primary human cells is still in its infancy. Consequently, development of ethical and regulatory frameworks that ensure their safe and effective use is an increasingly important consideration. Here, we review a number of issues that have the potential to impact the clinical implementation of genome-editing technologies, and suggest paths forward for resolving them such that new therapies can be safely and rapidly translated to the clinic.

Natural Killer Cells for Therapy of Leukemia

Clinical application of natural killer (NK) cells against leukemia is an area of intense investigation. In human leukocyte antigen-mismatched allogeneic hematopoietic stem cell transplantations (HSCT), alloreactive NK cells exert powerful anti-leukemic activity in preventing relapse in the absence of graft-versus-host disease, particularly in acute myeloid leukemia patients. Adoptive transfer of donor NK cells post-HSCT or in non-transplant scenarios may be superior to the currently widely used unmanipulated donor lymphocyte infusion. This concept could be further improved through transfusion of activated NK cells. Significant progress has been made in good manufacturing practice (GMP)-compliant large-scale production of stimulated effectors. However, inherent limitations remain. These include differing yields and compositions of the end-product due to donor variability and inefficient means for cryopreservation. Moreover, the impact of the various novel activation strategies on NK cell biology and in vivo behavior are barely understood. In contrast, reproduction of the third-party NK-92 drug from a cryostored GMP-compliant master cell bank is straightforward and efficient. Safety for the application of this highly cytotoxic cell line was demonstrated in first clinical trials. This novel 'off-the-shelf' product could become a treatment option for a broad patient population. For specific tumor targeting chimeric-antigen-receptor-engineered NK-92 cells have been designed.

Bispecific antibodies and CARs: generalized immunotherapeutics harnessing T cell redirection

To realize the full potential of cancer immunotherapy, the latest generation immunotherapeutics are designed to harness the potent tumor-killing capacity of T cells. Thus, to mobilize T cells, new optimized bispecific antibody (BsAb) designs, enabling efficient polyclonal redirection of cytotoxic activity through binding to CD3 and a Tumor Associated Antigen (TAA) and refined genetically modified T cells have recently expanded the arsenal of available options for cancer treatment. This review presents the current understanding of the parameters crucial to the design of optimal T cell redirecting BsAb and chimeric antigen receptor (CAR)-modified T cells. However, there are additional questions that require thorough elucidation. Both modalities will benefit from design changes that may increase the therapeutic window. One such approach could employ the discrimination afforded by multiple TAA to significantly increase selectivity.

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.

Salient Features of Endonuclease Platforms for Therapeutic Genome Editing

Emerging gene-editing technologies are nearing a revolutionary phase in genetic medicine: precisely modifying or repairing causal genetic defects. This may include any number of DNA sequence manipulations, such as knocking out a deleterious gene, introducing a particular mutation, or directly repairing a defective sequence by site-specific recombination. All of these edits can currently be achieved via programmable rare-cutting endonucleases to create targeted DNA breaks that can engage and exploit endogenous DNA repair pathways to impart site-specific genetic changes. Over the past decade, several distinct technologies for introducing site-specific DNA breaks have been developed, yet the different biological origins of these gene-editing technologies bring along inherent differences in parameters that impact clinical implementation. This review aims to provide an accessible overview of the various endonuclease-based gene-editing platforms, highlighting the strengths and weakness of each with respect to therapeutic applications.

Design of chimeric antigen receptors with integrated controllable transient functions

The ability to control T cells engineered to permanently express chimeric antigen receptors (CARs) is a key feature to improve safety. Here, we describe the development of a new CAR architecture with an integrated switch-on system that permits to control the CAR T-cell function. This system offers the advantage of a transient CAR T-cell for safety while letting open the possibility of multiple cytotoxicity cycles using a small molecule drug.

CAR T-cell immunotherapy: The path from the by-road to the freeway?

Chimeric antigen receptors are genetically encoded artificial fusion molecules that can re-program the specificity of peripheral blood polyclonal T-cells against a selected cell surface target. Unparallelled clinical efficacy has recently been demonstrated using this approach to treat patients with refractory B-cell malignancy. However, the approach is technically challenging and can elicit severe toxicity in patients. Moreover, solid tumours have largely proven refractory to this approach. In this review, we describe the important structural features of CARs and how this may influence function. Emerging clinical experience is summarized in both solid tumours and haematological malignancies. Finally, we consider the particular challenges imposed by solid tumours to the successful development of CAR T-cell immunotherapy, together with a number of innovative strategies that have been developed in an effort to reverse the balance in favour of therapeutic benefit.

Evaluation of TCR Gene Editing Achieved by TALENs, CRISPR/Cas9, and megaTAL Nucleases

Present adoptive immunotherapy strategies are based on the re-targeting of autologous T-cells to recognize tumor antigens. As T-cell properties may vary significantly between patients, this approach can result in significant variability in cell potency that may affect therapeutic outcome. More consistent results could be achieved by generating allogeneic cells from healthy donors. An impediment to such an approach is the endogenous T-cell receptors present on T-cells, which have the potential to direct dangerous off-tumor antihost reactivity. To address these limitations, we assessed the ability of three different TCR-α-targeted nucleases to disrupt T-cell receptor expression in primary human T-cells. We optimized the conditions for the delivery of each reagent and assessed off-target cleavage. The megaTAL and CRISPR/Cas9 reagents exhibited the highest disruption efficiency combined with low levels of toxicity and off-target cleavage, and we used them for a translatable manufacturing process to produce safe cellular substrates for next-generation immunotherapies.