Comparison of lentiviral and sleeping beauty mediated αβ T cell receptor gene transfer

Engineering of potent CAR NK cells using non-viral Sleeping Beauty transposition from minimalistic DNA vectors

Natural killer (NK) cells have high intrinsic cytotoxic capacity, and clinical trials have demonstrated their safety and efficacy for adoptive cancer therapy. Expression of chimeric antigen receptors (CARs) enhances NK cell target specificity, with these cells applicable as off-the-shelf products generated from allogeneic donors. Here, we present for the first time an innovative approach for CAR NK cell engineering employing a non-viral Sleeping Beauty (SB) transposon/transposase-based system and minimized DNA vectors termed minicircles. SB-modified peripheral blood-derived primary NK cells displayed high and stable CAR expression and more frequent vector integration into genomic safe harbors than lentiviral vectors. Importantly, SB-generated CAR NK cells demonstrated enhanced cytotoxicity compared with non-transfected NK cells. A strong antileukemic potential was confirmed using established acute lymphocytic leukemia cells and patient-derived primary acute B cell leukemia and lymphoma samples as targets in vitro and in vivo in a xenograft leukemia mouse model. Our data suggest that the SB-transposon system is an efficient, safe, and cost-effective approach to non-viral engineering of highly functional CAR NK cells, which may be suitable for cancer immunotherapy of leukemia as well as many other malignancies.

The paths toward non-viral CAR-T cell manufacturing: A comprehensive review of state-of-the-art methods

Although CAR-T cell therapy has emerged as a game-changer in cancer immunotherapy several bottlenecks limit its widespread use as a front-line therapy. Current protocols for the production of CAR-T cells rely mainly on the use of lentiviral/retroviral vectors. Nevertheless, according to the safety concerns around the use of viral vectors, there are several regulatory hurdles to their clinical use. Large-scale production of viral vectors under "Current Good Manufacturing Practice" (cGMP) involves rigorous quality control assessments and regulatory requirements that impose exorbitant costs on suppliers and as a result, lead to a significant increase in the cost of treatment. Pursuing an efficient non-viral method for genetic modification of immune cells is a hot topic in cell-based gene therapy. This study aims to investigate the current state-of-the-art in non-viral methods of CAR-T cell manufacturing. In the first part of this study, after reviewing the advantages and disadvantages of the clinical use of viral vectors, different non-viral vectors and the path of their clinical translation are discussed. These vectors include transposons (sleeping beauty, piggyBac, Tol2, and Tc Buster), programmable nucleases (ZFNs, TALENs, and CRISPR/Cas9), mRNA, plasmids, minicircles, and nanoplasmids. Afterward, various methods for efficient delivery of non-viral vectors into the cells are reviewed.

Nonviral technologies can pave the way for CAR-NK cell therapy

Natural killer cells are a promising platform for cancer immunotherapy. Natural killer cells have high intrinsic killing capability, and the insertion of a chimeric antigen receptor can further enhance their antitumor potential. In first-in-human trials, chimeric antigen receptor-natural killer cells demonstrated strong clinical activity without therapy-induced side effects. The applicability of natural killer cells as an "off-the-shelf" product makes them highly attractive for gene-engineered cell therapies. Traditionally, viral transduction has been used for gene editing; however, the use of viral vectors remains a safety concern and is associated with high costs and regulatory requirements. Here, we review the current landscape of nonviral approaches for chimeric antigen receptor-natural killer cell generation. This includes transfection of vector particles and electroporation of mRNA and DNA vectors, resulting in transient modification and chimeric antigen receptor expression. In addition, using nonviral transposon technologies, natural killer cells can be stably modified ensuring long-lasting chimeric antigen receptor expression. Finally, we discuss CRISPR/Cas9 tools to edit key genes for natural killer cell functionality.

Targeted delivery of a PD-1-blocking scFv by CD133-specific CAR-T cells using nonviral Sleeping Beauty transposition shows enhanced antitumour efficacy for advanced hepatocellular carcinoma

BACKGROUND

CD133 is considered a marker for cancer stem cells (CSCs) in several types of tumours, including hepatocellular carcinoma (HCC). Chimeric antigen receptor-specific T (CAR-T) cells targeting CD133-positive CSCs have emerged as a tool for the clinical treatment of HCC, but immunogenicity, the high cost of clinical-grade recombinant viral vectors and potential insertional mutagenesis limit their clinical application.

METHODS

CD133-specific CAR-T cells secreting PD-1 blocking scFv (CD133 CAR-T and PD-1 s cells) were constructed using a sleeping beauty transposon system from minicircle technology, and the antitumour efficacy of CD133 CAR-T and PD-1 s cells was analysed in vitro and in vivo.

RESULTS

A univariate analysis showed that CD133 expression in male patients at the late stage (II and III) was significantly associated with worse progression-free survival (PFS) (P = 0.0057) and overall survival (OS) (P = 0.015), and a multivariate analysis showed a trend toward worse OS (P = 0.041). Male patients with advanced HCC exhibited an approximately 20-fold higher PD-L1 combined positive score (CPS) compared with those with HCC at an early stage. We successfully generated CD133 CAR-T and PD-1 s cells that could secrete PD-1 blocking scFv based on a sleeping beauty system involving minicircle vectors. CD133 CAR-T and PD-1 s cells exhibited significant antitumour activity against HCC in vitro and in xenograft mouse models. Thus, CD133 CAR-T and PD-1 s cells may be a therapeutically tractable strategy for targeting CD133-positive CSCs in male patients with advanced HCC.

CONCLUSIONS

Our study provides a nonviral strategy for constructing CAR-T cells that could also secrete checkpoint blockade inhibitors based on a Sleeping Beauty system from minicircle vectors and revealed a potential benefit of this strategy for male patients with advanced HCC and high CD133 expression (median immunohistochemistry score > 2.284).

Recent Advancements in Electroporation Technologies: From Bench to Clinic

Over the past decade, the increased adoption of electroporation-based technologies has led to an expansion of clinical research initiatives. Electroporation has been utilized in molecular biology for mammalian and bacterial transfection; for food sanitation; and in therapeutic settings to increase drug uptake, for gene therapy, and to eliminate cancerous tissues. We begin this article by discussing the biophysics required for understanding the concepts behind the cell permeation phenomenon that is electroporation. We then review nano- and microscale single-cell electroporation technologies before scaling up to emerging in vivo applications.

Engineered Treg cells as putative therapeutics against inflammatory diseases and beyond

Regulatory T (Treg) cells ensure tolerance against self-antigens, limit excessive inflammation, and support tissue repair processes. Therefore, Treg cells are currently attractive candidates for the treatment of certain inflammatory diseases, autoimmune disorders, or transplant rejection. Early clinical trials have proved the safety and efficacy of certain Treg cell therapies in inflammatory diseases. We summarize recent advances in engineering Treg cells, including the concept of biosensors for inflammation. We assess Treg cell engineering possibilities for novel functional units, including Treg cell modifications influencing stability, migration, and tissue adaptation. Finally, we outline perspectives of engineered Treg cells going beyond inflammatory diseases by using custom-designed receptors and read-out systems, aiming to use Treg cells as in vivo diagnostic tools and drug delivery vehicles.

Minicircles for CAR T Cell Production by Sleeping Beauty Transposition: A Technological Overview

Development and application of chimeric antigen receptor (CAR) T cell therapy has led to a breakthrough in the treatment of hematologic malignancies. In 2017, the FDA approved the first commercialized CD19-specific CAR T cell products for treatment of patients with B-cell malignancies. This success increased the desire to broaden the availability of CAR T cells to a larger patient cohort with hematological but also solid tumors. A critical factor of CAR T cell production is the stable and efficient delivery of the CAR transgene into T cells. This gene transfer is conventionally achieved by viral vectors. However, viral gene transfer is not conducive to affordable, scalable, and timely manufacturing of CAR T cell products. Thus, there is a necessity for developing alternative nonviral engineering platforms, which are more cost-effective, less complex to handle and which provide the scalability requirement for a globally available therapy.One alternative method for engineering of T cells is the nonviral gene transfer by Sleeping Beauty (SB) transposition. Electroporation with two nucleic acids is sufficient to achieve stable CAR transfer into T cells. One of these vectors has to encode the gene of interest, which is the CAR , the second one a recombinase called SB transposase, the enzyme that catalyzes integration of the transgene into the host cell genome. As nucleic acids are easy to produce and handle SB gene transfer has the potential to provide scalability, cost-effectiveness, and feasibility for widespread use of CAR T cell therapies.Nevertheless, the electroporation of two large-size plasmid vectors into T cells leads to high T cell toxicity and low gene transfer rates and has hindered the prevalent clinical application of the SB system. To circumvent these limitations, conventional plasmid vectors can be replaced by minimal-size vectors called minicircles (MC ). MCs are DNA vectors that lack the plasmid backbone, which is relevant for propagation in bacteria, but has no function in a human cell. Thus, their size is drastically reduced compared to conventional plasmids. It has been demonstrated that MC-mediated SB CAR transposition into T cells enhances their viability and gene transfer rate enabling the production of therapeutic doses of CAR T cells. These improvements make CAR SB transposition from MC vectors a promising alternative for engineering of clinical grade CAR T cells.

Nanoparticle designs for delivery of nucleic acid therapeutics as brain cancer therapies

Glioblastoma (GBM) is an aggressive central nervous system cancer with a dismal prognosis. The standard of care involves surgical resection followed by radiotherapy and chemotherapy, but five-year survival is only 5.6% despite these measures. Novel therapeutic approaches, such as immunotherapies, targeted therapies, and gene therapies, have been explored to attempt to extend survival for patients. Nanoparticles have been receiving increasing attention as promising vehicles for non-viral nucleic acid delivery in the context of GBM, though delivery is often limited by low blood-brain barrier permeability, particle instability, and low trafficking to target brain structures and cells. In this review, nanoparticle design considerations and new advances to overcome nucleic acid delivery challenges to treat brain cancer are summarized and discussed.

Targeted T cell receptor gene editing provides predictable T cell product function for immunotherapy

Adoptive transfer of T cells expressing a transgenic T cell receptor (TCR) has the potential to revolutionize immunotherapy of infectious diseases and cancer. However, the generation of defined TCR-transgenic T cell medicinal products with predictable in vivo function still poses a major challenge and limits broader and more successful application of this "living drug." Here, by studying 51 different TCRs, we show that conventional genetic engineering by viral transduction leads to variable TCR expression and functionality as a result of variable transgene copy numbers and untargeted transgene integration. In contrast, CRISPR/Cas9-mediated TCR replacement enables defined, targeted TCR transgene insertion into the TCR gene locus. Thereby, T cell products display more homogeneous TCR expression similar to physiological T cells. Importantly, increased T cell product homogeneity after targeted TCR gene editing correlates with predictable in vivo T cell responses, which represents a crucial aspect for clinical application in adoptive T cell immunotherapy.

Delivery technologies for T cell gene editing: Applications in cancer immunotherapy

While initial approaches to adoptive T cell therapy relied on the identification and expansion of rare tumour-reactive T cells, genetic engineering has transformed cancer immunotherapy by enabling the modification of primary T cells to increase their therapeutic potential. Specifically, gene editing technologies have been utilized to create T cell populations with improved responses to antigens, lower rates of exhaustion, and potential for use in allogeneic applications. In this review, we provide an overview of T cell therapy gene editing strategies and the delivery technologies utilized to genetically engineer T cells. We also discuss recent investigations and clinical trials that have utilized gene editing to enhance the efficacy of T cells and broaden the application of cancer immunotherapies.

CAR T-Cell Production Using Nonviral Approaches

Chimeric antigen receptor T-cells (CAR T-cells) represent a novel and promising approach in cancer immunotherapy. According to the World Health Organization (WHO), the number of oncological patients is steadily growing in developed countries despite immense progress in oncological treatments, and the prognosis of individual patients is still relatively poor. Exceptional results have been recorded for CAR T-cell therapy in patients suffering from B-cell malignancies. This success opens up the possibility of using the same approach for other types of cancers. To date, the most common method for CAR T-cell generation is the use of viral vectors. However, dealing with virus-derived vectors brings possible obstacles in the CAR T-cell manufacturing process owing to strict regulations and high cost demands. Alternative approaches may facilitate further development and the transfer of the method to clinical practice. The most promising substitutes for virus-derived vectors are transposon-derived vectors, most commonly sleeping beauty, which offer great coding capability and a safe integration profile while maintaining a relatively low production cost. This review is aimed at summarizing the state of the art of nonviral approaches in CAR T-cell generation, with a unique perspective on the conditions in clinical applications and current Good Manufacturing Practice. If CAR T-cell therapy is to be routinely used in medical practice, the manufacturing cost and complexity need to be as low as possible, and transposon-based vectors seem to meet these criteria better than viral-based vectors.

Efficient lentiviral transduction method to gene modify cord blood CD8+ T cells for cancer therapy applications

Adoptive T cell therapy utilizing tumor-specific autologous T cells has shown promising results for cancer treatment. However, the limited numbers of autologous tumor-associated antigen (TAA)-specific T cells and the functional aberrancies, due to disease progression or treatment, remain factors that may significantly limit the success of the therapy. The use of allogeneic T cells, such as umbilical cord blood (CB) derived, overcomes these issues but requires gene modification to induce a robust and specific anti-tumor effect. CB T cells are readily available in CB banks and show low toxicity, high proliferation rates, and increased anti-leukemic effect upon transfer. However, the combination of anti-tumor gene modification and preservation of advantageous immunological traits of CB T cells represent major challenges for the harmonized production of T cell therapy products. In this manuscript, we optimized a protocol for expansion and lentiviral vector (LV) transduction of CB CD8⁺ T cells, achieving a transduction efficiency up to 83%. Timing of LV treatment, selection of culture media, and the use of different promoters were optimized in the transduction protocol. LentiBOOST was confirmed as a non-toxic transduction enhancer of CB CD8⁺ T cells, with minor effects on the proliferation capacity and cell viability of the T cells. Positively, the use of LentiBOOST does not affect the functionality of the cells, in the context of tumor cell recognition. Finally, CB CD8⁺ T cells were more amenable to LV transduction than peripheral blood (PB) CD8+ T cells and maintained a more naive phenotype. In conclusion, we show an efficient method to genetically modify CB CD8⁺ T cells using LV, which is especially useful for off-the-shelf adoptive cell therapy products for cancer treatment.

T cell receptor therapy against melanoma-Immunotherapy for the future?

Malignant melanoma has seen monumental changes in treatment options the last decade from the very poor results of dacarbazine treatment to the modern-day use of targeted therapies and immune checkpoint inhibitors. Melanoma has a high mutational burden making it more capable of evoking immune responses than many other tumours. Even when considering double immune checkpoint blockade with anti-CTLA-4 and anti-PD-1, we still have far to go in melanoma treatment as 50% of patients with metastatic disease do not respond to current treatment. Alternative immunotherapy should therefore be considered. Since melanoma has a high mutational burden, it is considered more immunogenic than many other tumours. T cell receptor (TCR) therapy could be a possible way forward, either alone or in combination, to improve the response rates of this deadly disease. Melanoma is one of the cancers where TCR therapy has been frequently applied. However, the number of antigens targeted remains fairly limited, although advanced personalized therapies aim at also targeting private mutations. In this review, we look at possible aspects of targeting TCR therapy towards melanoma and provide an implication of its use in the future.

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

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

Targeting CD33 in Chemoresistant AML Patient-Derived Xenografts by CAR-CIK Cells Modified with an Improved SB Transposon System

The successful implementation of chimeric antigen receptor (CAR)-T cell therapy in the clinical context of B cell malignancies has paved the way for further development in the more critical setting of acute myeloid leukemia (AML). Among the potentially targetable AML antigens, CD33 is insofar one of the main validated molecules. Here, we describe the feasibility of engineering cytokine-induced killer (CIK) cells with a CD33.CAR by using the latest optimized version of the non-viral Sleeping Beauty (SB) transposon system "SB100X-pT4." This offers the advantage of improving CAR expression on CIK cells, while reducing the amount of DNA transposase as compared to the previously employed "SB11-pT" version. SB-modified CD33.CAR-CIK cells exhibited significant antileukemic activity in vitro and in vivo in patient-derived AML xenograft models, reducing AML development when administered as an "early treatment" and delaying AML progression in mice with established disease. Notably, by exploiting an already optimized xenograft chemotherapy model that mimics human induction therapy in mice, we demonstrated for the first time that CD33.CAR-CIK cells are also effective toward chemotherapy resistant/residual AML cells, further supporting its future clinical development and implementation within the current standard regimens.

Development of CAR-T cell therapy for B-ALL using a point-of-care approach

Recently approved by the FDA and European Medicines Agency, CAR-T cell therapy is a new treatment option for B-cell malignancies. Currently, CAR-T cells are manufactured in centralized facilities and face bottlenecks like complex scaling up, high costs, and logistic operations. These difficulties are mainly related to the use of viral vectors and the requirement to expand CAR-T cells to reach the therapeutic dose. In this paper, by using Sleeping Beauty-mediated genetic modification delivered by electroporation, we show that CAR-T cells can be generated and used without the need for ex vivo activation and expansion, consistent with a point-of-care (POC) approach. Our results show that minimally manipulated CAR-T cells are effective in vivo against RS4;11 leukemia cells engrafted in NSG mice even when inoculated after only 4 h of gene transfer. In an effort to better characterize the infused CAR-T cells, we show that 19BBz T lymphocytes infused after 24 h of electroporation (where CAR expression is already detectable) can improve the overall survival and reduce tumor burden in organs of mice engrafted with RS4;11 or Nalm-6 B cell leukemia. A side-by-side comparison of POC approach with a conventional 8-day expansion protocol using Transact beads demonstrated that both approaches have equivalent antitumor activity in vivo. Our data suggest that POC approach is a viable alternative for the generation and use of CAR-T cells, overcoming the limitations of current manufacturing protocols. Its use has the potential to expand CAR immunotherapy to a higher number of patients, especially in the context of low-income countries.

Generation of CAR+ T Lymphocytes Using the Sleeping Beauty Transposon System

Adoptive immunotherapy of cancer using T cells expressing chimeric antigen receptors (CARs) is now an approved treatment for non-Hodgkin lymphoma (NHL) and B cell acute lymphoblastic leukemia (B-ALL), inducing high response rates in patients. The infusion products are generated by using retro- or lentiviral transduction to induce CAR expression in T cells followed by an in vitro expansion protocol. However, use of viral vectors is cumbersome and is associated with increased costs due to the required high titers, replication-competent retrovirus (RCR) detection and production/use in a biosafety level 2 culture rooms, and additional quality control tests. Nonviral methods, like the Sleeping Beauty transposon system, can stably integrate in the genome of target cells and can be delivered using straightforward methods like electroporation. This chapter describes a protocol for T cell genetic modification using Sleeping Beauty transposon system and electroporation with the Lonza Nucleofector II device for the stable expression of CAR molecules in T lymphocytes.

Expanding the CRISPR Toolbox with ErCas12a in Zebrafish and Human Cells

CRISPR and CRISPR-Cas effector proteins enable the targeting of DNA double-strand breaks to defined loci based on a variable length RNA guide specific to each effector. The guide RNAs are generally similar in size and form, consisting of a ∼20 nucleotide sequence complementary to the DNA target and an RNA secondary structure recognized by the effector. However, the effector proteins vary in protospacer adjacent motif requirements, nuclease activities, and DNA binding kinetics. Recently, ErCas12a, a new member of the Cas12a family, was identified in Eubacterium rectale. Here, we report the first characterization of ErCas12a activity in zebrafish and expand on previously reported activity in human cells. Using a fluorescent reporter system, we show that CRISPR-ErCas12a elicits strand annealing mediated DNA repair more efficiently than CRISPR-Cas9. Further, using our previously reported gene targeting method that utilizes short homology, GeneWeld, we demonstrate the use of CRISPR-ErCas12a to integrate reporter alleles into the genomes of both zebrafish and human cells. Together, this work provides methods for deploying an additional CRISPR-Cas system, thus increasing the flexibility researchers have in applying genome engineering technologies.

Efficient Non-Viral T-Cell Engineering by Sleeping Beauty Minicircles Diminishing DNA Toxicity and miRNAs Silencing the Endogenous T-Cell Receptors

Transposon-based vectors have entered clinical trials as an alternative to viral vectors for genetic engineering of T cells. However, transposon vectors require DNA transfection into T cells, which were found to cause adverse effects. T-cell viability was decreased in a dose-dependent manner, and DNA-transfected T cells showed a delayed response upon T-cell receptor (TCR) stimulation with regard to blast formation, proliferation, and surface expression of CD25 and CD28. Gene expression analysis demonstrated a DNA-dependent induction of a type I interferon response and interferon-β upregulation. By combining Sleeping Beauty transposon minicircle vectors with SB100X transposase-encoding RNA, it was possible to reduce the amount of total DNA required, and stable expression of therapeutic TCRs was achieved in >50% of human T cells without enrichment. The TCR-engineered T cells mediated effective tumor cell killing and cytokine secretion upon antigen-specific stimulation. Additionally, the Sleeping Beauty transposon system was further improved by miRNAs silencing the endogenous TCR chains. These miRNAs increased the surface expression of the transgenic TCR, diminished mispairing with endogenous TCR chains, and enhanced antigen-specific T-cell functionality. This approach facilitates the rapid non-viral generation of highly functional, engineered T cells for immunotherapy.

Creation of versatile cloning platforms for transgene expression and dCas9-based epigenome editing

Genetic manipulation via transgene overexpression, RNAi, or Cas9-based methods is central to biomedical research. Unfortunately, use of these tools is often limited by vector options. We have created a modular platform (pMVP) that allows a gene of interest to be studied in the context of an array of promoters, epitope tags, conditional expression modalities, and fluorescent reporters, packaged in 35 custom destination vectors, including adenovirus, lentivirus, PiggyBac transposon, and Sleeping Beauty transposon, in aggregate >108,000 vector permutations. We also used pMVP to build an epigenetic engineering platform, pMAGIC, that packages multiple gRNAs and either Sa-dCas9 or x-dCas9(3.7) fused to one of five epigenetic modifiers. Importantly, via its compatibility with adenoviral vectors, pMAGIC uniquely enables use of dCas9/LSD1 fusions to interrogate enhancers within primary cells. To demonstrate this, we used pMAGIC to target Sa-dCas9/LSD1 and modify the epigenetic status of a conserved enhancer, resulting in altered expression of the homeobox transcription factor PDX1 and its target genes in pancreatic islets and insulinoma cells. In sum, the pMVP and pMAGIC systems empower researchers to rapidly generate purpose-built, customized vectors for manipulation of gene expression, including via targeted epigenetic modification of regulatory elements in a broad range of disease-relevant cell types.

Generation of V α13/β21+T cell specific target CML cells by TCR gene transfer

Adoptive immunotherapy with antigen-specific T cells can be effective for treating melanoma and chronic myeloid leukemia (CML). However, to obtain sufficient antigen-specific T cells for treatment, the T cells have to be cultured for several weeks in vitro, but in vitro T cell expansion is difficult to control. Alternatively, the transfer of T cell receptors (TCRs) with defined antigen specificity into recipient T cells may be a simple solution for generating antigen-specific T cells. The objective of this study was to identify CML-associated, antigen-specific TCR genes and generate CML-associated, antigen-specific T cells with T cell receptor (TCR) gene transfer. Our previous study has screened an oligoclonal Vβ21 with a different oligoclonal Vα partner in peripheral blood mononuclear cells (PBMCs) derived from patients with CML. In this study, oligoclonally expanded TCR α genes, which pair with TCR Vβ21, were cloned into the pIRES eukaryotic expression vector (TCR Vα-IRES-Vβ21). Next, two recombinant plasmids, TCR Vα13-IRES-Vβ21 and TCR Vα18-IRES-Vβ21, were successfully transferred into T cells, and the TCR gene-modified T cells acquired CML-specific cytotoxicity with the best cytotoxic effects for HLA-A11⁺ K562 cells observed for the TCR Vα13/Vβ21 gene redirected T cells. In summary, our data confirmed TCRVα13/Vβ21 as a CML-associated, antigen-specific TCR. This study provided new evidence that genetically engineered antigen-specific TCR may become a druggable approach for gene therapy of CML.

A new approach to CAR T-cell gene engineering and cultivation using piggyBac transposon in the presence of IL-4, IL-7 and IL-21

BACKGROUND AIMS

Clinical-grade chimeric antigenic receptor (CAR)19 T cells are routinely manufactured by lentiviral/retroviral (LV/RV) transduction of an anti-CD3/CD28 activated T cells, which are then propagated in a culture medium supplemented with interleukin (IL)-2. The use of LV/RVs for T-cell modification represents a manufacturing challenge due to the complexity of the transduction approach and the necessity of thorough quality control.

METHODS

We present here a significantly improved protocol for CAR19 T-cell manufacture that is based on the electroporation of peripheral blood mononuclear cells with plasmid DNA encoding the piggyBac transposon/transposase vectors and their cultivation in the presence of cytokines IL-4, IL-7 and IL-21.

RESULTS

We found that activation of the CAR receptor by either its cognate ligand (i.e., CD19 expressed on the surface of B cells) or anti-CAR antibody, followed by cultivation in the presence of cytokines IL-4 and IL-7, enables strong and highly selective expansion of functional CAR19 T cells, resulting in >90% CAR⁺ T cells. Addition of cytokine IL-21 to the mixture of IL-4 and IL-7 supported development of immature CAR19 T cells with central memory and stem cell memory phenotypes and expressing very low amounts of inhibitory receptors PD-1, LAG-3 and TIM-3.

CONCLUSIONS

Our protocol provides a simple and cost-effective method for engineering high-quality T cells for adoptive therapies.

Immunotherapy of acute leukemia by chimeric antigen receptor-modified lymphocytes using an improved Sleeping Beauty transposon platform

Chimeric antigen receptor (CAR)-modified T-cell adoptive immunotherapy is a remarkable therapeutic option proven effective in the treatment of hematological malignancies. In order to optimize cell manufacturing, we sought to develop a novel clinical-grade protocol to obtain CAR-modified cytokine-induced killer cells (CIKs) using the Sleeping Beauty (SB) transposon system. Administration of irradiated PBMCs overcame cell death of stimulating cells induced by non-viral transfection, enabling robust gene transfer together with efficient T-cell expansion. Upon single stimulation, we reached an average of 60% expression of CD123- and CD19- specific 3rd generation CARs (CD28/OX40/TCRzeta). Furthermore, modified cells displayed persistence of cell subsets with memory phenotype, specific and effective lytic activity against leukemic cell lines and primary blasts, cytokine secretion, and proliferation. Adoptive transfer of CD123.CAR or CD19.CAR lymphocytes led to a significant anti-tumor response against acute myelogenous leukemia (AML) and acute lymphoblastic leukemia (ALL) disseminated diseases in NSG mice. Notably, we found no evidence of integration enrichment near cancer genes and transposase expression at the end of the differentiation. Taken all together, our findings describe a novel donor-derived non-viral CAR approach that may widen the repertoire of available methods for T cell-based immunotherapy.

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.

Enhanced CAR T-cell engineering using non-viral Sleeping Beauty transposition from minicircle vectors

Immunotherapy with T cell modified with gamma-retroviral or lentiviral (LV) vectors to express a chimeric antigen receptor (CAR) has shown remarkable efficacy in clinical trials. However, the potential for insertional mutagenesis and genotoxicity of viral vectors is a safety concern, and their cost and regulatory demands a roadblock for rapid and broad clinical translation. Here, we demonstrate that CAR T cells can be engineered through non-viral Sleeping Beauty (SB) transposition of CAR genes from minimalistic DNA vectors called minicircles (MCs). We analyzed genomic distribution of SB and LV integrations and show that a significantly higher proportion of MC-derived CAR transposons compared with LV integrants had occurred outside of highly expressed and cancer-related genes into genomic safe harbor loci that are not expected to cause mutagenesis or genotoxicity. CD19-CAR T cells engineered with our enhanced SB approach conferred potent reactivity in vitro and eradicated lymphoma in a xenograft model in vivo. Intriguingly, electroporation of SB MCs is substantially more effective and less toxic compared with conventional plasmids, and enables cost-effective rapid preparation of therapeutic CAR T-cell doses. This approach sets a new standard in advanced cellular and gene therapy and will accelerate and increase the availability of CAR T-cell therapy to treat hematologic malignancies.

Stable, Nonviral Expression of Mutated Tumor Neoantigen-specific T-cell Receptors Using the Sleeping Beauty Transposon/Transposase System

Neoantigens unique to each patient's tumor can be recognized by autologous T cells through their T-cell receptor (TCR) but the low frequency and/or terminal differentiation of mutation-specific T cells in tumors can limit their utility as adoptive T-cell therapies. Transfer of TCR genes into younger T cells from peripheral blood with a high proliferative potential could obviate this problem. We generated a rapid, cost-effective strategy to genetically engineer cancer patient T cells with TCRs using the clinical Sleeping Beauty transposon/transposase system. Patient-specific TCRs reactive against HLA-A*0201-restriced neoantigens AHNAK(S2580F) or ERBB2(H473Y) or the HLA-DQB*0601-restricted neoantigen ERBB2IP(E805G) were assembled with murine constant chains and cloned into Sleeping Beauty transposons. Patient peripheral blood lymphocytes were coelectroporated with SB11 transposase and Sleeping Beauty transposon, and transposed T cells were enriched by sorting on murine TCRβ (mTCRβ) expression. Rapid expansion of mTCRβ(+) T cells with irradiated allogeneic peripheral blood lymphocytes feeders, OKT3, interleukin-2 (IL-2), IL-15, and IL-21 resulted in a preponderance of effector (CD27(-)CD45RA(-)) and less-differentiated (CD27(+)CD45RA(+)) T cells. Transposed T cells specifically mounted a polyfunctional response against cognate mutated neoantigens and tumor cell lines. Thus, Sleeping Beauty transposition of mutation-specific TCRs can facilitate the use of personalized T-cell therapy targeting unique neoantigens.

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.

Minicircle-Based Engineering of Chimeric Antigen Receptor (CAR) T Cells

Plasmid DNA is being used as a pharmaceutical agent in vaccination, as well as a basic substance and starting material in gene and cell therapy, and viral vector production. Since the uncontrolled expression of backbone sequences present in such plasmids and the dissemination of antibiotic resistance genes may have profound detrimental effects, an important goal in vector development was to produce supercoiled DNA lacking bacterial backbone sequences: Minicircle (MC) DNA. The Sleeping Beauty (SB) transposon system is a non-viral gene delivery platform enabling a close-to-random profile of genomic integration. In combination, the MC platform greatly enhances SB transposition and transgene integration resulting in higher numbers of stably modified target cells. We have recently developed a strategy for MC-based SB transposition of chimeric antigen receptor (CAR) transgenes that enable improved transposition rates compared to conventional plasmids and rapid manufacturing of therapeutic CAR T cell doses (Monjezi et al. 2016). This advance enables manufacturing CAR T cells in a virus-free process that relies on SB-mediated transposition from MC DNA to accomplish gene-transfer. Advantages of this approach include a strong safety profile due to the nature of the MC itself and the genomic insertion pattern of MC-derived CAR transposons. In addition, stable transposition and high-level CAR transgene expression, as well as easy and reproducible handling, make MCs a preferred vector source for gene-transfer in advanced cellular and gene therapy. In this chapter, we will review our experience in MC-based CAR T cell engineering and discuss our recent advances in MC manufacturing to accelerate both pre-clinical and clinical implementation.

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.

Sleeping Beauty-Mediated Drug Resistance Gene Transfer in Human Hematopoietic Progenitor Cells

The Sleeping Beauty (SB) transposon system can insert sequences into mammalian chromosomes, supporting long-term expression of both reporter and therapeutic genes. Hematopoietic progenitor cells (HPCs) are an ideal therapeutic gene transfer target as they are used in therapy for a variety of hematologic and metabolic conditions. As successful SB-mediated gene transfer into human CD34(+) HPCs has been reported by several laboratories, we sought to extend these studies to the introduction of a therapeutic gene conferring resistance to methotrexate (MTX), potentially providing a chemoprotective effect after engraftment. SB-mediated transposition of hematopoietic progenitors, using a transposon encoding an L22Y variant dihydrofolate reductase fused to green fluorescent protein, conferred resistance to methotrexate and dipyridamole, a nucleoside transport inhibitor that tightens MTX selection conditions, as assessed by in vitro hematopoietic colony formation. Transposition of individual transgenes was confirmed by sequence analysis of transposon-chromosome junctions recovered by linear amplification-mediated PCR. These studies demonstrate the potential of SB-mediated transposition of HPCs for expression of drug resistance genes for selective and chemoprotective applications.

Adoptive immunotherapy for acute leukemia: New insights in chimeric antigen receptors

Relapses remain a major concern in acute leukemia. It is well known that leukemia stem cells (LSCs) hide in hematopoietic niches and escape to the immune system surveillance through the outgrowth of poorly immunogenic tumor-cell variants and the suppression of the active immune response. Despite the introduction of new reagents and new therapeutic approaches, no treatment strategies have been able to definitively eradicate LSCs. However, recent adoptive immunotherapy in cancer is expected to revolutionize our way to fight against this disease, by redirecting the immune system in order to eliminate relapse issues. Initially described at the onset of the 90’s, chimeric antigen receptors (CARs) are recombinant receptors transferred in various T cell subsets, providing specific antigens binding in a non-major histocompatibility complex restricted manner, and effective on a large variety of human leukocyte antigen-divers cell populations. Once transferred, engineered T cells act like an expanding “living drug” specifically targeting the tumor-associated antigen, and ensure long-term anti-tumor memory. Over the last decades, substantial improvements have been made in CARs design. CAR T cells have finally reached the clinical practice and first clinical trials have shown promising results. In acute lymphoblastic leukemia, high rate of complete and prolonged clinical responses have been observed after anti-CD19 CAR T cell therapy, with specific but manageable adverse events. In this review, our goal was to describe CAR structures and functions, and to summarize recent data regarding pre-clinical studies and clinical trials in acute leukemia.

Adoptive T-cell therapy for cancer in the United kingdom: a review of activity for the British Society of Gene and Cell Therapy annual meeting 2015

Adoptive T-cell therapy is delivering objective clinical responses across a number of cancer indications in the early phase clinical setting. Much of this clinical activity is taking place at major clinical academic centers across the United States. This review focuses upon cancer-focused cell therapy activity within the United Kingdom as a contribution to the 2015 British Society of Gene and Cell Therapy annual general meeting. This overview reflects the diversity and expansion of clinical and preclinical studies within the United Kingdom while considering the background context of this work against new infrastructural developments and the requirements of nationalized healthcare delivery within the UK National Health Service.

Chimeric antigen receptor-redirected CD45RA-negative T cells have potent antileukemia and pathogen memory response without graft-versus-host activity

Chimeric antigen receptor (CAR)-redirected cellular therapy is an attractive modality for cancer treatment. We hypothesized that allogeneic CAR-engineered CD45RA-negative T cells can control cancer and infection without the risk of graft-versus-host disease (GVHD). We used CD19(+) MLL-rearranged leukemia as prototype because it is an aggressive and generally drug-resistant malignancy. CD45RA(-) cells that were transduced with anti-CD19 CAR containing 4-1BB and CD3ζ signaling domains effectively lysed MLL-rearranged leukemia cell lines and primary blasts in vitro. In a disseminated leukemia mouse model, CAR(+)CD45RA(-) cells significantly reduced leukemia burdens and prolonged overall survival without GVHD. CAR(+) cells were sustainable in blood, and all the treated mice remained leukemia-free even after they were re-challenged with leukemia cells. Despite the transduction process, CD45RA(-) cells retained recall activity both in vitro and in vivo against human pathogens commonly found in cancer patients. In comparison with CD45RA(+) cells, CD45RA(-) cells showed less allogeneic activity in mixed leukocyte reactions and in mouse models. Thus, the use of CAR(+)CD45RA(-) cells can separate GVHD from graft-versus-malignancy effect and infection control. These cells should also be useful in nontransplant settings and may be administered as off-the-shelf third-party cells.

Manufacture of T cells using the Sleeping Beauty system to enforce expression of a CD19-specific chimeric antigen receptor

T cells can be reprogrammed to redirect specificity to tumor-associated antigens (TAAs) through the enforced expression of chimeric antigen receptors (CARs). The prototypical CAR is a single-chain molecule that docks with TAA expressed on the cell surface and, in contrast to the T-cell receptor complex, recognizes target cells independent of human leukocyte antigen. The bioprocessing to generate CAR(+) T cells has been reduced to clinical practice based on two common steps that are accomplished in compliance with current good manufacturing practice. These are (1) gene transfer to stably integrate the CAR using viral and nonviral approaches and (2) activating the T cells for proliferation by crosslinking CD3 or antigen-driven numeric expansion using activating and propagating cells (AaPCs). Here, we outline our approach to nonviral gene transfer using the Sleeping Beauty system and the selective propagation of CD19-specific CAR(+) T cells on AaPCs.

Genomic analysis of Sleeping Beauty transposon integration in human somatic cells

The Sleeping Beauty (SB) transposon is a non-viral integrating vector system with proven efficacy for gene transfer and functional genomics. However, integration efficiency is negatively affected by the length of the transposon. To optimize the SB transposon machinery, the inverted repeats and the transposase gene underwent several modifications, resulting in the generation of the hyperactive SB100X transposase and of the high-capacity “sandwich” (SA) transposon. In this study, we report a side-by-side comparison of the SA and the widely used T2 arrangement of transposon vectors carrying increasing DNA cargoes, up to 18 kb. Clonal analysis of SA integrants in human epithelial cells and in immortalized keratinocytes demonstrates stability and integrity of the transposon independently from the cargo size and copy number-dependent expression of the cargo cassette. A genome-wide analysis of unambiguously mapped SA integrations in keratinocytes showed an almost random distribution, with an overrepresentation in repetitive elements (satellite, LINE and small RNAs) compared to a library representing insertions of the first-generation transposon vector and to gammaretroviral and lentiviral libraries. The SA transposon/SB100X integrating system therefore shows important features as a system for delivering large gene constructs for gene therapy applications.

Adoptive cellular therapy of cancer: exploring innate and adaptive cellular crosstalk to improve anti-tumor efficacy

ABSTRACT 

The mammalian immune system has evolved to produce multi-tiered responses consisting of both innate and adaptive immune cells collaborating to elicit a functional response to a pathogen or neoplasm. Immune cells possess a shared ancestry, suggestive of a degree of coevolution that has resulted in optimal functionality as an orchestrated and highly collaborative unit. Therefore, the development of therapeutic modalities that harness the immune system should consider the crosstalk between cells of the innate and adaptive immune systems in order to elicit the most effective response. In this review, the authors will discuss the success achieved using adoptive cellular therapy in the treatment of cancer, recent trends that focus on purified T cells, T cells with genetically modified T-cell receptors and T cells modified to express chimeric antigen receptors, as well as the use of unfractionated immune cell reprogramming to achieve optimal cellular crosstalk upon infusion for adoptive cellular therapy.

Progress and prospects for engineered T cell therapies

Proof-of-concept studies have demonstrated the therapeutic potential of engineered T cells. Transfer of recombinant antigen-specific T cell receptors (TCR) and chimaeric antigen receptors (CARs) against tumour and viral antigens are under investigation by multiple approaches, including viral- and nonviral-mediated gene transfer into both autologous and allogeneic T cell populations. There have been notable successes recently using viral vector-mediated transfer of CARs specific for B cell antigens, but also reports of anticipated and unanticipated complications in these and other studies. We review progress in this promising area of cellular therapy, and consider developments in antigen receptor therapies including the application of emerging gene-editing technologies.