Manufacture of clinical-grade CD19-specific T cells stably expressing chimeric antigen receptor using Sleeping Beauty system and artificial antigen presenting cells

Collagen-disruptive cell therapy: adoptive transfer of membrane-anchored, tumor cell surface vimentin-targeted interleukin 12-armed TILs suppress collagen expression to boost deep T-cell infiltration via dual signaling activation and significant CCKAR reduction

Tumor-targeted T-cell therapies of various types have been booming, but T-cell therapy is limited by its inability to penetrate the collagen barrier surrounding tumors. The destruction of tumor collagen is significant because collagen both suppresses T cells and contributes to the formation of the extracellular matrix. Our previously reported cell surface vimentin (CSV)-targeted and membrane-anchored IL12-armed (attIL12) T cells can reduce collagen production by killing cancer-associated fibroblasts, thereby increasing T-cell infiltration. However, attIL12-T cells cannot reduce collagen expression by tumors that highly express CCKAR. In this study, we discovered that CCKAR directly boosts collagen production by tumor cells in vitro and in vivo. attIL12-modified tumor-infiltrating lymphocytes (TILs) disabled collagen production by CCKAR-high autologous tumor cells in vitro and sarcoma patient-derived xenografts (PDXs) in vivo. This disruption of collagen production by tumor cells required a simultaneous interaction between the CSV on autologous tumor cells, which is targeted by attIL12, and HLA-TCR on attIL12-TILs; when either interaction was abrogated, collagen production and CCKAR expression were not shut down. Mechanistically, the interaction between attIL12-TILs and autologous tumor cells synergized IFNγ production, which in combination with CCKAR downregulation reduced collagen expression through suppression of both TGFβ-stimulated SMAD activation and CCKAR-AKT signaling. Diminishing collagen expression from tumor cells significantly increased T-cell infiltration and improved tumor growth inhibition in PDX sarcomas. This study thus uncovers the first tumor collagen-disrupting T-cell therapy we know of. This is significant because collagen is enriched in most high-grade CCKAR+ human sarcomas. Thus, this attIL12-TIL therapy holds great clinical potential for boosting T-cell infiltration in high-grade, collagen-rich tumors.

Survival advantage of native and engineered T cells is acquired by mitochondrial transfer from mesenchymal stem cells

BACKGROUND

Apoptosis, a form of programmed cell death, is critical for the development and homeostasis of the immune system. Chimeric antigen receptor T (CAR-T) cell therapy, approved for hematologic cancers, retains several limitations and challenges associated with ex vivo manipulation, including CAR T-cell susceptibility to apoptosis. Therefore, strategies to improve T-cell survival and persistence are required. Mesenchymal stem/stromal cells (MSCs) exhibit immunoregulatory and tissue-restoring potential. We have previously shown that the transfer of umbilical cord MSC (UC-MSC)-derived mitochondrial (MitoT) prompts the genetic reprogramming of CD3+ T cells towards a Treg cell lineage. The potency of T cells plays an important role in effective immunotherapy, underscoring the need for improving their metabolic fitness. In the present work, we evaluate the effect of MitoT on apoptotis of native T lymphocytes and engineered CAR-T cells.

METHODS

We used a cell-free approach using artificial MitoT (Mitoception) of UC-MSC derived MT to peripheral blood mononuclear cells (PBMCs) followed by RNA-seq analysis of CD3+ MitoTpos and MitoTneg sorted cells. Target cell apoptosis was induced with Staurosporine (STS), and cell viability was evaluated with Annexin V/7AAD and TUNEL assays. Changes in apoptotic regulators were assessed by flow cytometry, western blot, and qRT-PCR. The effect of MitoT on 19BBz CAR T-cell apoptosis in response to electroporation with a non-viral transposon-based vector was assessed with Annexin V/7AAD.

RESULTS

Gene expression related to apoptosis, cell death and/or responses to different stimuli was modified in CD3+ T cells after Mitoception. CD3+MitoTpos cells were resistant to STS-induced apoptosis compared to MitoTneg cells, showing a decreased percentage in apoptotic T cells as well as in TUNEL+ cells. Additionally, MitoT prevented the STS-induced collapse of the mitochondrial membrane potential (MMP) levels, decreased caspase-3 cleavage, increased BCL2 transcript levels and BCL-2-related BARD1 expression in FACS-sorted CD3+ T cells. Furthermore, UC-MSC-derived MitoT reduced both early and late apoptosis in CAR-T cells following electroporation, and exhibited an increasing trend in cytotoxic activity levels.

CONCLUSIONS

Artificial MitoT prevents STS-induced apoptosis of human CD3+ T cells by interfering with the caspase pathway. Furthermore, we observed that MitoT confers protection to apoptosis induced by electroporation in MitoTpos CAR T-engineered cells, potentially improving their metabolic fitness and resistance to environmental stress. These results widen the physiological perspective of organelle-based therapies in immune conditions while offering potential avenues to enhance CAR-T treatment outcomes where their viability is compromised.

Artificial antigen-presenting cells: the booster for the obtaining of functional adoptive cells

Adoptive cell therapy (ACT) achieves substantial efficacy in the treatment of hematological malignancies and solid tumours, while enormous endeavors have been made to reduce relapse and extend the remission duration after ACT. For the genetically engineered T cells, their functionality and long-term anti-tumour potential depend on the specificity of the T cell receptor (TCR) or chimeric antigen receptor (CAR). In addition, the therapeutic benefit is directly to sufficient activation and proliferation of engineered T cells. Artificial antigen-presenting cells (aAPCs), as powerful boosters for ACT, have been applied to provide sustained stimulation of the cognate antigen and facilitate the expansion of sufficient T cells for infusion. In this review, we summarize the aAPCs used to generate effector cells for ACT and underline the mechanism by which aAPCs enhance the functionality of the effector cells. The manuscript includes investigations ranging from basic research to clinical trials, which we hope will highlight the importance of aAPCs and provide guidance for novel strategies to improve the effectiveness of ACT.

AAV-mediated delivery of a Sleeping Beauty transposon and an mRNA-encoded transposase for the engineering of therapeutic immune cells

Engineering cells for adoptive therapy requires overcoming limitations in cell viability and, in the efficiency of transgene delivery, the duration of transgene expression and the stability of genomic integration. Here we report a gene-delivery system consisting of a Sleeping Beauty (SB) transposase encoded into a messenger RNA delivered by an adeno-associated virus (AAV) encoding an SB transposon that includes the desired transgene, for mediating the permanent integration of the transgene. Compared with lentiviral vectors and with the electroporation of plasmids of transposon DNA or minicircle DNA, the gene-delivery system, which we named MAJESTIC (for 'mRNA AAV-SB joint engineering of stable therapeutic immune cells'), offers prolonged transgene expression, as well as higher transgene expression, therapeutic-cell yield and cell viability. MAJESTIC can deliver chimeric antigen receptors (CARs) into T cells (which we show lead to strong anti-tumour activity in vivo) and also transduce natural killer cells, myeloid cells and induced pluripotent stem cells with bi-specific CARs, kill-switch CARs and synthetic T-cell receptors.

Engineered CAR-T cells: An immunotherapeutic approach for cancer treatment and beyond

Chimeric Antigen Receptor (CAR) T cell therapy is a type of adoptive immunotherapy that offers a promising avenue for enhancing cancer treatment since traditional cancer treatments like chemotherapy, surgery, and radiation therapy have proven insufficient in completely eradicating tumors, despite the relatively positive outcomes. It has been observed that CAR-T cell therapy has shown promising results in treating the majority of hematological malignancies but also have a wide scope for other cancer types. CAR is an extra receptor on the T-cell that helps to increase and accelerate tumor destruction by efficiently activating the immune system. It is made up of three domains, the ectodomain, transmembrane, and the endodomain. The ectodomain is essential for antigen recognition and binding, whereas the co-stimulatory signal is transduced by the endodomain. To date, the Food and Drug Administration (FDA) has granted approval for six CAR-T cell therapies. However, despite its remarkable success, CAR-T therapy is associated with numerous adverse events and has certain limitations. This chapter focuses on the structure and function of the CAR domain, various generations of CAR, and the process of CAR-T cell development, adverse effects, and challenges in CAR-T therapy. CAR-T cell therapy also has scopes in other disease conditions which include systemic lupus erythematosus, multiple sclerosis, and myocardial fibrosis, etc.

Effects of polybrene and retronectin as transduction enhancers on the development and phenotypic characteristics of VHH-based CD19-redirected CAR T cells: a comparative investigation

Chimeric antigen receptor T cells (CAR T cells) have improved the prognosis of patients with certain hematologic malignancies. However, broader clinical application of this type of therapy is dependent on production protocols. We characterized VHH-based CD19-redirected CAR T cells generated using the transduction enhancers (TEs) polybrene or retronectin. The proliferation rate of activated T cells transduced using polybrene concentrations > 6 mg/mL decreased compared with untreated group. There was a direct relationship between polybrene concentration and transduction efficacy. Moreover, we demonstrated the proliferation of retronectin-transduced T cells increased in a dose-dependent manner (4-20 μg/mL). Whereas, different retronectin concentrations did not mediate a significant increase in T cell transduction rate. Moreover, lentiviral transduction rate was also dependent on the concentration of lentiviruses. At optimized TE concentrations, multiplicity of infection (MOI) of > 10 decreased living T cell transduction rate. Additionally, we demonstrated that CAR T cell phenotype is highly affected by TE type. Naïve T cell differentiation to central memory T cell was observed in the beginning of the expansion process and effector memory T cells became the predominant subset in the second week of expansion. Importantly, retronectin increased the proliferation of CAR T cells alongside medicating higher transduction rates, resulting in more naïve and central memory T cells. We demonstrated that a higher percentage of CAR T cells were generated using retronectin (with a less differentiated phenotype) making retronectin a more effective TE than polybrene for long-term CAR T cell processing in preclinical or clinical studies.

Co-infusion of CAR T cells with aAPCs expressing chemokines and costimulatory ligands enhances the anti-tumor efficacy in mice

Chimeric antigen receptor-modified T (CAR-T) cell therapy has shown curable efficacy for treating hematological malignancies, while in solid tumors, the immunosuppressive microenvironment causes poor activation, expansion and survival of CAR-T cells, accounting mainly for the unsatisfactory efficacy. The artificial antigen-presenting cells (aAPCs) have been used for ex vivo expansion and manufacturing of CAR-T cells. Here, we constructed a K562 cell-based aAPCs expressing human epithelial cell adhesion molecule (EpCAM), chemokines (CCL19 and CCL21) and co-stimulatory molecular ligands (CD80 and 4-1BBL). Our data demonstrated that the novel aAPCs enhanced the expansion, and increased the immune memory phenotype and cytotoxicity of CAR-T cells recognizing EpCAM, in vitro. Of note, co-infusion CAR-T and aAPC enhances the infiltration of CAR-T cells in solid tumors, which has certain potential for the treatment of solid tumors Moreover, IL-2-9-21, a cytokine cocktail, prevents CAR-T cells from entering the state of exhaustion prematurely following continuous antigen engagement and boosts the anti-tumor activity of CAR-T cells co-infused with aAPCs. These data provide a new strategy to enhance the therapeutic potential of CAR-T cell therapy for the treatment of solid tumors.

The safety of CAR-T cells and PD-1 antibody combination on an experimental model

Chimeric antigen receptor (CAR) T cells and PD-1 antibodies (PD-1 Ab) are emergent immunotherapies with unprecedented efficacy. The presence of PD-1 on T cells contributes to hypofunction of CAR-T therapy and inhibition of PD-1 enhances anti-cancer effect of CAR-T cells. Therefore, the combination of CAR-T cells and PD-1 antibody is a promissing strategy for cancer treatment. This study aims to establish our in-house CAR-T cells and evaluate the safety of CAR-T cells in combination with PD-1 antibody in animals. The toxicity of CD19-CAR-T cells was examined using Swiss Webster mice. Four mouse groups were treated with control, CAR-T, PD-1 antibody or CAR-T + PD-1 antibody. Mice's overall status was monitored and recorded. At the end-point, hematological and biochemical indices were quantified, histopathology of liver and kidney was evaluated by pathologists. The relative abnormal ratio and absolute values were compared between groups. We generated our in-house CAR-T cells and used them for safety evaluation in mice. The increase in mouse weight was observed in all groups after treatment and the weight was comparable between groups. The hematological, biochemical and histopathological parameters were equivalent between groups, except for liver grain degeneration occurred in treatment groups. Thus, CAR-T cells, PD-1 Ab and their combination were safe in mice. We successfully produced our in-house CAR-T cells and the combination of our CAR-T cells and PD-1 antibody was safe in mice with comparable values of hematopoietic indices, liver and kidney functions. Longer follow-up might be necessary to evaluate their effect on the liver.

Therapeutic immune cell engineering with an mRNA : AAV- Sleeping Beauty composite system

Adoptive cell therapy has shown clinical success in patients with hematological malignancies. Immune cell engineering is critical for production, research, and development of cell therapy; however, current approaches for generation of therapeutic immune cells face various limitations. Here, we establish a composite gene delivery system for the highly efficient engineering of therapeutic immune cells. This system, termed MAJESTIC ( m RNA A AV-Sleeping-Beauty J oint E ngineering of S table T herapeutic I mmune C ells), combines the merits of mRNA, AAV vector, and transposon into one composite system. In MAJESTIC, the transient mRNA component encodes a transposase that mediates permanent genomic integration of the Sleeping Beauty (SB) transposon, which carries the gene-of-interest and is embedded within the AAV vector. This system can transduce diverse immune cell types with low cellular toxicity and achieve highly efficient and stable therapeutic cargo delivery. Compared with conventional gene delivery systems, such as lentiviral vector, DNA transposon plasmid, or minicircle electroporation, MAJESTIC shows higher cell viability, chimeric antigen receptor (CAR) transgene expression, therapeutic cell yield, as well as prolonged transgene expression. CAR-T cells generated by MAJESTIC are functional and have strong anti-tumor activity in vivo . This system also demonstrates versatility for engineering different cell therapy constructs such as canonical CAR, bi-specific CAR, kill switch CAR, and synthetic TCR; and for CAR delivery into various immune cells, including T cells, natural killer cells, myeloid cells, and induced pluripotent stem cells.

Digital polymerase chain reaction strategies for accurate and precise detection of vector copy number in chimeric antigen receptor T-cell products

BACKGROUND AIMS

Vector copy number (VCN), an average quantification of transgene copies unique to a chimeric antigen receptor (CAR) T-cell product, is a characteristic that must be reported prior to patient administration, as high VCN increases the risk of insertional mutagenesis. Historically, VCN assessment in CAR T-cell products has been performed via quantitative polymerase chain reaction (qPCR). qPCR is reliable along a broad range of concentrations, but quantification requires use of a standard curve and precision is limited. Digital PCR (dPCR) methods were developed for absolute quantification of target sequences by counting nucleic acid molecules encapsulated in discrete, volumetrically defined partitions. Advantages of dPCR compared with qPCR include simplicity, reproducibility, sensitivity and lack of dependency on a standard curve for definitive quantification. In the present study, the authors describe a dPCR assay developed for analysis of the novel bicistronic CD19 × CD22 CAR T-cell construct.

METHODS

The authors compared the performance of the dPCR assay with qPCR on both the QX200 droplet dPCR (ddPCR) system (Bio-Rad Laboratories, Inc, Hercules, CA, USA) and the QIAcuity nanoplate-based dPCR (ndPCR) system (QIAGEN Sciences, Inc, Germantown, MD, USA). The primer-probe assay was validated with qPCR, ndPCR and ddPCR using patient samples from pre-clinical CAR T-cell manufacturing production runs as well as Jurkat cell subclones, which stably express this bicistronic CAR construct.

RESULTS

ddPCR confirmed the specificity of this assay to detect only the bicistronic CAR product. Additionally, the authors' assay gave accurate, precise and reproducible CAR T-cell VCN measurements across qPCR, ndPCR and ddPCR modalities.

CONCLUSIONS

The authors demonstrate that dPCR strategies can be utilized for absolute quantification of CAR transgenes and VCN measurements, with improved test-retest reliability, and that specific assays can be developed for detection of unique constructs.

Sleeping beauty generated CD19 CAR T-Cell therapy for advanced B-Cell hematological malignancies

Chimeric antigen receptor (CAR) T-cell therapy has emerged recently as a standard of care treatment for patients with relapsed or refractory acute lymphoblastic leukemia (ALL) and several subtypes of B-cell non-Hodgkin lymphoma (NHL). However, its use remains limited to highly specialized centers, given the complexity of its administration and its associated toxicities. We previously reported our experience in using a novel Sleeping Beauty (SB) CD19-specific CAR T-cell therapy in the peri-transplant setting, where it exhibited an excellent safety profile with encouraging survival outcomes. We have since modified the SB CD19 CAR construct to improve its efficacy and shorten its manufacturing time. We report here the phase 1 clinical trial safety results. Fourteen heavily treated patients with relapsed/refractory ALL and NHL were infused. Overall, no serious adverse events were directly attributed to the study treatment. Three patients developed grades 1-2 cytokine release syndrome and none of the study patients experienced neurotoxicity. All dose levels were well tolerated and no dose-limiting toxicities were reported. For efficacy, 3 of 8 (38%) patients with ALL achieved CR/CRi (complete remission with incomplete count recovery) and 1 (13%) patient had sustained molecular disease positivity. Of the 4 patients with DLBCL, 2 (50%) achieved CR. The SB-based CAR constructs allow manufacturing of targeted CAR T-cell therapies that are safe, cost-effective and with encouraging antitumor activity.

Institutional and infrastructure challenges for hospitals producing advanced therapies in the UK: the concept of 'point-of-care manufacturing readiness'

Aim: To propose the concept of point-of-care manufacturing readiness for analyzing the capacity that a country, a health system or an institution has developed to manufacture therapies in clinical settings (point-of-care manufacture). The focus is on advanced therapies (cell, gene and tissue engineering therapies) in the UK. Materials & methods: Literature review, analysis of quantitative data, and qualitative interviews with professionals and practitioners developing and administering advanced therapies. Results: Three components of point-of-care manufacturing readiness are analyzed staff and institutional procedures, infrastructure, and relations between hospitals and service providers. Conclusion: The technical and regulatory experience that has been gained through manufacturing advanced therapies at small scale in hospitals qualifies the UK for more complex and larger-scale production of therapies in the future.

Immunotherapy and immunoengineering for breast cancer; a comprehensive insight into CAR-T cell therapy advancements, challenges and prospects

BACKGROUND

Breast cancer (BC) is a highly prevalent solid cancer with a high-rise infiltration of immune cells, turning it into a significant candidate for tumor-specific immunotherapies. Chimeric antigen receptor (CAR)-T cells are emerging as immunotherapeutic tools with genetically engineered receptors to efficiently recognize and attack tumor cells that express specific target antigens. Technological advancements in CAR design have provided five generations of CAR-T cells applicable to a wide range of cancer patients while boosting CAR-T cell therapy safety. However, CAR-T cell therapy is ineffective against breast cancer because of the loss of specified antigens, the immunosuppressive nature of the tumor and CAR-T cell-induced toxicities. Next-generation CAR-T cells actively pass through the tumor vascular barriers, persist for extended periods and disrupt the tumor microenvironment (TME) to block immune escape.

CONCLUSION

CAR-T cell therapy embodies advanced immunotherapy for BC, but further pre-clinical and clinical assessments are recommended to achieve maximized efficiency and safety.

Impact of Consolidative Unrelated Cord Blood Transplantation on Clinical Outcomes of Patients With Relapsed/Refractory Acute B Lymphoblastic Leukemia Entering Remission Following CD19 Chimeric Antigen Receptor T Cells

Background

While chimeric antigen receptor (CAR)-T cell therapy is becoming widely used in hematological malignancies with remarkable remission rate, their high recurrence remains an obstacle to overcome. The role of consolidative transplantation following CAR-T cell-mediated remission remains controversial. We conducted a retrospective study to explore whether bridging to unrelated cord blood transplantation (UCBT) could improve the prognosis of patients entering remission after CAR-T therapy with different characteristics through subgroup analyses.

Methods

We reviewed 53 patients with relapsed/refractory (R/R) B-cell acute lymphoblastic leukemia (B-ALL) successfully infused with CD19 CAR-T cells and achieved complete remission (CR). In this study, 25 patients received consolidative UCBT (UCBT group) and 28 patients did not accept any intervention until relapse (non-UCBT group). Subgroup analysis on prognosis was then performed according to gender, age, number of previous relapses, tumor burden, presence of poor prognostic markers, and structure of CAR.

Results

Compared with the non-UCBT group, patients who underwent consolidative UCBT had better median event-free survival (EFS; 12.3 months vs. 6.2 months; P = 0.035) and relapse-free survival (RFS; 22.3 months vs. 7.2 months; P = 0.046), while no significant difference was found in overall survival (OS; 30.8 months vs. 15.3 months; P = 0.118). Subsequent multivariate analysis revealed that bridging to UCBT was a protective factor for RFS (P = 0.048) but had no significant effect on EFS (P = 0.205) or OS (P = 0.541). In the subgroup analysis, UCBT has an added benefit in patients with specific characteristics. Patients who experienced ≥2 relapses or with sustained non-remission (NR) showed better RFS (P = 0.025) after UCBT. Better EFS was seen in patients with poor prognostic markers (P = 0.027). In the subgroup with pre-infusion minimal residual disease (MRD) ≥5% or with extramedullary disease (EMD), UCBT significantly prolonged EFS (P = 0.009), RFS (P = 0.017), and OS (P = 0.026). Patients with occurrence of acute graft-versus-host disease (aGVHD) appeared to have a longer duration of remission (P = 0.007).

Conclusion

Consolidative UCBT can, to some extent, improve clinical outcomes of patients with R/R B-ALL entering remission following CD19 CAR-T therapy, especially in patients with more recurrences before treatment, patients with poor prognostic markers, and patients with a higher tumor burden. The occurrence of aGVHD after UCBT was associated with better RFS.

High-dimensional functional phenotyping of preclinical human CAR T cells using mass cytometry

Here, we present a comprehensive protocol for the generation and functional characterization of chimeric antigen receptor (CAR) T cells and their products by mass cytometry in a reproducible and scalable manner. We describe the production of CAR T cells from human peripheral blood mononuclear cells. We then detail a three-step staining protocol with metal-labeled antibodies and the subsequent mass cytometry analysis. This protocol allows simultaneous characterization of CAR T cell intracellular signaling, activation, proliferation, cytokine production, and phenotype in a single assay.

Generation of CAR-T Cells with Sleeping Beauty Transposon Gene Transfer

Human T lymphocytes that transgenically express a chimeric antigen receptor (CAR) have proven efficacy and safety in gene- and cell-based immunotherapy of certain hematological cancers. Appropriate gene vectors and methods of genetic engineering are required for therapeutic cell products to be biologically potent and their manufacturing to be economically viable. Transposon-based gene transfer satisfies these needs, and is currently being evaluated in clinical trials. In this protocol we describe the basic Sleeping Beauty (SB) transposon vector components required for stable gene integration in human cells, with special emphasis on minicircle DNA vectors and the use of synthetic mRNA. We provide a protocol for functional validation of the vector components in cultured human cell lines on the basis of fluorescent reporter gene expression. Finally, we provide a protocol for CAR-T cell engineering and describe assays that address transgene expression, biological potency and genomic vector copy numbers in polyclonal cell populations. Because transposons allow virus-free gene transfer with naked nucleic acids, the protocol can be adopted by any laboratory equipped with biological safety level S1 facilities.

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.

Particles in Biopharmaceutical Formulations, Part 2: An Update on Analytical Techniques and Applications for Therapeutic Proteins, Viruses, Vaccines and Cells

Particles in biopharmaceutical formulations remain a hot topic in drug product development. With new product classes emerging it is crucial to discriminate particulate active pharmaceutical ingredients from particulate impurities. Technical improvements, new analytical developments and emerging tools (e.g., machine learning tools) increase the amount of information generated for particles. For a proper interpretation and judgment of the generated data a thorough understanding of the measurement principle, suitable application fields and potential limitations and pitfalls is required. Our review provides a comprehensive overview of novel particle analysis techniques emerging in the last decade for particulate impurities in therapeutic protein formulations (protein-related, excipient-related and primary packaging material-related), as well as particulate biopharmaceutical formulations (virus particles, virus-like particles, lipid nanoparticles and cell-based medicinal products). In addition, we review the literature on applications, describe specific analytical approaches and illustrate advantages and drawbacks of currently available techniques for particulate biopharmaceutical formulations.

Investigation of product-derived lymphoma following infusion of piggyBac-modified CD19 chimeric antigen receptor T cells

We performed a phase 1 clinical trial to evaluate outcomes in patients receiving donor-derived CD19-specific chimeric antigen receptor (CAR) T cells for B-cell malignancy that relapsed or persisted after matched related allogeneic hemopoietic stem cell transplant. To overcome the cost and transgene-capacity limitations of traditional viral vectors, CAR T cells were produced using the piggyBac transposon system of genetic modification. Following CAR T-cell infusion, 1 patient developed a gradually enlarging retroperitoneal tumor due to a CAR-expressing CD4+ T-cell lymphoma. Screening of other patients led to the detection, in an asymptomatic patient, of a second CAR T-cell tumor in thoracic para-aortic lymph nodes. Analysis of the first lymphoma showed a high transgene copy number, but no insertion into typical oncogenes. There were also structural changes such as altered genomic copy number and point mutations unrelated to the insertion sites. Transcriptome analysis showed transgene promoter-driven upregulation of transcription of surrounding regions despite insulator sequences surrounding the transgene. However, marked global changes in transcription predominantly correlated with gene copy number rather than insertion sites. In both patients, the CAR T-cell-derived lymphoma progressed and 1 patient died. We describe the first 2 cases of malignant lymphoma derived from CAR gene-modified T cells. Although CAR T cells have an enviable record of safety to date, our results emphasize the need for caution and regular follow-up of CAR T recipients, especially when novel methods of gene transfer are used to create genetically modified immune therapies. This trial was registered at www.anzctr.org.au as ACTRN12617001579381.

Genetic Modification of Cytokine Signaling to Enhance Efficacy of CAR T Cell Therapy in Solid Tumors

Chimeric antigen receptor (CAR) T cell therapy has shown unprecedented success in treating advanced hematological malignancies. Its effectiveness in solid tumors has been limited due to heterogeneous antigen expression, a suppressive tumor microenvironment, suboptimal trafficking to the tumor site and poor CAR T cell persistence. Several approaches have been developed to overcome these obstacles through various strategies including the genetic engineering of CAR T cells to blunt the signaling of immune inhibitory receptors as well as to modulate signaling of cytokine/chemokine molecules and their receptors. In this review we offer our perspective on how genetically modifying cytokine/chemokine molecules and their receptors can improve CAR T cell qualities such as functionality, persistence (e.g. resistance to pro-apoptotic signals) and infiltration into tumor sites. Understanding how such modifications can overcome barriers to CAR T cell effectiveness will undoubtedly enhance the potential of CAR T cells against solid tumors.

Formulation Considerations for Autologous T Cell Drug Products

Genetically modified autologous T cells have become an established immunotherapy in the fight against cancer. The manufacture of chimeric antigen receptor (CAR) and αβ-T cell receptor (TCR) transduced T cells poses unique challenges, including the formulation, cryopreservation and fill-finish steps, which are the focus of this review. With an increasing number of marketing approvals for CAR-T cell therapies, comparison of their formulation design and presentation for administration can be made. These differences will be discussed alongside the emergence of automated formulation and fill-finish processes, the formulation design space, Monte Carlo simulation applied to risk analysis, primary container selection, freezing profiles and thaw and the use of dimethyl sulfoxide and alternative solvents/excipients as cryopreservation agents. The review will conclude with a discussion of the pharmaceutical solutions required to meet the simplification of manufacture and flexibility in dosage form for clinical treatment.

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.

Enriching leukapheresis improves T cell activation and transduction efficiency during CAR T processing

The majority of CD19-directed CAR T cell products are manufactured using an autologous process. Although using a patient's leukapheresis reduces the risks of rejection, it introduces variability in starting material composition and the presence of cell populations that might negatively affect production of chimeric antigen receptor (CAR) T cells, such as myeloid cells. In this work, the effect of monocytes (CD14) on the level of activation, growth, and transduction efficiency was monitored across well plate and culture bag platforms using healthy donor leukapheresis. Removal of monocytes from leukapheresis improved the level of activation 2-fold, achieving the same level of activation as when initiating the process with a purified T cell starting material. Two activation reagents were tested in well plate cultures, revealing differing sensitivities to starting material composition. Monocyte depletion in culture bag systems had a significant effect on transduction efficiency, improving consistency and increasing the level of CAR expression by up to 64% compared to unsorted leukapheresis. Cytotoxicity assays revealed that CAR T cell products produced from donor material depleted of monocytes and isolated T cells consistently outperformed those made from unsorted leukapheresis. Analysis of memory phenotypes and gene expression indicated that CAR T cells produced using depleted starting material displayed a more rested and naive state.

Challenges and Clinical Strategies of CAR T-Cell Therapy for Acute Lymphoblastic Leukemia: Overview and Developments

Chimeric antigen receptor (CAR) T-cell therapy exhibits desirable and robust efficacy in patients with acute lymphoblastic leukemia (ALL). Stimulated by the revolutionized progress in the use of FDA-approved CD19 CAR T cells, novel agents with CAR designs and targets are being produced in pursuit of superior performance. However, on the path from bench to bedside, new challenges emerge. Accessibility is considered the initial barrier to the transformation of this patient-specific product into a commercially available product. To ensure infusion safety, profound comprehension of adverse events and proactive intervention are required. Additionally, resistance and relapse are the most critical and intractable issues in CAR T-cell therapy for ALL, thus precluding its further development. Understanding the limitations through up-to-date insights and characterizing multiple strategies will be critical to leverage CAR T-cell therapy flexibly for use in clinical situations. Herein, we provide an overview of the application of CAR T-cell therapy in ALL, emphasizing the main challenges and potential clinical strategies in an effort to promote a standardized set of treatment paradigms for ALL.

Optimized Production of Lentiviral Vectors for CAR-T Cell

Advances in the use of lentiviral vectors for gene therapy applications have created a need for large-scale manufacture of clinical-grade viral vectors for transfer of genetic materials. Lentiviral vectors can transduce a wide range of cell types and integrate into the host genome of dividing and nondividing cells, resulting in long-term expression of the transgene both in vitro and in vivo. In this chapter, we present a method to transfect human cells, creating an easy platform to produce lentiviral vectors for CAR-T cell application.

Cell-Based Therapy Manufacturing in Stirred Suspension Bioreactor: Thoughts for cGMP Compliance

Cell-based therapy (CBT) is attracting much attention to treat incurable diseases. In recent years, several clinical trials have been conducted using human pluripotent stem cells (hPSCs), and other potential therapeutic cells. Various private- and government-funded organizations are investing in finding permanent cures for diseases that are difficult or expensive to treat over a lifespan, such as age-related macular degeneration, Parkinson’s disease, or diabetes, etc. Clinical-grade cell manufacturing requiring current good manufacturing practices (cGMP) has therefore become an important issue to make safe and effective CBT products. Current cell production practices are adopted from conventional antibody or protein production in the pharmaceutical industry, wherein cells are used as a vector to produce the desired products. With CBT, however, the “cells are the final products” and sensitive to physico- chemical parameters and storage conditions anywhere between isolation and patient administration. In addition, the manufacturing of cellular products involves multi-stage processing, including cell isolation, genetic modification, PSC derivation, expansion, differentiation, purification, characterization, cryopreservation, etc. Posing a high risk of product contamination, these can be time- and cost- prohibitive due to maintenance of cGMP. The growing demand of CBT needs integrated manufacturing systems that can provide a more simple and cost-effective platform. Here, we discuss the current methods and limitations of CBT, based upon experience with biologics production. We review current cell manufacturing integration, automation and provide an overview of some important considerations and best cGMP practices. Finally, we propose how multi-stage cell processing can be integrated into a single bioreactor, in order to develop streamlined cGMP-compliant cell processing systems.

Gene Modified CAR-T Cellular Therapy for Hematologic Malignancies

With advances in the understanding of characteristics of molecules, specific antigens on the surface of hematological malignant cells were identified and multiple therapies targeting these antigens as neoplasm treatments were developed. Among them, chimeric antigen receptor (CAR) T-cell therapy, which got United States Food and Drug Administration (FDA) approval for relapsed/refractory (r/r) diffuse large B-cell lymphoma (DLBCL) as well as for recurrent acute lymphoblastic leukemia (ALL) within the past five years, and for r/r mantle cell lymphoma (MCL) this year, represents one of the most rapidly evolving immunotherapies. Nevertheless, its applicability to other hematological malignancies, as well as its efficacy and persistence are fraught with clinical challenges. Currently, more than one thousand clinical trials in CAR T-cell therapy are ongoing and its development is changing rapidly. This review introduces the current status of CAR T-cell therapy in terms of the basic molecular aspects of CAR T-cell therapy, its application in hematological malignancies, adverse reactions during clinical use, remaining challenges, and future utilization.

Redirecting Vesicular Transport to Improve Nonviral Delivery of Molecular Cargo

Cell engineering relies heavily on viral vectors for the delivery of molecular cargo into cells due to their superior efficiency compared to nonviral ones. However, viruses are immunogenic and expensive to manufacture, and have limited delivery capacity. Nonviral delivery approaches avoid these limitations but are currently inefficient for clinical applications. This work demonstrates that the efficiency of nonviral delivery of plasmid DNA, mRNA, Sleeping Beauty transposon, and ribonucleoprotein can be significantly enhanced through pretreatment of cells with the nondegradable sugars (NDS), such as sucrose, trehalose, and raffinose. The enhancement is mediated by the incorporation of the NDS into cell membranes, causing enlargement of lysosomes and formation of large (>500 nm) amphisome-like bodies (ALBs). The changes in subcellular structures redirect transport of cargo to ALBs rather than to lysosomes, reducing cargo degradation in cells. The data indicate that pretreatment of cells with NDS is a promising approach to improve nonviral cargo delivery in biomedical applications.

Transposon-Based CAR T Cells in Acute Leukemias: Where are We Going?

Chimeric Antigen Receptor (CAR) T-cell therapy has become a new therapeutic reality for refractory and relapsed leukemia patients and is also emerging as a potential therapeutic option in solid tumors. Viral vector-based CAR T-cells initially drove these successful efforts; however, high costs and cumbersome manufacturing processes have limited the widespread clinical implementation of CAR T-cell therapy. Here we will discuss the state of the art of the transposon-based gene transfer and its application in CAR T immunotherapy, specifically focusing on the Sleeping Beauty (SB) transposon system, as a valid cost-effective and safe option as compared to the viral vector-based systems. A general overview of SB transposon system applications will be provided, with an update of major developments, current clinical trials achievements and future perspectives exploiting SB for CAR T-cell engineering. After the first clinical successes achieved in the context of B-cell neoplasms, we are now facing a new era and it is paramount to advance gene transfer technology to fully exploit the potential of CAR T-cells towards next-generation immunotherapy.

Optimized Assessment of qPCR-Based Vector Copy Numbers as a Safety Parameter for GMP-Grade CAR T Cells and Monitoring of Frequency in Patients

Chimeric antigen receptor (CAR) T cells are considered genetically modified organisms (GMOs) and constitute gene therapy medicinal products. Thus, CAR T cell manufacturing for clinical application is strictly regulated. Appropriate methods to assess vector copy numbers (VCNs) in CAR T cell products and monitoring of CAR T cell frequencies in patients are required. Quantitative polymerase chain reaction (qPCR) is the preferred method for VCN assessment. However, no standardized procedure with high reproducibility has been described yet. Here, we report on a single copy gene (SCG)-based duplex (DP)-qPCR assay (SCG-DP-PCR) to determine VCN in CAR T cell products. SCG-DP-PCR was validated and compared to the absolute standard curve method (ACM) within the framework of a clinical trial treating patients with good manufacturing practice (GMP)-grade CAR T cells at the University Hospital Heidelberg. Methodologically, SCG-DP-PCR displayed technical advantages over ACM and minimized mathematical analysis. SCG-DP-PCR, as a highly reproducible approach, can be used for clinical follow-up of patients treated with CAR T cells or other GMOs and might replace established methods for VCN quantification. This work will enable clinicians to assess VCN, as well as CAR T cell frequencies, in patients as a basis for decisions on subsequent therapies, including repeated CAR T cell administration.

Engineering T cells for immunotherapy of primary human hepatocellular carcinoma

Liver cancers, majority of which are primary hepatocellular carcinoma (HCC), continue to be on the rise in the world. Furthermore, due to the lack of effective treatments, liver cancer ranks the 4^th most common cause of male cancer deaths. Novel therapies are urgently needed. Over the last few years, immunotherapies, especially the checkpoint blockades and adoptive cell therapies of engineered T cells, have demonstrated a great potential for treating malignant tumors including HCC. In this review, we summarize the current ongoing research of antigen-specific immunotherapies including cancer vaccines and adoptive cell therapies for HCC. We briefly discuss the HCC cancer vaccine and then focus on the antigen-specific T cells genetically engineered with the T cell receptor genes (TCRTs) and the chimeric antigen receptor genes (CARTs). We first review the current options of TCRTs and CARTs immunotherapies for HCC, and then analyze the factors and parameters that may help to improve the design of TCRTs and CARTs to enhance their antitumor efficacy and safety. Our goals are to render readers a panoramic view of the current stand of HCC immunotherapies and provide some strategies to design better TCRTs and CARTs to achieve more effective and durable antitumor effects.

Advances and Challenges of CAR T Cells in Clinical Trials

As a specifically programmable, living immunotherapeutic drug, chimeric antigen receptor (CAR)-modified T cells are providing an alternative treatment option for a broad variety of diseases including so far refractory cancer. By recognizing a tumor-associated antigen, the CAR triggers an anti-tumor response of engineered patient's T cells achieving lasting remissions in the treatment of leukemia and lymphoma. During the last years, significant progress was made in optimizing the CAR design, in manufacturing CAR-engineered T cells, and in the clinical management of patients showing promise to establish adoptive CAR T cell therapy as an effective treatment option in the forefront.

Optimizing Manufacturing Protocols of Chimeric Antigen Receptor T Cells for Improved Anticancer Immunotherapy

Chimeric antigen receptor (CAR) T cell therapy can achieve outstanding response rates in heavily pretreated patients with hematological malignancies. However, relapses occur and they limit the efficacy of this promising treatment approach. The cellular composition and immunophenotype of the administered CART cells play a crucial role for therapeutic success. Less differentiated CART cells are associated with improved expansion, long-term in vivo persistence, and prolonged anti-tumor control. Furthermore, the ratio between CD4+ and CD8+ T cells has an effect on the anti-tumor activity of CART cells. The composition of the final cell product is not only influenced by the CART cell construct, but also by the culturing conditions during ex vivo T cell expansion. This includes different T cell activation strategies, cytokine supplementation, and specific pathway inhibition for the differentiation blockade. The optimal production process is not yet defined. In this review, we will discuss the use of different CART cell production strategies and the molecular background for the generation of improved CART cells in detail.

Clinical Advancement and Challenges of ex vivo Expansion of Human Cord Blood Cells

Apart from peripheral blood stem cell (PBSC), umbilical cord blood (UCB) is now a recognized source of stem cells for transplantation. UCB is an especially important source of stem cells for minority populations, which would otherwise be unable to find appropriately matched adult donors. UCB has fewer mature T lymphocytes compared with peripheral blood, thus making a UCB transplantation (UCBT) with a greater degree of HLA mismatch possible. The limited cell dose per UCB sample is however associated with delayed engraftment and a higher risk of graft failure, especially in adult recipients. This lower cell dose can be optimized by performing double unit UCBT, ex vivo UCB expansion prior to transplant and enhancement of the capabilities of the stem cells to home to the bone marrow. UCB contains naïve and immature T cells, thus posing significant challenges with increased risk of infections, graft versus host diseases (GVHD) and relapse following UCBT. Cell engineering techniques have been developed to circumnavigate the immaturity of the T cells, and include virus-specific cytotoxic T cells (VSTs), T cells transduced with disease-specific chimeric antigen receptor (CAR T cells) and regulatory T cell (Tregs) engineering. In this article, we review the advances in UCB ex vivo expansion and engineering to improve engraftment and reduce complications. As further research continues to find ways to overcome the current challenges, outcomes from UCBT will likely improve.

Mechanisms of Relapse After CD19 CAR T-Cell Therapy for Acute Lymphoblastic Leukemia and Its Prevention and Treatment Strategies

Chimeric antigen receptor (CAR) T-cell therapy is highly effective in the treatment of B-cell acute lymphoblastic leukemia (ALL) or B-cell lymphoma, providing alternative therapeutic options for patients who failed to respond to conventional treatment or relapse. Moreover, it can bridge other therapeutic strategies and greatly improve patient prognosis, with broad applicable prospects. Even so, 30–60% patients relapse after treatment, probably due to persistence of CAR T-cells and escape or downregulation of CD19 antigen, which is a great challenge for disease control. Therefore, understanding the mechanisms that underlie post-CAR relapse and establishing corresponding prevention and treatment strategies is important. Herein, we discuss post-CAR relapse from the aspects of CD19-positive and CD19-negative and provide some reasonable prevention and treatment strategies.

GMP-Compliant Manufacturing of NKG2D CAR Memory T Cells Using CliniMACS Prodigy

Natural killer group 2D (NKG2D) is a natural killer (NK) cell-activating receptor that recognizes different stress-induced ligands that are overexpressed in a variety of childhood and adult tumors. NKG2D chimeric antigen receptor (CAR) T cells have shown potent anticancer effects against different cancer types. A second-generation NKG2D CAR was generated by fusing full-length human NKG2D to 4-1BB costimulatory molecule and CD3ζ signaling domain. Patient-derived CAR T cells show limitations including inability to manufacture CAR T cells from the patients' own T cells, disease progression, and death prior to return of engineered cells. The use of allogeneic T cells for CAR therapy could be an attractive alternative, although undesirable graft vs. host reactions may occur. To avoid such adverse effects, we used CD45RA⁻ memory T cells, a T-cell subset with less alloreactivity, as effector cells to express NKG2D CAR. In this study, we developed a protocol to obtain large-scale NKG2D CAR memory T cells for clinical use by using CliniMACS Prodigy, an automated closed system compliant with Good Manufacturing Practice (GMP) guidelines. CD45RA⁺ fraction was depleted from healthy donors' non-mobilized apheresis using CliniMACS CD45RA Reagent and CliniMACS Plus device. A total of 10⁸ CD45RA⁻ cells were cultured in TexMACS media supplemented with 100 IU/mL IL-2 and activated at day 0 with T Cell TransAct. Then, we used NKG2D-CD8TM-4-1BB-CD3ζ lentiviral vector for cell transduction (MOI = 2). NKG2D CAR T cells expanded between 10 and 13 days. Final cell products were analyzed to comply with the specifications derived from the quality and complementary controls carried out in accordance with the instructions of the Spanish Regulatory Agency of Medicines and Medical Devices (AEMPS) for the manufacture of investigational advanced therapy medicinal products (ATMPs). We performed four validations. The manufacturing protocol here described achieved large numbers of viable NKG2D CAR memory T cells with elevated levels of NKG2D CAR expression and highly cytotoxic against Jurkat and 531MII tumor target cells. CAR T cell final products met release criteria, except for one showing myc overexpression and another with viral copy number higher than five. Manufacturing of clinical-grade NKG2D CAR memory T cells using CliniMACS Prodigy is feasible and reproducible, widening clinical application of CAR T cell therapies.

Preservation of cell-based immunotherapies for clinical trials

In the unique supply chain of cellular therapies, preservation is important to keep the cell product viable. Many factors in cryopreservation affect the outcome of a cell therapy: (i) formulation and introduction of a freezing medium, (ii) cooling rate, (iii) storage conditions, (iv) thawing conditions and (v) post-thaw processing. This article surveys clinical trials of cellular immunotherapy that used cryopreserved regulatory, chimeric antigen receptor or gamma delta T cells, dendritic cells or natural killer (NK) cells. Several observations are summarized from the given information. The aforementioned cell types have been similarly frozen in media containing 5-10% dimethyl sulfoxide (DMSO) with plasma, serum or human serum albumin. Two common freezing methods are an insulated freezing container such as Nalgene Mr. Frosty and a controlled-rate freezer at a cooling rate of -1°C/min. Water baths at approximately 37°C have been commonly used for thawing. Post-thaw processing of cryopreserved cells varied greatly: some studies infused the cells immediately upon thawing; some diluted the cells in a carrier solution of varying formulation before infusion; some washed cells to remove cryoprotective agents; and others re-cultured cells to recover cell viability or functionality lost due to cryopreservation. Emerging approaches to preserving cellular immunotherapies are also described. DMSO-free formulations of the freezing media have demonstrated improved preservation of cell viability in T lymphocytes and of cytotoxic function in natural killer cells. Saccharides are a common type of molecule used as an alternative cryoprotective agent to DMSO. Improving methods of preservation will be critical to growth in the clinical use of cellular immunotherapies.

Production of CAR T-cells by GMP-grade lentiviral vectors: latest advances and future prospects

Chimeric antigen receptor (CAR) T-cells represent a paradigm shift in cancer immunotherapy and a new milestone in the history of oncology. In 2017, the Food and Drug Administration approved two CD19-targeted CAR T-cell therapies (Kymriah™, Novartis, and Yescarta™, Kite Pharma/Gilead Sciences) that have remarkable efficacy in some B-cell malignancies. The CAR approach is currently being evaluated in multiple pivotal trials designed for the immunotherapy of hematological malignancies as well as solid tumors. To generate CAR T-cells ex vivo, lentiviral vectors (LVs) are particularly appealing due to their ability to stably integrate relatively large DNA inserts, and to efficiently transduce both dividing and nondividing cells. This review discusses the latest advances and challenges in the design and production of CAR T-cells, and the good manufacturing practices (GMP)-grade production process of LVs used as a gene transfer vehicle. New developments in the application of CAR T-cell therapy are also outlined with particular emphasis on next-generation allogeneic CAR T-cells.

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.

T-cell receptor gene-modified cells: past promises, present methodologies and future challenges

Immunotherapy constitutes an exciting and rapidly evolving field, and the demonstration that genetically modified T-cell receptors (TCRs) can be used to produce T-lymphocyte populations of desired specificity offers new opportunities for antigen-specific T-cell therapy. Overall, TCR-modified T cells have the ability to target a wide variety of self and non-self targets through the normal biology of a T cell. Although major histocompatibility complex (MHC)-restricted and dependent on co-receptors, genetically engineered TCRs still present a number of characteristics that ensure they are an important alternative strategy to chimeric antigen receptors (CARs), and high-affinity TCRs can now be successfully engineered with the potential to enhance therapeutic efficacy while minimizing adverse events. This review will focus on the main characteristics of TCR gene-modified cells, their potential clinical application and promise to the field of adoptive cell transfer (ACT), basic manufacturing procedures and characterization protocols and overall challenges that need to be overcome so that redirection of TCR specificity may be successfully translated into clinical practice, beyond early-phase clinical trials.

CAR T Cells: A Snapshot on the Growing Options to Design a CAR

Adoptive cell therapy of malignant diseases with chimeric antigen receptor (CAR) modified T cells rapidly advanced from pre-clinical models to commercial approvals within 2 decades. CARs redirect patient's T cells towards cancer cells and activate the engineered cells for a cytolytic attack resulting in the destruction of the cognate target cell. CAR T cells have demonstrated their powerful capacities in inducing complete and lasting remissions of leukemia/lymphoma in an increasing number of trials worldwide. Since the early 90's, the design of CARs went through various steps of optimization until the very recent developments which include CARs with logic gating in the recognition of antigen patterns on target cells and TRUCKs with a target recognition induced delivery of immune modulating agents. Here we review the generations in CAR design, the impact of specific modifications, the strategies to improve the safety of CAR T cell therapy, and the challenges to adapt the CAR design for broader applications.

Manufacturing chimeric antigen receptor T cells: issues and challenges

Clinical trials of adoptively transferred CD19 chimeric antigen receptor (CAR) T cells have delivered unprecedented responses in patients with relapsed refractory B-cell malignancy. These results have prompted Food and Drug Administration (FDA) approval of two CAR T-cell products in this high-risk patient population. The widening range of indications for CAR T-cell therapy and increasing patient numbers present a significant logistical challenge to manufacturers aiming for reproducible delivery systems for high-quality clinical CAR T-cell products. This review discusses current and novel CAR T-cell processing methodologies and the quality control systems needed to meet the increasing clinical demand for these exciting new therapies.

Engineering and Design of Chimeric Antigen Receptors

T cells engineered with chimeric antigen receptors (CARs) have emerged as a potent new class of therapeutics for cancer, based on their remarkable potency in blood cancers. Since the first clinical reports of their efficacy emerged 7 years ago, investigators have focused on the mechanisms and properties that make CARs effective or toxic, and their effects on T cell biology. Novel CAR designs coupled with improvements in gene transfer technology, incorporating advances in gene editing, have the potential to increase access to engineered cell therapies, as well as improve their potency in solid tumors.

Efficient and Non-genotoxic RNA-Based Engineering of Human T Cells Using Tumor-Specific T Cell Receptors With Minimal TCR Mispairing

Genetic engineering of T cells with tumor specific T-cell receptors (TCR) is a promising strategy to redirect their specificity against cancer cells in adoptive T cell therapy protocols. Most studies are exploiting integrating retro- or lentiviral vectors to permanently introduce the therapeutic TCR, which can pose serious safety issues when treatment-related toxicities would occur. Therefore, we developed a versatile, non-genotoxic transfection method for human unstimulated CD8⁺ T cells. We describe an optimized double sequential electroporation platform whereby Dicer-substrate small interfering RNAs (DsiRNA) are first introduced to suppress endogenous TCR α and β expression, followed by electroporation with DsiRNA-resistant tumor-specific TCR mRNA. We demonstrate that double sequential electroporation of human primary unstimulated T cells with DsiRNA and TCR mRNA leads to unprecedented levels of transgene TCR expression due to a strongly reduced degree of TCR mispairing. Importantly, superior transgenic TCR expression boosts epitope-specific CD8⁺ T cell activation and killing activity. Altogether, DsiRNA and TCR mRNA double sequential electroporation is a rapid, non-integrating and highly efficient approach with an enhanced biosafety profile to engineer T cells with antigen-specific TCRs for use in early phase clinical trials.

Artificial antigen-presenting cells are superior to dendritic cells at inducing antigen-specific cytotoxic T lymphocytes

Adoptive immunotherapy is a promising cancer treatment that entails infusion of immune cells manipulated to have antitumor specificity, in vitro. Antigen-specific cytotoxic T lymphocytes are the main executors of transformed cells during cancer immunotherapy. To induce antigen-specific cytotoxic T lymphocytes, we developed artificial antigen-presenting cells (aAPCs) by engineering K562 cells with electroporation to direct the stable expression of HLA-A∗0201, CD80, and 4-1BBL. Our findings demonstrate that after three stimulation cycles, the aAPCs promoted the induction of antigen-specific cytotoxic T lymphocytes with a less differentiated "young" phenotype, which enhanced immune responses with superior cytotoxicity. This novel, easy, and cost-effective approach to inducing antigen-specific cytotoxic T lymphocytes provides the possibility of improved cancer therapies.

Wide Awake and Ready to Move: 20 Years of Non-Viral Therapeutic Genome Engineering with the Sleeping Beauty Transposon System

Gene therapies will only become a widespread tool in the clinical treatment of human diseases with the advent of gene transfer vectors that integrate genetic information stably, safely, effectively, and economically. Two decades after the discovery of the Sleeping Beauty (SB) transposon, it has been transformed into a vector system that is fulfilling these requirements. SB may well overcome some of the limitations associated with viral gene transfer vectors and transient non-viral gene delivery approaches that are being used in the majority of ongoing clinical trials. The SB system has achieved a high level of stable gene transfer and sustained transgene expression in multiple primary human somatic cell types, representing crucial steps that may permit its clinical use in the near future. This article reviews the most important aspects of SB as a tool for gene therapy, including aspects of its vectorization and genomic integration. As an illustration, the clinical development of the SB system toward gene therapy of age-related macular degeneration and cancer immunotherapy is highlighted.