High-level transgene expression in primary human T lymphocytes and adult bone marrow CD34+ cells via electroporation-mediated gene delivery

Engineering Efficient CAR-T Cells via Electroactive Nanoinjection

Chimeric antigen receptor (CAR)-T cell therapy has emerged as a promising cell-based immunotherapy approach for treating blood disorders and cancers, but genetically engineering CAR-T cells is challenging due to primary T cells' sensitivity to conventional gene delivery approaches. The current viral-based method can typically involve significant operating costs and biosafety hurdles, while bulk electroporation (BEP) can lead to poor cell viability and functionality. Here, a non-viral electroactive nanoinjection (ENI) platform is developed to efficiently negotiate the plasma membrane of primary human T cells via vertically configured electroactive nanotubes, enabling efficient delivery (68.7%) and expression (43.3%) of CAR genes in the T cells, with minimal cellular perturbation (>90% cell viability). Compared to conventional BEP, the ENI platform achieves an almost threefold higher CAR transfection efficiency, indicated by the significantly higher reporter GFP expression (43.3% compared to 16.3%). By co-culturing with target lymphoma Raji cells, the ENI-transfected CAR-T cells' ability to effectively suppress lymphoma cell growth (86.9% cytotoxicity) is proved. Taken together, the results demonstrate the platform's remarkable capacity to generate functional and effective anti-lymphoma CAR-T cells. Given the growing potential of cell-based immunotherapies, such a platform holds great promise for ex vivo cell engineering, especially in CAR-T cell therapy.

A review of PD-1/PD-L1 siRNA delivery systems in immune T cells and cancer cells

OBJECTIVES

Programmed cell death 1 (PD-1) is a member of the CD28/CTLA-4 family of inhibitory immunological checkpoint receptors that's also widely produced by exhausted T lymphocytes in an immunosuppressive tumor microenvironment. PD-1 binds to programmed death ligand (PD-L1) and suppresses anti-cancer activity of T lymphocytes. We examined the current literature on how siRNA delivery systems can be used to target PD-1 and PD-L1, as well as the anti-cancer mechanisms and challenges associated with siRNA molecules. We look at studies that use program death 1 siRNA or program death 1 ligand siRNA to treat cancer. Several databases have been used for this purpose, including NCBI, Scopus, and Google Scholar.

KEY FINDINGS

This study looked at several methods for delivering siRNA to immune cells and cancer cells. According to these findings, suppressing PD-1 in T cells increases T lymphocyte activity. PD-L1 suppression in DCs improves antigen presentation and co-stimulatory signals on their surface, resulting in T cell activation. Chemotherapy resistance and cancer cell suppression of T cells are reduced when PD-L1/2 is suppressed in cancer cells.

CONCLUSION

The findings of this study indicated that several strategies for siRNA transfection to immune and cancer cells have been evaluated in recent decades, some of which effectively transfect siRNA to target cells, and defined PD-1 siRNA as a promising strategy for cancer treatment.

Reactivation of γ-globin expression using a minicircle DNA system to treat β-thalassemia

Reactivation of fetal hemoglobin by editing the B-cell lymphoma/leukemia 11A (BCL11A) erythroid enhancer is an effective gene therapy for β-thalassemia. Using the CRISPR/Cas9 system, fetal γ-globin expression can be robustly reactivated to mitigate the clinical course of β-thalassemia. In our study, we found that the transfection efficiencies of CD34+ hematopoietic stem/progenitor cells (HSPCs) were significantly and negatively correlated with the length of plasmids and greatly affected by the linearization of plasmids. Furthermore, the transgene expression of minicircles (MC) without plasmid backbone sequences was better both in vitro and in vivo compared with conventional plasmids. Thus, MC DNA was used to deliver the cassette of Staphylococcus aureus Cas9 (SaCas9) into HSPCs, and a single-guide RNA targeting the erythroid enhancer region of BCL11A was selected. After electroporation with MC DNA, an evident efficiency of gene editing and reactivation of γ-globin expression in erythroblasts derived from unsorted HSPCs was acquired. No significant off-target effects were found by deep sequencing. Furthermore, fragments derived from lentiviral vectors, but not MC DNA, were highly enriched in promoter, exon, intron, distal-intergenic, and cancer-associated genes, indicating that MC DNA provided a relatively safe and efficient vector for delivering transgenes. The developed MC DNA vector provided a potential approach for the delivery of SaCas9 cassette and the reactivation of γ-globin expression for ameliorating syndromes of β-thalassemia.

High transfection efficiency and cell viability of immune cells with nanomaterials-based transfection reagent

Gene manipulation in non-adhesive cells, especially lymphocytes, was difficult due to their low efficiency and high toxicity. Electroporation was reported as a highly efficient method for human and mouse lymphocytes. However, this method requires expensive equipment and causes severe cell damage. Here, the authors present a simple and efficient method to deliver siRNA into lymphocytes with high efficiency and cell viability. This nanomaterials-based transfection reagent was simple and cost-effective and can perform multiple transfections, which further increase the overall efficiency. This method should be applicable for many cell lines and can be used to decipher gene functions of lymphocytes.

Cas9 protein delivery non-integrating lentiviral vectors for gene correction in sickle cell disease

Gene editing with the CRISPR-Cas9 system could revolutionize hematopoietic stem cell (HSC)-targeted gene therapy for hereditary diseases, including sickle cell disease (SCD). Conventional delivery of editing tools by electroporation limits HSC fitness due to its toxicity; therefore, efficient and non-toxic delivery remains crucial. Integrating lentiviral vectors are established for therapeutic gene delivery to engraftable HSCs in gene therapy trials; however, their sustained expression and size limitation preclude their use for CRISPR-Cas9 delivery. Here, we developed a Cas9 protein delivery non-integrating lentiviral system encoding guide RNA and donor DNA, allowing for transient endonuclease function and inclusion of all editing tools in a single vector (all-in-one). We demonstrated efficient one-time correction of the SCD mutation in the endogenous βs-globin gene up to 42% at the protein level (p < 0.01) with the Cas9 protein delivery non-integrating lentiviral all-in-one system without electroporation. Our findings improve prospects for efficient and safe genome editing.

Steroid receptor coactivator 3 (SRC-3/AIB1) is enriched and functional in mouse and human Tregs

A subset of CD4 + lymphocytes, regulatory T cells (Tregs), are necessary for central tolerance and function as suppressors of autoimmunity against self-antigens. The SRC-3 coactivator is an oncogene in multiple cancers and is capable of potentiating numerous transcription factors in a wide variety of cell types. Src-3 knockout mice display broad lymphoproliferation and hypersensitivity to systemic inflammation. Using publicly available bioinformatics data and directed cellular approaches, we show that SRC-3 also is highly enriched in Tregs in mice and humans. Human Tregs lose phenotypic characteristics when SRC-3 is depleted or pharmacologically inhibited, including failure of induction from resting T cells and loss of the ability to suppress proliferation of stimulated T cells. These data support a model for SRC-3 as a coactivator that actively participates in protection from autoimmunity and may support immune evasion of cancers by contributing to the biology of Tregs.

Nonviral gene delivery to T cells with Lipofectamine LTX

Retroviral gene delivery is widely used in T cell therapies for hematological cancers. However, viral vectors are expensive to manufacture, integrate genes in semirandom patterns, and their transduction efficiency varies between patients. In this study, several nonviral gene delivery vehicles, promoters, and additional variables were compared to optimize nonviral transgene delivery and expression in both Jurkat and primary T cells. Transfection of Jurkat cells was maximized to a high efficiency (63.0% ± 10.9% EGFP⁺  cells) by transfecting cells with Lipofectamine LTX in X-VIVO 15 media. However, the same method yielded a much lower transfection efficiency in primary T cells (8.1% ± 0.8% EGFP⁺ ). Subsequent confocal microscopy revealed that a majority of the lipoplexes did not enter the primary T cells, which might be due to relatively low expression levels of heparan sulfate proteoglycans detected via messenger RNA-sequencing. Pyrin and HIN (PYHIN) DNA sensors (e.g., AIM2 and IFI16) that can induce apoptosis or repress transcription after binding cytoplasmic DNA were also detected at high levels in primary T cells. Therefore, transfection of primary T cells appears to be limited at the level of cellular uptake or DNA sensing in the cytoplasm. Both of these factors should be considered in the development of future viral and nonviral T cell gene delivery methods.

Optimization of electroporation and other non-viral gene delivery strategies for T cells

CAR-T therapy is a particularly effective treatment for some types of cancer that uses retroviruses to deliver the gene for a chimeric antigen receptor (CAR) to a patient's T cells ex vivo. The CAR enables the T cells to bind and eradicate cells with a specific surface marker (e.g., CD19⁺ B cells) after they are transfused back into the patient. This treatment was proven to be particularly effective in treating non-Hodgkin's lymphoma (NHL) and acute lymphoblastic leukemia (ALL), but the current CAR-T cell manufacturing process has a few significant drawbacks. For example, while lentiviral and gammaretroviral transduction are both relatively effective, the process of producing viral vectors is time-consuming and costly. Additionally, patients must undergo follow up appointments for several years to monitor them for any unanticipated side effects associated with the virus. Therefore, several studies have endeavored to find alternative non-viral gene delivery methods that are less expensive, more precise, simple, and safe. This review focuses on the current state of the most promising non-viral gene delivery techniques, including electroporation and transfection with cationic polymers or lipids.

Surface-Mediated Intracellular Delivery by Physical Membrane Disruption

Effective and nondestructive intracellular delivery of exogenous molecules and other functional materials into living cells is of importance for diverse biological fundamental research and therapeutic applications, such as gene editing and cell-based therapies. However, for most exogenous molecules, the cell plasma membrane is effectively impermeable and thus remains the greatest barrier to intracellular delivery. In recent years, methods based on surface-mediated physical membrane disruption have attracted considerable attention. These methods exploit the physical properties of the surface to transiently increase the membrane permeability of cells come in contact thereto, thereby facilitating the efficient intracellular delivery of molecules regardless of molecule or target cell type. In this Review, we focus on recent progress, particularly over the past decade, on these surface-mediated membrane disruption-based delivery systems. According to the membrane disruption mechanism, three categories can be recognized: (i) mechanical penetration, (ii) electroporation, and (iii) photothermal poration. Each of these is discussed in turn and a brief perspective on future developments in this promising area is presented.

Acoustophoretic rapid media exchange and continuous-flow electrotransfection of primary human T cells for applications in automated cellular therapy manufacturing

Autologous cellular therapies based on modifying T cells to express chimeric antigen receptor genes have been highly successful in treating hematological cancers. Deployment of these therapies is limited by the complexity and costs associated with their manufacturing. Transitioning these processes from virus-based methods for gene delivery to a non-viral method, such as electroporation, has the potential to greatly reduce cost and manufacturing time while increasing safety and efficacy. Major challenges with electroporation are the negative impacts on cell health associated with exposure to high-magnitude electric fields, and that most commercial bulk electroporators are low-precision instruments designed for manually-operated, lower-throughput batch processing of cells. Negative effects on cell health can be mitigated by use of specialized electroporation medias, but this adds processing steps, and long-term exposure to these medias can reduce transfection efficiency and post-transfection viability. To enable automated, clinical-scale production of cellular therapies using electrotransfection in specialized medias, we developed a high-precision microfluidic platform that automatically and continuously transfers cells from culture media into electroporation media using acoustophoresis, and then immediately applies electric fields from integrated electrodes. This limits cell residence time in electroporation media to seconds, and enables high transfection efficiency with minimum impact on cell viability. We tested our system by transferring primary human T cells from a standard cell media to electroporation media, and then transfecting them with mRNA encoding an mCherry fluorescent protein. We achieved a media exchange efficiency of 86% and transfection efficiency of up to 60%, with less than a 5% reduction in viability.

Optimized DNA electroporation for primary human T cell engineering

Background

Effective gene-delivery systems for primary human T cell engineering are useful tools for both basic research and clinical immunotherapy applications. Pseudovirus-based systems and electro-transfection are the most popular strategies for genetic material transduction. Compared with viral-particle-mediated approaches, electro-transfection is theoretically safer, because it does not promote transgene integration into the host genome. Additionally, the simplicity and speed of the procedure increases the attractiveness of electroporation. Here, we developed and optimized an electro-transfection method for the production of engineered chimeric antigen receptor (CAR)-T cells.

Results

Stimulation of T cells had the greatest effect on their transfection, with stimulation of cells for up to 3 days substantially improving transfection efficiency. Additionally, the strength of the external electric field, input cell number, and the initial amount of DNA significantly affected transfection performance. The voltage applied during electroporation affected plasmid permeation and was negatively correlated with the number of viable cells after electroporation. Moreover, higher plasmid concentration increased the proportion of positively transfected cells, but decreased cell viability, and for single-activated cells, higher cell density enhanced their viability. We evaluated the effects of two clinically relevant factors, serum supplementation in the culture medium and cryopreservation immediately after the isolation of peripheral blood lymphocytes. Our findings showed that our protocol performed well using xeno-free cultured, fresh T cells, with application resulting in a lower but acceptable transfection efficiency of cells cultured with fetal bovine serum or thawed cells. Furthermore, we described an optimized procedure to generate CAR-T cells within 6 days and that exhibited cytotoxicity toward targeted cells.

Conclusions

Our investigation of DNA electro-transfection for the use in human primary T cell engineering established and validated an optimized method for the construction of functional CAR-T cells.

Electronic supplementary material

The online version of this article (10.1186/s12896-018-0419-0) contains supplementary material, which is available to authorized users.

Paralleled comparison of vectors for the generation of CAR-T cells

T-lymphocytes genetically engineered with the chimeric antigen receptor (CAR-T) have shown great therapeutic potential in cancer treatment. A variety of preclinical researches and clinical trials of CAR-T therapy have been carried out to lay the foundation for future clinical application. In these researches, several gene-transfer methods were used to deliver CARs or other genes into T-lymphocytes, equipping CAR-modified T cells with a property of recognizing and attacking antigen-expressing tumor cells in a major histocompatibility complex-independent manner. Here, we summarize the gene-transfer vectors commonly used in the generation of CAR-T cell, including retrovirus vectors, lentivirus vectors, the transposon/transposase system, the plasmid-based system, and the messenger RNA electroporation system. The following aspects were compared in parallel: efficiency of gene transfer, the integration methods in the modified T cells, foreground of scale-up production, and application and development in clinical trials. These aspects should be taken into account to generate the optimal CAR-gene vector that may be suitable for future clinical application.

A novel rapid and reproducible flow cytometric method for optimization of transfection efficiency in cells

Transfection is one of the most frequently used techniques in molecular biology that is also applicable for gene therapy studies in humans. One of the biggest challenges to investigate the protein function and interaction in gene therapy studies is to have reliable monospecific detection reagents, particularly antibodies, for all human gene products. Thus, a reliable method that can optimize transfection efficiency based on not only expression of the target protein of interest but also the uptake of the nucleic acid plasmid, can be an important tool in molecular biology. Here, we present a simple, rapid and robust flow cytometric method that can be used as a tool to optimize transfection efficiency at the single cell level while overcoming limitations of prior established methods that quantify transfection efficiency. By using optimized ratios of transfection reagent and a nucleic acid (DNA or RNA) vector directly labeled with a fluorochrome, this method can be used as a tool to simultaneously quantify cellular toxicity of different transfection reagents, the amount of nucleic acid plasmid that cells have taken up during transfection as well as the amount of the encoded expressed protein. Finally, we demonstrate that this method is reproducible, can be standardized and can reliably and rapidly quantify transfection efficiency, reducing assay costs and increasing throughput while increasing data robustness.

Rigorous optimization and validation of potent RNA CAR T cell therapy for the treatment of common epithelial cancers expressing folate receptor

Using lentiviral technology, we recently demonstrated that incorporation of CD27 costimulation into CARs greatly improves antitumor activity and T cell persistence. Still, virus-mediated gene transfer is expensive, laborious and enables long-term persistence, creating therapies which cannot be easily discontinued if toxic. To address these concerns, we utilized a non-integrating RNA platform to engineer human T cells to express FRα-specific, CD27 CARs and tested their capacity to eliminate human FRα(+) cancer. Novel CARs comprised of human components were constructed, C4-27z and C4opt-27z, a codon-optimized variant created for efficient expression. Following RNA electroporation, C4-27z and C4opt-27z CAR expression is initially ubiquitous but progressively declines across T cell populations. In addition, C4-27z and C4opt-27z RNA CAR T cells secrete high levels of Th-1 cytokines and display strong cytolytic function against human FRα(+) cancers in a time- and antigen-dependent manner. Further, C4-27z and C4opt-27z CAR T cells exhibit significant proliferation in vivo, facilitate the complete regression of fully disseminated human ovarian cancer xenografts in mice and reduce the progression of solid ovarian cancer. These results advocate for rapid progression of C4opt-27z RNA CAR to the clinic and establish a new paradigm for preclinical optimization and validation of RNA CAR candidates destined for clinical translation.

Pluripotent state induction in mouse embryonic fibroblast using mRNAs of reprogramming factors

Reprogramming of somatic cells has great potential to provide therapeutic treatments for a number of diseases as well as provide insight into mechanisms underlying early embryonic development. Improvement of induced Pluripotent Stem Cells (iPSCs) generation through mRNA-based methods is currently an area of intense research. This approach provides a number of advantages over previously used methods such as DNA integration and insertional mutagenesis. Using transfection of specifically synthesized mRNAs of various pluripotency factors, we generated iPSCs from mouse embryonic fibroblast (MEF) cells. The genetic, epigenetic and functional properties of the iPSCs were evaluated at different times during the reprogramming process. We successfully introduced synthesized mRNAs, which localized correctly inside the cells and exhibited efficient and stable translation into proteins. Our work demonstrated a robust up-regulation and a gradual promoter de-methylation of the pluripotency markers, including non-transfected factors such as Nanog, SSEA-1 (stage-specific embryonic antigen 1) and Rex-1 (ZFP-42, zinc finger protein 42). Using embryonic stem cells (ESCs) conditions to culture the iPS cells resulted in formation of ES-like colonies after approximately 12 days with only five daily repeated transfections. The colonies were positive for alkaline phosphatase and pluripotency-specific markers associated with ESCs. This study revealed the ability of pluripotency induction and generation of mouse mRNA induced pluripotent stem cells (mRNA iPSCs) using transfection of specifically synthesized mRNAs of various pluripotency factors into mouse embryonic fibroblast (MEF) cells. These generated iPSCs exhibited molecular and functional properties similar to ESCs, which indicate that this method is an efficient and viable alternative to ESCs and can be used for further biological, developmental and therapeutic investigations.

In vivo imaging of T cells loaded with gold nanoparticles: a pilot study

PURPOSE

Malignant tumours develop strategies to avoid immune recognition and elimination by T cells, even in individuals with a fully functioning immune system. To explore the treatment approach of adoptive immunotherapy, we exploited T cells loaded with radiolabelled gold nanoparticles (AuNPs) to track T cells in vivo.

MATERIALS AND METHODS

Surface-modified AuNPs were radiolabelled with (111)In or (64)Cu. They were then transferred into T cells via electroporation. To evaluate the effectiveness of this process, T cells loaded with (111)In-radiolabelled AuNPs were injected directly into the right lung of nude mice for in vivo imaging by micro-SPECT/CT. T cells loaded with (64)Cu-radiolabelled AuNPs were then injected into the tail vein of nude mice and imaged by micro-PET/CT.

RESULTS

High uptake signals were observed in the right lung following the direct injection of T cells containing (111)In-labelled AuNPs. Imaging showed a marked difference in the dynamic biodistribution of T cells containing (64)Cu-labelled AuNPs when compared with (64)Cu-labelled AuNPs alone.

CONCLUSIONS

This study demonstrated the feasibility of the in vivo imaging of T cells loaded with radiolabelled AuNPs.

Cell-penetrating peptide-mediated delivery of TALEN proteins via bioconjugation for genome engineering

Transcription activator-like (TAL) effector nucleases (TALENs) have enabled the introduction of targeted genetic alterations into a broad range of cell lines and organisms. These customizable nucleases are comprised of programmable sequence-specific DNA-binding modules derived from TAL effector proteins fused to the non-specific FokI cleavage domain. Delivery of these nucleases into cells has proven challenging as the large size and highly repetitive nature of the TAL effector DNA-binding domain precludes their incorporation into many types of viral vectors. Furthermore, viral and non-viral gene delivery methods carry the risk of insertional mutagenesis and have been shown to increase the off-target activity of site-specific nucleases. We previously demonstrated that direct delivery of zinc-finger nuclease proteins enables highly efficient gene knockout in a variety of mammalian cell types with reduced off-target effects. Here we show that conjugation of cell-penetrating poly-Arg peptides to a surface-exposed Cys residue present on each TAL effector repeat imparted cell-penetrating activity to purified TALEN proteins. These modifications are reversible under reducing conditions and enabled TALEN-mediated gene knockout of the human CCR5 and BMPR1A genes at rates comparable to those achieved with transient transfection of TALEN expression vectors. These findings demonstrate that direct protein delivery, facilitated by conjugation of chemical functionalities onto the TALEN protein surface, is a promising alternative to current non-viral and viral-based methods for TALEN delivery into mammalian cells.

Advances in siRNA delivery to T-cells: potential clinical applications for inflammatory disease, cancer and infection

The specificity of RNAi and its ability to silence ‘undruggable’ targets has made inhibition of gene expression in T-cells with siRNAs an attractive potential therapeutic strategy for the treatment of inflammatory disease, cancer and infection. However, delivery of siRNAs into primary T-cells represents a major hurdle to their use as potential therapeutic agents. Recent advances in siRNA delivery through the use of electroporation/nucleofection, viral vectors, peptides/proteins, nanoparticles, aptamers and other agents have now enabled efficient gene silencing in primary T-cells both in vitro and in vivo. Overcoming such barriers in siRNA delivery offers exciting new prospects for directly targeting T-cells systemically with siRNAs, or adoptively transferring T-cells back into patients following ex vivo manipulation with siRNAs. In the present review, we outline the challenges in delivering siRNAs into primary T-cells and discuss the mechanism and therapeutic opportunities of each delivery method. We emphasize studies that have exploited RNAi-mediated gene silencing in T-cells for the treatment of inflammatory disease, cancer and infection using mouse models. We also discuss the potential therapeutic benefits of manipulating T-cells using siRNAs for the treatment of human diseases.

Large volume flow electroporation of mRNA: clinical scale process

Genetic modification for enhancing cellular function has been continuously pursued for fighting diseases. Messenger RNA (mRNA) transfection is found to be a promising solution in modifying hematopoietic and immune cells for therapeutic purpose. We have developed a flow electroporation-based system for large volume electroporation of cells with various molecules, including mRNA. This allows robust and scalable mRNA transfection of primary cells of different origin. Here we describe transfection of chimeric antigen receptor (CAR) mRNA into NK cells to modulate the ability of NK cells to target tumor cells. High levels of CAR expression in NK cells can be maintained for 3-7 days post transfection. CD19-specific CAR mRNA transfected NK cells demonstrate targeted lysis of CD19-expressing tumor cells OP-1, primary B-CLL tumor cells, and autologous CD19+ B cells in in vitro assays with enhanced potency: >80% lysis at effector-target ratio of 1:1. This allows current good manufacturing practices (cGMP) and regulatory compliant manufacture of CAR mRNA transfected NK cells for clinical delivery.

Targeted gene knockout by direct delivery of zinc-finger nuclease proteins

Zinc-finger nucleases (ZFNs) are versatile reagents that have redefined genome engineering. Realizing the full potential of this technology requires the development of safe and effective methods for delivering ZFNs into cells. We demonstrate the intrinsic cell-penetrating capabilities of the standard ZFN architecture and show that direct delivery of ZFNs as proteins leads to efficient endogenous gene disruption in various mammalian cell types with minimal off-target effects.

Expression of chimeric antigen receptors in natural killer cells with a regulatory-compliant non-viral method

Natural killer (NK) cells hold promise for cancer therapy. NK cytotoxicity can be enhanced by expression of chimeric antigen receptors that re-direct specificity toward target cells by engaging cell surface molecules expressed on target cells. We developed a regulatory-compliant, scalable non-viral approach to engineer NK cells to be target-specific based on transfection of mRNA encoding chimeric receptors. Transfection of eGFP mRNA into ex vivo expanded NK cells (N=5) or purified unstimulated NK cells from peripheral blood (N=4) resulted in good cell viability with eGFP expression in 85+/-6% and 86+/-4%, 24 h after transfection, respectively. An mRNA encoding a receptor directed against CD19 (anti-CD19-BB-z) was also transfected into NK cells efficiently. Ex vivo expanded and purified unstimulated NK cells expressing anti-CD19-BB-z exhibited enhanced cytotoxicity against CD19(+) target cells resulting in > or =80% lysis of acute lymphoblastic leukemia and B-lineage chronic lymphocytic leukemia cells at effector target ratios lower than 10:1. The target-specific cytotoxicity for anti-CD19-BB-z mRNA-transfected NK cells was observed as early as 3 h after transfection and persisted for up to 3 days. The method described here should facilitate the clinical development of NK-based antigen-targeted immunotherapy for cancer.

Characterization of BAX inhibitor-1 as a novel leukemia-associated antigen

Using dendritic cells (DCs) electroporated with whole RNA isolated from blasts of a patient with acute myeloid leukemia (AML), we were able to generate leukemia-specific cytotoxic T lymphocytes (CTLs) capable of recognizing the leucemic cells. To identify T-cell epitopes mediating lysis of malignant cells, peptides were eluted from the patient's blasts and analyzed by mass spectrometry (LC/MS)-based peptide sequencing. Using this approach, an HLA-A24-binding peptide derived from Bax inhibitor-1 (BI-1), a regulator of apoptosis pathways, was identified as an epitope recognized by the generated CTLs. To further characterize this novel antigenic peptide, CTLs were induced using DCs electroporated with RNA coding for BI-1 or pulsed with the cognate peptide. These CTLs generated from healthy donors in vitro efficiently lysed the patient's blasts as well as other HLA-matched leukemic cells. In conclusion, we identified a BI-1 peptide as a novel immunogenic tumor-associated antigen (TAA) in AML. In vitro induction of BI-1-specific CTLs by RNA transfection or pulsing of DCs with the synthetically generated peptide was a feasible and highly effective method to generate leukemia-specific CTLs. As BI-1 is (over-) expressed in a broad variety of malignancies, it may represent an interesting novel TAA in the context of cancer vaccines.

Nucleofection, an efficient nonviral method to transfer genes into human hematopoietic stem and progenitor cells

The targeted manipulation of the genetic program of single cells as well as of complete organisms has strongly enhanced our understanding of cellular and developmental processes and should also help to increase our knowledge of primary human stem cells, e.g., hematopoietic stem cells (HSCs), within the next few years. An essential requirement for such genetic approaches is the existence of a reliable and efficient method to introduce genetic elements into living cells. Retro- and lentiviral techniques are efficient in transducing primary human HSCs, but remain labor and time consuming and require special safety conditions, which do not exist in many laboratories. In our study, we have optimized the nucleofection technology, a modified electroporation strategy, to introduce plasmid DNA into freshly isolated human HSC-enriched CD34(+) cells. Using enhanced green fluorescent protein (eGFP)-encoding plasmids, we obtained transfection efficiencies of approximately 80% and a mean survival rate of 50%. Performing functional assays using GFU-GEMM and long-term culture initiating cells (LTC-IC), we demonstrate that apart from a reduction in the survival rate the nucleofection method itself does not recognizably change the short- or long-term cell fate of primitive hematopoietic cells. Therefore, we conclude, the nucleofection method is a reliable and efficient method to manipulate primitive hematopoietic cells genetically.

Gene transfer into human hematopoietic progenitor cells with an episomal vector carrying an S/MAR element

Episomally maintained self-replicating systems present attractive alternative vehicles for gene therapy applications. Recent insights into the ability of chromosomal scaffold/matrix attachment regions (S/MARs) to mediate episomal maintenance of genetic elements allowed the development of a small circular episomal vector that functions independently of virally encoded proteins. In this study, we investigated the potential of this vector, pEPI-eGFP, to mediate gene transfer in hematopoietic progenitor cell lines and primary human cells. pEPI-eGFP was episomally maintained and conferred sustained eGFP expression even in nonselective conditions in the human cell line, K562, as well as in primary human fibroblast-like cells. In contrast, in the murine erythroleukemia cell line, MEL, transgene expression was silenced through histone deacetylation, despite the vector's episomal persistence. Hematopoietic semisolid cell colonies derived from transfected human cord blood CD34(+) cells expressed eGFP, albeit at low levels. After 4 weeks, the vector is retained in approximately 1% of progeny cells. Our results provide the first evidence that S/MAR-based plasmids can function as stable episomes in primary human cells, supporting long-term transgene expression. However, they do not display universal behavior in all cell types.

Genetic modification of hematopoietic stem cells with nonviral systems: past progress and future prospects

Serious unwanted complications provoked by retroviral gene transfer into hematopoietic stem cells (HSCs) have recently raised the need for the development and assessment of alternative gene transfer vectors. Within this context, nonviral gene transfer systems are attracting increasing interest. Their main advantages include low cost, ease of handling and large-scale production, large packaging capacity and, most importantly, biosafety. While nonviral gene transfer into HSCs has been restricted in the past by poor transfection efficiency and transient maintenance, in recent years, biotechnological developments are converting nonviral transfer into a realistic approach for genetic modification of cells of hematopoietic origin. Herein we provide an overview of past accomplishments in the field of nonviral gene transfer into hematopoietic progenitor/stem cells and we point at future challenges. We argue that episomally maintained self-replicating vectors combined with physical methods of delivery show the greatest promise among nonviral gene transfer strategies for the treatment of disorders of the hematopoietic system.

High-efficiency transfection of primary human and mouse T lymphocytes using RNA electroporation

The use of nonviral gene transfer methods in primary lymphocytes has been hampered by low gene transfer efficiency and high transfection-related toxicity. In this report, high gene transfection efficiency with low transfection-related toxicity was achieved by electroporation using in vitro-transcribed mRNA. Using these methods, >90% transgene expression with >80% viable cells was observed in stimulated primary human and murine T lymphocytes transfected with GFP or mCD62L. Electroporation of unstimulated human PBMCs or murine splenocytes with GFP RNA yielded 95 and 56% GFP+ cells, respectively. Electroporation of mRNA for NY-ESO-1, MART-1, and p53 antigen-specific TCRs into human T lymphocytes redirected these lymphocytes to recognize melanoma cell lines in an MHC-restricted manner. The onset of gene expression was rapid (within 30 min) and durable (up to 7 days postelectroporation) using both GFP and TCR-mediated recognition of target cells. There was no adverse effect observed on the T lymphocytes subjected to RNA electroporation evaluated by cell growth rate, annexin-V staining of apoptotic cells, BrdU incorporation, tumor antigen-specific recognition or antigen-specific TCR affinity. The results of this study indicate that mRNA electroporation provides a powerful tool to introduce genes into both human and murine primary T lymphocytes.

RNA-based gene transfer for adult stem cells and T cells

Electroporation of mRNA has become an established method for gene transfer into dendritic cells for immunotherapeutic purposes. However, many more cell types and applications might benefit from an efficient mRNA-based gene transfer method. In this study, we investigated the potential of mRNA-based gene transfer to induce short-term transgene expression in adult stem cells and activated T cells, based on electroporation with mRNA encoding the enhanced green fluorescent protein. The results show efficient transgene expression in CD34-positive hematopoietic progenitor cells (35%), in in vitro cultured mesenchymal cells (90%) and in PHA-stimulated T cells (50%). Next to presentation of gene transfer results, potential applications of mRNA-based gene transfer in stem cells and T cells are discussed.

Gene transfer into human T lymphocytes and natural killer cells by Ad5/F35 chimeric adenoviral vectors

OBJECTIVE

Genetic modification of effector lymphocytes, such as T cells and natural killer (NK) cells, is essential for many approaches to gene-based immunotherapy of cancer. However, transduction of lymphocytes has proven difficult by currently available gene transfer methods. Previous studies have shown that chimeric fiber-modified Ad5/F35 adenoviral vectors are able to efficiently transduce hematopoietic cells including immature progenitors. In this study, we examined the gene transfer into T lymphocytes and NK cells using Ad5/F35 compared with conventional Ad5 adenovectors.

METHODS

Primary T and NK cells were isolated from healthy donors' peripheral blood leukocytes by immunomagnetic selection. Cell lines and primary lymphocytes were transduced with replication-defective Ad5/F35 and Ad5, both containing a GFP reporter gene under the control of a CMV promoter. Transduction efficiencies were monitored by flow cytometry. The function of transduced lymphocytes was assessed by analysis of proliferative responses to mitogenic agents and in mixed leukocyte reactions.

RESULTS

Transgene expression was detected in up to 45% of primary CD3+ T lymphocytes and in up to 60% of primary NK cells using Ad5/F35. In contrast, conventional Ad5 transduced less than 8% and 5% of primary T cells and NK cells, respectively. Transduction efficiencies were similar in CD4+ and CD8+ T lymphocytes, and transgene expression could be detected for up to seven days. Activation of T cells significantly enhanced the efficiency of Ad5/F35-mediated gene transfer. Adenoviral transduction of lymphocytes did not result in any impairment of proliferative functions.

CONCLUSION

The results of this study demonstrate that both T lymphocytes and NK cells can be transduced by chimeric Ad5/F35 adenoviral vectors.

Novel non-viral method for transfection of primary leukemia cells and cell lines

BACKGROUND: Tumor cells such as leukemia and lymphoma cells are possible targets for gene therapy. However, previously leukemia and lymphoma cells have been demonstrated to be resistant to most of non-viral gene transfer methods. METHODS: The aim of this study was to analyze various methods for transfection of primary leukemia cells and leukemia cell lines and to improve the efficiency of gene delivery. Here, we evaluated a novel electroporation based technique called nucleofection. This novel technique uses a combination of special electrical parameters and specific solutions to deliver the DNA directly to the cell nucleus under mild conditions. RESULTS: Using this technique for gene transfer up to 75% of primary cells derived from three acute myeloid leukemia (AML) patients and K562 cells were transfected with the green flourescent protein (GFP) reporter gene with low cytotoxicity. In addition, 49(+/- 9.7%) of HL60 leukemia cells showed expression of GFP. CONCLUSION: The non-viral transfection method described here may have an impact on the use of primary leukemia cells and leukemia cell lines in cancer gene therapy.

Reproductive tract gene transfer

OBJECTIVE

Gene therapy is a rapidly evolving novel treatment for human disease. This review discusses the latest development in gene transfer technology and its potential use in the female reproductive tract.

METHODS

A comprehensive search using the MEDLINE database was performed to review current, innovative trends in gene transfer technology. In addition, articles on reproductive tract gene transfer were reviewed.

CONCLUSION(S)

Recent developments, such as the Human Genome Project, have generated great interest in the genetic basis of human health and disease. Gene therapy is a rapidly evolving field that uses gene transfer to treat disease. Ongoing research in the field focuses on improving vector technology to enable efficient in vivo gene transfer. Although multiple techniques for gene transfer have been described, no single technique can be used in all instances. The human female reproductive tract is easily accessible and can be readily transfected. In vivo gene transfer has resulted in successful alteration of implantation rates and has demonstrated potential for use in treatment of ovarian cancer.

Efficient removal of LoxP-flanked genes by electroporation of Cre-recombinase mRNA

Introduction of Cre-recombinase in target cells is currently achieved by transfection of plasmid DNA or by viral-mediated transduction. However, efficiency of non-viral DNA transfection is often low in many cell types, and the use of viral vectors for transduction implies a more complex and laborious manipulation associated with safety issues. We have developed a non-viral non-DNA technique for rapid and highly efficient excision of LoxP-flanked DNA sequences based on electroporation of in vitro transcribed mRNA encoding Cre-recombinase. A K562-DSRed[EGFP] cell line was developed in order to measure Cre-mediated recombination by flow cytometric analysis. These cells have a stable integrated DSRed reporter gene flanked by two LoxP sites, and an EGFP reporter gene, which could only be transcribed when the coding sequence for DSRed was removed. The presented data show recombination efficiencies, as measured by appearance of EGFP-fluorescence, of up to 85% in Cre-recombinase mRNA-electroporated K562-DSRed[EGFP] cells. In conclusion, mRNA electroporation of Cre-recombinase is a powerful, safe, and clinically applicable alternative to current technologies used for excision of stably integrated LoxP-flanked DNA sequences.

The application of electroporation to transfect hematopoietic cells and to deliver drugs and vaccines transcutaneously for cancer treatment

Electroporation and the associated phenomenon of electrofusion have been widely adapted as tools to a broad range of biomedical research and therapy. In this article, we summarize our adaptation of the electroporation and electrofusion technology in two fronts of cancer research and treatment. The first is genetic manipulation of hematopoietic cells for the purpose of cancer treatment. High efficiency transfection methods have been developed to transfect NK cells, peripheral blood stem cells, and bone marrow derived dendritic cells. Hybrids of tumor cells and bone marrow derived dendritic cells have been formed by electrofusion for the purpose of tumor vaccines. The second front is the use of transcutaneous electroporation to deliver anticancer drugs and vaccines across the skin. Methods to extend the upper molecular weight limit of transcutaneous electroporation have been developed. The pro-photosensitizer drug, delta-amino levulinic acid, the anticancer drug methotrexate, and peptide vaccines designed for cancer prevention and immunotherapy have been delivered transcutaneously by electroporation. These studies hold promise for the treatment of cancers in human.

Gene therapy of lymphoma

Gene therapy offers new and promising treatment for patients with hematological malignancies. Tumor cells--lymphoma cells, for example--are possible targets for gene therapy. In general, gene therapeutic approaches require efficient gene transfer into host cells and sufficient transgene expression. Although many methods of gene transfer into mammalian cells exist, most do not allow efficient DNA transfer into primary lymphocytes. In contrast to gene transfer into tumor cells and many other cell types, which can be successfully performed using a variety of methods, the efficient expression of foreign DNA in lymphoma cells presents unique problems and challenges, requiring a careful selection of the mode of gene transfer. In this review, we discuss the current strategies for gene therapy in the treatment of lymphoma. We also summarize the current gene transfer methods for lymphoma cells and efficiency of transgene expression.

Direct transfer of p65 into T lymphocytes from systemic lupus erythematosus patients leads to increased levels of interleukin-2 promoter activity

The recent identification of a number of molecular defects in T cells from patients with systemic lupus erythematosus (SLE) has raised expectations for gene replacement therapy as an option in the treatment of these diseases. In this report, we have adapted an electroporation-based technique to transfer successfully DNA to peripheral blood T cells from normal individuals and patients with systemic lupus erythematosus and rheumatoid arthritis. Transfection efficiency, judged by the percentage of live cells expressing green fluorescence after transfection with a pGFP (green fluorescence protein), reached 32 +/- 3% in normal, 13 +/- 3% in SLE, and 17 +/- 13% in RA T cells. The transfection efficiency was slightly higher in CD8+ than in CD4+ cells, and the cells maintained acceptable (75%) viability up to the fourth post-transfection day. SLE T cells have been shown to display low levels of the p65 subunit of the NF-kappaB transcription factor and decreased production of IL-2. Since NF-kappaB contributes to the transcriptional regulation of the IL-2 promoter, the effect of the forced replenishment of p65 on IL-2 transcription was tested. The low level of interleukin-2 promoter activity in SLE T cells increased to normal levels following transfection with cDNA encoding the NF-kappaB p65 subunit. Taken together, these results demonstrate the feasibility of transfection of T cells from SLE patients by electroporation and the reversal of decreased interleukin-2 promoter activity in SLE T cells, and are an early step toward gene therapy as a method of treatment for these individuals.

Phosphorylation and O-linked glycosylation of Elf-1 leads to its translocation to the nucleus and binding to the promoter of the TCR zeta-chain

Elf-1, a member of the E 26-specific transcription factor family with a predicted molecular mass of 68 kDa, is involved in the transcriptional regulation of several hematopoietic cell genes. We demonstrate that Elf-1 exists primarily as a 98-kDa form in the nucleus and as an 80-kDa form in the cytoplasm. Phosphorylation and O-linked glycosylation contribute to the increased posttranslational molecular mass of Elf-1. The 98-kDa Elf-1 is released from the cytoplasm tethering retinoblastoma protein and moves to the nucleus, where it binds to the promoter of the TCR zeta-chain gene. Finally, the cytoplasmic 98-kDa form enters the proteasome pathway and undergoes degradation. In conclusion, different forms of Elf-1 are the products of posttranslational modifications that determine its subcellular localization, activity, and metabolic degradation.

High efficiency electroporation of human umbilical cord blood CD34+ hematopoietic precursor cells

Human umbilical cord blood provides an alternative source of hematopoietic cells for purposes of transplantation or ex vivo genetic modification. The objective of this study was to evaluate electroporation as a means to introduce foreign genes into human cord blood CD34+ cells and evaluate gene expression in CD34+/CD38(dim) and committed myeloid progenitors (CD33+, CD11b+). CD34+ cells were cultured in X-VIVO 10 supplemented with thrombopoietin, stem cell factor, and Flt-3 ligand. Electroporation efficiency and cell viability measured by flow cytometry using enhanced green fluorescent protein (EGFP) as a reporter indicated 31% +/- 2% EGFP+ /CD34+ efficiency and 77% +/- 3% viability as determined 48 hours post-electroporation. The addition of allogeneic cord blood plasma increased the efficiency to 44% +/- 5% with no effect on viability. Of the total CD34+ cells 48 hours post-electroporation, 20% were CD38(dim)/EGFP+. CD34+ cells exposed to interleukin-3, GM-CSF and G-CSF for an additional 11 days differentiated into CD33+ and CD11b+ cells, and 9% +/- 3% and 8% +/- 7% were expressing the reporter gene, respectively. We show that electroporation can be used to introduce foreign genes into early hematopoietic stem cells (CD34+/CD38(dim)), and that the introduced gene is functionally expressed following expansion into committed myeloid progenitors (CD33+, CD11b+) in response to corresponding cytokines. Further investigation is needed to determine the transgene expression in functional terminal cells derived from the genetically modified CD34+ cells, such as T cells and dendritic cells.

Targeted beta-globin gene conversion in human hematopoietic CD34(+ )and Lin(-)CD38(-)cells

Chimeric oligonucleotides have been used successfully to correct point and frameshift mutations in several cell types, as well as in animal and plant models. However, their application to primitive human blood cells has been limited. In this investigation, chimeric oligonucleotides designed to direct a site-specific nucleotide exchange in the human beta-globin gene (an A to T substitution within codon 6) were introduced into normal human CD34(+) and Lin(-)CD38(-) cells via microinjection. This A to T nucleotide exchange introduces the single site mutation responsible for sickle cell anemia. In 23% of experimental samples, gene conversion was detected in the progeny of microinjected CD34(+) and Lin(-)CD38(-) cells that were cultured for at least 4 weeks. In addition, gene conversion was detected in the erythroid progeny of Lin(-)CD38(-) cells at the mRNA level. Conversion rates as high as 10-15% in 11% (five of 44) of experimental samples were confirmed by allele-specific PCR and sequence analysis of genomic DNA from the progeny of microinjected Lin(-)CD38(-) cells. Given that as few as 10% normal hematopoietic cells are sufficient to keep patients free of sickle cell disease, the level of conversion we have achieved in some samples may well be of therapeutic benefit in patients with sickle cell disease.

Overcoming the nuclear barrier: cell cycle independent nonviral gene transfer with linear polyethylenimine or electroporation

In many cases, nonviral particle-mediated gene delivery is highly dependent on the cell cycle status of transfected cells. Here we compare particle-mediated delivery with linear polyethylenimine (PEI) and physical transfer of DNA by electroporation with branched PEI and lipofection for their ability to transfect cells at different stages of the cell cycle. In contrast to other particle-mediated delivery methods (using Lipofectamine or branched PEI) linear PEI led to only small differences (within 1 log unit) in gene transfer between HeLa cells transfected in G1 and those in S/G2. Parallel transfections (lipofection or branched PEI) resulted in 2 to > 3 log-unit differences in luciferase expression between cells transfected in G1 and S/G2. Gene transfer by electroporation also revealed hardly any cell cycle dependence and displayed completely different expression kinetics. Reporter gene expression is already very high 3 hours after electroporation with roughly the same level of reporter gene expression in all cell cycle phases. We suggest that DNA electroporation and DNA transfection with linear PEI particles have improved nuclear import characteristics relative to the other tested DNA delivery systems.

Successful and optimized in vivo gene transfer to rabbit carotid artery mediated by electronic pulse

Several gene transfer methods, including viral or nonviral vehicles have been developed, however, efficacy, safety or handling continue to present problems. We developed a nonviral and plasmid-based method for arterial gene transfer by in vivo electronic pulse, using a newly designed T-shaped electrode. Using rabbit carotid arteries, we first optimized gene transfer efficiency, and firefly luciferase gene transfer via electronic pulse under 20 voltage (the pulse length: P(on)time 20 ms, the pulse interval: P(off) time 80 ms, number of pulse: 10 times) showed the highest gene expression. Exogenous gene expression was detectable for at least up to 14 days. Electroporation-mediated gene transfer of E. coli lacZ with nuclear localizing signal revealed successful gene transfer to luminal endothelial cells and to medial cells. Histological damage was recognized as the voltage was increased but neointima formation 4 weeks after gene transfer was not induced. In vivo electroporation-mediated arterial gene transfer is readily facilitated, is safe and may prove to be an alternative form of gene transfer to the vasculature.

Optimization of culture conditions to enhance transfection of human CD34+ cells by electroporation

The ability to culture CD34+ stem cells, while maintaining their pluripotency, is essential for manipulations such as gene transfection for therapeutic trials. Human peripheral blood (PB) CD34+ cells (> or = 90% purity) were cultured for up to 4 days in serum-free culture medium supplemented with thrombopoietin (TPO), stem cell factor (SCF), Flt-3 ligand (Flt-3L), with or without PIXY321 (IL-3/GM-CSF fusion protein) and human serum. The CD34 mean fluorescence intensity (MFI) and cell cycle status were evaluated daily using flow cytometry and hypotonic propidium iodide. Prior to culture (day 0), 97.0 +/- 0.9%, 1.9 +/- 0.3% and 1.0 +/- 0.6% of the selected CD34+ cells were in G0-G1, S-phase, or G2-M, respectively. After 2-4 days in culture with TPO/SCF/Flt-3L, there was an increase in the percent of cells in S-phase to 26.4 +/- 0.1% without significant loss of CD34 MFI. The addition of PIXY321 increased.the percentage of CD34+ cells in S-phase to 36.3 +/- 4.0%, but the CD34 MFI and numbers of CFU (colony-forming units) were significantly decreased at day 3 when cultured with PIXY321 or various recombinant cytokine combinations that included IL-3 and IL-6. There is an increase from day 0 to day 4 in the percentages of CD34+ with CD38-, HLA-DR-, and c-kit(low), but not Thy-1+ cells. Electroporation with EGFP reporter gene showed that 1-2 days of pre-stimulation in X-VIVO 10 supplemented with TPO/SCF/Flt-3L was necessary and sufficient for efficient transfection. Flow cytometry analysis demonstrated that 22% of the viable cells are CD34+/EGFP+ 48 h post electroporation. The introduced reporter gene appears to be stable as determined by EGFP+/LTC-IC (long-term colony-initiating cells), at 30-40 positive colonies (16 +/- 7%) per 1 x 10(5) electroporated CD34+ cells.

Gene therapy: principles and applications to hematopoietic cells

Ever since the development of technology allowing the transfer of new genes into eukaryotic cells, the hematopoietic system has been an obvious and desirable target for gene therapy. The last 10 years have witnessed an explosion of interest in this approach to treat human disease, both inherited and acquired, with the initiation of multiple clinical protocols. All gene therapy strategies have two essential technical requirements. These are: (1) the efficient introduction of the relevant genetic material into the target cell and (2) the expression of the transgene at therapeutic levels. Conceptual and technical hurdles involved with these requirements are still the objects of active research. To date, the most widely used and best understood vectors for gene transfer in hematopoietic cells are derived from retroviruses, although they suffer from several limitations. However, as gene transfer mechanisms become more efficient and long-term gene expression is enhanced, the variety of diseases that can be tackled by gene therapy will continue to expand. However, until the problem of delivery and subsequent expression is adequately resolved, gene therapy will not realize its full potential. The first part of this review gives an overview of the gene delivery technology available at present to transfer genetic sequences in human somatic cells. The relevance of the hematopoietic system to the development of gene therapy strategies as well as hematopoietic cell-based gene therapy is discussed in the second part.