Functional transfer of CD40L gene in human B-cell precursor ALL blasts by second-generation SIN lentivectors

Anti-CD19 CARs displayed at the surface of lentiviral vector particles promote transduction of target-expressing cells

Recently, a rare type of relapse was reported upon treating a B cell acute lymphoblastic leukemia (B-ALL) patient with anti-CD19 chimeric antigen receptor (CAR)-T cells caused by unintentional transduction of residual malignant B cells (CAR-B cells). We show that anti-CD19 and anti-CD20 CARs are presented on the surface of lentiviral vectors (LVs), inducing specific binding to the respective antigen. Binding of anti-CD19 CAR-encoding LVs containing supernatant was reduced by CD19-specific blocking antibodies in a dose-dependent manner, and binding was absent for unspecific LV containing supernatant. This suggests that LVs bind via displayed CAR molecules to CAR antigen-expressing cells. The relevance for CAR-T cell manufacturing was evaluated when PBMCs and B-ALL malignant B cells were mixed and transduced with anti-CD19 or anti-CD20 CAR-displaying LVs in clinically relevant doses to mimic transduction conditions of unpurified patient leukapheresis samples. Malignant B cells were transduced at higher levels with LVs displaying anti-CD19 CARs compared to LVs displaying non-binding control constructs. Stability of gene transfer was confirmed by applying a potent LV inhibitor and long-term cultures for 10 days. Our findings provide a potential explanation for the emergence of CAR-B cells pointing to safer manufacturing procedures with reduced risk of this rare type of relapse in the future.

Human mesenchymal stromal/stem cells recruit resident pericytes and induce blood vessels maturation to repair experimental spinal cord injury in rats

Angiogenesis is considered to mediate the beneficial effects of mesenchymal cell therapy in spinal cord injury. After a moderate balloon-compression injury in rats, injections of either human adipose tissue-derived stromal/stem cells (hADSCs) or their conditioned culture media (CM-hADSC) elicited angiogenesis around the lesion site. Both therapies increased vascular density, but the presence of hADSCs in the tissue was required for the full maturation of new blood vessels. Only animals that received hADSC significantly improved their open field locomotion, assessed by the BBB score. Animals that received CM-hADSC only, presented haemorrhagic areas and lack pericytes. Proteomic analyses of human angiogenesis-related factors produced by hADSCs showed that both pro- and anti-angiogenic factors were produced by hADSCs in vitro, but only those related to vessel maturation were detectable in vivo. hADSCs produced PDGF-AA only after insertion into the injured spinal cord. hADSCs attracted resident pericytes expressing NG2, α-SMA, PDGF-Rβ and nestin to the lesion, potentially contributing to blood vessel maturation. We conclude that the presence of hADSCs in the injured spinal cord is essential for tissue repair.

An Efficient Electroporation Protocol for the Genetic Modification of Mammalian Cells

Genetic modification of cell lines and primary cells is an expensive and cumbersome approach, often involving the use of viral vectors. Electroporation using square-wave generating devices, like Lonza's Nucleofector, is a widely used option, but the costs associated with the acquisition of electroporation kits and the transient transgene expression might hamper the utility of this methodology. In the present work, we show that our in-house developed buffers, termed Chicabuffers, can be efficiently used to electroporate cell lines and primary cells from murine and human origin. Using the Nucleofector II device, we electroporated 14 different cell lines and also primary cells, like mesenchymal stem cells and cord blood CD34+, providing optimized protocols for each of them. Moreover, when combined with sleeping beauty-based transposon system, long-term transgene expression could be achieved in all types of cells tested. Transgene expression was stable and did not interfere with CD34+ differentiation to committed progenitors. We also show that these buffers can be used in CRISPR-mediated editing of PDCD1 gene locus in 293T and human peripheral blood mononuclear cells. The optimized protocols reported in this study provide a suitable and cost-effective platform for the genetic modification of cells, facilitating the widespread adoption of this technology.

Human mesenchymal cells from adipose tissue deposit laminin and promote regeneration of injured spinal cord in rats

Cell therapy is a promising strategy to pursue the unmet need for treatment of spinal cord injury (SCI). Although several studies have shown that adult mesenchymal cells contribute to improve the outcomes of SCI, a description of the pro-regenerative events triggered by these cells is still lacking. Here we investigated the regenerative properties of human adipose tissue derived stromal cells (hADSCs) in a rat model of spinal cord compression. Cells were delivered directly into the spinal parenchyma immediately after injury. Human ADSCs promoted functional recovery, tissue preservation, and axonal regeneration. Analysis of the cord tissue showed an abundant deposition of laminin of human origin at the lesion site and spinal midline; the appearance of cell clusters composed of neural precursors in the areas of laminin deposition, and the appearance of blood vessels with separated basement membranes along the spinal axis. These effects were also observed after injection of hADSCs into non-injured spinal cord. Considering that laminin is a well-known inducer of axonal growth, as well a component of the extracellular matrix associated to neural progenitors, we propose that it can be the paracrine factor mediating the pro-regenerative effects of hADSCs in spinal cord injury.

An efficient low cost method for gene transfer to T lymphocytes

Gene transfer to T lymphocytes has historically relied on retro and lentivirus, but recently transposon-based gene transfer is rising as a simpler and straight forward approach to achieve stable transgene expression. Transfer of expression cassettes to T lymphocytes remains challenging, being based mainly on commercial kits.

AIMS

We herein report a convenient and affordable method based on in house made buffers, generic cuvettes and utilization of the widely available Lonza nucleofector II device to promote efficient gene transfer to T lymphocytes.

RESULTS

This approach renders high transgene expression levels in primary human T lymphocytes (mean 45%, 41-59%), the hard to transfect murine T cells (mean 38%, 36-42% for C57/BL6 strain) and human Jurkat T cell line. Cell viability levels after electroporation allowed further manipulations such as in vitro expansion and Chimeric Antigen Receptor (CAR) mediated gain of function for target cell lysis.

CONCLUSIONS

We describe here an efficient general protocol for electroporation based modification of T lymphocytes. By opening access to this protocol, we expect that efficient gene transfer to T lymphocytes, for transient or stable expression, may be achieved by an increased number of laboratories at lower and affordable costs.

pLR: a lentiviral backbone series to stable transduction of bicistronic genes and exchange of promoters

Gene transfer based on lentiviral vectors allow the integration of exogenous genes into the genome of a target cell, turning these vectors into one of the most used methods for stable transgene expression in mammalian cells, in vitro and in vivo. Currently, there are no lentivectors that allow the cloning of different genes to be regulated by different promoters. Also, there are none that permit the analysis of the expression through an IRES (internal ribosome entry site)-- reporter gene system. In this work, we have generated a series of lentivectors containing: (1) a malleable structure to allow the cloning of different target genes in a multicloning site (mcs); (2) unique site to exchange promoters, and (3) IRES followed by one of two reporter genes: eGFP or DsRed. The series of the produced vectors were named pLR (for lentivirus and RSV promoter) and were fairly efficient with a strong fluorescence of the reporter genes in direct transfection and viral transduction experiments. This being said, the pLR series have been found to be powerful biotechnological tools for stable gene transfer and expression.

T cells stimulated by CD40L positive leukemic blasts-pulsed dendritic cells meet optimal functional requirements for adoptive T-cell therapy

Adoptive T-cell immunotherapy may provide complementary therapy for childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL). In this study, we have analyzed the functional characteristics of anti-BCP-ALL effector T cells generated by co-culturing T lymphocytes and dendritic cells (DC) from allogeneic human stem cell transplantation (HSCT) donors. After 21-day co-culture with DC pulsed with CD40L+ apoptotic BCP-ALL blasts, T cells presented with both effector and central memory phenotype, and showed high and specific cytotoxic activity against leukemic cells (average lysis = 77%), mostly mediated by CD8+ T cells. Noticeably, growth of CD4 T cells was maintained (45% of total cells), which actively produced Th1 cytokines (IFN-gamma, TNF-alpha, IL-2), but not IL-4, IL-5 and IL-10. Anti-BCP-ALL T cells expressed CD49d and CXCR4 (implicated in the recruitment to bone marrow), and CD62L and CCR7 (involved in the migration to lymphoid organs). In accordance with this profile, T cells significantly migrated in response to the chemokines CXCL12 and CCL19. In conclusion, stimulation of T cells with CD40L+BCP-ALL cells-loaded DC not only elicited the generation of potent and specific anti-leukemic cytotoxic effectors, but also the differentiation of specific and functional Th-1 CD4 lymphocytes. These effectors are fully equipped to reach leukemia-infiltrated tissues and have characteristics to support and orchestrate the anti-tumor immune-response.

Epstein-Barr virus vector-mediated gene transfer into human B cells: potential for antitumor vaccination

The efficient gene transfer of immunostimulatory cytokines into autologous tumor cells or the transfer of tumor-associated antigens into professional antigen-presenting cells is a prerequisite for many immunotherapeutic approaches. In particular with B cells, the efficiency of gene uptake is one of the limiting factors in cell-based vaccine strategies, since normal and malignant human B cells are commonly refractory to transducing gene vectors. Due to its natural tropism for human B cells, Epstein-Barr virus (EBV), a human herpes virus, might be an option, which we wanted to explore. EBV efficiently infects human B cells and establishes a latent infection, while the viral genome is maintained extrachromosomally. Although these characteristics are attractive, EBV is an oncogenic virus. Here, we present a novel EBV-derived vector, which lacks three EBV genes including two viral oncogenes and an essential lytic gene, and encodes granulocyte-macrophage colony-stimulating factor (GM-CSF) as a cytokine of therapeutic interest. We could show that EBV vectors efficiently transduce different B-cell lines, primary resting B cells, and tumor cells of B-cell lineage. Vector-derived GM-CSF was expressed in sufficient amounts to support the maturation of dendritic cells and their presentation of model antigens to cognate T-cell clones in autologous settings and an allogeneic, HLA-matched assay. We conclude that the EBV vector system might offer an option for ex vivo manipulation of B cells and gene therapy of B-cell lymphomas.

Potential use of CD40 ligand for immunotherapy of childhood B-cell precursor acute lymphoblastic leukaemia

Around 20% of children affected by B-cell precursor acute lymphoblastic leukaemia (BCP-ALL) still experience a recurrence of the disease after diagnosis, despite a significant improvement in the cure rate (80%). Moreover, standard therapies have high and often unacceptable acute and chronic organ toxicity, with an increased risk for secondary malignancies. Therefore, new strategies are needed to improve overall survival and decrease treatment-associated morbidity. Recent in-vitro and in-vivo studies have demonstrated that CD40 engagement improves tumour immunogenicity and, consequently, generates a strong antitumour immune response. The CD40-CD40 ligand (CD40L) system is of pivotal importance in the immune response via interactions between T cells and antigen-presenting cells. The general aim of this chapter is to review the feasibility of developing cellular strategies to increase childhood BCP-ALL immunogenicity, and the potential use of CD40L as a new strategy to induce an antileukaemia immune response in BCP-ALL.

Molecular evidence of inefficient transduction of proliferating human B lymphocytes by VSV-pseudotyped HIV-1-derived lentivectors

Lentiviral vectors are attractive tools to transduce dividing and nondividing cells. Human tonsillar B lymphocytes have been purified and induced to proliferate by the addition of anti-CD40 + IL-4 or anti-CD40 + anti-micro signals and transduced at high MOI with a VSV pseudotyped lentivector carrying the eGFP gene under the control of the PGK promoter. Parallel cultures of PHA-stimulated T lymphocytes containing a comparable amount of cycling cells during the infection reached over 70% eGFP transduction. By contrast, only less than 3% B lymphocytes became eGFP positive after 7 days from transduction. Molecular analysis of the viral life cycle shows that cytoplasmic retrotranscribed cDNA and nuclear 2LTR circles are detectable at lower levels and for a shorter period of time in proliferating B cells with respect to proliferating T lymphocytes. Moreover, FACS-sorted eGFP-positive and negative B cell populations were both positive for the presence of retrotranscribed cDNA and 2LTR circles nuclear forms. By contrast, nested Alu-LTR PCR allowed us to detect an integrated provirus in FACS-sorted eGFP-positive cells only. Together with the demonstration that infection in saturation conditions led to an increase in the percentage of transduced cells (reaching 9%), these findings suggest that in proliferating B lymphocytes, lentiviral transduction is an inefficient process blocked at the early steps of the viral life cycle possibly involving partially saturable restriction factors.