Induced transgene expression for the treatment of solid tumors by hematopoietic stem cell-based gene therapy

Cell-based therapies for glioblastoma: Promising tools against tumor heterogeneity

Glioblastoma (GBM) is a highly aggressive tumor with a devastating impact on quality-of-life and abysmal survivorship. Patients have very limited effective treatment options. The successes of targeted small molecule drugs and immune checkpoint inhibitors seen in various solid tumors have not translated to GBM, despite significant advances in our understanding of its molecular, immune, and microenvironment landscapes. These discoveries, however, have unveiled GBM's incredible heterogeneity and its role in treatment failure and survival. Novel cellular therapy technologies are finding successes in oncology and harbor characteristics that make them uniquely suited to overcome challenges posed by GBM, such as increased resistance to tumor heterogeneity, modularity, localized delivery, and safety. Considering these advantages, we compiled this review article on cellular therapies for GBM, focusing on cellular immunotherapies and stem cell-based therapies, to evaluate their utility. We categorize them based on their specificity, review their preclinical and clinical data, and extract valuable insights to help guide future cellular therapy development.

A Novel Splice Variant of Human TGF-β Type II Receptor Encodes a Soluble Protein and Its Fc-Tagged Version Prevents Liver Fibrosis in vivo

We describe, for the first time, a new splice variant of the human TGF-β type II receptor (TβRII). The new transcript lacks 149 nucleotides, resulting in a frameshift and the emergence of an early stop codon, rendering a truncated mature protein of 57 amino acids. The predicted protein, lacking the transmembrane domain and with a distinctive 13-amino-acid stretch at its C-terminus, was named TβRII-Soluble Endogenous (TβRII-SE). Binding predictions indicate that the novel 13-amino-acid stretch interacts with all three TGF-β cognate ligands and generates a more extensive protein–protein interface than TβRII. TβRII-SE and human IgG1 Fc domain were fused in frame in a lentiviral vector (Lv) for further characterization. With this vector, we transduced 293T cells and purified TβRII-SE/Fc by A/G protein chromatography from conditioned medium. Immunoblotting revealed homogeneous bands of approximately 37 kDa (reduced) and 75 kDa (non-reduced), indicating that TβRII-SE/Fc is secreted as a disulfide-linked homodimer. Moreover, high-affinity binding of TβRII-SE to the three TGF-β isoforms was confirmed by surface plasmon resonance (SPR) analysis. Also, intrahepatic delivery of Lv.TβRII-SE/Fc in a carbon tetrachloride-induced liver fibrosis model revealed amelioration of liver injury and fibrosis. Our results indicate that TβRII-SE is a novel member of the TGF-β signaling pathway with distinctive characteristics. This novel protein offers an alternative for the prevention and treatment of pathologies caused by the overproduction of TGF-β ligands.

Hematopoietic stem cell gene therapy targeting TGFβ enhances the efficacy of irradiation therapy in a preclinical glioblastoma model

Patients with glioblastoma (GBM) have a poor prognosis, and inefficient delivery of drugs to tumors represents a major therapeutic hurdle. Hematopoietic stem cell (HSC)-derived myeloid cells efficiently home to GBM and constitute up to 50% of intratumoral cells, making them highly appropriate therapeutic delivery vehicles. Because myeloid cells are ubiquitously present in the body, we recently established a lentiviral vector containing matrix metalloproteinase 14 (MMP14) promoter, which is active specifically in tumor-infiltrating myeloid cells as opposed to myeloid cells in other tissues, and resulted in a specific delivery of transgenes to brain metastases in HSC gene therapy. Here, we used this novel approach to target transforming growth factor beta (TGFβ) as a key tumor-promoting factor in GBM. Transplantation of HSCs transduced with lentiviral vector expressing green fluorescent protein (GFP) into lethally irradiated recipient mice was followed by intracranial implantation of GBM cells. Tumor-infiltrating HSC progeny was characterized by flow cytometry. In therapy studies, mice were transplanted with HSCs transduced with lentiviral vector expressing soluble TGFβ receptor II-Fc fusion protein under MMP14 promoter. This TGFβ-blocking therapy was compared with the targeted tumor irradiation, the combination of the two therapies, and control. Tumor growth and survival were quantified (statistical significance determined by t-test and log-rank test). T cell memory response was probed through a repeated tumor challenge. Myeloid cells were the most abundant HSC-derived population infiltrating GBM. TGFβ-blocking HSC gene therapy in combination with irradiation significantly reduced tumor burden as compared with monotherapies and the control, and significantly prolonged survival as compared with the control and TGFβ-blocking monotherapy. Long-term protection from GBM was achieved only with the combination treatment (25% of the mice) and was accompanied by a significant increase in CD8+ T cells at the tumor implantation site following tumor rechallenge. We demonstrated a preclinical proof-of-principle for tumor myeloid cell-specific HSC gene therapy in GBM. In the clinic, HSC gene therapy is being successfully used in non-cancerous brain disorders and the feasibility of HSC gene therapy in patients with glioma has been demonstrated in the context of bone marrow protection. This indicates an opportunity for clinical translation of our therapeutic approach.

Towards Clinical Implementation of Adeno-Associated Virus (AAV) Vectors for Cancer Gene Therapy: Current Status and Future Perspectives

Adeno-associated virus (AAV) vectors have gained tremendous attention as in vivo delivery systems in gene therapy for inherited monogenetic diseases. First market approvals, excellent safety data, availability of large-scale production protocols, and the possibility to tailor the vector towards optimized and cell-type specific gene transfer offers to move from (ultra) rare to common diseases. Cancer, a major health burden for which novel therapeutic options are urgently needed, represents such a target. We here provide an up-to-date overview of the strategies which are currently developed for the use of AAV vectors in cancer gene therapy and discuss the perspectives for the future translation of these pre-clinical approaches into the clinic.

Concise Review: Modulating Cancer Immunity with Hematopoietic Stem and Progenitor Cells

Hematopoietic stem and progenitor cells (HSPCs) are the progenitor cells that can regenerate the entire blood compartment, including the immune system. Recent studies have unearthed considerable immune-modulating potential of these cells. They can migrate through chemotactic gradients, differentiate into functional immune cells, and crosstalk with immune cells during infections, autoimmune diseases, and cancers. Although the primary role of HSPCs during solid malignancies is considered immunosuppressive, recent studies have discovered immune-activating HSPCs and progeny. In this review, we will discuss the recent evidence that HSPCs act as immunomodulators during solid cancers and highlight the future directions of discovery. Stem Cells 2019;37:166-175.

Bioengineering a non-genotoxic vector for genetic modification of mesenchymal stem cells

Vectors used for stem cell transfection must be non-genotoxic, in addition to possessing high efficiency, because they could potentially transform normal stem cells into cancer-initiating cells. The objective of this research was to bioengineer an efficient vector that can be used for genetic modification of stem cells without any negative somatic or genetic impact. Two types of multifunctional vectors, namely targeted and non-targeted were genetically engineered and purified from E. coli. The targeted vectors were designed to enter stem cells via overexpressed receptors. The non-targeted vectors were equipped with MPG and Pep1 cell penetrating peptides. A series of commercial synthetic non-viral vectors and an adenoviral vector were used as controls. All vectors were evaluated for their efficiency and impact on metabolic activity, cell membrane integrity, chromosomal aberrations (micronuclei formation), gene dysregulation, and differentiation ability of stem cells. The results of this study showed that the bioengineered vector utilizing VEGFR-1 receptors for cellular entry could transfect mesenchymal stem cells with high efficiency without inducing genotoxicity, negative impact on gene function, or ability to differentiate. Overall, the vectors that utilized receptors as ports for cellular entry (viral and non-viral) showed considerably better somato- and genosafety profiles in comparison to those that entered through electrostatic interaction with cellular membrane. The genetically engineered vector in this study demonstrated that it can be safely and efficiently used to genetically modify stem cells with potential applications in tissue engineering and cancer therapy.

Co-delivery of doxorubicin and recombinant plasmid pHSP70-Plk1-shRNA by bacterial magnetosomes for osteosarcoma therapy

To explore a novel combination of chemotherapy, gene therapy, and thermotherapy for osteosarcoma, a targeted heat-sensitive co-delivery system based on bacterial magnetosomes (BMs) was developed. The optimal culture conditions of magnetotactic bacteria (MTB) AMB-1 and characterization of BMs were achieved. A recombinant eukaryotic plasmid heat shock protein 70-polo-like kinase 1-short hairpin RNA (pHSP70-Plk1-shRNA) under transcriptional control of a thermosensitive promoter (human HSP70 promoter) was constructed for gene therapy. Doxorubicin (DOX) and pHSP70-Plk1-shRNA were included in the targeted thermosensitive co-delivery system, and in vitro DOX release activity, targeted gene silencing efficiency and in vitro antitumor efficacy were investigated. The results showed that the optimal culture conditions of MTB AMB-1 are an oxygen concentration of 4.0%, a pH value of 7.0, 20 μmol/L of ferrous sulfate, 800 mg/L of sodium nitrate, and 200 mg/L of succinic acid. The temperature of BMs reached 43°C within 3 minutes and could be maintained for 30 minutes by adjusting the magnitude of the alternating magnetic field (AMF). The diameters of BMs, BM-DOX, BM-recombinant eukaryotic plasmid pHSP70-Plk1-shRNA (shPlk1), and BM-DOX-shPlk1 were 43.7±4.6, 79.2±5.4, 88.9±7.8, and 133.5±11.4 nm, respectively. The zeta potentials of BMs, BM-DOX, BM-shPlk1, and BM-DOX-shPlk1 were -29.4±6.9, -9.5±5.6, -16.7±4.8, and -10.3±3.1 mV, respectively. Besides, the system exhibited good release behavior. DOX release rate from BM-DOX-shPlk1 was 54% after incubation with phosphate-buffered saline at 43°C and 37% after incubation with 50% fetal bovine serum, which was significantly higher than that at 37°C (P<0.05). In addition, the expressions of Plk1 mRNA and protein were significantly suppressed in cells treated with BM-DOX-shPlk1 following hyperthermia treatment under the influence of an AMF compared to other groups (P<0.05). Furthermore, evaluation of the effect of in vitro antitumor revealed that BM-DOX-shPlk1 following hyperthermia treatment under the influence of an AMF was significantly more effective than others in tumor inhibition. In conclusion, the new heat-sensitive co-delivery system represents a promising approach for the treatment of cancer.

Impact of Different Promoters on Episomal Vectors Harbouring Characteristic Motifs of Matrix Attachment Regions

We previously demonstrated that the characteristic sequence of matrix attachment regions (MARs) allows transgenes to be maintained episomally in CHO cells. In the present study, six commonly used promoters from human cytomegalovirus major immediate-early (CMV), simian vacuolating virus 40 (SV40), Rous sarcoma virus, Homo sapiens ubiquitin C, phosphoglycerate kinase, and β-globin, respectively, were evaluated to determine their effects on transgene expression and stability in CHO cells stably transfected via the episomal vector harbouring characteristic MAR motifs. The CHO cells were transfected with vectors and then screened using G418, after which the stably transfected cells were split into two and further cultured either in the presence or absence of G418. Of the six promoters, the CMV promoter yielded the highest transgene expression levels and the highest transfection efficiency, whereas the SV40 promoter maintained transgene expression more stably during long-term culture than the other promoters did. The CMV and SV40 promoter-containing vectors were furthermore episomally maintained and conferred sustained eGFP expression in the cells even under nonselective conditions. On the basis of these findings, we conclude that the CMV promoter performs best in terms of yielding both high expression levels and high levels of stability using this episomal vector system.

Naive tumour-specific CD4+ T cells were efficiently primed in acute lymphoblastic leukaemia

The recognition and neutralization of tumour cells is one of the big challenges in immunity. The immune system has to recognize syngeneic tumour cells and has to be primed and respond in an adequate manner. Priming of a leukaemia-specific immune response is a crucial step in tumour immunology that can mislead to tumour tolerance either by T cell ignorance, deletion or Treg induction. To resemble the situation of acute lymphoblastic leukaemia (ALL) in patients, we used the murine BALB/c model with syngeneic BM185 tumour cells. We established a tumour cell line that expresses the neo-antigen ovalbumin (BM185-OVA/GFP) to allow the application of T cell receptor transgenic, antigen-specific CD4(+) T cells. Here, we demonstrate that effective anti-ALL immunity can be established by in vivo priming of CD4(+) T cells that is sufficient to differentiate into effector cells. Yet they failed to control tumour alone, but initiated a Th1 response. An efficient tumour clearance was dependent on both antigen-specific CD4(+) T cells and CD8(+) effector T cells from the endogenous repertoire. The tolerogeneic milieu was characterized by increased Tregs numbers and elevated IL-10 level. Tregs hamper effective antitumour immune response, but their depletion did not result in reduced tumour growth. In contrast, neutralization of IL-10 improved median mouse survival. Future therapies should focus on establishing a strong CD4+ T cells response, either by adjuvant or by adoptive transfer.

Exchange of cytosolic content between T cells and tumor cells activates CD4 T cells and impedes cancer growth

BACKGROUND

T cells are known to participate in the response to tumor cells and react with cytotoxicity and cytokine release. At the same time tumors established versatile mechanisms for silencing the immune responses. The interplay is far from being completely understood. In this study we show contacts between tumor cells and lymphocytes revealing novel characteristics in the interaction of T cells and cancer cells in a way not previously described.

METHODS/ FINDINGS

Experiments are based on the usage of a hydrophilic fluorescent dye that occurs free in the cytosol and thus transfer of fluorescent cytosol from one cell to the other can be observed using flow cytometry. Tumor cells from cell lines of different origin or primary hepatocellular carcinoma (HCC) cells were incubated with lymphocytes from human and mice. This exposure provoked a contact dependent uptake of tumor derived cytosol by lymphocytes--even in CD4⁺ T cells and murine B cells--which could not be detected after incubation of lymphocytes with healthy cells. The interaction was a direct one, not requiring the presence of accessory cells, but independent of cytotoxicity and TCR engagement. Electron microscopy disclosed 100-200 nm large gaps in the cell membranes of connected cells which separated viable and revealed astonishing outcome. While the lymphocytes were induced to proliferate in a long term fashion, the tumor cells underwent a temporary break in cell division. The in vitro results were confirmed in vivo using a murine acute lymphoblastic leukemia (ALL) model. The arrest of tumor proliferation resulted in a significant prolonged survival of challenged mice.

CONCLUSIONS

The reported cell-cell contacts reveal new characteristics i.e. the enabling of cytosol flow between the cells including biological active proteins that influence the cell cycle and biological behaviour of the recipient cells. This adds a completely new aspect in tumor induced immunology.

[Mesenchymal stem cells as an antitumor therapy tool]

Development of antitumor preparations with low toxicity and high selectivity of action is one of the top priorities of cancer gene therapy. Mesenchymal stem cells possess natural tropism towards tumors, a property that makes possible their use as a vehicle for targeted delivery of therapeutic genes into tumors of various etiologies. At present, genes encoding enzymes (cytosine deaminase, thymidine kinase, carboxyl esterase), cytokines (IL-2, IL-4, IL-12, IFN-beta) and apoptosis inducing factors (TRAIL) are used as therapeutic genes. Mesenchymal stem cells, as demonstrated using experimental models of tumors of various etiologies as well as animals with metastases in brain and lungs, are able to successfully deliver therapeutic genes into tumors and produce significant antitumor effect. However, to effectively use this therapeutic strategy in clinic, one still has to solve a number of technical problems.

Advances in stem cell therapy against gliomas

Malignant gliomas are one of the most lethal cancers, and despite extensive research very little progress has been made in improving prognosis. Multimodality treatment combining surgery, radiation, and chemotherapy is the current gold standard, but effective treatment remains difficult due to the invasive nature and high recurrence of gliomas. Stem cell-based therapy using neural, mesenchymal, or hematopoietic stem cells may be an alternative approach because it is tumor selective and allows targeted therapy that spares healthy brain tissue. Stem cells can be used to establish a long-term antitumor response by stimulating the immune system and delivering prodrug, metabolizing genes, or oncolytic viruses. In this review, we discuss current trends and the latest developments in stem cell therapy against malignant gliomas from both the experimental laboratory and the clinic.