Ex vivo gene transfer for improved adoptive immunotherapy of cancer

"Therapeutic applications of the 'NPGP' family of viral 2As"

Oligopeptide "2A" and "2A-like" sequences ("2As"; 18-25aa) are found in a range of RNA virus genomes controlling protein biogenesis through "recoding" of the host-cell translational apparatus. Insertion of multiple 2As within a single open reading frame (ORF) produces multiple proteins; hence, 2As have been used in a very wide range of biotechnological and biomedical applications. During translation, these 2A peptide sequences mediate a eukaryote-specific, self-"cleaving" event, termed "ribosome skipping" with very high efficiency. A particular advantage of using 2As is the ability to simultaneously translate a number of proteins at an equal level in all eukaryotic systems although, naturally, final steady-state levels depend upon other factors-notably protein stability. By contrast, the use of internal ribosome entry site elements for co-expression results in an unbalanced expression due to the relative inefficiency of internal initiation. For example, a 1:1 ratio is of particular importance for the biosynthesis of the heavy-chain and light-chain components of antibodies: highly valuable as therapeutic proteins. Furthermore, each component of these "artificial polyprotein" systems can be independently targeted to different sub-cellular sites. The potential of this system was vividly demonstrated by concatenating multiple gene sequences, linked via 2A sequences, into a single, long, ORF-a polycistronic construct. Here, ORFs comprising the biosynthetic pathways for violacein (five gene sequences) and β-carotene (four gene sequences) were concatenated into a single cistron such that all components were co-expressed in the yeast Pichia pastoris. In this review, we provide useful information on 2As to serve as a guide for future utilities of this co-expression technology in basic research, biotechnology, and clinical applications.

CTLA4-CD28 chimera gene modification of T cells enhances the therapeutic efficacy of donor lymphocyte infusion for hematological malignancy

Donor lymphocyte infusion (DLI) followed by hematopoietic stem cell transplantation has served as an effective prevention/treatment modality against the relapse of some hematologic tumors, such as chronic myeloid leukemia (CML). However, the therapeutic efficacies of DLI for other types of leukemia, including acute lymphocytic leukemia (ALL), have been limited thus far. Therefore, we examined whether increasing the reactivity of donor T cells by gene modification could enhance the therapeutic efficacy of DLI in a murine model of ALL. When a CTLA4-CD28 chimera gene (CTC28) in which the intracellular signaling domain of CTLA4 was replaced with the CD28 signaling domain was introduced into CD4 and CD8 T cells in DLI, the graft-versus-tumor (GVT) effect was significantly increased. This effect was correlated with an increased expansion of donor CD8 T cells in vivo, and the depletion of CD8 T cells abolished this effect. The CD8 T cell expansion and the enhanced GVT effect were dependent on the transduction of both CD4 and CD8 T cells with CTC28, which emphasizes the role of dual modification in this therapeutic effect. The CTC28-transduced T cells that expanded in vivo also exhibited enhanced functionality. Although the potentiation of the GVT effect mediated by the CTC28 gene modification of T cells was accompanied by an increase of graft-versus-host disease (GVHD), the GVHD was not lethal and was mitigated by treatment with IL-10 gene-modified third-party mesenchymal stem cells. Thus, the combined genetic modification of CD4 and CD8 donor T cells with CTC28 could be a promising strategy for enhancing the therapeutic efficacy of DLI.

Cellular immunotherapy for malignant gliomas

INTRODUCTION

Cancer immunotherapy has made much progress in recent years. Clinical trials evaluating a variety of immunotherapeutic approaches are underway in patients with malignant gliomas. Thanks to recent advancements in cell engineering technologies, infusion of ex vivo prepared immune cells have emerged as promising strategies of cancer immunotherapy.

AREAS COVERED

Herein, the authors review recent and current studies using cellular immunotherapies for malignant gliomas. Specifically, they cover the following areas: a) cellular vaccine approaches using tumor cell-based or dendritic cell (DC)-based vaccines, and b) adoptive cell transfer (ACT) approaches, including lymphokine-activated killer (LAK) cells, γδ T cells, tumor-infiltrating lymphocytes (TIL), chimeric antigen receptor (CAR)-T cells and T-cell receptor (TCR) transduced T cells.

EXPERT OPINION

While some of the recent studies have shown promising results, the ultimate success of cellular immunotherapy in brain tumor patients would require improvements in the following areas: 1) feasibility in producing cellular therapeutics; 2) identification and characterization of targetable antigens given the paucity and heterogeneity of tumor specific antigens; 3) the development of strategies to promote effector T-cell trafficking; 4) overcoming local and systemic immune suppression, and 5) proper interpretation of imaging data for brain tumor patients receiving immunotherapy.

Influence of cell physiological state on gene delivery to T lymphocytes by chimeric adenovirus Ad5F35

Adoptive transfer of genetically-modified T cells is a promising approach for treatment of both human malignancies and viral infections. Due to its ability to efficiently infect lymphocytes, the chimeric adenovirus Ad5F35 is potentially useful as an immunotherapeutic for the genetic modification of T cells. In previous studies, it was found that the infection efficiency of Ad5F35 was significantly increased without enhanced expression of the viral receptor after T cell stimulation; however, little is known about the underlying mechanism. Nonetheless, cell physiology has long been thought to affect viral infection. Therefore, we aimed to uncover the physiologic changes responsible for the increased infection efficiency of Ad5F35 following T cell stimulation. Given the complexity of intracellular transport we analyzed viral binding, entry, and escape using a Jurkat T cell model and found that both cell membrane fluidity and endosomal escape of Ad5F35 were altered under different physiological states. This, in turn, resulted in differences in the amount of virus entering cells and reaching the cytoplasm. These results provide additional insight into the molecular mechanisms underlying Ad5F35 infection of T cells and consequently, will help further the clinical application of genetically-modified T cells for immunotherapy.

Mathematical Modelling and Analysis of the Tumor Treatment Regimens with Pulsed Immunotherapy and Chemotherapy

To begin with, in this paper, single immunotherapy, single chemotherapy, and mixed treatment are discussed, and sufficient conditions under which tumor cells will be eliminated ultimately are obtained. We analyze the impacts of the least effective concentration and the half-life of the drug on therapeutic results and then find that increasing the least effective concentration or extending the half-life of the drug can achieve better therapeutic effects. In addition, since most types of tumors are resistant to common chemotherapy drugs, we consider the impact of drug resistance on therapeutic results and propose a new mathematical model to explain the cause of the chemotherapeutic failure using single drug. Based on this, in the end, we explore the therapeutic effects of two-drug combination chemotherapy, as well as mixed immunotherapy with combination chemotherapy. Numerical simulations indicate that combination chemotherapy is very effective in controlling tumor growth. In comparison, mixed immunotherapy with combination chemotherapy can achieve a better treatment effect.

Enhanced NK cell adoptive antitumor effects against breast cancer in vitro via blockade of the transforming growth factor-β signaling pathway

Natural killer (NK) cells have great potential for improving cancer immunotherapy. Adoptive NK cell transfer, an adoptive immunotherapy, represents a promising nontoxic anticancer therapy. However, existing data indicate that tumor cells can effectively escape NK cell-mediated apoptosis through immunosuppressive effects in the tumor microenvironment, and the therapeutic activity of adoptive NK cell transfer is not as efficient as anticipated. Transforming growth factor-beta (TGF-β) is a potent immunosuppressant. Genetic and epigenetic events that occur during mammary tumorigenesis circumvent the tumor-suppressing activity of TGF-β, thereby permitting late-stage breast cancer cells to acquire an invasive and metastatic phenotype in response to TGF-β. To block the TGF-β signaling pathway, NK cells were genetically modified with a dominant-negative TGF-β type II receptor by optimizing electroporation using the Amaxa Nucleofector system. These genetically modified NK cells were insensitive to TGF-β and resisted the suppressive effect of TGF-β on MCF-7 breast cancer cells in vitro. Our results demonstrate that blocking the TGF-β signaling pathway to modulate the tumor microenvironment can improve the antitumor activity of adoptive NK cells in vitro, thereby providing a new rationale for the treatment of breast cancer.

Modulation of Immune Cell Functions by the E3 Ligase Cbl-b

Maintenance of immunological tolerance is a critical hallmark of the immune system. Several signaling checkpoints necessary to balance activating and inhibitory input to immune cells have been described so far, among which the E3 ligase Cbl-b appears to be a central player. Cbl-b is expressed in all leukocyte subsets and regulates several signaling pathways in T cells, NK cells, B cells, and different types of myeloid cells. In most cases, Cbl-b negatively regulates activation signals through antigen or pattern recognition receptors and co-stimulatory molecules. In line with this function, cblb-deficient immune cells display lower activation thresholds and cblb knockout mice spontaneously develop autoimmunity and are highly susceptible to experimental autoimmunity. Interestingly, genetic association studies link CBLB-polymorphisms with autoimmunity also in humans. Vice versa, the increased activation potential of cblb-deficient cells renders them more potent to fight against malignancies or infections. Accordingly, several reports have shown that cblb knockout mice reject tumors, which mainly depends on cytotoxic T and NK cells. Thus, targeting Cbl-b may be an interesting strategy to enhance anti-cancer immunity. In this review, we summarize the findings on the molecular function of Cbl-b in different cell types and illustrate the potential of Cbl-b as target for immunomodulatory therapies.

Fine-tuning Tumor Immunity with Integrin Trans-regulation

Inefficient T-cell homing to tissues limits adoptive T-cell immunotherapy of solid tumors. αLβ2 and α4β1 integrins mediate trafficking of T cells into tissues via engagement of ICAM-1 and VCAM-1, respectively. Inhibiting protein kinase A (PKA)-mediated phosphorylation of α4 integrin in cells results in an increase in αLβ2-mediated migration on mixed ICAM-1-VCAM-1 substrates in vitro, a phenomenon termed "integrin trans-regulation." Here, we created an α4(S988A)-bearing mouse, which precludes PKA-mediated α4 phosphorylation, to examine the effect of integrin trans-regulation in vivo. The α4(S988A) mouse exhibited a dramatic and selective increase in migration of lymphocytes, but not myeloid cells, to sites of inflammation. Importantly, we found that the α4(S988A) mice exhibited a marked increase in T-cell entry into and reduced growth of B16 melanomas, consistent with antitumor roles of infiltrating T cells and progrowth functions of tumor-associated macrophages. Thus, increased α4 trans-regulation of αLβ2 integrin function biases leukocyte emigration toward lymphocytes relative to myeloid cells and enhances tumor immunity.

Blocking transforming growth factor-β signaling pathway augments antitumor effect of adoptive NK-92 cell therapy

Natural killer (NK) cells hold great potential for improving the immunotherapy of cancer. However, existing data indicate that tumor cells can effectively escape NK cell-mediated apoptosis through immunosuppressive effect in the tumor microenvironment. Transforming growth factor-β (TGF-β) is a potent immunosuppressant. The present study was intended to develop a treatment strategy through adoptive transfer of TGF-β insensitive NK-92 cells. To block TGF-β signaling pathway, NK-92 cells were genetically modified with dominant negative TGF-β type II receptor (DNTβRII) by optimizing electroporation using the Amaxa Nucleofector system. These genetically modified NK-92 cells were insensitive to TGF-β and able to resist the suppressive effect of TGF-β on Calu-6 lung cancer cells in vitro. To determine the antitumor activity in vivo, recipient mice were challenged with a single subcutaneous injection of Calu-6 cells. Adoptive transfer of TGF-β insensitive NK-92 cells decreased tumor proliferation, reduced lung metastasis, produced more IFN-γ, and increased the survival rate of nude mice bearing established Calu-6 cells. Hence, we have demonstrated that blocking transforming growth factor-β signaling pathway in NK cells provides a novel therapeutic strategy and warrants further investigation.

Current status of local therapy in malignant gliomas--a clinical review of three selected approaches

Malignant gliomas are the most frequently occurring, devastating primary brain tumors, and are coupled with a poor survival rate. Despite the fact that complete neurosurgical resection of these tumors is impossible in consideration of their infiltrating nature, surgical resection followed by adjuvant therapeutics, including radiation therapy and chemotherapy, is still the current standard therapy. Systemic chemotherapy is restricted by the blood-brain barrier, while methods of local delivery, such as with drug-impregnated wafers, convection-enhanced drug delivery, or direct perilesional injections, present attractive ways to circumvent these barriers. These methods are promising ways for direct delivery of either standard chemotherapeutic or new anti-cancer agents. Several clinical trials showed controversial results relating to the influence of a local delivery of chemotherapy on the survival of patients with both recurrent and newly diagnosed malignant gliomas. Our article will review the development of the drug-impregnated release, as well as convection-enhanced delivery and the direct injection into brain tissue, which has been used predominantly in gene-therapy trials. Further, it will focus on the use of convection-enhanced delivery in the treatment of patients with malignant gliomas, placing special emphasis on potential shortcomings in past clinical trials. Although there is a strong need for new or additional therapeutic strategies in the treatment of malignant gliomas, and although local delivery of chemotherapy in those tumors might be a powerful tool, local therapy is used only sporadically nowadays. Thus, we have to learn from our mistakes in the past and we strongly encourage future developments in this field.

Death signalobody: inducing conditional cell death in response to a specific antigen

As the possibility of tumorigenesis and undesirable immune responses in patients cannot be completely excluded in gene and cell therapies, a conditional death switch to eliminate the therapeutic cells would be a valuable tool to enhance the safety of these therapies. A few ligand-receptor conditional death switches have already been developed; however, they cannot be used if patients exhibit side effects upon administration of the ligand. Here we demonstrate a death-inducing chimeric antibody named "death signalobody," in which the antigen-antibody system, having virtually infinite ligand-receptor combinations, is utilized for the activation of death signaling. We designed a death signalobody named "SFas," which has an antifluorescein single-chain variable fragment and the cytoplasmic domain of Fas. SFas efficiently induced conditional apoptosis in murine pro-B Ba/F3 cells in response to fluorescein-conjugated bovine serum albumin. Moreover, SFas was also able to induce antigen-dependent conditional apoptosis in human cancer cell lines. The death signalobody technique will be a valuable tool for the conditional elimination of cells of interest in multiple therapeutic applications.

An Influenza Virus M2 Protein Specific Chimeric Antigen Receptor Modulates Influenza A/WSN/33 H1N1 Infection In Vivo

A potential target for the development of universal vaccine strategies against Influenza A is the M2 protein – a membrane protein with a highly conserved extracellular domain. In this study we developed engineered T-cell receptors, by fusing M2-specific antibody sequences with T-cell receptor transmembrane and signaling domains to target influenza infected cells. When expressed on T-cells, these novel T-cell receptors (chimeric antigen receptors - CARs) are able to recognize specific antigens on the surface of target cells via an MHC-independent mechanism. Using an existing monoclonal antibody (14C2) specific for the M2 ectodomain (M2e), we generated an M2-specific CAR. We tested the specificity of this M2 CAR in vitro by measuring the activation of T-cells in response to M2-specific peptides or M2-expressing cell lines. Both Jurkat T-cells and peripheral blood mononuclear cells expressing the M2-specific CAR responded to specific antigen stimulation by upregulating NFAT and producing γ-interferon. To test whether the M2-specific CAR are effective at recognizing influenza infected cells in vivo we used an established BALB/c murine infection model. At day 4 post-infection, when M2 CAR expressing splenocytes could be detected in the lung, the Influenza A/WSN/33 virus titre was around 50% of that in control mice. Although the lung virus titre later increased in the treated group, virus was cleared in both groups of mice by day 8. The results provide support for the development of M2e as a target for cell mediated immunotherapy.

Passive immunotherapeutic strategies for the treatment of malignant gliomas

This review provides historical and recent perspectives related to passive immunotherapy for high-grade gliomas. The authors discuss approaches that use lymphokine-activated killer cells, cytotoxic T lymphocytes, and monoclonal antibodies.

Successful allogeneic hematopoietic cell engraftment after a minimal conditioning regimen in children with relapsed or refractory solid tumors

Children with relapsed or refractory solid tumors face dismal prognoses, and novel therapies are desperately needed. Allogeneic hematopoietic cell transplantation (HCT) offers potential for cell-based therapy, but the toxicity of myeloablation limits this approach in heavily pretreated patients. We sought to determine the feasibility of HCT in a cohort of 24 children with incurable solid tumors using human leukocyte antigen-matched sibling or unrelated donors and a minimal conditioning regimen. Before stem cell infusion, all patients received 3 daily doses of 30 mg/m(2) fludarabine followed by 2 Gy of total body irradiation. Hematopoietic cell recovery was rapid and reliable. Median time to neutrophil engraftment was 13.5 days for sibling donors and 12 days for unrelated donors. Donor lymphocyte infusions were used safely in 4 patients, all of whom had either improved chimerism or apparent tumor response. Graft-versus-host disease was comparable across donor sources and did not affect survival. Relapse remains a substantial barrier, although objective graft-versus-tumor effect was observed in several patients. Four patients with detectable disease before HCT achieved a complete response for at least 30 days after HCT, and two remain long-term survivors. Three patients were in complete response before HCT and remained in remission for 3, 6, and 74 months after HCT. Early disease response was associated with improved survival. Allogeneic HCT using this conditioning regimen offers a potential platform for novel immunotherapies.

Genetic modification of lymphocytes by retrovirus-based vectors

The genetic modification of lymphocytes is an important topic in the emerging field of gene therapy. Many clinical trials targeting immunodeficiency syndromes or cancer have shown therapeutic benefit; further applications address inflammatory and infectious disorders. Retroviral vector development requires a detailed understanding of the interactions with the host. Most researchers have used simple gammaretroviral vectors to modify lymphocytes, either directly or via hematopoietic stem and progenitor cells. Lentiviral, spumaviral (foamyviral) and alpharetroviral vectors were designed to reduce the necessity for cell stimulation and to utilize potentially safer integration properties. Novel surface modifications (pseudotyping) and transgenes, built using synthetic components, expand the retroviral toolbox, altogether promising increased specificity and potency. Product consistency will be an important criterion for routine clinical use.

Expression of IL-15 in NK cells results in rapid enrichment and selective cytotoxicity of gene-modified effectors that carry a tumor-specific antigen receptor

Natural killer (NK) cells hold promise for adoptive cancer immunotherapy but are dependent on cytokines such as interleukin (IL)-2 for growth and cytotoxicity. Here, we investigated the consequences of ectopic expression of IL-15 in human NK cells. IL-2 and IL-15 belong to the common γ chain family of cytokines and have overlapping activities. Transduction of clinically applicable NK-92 cells with lentiviral vectors encoding human IL-15 resulted in predominantly intracellular expression of the cytokine, and STAT5 activation, proliferation and cytotoxicity of the producer cells in the absence of IL-2. Growth of non-transduced bystander cells was not supported, allowing rapid enrichment of gene-modified cells solely by IL-2 withdrawal. This was also the case upon transduction of NK-92 and NKL cells with a bicistronic lentiviral vector encoding IL-15 and a chimeric antigen receptor (CAR) targeting the pancarcinoma antigen EpCAM. Effector cells co-expressing CAR and IL-15 continued to proliferate in the absence of exogenous cytokines and displayed high and selective cell-killing activity against EpCAM-expressing breast carcinoma cells that were resistant to the natural cytotoxicity of unmodified NK cells. This strategy facilitates rapid isolation and continuous expansion of retargeted NK cells and may extend their potential clinical utility.

Armed and accurate: engineering cytotoxic T cells for eradication of leukemia

Translational medicine depends on a rapid and efficient exchange of results between the bench and the bedside. A recent example from the field of cancer immunotherapy highlights the essential nature of this exchange. Methods have been developed to convert a patient's cytotoxic T cells into efficient and specific killers of cancer cells in patients with leukemia. By using recombinant DNA techniques, a lentiviral vector was constructed to express chimeric antigen receptors in cytotoxic T cells from patients with advanced chronic lymphocytic leukemia. The purpose of the chimeric receptors was to direct the cytotoxic T cell activity against cells causing the cancer. The effect of infusing the engineered T cells back into the cancer patients was tested in a Phase I trial at the University of Pennsylvania, and the initial results were described in two articles from the research team of Dr. Carl June. The remarkable success of this trial should energize further applications of biotechnology in the development of new cancer immunotherapies.

A short perspective on gene therapy: Clinical experience on gene therapy of gliomablastoma multiforme

More than two decades have passed since the first gene therapy clinical trial was conducted. During this time, we have gained much knowledge regarding gene therapy in general, but also learned to understand the fear that persists in society. We have experienced drawbacks and successes. More than 1700 clinical trials have been conducted where gene therapy is used as a means for therapy. In the very first trial, patients with advanced melanoma were treated with tumor infiltrating lymphocytes genetically modified ex-vivo to express tumor necrosis factor. Around the same time the first gene therapy trial was conducted, the ethical aspects of performing gene therapy on humans was intensively discussed. What are the risks involved with gene therapy? Can we control the technology? What is ethically acceptable and what are the indications gene therapy can be used for? Initially, gene therapy was thought to be implemented mainly for the treatment of monogenetic diseases, such as adenosine deaminase deficiency. However, other therapeutic areas have become of interest and currently cancer is the most studied therapeutic area for gene therapy based medicines. In this review I will be giving a short introduction into gene therapy and will direct the discussion to where we should go from here. Furthermore, I will focus on the use of the Herpes simplex virus-thymidine kinase for gene therapy of malignant gliomas and highlight the efficacy of gene therapy for the treatment of malignant gliomas, but other strategies will also be mentioned.