Retroviral transduction of T lymphocytes for suicide gene therapy in allogeneic stem cell transplantation

T cell receptor fingerprinting enables in-depth characterization of the interactions governing recognition of peptide-MHC complexes

The promiscuous nature of T-cell receptors (TCRs) allows T cells to recognize a large variety of pathogens, but makes it challenging to understand and control T-cell recognition. Existing technologies provide limited information about the key requirements for T-cell recognition and the ability of TCRs to cross-recognize structurally related elements. Here we present a 'one-pot' strategy for determining the interactions that govern TCR recognition of peptide-major histocompatibility complex (pMHC). We measured the relative affinities of TCRs to libraries of barcoded peptide-MHC variants and applied this knowledge to understand the recognition motif, here termed the TCR fingerprint. The TCR fingerprints of 16 different TCRs were identified and used to predict and validate cross-recognized peptides from the human proteome. The identified fingerprints differed among TCRs recognizing the same epitope, demonstrating the value of this strategy for understanding T-cell interactions and assessing potential cross-recognition before selection of TCRs for clinical development.

Suicide gene-modified killer cells as an allogeneic alternative to autologous cytokine-induced killer cell immunotherapy of hepatocellular carcinoma

Adoptive immunotherapy using autologous cytokine-induced killer (CIK) cells reduces the recurrence rate of hepatocellular carcinoma (HCC) in association with transarterial chemoembolization or radiofrequency. However, a large‑scale development of this immunotherapy remains difficult to consider in an autologous setting, considering the logistical hurdles associated with the production of this cell therapy product. A previous study has provided the in vitro and in vivo proof‑of‑concept that allogeneic suicide gene‑modified killer cells (aSGMKCs) from healthy blood donors (a cell therapy product previously demonstrated to provide anti‑leukemic effects to patients receiving allogeneic hematopoietic transplantation) may exert a potent anti‑tumor effect towards HCC. Therefore, the development of a bank of 'ready‑for‑use' aSGMKCs was proposed as an approach allowing for the development of immunotherapies that are more convenient and on a broader scale than that of autologous therapies. In the present study, aSGMKCs were compared with CIK cells generated according to three different protocols. Similar to CIK cells, the cytotoxic activity of aSGMKCs toward the Huh‑7 HCC cell line was mediated by tumor necrosis factor‑related apoptosis‑inducing ligand, tumor necrosis factor‑α and interferon‑γ. Furthermore, the frequency of natural killer (NK), NK‑like T and T cells, and their in vitro and in vivo cytotoxicity activities were similar between aSGMKCs and CIK cells. Thus, the present study demonstrated that aSGMKCs are similar to CIK cells, further suggesting the possibility for future use of aSGMKCs in the treatment of solid tumors, including HCC.

Retroviral vector insertions in T-lymphocytes used for suicide gene therapy occur in gene groups with specific molecular functions

Graft-versus-host disease (GvHD) is a severe complication in the context of allogeneic stem cell transplantation and adoptive immunotherapy. The transfer of a suicide gene into donor T-lymphocytes (TLCs) allows selective elimination of GvHD-causing cells. As retroviral gene transfer into hematopoietic stem cells can induce leukaemia, there is an urgent need also to analyze retroviral integration sites in TLCs. We examined suicide gene-transduced TLCs in four grafts and from four transplanted patients. One-hundred and fifteen integration sites were detected in vitro. Of these 90 could be mapped to the human genome; 50% (45) were located in genes and 32% (29) were detected 10 kb upstream or downstream of transcription start sites. We found a significant overrepresentation of genes encoding for proteins with receptor activity, signal transducer activity, transcription regulator activity, nucleic acid binding activity and translation regulator activity. Similar data were obtained from patient samples. Our results point to preferred vector integration patterns, which are specific for the target cell population and probably independent of selection processes. Thus, future preclinical analysis of the integration repertoire with abundant amounts of transduced cells could allow a prediction also for the in vivo situation, where target cells are scarce.

Inhibition of human immunodeficiency virus type 1 entry in cells expressing gp41-derived peptides

As the limitations of antiretroviral drug therapy, such as toxicity and resistance, become evident, interest in alternative therapeutic approaches for human immunodeficiency virus (HIV) infection is growing. We developed the first gene therapeutic strategy targeting entry of a broad range of HIV type 1 (HIV-1) variants. Infection was inhibited at the level of membrane fusion by retroviral expression of a membrane-anchored peptide derived from the second heptad repeat of the HIV-1 gp41 transmembrane glycoprotein. To achieve maximal expression and antiviral activity, the peptide itself, the scaffold for presentation of the peptide on the cell surface, and the retroviral vector backbone were optimized. This optimized construct effectively inhibited virus replication in cell lines and primary blood lymphocytes. The membrane-anchored C-peptide was also shown to bind to free gp41 N peptides, suggesting that membrane-anchored antiviral C peptides have a mode of action similar to that of free gp41 C peptides. Preclinical toxicity and efficacy studies of this antiviral vector have been completed, and clinical trials are in preparation.

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.

Suicide gene therapy: possible applications in haematopoietic disorders

Although the treatment results for some forms of haematologic malignancies are excellent, especially for the childhood acute leukaemias, there is still a significant fraction of patients that will not benefit from the therapy available today. The identification of new techniques, such as gene therapy, may therefore be of great importance for future therapeutic applications. Suicide gene therapy is one of several gene therapeutic approaches to treat cancer. A suicide gene is a gene encoding a protein, frequently an enzyme, that in itself is nontoxic to the genetically modified cell. However, when a cell is exposed to a specific nontoxic prodrug, this is selectively converted by the gene product into toxic metabolites that kill the cell. The suicide gene most commonly employed, both in experimental and a clinical settings, is herpes simplex thymidine kinase (HSVtk). Some suicide gene products also induce a so-called 'bystander effect', i.e. a toxic effect on adjacent nongene modified tumour cells and sometimes also on more distant tumour cells. The bystander effect is most evident in tumour cells that have a high number of gap junctions, cellular channels build up by proteins called connexins. Many tumours, amongst them many haematological ones, have a low number of gap junctions. Therefore, it is important to develop gap junction independent drug delivery systems. Suicide gene technology may also be used for the ex vivo purging of tumour cells in bone marrow or peripheral blood stem cell autografts or for inactivation of effector cells, such as antitumour T donor lymphocytes in allogeneic transplantation to prevent severe graft versus host reactions. New constructs, e.g. combining suicide genes and immune response enhancing genes or suicide genes and connexin inducing genes may further improve the value of suicide gene therapy.