Lack of functional Pit-1 and Pit-2 expression on hematopoietic stem cell lines

Genetically modified dendritic cells--a new, promising cancer treatment strategy?

Dendritic cells (DCs), the most potent antigen-presenting cells (APCs), were discovered almost 30 years ago. Due to the priming of antigen-specific immune responses mediated by CD4+ and CD8+ lymphocytes, DCs are crucial for the induction of adaptive immunity against cancer. Therefore, vaccination of cancer patients with DCs presenting tumour-associated antigens (TAAs) have been believed to be a promising anticancer strategy. Multiple clinical trials have been carried out in order to evaluate the safety and efficacy of cancer vaccines based on antigen-pulsed DCs. However, pulsing of DCs with particular peptides has several disadvantages: i) short-time duration of antigen-major histocompatability complex (MHC) complexes, ii) a requirement for matching defined peptides with MHC complexes and iii) exclusive presentation of single antigen epitopes. Application of gene transfer technologies in the field of DC-based vaccines made possible the development of novel, anticancer immunisation strategies. In several animal models, DCs modified with genes encoding TAA or immunostimulatory proteins have been shown to be effective in the induction of antitumour immune responses. Based on these encouraging results, a first clinical trial of prostate cancer patients vaccinated with gene modified DCs has recently been initiated. In this article, methods used for genetic modification of DCs and anticancer vaccination strategies based on genetically modified DCs are reviewed.

In vivo gene transfer using a nonprimate lentiviral vector pseudotyped with Ross River Virus glycoproteins

Vectors derived from lentiviruses provide a promising gene delivery system. We examined the in vivo gene transfer efficiency and tissue or cell tropism of a feline immunodeficiency virus (FIV)-based lentiviral vector pseudotyped with the glycoproteins from Ross River Virus (RRV). RRV glycoproteins were efficiently incorporated into FIV virions, generating preparations of FIV vector, which after concentration attain titers up to 1.5 x 10(8) TU/ml. After systemic administration, RRV-pseudotyped FIV vectors (RRV/FIV) predominantly transduced the liver of recipient mice. Transduction efficiency in the liver with the RRV/FIV was ca. 20-fold higher than that achieved with the vesicular stomatitis virus G protein (VSV-G) pseudotype. Moreover, in comparison to VSV-G, the RRV glycoproteins caused less cytotoxicity, as determined from the levels of glutamic pyruvic transaminase and glutamic oxalacetic transaminase in serum. Although hepatocytes were the main liver cell type transduced, nonhepatocytes (mainly Kupffer cells) were also transduced. The percentages of the transduced nonhepatocytes were comparable between RRV and VSV-G pseudotypes and did not correlate with the production of antibody against the transgene product. After injection into brain, RRV/FIV preferentially transduced neuroglial cells (astrocytes and oligodendrocytes). In contrast to the VSV-G protein that targets predominantly neurons, <10% of the brain cells transduced with the RRV pseudotyped vector were neurons. Finally, the gene transfer efficiencies of RRV/FIV after direct application to skeletal muscle or airway were also examined and, although transgene-expressing cells were detected, their proportions were low. Our data support the utility of RRV glycoprotein-pseudotyped FIV lentiviral vectors for hepatocyte- and neuroglia-related disease applications.

Efficient retrovirus-mediated transfer of the multidrug resistance 1 gene into autologous human long-term repopulating hematopoietic stem cells

Pre-clinical studies indicate that efficient retrovirus-mediated gene transfer into hematopoietic stem cells and progenitor cells can be achieved by co-localizing retroviral particles and target cells on specific adhesion domains of fibronectin. In this pilot study, we used this technique to transfer the human multidrug resistance 1 gene into stem and progenitor cells of patients with germ cell tumors undergoing autologous transplantation. There was efficient gene transfer into stem and progenitor cells in the presence of recombinant fibronectin fragment CH-296. The infusion of these cells was associated with no harmful effects and led to prompt hematopoietic recovery. There was in vivo vector expression, but it may have been limited by the high rate of aberrant splicing of the multidrug resistance 1 gene in the vector. Gene marking has persisted more than a year at levels higher than previously reported in humans.

Latest developments in gene transfer technology: achievements, perspectives, and controversies over therapeutic applications

Over the last decade, more than 300 phase I and phase II gene-based clinical trials have been conducted worldwide for the treatment of cancer and monogenic disorders. Lately, these trials have been extended to the treatment of AIDS and, to a lesser extent, cardiovascular diseases. There are 27 currently active gene therapy protocols for the treatment of HIV-1 infection in the USA. Preclinical studies are currently in progress to evaluate the possibility of increasing the number of gene therapy clinical trials for cardiopathies, and of beginning new gene therapy programs for neurologic illnesses, autoimmuno diseases, allergies, regeneration of tissues, and to implement procedures of allogeneic tissues or cell transplantation. In addition, gene transfer technology has allowed for the development of innovative vaccine design, known as genetic immunization. This technique has already been applied in the AIDS vaccine programs in the USA. These programs aim to confer protective immunity against HIV-1 transmission to individuals who are at risk of infection. Research programs have also been considered to develop therapeutic vaccines for patients with AIDS and generate either preventive or therapeutic vaccines against malaria, tuberculosis, hepatitis A, B and C viruses, influenza virus, La Crosse virus, and Ebola virus. The potential therapeutic applications of gene transfer technology are enormous. However, the effectiveness of gene therapy programs is still questioned. Furthermore, there is growing concern over the matter of safety of gene delivery and controversy has arisen over the proposal to begin in utero gene therapy clinical trials for the treatment of inherited genetic disorders. From this standpoint, despite the latest significant achievements reported in vector design, it is not possible to predict to what extent gene therapeutic interventions will be effective in patients, and in what time frame.

Modulation of phosphate uptake and amphotropic murine leukemia virus entry by posttranslational modifications of PIT-2

PIT-2 is a type III sodium phosphate cotransporter and the receptor for amphotropic murine leukemia viruses. We have investigated the expression and the functions of a tagged version of PIT-2 in CHO cells. PIT-2 remained equally abundant at the cell surface within 6 h following variation of the phosphate supply. In contrast, the efficiency of phosphate uptake and retrovirus entry was inversely related to the extracellular phosphate concentration, indicating that PIT-2 activities are modulated by posttranslational modifications of cell surface molecules induced by phosphate. Conformational changes of PIT-2 contribute to both activities, as shown by the inhibitory effect of sulfhydryl reagents known as inhibitors of type II cotransporters. A physical association of PIT-2 with actin was demonstrated. Modifications of the actin network were induced by variations of the concentrations of extracellular phosphate, cytochalasin D, or lysophosphatidic acid. They revealed that the formation of actin stress fibers determines the cell surface distribution of PIT-2, the internalization of the receptor in response to virus binding, and the capacity to process retrovirus entry. Thus, the presence of PIT-2 at the cell surface is not sufficient to ensure phosphate transport and susceptibility to amphotropic retrovirus infection. Further activation of cell surface PIT-2 molecules is required for these functions.

RNA levels of human retrovirus receptors Pit1 and Pit2 do not correlate with infectibility by three retroviral vector pseudotypes

The gibbon ape leukemia virus (GaLV) and the amphotropic murine leukemia virus (A-MuLV) infect human cells via specific receptors, Pit1 and Pit2, respectively. mRNA levels of these receptors were determined by Northern analysis and for Pit2 in addition by quantitative RT-PCR. Pit1 and Pit2 were expressed in different amounts in human tissues and cell lines; Pit1-specific mRNA was generally more abundant than Pit2 mRNA. No correlation was found between Pit1 and Pit2 RNA levels and infectibility by GaLV and A-MuLV pseudotyped vectors, respectively. GaLV and A-MuLV revealed a partial reciprocal interference. MuLV-10A1 can utilize both Pit1 and Pit2 for entry into cells but could not infect any of the 14 human cell lines more efficiently than A-MuLV or GaLV. Interference assays suggested that MuLV-10A1 has a higher affinity for and infected most cells predominantly by Pit2. However, at least in one cell line it used Pit1 more efficiently for entry. We conclude that (1) Pit1 and Pit2 mRNA levels in human cells are not indicative of the infectibility by GaLV and A-MuLV pseudotypes, respectively; (2) A-MuLV can infect target cells as efficiently as can GaLV, although Pit2 RNA is less abundant than Pit1 RNA; (3) factor(s) in addition to the presence of Pit1 and Pit2 are involved in retroviral infection; and (4) MuLV-10A1 pseudotype does not infect human cells more efficiently than do A-MuLV and GaLV pseudotypes.