Heterogeneous nuclear ribonucleoprotein K promotes cap-independent translation initiation of retroviral mRNAs.

Translation initiation of the human immunodeficiency virus-type 1 (HIV-1) genomic mRNA (vRNA) is cap-dependent or mediated by an internal ribosome entry site (IRES). The HIV-1 IRES requires IRES-transacting factors (ITAFs) for function. In this study, we evaluated the role of the heterogeneous nuclear ribonucleoprotein K (hnRNPK) as a potential ITAF for the HIV-1 IRES. In HIV-1-expressing cells, the depletion of hnRNPK reduced HIV-1 vRNA translation. Furthermore, both the depletion and overexpression of hnRNPK modulated HIV-1 IRES activity. Phosphorylations and protein arginine methyltransferase 1 (PRMT1)-induced asymmetrical dimethylation (aDMA) of hnRNPK strongly impacted the protein's ability to promote the activity of the HIV-1 IRES. We also show that hnRNPK acts as an ITAF for the human T cell lymphotropic virus-type 1 (HTLV-1) IRES, present in the 5'UTR of the viral sense mRNA, but not for the IRES present in the antisense spliced transcript encoding the HTLV-1 basic leucine zipper protein (sHBZ). This study provides evidence for a novel role of the host hnRNPK as an ITAF that stimulates IRES-mediated translation initiation for the retroviruses HIV-1 and HTLV-1.

Phylogenetic classification of feline immunodeficiency virus

Background: The feline immunodeficiency virus (FIV) is responsible for a retroviral disease that affects domestic and wild cats worldwide, causing Feline Acquired Immunodeficiency Syndrome (FAIDS). FIV is a lentivirus from the family Retroviridae and its genome has 3 main structural genes: gag, pol and env. Phylogenetic studies have classified FIV into 7 subtypes according to the diversity among strains from the World, mainly in the env gene. Epidemiological analyses have demonstrated the high predominance of FIV-A and FIV-B. This in silico study aimed to perform a phylogenetic analysis to study FIV diversity worldwide. Materials, Methods & Results: A total of 60 whole genome sequences (WGS) and 122 FIV env gene sequences were included in 2 datasets, which were aligned using MAFFT version 7. Recombination among genomes and/or env genes was analyzed with RDP5 software. Phylogenetic analyses with both datasets were performed, after removing the recombinant sequences, by the W-IQ-TREE and constructed and edited by the FigTree. A total of 12 recombination events involving 19 WGS were detected. In addition, 27 recombination events involving 49 sequences were observed in the env gene. A high rate of recombinants was observed inter-subtypes (A/B and B/D) and intra-subtypes (A/A). All recombinants were removed from the subsequent phylogenetic analyses. Phylogenies demonstrated 6 distinct main clades, 5 from domestic cats (A, B, C, E, U) and 1 from wild cat sequences (W) in the WGS, as well as in the specific env gene analyses. Most clustered with subtype B sequences. In the WGS analysis, clade B had a prevalence of 65.9% Brazilian sequences (27/41) and 2.4% Japanese sequences (1/41). In the env gene analyses, clade B showed a prevalence of 43.8% of Brazilian sequences (32/73) and 20.5% of USA sequences (15/73). The results of both analyses also confirm the FIV-wide geographical distribution around the world. In the phylogenetic analyses carried out with WGS, sequences from China (1/41; 2.4%), Colombia (1/41; 2.4%) and the USA (1/41; 2.4%) were identified in clade A; sequence from Canada in clade C (1/41; 2.4%); sequence from Botswana belonged to clade E (1/41; 2.4%); sequences from Brazil clustered into clade U (2/41; 5% - data not yet published); and sequences belonging to the clade W were from Canada (1/41; 2.4%) and the USA (5/41; 12.3%). Specific env gene phylogenetic analyses showed sequences from Colombia (1/73; 1.4%), France (2/73; 2.7%), the Netherlands (3/73; 4.1%), Switzerland (2/73; 2.7%), USA (6/73; 8.3%), belonging to clade A; sequence from Canada belonging to clade C (1/73; 1.4%); sequences from Brazil belonging to clade U (2/73; 5% - data not yet published); and sequences belonging to clade W from the USA (6/73; 8.3%). Discussion: The results presented here demonstrate that FIV has a rapid viral evolution due to recombination and mutation events, more specifically in the env gene, which is highly variable. Currently, this retrovirus is classified into 7 subtypes (A, B, C, D, E, F and U-NZenv) according to their high genomic diversity. It also highlighted the importance of in silico sequence and phylogeny studies to demonstrate evolutionary processes. This was the first study to address the WGS FIV diversity with a phylogenetic approach.

Immunotherapy and Gene Therapy for Oncoviruses Infections: A Review.

Immunotherapy has been shown to be highly effective in some types of cancer caused by viruses. Gene therapy involves insertion or modification of a therapeutic gene, to correct for inappropriate gene products that cause/may cause diseases. Both these types of therapy have been used as alternative ways to avoid cancers caused by oncoviruses. In this review, we summarize recent studies on immunotherapy and gene therapy including the topics of oncolytic immunotherapy, immune checkpoint inhibitors, gene replacement, antisense oligonucleotides, RNA interference, clustered regularly interspaced short palindromic repeats Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-based gene editing, transcription activator-like effector nucleases (TALENs) and custom treatment for Epstein-Barr virus, human T-lymphotropic virus 1, hepatitis B virus, human papillomavirus, hepatitis C virus, herpesvirus associated with Kaposi's sarcoma, Merkel cell polyomavirus, and cytomegalovirus.

Cap-independent translation initiation of the unspliced RNA of retroviruses.

Retroviruses are a unique family of RNA viruses that utilize a virally encoded reverse transcriptase (RT) to replicate their genomic RNA (gRNA) through a proviral DNA intermediate. The provirus is permanently integrated into the host cell chromosome and is expressed by the host cell transcription, RNA processing, and translation machinery. Retroviral messenger RNAs (mRNAs) entirely resemble a cellular mRNA as they have a 5'cap structure, 5'untranslated region (UTR), an open reading frame (ORF), 3'UTR, and a 3'poly(A) tail. The primary transcription product interacts with the cellular RNA processing machinery and is spliced, exported to the cytoplasm, and translated. However, a proportion of the pre-mRNA subverts typical RNA processing giving rise to the full-length RNA. In the cytoplasm, the full-length retroviral RNA fulfills a dual role acting as mRNA and as the gRNA. Simple retroviruses generate two pools of full-length RNA, one for each purpose. However, complex retroviruses have a single pool of full-length RNA, which is destined for translation or encapsidation. As for eukaryotic mRNAs, translational control of retroviral protein synthesis is mostly exerted at the step of initiation. Interestingly, some retroviral mRNAs, both simple and complex, use a dual mechanism to initiate protein synthesis, a cap-dependent initiation mechanism, or via internal initiation using an internal ribosome entry site (IRES). In this review, we describe and discuss data regarding the molecular mechanism driving the canonical cap-dependent and IRES-mediated translation initiation for retroviral mRNA, focusing the discussion mainly on the most studied retroviral mRNA, the HIV-1 mRNA.

Retroviral vectors and transposons for stable gene therapy: advances, current challenges and perspectives.

Gene therapy protocols require robust and long-term gene expression. For two decades, retrovirus family vectors have offered several attractive properties as stable gene-delivery vehicles. These vectors represent a technology with widespread use in basic biology and translational studies that require persistent gene expression for treatment of several monogenic diseases. Immunogenicity and insertional mutagenesis represent the main obstacles to a wider clinical use of these vectors. Efficient and safe non-viral vectors are emerging as a promising alternative and facilitate clinical gene therapy studies. Here, we present an updated review for beginners and expert readers on retro and lentiviruses and the latest generation of transposon vectors (sleeping beauty and piggyBac) used in stable gene transfer and gene therapy clinical trials. We discuss the potential advantages and disadvantages of these systems such as cellular responses (immunogenicity or genome modification of the target cell) following exogenous DNA integration. Additionally, we discuss potential implications of these genome modification tools in gene therapy and other basic and applied science contexts.

Retroviral DNA Sequences as a Means for Determining Ancient Diets.

For ages, specialists from varying fields have studied the diets of the primeval inhabitants of our planet, detecting diet remains in archaeological specimens using a range of morphological and biochemical methods. As of recent, metagenomic ancient DNA studies have allowed for the comparison of the fecal and gut microbiomes associated to archaeological specimens from various regions of the world; however the complex dynamics represented in those microbial communities still remain unclear. Theoretically, similar to eukaryote DNA the presence of genes from key microbes or enzymes, as well as the presence of DNA from viruses specific to key organisms, may suggest the ingestion of specific diet components. In this study we demonstrate that ancient virus DNA obtained from coprolites also provides information reconstructing the host's diet, as inferred from sequences obtained from pre-Columbian coprolites. This depicts a novel and reliable approach to determine new components as well as validate the previously suggested diets of extinct cultures and animals. Furthermore, to our knowledge this represents the first description of the eukaryotic viral diversity found in paleofaeces belonging to pre-Columbian cultures.

Convergent capture of retroviral superantigens by mammalian herpesviruses.

Horizontal gene transfer from retroviruses to mammals is well documented and extensive, but is rare between unrelated viruses with distinct genome types. Three herpesviruses encode a gene with similarity to a retroviral superantigen gene (sag) of the unrelated mouse mammary tumour virus (MMTV). We uncover ancient retroviral sags in over 20 mammals to reconstruct their shared history with herpesviral sags, revealing that the acquisition is a convergent evolutionary event. A retrovirus circulating in South American primates over 10 million years ago was the source of sag in two monkey herpesviruses, and a different retrovirus was the source of sag in a Peruvian rodent herpesvirus. We further show through a timescaled phylogenetic analysis that a cross-species transmission of monkey herpesviruses occurred after the acquisition of sag. These results reveal that a diverse range of ancient sag-containing retroviruses independently donated sag twice from two separate lineages that are distinct from MMTV.

Virus-like attachment sites and plastic CpG islands:landmarks of diversity in plant Del retrotransposons.

Full-length Del elements from ten angiosperm genomes, 5 monocot and 5 dicot, were retrieved and putative attachment (att) sites were identified. In the 2432 Del elements, two types of U5 att sites and a single conserved type of U3 att site were identified. Retroviral att sites confer specificity to the integration process, different att sites types therefore implies lineage specificity. While some features are common to all Del elements, CpG island patterns within the LTRs were particular to lineage specific clusters. All eudicot copies grouped into one single clade while the monocots harbour a more diverse collection of elements. Furthermore, full-length Del elements and truncated copies were unevenly distributed amongst chromosomes. Elements of Del lineage are organized in plants into three clusters and each cluster is composed of elements with distinct LTR features. Our results suggest that the Del lineage efficiently amplified in the monocots and that one branch is probably a newly emerging sub-lineage. Finally, sequences in all groups are under purifying selection. These results show the LTR region is dynamic and important in the evolution of LTR-retrotransposons, we speculate that it is a trigger for retrotransposon diversification.

Gene delivery strategies for the treatment of mucopolysaccharidoses.

INTRODUCTION: Mucopolysaccharidosis (MPS) disorders are genetic diseases caused by deficiencies in the lysosomal enzymes responsible for the degradation of glycosaminoglycans. Current treatments are not able to correct all disease symptoms and are not available for all MPS types, which makes gene therapy especially relevant. Multiple gene therapy approaches have been tested for different types of MPS, and our aim in this study is to critically analyze each of them. AREAS COVERED: In this review, we have included the major studies that describe the use of adeno-associated retroviral and lentiviral vectors, as well as relevant non-viral approaches for MPS disorders. EXPERT OPINION: Some protocols such as the use of adeno-associated vectors and lentiviral vectors are approaching the clinic for these disorders and, along with combined approaches, seem to be the future of gene therapy for MPS.

Granule cells born in the adult rat hippocampus can regulate the expression of GABAergic markers.

The granule cells (GCs) of the dentate gyrus transiently express markers of the GABAergic phenotype early during development. However, GCs are generated throughout life, posing the question of whether the newborn neurons in the adult rodent recapitulate the development of the neurotransmitter phenotype of GCs generated during embryonic and early postnatal development. In this work we asked whether newborn GCs transiently express a GABAergic phenotype during their development in the adult rat. Using retroviral infection, we labeled dividing cells in the dorsal hippocampus with GFP, identified them as granule cells, and determined their expression of GABAergic markers at different developmental stages. We found that GFP-positive cells express Prox-1 and calbindin, identifying them as GCs. GABA or GAD(67) was expressed in 13% of GFP-positive cells at 7 dpi, in 16% at 10 dpi and in 20% at 15 dpi. At 30 dpi, however, no GFP-positive cell somata containing GABAergic markers were detected, but their mossy fiber boutons did contain GAD(67). Interestingly, developing GCs detected with doublecortin and PSA-NCAM in non-injected adult rats, did not express GABAergic markers, suggesting that retroviral injection/infection stimulates their transient expression. However, in non-injected rats, a number of mossy fiber boutons of newborn granule cells detected with PSA-NCAM did express GAD(67). Our findings reveal that developing GCs born in the adult are able to transiently up-regulate the expression of GABAergic markers to be detected in their soma in response to insults, while they constitutively express GAD(67) in their mossy fibers.

Production of human factor VIII-FL in 293T cells using the bicistronic MGMT(P140K)-retroviral vector.

Hemophilia A is the most common X-linked bleeding disorder; it is caused by deficiency of coagulation factor VIII (FVIII). Replacement therapy with rFVIII produced from human cell line is a major goal for treating hemophilia patients. We prepared a full-length recombinant FVIII (FVIII-FL), using the pMFG-P140K retroviral vector. The IRES DNA fragment was cloned upstream to the P140K gene, providing a 9.34-kb bicistronic vector. FVIII-FL cDNA was then cloned upstream to IRES, resulting in a 16.6-kb construct. In parallel, an eGFP control vector was generated, resulting in a 10.1- kb construct. The 293T cells were transfected with these constructs, generating the 293T-FVIII-FL/P140K and 293T-eGFP/P140K cell lines. In 293T-FVIII-FL/P140K cells, FVIII and P140K mRNAs levels were 4,410 (±931.7)- and 295,400 (±75,769)-fold higher than in virgin cells. In 293T-eGFP/P140K cells, the eGFP and P140K mRNAs levels were 1,501,000 (±493,700)- and 308,000 (±139,300)-fold higher than in virgin cells. The amount of FVIII-FL was 0.2 IU/mL and 45 ng/mL FVIII cells or 4.4 IU/µg protein. These data demonstrate the efficacy of the bicistronic retroviral vector expressing FVIII-FL and MGMT(P140K), showing that it could be used for producing the FVIII-FL protein in a human cell line.

Endostatin- and interleukin-2-expressing retroviral bicistronic vector for gene therapy of metastatic renal cell carcinoma.

BACKGROUND: Metastatic renal cell carcinoma (mRCC) is one of the most treatment-resistant malignancies. Despite all new therapeutic advances, almost all patients develop resistance to treatment and cure is rarely seen. In the present study, we evaluated the antitumor effect of a bicistronic retrovirus vector encoding both endostatin (ES) and interleukin (IL)-2 using an orthotopic metastatic RCC mouse model. METHODS: Balb/C-bearing Renca cells were treated with NIH/3T3-LendIRES-IL-2-SN cells. In the survival studies, mice were monitored daily until they died. At the end of the in vivo experiment, serum levels of IL-2 and ES were measured, the lung was weighed, and the number of metastatic nodules, nodule area, tumor vessels and proliferation of tumor-infiltrating Renca cells were determined. RESULTS: Inoculation of NIH/3T3-LendIRES-IL-2-SN cells resulted in an increase in ES and IL-2 levels in the treated group (p < 0.05). There was a significant decrease in lung wet weight, lung nodule area and tumor vessels in the treated group compared to the control group (p < 0.001). The proliferation of Renca cells in the bicistronic-treated group was significantly reduced compared to the control group (p < 0.05). Kaplan-Meier survival curves showed that the probability of survival was significantly higher for mice submitted to bicistronic therapy (log-rank test, p = 0.0016). Bicistronic therapy caused an increase in the infiltration of CD4, CD4 interferon (IFN)γ-producing, CD8, CD8 IFNγ-producing and natural killer (CD49b) cells. CONCLUSIONS: Retroviral bicistronic gene transfer led to the secretion of functional ES and IL-2 that was sufficiently active to: (i) inhibit tumor angiogenesis and tumor cell proliferation and (ii) increase the infiltration of immune cells.

Activation of endogenous p53 by combined p19Arf gene transfer and nutlin-3 drug treatment modalities in the murine cell lines B16 and C6.

BACKGROUND: Reactivation of p53 by either gene transfer or pharmacologic approaches may compensate for loss of p19Arf or excess mdm2 expression, common events in melanoma and glioma. In our previous work, we constructed the pCLPG retroviral vector where transgene expression is controlled by p53 through a p53-responsive promoter. The use of this vector to introduce p19Arf into tumor cells that harbor p53wt should yield viral expression of p19Arf which, in turn, would activate the endogenous p53 and result in enhanced vector expression and tumor suppression. Since nutlin-3 can activate p53 by blocking its interaction with mdm2, we explored the possibility that the combination of p19Arf gene transfer and nutlin-3 drug treatment may provide an additive benefit in stimulating p53 function. METHODS: B16 (mouse melanoma) and C6 (rat glioma) cell lines, which harbor p53wt, were transduced with pCLPGp19 and these were additionally treated with nutlin-3 or the DNA damaging agent, doxorubicin. Viral expression was confirmed by Western, Northern and immunofluorescence assays. p53 function was assessed by reporter gene activity provided by a p53-responsive construct. Alterations in proliferation and viability were measured by colony formation, growth curve, cell cycle and MTT assays. In an animal model, B16 cells were treated with the pCLPGp19 virus and/or drugs before subcutaneous injection in C57BL/6 mice, observation of tumor progression and histopathologic analyses. RESULTS: Here we show that the functional activation of endogenous p53wt in B16 was particularly challenging, but accomplished when combined gene transfer and drug treatments were applied, resulting in increased transactivation by p53, marked cell cycle alteration and reduced viability in culture. In an animal model, B16 cells treated with both p19Arf and nutlin-3 yielded increased necrosis and decreased BrdU marking. In comparison, C6 cells were quite susceptible to either treatment, yet p53 was further activated by the combination of p19Arf and nutlin-3. CONCLUSIONS: To the best of our knowledge, this is the first study to apply both p19Arf and nutlin-3 for the stimulation of p53 activity. These results support the notion that a p53 responsive vector may prove to be an interesting gene transfer tool, especially when combined with p53-activating agents, for the treatment of tumors that retain wild-type p53.

Serial bone marrow transplantation reveals in vivo expression of the pCLPG retroviral vector.

BACKGROUND: Gene therapy in the hematopoietic system remains promising, though certain aspects of vector design, such as transcriptional control elements, continue to be studied. Our group has developed a retroviral vector where transgene expression is controlled by p53 with the intention of harnessing the dynamic and inducible nature of this tumor suppressor and transcription factor. We present here a test of in vivo expression provided by the p53-responsive vector, pCLPG. For this, we used a model of serial transplantation of transduced bone marrow cells. RESULTS: We observed, by flow cytometry, that the eGFP transgene was expressed at higher levels when the pCLPG vector was used as compared to the parental pCL retrovirus, where expression is directed by the native MoMLV LTR. Expression from the pCLPG vector was longer lasting, but did decay along with each sequential transplant. The detection of eGFP-positive cells containing either vector was successful only in the bone marrow compartment and was not observed in peripheral blood, spleen or thymus. CONCLUSIONS: These findings indicate that the p53-responsive pCLPG retrovirus did offer expression in vivo and at a level that surpassed the non-modified, parental pCL vector. Our results indicate that the pCLPG platform may provide some advantages when applied in the hematopoietic system.

Expression of the selectable marker gene bsrm in BALB/MK cells induces apoptosis by overproduction of hydrogen peroxide.

Transduction of the retroviral vector LBmSN, which expresses the blasticidin S resistance gene bsrm in the murine keratinocyte cell line BALB/MK, induces death in these cells. Cell death is caused by a factor called DOKEB (death factor obtained from keratinocytes expressing bsrm), which is released before the cells' death. In this report we describe and discuss the purification and characterization of DOKEB. Our results were as follows. (i) The 5-day-old medium from the modified BALB/MK cells with LBmSN was used for purification and characterization by filtration and chromatography: DOKEB was a stable and highly hydrophilic compound, with a molecular mass less than that of 1 amino acid. (ii) The conditioned medium containing DOKEB was reactive against thiobarbituric acid and dichlorofluorescein diacetate. (iii) DOKEB activity was neutralized by the incubation of the conditioned medium with catalase. Therefore, our conclusion is that the BALB/MK cells expressing bsrm produce a large amount of hydrogen peroxide, which catalyzes the process of apoptosis of those cells.

Anti-tumor effect of endostatin mediated by retroviral gene transfer in mice bearing renal cell carcinoma.

We investigated whether transfer of the gene encoding the angiogenesis inhibitor endostatin into the NIH/3T3 fibroblast cell line could inhibit renal tumor growth in vivo. NIH/3T3 cells were transduced with retroviral vectors containing the murine endostatin (ES) gene. SCID mice bearing CaKi-1 derived tumors were given a subcutaneous injection of either ES-transduced cells or control cells and were monitored for tumor growth. At the end of the in vivo experiment, the mean tumor volume of treated mice was 51.6 +/- 2.4 mm3, while the tumor volume of control was 234.5 +/- 14.8 mm3. Microvascular density was significantly decreased on treatment (control 9.79 vs. ES 2.53%, <0.001) accompanied by a 23-fold increase in intratumoral necrotic area and a 2.94-fold increase in the apoptotic index, determined by immunohistochemistry with anti-activated caspase-3. Apoptotic cells were found in foci enriched in infiltrating leukocytes. In conclusion, retroviral endostatin gene transfer led to secretion of functional endostatin that was sufficiently active to inhibit tumor angiogenesis and tumor growth. A second mechanism may also be implied in endostatin-dependent tumor regression, associated with tumor infiltration of leukocytes. Besides its antiangiogenic properties, endostatin may be a promising adjuvant to immunotherapy.

S-phase reduction in T47D human breast cancer epithelial cells induced by an S100P antisense-retroviral construct.

S100P is expressed in several malignant neoplasms. It was previously demonstrated that S100P is involved in the very early stages of breast carcinogenesis. In the present study we used a retrovirus-mediated transfer of antisense-S100P in order to check whether the decrease in expression of this protein could lead to alterations in the cell cycle of epithelial cells of human breast cancer. The T47D breast carcinoma cell line, a human breast epithelial cell that expresses high levels of S100P, was a tool used in this study to investigate the alteration in cell cycle induced by a retrovirus-mediated transfer of antisense-S100P. First we used the real-time PCR technique to quantify the gene expression. The results showed a reduction of 63% of expression within the T47D-S100P-A/S infected population compared with control T47D-LXSN clones. To determine the impact of the S100P antisense technique on protein expression in T47D cells, we performed immunofluorescence staining and analyzed the resulting images using a confocal microscope. The images showed much less pronounced antibody marking of the S100P protein in the T47D-S100P-A/S compared with control cells. To evaluate whether the antisense approach caused any alteration in the cell cycle, we concluded the study with flow cytometric analysis of the cell distribution. Our findings indicated that, in our model, S100P-antisense cells showed a 23% reduction of cells at the S-phase. Using transduction techniques with an S100P antisense-retroviral construct we were able to demonstrate a significant reduction in S-phase of the T47D cell cycle. To the best of our knowledge, this is the first time that an antisense approach has been used against S100P mRNA in breast cancer epithelial cells. The results showed here seem to further classify S100P as a protein that might be involved in the cell cycle imbalance observed during breast carcinogenesis.

High-level secretion of growth hormone by retrovirally transduced primary human keratinocytes: prospects for an animal model of cutaneous gene therapy.

A gene therapy clinical trial for treatment of growth hormone (GH) deficiency has not been reached yet, but several strategies using different gene transfer methodologies and animal models have been developed and showed successful results. We have set up an ex vivo gene therapy protocol using primary human keratinocytes transduced with an efficient retroviral vector (LXSN) encoding the human (hGH) or mouse GH (mGH) genes. These stably modified cells presented high in vitro expression levels of hGH (7 microg/106 cells/d) and mGH (11 microg/106 cells/d) after selection with geneticin. When the hGH-secreting keratinocytes were grafted onto immunodeficient dwarf mice (lit/scid), hGH levels in the circulation were about 0.2-0.3 ng/mL during a 12-d assay and these animals presented a significant body weight increase (p < 0.01) compared to the control. Substitution of conventional grafting methodologies with organotypic raft cultures revealed a peak value of up to 20 ng mGH/mL in the circulation of grafted lit/scid mice at 1 h postimplantation, followed by a rapid decline to baseline (approximately 2 ng/mL) within 24 h. One week after grafting, however, the cultured excised implants still presented approx 45% of their original in vitro secretion efficiency. Further studies are being carried out to identify the main factor(s) that still constitute one of the major impediments to the success of this promising model of cutaneous gene therapy.

High efficiency and long-term foreign gene expression in cultured liver sinusoidal endothelial cells by retroviral transduction.

The liver sinusoidal endothelial cells (LSECs) constitute a very specialized endothelium. Due to their multiple functions and privileged location in the liver, these cells constitute an excellent target for gene therapy. In this work, the authors investigate the efficiency of retroviral gene transduction as a method for in vitro gene delivery into murine LSECs. Gene transduction into murine LSECs was performed using the PCMMP-eGFP/pIK-MLVgp retrovirus pseudotyped with the vesicular stomatitis virus G glycoprotein (VSV-g), containing eGFP as a reporter gene. Retroviral transduction resulted in a high efficiency of gene transfer (99%) and stable expression of eGFP in LSECs. The retroviral transduction protocol did not affect the morphology or expression of endothelial cell markers or the biological functions of LSECs. The authors have developed conditions for high-efficiency and stable retroviral gene transduction of LSECs. These results raise the possibility of liver gene therapy using LSECs as vehicle for the delivery of therapeutic proteins by means of retroviral vectors.

From leading role to the backstage: mesenchymal stem cells as packaging cell lines for in situ production of viral vectors.

Gene therapy is based on the genetic manipulation of target cells. The genetic information required to genetically engineer these cells can be delivered through non-viral or viral vectors that present different biologic properties. The production of viral vectors for gene therapy depends on the nature of the cells transfected with plasmids containing the genetic information for recombinant viral assemblage. These so-called packaging cell lines (PCL) can be injected into the target organ, for the in situ transduction of target cells. There have been recent reports about the capacity of mesenchymal stem cells (MSCs) to target tumor cells. Different research groups, including our own, have isolated these MSCs, but they have not yet been studied as potential PCL to produce viral vectors. We propose here that a MSC packaging cell line could be employed for in situ gene therapy of solid tumors. The tropism of MSCs for tumor cells may render this PCL more efficient in that microenvironment, producing viral vectors for longer periods of time, shifting MSCs from target cell to the backstage level of viral gene therapy.