Development of retroviral vectors as safe, targeted gene delivery systems

Minimal amino acid exchange in human TCR constant regions fosters improved function of TCR gene-modified T cells

TCR gene therapy using adoptive transfer of TCR gene-modified T cells is a new strategy for treatment of cancer. One critical prerequisite for TCR gene therapy is sufficient expression of transferred TCRs. Several strategies to achieve optimal expression were developed, including "murinization," which replaces the human TCRalpha and TCRbeta constant regions by their murine counterparts. Using a series of mouse-human hybrid constructs, we have identified nine amino acids responsible for the improved expression of murinized TCRs. Five essential amino acid exchanges were identified in the TCRbeta C region, with exchange of a glutamic acid (human) for a basic lysine (mouse) at position 18 of the C region, being most important. For the TCRalpha C region, an area of four amino acids was sufficient for improved expression. The minimally murinized TCR variants (harboring only nine residues of the mouse sequence) enhanced expression of human TCRs by supporting preferential pairing of transferred TCR chains and a more stable association with the CD3 proteins. Most important, usage of minimally murinized TCR chains improved the function of transduced primary human T cells in comparison with cells transduced with wild-type TCRs. For TCR gene therapy, the utilization of minimally instead of completely murinized constant regions dramatically reduces the number of foreign residues and thereby the risk for immunogenicity of therapeutic TCRs.

Gene transfer in human vestibular epithelia and the prospects for inner ear gene therapy

Transfer of exogenous genetic material into the mammalian inner ear using viral vectors has been characterized over the last decade. A number of different viral vectors have been shown to transfect the varying cell types of the nonprimate mammalian inner ear. Several routes of delivery have been identified for introduction of vectors into the inner ear while minimizing injury to existing structures and at the same time ensuring widespread distribution of the agent throughout the cochlea and the rest of the inner ear. These studies raise the possibility that gene transfer may be developed as a potential strategy for treating inner ear dysfunction in humans. Furthermore, a recent report showing successful transfection of excised human vestibular epithelia offers proof of principle that viral gene transfer is a viable strategy for introduction and expression of exogenous genetic material to restore function to the inner ear. Human vestibular epithelia were harvested from patients undergoing labyrinthectomy, either for intractable Ménière's disease or vestibular schwannoma resection, and cultured for as long as 5 days. In those experiments, recombinant, multiply-deleted, replication-deficient adenoviral vectors were used to transfect and express a reporter gene as well as the functionally relevant gene, wild-type KCNQ4, a potassium channel gene that when mutated causes the autosomal dominant HL DFNA2.Here, we review the current state of viral-mediated gene transfer in the inner ear and discuss different viral vectors, routes of delivery, and potential applications of gene therapy. Emphasis is placed on experiments demonstrating viral transfection of human inner ear tissue and implications of these findings and for the future of gene therapy in the human inner ear.

Spleen necrosis virus-based vector delivery of anti-HIV-1 genes potently protects human hematopoietic cells from HIV-1 infection

In this study, we report on the efficacy of using a spleen necrosis virus (SNV)-based vector delivery system to block human immunodeficiency virus type I (HIV-1) replication in human hematopoietic cells. These efforts were directed towards the development of human immune system cell resistance to HIV-1 infection, based on the strategy of "intracellular immunization" via generation of a series of anti-HIV-1 therapeutic constructs carrying scFvs, single-chain variable fragments, against HIV-1 integrase and reverse transcriptase in combination with the trans-dominant mutant of HIV-1 Rev, RevM10. The efficiency of the anti-HIV-1 constructs were tested in viral challenge assays with different doses of HIV-1 NL4-3, Bal, 89.6 and R7-GFP strains. These experiments demonstrated the reduction of HIV-1 replication by these retroviral vector constructs in a range of 4- to 10-fold in CD4+ T-lymphocytes, human peripheral blood mononuclear cells (PBMCs), and primary human macrophages. We observed selective efficiency of SNV-based therapeutics in H9, C8166 and Jurkat T-lymphocytic cell lines, demonstrating the most efficient inhibition of HIV-1 replication in Jurkat T-cells. Thus, these data are the first demonstration of the ability of SNV-based retroviral vectors with select transgenes, which may have certain molecular advantages over other retroviral vector systems, to combat HIV-1 replication in human hematopoietic cells and support the potential for using SNV-expressed constructs in anti-HIV-1 molecular therapeutics.

Assessment of retroviral activity using a universal retrovirus chip

A DNA chip-based assay is described for parallel detection and identification of a wide variety of human and mammalian exogenous and endogenous retroviruses. The assay combines multiplex polymerase chain reaction (PCR) using fluorochrome-modified primer mixtures and chip hybridization. The microarray is composed of retrovirus-specific synthetic oligonucleotides as capture probes deposited on glass slides. The retrovirus chip can be used to assess the occurrence of reverse transcriptase (RT)-related transcripts in biological samples of human and mammalian origin. For example, distinct expression profiles of human endogenous retroviruses (HERV) were established reproducibly in human white blood cells, mammary gland and other human tissues. In particles released by human cells, packaging of specific HERV transcripts could be observed. Monitoring of human exogenous retroviruses (HIV, HTLV) and detection of putative cross-species transmissions (MLV, PERV) in human samples was efficient and reliable. The DNA chip should be an excellent tool for the detection of most relevant retroviruses and offers insights into differential retroviral activities and replication strategies. Furthermore, it could improve significantly the safety of gene therapy, tissue engineering, xenotransplantation and production of therapeutic polypeptides in cell culture.

Green fluorescent protein-adenoviral construct as a model for transient gene therapy for human cultured keratinocytes in an athymic mouse model

BACKGROUND

The goal of gene therapy for cultured keratinocyte grafts is to accelerate growth and wound healing following engraftment without producing long-term complications from the delivered gene. We studied a Green Fluorescent Protein-Adenoviral construct (GFP-ADV) to determine the characteristics of gene expression in human cultured keratinocyte grafts.

METHODS

Twelve GFP-ADV grafts and twelve control grafts were transplanted to the flanks of 24 athymic mice. Mouse flanks were monitored with fluorescence-filtered microscopy and, on Day 21, were sectioned and stained with anti-human MHC Class I with H&E counterstaining. Real-time PCR was performed on graft biopsies for adenoviral DNA.

RESULTS

Fluorescence decreased from Days 3 to 5 resulting in no difference between GFP-ADV and control grafts from days 5 to 10. All grafts were positive for human MHC Class I with an epithelial architecture by H&E. Day 21 GFP-ADV grafts were negative for adenoviral DNA.

CONCLUSION

The delivered gene was transiently expressed without the persistence of viral DNA, demonstrating the potential of adenoviral gene delivery for the improvement of wound healing without long-term adverse effects to the graft.

Gene therapy in plastic surgery

Recent developments in gene therapy have shown promise in the treatment of soft-tissue repair, bone formation, nerve regeneration, and cranial suture development. This special topic article reviews commonly used methods of gene therapy and discusses their various advantages and disadvantages. In addition, an overview of new developments in gene therapy as they relate to plastic surgery is provided.

Retargeting of viral vectors to the folate receptor endocytic pathway

Viral vectors with high transfection efficiencies are not always those with optimal target cell binding specificities. As a consequence, virus pseudotyping has been developed to endow transfection competent viruses with improved cell binding specificities and affinities. We have hypothesized that chemical conjugation of a virus to a cell specific ligand might also alter its target cell specificity and produce a virus that would transfect only the desired cell type. To test this concept, an ecotropic replication-defective myeloproliferative sarcoma retrovirus and an amphotropic murine adenovirus containing the gene for beta-galactosidase were chemically derivatized with folic acid. As expected from its strong ecotropism, the unmodified retrovirus did not induce beta-galactosidase expression in nonhost KB cells, while the amphotropic adenovirus yielded high levels of gene expression in the same cell line. Surprisingly, although folate derivatization enabled avid binding of both viruses to folate receptor expressing KB cells, the folate conjugation did not promote retroviral gene expression and actually prevented the normal beta-galactosidase expression seen with the adenoviral vector. The fact that co-administration of excess free folic acid to block uptake by folate receptor-mediated endocytosis restored adenoviral gene expression to the level obtained with unmodified virus suggests that folate derivatization per se does not hamper viral activity. We, therefore, conclude that neither retroviral nor adenoviral delivery via the folate endocytosis pathway is compatible with viral gene expression in KB cells.

Delivery systems intended for in vivo gene therapy of cancer: targeting and replication competent viral vectors

Cancer gene therapy represents one of the most rapidly evolving areas in pre-clinical and clinical cancer research. Application of gene transfer techniques in clinical trials has made increasingly obvious that several issues will need to be addressed prior to meaningful incorporation of gene therapy in the care of cancer patients. Two of the most important problems to overcome are lack of selectivity of the existing vectors and low efficiency of gene transfer. This review focuses on use of targeting and replication competent vectors in order to overcome these obstacles. Targeted gene therapy of malignancies can be achieved through vector targeting or transcriptional targeting and can improve the therapeutic index of gene transfer by preventing damage of normal tissues, an important requirement if systemic gene delivery is contemplated. Replication competent viral vectors can improve the efficiency of gene transfer. Provisionally replicating viruses can also improve the therapeutic index by targeting toxicity to tumor cells. A variety of provisionally replicating viruses, such as the attenuated adenovirus ONYX-015, the adenovirus CN706 that selectively replicates in prostate cancer cells, the double mutant herpes simplex virus G207, the human reovirus, and the Newcastle disease virus are currently in clinical trials. Early clinical results and limitations in the application of these vectors are discussed.

Molecular therapeutics of liver disease

Fundamental advances in biomedical research will revolutionize the prevention and treatment of liver disease during the early twenty-first century. Recent progress in gene-, cell-, and recombinant protein-based therapeutics will contribute to this revolution, although formidable obstacles currently prevent the clinical application of these novel therapies. Eventually, these obstacles will be overcome, and molecular therapeutics of liver disease will become a clinical reality. As a result, the new millennium will be a very interesting time to practice hepatology.

Viral IL-10-induced immunosuppression requires Th2 cytokines and impairs APC function within the allograft

Previous reports demonstrated that retroviral mediated gene transfer of viral IL-10 (vIL-10) prolongs allograft survival by decreasing donor-specific cytotoxic T lymphocyte precursor (CTLp) and IL-2-secreting helper T lymphocyte precursor (HTLp) frequency within graft-infiltrating cells (GIC). This report now shows that vIL-10 efficacy is dependent on CD4(+) T cells, suggesting that immunosuppression may involve a switch from a Th1 to a Th2 alloresponse. In support of this, anti-IL-4 or anti-murine IL-10 (anti-mIL-10) mAbs, but not anti-IFN-gamma mAb, administered at the time of vIL-10 gene transfer prevents enhanced graft survival. Because Th switching involves APC function, GIC were examined for their ability to present alloantigen. GIC from vIL-10-treated grafts were shown to be mostly of recipient (CBA) origin, yet were unable to elicit alloproliferative responses from donor type (C57BL/6) or third party (BALB/c) responders. The inability of vIL-10-treated GIC to stimulate the MLR was not due to the generation of negative regulatory cells or the production of immunosuppressive cytokines such as IL-4, mIL-10, or TGFbeta. Using fractionated GIC subpopulations, the number of recipient type cells in the allografts was modestly reduced by vIL-10 gene transfer, while maintaining both APC phenotype and alloantigen presenting function. Conversely, after vIL-10 gene transfer, donor type GIC were unable to participate in direct alloantigen presentation. Therefore, local immunosuppression induced by vIL-10 gene transfer is CD4 T cell and IL-4 and mIL-10 dependent, and impairs direct alloantigen presentation through an alteration of donor type APC function.

Modulation of Moloney leukemia virus long terminal repeat transcriptional activity by the murine CD4 silencer in retroviral vectors

We investigated whether CD4 gene regulatory sequences might be useful for developing transcriptionally targeted Moloney murine leukemia virus (Mo-MLV)-based retroviral vectors for gene expression specifically in CD4(+) cells. We could modulate Mo-MLV long terminal repeat (LTR) activity by inserting a 438-bp-long fragment containing the murine CD4 silencer in the LTR of the vector; both beta-galactosidase and green fluorescent protein reporter gene activities were strongly down-regulated in both murine and human CD8(+) cells, but not in CD4(+) lymphoid cell lines and freshly isolated lymphocytes transduced with this vector, compared with the findings using a control vector carrying wild-type LTRs. Titration experiments on NIH-3T3 cells revealed that inclusion of the CD4 silencer in the LTRs did not reduce the titer of the vectors. These findings indicate that a cellular silencer can be successfully included in retroviral vectors, where it maintains its transcription-regulatory function, thus suggesting a novel approach to transcriptional targeting.

Enhanced folate receptor mediated gene therapy using a novel pH-sensitive lipid formulation

Liposomal gene therapy vectors that penetrate cells by endocytosis must escape an endosomal compartment in order to enter the target cell's nucleus. Because such endosomal compartments are generally acidic in nature, pH-sensitive liposomes have been designed that are stable at extracellular pH ( approximately pH 7.4) but fusogenic at endosomal pH values ( approximately pH 5). We report here the use of a novel folate-targeted, pH-sensitive, anionic liposomal vector that mediates the efficient delivery of DNA into folate receptor-bearing cells and discharges the DNA into the cytoplasm. N-Citraconyl-dioleoylphosphatidylethanolamine (C-DOPE), a derivative of dioleylphosphatidylethanolamine (DOPE) that hydrolyzes rapidly at pH 5 to yield DOPE, was synthesized and incorporated with DOPE and folate-polyethyleneglycol-DOPE into liposomes. The resulting liposomes were stable at neutral pH but fusogenic at pH 5. Folate-labeled gene transfer vectors were prepared by compacting plasmid DNA with polylysine at a 1:0.75 (w/w) ratio and complexing the condensed cationic plasmid with the above anionic liposomes. Association of the polylysine-DNA with the liposomes was confirmed by sucrose gradient centrifugation, where migration of the folate-labeled vectors was midway between that of the free liposomes and condensed polylysine-DNA. Transfection of cultured cancer cells with the pH-sensitive liposomal vectors was found to be significantly more efficient than transfection with DOPE-cholesterol hemisuccinate-based vectors, the more commonly used pH-dependent, liposomal transfection formulation. Optimization studies revealed that inclusion of only 3% C-DOPE and 0.1% folate-derivatized DOPE yielded the highest transfection activity. Nearly quantitative competition with free folic acid as well as direct correlation of transfection efficiency with folate receptor density for several different cell lines further documented that vector uptake was mediated by folate receptor endocytosis. Taken together, these data argue that C-DOPE warrants further consideration as a pH sensitive component of lipid-based gene delivery formulations.

Tissue-specific consequences of the anti-adenoviral immune response: implications for cardiac transplants

The immune response to adenoviral vectors can induce inflammation and loss of transgene expression in transfected tissues. This would limit the use of adenovirus-mediated gene transfer in disease states in which long-term gene expression is required. While studying the effect of the anti-adenoviral immune response in transplantation, we found that transgene expression persisted in cardiac isografts transfected with an adenovirus encoding beta-galactosidase. Transfected grafts remained free of inflammation, despite the presence of an immune response to the vector. Thus, adenovirus-mediated gene transfer may have therapeutic value in cardiac transplantation and heart diseases. Furthermore, immunological limitations of adenoviral vectors for gene therapy are not universal for all tissue types.

Neurotensin-SPDP-poly-L-lysine conjugate: a nonviral vector for targeted gene delivery to neural cells

We report herein the synthesis of a novel DNA delivery system and in vitro evidence of its ability to transfect cell lines by binding to the high-affinity neurotensin receptor and subsequent internalization of ligand-receptor complexes. The targeting vehicle consisted of neurotensin crosslinked with poly-L-lysine via N-succinimidyl-3-(2-pyridyldithio) propionate (SPDP). The SPDP-derivatives with either neurotensin or poly-L-lysine were purified by gel filtration. The conjugate resulting of the reaction of neurotensin-SPDP with HS-SPDP-poly-L-lysine was purified through Biogel A 1.5. The neurotensin-SPDP-poly-L-lysine conjugate was able to bind plasmidic DNAs (pSV2cat and pGreen Lantern-1) at optimal molar ratios of 1:5 and 1:6 (DNA: conjugate), respectively. The conjugate internalized those plasmids in the cell lines (N1E-115 and HT-29) bearing the high-affinity neurotensin receptor. Expression of the plasmid products, chloramphenicol acetyltransferase and green fluorescent protein, was observed in such cell lines. Both internalization and expression of the plasmids transferred by the neurotensin-SPDP-poly-L-lysine conjugate were prevented by neurotensin (1 microM) and SR-48692 (100 nM), a specific antagonist of the high-affinity neurotensin receptor. The neurotensin-SPDP-poly-L-lysine conjugate was unable to transfect cell lines lacking the neurotensin receptor (COS-7 and L-929). In rat brain, the high-affinity neurotensin receptor is expressed by specific neurons such as those of the nigrostriatal and mesolimbic dopaminergic systems. Therefore, the neurotensin-SPDP-poly-L-lysine conjugate could be a useful tool for gene delivery to those neuronal systems.

Retrovirus-mediated in vivo gene transfer in the replicating liver using recombinant hepatocyte growth factor without liver injury or partial hepatectomy

Retrovirus-mediated gene delivery into hepatocytes in vivo provides long-term gene expression, which is of great importance for treating most genetic and metabolic disorders. However, clinical application has not been realized because of the requirement for prior 70% partial hepatectomy or chemical (toxic) liver injury to initiate hepatocyte replication at the time of retroviral gene transduction. In this paper, we describe a novel gene delivery system that uses recombinant hepatocyte growth factor (rHGF) prior to retrovirus-mediated in vivo gene transfer in the liver without partial hepatectomy or liver injury. A single retroviral infusion through the portal vein following five systemic injections (via the tail vein) of 100 microg/kg rHGF resulted in a 10.4% 5-bromo-2'-deoxyuridine (BrdU) labeling index (BLI) and 0.14% retroviral gene transduction efficiency (RGTE) in hepatocytes, which were 6.3- and 12.9-fold higher than those of controls, respectively. Modest additional increases in BLI and RGTE (13.4% and 0.22%, respectively) were seen after five systemic injections of 500 microg/kg rHGF. The correlation between BLI and RGTE was statistically confirmed regardless of treatment. When rats received multiple retroviral infusions through a cannulated portal vein following five portal injections of 100 microg/kg rHGF, RGTE was dramatically increased (1.3%) and in some areas of the liver exceeded more than 10%. There was no evidence of liver injury in any animal. This approach has great potential for clinical application in terms of avoiding invasive procedures or liver injury.

Expression of antimicrobial peptides has an antitumour effect in human cells

The antimicrobial peptides cecropin and melittin are known to exhibit antitumour activity in tumour derived cell lines. To achieve a similar effect in vivo these peptides would have to be given repeatedly to maintain therapeutic levels, which may be pharmacologically unfavourable. The expression of the genes encoding such antimicrobial peptides in the desired cell type may circumvent these problems. Expression constructs carrying cecropin or melittin have been introduced into a human bladder carcinoma derived cell line and the resultant cell clones analysed for tumorigenicity in nude mice. Expression of cecropin resulted in either a complete loss of tumorigenicity in some clones or reduced tumorigenicity, as measured by latency of tumour formation. These results suggest that vector mediated delivery of this gene to tumour cells may prove useful for cancer gene therapy.

G protein-coupled receptors: functional and mechanistic insights through altered gene expression

G protein-coupled receptors (GPCRs) comprise a large and diverse family of molecules that play essential roles in signal transduction. In addition to a constantly expanding pharmacological repertoire, recent advances in the ability to manipulate GPCR expression in vivo have provided another valuable approach in the study of GPCR function and mechanism of action. Current technologies now allow investigators to manipulate GPCR expression in a variety of ways. Graded reductions in GPCR expression can be achieved through antisense strategies or total gene ablation or replacement can be achieved through gene targeting strategies, and exogenous expression of wild-type or mutant GPCR isoforms can be accomplished with transgenic technologies. Both the techniques used to achieve these specific alterations and the consequences of altered expression patterns are reviewed here and discussed in the context of GPCR function and mechanism of action.

Delivery of tumor suppressor genes to reverse the malignant phenotype

Despite early enthusiasm and excitement, the treatment of cancer via gene therapy is a long way from reaching fruition. The objective of this review is to describe the rationale as to why the delivery of genes encoding functional proteins whose activity has been lost during the initiation and development of cancer may be a feasible therapeutic option. In addition we will evaluate the limitations of the current delivery systems and discuss how these limitations have impacted upon the progress of gene therapy. Finally, we will describe and discuss the most recent attempts to deliver tumor suppressor genes to rodent models of human cancer and perhaps more importantly to human patients. As will become apparent during this review the excitement and enthusiasm for gene therapy remains high, however, this should not diminish the challenges that must be overcome before gene therapy becomes routine.

Proliferation of multipotent hematopoietic cells controlled by a truncated erythropoietin receptor transgene

The long-term efficacy of gene therapy using bone marrow transplantation requires the engraftment of genetically altered totipotent hematopoietic stem cells (THSCs). Ex vivo expansion of corrected THSCs is one way to increase the efficiency of the procedure. Similarly, selective in vivo expansion of the therapeutic THSCs rather than the endogenous THSCs could favor the transplant. To test whether a conferred proliferative advantage gene can facilitate the in vitro and in vivo expansion of hematopoietic stem cells, we have generated transgenic mice expressing a truncated receptor for the growth factor erythropoietin. These mice are phenotypically normal, but when treated in vivo with exogenous erythropoietin they exhibit a marked increase in multipotent, clonogenic hematopoietic cells [colony-forming units in the spleen (CFU-S) and CFUs that give rise to granulocytes, erythroid cells, macrophages, and megakaryocytes within the same colony (CFU-GEMM)] in comparison with the wild-type mice. In addition, long-term in vitro culture of tEpoR transgenic bone marrow in the presence of erythropoietin induces exponential expansion of trilineage hematopoietic stem cells not seen with wild-type bone marrow. Thus, the truncated erythropoietin receptor gene shows promise as a means for obtaining cytokine-inducible hematopoietic stem cell proliferation to facilitate the direct targeting of THSCs and to provide a competitive repopulation advantage for transplanted therapeutic stem cells.