An autoregulated dual-function antitat gene for human immunodeficiency virus type 1 gene therapy

Gene Therapy: Recent Advances and Applications in Dermatology

Background:

Gene therapy is an innovative and exciting new branch of medicine. Despite the fact that a human disease has yet to be cured using this therapeutic approach, numerous clinical trials are taking place around the world based on encouraging preclinical data.

Objective:

The aim of this review is to bring the reader up to date with this rapidly advancing field and to highlight the technical advances that must occur before gene therapy will become common practice in dermatology.

Methods:

The current level of gene delivery technology restricts the applications. The advantages and disadvantages of viral and nonviral gene delivery systems are discussed.

Results:

Considerable advances are being made in the areas of cancer immunotherapy and vaccines. Of particular importance to the treatment of skin diseases will be the isolation and ex vivo manipulation of epidermal stem cells, the development of skin-specific regulatory sequences for gene expression, and the formulation of gene delivery systems suitable for systemic administration.

Conclusions:

In general, skin and keratinocytes are considered to be good targets for gene transfer applications, and several diseases have been identified as potential candidates for treatment in the near future.

Molecular strategies to inhibit HIV-1 replication

The human immunodeficiency virus type 1 (HIV-1) is the primary cause of the acquired immunodeficiency syndrome (AIDS), which is a slow, progressive and degenerative disease of the human immune system. The pathogenesis of HIV-1 is complex and characterized by the interplay of both viral and host factors. An intense global research effort into understanding the individual steps of the viral replication cycle and the dynamics during an infection has inspired researchers in the development of a wide spectrum of antiviral strategies. Practically every stage in the viral life cycle and every viral gene product is a potential target. In addition, several strategies are targeting host proteins that play an essential role in the viral life cycle. This review summarizes the main genetic approaches taken in such antiviral strategies.

SV40-derived vectors provide effective transgene expression and inhibition of HIV-1 using constitutive, conditional,and pol III promoters

Vectors based on recombinant SV40 viruses (rSV40) are highly effective in delivering transgene expression driven by constitutive promoters. We tested here whether these vectors could be used with conditional promoters and promoters using RNA polymerase III transcription, with inhibition of HIV-1 by Tat activation response (TAR) decoys as a functional measure of effective transgene delivery and activity. TAR decoys inhibit HIV-1 Tat, a trans-activator of HIV-1 transcription. Tat acts early in the viral replicative cycle and is essential for efficient viral replication. We evaluated rSV40 gene delivery using two different inhibitors of Tat. One was a dual function polyTAR gene encoding 25 sequential TAR elements (TAR(25)), plus an antisense tat, driven either by HIV-1 long terminal repeat (HIV-LTR) as a conditional promoter, or by cytomegalovirus immediate-early promoter (CMV-IEP) as a constitutive promoter. The other inhibitor was a single TAR decoy, driven by the U6 small nuclear RNA promoter (U6-P). These decoys were delivered to unselected cells in two different human T lymphocyte lines and to unstimulated primary human peripheral blood mononuclear cells (pbmc). Gene delivery was confirmed by PCR, and expression by RT-PCR. By in situ hybridization analysis, >95% of cells were transduced. These transgene constructs protected all cell types tested from HIV-1, as measured by syncytia formation and p24 antigen release. Somewhat better inhibition of HIV-1 replication was achieved with HIV-1 long terminal repeat (HIV-1 LTR) as a conditional promoter than with the constitutive CMV-IEP. The U6-P was also very effective, driving a TAR(1) transcript. Cell viability was not detectably affected by TAR decoy expression. Thus, rSV40 vectors effectively deliver HIV-1-inhibitory RNAs using either constitutive or conditional pol II promoters, or using a pol III promoter. The versatility of this gene delivery system may prove to be useful in anti-HIV-1 therapeutics.

Investigation of RNA transcripts containing HIV-1 packaging signal sequences as HIV-1 antivirals: generation of cell lines resistant to HIV-1

Based on the success of RNA decoy approaches using RRE and TAR sequences to inhibit HIV-1 replication, we studied the ability of HIV-1 packaging signal sequences to interfere with viral RNA encapsidation and formation of infectious particles. We made a variety of plasmid constructs in which the sequence context or number of repeats of the viral packaging signal was varied, and investigated the ability of these transcripts to inhibit replication of HIV-1 in stably transfected Jurkat T lymphocytes. We found that certain lines showed strong inhibition of HIV-1 replication, an effect that persisted at high input amounts of virus and significantly delayed viral replication for up to 4 weeks. An investigation of the mechanism of inhibition revealed that in these cell lines the packaging efficiency of the genomic HIV-1 transcript was unaffected. Further studies identified an antiviral effect on both HIV-1 and HIV-2 that did not correlate with decoy expression, and was substantially independent of CD4 expression or cellular proliferative capacity. Study of these resistant cell lines may lead to new insights into mechanisms of inhibition of HIV-1 replication.

Combination gene therapy: synergistic inhibition of human immunodeficiency virus Tat and Rev functions by a single RNA molecule

Current drug combinations can achieve long-term suppression of HIV replication in infected individuals. Unfortunately, complicated dosing schedules and high toxicity make long-term compliance with drug regimens difficult for most patients. Gene therapy may provide a permanent solution for HIV disease by generating cells genetically resistant to virus replication. As with the highly active antiretroviral therapies, genetic drugs must have strong antiviral potency and the ability to prevent the emergence of escape mutants. We have constructed antiviral genes containing unique combinations of Tat- and Rev-binding decoys. The new antiviral molecules are chimeric TAR-RRE RNAs that are expressed only in HIV infected cells in a Tat-regulated manner. One RNA molecule competes for both Tat and Rev binding, and thus blocks the activation and the expression of all viral genes. The two functional Tat- and Rev-binding domains exhibit the highest synergy at the lowest concentration. Conservative quantitative estimates of this synergistic effect were I = 0.24 at 50% inhibition, in terms of the Berenbaum "interaction index," indicating that the combined construct was approximately fourfold more potent than would be predicted on the basis of additive effects. The possibility of HIV escape from this inhibition is unlikely, because it requires simultaneous mutation of TAR and RRE in a manner in which both Tat and Rev preserve their respective functions. TAR-RRE combination decoys represent the first example of mathematically proven synergistic antiviral activity between two domains of the same molecule.

Inhibition of HIV-1 replication in chronically infected cell lines and peripheral blood mononuclear cells by retrovirus-mediated antitat gene transfer

Among potential genetic targets for intervention in the HIV-1 life cycle, the tat gene product is a key target. We investigated the ability of an antitat gene to inhibit HIV-1 activation and replication in chronically infected promonocyte (U1) and T cell (ACH-2) lines in vitro. U1 and ACH-2 cells were transduced with an antitat gene expressing RNA with dual (polymeric Tat activation response element and antisense-tat) function that interferes with HIV-1 replication. Tumor necrosis factor-alpha (TNF-alpha) plus phorbol 12- myristate 13-acetate (PMA)-induced HIV-1 expression, as determined by reverse transcribed PCR and reverse transcriptase (RT) assays, was significantly inhibited in U1 and ACH-2 cells transduced with the antitat gene, compared with the cells transduced with control vector and untransduced cells. This resistance to TNF-alpha plus PMA-induced HIV-1 expression was demonstrated in antitat gene-transduced U1 and ACH-2 cells maintained in G418-free media for 5 months, suggesting that functional antitat gene may persist for many months in transduced cells and their progeny. Most importantly, we demonstrate that the antitat gene, when introduced into peripheral blood mononuclear cells (PBMC) isolated from patients with HIV-1 infection, inhibited TNF-alpha plus PMA-induced viral replication as determined by RT-PCR and RT activity. In addition, the antitat gene enhanced the survival of CD4+ T lymphocytes from such patients. These data suggest the feasibility of utilizing antitat gene therapy to block activation and replication of HIV-1 in latently infected monocytes and T- lymphocytes in vivo. Gene Therapy (2000) 7, 321-328.

Interference between effector RNAs expressed from conventional dual-function anti-HIV retroviral vectors can be circumvented using dual-effector-cassette retroviral vectors

Coexpression of different effector molecules from a single vector (a dual-function vector) may provide enhanced efficacy. Thus far most of the reported anti-HIV dual-function vectors express different effector RNAs as a chimeric molecule. In our study involving retroviral vectors coexpressing a U5 ribozyme and either an anti-tat or anti-rev antisense RNA, chimeric vectors exhibit poor potency in several important functional aspects, including inhibition of HIV replication, protection against cytopathic effects, and suppression of target gene function. Surprisingly, such a poor efficacy of chimeric vector function was not associated with a lower level of effector RNA expression. These results indicate that expression of two effector RNAs as a chimeric molecule can lead to interference, reducing their global biological effects. More importantly, we have demonstrated that such interference can be avoided by coexpressing these effector RNAs as separate molecules through a new dual-function vector, called a dual-effector cassette (Dec) vector, developed in this study. We also define some of the design alterations that might affect the efficacy of the Dec vector and demonstrate that forward-designed Dec vectors are more efficacious than reverse-designed Dec vectors, which express a lower level of effector RNA owing to the instability of the 5' effector cassettes in the provirus. We believe that the principle of Dec vector design may also be applicable for the coexpression of other therapeutic RNA effectors in many gene therapy applications.

Examination of antisense RNA and oligodeoxynucleotides as potential inhibitors of avian leukosis virus replication in RP30 cells

Avian leukosis virus (ALV) is an economically important pathogen of chickens. Both antisense RNA and antisense oligodeoxynucleotides (ODN) have been used to diminish the replication and spread of other retroviruses. The use of antisense RNA and ODN to inhibit ALV replication has been examined in cultured RP30 cells. Using an expression system that constitutively transcribes antisense ALV RNA, one transfected cell clone showed a significant reduction in virus growth. However, this effect was not reproducibly observed in other transfected cell lines or in cells in which the antisense transcript was expressed from a regulatable promoter, even though a substantial amount of antisense transcript was generated. Antisense ODN complementary to several different target sites near the 5' end of the ALV genome were also tested for antiviral activity, by comparison of antisense ODN effects to those of randomized sequence controls. An antisense ODN complementary to the ALV primer binding site demonstrated a reproducible reduction in viral replication. However, when the corresponding region was specifically employed as a target for intracellular antisense RNA expression, there again was no significant inhibition of ALV. These results suggest that in vivo expression of antisense RNA is unlikely to be an effective way to generate transgenic poultry that are resistant to field strains of ALV.

Co-packaging of sense and antisense RNAs: a novel strategy for blocking HIV-1 replication

Retroviral vectors were engineered to express either sense (MoTiN-TRPsie+) or sense and antisense (MoTN-TRPsie+/-) RNAs containing the human immunodeficiency virus type-1 (HIV-1) trans -activation response (TAR) element and the extended packaging (Psie) signal. The Psie signal includes the dimer linkage structure (DLS) and the Rev response element (RRE). Amphotropic vector particles were used to transduce a human CD4+ T-lymphoid (MT4) cell line. Stable transductants were then tested for sense and antisense RNA production and susceptibility to HIV-1 infection. HIV-1 production was significantly decreased in cells transduced with MoTiN-TRPsie+ and MoTN-TRPsie+/-vectors. Efficient packaging of sense and most remarkably of antisense RNA was observed within the virus progeny. Infectivity of this virus was significantly decreased in both cases, suggesting that the interfering RNAs were co-packaged with HIV-1 RNA. Vector transduction was not expected to occur and was not observed. Inhibition of HIV-1 replication was also demonstrated in human peripheral blood lymphocytes transduced with retroviral vectors expressing antisense RNA. These results suggest that (i) both sense and antisense RNAs were co-packaged with HIV-1 RNA, (ii) the co-packaged sense and antisense RNAs inhibited virus infectivity and (iii) the co-packaged sense and antisense RNAs were not transduced. Sense and antisense RNA-based strategies may also be used to co-package other interfering RNAs (e.g. ribozymes) to cleave HIV-1 virion RNA.

In vitro selection of HIV-1 TAR variants by the Tat protein

Starting from a pool of 10(13) RNA sequences, we isolated a number of TAR RNA variants after nine rounds of selection by binding to recombinant Tat in vitro (SELEX procedure). Sequence analysis of part of the selected molecular species indicated that two TAR variants (clones A and B) were, respectively, represented five and four times. These two groups of sequences constituted approximately 25% of the total number of analyzed clones (9/34). As far as the primary and presumptive secondary structures of the wild-type TAR are concerned, the selected A and B variants showed an almost complete sequence conservation of the Tat-binding domain, but the configuration of this nucleotide region differed within the secondary structure. Despite this difference, as verified by gel retardation and filter binding assays, both the A and B variants bound Tat in vitro with an affinity that was very close to that of the wild-type TAR. Conversely, neither variant sustained Tat-mediated trans-activation in vivo when they replaced the wild-type TAR inside the long terminal repeat of HIV_1. Taken together, our results suggest that these TAR variants have lost the ability to bind cell factor(s) in vivo and may therefore represent useful decoys for the inhibition of HIV-1 replication.

Transduction of CD34+ hematopoietic progenitor cells with an antitat gene protects T-cell and macrophage progeny from AIDS virus infection

Transduction of hematopoietic stem cells with genes that inhibit human immunodeficiency virus (HIV) replication has the potential to reconstitute immune function in individuals with AIDS. We evaluated the ability of an autoregulated gene, antitat, to inhibit replication of simian immunodeficiency virus (SIV) and HIV type 1 (HIV-1) in hematopoietic cells derived from transduced progenitor cells. The antitat gene expresses an antiviral RNA encoding polymeric Tat activation response elements in combination with an antisense tat moiety under the control of the HIV-1 long terminal repeat. CD34+ hematopoietic progenitor cells were transduced with a retroviral vector containing the antitat gene and then cultured under conditions that support in vitro differentiation of T cells or macrophage-like cells. Rhesus macaque CD4+ T cells and macrophage-like cells derived from CD34+ bone marrow cells transduced with the antitat gene were highly resistant to challenge with SIV, reflecting a 2- to 3-log reduction in peak SIV replication compared with controls. Similarly, human CD4+ T cells derived from CD34+ cord blood cells transduced with antitat were also resistant to infection with HIV-1. No evidence for toxicity of the antitat gene was observed in any of five different lineages derived from transduced hematopoietic cells. These results demonstrate that a candidate therapeutic gene introduced into hematopoietic progenitor cells can retain the ability to inhibit AIDS virus replication following T-cell differentiation and support the potential use of the antitat gene for stem cell gene therapy.

What is new in clinical research of viral diseases of the skin

Viral diseases of the skin have become a much more serious problem with the increasing number of patients immunosuppressed by either AIDS or cancer chemotherapy. The emphasis in research on the diagnosis and treatment of these diseases is similar to that on the bacterial diseases several decades ago.

Efficacy of antitat gene therapy in the presence of high multiplicity infection and inflammatory cytokines

Because human immunodeficiency virus type 1 (HIV-1) infection is characterized by a large number of viral replication cycles and rapid cell turnover in vivo, successful gene therapy requires an approach effective under these conditions. The antitat gene has been proposed for gene therapy because it effectively blocks Tat function and the replication of HIV-1. However, neither antitat nor any other antiviral gene has been shown to inhibit HIV in the presence of high viral load and inflammatory cytokines, a condition closer to the in vivo situation. We show that cells transduced with antitat retrovirus vector are resistant to high multiplicity of HIV infection. In the presence of inflammatory cytokines, including interleukin-1 and tumor necrosis factor, both known to activate viral gene expression independently of Tat, antitat suppressed virus replication. HIV-1 inhibition was observed when cell were treated with a mixture of inflammatory cytokines able to induce acquired immunodeficiency syndrome (AIDS) Kaposi's sarcoma cell growth. These molecules have been shown to be increased in HIV-1-infected individuals, and it is suggested they play a role in the pathogenesis of AIDS. Our results suggest that antitat is effective under conditions present in vivo and therefore a primary candidate for HIV-1 gene therapy.

Murine leukemia virus-based Tat-inducible long terminal repeat replacement vectors: a new system for anti-human immunodeficiency virus gene therapy

We have constructed new murine leukemia virus (MLV)-based vectors (TIN vectors) which, following integration, contain human immunodeficiency virus (HIV) type 1 U3 and R sequences in place of the MLV U3 and R regions. This provides, for the first time, single transcriptional unit retroviral vectors under the control of Tat. TIN vectors have several advantages for anti-HIV gene therapy applications.

Inhibition of human immunodeficiency virus type 1 and type 2 Tat function by transdominant Tat protein localized to both the nucleus and cytoplasm

We introduced various mutations into the activation and RNA binding domains of human immunodeficiency virus type 1 (HIV-1) Tat in order to develop a novel and potent transdominant Tat protein and to characterize its mechanism of action. The different mutant Tat proteins were characterized for their abilities to activate the HIV LTR and inhibit the function of wild-type Tat in trans. A Tat protein containing a deletion of the basic domain (Tat(delta)49-57) localized exclusively to the cytoplasm of transfected human cells was nonfunctional and inhibited both HIV-1 and HIV-2 Tat function in a transdominant manner. Tat proteins containing mutations in the cysteine-rich and core domains were nonfunctional but failed to inhibit Tat function in trans. When Tat nuclear or nucleolar localization signals were fused to the carboxy terminus of Tat(delta)49-57, the chimeric proteins localized to the nucleus or nucleolus, respectively, and remained capable of acting in a transdominant manner. Introduction of secondary mutations in the cysteine-rich and core domains of the various transdominant Tat proteins completely eliminated their abilities to act in a transdominant fashion. Our data best support a mechanism in which these transdominant Tat proteins squelch a cellular factor or factors that interact with the Tat activation domain and are required for Tat to function.

AIDS-related Kaposi's sarcoma. A template for the translation of molecular pathogenesis into targeted therapeutic approaches

AIDS-related Kaposi's sarcoma (KS) represents a complex interaction of host and viral factors. There are a number of fundamental questions surrounding the interplay between the disparate factors that can contribute to the pathogenesis and pathophysiology of this disease. Targets such as the enhancement of immune function, inhibition of angiogenic factors or immunostimulatory cytokines, inhibition of viral proteins such as Tat, or hormonal manipulations are now or will in the future become the focus of research to develop innovative anti-KS therapy and prevention measures. Antiviral approaches aimed at HIV or other viruses may potentially target a number of steps in KS pathogenesis. This article reviews diverse modalities--cytotoxic, antiviral, gene-directed, growth factor-targeted, and antiangiogenesis--that singly, or more likely in combination, stand to make an impact on the cure and prevention of AIDS-related KS.

TAR- and Tat-independent replication of human immunodeficiency virus type 1 in human hepatoma cells

The molecular mechanisms involved in the regulation of human immunodeficiency virus type 1 (HIV-1) replication may differ in various cell types and with various exogenous stimuli. TAR/Tat interactions play important roles in HIV-1-long terminal repeat (LTR)-directed transcription, and have become specific targets in molecular therapies for blocking HIV-1 replication. As we previously reported, astrocytic glial cells, which can support HIV-1 replication in cell culture and may be infected in vivo, provide an intracellular milieu in which TAR mutant HIV-1 viruses may replicate. In further studies of this molecular model, several divergent human cell types were analyzed for both TAR- and Tat-independent HIV-1 replication. Human hepatoma cell lines, which can be productively infected by HIV-1 after the hepatoma cells are transduced with the human CD4 receptor gene, were found to support high levels of HIV-1 replication. In these studies, utilizing a transient transfection system with wild-type and various TAR, Tat, or combined TAR/Tat mutant HIV-1 proviral constructs, we demonstrate TAR-independent replication in unstimulated human hepatoma cells. Remarkably, in human hepatoma cells, HIV-1 replication is not only independent of TAR but also can be independent of Tat expression. It is further demonstrated, using electrophoretic mobility shift assays (EMSAs) and an in situ UV cross-linking system, that human hepatoma cells contain novel endogenous cellular proteins that bind to the proviral HIV-1 5' LTR in the downstream region, between nucleotides +38 to +125 on proviral DNA. This alternative regulatory pathway of TAR- and Tat-independent viral production may provide a new system to dissect further the interactions of Tat/TAR and determine the role of the TAR element, in its DNA form, in HIV-1 replication.

Inhibition of human immunodeficiency virus type 1 replication is enhanced by a combination of transdominant Tat and Rev proteins

Mutation of either of two critical human immunodeficiency virus type 1 (HIV-1) regulatory proteins, Tat and Rev, results in marked defects in viral replication. Thus, inhibition of the function of one or both of these proteins can significantly inhibit viral growth. In the present study, we constructed a novel transdominant Tat mutant protein and compared its efficiency in inhibiting HIV-1 replication with that of transdominant mutant Rev M10 when these proteins were stably expressed either alone or in combination in T-lymphocyte cell lines. The transdominant Tat mutant protein alone resulted in a modest inhibition of HIV replication, but it was able to enhance the ability of the M10 Rev mutant protein to inhibit HIV-1 replication. These results suggest a possible synergistic effect of these transdominant mutant proteins in inhibiting HIV-1 replication.

In vitro T lymphopoiesis: a model system for stem cell gene therapy for AIDS

Stable introduction of therapeutic genes into hematopoietic stem cells has the potential to reconstitute immunity in individuals with HIV infection. However, many important questions regarding the safety and efficacy of this approach remain unanswered and may be addressed in a non-human primate model. To facilitate evaluation of expression of foreign genes in T cells derived from transduced hematopoietic progenitor cells, we have established a culture system that supports the differentiation of rhesus macaque and human CD34+ bone marrow derived cells into mature T cells. Thymic stromal monolayers were prepared from the adherent cell fraction of collagenase digested fetal or neonatal thymus. After 10-14 days, purified rhesus CD34+ bone marrow-derived cells cultured on thymic stromal monolayers yielded CD3+CD4+CD8+, CD3+CD4+CD8-, and CD3+CD4-CD8+ cells. Following stimulation with mitogens, these T cells derived from CD34+ cells could be expanded over 1,000-fold and maintained in culture for up to 20 weeks. We next evaluated the ability of rhesus CD34+ cells transduced with a retroviral vector containing the marker gene neo to undergo in vitro T cell differentiation. CD34+ cells transduced in the presence of bone marrow stroma and then cultured on rhesus thymic stroma resulted in T cells containing the retroviral marker gene. These studies should facilitate both in vitro and in vivo studies of hematopoietic stem cell therapeutic strategies for AIDS.

A new antisense tRNA construct for the genetic treatment of human immunodeficiency virus type 1 infection

Different strategies proposed in the literature to attempt gene therapy of AIDS are based mainly on the intracellular production of RNA and protein therapeutics. This report describes the construction and the anti-human immunodeficiency virus type 1 (HIV-1) activity of a new type of antisense tRNA directed against a nucleotide region in the first coding exon of HIV-1 tat (nucleotides 5924 to 5943; Los Alamos data bank) which is conserved among many HIV-1 clones. The anti-tat antisense sequence was inserted into a tRNA(Pro) backbone by replacement of the anticodon loop, without altering the tRNA canonic tetraloop structure. The antisense tRNA was able to interact effectively with its target in vitro. Jurkat cells that constitutively expressed the anti-tat tRNA following retroviral vector transduction exhibited significant resistance to HIV-1 de novo infection. Resistance seemed to correlate with the level of antisense expression. This is the first time that such a tRNA antisense strategy has been shown to be effective as a genetic treatment of HIV-1 infection in tissue culture. The construct design proposed in this report has some intrinsic advantages: the transcript is driven by a polymerase III promoter, the short length of the RNA minimizes effects of intramolecular base pairing that may impair target recognition, and the antisense RNA has the stability and intracellular fate of a native tRNA molecule.