Gene therapy for HIV infection: what does it need to make it work?

Stem cell transplantation in strategies for curing HIV/AIDS

HIV-1 can persist in a latent form in resting memory CD4+ cells and macrophages carrying an integrated copy of the HIV genome. Because of the presence of these stable reservoir cells, eradication by antiretroviral therapy is unlikely and in order to achieve eradication, alternative treatment options are required. Stem cell transplantation has been considered previously to effect the clinical course of HIV-infection but in practice eradication or virus control was not achievable. However, modifications of stem cell transplantation using natural or artificial resistant cell sources, combination with new techniques of gene editing or generating cytotoxic anti HIV effector cells have stimulated this field of HIV cell therapy substantially. Here, we look back on 30 years of stem cell therapy in HIV patients and discuss most recent developments in this direction.

Comblike Polyethylenimine-Based Polyplexes: Balancing Toxicity, Cell Internalization, and Transfection Efficiency via Polymer Chain Topology

Comblike polyethylenimines with varying degrees of polymerization of both the main and side chains as well as different grafting densities were evaluated as gene delivery vectors. They were able to condense linear and plasmid DNA into nanosized polyplex particles with dimensions and surface potentials in the 130-330 nm and -30 to +15 mV ranges, respectively, depending on the amine/phosphate (N/P) ratio. The polyplexes remained stable in aqueous and buffer solutions from several hours up to several days. The moderate colloidal stability was also manifested in a relatively broad size distribution (PDI typically above 0.2) and structural polymorphism observed by transmission electron microscopy. Both the neat polymers and polyplexes displayed low cytotoxicity in WISH cells as the relative cell viability was more than 60%. Experiments with lysosomal fluorescence staining revealed that the internalization pathways and, in turn, transfection efficiency of the polyplex nanoparticles depended on the polymer chain topology. The vector systems based on the polymers of denser structure can be considered to be promising systems for gene transfection in eukaryotic cells.

mRNA transfection of a novel TAL effector nuclease (TALEN) facilitates efficient knockout of HIV co-receptor CCR5

Homozygosity for a natural deletion variant of the HIV-coreceptor molecule CCR5, CCR5Δ32, confers resistance toward HIV infection. Allogeneic stem cell transplantation from a CCR5Δ32-homozygous donor has resulted in the first cure from HIV ('Berlin patient'). Based thereon, genetic disruption of CCR5 using designer nucleases was proposed as a promising HIV gene-therapy approach. Here we introduce a novel TAL-effector nuclease, CCR5-Uco-TALEN that can be efficiently delivered into T cells by mRNA electroporation, a gentle and truly transient gene-transfer technique. CCR5-Uco-TALEN mediated high-rate CCR5 knockout (>90% in PM1 and >50% in primary T cells) combined with low off-target activity, as assessed by flow cytometry, next-generation sequencing and a newly devised, very convenient gene-editing frequency digital-PCR (GEF-dPCR). GEF-dPCR facilitates simultaneous detection of wild-type and gene-edited alleles with remarkable sensitivity and accuracy as shown for the CCR5 on-target and CCR2 off-target loci. CCR5-edited cells were protected from infection with HIV-derived lentiviral vectors, but also with the wild-type CCR5-tropic HIV-1BaL strain. Long-term exposure to HIV-1BaL resulted in almost complete suppression of viral replication and selection of CCR5-gene edited T cells. In conclusion, we have developed a novel TALEN for the targeted, high-efficiency knockout of CCR5 and a useful dPCR-based gene-editing detection method.

C peptides as entry inhibitors for gene therapy

Peptides derived from the C-terminal heptad repeat 2 region of the HIV-1 gp41 envelope glycoprotein, so-called C peptides, are very potent HIV-1 fusion inhibitors. Antiviral genes encoding either membrane-anchored (ma) or secreted (iSAVE) C peptides have been engineered and allow direct in vivo production of the therapeutic peptides by genetically modified host cells. Membrane-anchored C peptides expressed in the HIV-1 target cells by T-cell or hematopoietic stem cell gene therapy efficiently prevent virus entry into the modified cells. Such gene-protection confers a selective survival advantage and allows accumulation of the genetically modified cells. Membrane-anchored C peptides have been successfully tested in a nonhuman primate model of AIDS and were found to be safe in a phase I clinical trial in AIDS patients transplanted with autologous gene-modified T-cells. Secreted C peptides have the crucial advantage of not only protecting genetically modified cells from HIV-1 infection, but also neighboring cells, thus suppressing virus replication even if only a small fraction of cells is genetically modified. Accordingly, various cell types can be considered as potential in vivo producer cells for iSAVE-based gene therapeutics, which could even be modified by direct in vivo gene delivery in future. In conclusion, C peptide gene therapeutics may provide a strong benefit to AIDS patients and could present an effective alternative to current antiretroviral drug regimens.

Enhanced gene expression promoted by hybrid magnetic/cationic block copolymer micelles

We report on novel gene delivery vector systems based on hybrid polymer-magnetic micelles. The hybrid micelles were prepared by codissolution of hydrophobically surface modified iron oxide and amphiphilic polystyrene-b-poly(quaternized 2-vinylpyridine) block copolymer (PS-b-P2QVP) in organic solvent. After extensive dialysis against water, micelles with positively charged hydrophilic corona of PQVP and hydrophobic PS core were prepared, in which magnetic nanoparticles were randomly distributed. The hybrid micelles were used to form complexes with linear (salmon sperm, 2000 bp, corresponding to M(w) of 1.32 × 10(6) Da) and plasmid (pEGFP-N1, 4730 bp, corresponding to M(w) of 3.12 × 10(6) Da) DNA. The resulting magnetopolyplexes of phosphate:amine (P/N) ratios in the 0.05-20 range were characterized by light scattering, ζ-potential measurements, and transmission electron microscopy as well as cytotoxicity and gel retardation assays. The investigated systems displayed a narrow size distribution, particle dimensions below 360 nm, whereas their ζ-potential values varied from positive to negative depending of the P/N ratio. The resulting vector nanosystems exhibited low toxicity. They were able to introduce pEGFP-N1 molecules into the cells. The application of a magnetic field markedly boosted the transgene expression efficiency of the magnetopolyplexes, which was even superior to those of commercial transfectants such as Lipofectamine and dendritic polyethylenimine.

A quantitative comparison of anti-HIV gene therapy delivered to hematopoietic stem cells versus CD4+ T cells

Gene therapy represents an alternative and promising anti-HIV modality to highly active antiretroviral therapy. It involves the introduction of a protective gene into a cell, thereby conferring protection against HIV. While clinical trials to date have delivered gene therapy to CD4+T cells or to CD34+ hematopoietic stem cells (HSC), the relative benefits of each of these two cellular targets have not been conclusively determined. In the present analysis, we investigated the relative merits of delivering a dual construct (CCR5 entry inhibitor + C46 fusion inhibitor) to either CD4+T cells or to CD34+ HSC. Using mathematical modelling, we determined the impact of each scenario in terms of total CD4+T cell counts over a 10 year period, and also in terms of inhibition of CCR5 and CXCR4 tropic virus. Our modelling determined that therapy delivery to CD34+ HSC generally resulted in better outcomes than delivery to CD4+T cells. An early one-off therapy delivery to CD34+ HSC, assuming that 20% of CD34+ HSC in the bone marrow were gene-modified (G+), resulted in total CD4+T cell counts ≥ 180 cells/ µL in peripheral blood after 10 years. If the uninfected G+ CD4+T cells (in addition to exhibiting lower likelihood of becoming productively infected) also exhibited reduced levels of bystander apoptosis (92.5% reduction) over non gene-modified (G-) CD4+T cells, then total CD4+T cell counts of ≥ 350 cells/ µL were observed after 10 years, even if initially only 10% of CD34+ HSC in the bone marrow received the protective gene. Taken together our results indicate that: 1.) therapy delivery to CD34+ HSC will result in better outcomes than delivery to CD4+T cells, and 2.) a greater impact of gene therapy will be observed if G+ CD4+T cells exhibit reduced levels of bystander apoptosis over G- CD4+T cells.

Preclinical safety and efficacy of an anti-HIV-1 lentiviral vector containing a short hairpin RNA to CCR5 and the C46 fusion inhibitor

Gene transfer has therapeutic potential for treating HIV-1 infection by generating cells that are resistant to the virus. We have engineered a novel self-inactivating lentiviral vector, LVsh5/C46, using two viral-entry inhibitors to block early steps of HIV-1 cycle. The LVsh5/C46 vector encodes a short hairpin RNA (shRNA) for downregulation of CCR5, in combination with the HIV-1 fusion inhibitor, C46. We demonstrate here the effective delivery of LVsh5/C46 to human T cell lines, peripheral blood mononuclear cells, primary CD4(+) T lymphocytes, and CD34(+) hematopoietic stem/progenitor cells (HSPC). CCR5-targeted shRNA (sh5) and C46 peptide were stably expressed in the target cells and were able to effectively protect gene-modified cells against infection with CCR5- and CXCR4-tropic strains of HIV-1. LVsh5/C46 treatment was nontoxic as assessed by cell growth and viability, was noninflammatory, and had no adverse effect on HSPC differentiation. LVsh5/C46 could be produced at a scale sufficient for clinical development and resulted in active viral particles with very low mutagenic potential and the absence of replication-competent lentivirus. Based on these in vitro results, plus additional in vivo safety and efficacy data, LVsh5/C46 is now being tested in a phase 1/2 clinical trial for the treatment of HIV-1 disease.

Gene therapy strategies to exploit TRIM derived restriction factors against HIV-1

Restriction factors are a collection of antiviral proteins that form an important aspect of the innate immune system. Their constitutive expression allows immediate response to viral infection, ahead of other innate or adaptive immune responses. We review the molecular mechanism of restriction for four categories of restriction factors; TRIM5, tetherin, APOBEC3G and SAMHD1 and go on to consider how the TRIM5 and TRIMCyp proteins in particular, show promise for exploitation using gene therapy strategies. Such approaches could form an important alternative to current anti-HIV-1 drug regimens, especially if combined with strategies to eradicate HIV reservoirs. Autologous CD4+ T cells or their haematopoietic stem cell precursors engineered to express TRIMCyp restriction factors, and provided in a single therapeutic intervention could then be used to restore functional immunity with a pool of cells protected against HIV. We consider the challenges ahead and consider how early clinical phase testing may best be achieved.

Antiviral activity of recombinant ankyrin targeted to the capsid domain of HIV-1 Gag polyprotein

Background

Ankyrins are cellular mediators of a number of essential protein-protein interactions. Unlike intrabodies, ankyrins are composed of highly structured repeat modules characterized by disulfide bridge-independent folding. Artificial ankyrin molecules, designed to target viral components, might act as intracellular antiviral agents and contribute to the cellular immunity against viral pathogens such as HIV-1.

Results

A phage-displayed library of artificial ankyrins was constructed, and screened on a polyprotein made of the fused matrix and capsid domains (MA-CA) of the HIV-1 Gag precursor. An ankyrin with three modules named Ank^GAG1D4 (16.5 kDa) was isolated. Ank^GAG1D4 and MA-CA formed a protein complex with a stoichiometry of 1:1 and a dissociation constant of K_d ~ 1 μM, and the Ank^GAG1D4 binding site was mapped to the N-terminal domain of the CA, within residues 1-110. HIV-1 production in SupT1 cells stably expressing Ank^GAG1D4 in both N-myristoylated and non-N-myristoylated versions was significantly reduced compared to control cells. Ank^GAG1D4 expression also reduced the production of MLV, a phylogenetically distant retrovirus. The Ank^GAG1D4-mediated antiviral effect on HIV-1 was found to occur at post-integration steps, but did not involve the Gag precursor processing or cellular trafficking. Our data suggested that the lower HIV-1 progeny yields resulted from the negative interference of Ank^GAG1D4-CA with the Gag assembly and budding pathway.

Conclusions

The resistance of Ank^GAG1D4-expressing cells to HIV-1 suggested that the CA-targeted ankyrin Ank^GAG1D4 could serve as a protein platform for the design of a novel class of intracellular inhibitors of HIV-1 assembly based on ankyrin-repeat modules.

Zinc-finger nuclease editing of human cxcr4 promotes HIV-1 CD4(+) T cell resistance and enrichment

HIV-1-infected individuals can harbor viral isolates that can use CCR5, as well as CXCR4, for viral entry. To genetically engineer HIV-1 resistance in CD4(+) T cells, we assessed whether transient, adenovirus delivered zinc-finger nuclease (ZFN) disruption of genomic cxcr4 or stable lentiviral expression of short hairpin RNAs (shRNAs) targeting CXCR4 mRNAs provides durable resistance to HIV-1 challenge. ZFN-modification of cxcr4 in CD4(+) T cells was found to be superior to cell integrated lentivirus-expressing CXCR4 targeting shRNAs when CD4(+) T cells were challenged with HIV-1s that utilizes CXCR4 for entry. Cxcr4 disruption in CD4(+) T cells was found to be stable, conferred resistance, and provided for continued cell enrichment during HIV-1 infection in tissue culture and, in vivo, in peripheral blood mononuclear cell transplanted NSG mice. Moreover, HIV-1-infected mice with engrafted cxcr4 ZFN-modified CD4(+) T cells demonstrated lower viral levels in contrast to mice engrafted with unmodified CD4(+) T cells. These findings provide evidence that ZFN-mediated disruption of cxcr4 provides a selective advantage to CD4(+) T cells during HIV-1 infection.

Gene therapy strategies: can we eradicate HIV?

Despite the tremendous advances in antiretroviral combination therapy over the last decade, eradication of HIV from the infected organism is still an elusive goal. Lifelong therapy is associated with potential long-term toxicity, adherence problems, and development of drug resistance. Thus, gene therapy approaches targeting viral eradication are still attractive. Here a number of studies have failed to show a clear clinical benefit yet. Current approaches were mainly limited by a low number of transduced cells and genotoxicity. The use of new vector systems and the right choice of target cells and improved transduction protocols may overcome these obstacles. Recent reports on the use of newly developed transgenes either allowing for an enrichment of transduced cells by an in vivo selection advantage or restoration of a functional immune system which is resistant to HIV infection nourished the hope for continuous progress in this field. Indeed the intriguing finding that HIV seems to be eradicated in an individual case study after stem cell transplantation with a mutant coreceptor (CCR5 delta 32 deletion) underlines the proof of the concept.

Phase I/II Clinical Trials Using Gene-Modified Adult Hematopoietic Stem Cells for HIV: Lessons Learnt

Gene therapy for individuals infected with HIV has the potential to provide a once-only treatment that will act to reduce viral load, preserve the immune system, and mitigate cumulative toxicities associated with highly active antiretroviral therapy (HAART). The authors have been involved in two clinical trials (phase I and phase II) using gene-modified adult hematopoietic stem cells (HSCs), and these are discussed as prototypic trials within the general field of HSC gene therapy trials for HIV. Taken as a group these trials have shown (i) the safety of both the procedure and the anti-HIV agents themselves and (ii) the feasibility of the approach. They point to the requirement for (i) the ability to transduce and infuse as many as possible gene-containing HSC and/or (ii) high engraftment and in vivo expansion of these cells, (iii) potentially increased efficacy of the anti-HIV agent(s) and (iv) automation of the cell processing procedure.

Secreted antiviral entry inhibitory (SAVE) peptides for gene therapy of HIV infection

Gene therapeutic strategies for human immunodeficiency virus type 1 (HIV-1) infection could potentially overcome the limitations of standard antiretroviral drug therapy (ART). However, in none of the clinical gene therapy trials published to date, therapeutic levels of genetic protection have been achieved in the target cell population for HIV-1. To improve systemic antiviral efficacy, C peptides, which are efficient inhibitors of HIV-1 entry, were engineered for high-level secretion by genetically modified cells. The size restrictions for efficient peptide export through the secretory pathway were overcome by expressing the C peptides as concatemers, which were processed into monomers by furin protease cleavage. These secreted antiviral entry inhibitory (SAVE) peptides mediated a substantial protective bystander effect on neighboring nonmodified cells, thus suppressing virus replication even if only a small fraction of cells was genetically modified. Accordingly, these SAVE peptides may provide a strong benefit to AIDS patients in future, and, if applied by direct in vivo gene delivery, could present an effective alternative to antiretroviral drug regimen.

In silico modeling indicates the development of HIV-1 resistance to multiple shRNA gene therapy differs to standard antiretroviral therapy

BACKGROUND

Gene therapy has the potential to counter problems that still hamper standard HIV antiretroviral therapy, such as toxicity, patient adherence and the development of resistance. RNA interference can suppress HIV replication as a gene therapeutic via expressed short hairpin RNAs (shRNAs). It is now clear that multiple shRNAs will likely be required to suppress infection and prevent the emergence of resistant virus.

RESULTS

We have developed the first biologically relevant stochastic model in which multiple shRNAs are introduced into CD34+ hematopoietic stem cells. This model has been used to track the production of gene-containing CD4+ T cells, the degree of HIV infection, and the development of HIV resistance in lymphoid tissue for 13 years. In this model, we found that at least four active shRNAs were required to suppress HIV infection/replication effectively and prevent the development of resistance. The inhibition of incoming virus was shown to be critical for effective treatment. The low potential for resistance development that we found is largely due to a pool of replicating wild-type HIV that is maintained in non-gene containing CD4+ T cells. This wild-type HIV effectively out-competes emerging viral strains, maintaining the viral status quo.

CONCLUSIONS

The presence of a group of cells that lack the gene therapeutic and is available for infection by wild-type virus appears to mitigate the development of resistance observed with systemic antiretroviral therapy.

Computational models of HIV-1 resistance to gene therapy elucidate therapy design principles

Gene therapy is an emerging alternative to conventional anti-HIV-1 drugs, and can potentially control the virus while alleviating major limitations of current approaches. Yet, HIV-1's ability to rapidly acquire mutations and escape therapy presents a critical challenge to any novel treatment paradigm. Viral escape is thus a key consideration in the design of any gene-based technique. We develop a computational model of HIV's evolutionary dynamics in vivo in the presence of a genetic therapy to explore the impact of therapy parameters and strategies on the development of resistance. Our model is generic and captures the properties of a broad class of gene-based agents that inhibit early stages of the viral life cycle. We highlight the differences in viral resistance dynamics between gene and standard antiretroviral therapies, and identify key factors that impact long-term viral suppression. In particular, we underscore the importance of mutationally-induced viral fitness losses in cells that are not genetically modified, as these can severely constrain the replication of resistant virus. We also propose and investigate a novel treatment strategy that leverages upon gene therapy's unique capacity to deliver different genes to distinct cell populations, and we find that such a strategy can dramatically improve efficacy when used judiciously within a certain parametric regime. Finally, we revisit a previously-suggested idea of improving clinical outcomes by boosting the proliferation of the genetically-modified cells, but we find that such an approach has mixed effects on resistance dynamics. Our results provide insights into the short- and long-term effects of gene therapy and the role of its key properties in the evolution of resistance, which can serve as guidelines for the choice and optimization of effective therapeutic agents.

A primary obstacle to the success of any anti-HIV treatment is HIV's ability to rapidly resist it by generating new viral strains whose vulnerability to the treatment is reduced. Gene therapies represent a novel class of treatments for HIV infection that may supplement or replace present therapies, as they alleviate some of their major shortcomings. The design of gene therapeutic agents that effectively reduce viral resistance can be aided by a quantitative elucidation of the processes by which resistance is acquired following therapy initiation. We developed a computational model that describes a patient's response to therapy and used it to quantify the influence of therapy parameters and strategies on the development of viral resistance. We find that gene therapy induces different clinical conditions and a much slower viral response than present therapies. These dictate different design principles such as a greater significance to the virus' competence in the absence of therapy. We also show that one can effectively delay emergence of resistance by delivering distinct therapeutic genes into separate cell populations. Our results highlight the differences between traditional and gene therapies and provide a basic understanding of how key controllable parameters and strategies affect resistance development.

Mathematical modelling of the impact of haematopoietic stem cell-delivered gene therapy for HIV

BACKGROUND

Gene therapy represents a new treatment paradigm for HIV that is potentially delivered by a safe, once-only therapeutic intervention.

METHODS

Using mathematical modelling, we assessed the possible impact of autologous haematopoietic stem cell (HSC) delivered, anti-HIV gene therapy. The therapy comprises a ribozyme construct (OZ1) directed to a conserved region of HIV-1 delivered by transduced HSC (OZ1+HSC). OZ1+HSC contributes to the CD4+ T lymphocyte and monocyte/macrophage cell pools that preferentially expand under the selective pressure of HIV infection. The model was used to predict the efficacy of OZ1 in a highly active antiretroviral therapy (HAART) naïve individual and a HAART-experienced individual undergoing two structured treatment operations. In the standard scenario, OZ1+HSC was taken as 20% of total body HSC.

RESULTS

For a HAART-naïve individual, modelling predicts a reduction of HIV RNA at 1 and 2 years post-OZ1 therapy of 0.5 log(10) and 1 log(10), respectively. Eight years after OZ1 therapy, the CD4+ T-lymphocyte count was 271 cells/mm(3) compared to 96 cells/mm(3) for an untreated individual. In a HAART-experienced individual HIV RNA was reduced by 0.34 log(10) and 0.86 log(10) at 1 and 2 years. The OZ1 effect was maximal when both CD4+ T lymphocytes and monocytes/macrophages were protected from successful, productive infection by OZ1.

CONCLUSIONS

The modelling indicates a single infusion of HSC cell-delivered gene therapy can impact on HIV viral load and CD4 T-lymphocyte count. Given that gene therapy avoids the complications associated with HAART, there is significant potential for this approach in the treatment of HIV.

Specific transgene expression in HIV-infected cells using protease-cleavable transcription regulator

Gene therapy is a promising strategy for the treatment of HIV infection, but cell specificity remains an issue. Recently we have developed a new concept for a drug or gene delivery system responding to cellular signals (D-RECS) to achieve cell-specific transgene expression using a non-viral polymer-based vehicle. According to this concept, intracellular signaling enzymes, which are activated specifically in target cells, are used to trigger transgene expression. We previously applied this concept to HIV-1 protease and showed that the recombinant protease could act as a suitable signal. Here we further developed this system to achieve highly specific transgene expression in HIV-infected cells. We prepared a polymeric gene regulator grafted with a cationic peptide containing the HIV-Tat peptide via a specific substrate for HIV-1 protease. The regulator formed a stable polyplex with the transgene, suppressing its transcription. HIV-1 protease cleaved the peptide and released the transgene, which was consequently expressed specifically in activated HIV-infected cells, but remained unreleased and inactive in uninfected cells. The validity of this approach was further confirmed by applying it to the CVB1 2A protease of coxsackievirus (Picornaviridae family). This strategy should be widely applicable for specific expression of a variety of therapeutic genes in virus-infected cells.

Combinatorial evaluation of cations, pH-sensitive and hydrophobic moieties for polymeric vector design

Three combinatorial libraries of polymeric vectors were evaluated to investigate the functional roles of molecular weight (MW), cations, pH-sensitive moieties, and hydrophobic derivitization in polymer-mediated gene delivery. Four cationic and pH-sensitive moieties (imidazole, primary, secondary, and tertiary amino) and three hydrophobic residues (C4 butyl, C6 hexyl, and C8 octyl) were assessed in single and serially incremented, binary combinations. Three MWs were evaluated-10, 30, and 50 kDa. The highest levels of transfection, comparable to branched PEI (25 kDa), were achieved by 30 kDa and 50 kDa formulations containing primary amino and imidazole groups. Primary amino groups offered superior charge-neutralizing and size-condensing capacity, while imidazole groups appeared to bind with DNA via nonelectrostatically mediated interactions to produce stable polyplexes that were resistant to premature dissociation. Eight of the 10 highest-transfecting polymers possessed IC(50) values greater than the maximum concentration of free polymers exposed to cells (200 microg/ml). The results herein have identified highly efficient polymeric formulations with superb toxicity profiles and have revealed the functional roles that the investigated pendant groups play in the transfection process. The reported polymeric system offers a versatile and robust platform upon which future structure-function studies may be based to create safer and more efficient polymeric vectors.

Phase 2 gene therapy trial of an anti-HIV ribozyme in autologous CD34+ cells

Gene transfer has potential as a once-only treatment that reduces viral load, preserves the immune system, and avoids lifetime highly active antiretroviral therapy. This study, the first randomized, double-blind, placebo-controlled, phase II cell-delivered gene transfer clinical trial, was conducted in 74 HIV-1 infected adults who received a tat/vpr specific anti-HIV ribozyme (OZ1) or placebo delivered in autologous CD34+ hematopoietic progenitor cells. There were no OZ1-related adverse events. There was no statistical difference in viral load between the OZ1 and placebo group at the primary end-point (average at weeks 47 and 48) but time weighted areas under the curve from weeks 40-48 and 40-100 were significantly lower in the OZ1 group. Throughout the 100 weeks, CD4+ lymphocyte counts were higher in the OZ1 group. This study provides the first indication that cell-delivered gene transfer is safe and biologically active in HIV patients and can be developed as a conventional therapeutic product.

The F12-Vif derivative Chim3 inhibits HIV-1 replication in CD4+ T lymphocytes and CD34+-derived macrophages by blocking HIV-1 DNA integration

The viral infectivity factor (Vif) is essential for HIV-1 infectivity and hence is an ideal target for promising anti-HIV-1/AIDS gene therapy. We previously demonstrated that F12-Vif mutant inhibits HIV-1 replication in CD4(+) T lymphocytes. Despite macrophage relevance to HIV-1 pathogenesis, most gene therapy studies do not investigate macrophages because of their natural resistance to genetic manipulation. Here, we confirm the F12-Vif antiviral activity also in macrophages differentiated in vitro from transduced CD34(+) human stem cells (HSCs). Moreover, we identified the 126- to 170-amino-acid region in the C-terminal half of F12-Vif as responsible for its antiviral function. Indeed, Chim3 protein, containing this 45-amino-acid region embedded in a WT-Vif backbone, is as lethal as F12-Vif against HIV-1. Of major relevance, we demonstrated a dual mechanism of action for Chim3. First, Chim3 functions as a transdominant factor that preserves the antiviral function of the natural restriction factor APOBEC3G (hA3G). Second, Chim3 blocks the early HIV-1 retrotranscript accumulation and thereby HIV-1 DNA integration regardless of the presence of WT-Vif and hA3G. In conclusion, by impairing the early steps of HIV-1 life cycle, Chim3 conceivably endows engineered cells with survival advantage, which is required for the efficient immune reconstitution of patients living with HIV/AIDS.

Antiviral strategies

Viruses are obligatory intracellular parasites, whose replication depends on pathways and functions of the host cell. Consequently, it is difficult to define virus-specific functions as suitable targets for anti-infective therapy. However, significant progress has been made in the past 50 years towards the development of effective and specific antivirals. In particular, human immunodeficiency virus, hepatitis C virus, and hepatitis B virus, which cause chronic infections affecting millions of individuals world-wide, are a major focus of antiviral research. Initially, antivirals were mainly directed against virus-specific enzymes; more recently, drugs inhibiting the steps of virus entry or release have been developed. Rational approaches towards drug development, based on information about structure and function of viral proteins and molecular mechanisms of virus-host interactions, have become increasingly successful. Novel strategies currently explored in basic research or preclinical studies include approaches targeting host factors important for virus replication, the exploitation of the innate immune response system as well as the use of gene silencing strategies aimed at interfering with viral gene expression. Today, a number of effective virostatics targeting various viral replication steps are approved for treatment of important viral diseases. However, the use of these drugs is limited by the rapid development of antiviral resistance, which represents a central problem of current antiviral therapy.

Antiviral gene therapy

This chapter describes the major gene therapeutic approaches for viral infections. The vast majority of published approaches target severe chronic viral infections such as hepatitis B or C and HIV infection. Two basic gene therapy strategies are introduced here. The first involves the expression of a protein or an RNA that inhibits viral replication by targeting crucial steps of the viral life cycle or by interfering with a cellular factor required for virus replication. The major limitation of this approach is that primary levels of gene modification have generally not been sufficient to reduce the availability of target cells permissive for virus replication to a level that significantly decreases overall viral load. Thus, investigators have banked on the expectation that gene-protected cells have a sufficient selective advantage to accumulate and gain prevalence over time, a prediction that so far could not be confirmed in clinical trials. In vivo levels of gene modification can be improved, however, by introducing an additional selectable marker. In addition, a secreted antiviral gene product that exerts a bystander effect could significantly reduce overall virus replication despite relatively low levels of gene modification. In addition to these direct antiviral approaches, several strategies have been developed that employ or aim to enhance host immune responses. The innate immune response has been enhanced, for example, by the in vivo expression of interferons. Alternatively, T cells can be grafted with recombinant receptors to boost adaptive virus-specific immunity. These approaches are especially promising for chronic virus infection, where natural immune responses are evidently not sufficient to effectively control virus replication.

Efficient entry inhibition of human and nonhuman primate immunodeficiency virus by cell surface-expressed gp41-derived peptides

Membrane-anchored C-peptides (for example, maC46) derived from human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp41 effectively inhibit HIV-1 entry in cell lines and primary human CD4+ cells in vitro. Here we evaluated this gene therapy approach in animal models of AIDS. We adapted the HIV gp41-derived maC46 vector construct for use in rhesus monkeys. Simian immunodeficiency virus (SIV and SHIV) sequence-adapted maC46 peptides, and the original HIV-1-derived maC46 expressed on the surface of established cell lines blocked entry of HIV-1, SIVmac251 and SHIV89.6P. Furthermore, primary rhesus monkey CD4+ T cells expressing HIV sequence-based maC46 peptides were also protected from SIV entry. Depletion of CD8+ T cells from PBMCs enhanced the yield of maC46-transduced CD4+ T cells. Supplementation with interleukin-2 (IL-2) increased transduction efficiency, whereas IL-7 and/or IL-15 provided no additional benefit. Phenotypic analysis showed that maC46-transduced and expanded cells were predominantly central memory CD4+ T cells that expressed low levels of CCR5 and slightly elevated levels of CD62L, beta7-integrin and CXCR4. These findings show that maC46-based cell surface-expressed peptides can efficiently inhibit primate immunodeficiency virus infection, and therefore serve as the basis for evaluation of this gene therapy approach in an animal model for AIDS.

Recent advances in delivery systems for anti-HIV1 therapy

In the last years, different non-biological and biological carrier systems have been developed for anti-HIV1 therapy. Liposomes are excellent potential anti-HIV1 carriers that have been tested with drugs, antisense oligonucleotides, ribozymes and therapeutic genes. Nanoparticles and low-density lipoproteins (LDLs) are cell-specific transporters of drugs against macrophage-specific infections such as HIV1. Through a process of protein transduction, cell-permeable peptides of natural origin or designed artificially allow the delivery of drugs and genetic material inside the cell. Erythrocyte ghosts and bacterial ghosts are a promising delivery system for therapeutic peptides and HIV vaccines. Of interest are the advances made in the field of HIV gene therapy by the use of autologous haematopoietic stem cells and viral vectors for HIV vaccines. Although important milestones have been reached in the development of carrier systems for the treatment of HIV, especially in the field of gene therapy, further clinical trials are required so that the efficiency and safety of these new systems can be guaranteed in HIV patients.

Transfer of Autologous Gene-modified T Cells in HIV-infected Patients with Advanced Immunodeficiency and Drug-resistant Virus

Drug toxicity and viral resistance limit the long-term efficacy of antiviral drug treatment for human immunodeficiency virus (HIV) infection. Thus, alternative therapies need to be explored. We tested the infusion of T lymphocytes transduced with a retroviral vector (M87o) that expresses an HIV entry-inhibitory peptide (maC46). Gene-modified autologous T cells were infused into ten HIV-infected patients with advanced disease and multidrug-resistant virus during anti-retroviral combination therapy. T-cell infusions were tolerated well, with no severe side effects. A significant increase of CD4 counts was observed after infusion. At the end of the 1-year follow-up, the CD4 counts of all patients were still around or above baseline. Gene-modified cells could be detected in peripheral blood, lymph nodes, and bone marrow throughout the 1-year follow-up, and marking levels correlated with the cell dose. No significant changes of viral load were observed during the first 4 months. Four of the seven patients who changed their antiviral drug regimen thereafter responded with a significant decline in plasma viral load. In conclusion, the transfer of gene-modified cells was safe, led to sustained levels of gene marking, and may improve immune competence in HIV-infected patients with advanced disease and multidrug-resistant virus.