Inhibition of human and simian immunodeficiency virus protease function by targeting Vpx-protease-mutant fusion protein into viral particles

Positioning of darunavir/cobicistat-containing antiretroviral regimens in real life: results from a large multicentre observational prospective cohort (SCOLTA)

Background

Study aim was to evaluate the safety and durability of darunavir/cobicistat (DRV/c) in a real life setting.

Methods

Multicentre prospective cohort study performed in the context of SCOLTA (Surveillance Cohort Long-Term Toxicity Antiretrovirals). Patients were evaluated at baseline, week 24 and 48. Changes were evaluated using the paired t test or signed rank test. The multivariable analysis was performed using a general linear model, after ranking of not normally distributed variables.

Results

A total of 249 patients were included, 72 (29%) were in DRV/c-based dual therapies (DT). Hypercholesterolemia, HC, (total cholesterol (TC) ≥ 200 mg/dL or low density-C (LDL-C) ≥ 130 or statin use) was present in 121 (48.6%) and hypertriglyceridemia, (triglycerides (TG) ≥ 200 mg/dl or fibrate use) in 41 (16.5%) patients. Blood lipid profile did not change significantly in either the global population or patients with HC. After a median observation of 17 months (IQR 13–20), 59 (25.3%) patients discontinued DRV/c, of which 13 were in DT. The durability DT resulted higher than that of triple therapy (log-rank test p = 0.01). Main reasons for stopping DRV/c were simplification (15 patients), adverse events (13 patients), planned discontinuation for treatment initiation with DAA (4 patients), treatment failure (2 patients); death (2 patients), other causes (10 patients). Twenty-six were lost to follow-up.

Conclusions

DRV/c was safe and well tolerated. Dual therapies showed a better profile of tolerability and a longer durability compared to triple therapies.

Cell and Gene Therapy for HIV Cure

As the HIV pandemic rapidly spread worldwide in the 1980s and 1990s, a new approach to treat cancer, genetic diseases, and infectious diseases was also emerging. Cell and gene therapy strategies are connected with human pathologies at a fundamental level, by delivering DNA and RNA molecules that could correct and/or ameliorate the underlying genetic factors of any illness. The history of HIV gene therapy is especially intriguing, in that the virus that was targeted was soon co-opted to become part of the targeting strategy. Today, HIV-based lentiviral vectors, along with many other gene delivery strategies, have been used to evaluate HIV cure approaches in cell culture, small and large animal models, and in patients. Here, we trace HIV cell and gene therapy from the earliest clinical trials, using genetically unmodified cell products from the patient or from matched donors, through current state-of-the-art strategies. These include engineering HIV-specific immunity in T-cells, gene editing approaches to render all blood cells in the body HIV-resistant, and most importantly, combination therapies that draw from both of these respective "offensive" and "defensive" approaches. It is widely agreed upon that combinatorial approaches are the most promising route to functional cure/remission of HIV infection. This chapter outlines cell and gene therapy strategies that are poised to play an essential role in eradicating HIV-infected cells in vivo.

Effect of plasmid DNA vaccine design and in vivo electroporation on the resulting vaccine-specific immune responses in rhesus macaques

Since human immunodeficiency virus (HIV)-specific cell-mediated immune (CMI) responses are critical in the early control and resolution of HIV infection and correlate with postchallenge outcomes in rhesus macaque challenge experiments, we sought to identify a plasmid DNA (pDNA) vaccine design capable of eliciting robust and balanced CMI responses to multiple HIV type 1 (HIV-1)-derived antigens for further development. Previously, a number of two-, three-, and four-vector pDNA vaccine designs were identified as capable of eliciting HIV-1 antigen-specific CMI responses in mice (M. A. Egan et al., Vaccine 24:4510-4523, 2006). We then sought to further characterize the relative immunogenicities of these two-, three-, and four-vector pDNA vaccine designs in nonhuman primates and to determine the extent to which in vivo electroporation (EP) could improve the resulting immune responses. The results indicated that a two-vector pDNA vaccine design elicited the most robust and balanced CMI response. In addition, vaccination in combination with in vivo EP led to a more rapid onset and enhanced vaccine-specific immune responses. In macaques immunized in combination with in vivo EP, we observed a 10- to 40-fold increase in HIV-specific enzyme-linked immunospot assay responses compared to those for macaques receiving a 5-fold higher dose of vaccine without in vivo EP. This increase in CMI responses translates to an apparent 50- to 200-fold increase in pDNA vaccine potency. Importantly, in vivo EP enhanced the immune response against the less immunogenic antigens, resulting in a more balanced immune response. In addition, in vivo EP resulted in an approximate 2.5-log(10) increase in antibody responses. The results further indicated that in vivo EP was associated with a significant reduction in pDNA persistence and did not result in an increase in pDNA associated with high-molecular-weight DNA relative to macaques receiving the pDNA without EP. Collectively, these results have important implications for the design and development of an efficacious vaccine for the prevention of HIV-1 infection.

Rational design of a plasmid DNA vaccine capable of eliciting cell-mediated immune responses to multiple HIV antigens in mice

Given the importance of the HIV-specific cell-mediated immune response in the early control and resolution of HIV infection and the observed correlation between pre-challenge vaccine elicited CTL responses and post challenge outcome in SHIV/rhesus macaque experiments, we sought to identify several candidate plasmid DNA (pDNA) vaccine designs capable of eliciting robust and balanced cell-mediated immune responses to multiple HIV-1 derived antigens in mice for further vaccine development. To rationally construct candidate vaccines for immunogenicity testing, we determined the relative immunogenicity of the individual HIV-derived vaccine antigens (env, gag, pol, nef, tat and vif) and the relative strength of various transcriptional control elements (HCMV, SCMV, HSV Lap1) in Balb/c mice. Next, a number of 1-, 2-, 3- and 4-vector pDNA vaccine designs were tested for their ability to elicit HIV-1 antigen-specific CMI responses. For these studies, Balb/c mice were immunized with a fixed total pDNA vaccine dose of 100 mcg in combination with 25 mcg plasmid-based murine IL-12 and tested for the induction of HIV-1 antigen-specific CMI responses by IFN-gamma ELISpot analysis. The results of this study indicate that all pDNA vaccine designs were capable of eliciting CMI responses to multiple HIV-1 antigens. As a result of this iterative comparative analysis, we have identified a number of pDNA vaccine candidates capable of eliciting potent, balanced CMI responses to multiple HIV-1 derived antigens. These results have important implications for the design and development of an efficacious vaccine for the prevention of HIV-1 infection.

Virion-targeted viral inactivation: new therapy against viral infection

BACKGROUND

Acquired immune deficiency syndrome (AIDS) is resistant to all current therapy. Gene therapy is an attractive alternative or additive to current, unsatisfactory AIDS therapy.

MATERIALS AND METHODS

To develop an antiviral molecule targeting viral integrase (HIV IN), we generated a single-chain antibody, termed scAb, which interacted with human immunodeficiency virus type 1 (HIV-1) IN and inhibited virus replication at the integration step when expressed intracellularly. To reduce infectivity from within the virus particles, we made expression plasmids (pC-scAbE-Vpr, pC-scAbE-CA, and pC-scAbE-WXXF), which expressed the anti-HIV IN scAb fused to the N-terminus of HIV-1-associated accessory protein R (Vpr), capsid protein (CA), and specific binding motif to Vpr (WXXF), respectively. All fusion proteins were tagged with a nine-amino acid peptide derived from influenza virus hemagglutinin (HA) at the C terminus.

RESULTS

The fusion molecules, termed scAbE-Vpr, scAbE-CA, and scAbE-WXXF, interacted specifically with HIV IN immobilized on a nitrocellulose membrane. Immunoblot analysis showed that scAbE-Vpr, scAbE-CA, and scAbE-WXXF were incorporated into the virions produced by cotransfection of 293T cells with HIV-1 infectious clone DNA (pLAI) and pC-scAbE-Vpr, pC-scAbE-WXXF. A multinuclear activation galactosidase indicator (MAGI) assay revealed that the virions released from 293T cells cotransfected with pLAI and pC-scAbE-Vpr, pC-scAbE-WXXF had as little 1000-fold of the infectivity of the control wild-type virions, which were produced from the 293T cells transfected with pLAI alone. Furthermore, the virions produced from the 293T cells cotransfected with pLAI and an scAb expression vector (pC-scAb) showed only 1% of the infectivity of the control HIV-1 in a MAGI assay, although scAb was not incorporated into the virions. In either instance, the total quantity of the progeny virions released from the transfected 293T cells and the patterns of the virion proteins were hardly affected by the presence of scAb, scAbE-Vpr, or scAbE-WXXF, as determined by virion-associated reverse transcriptase assay and by immunoblot analysis, respectively. Because G418-selected HeLa clones carrying the expression plasmid for scAbE-WXXF were obtained much more frequently than those for scAbE-Vpr, scAbE-WXXF was inferred to be less toxic to cells than scAbE-Vpr. The result that scAbE-WXXF with viral incorporation achieved more than a 10-fold reduction in infectivity of the progeny virions than scAb without incorporation suggests that scAbE-WXXF is a potential antiviral molecule, inhibiting replication by neutralization of HIV IN activity both within cells and within virions. Moreover, it is nontoxic to human cells. We termed this gene therapy "virion-"targeted-viral inactivation" and these molecules "packageable antiviral therapeutics."

CONCLUSION

This new gene therapy has the potential for wide application in many viral infectious diseases.

Intravirion display of a peptide corresponding to the dimer structure of protease attenuates HIV-1 replication

Current treatment of HIV-1-infected individuals involves the administration of several drugs, all of which target either the reverse transcriptase or the protease activity of the virus. Unfortunately, the benefits of such treatments are compromised by the emergence of viruses exhibiting resistance to the drugs. This situation warrants new approaches for interfering with virus replication. Considering the activation of protease in the virus particles, a novel strategy to inhibit HIV-1 replication was tested targeting the dimerization domain of the protease. To test this idea, we have selected four residues from the C terminus of HIV-1 protease that map to the dimer interface region of the enzyme. We have exploited Vpr to display the peptides in the virus particles. The chimeric Vpr exhibited expression and virion incorporation similar to wildtype Vpr. The virus derived from the HIV-1 proviral DNA containing chimeric Vpr sequences registered a reduced level of replication in CEM and CEM X 174 cells in comparison with viruses containing wildtype Vpr. Similar results were observed in a single-round replication assay. These results suggest that the intravirion display of peptides targeting viral proteins is a powerful approach for developing antiviral agents and for dissecting the dynamic interactions between structural proteins during virus assembly and disassembly.

Biochemical analyses of the interactions between human immunodeficiency virus type 1 Vpr and p6(Gag)

The nonstructural human immunodeficiency virus type 1 Vpr protein is packaged into progeny virions at significant levels (approximately 200 copies/virion). Genetic analyses have demonstrated that efficient Vpr packaging is dependent upon a leucine-X-X-leucine-phenylalanine (LXXLF) motif located in the p6(Gag) domain of the structural Gag polyprotein. Recombinant proteins spanning full-length Vpr (Vpr(1-97)) or the amino-terminal 71 amino acids (Vpr(1-71)) formed specific complexes with recombinant p6 proteins in vitro. Complex formation required an intact LXXLF motif and exhibited an intrinsic dissociation constant of approximately 75 microM. Gel filtration and cross-linking analyses further revealed that Vpr(1-71) self-associated in solution. Our experiments demonstrate that Vpr can bind directly and specifically to p6 and suggest that oligomerization of both Vpr and Gag may serve to increase the avidity and longevity of Vpr-Gag complexes, thereby ensuring efficient Vpr packaging.

Therapeutic effect of a Gag-nuclease fusion protein against retroviral infection in vivo

Recently, remarkable progress has been made in developing effective combination drug therapies that can control but not cure retroviral replication. Even when effective, these drug regimens are toxic, they require demanding administration schedules, and resistant viruses can emerge. Thus the need for new gene-based therapies continues. In one such approach, capsid-targeted viral inactivation (CTVI), nucleases fused to viral coat proteins are expressed in infected cells and become incorporated during virion assembly. CTVI can eliminate infectious murine retrovirus titer in tissue culture. Here we describe transgenic mice expressing fusions of the Moloney murine leukemia virus (Mo-MuLV) Gag protein to staphylococcal nuclease. This work tests the protective effect and demonstrates in vivo proof-of-principle of CTVI in transgenic mice expressing endogenous proviral copies of Mo-MuLV. The antiviral protein-expressing mice are phenotypically normal, attesting to the lack of toxicity of the fusion protein. The Mo-MuLV infection was much less virulent in transgenic littermates than in nontransgenic littermates. Gag-nuclease expression reduced infectious titers in blood up to 10-fold, decreased splenomegaly and leukemic infiltration, and increased life spans up to 2.5-fold in transgenic relative to nontransgenic infected animals. These results suggest that gene therapies based on similar fusion proteins, designed to attack human immunodeficiency virus or other retroviruses, could provide substantial therapeutic benefits.

Epitope-tagging approach to determine the stoichiometry of the structural and nonstructural proteins in the virus particles: amount of Vpr in relation to Gag in HIV-1

We used an epitope-tagging approach to determine the ratio of Gag (structural) to Vpr (nonstructural) in the virus particles directed by human immunodeficiency virus type 1. For this purpose, chimeric Gag and Vpr expression plasmids were constructed with the Flag epitope (DYKDDDDK), and the sequences corresponding to the chimeric protein were introduced into human immunodeficiency virus type 1 proviral DNA (NL4-3) to determine the ratio in the virus particles when these proteins are expressed in cis. In addition, NL4-3 DNA was modified to disrupt Vpr synthesis to determine the extent of incorporation of Vpr-FL when it is expressed in trans through a heterologous promoter. The analysis of virus particles generated by transfection of proviral DNA into RD cells indicated that (1) the ratio of Gag to Vpr in virus particles, when Vpr-FL is expressed in cis (in the context of proviral DNA), is in the range of 150-200:1 (14-18 molecules of Vpr per virion) and (2) the expression of Vpr-FL in trans showed efficient incorporation with a Gag to Vpr ratio of 5-7:1 (392-550 molecules of Vpr). These results suggest that the presence of the same epitope on different viral proteins may provide an accurate comparison of these proteins in the virus particles.

Extent of incorporation of HIV-1 Vpr into the virus particles is flexible and can be modulated by expression level in cells

To examine the factors that control the extent of incorporation of Vpr into the virus particles, we utilized an epitope-tagging approach with Flag (FL) as the epitope for quantitation. We generated expression plasmids containing Vpr-FL and Vpr E21,24P-FL and also HIV-1 proviral DNA containing Vpr-FL (NL-Vpr-FL). Immunoblot analysis using Flag antibodies revealed that virus particles derived from co-transfection of NL-Vpr-FL and Vpr-FL showed an enhanced level of Vpr-FL in comparison to NL-Vpr-FL derived virus. These results suggest that the amount of incorporation of Vpr into the virus particles is flexible and may be modulated by its expression level in cells.

Packageable antiviral therapeutics against human immunodeficiency virus type 1: virion-targeted virus inactivation by incorporation of a single-chain antibody against viral integrase into progeny virions

To determine their activities as an antiviral agent packageable within virions and suitable for continued expression in cells, we tested a single-chain antibody (scAb) against human immunodeficiency virus type 1 (HIV-1) integrase and its three fusion proteins: fused to viral protein R (scab-Vpr), a double-cassette of the WXXF motif binding to Vpr (scAb-WXXF), and viral major capsid protein (scAb-CA), respectively. Cotransfection of human 293T cells with expression plasmid for scAb-Vpr or -WXXF along with HIV-1 clone pLAI resulted in the production of a normal amount of progeny virions with infectivity decreased by more than 10(3)-fold. Immunoblot analyses showed that scAb-Vpr or -WXXF was associated with virions, whereas scAb or scAb-CA was not, suggesting that scAb-Vpr or -WXXF was incorporated into virions. The incorporation of scAb-WXXF appeared to be Vpr dependent, because the fusion protein was associated with the wild-type but not with Vpr-truncated HIV-1 virions. Since G418-selected HeLa clones carrying expression plasmid for scAb-WXXF were obtained much more frequently than those for scAb-Vpr, scAb-WXXF was inferred to be less toxic to cells than scAb-Vpr. These results suggest that scAb-WXXF may serve as a novel class of antiviral therapeutic that inactivates progeny HIV virions from within.

HIV-1 Vpr-chloramphenicol acetyltransferase fusion proteins: sequence requirement for virion incorporation and analysis of antiviral effect

The human immunodeficiency virus type 1 Vpr is a virion-associated protein that is incorporated in trans into viral particles, presumably via an interaction with the p6 domain of the Gag polyprotein precursor. Recently, several studies demonstrated that Vpr fusion proteins could be used as intravirion inactivating agents. In this study, we compared different Vpr-chloramphenicol acetyltransferase (CAT) fusion proteins for their virion incorporation ability and their effect on the infectivity of HIV viruses. Our deletion analysis indicates that both the N-terminal alpha-helical domain and the leucine/isoleucine-rich (LR) domain located in the middle region of Vpr are required for optimal virion incorporation of Vpr-CAT fusion proteins. The C-terminal basic region, associated with Vpr's ability to mediate cell cycle arrest in G2, was not required for virion incorporation, thus allowing the development of Vpr-based chimeric proteins devoid of any effect on cell growth. The fusion of Vpr at the N- or C-terminus of CAT targeted with equal efficiency the chimeric protein into virions. While the virion incorporation of most Vpr-CAT fusion proteins tested in this study was dependent on the presence of an intact p6 domain, fusion proteins containing only the N-terminal alpha-helical domain of Vpr (amino acid 1 to 42) were incorporated into virions in a p6-independent manner. Virion incorporation of Vpr-CAT fusion proteins was shown to decrease viral infectivity. Moreover, the insertion of HIV protease-cleavage sites between Vpr and CAT not only efficiently delivered and released the cleaved CAT product into HIV viral particles, but also greatly potentiated the inhibition of progeny virion infectivity. Overall, our study: (1) defines the Vpr sequence requirement and configuration necessary for the specific and optimal incorporation of Vpr fusion protein into HIV particles; (2) shows that Vpr fusion proteins have the ability to suppress HIV infectivity by targeting multiple steps of viral morphogenesis.

Human immunodeficiency virus type 1 integrase protein promotes reverse transcription through specific interactions with the nucleoprotein reverse transcription complex

The human immunodeficiency virus type 1 (HIV-1) integrase protein (IN) is essential for integration of the viral DNA into host cell chromosomes. Since IN is expressed and assembled into virions as part of the 160-kDa Gag-Pol precursor polyprotein and catalyzes integration of the provirus in infected cells as a mature 32-kDa protein, mutations in IN are pleiotropic and may affect virus replication at different stages of the virus life cycle in addition to integration. Several different phenotypes have been observed for IN mutant viruses, including defects in virion morphology, protein composition, reverse transcription, nuclear import, and integration. Because the effects of mutations in the IN domain of Gag-Pol can not always be distinguished from those of mutations in the mature IN protein, there remains a significant gap in our understanding of IN function in vivo. To directly analyze the function of the mature IN protein itself, in the context of a replicating virus but independently from that of Gag-Pol, we used an approach developed in our laboratory for incorporating proteins into HIV virions by their expression in trans as fusion partners of either Vpr or Vpx. By providing IN in trans as a Vpr-IN fusion protein, our analysis revealed, for the first time, that the mature IN protein is essential for the efficient initiation of reverse transcription in infected cells and that this function does not require the IN protein to be enzymatically (integration) active. Our findings of a direct physical interaction between IN and reverse transcriptase and the failure of heterologous HIV-2 IN protein to efficiently support reverse transcription indicate that this novel function occurs through specific interactions with other viral components of the reverse transcription initiation complex. Studies involving complementation between integration- and DNA synthesis-defective IN mutants further support this conclusion and reveal that the highly conserved HHCC motif of IN is important for both activities. These findings provide important new insights into IN function and reverse transcription in the context of the nucleoprotein reverse transcription complex within the infected cell. Moreover, they validate a novel approach that obviates the need to mutate Gag-Pol in order to study the role of its individual mature components at the virus replication level.

Production of uninfectious human immunodeficiency virus type 1 containing viral protein R fused to a single-chain antibody against viral integrase

A single-chain antibody (scAb) against human immunodeficiency virus type 1 (HIV-1) integrase was expressed as a fusion protein of scAb and HIV-1 viral protein R (Vpr), together with the HIV-1 genome, in human 293T cells. The expression did not affect virion production much but markedly reduced the infectivity of progeny virions. The fusion protein was found to be incorporated into the virions. The incorporation appears to account for the reduced infectivity.

Virion-targeted viral inactivation of human immunodeficiency virus type 1 by using Vpr fusion proteins

Inactivation of progeny virions with chimeric virion-associated proteins represents a novel therapeutic approach against human immunodeficiency virus (HIV) replication. The HIV type 1 (HIV-1) Vpr gene product, which is packaged into virions, is an attractive candidate for such a strategy. In this study, we developed Vpr-based fusion proteins that could be specifically targeted into mature HIV-1 virions to affect their structural organization and/or functional integrity. Two Vpr fusion proteins were constructed by fusing to the first 88 amino acids of HIV-1 Vpr the chloramphenicol acetyltransferase enzyme (VprCAT) or the last 18 C-terminal amino acids of the HIV-1 Vpu protein (VprIE). These Vpr fusion proteins were initially designed to quantify their efficiency of incorporation into HIV-1 virions when produced in cis from the provirus. Subsequently, CD4+ Jurkat T-cell lines constitutively expressing the VprCAT or the VprIE fusion protein were generated with retroviral vectors. Expression of the VprCAT or the VprIE fusion protein in CD4+ Jurkat T cells did not interfere with cellular viability or growth but conferred substantial resistance to HIV replication. The resistance to HIV replication was more pronounced in Jurkat-VprIE cells than in Jurkat-VprCAT cells. Moreover, the antiviral effect mediated by VprIE was dependent on an intact p6(gag) domain, indicating that the impairment of HIV-1 replication required the specific incorporation of Vpr fusion protein into virions. Gene expression, assembly, or release was not affected upon expression of these Vpr fusion proteins. Indeed, the VprIE and VprCAT fusion proteins were shown to affect the infectivity of progeny virus, since HIV virions containing the VprCAT or the VprIE fusion proteins were, respectively, 2 to 3 times and 10 to 30 times less infectious than the wild-type virus. Overall, this study demonstrated the successful transfer of resistance to HIV replication in tissue cultures by use of Vpr-based antiviral genes.

Incorporation of functional human immunodeficiency virus type 1 integrase into virions independent of the Gag-Pol precursor protein

Retroviral integrase (IN) is expressed and incorporated into virions as part of the Gag-Pol polyprotein precursor. IN catalyzes integration of the proviral DNA into host cell chromosomes during the early stages of the virus life cycle, and as a component of Gag-Pol, it is involved in virion morphogenesis during late stages. It is unknown whether the scheme, conserved among retroviruses, for expressing and incorporating IN as a component of the Gag-Pol precursor protein is necessary for its function in the infected cell after viral entry. We have developed human immunodeficiency virus (HIV) virion-associated accessory proteins (Vpr and Vpx) as vehicles to deliver both foreign and viral proteins into the virus particle by their expression in trans as heterologous fusion proteins (X. Wu, et al., J. Virol. 69:3389-3398, 1995; X. Wu, et al., J. Virol. 70:3378-3384, 1996; X. Wu, et al., EMBO J. 16:5113-5122, 1977). To analyze IN function independent of its expression as a part of Gag-Pol, we expressed and incorporated IN into HIV type 1 (HIV-1) virions in trans as a fusion partner of Vpr (Vpr-IN). Our results demonstrate that the Vpr-IN fusion protein is efficiently incorporated into virions and then processed by the viral protease to liberate the IN protein. Virus derived from IN-minus provirus is noninfectious. However, this defect is overcome by trans complementation with the Vpr-IN fusion protein. Moreover, complemented virions are able to replicate through a complete cycle of infection, including formation of the provirus (integration). These results show, for the first time, that full IN function can be provided in trans, independent of its expression and incorporation into virions as a component of Gag-Pol. This finding also indicates that the IN domain of Gag-Pol is not required for the formation of infectious virions when IN is provided in trans. The ability to incorporate functional IN into retroviral particles in trans will provide unique opportunities to explore the function of this critical enzyme in a biologically relevant context, i.e., in infected cells as part of the nucleoprotein/preintegration complex.

Expression of a murine leukemia virus Gag-Escherichia coli RNase HI fusion polyprotein significantly inhibits virus spread

The antiviral strategy of capsid-targeted viral inactivation (CTVI) was designed to disable newly produced virions by fusing a Gag or Gag-Pol polyprotein to a degradative enzyme (e.g., a nuclease or protease) that would cause the degradative enzyme to be inserted into virions during assembly. Several new experimental approaches have been developed that increase the antiviral effect of the CTVI strategy on retroviral replication in vitro. A Moloney murine leukemia virus (Mo-MLV) Gag-Escherichia coli RNase HI fusion has a strong antiviral effect when used prophylactically, inhibiting the spread of Mo-MLV and reducing virus titers 1,500- to 2,500-fold. A significant (approximately 100-fold) overall improvement of the CTVI prophylactic antiviral effect was produced by a modification in the culture conditions which presumably increases the efficiency of delivery and expression of the Mo-MLV Gag fusion polyproteins. The therapeutic effect of Mo-MLV Gag-RNase HI polyproteins is to reduce the production of infectious Mo-MLV up to 18-fold. An Mo-MLV Gag-degradative enzyme fusion junction was designed that can be cleaved by the Mo-MLV protease to release the degradative enzyme.

Development of a novel anti-HIV-1 agent from within: effect of chimeric Vpr-containing protease cleavage site residues on virus replication

Effective antiviral agents will be of great value in controlling virus replication and delaying the onset of HIV-1-related disease symptoms. Current therapy involves the use of antiviral agents that target the enzymatic functions of the virus, resulting in the emergence of resistant viruses to these agents, thus lowering their effectiveness. To overcome this problem, we have considered the idea of developing novel agents from within HIV-1 as inhibitors of virus replication. The specificity of the Vpr protein for the HIV-1 virus particle makes it an attractive molecule for the development of antiviral agents targeting the events associated with virus maturation. We have generated chimeric Vpr proteins containing HIV-1-specific sequences added to the C terminus of Vpr. These sequences correspond to nine cleavage sites of the Gag and Gag-Pol precursors of HIV-1. The chimeric Vpr constructs were introduced into HIV-1 proviral DNA to assess their effect on virus infectivity using single- and multiple-round replication assays. The virus particles generated exhibited a variable replication pattern depending on the protease cleavage site used as a fusion partner. Interestingly, the chimeric Vpr containing the cleavage sequences from the junction of p24 and p2, 24/2, completely abolished virus infectivity. These results show that chimeric proteins generated from within HIV-1 have the ability to suppress HIV-1 replication and make ideal agents for gene therapy or intracellular immunization to treat HIV-1 infection.

Destroying retroviruses from within

One strategy for neutralizing retroviral infectivity is to induce the incorporation of lethal fusion proteins, such as capsid protein-nuclease fusions, into the virion during the normal viral assembly process. Genes encoding such antiviral fusion proteins must be nontoxic to the host, lethal to the virus, and must be efficiently delivered to, and expressed in, appropriate target cells.