Molecular inhibition of HIV type 1 by HIV type 2: effectiveness in peripheral blood mononuclear cells

HIV-2 as a model to identify a functional HIV cure

Two HIV virus types exist: HIV-1 is pandemic and aggressive, whereas HIV-2 is confined mainly to West Africa and less pathogenic. Despite the fact that it has been almost 40 years since the discovery of AIDS, there is still no cure or vaccine against HIV. Consequently, the concepts of functional vaccines and cures that aim to limit HIV disease progression and spread by persistent control of viral replication without life-long treatment have been suggested as more feasible options to control the HIV pandemic. To identify virus-host mechanisms that could be targeted for functional cure development, researchers have focused on a small fraction of HIV-1 infected individuals that control their infection spontaneously, so-called elite controllers. However, these efforts have not been able to unravel the key mechanisms of the infection control. This is partly due to lack in statistical power since only 0.15% of HIV-1 infected individuals are natural elite controllers. The proportion of long-term viral control is larger in HIV-2 infection compared with HIV-1 infection. We therefore present the idea of using HIV-2 as a model for finding a functional cure against HIV. Understanding the key differences between HIV-1 and HIV-2 infections, and the cross-reactive effects in HIV-1/HIV-2 dual-infection could provide novel insights in developing functional HIV cures and vaccines.

Mortality rates in people dually infected with HIV-1/2 and those infected with either HIV-1 or HIV-2: a systematic review and meta-analysis

OBJECTIVE

As compared to HIV-1 infection, HIV-2 is less transmissible, disease progression is slower, and the mortality risk is lower. It has been suggested that HIV-2 infection inhibits the progression of HIV-1 in individuals dually infected by HIV-1 and HIV-2 (HIV-D). We examined whether the mortality rates in dually infected individuals differ from those in persons infected with either HIV-1 or HIV-2.

DESIGN

We conducted a systematic review and meta-analysis.

METHODS

Medline and Embase databases were searched for studies that reported the number of deaths and person-years of observation (PY) for at least two of the three HIV groups (i.e. HIV-1, HIV-2, and HIV-D). Meta-analyses were then performed with random-effects models, estimating combined mortality rate ratios (MRRs).

RESULTS

Of the 631 identified titles, six articles were included in the meta-analysis of HIV-D-infected individuals versus HIV-mono-infected persons, and seven were included in the analysis of HIV-1-mono-infected versus HIV-2-mono-infected individuals. The overall MRR of those infected with HIV-D versus HIV-1 was 1.11 [95% confidence interval (CI) 0.95-1.30]. The overall MRR of those infected with HIV-D versus HIV-2 was 1.81 (95% CI 1.43-2.30) and the MRR of those infected with HIV-1 versus HIV-2 was 1.86 (95% CI 1.44-2.39).

CONCLUSION

HIV-2-mono-infected persons have a lower mortality rate than those mono-infected with HIV-1 and those with HIV-D. There is no evidence that HIV-2 delays progression to death in HIV-D-infected individuals.

Inhibition of HIV-1 disease progression by contemporaneous HIV-2 infection

BACKGROUND

Progressive immune dysfunction and the acquired immunodeficiency syndrome (AIDS) develop in most persons with untreated infection with human immunodeficiency virus type 1 (HIV-1) but in only approximately 20 to 30% of persons infected with HIV type 2 (HIV-2); among persons infected with both types, the natural history of disease progression is poorly understood.

METHODS

We analyzed data from 223 participants who were infected with HIV-1 after enrollment (with either HIV-1 infection alone or HIV-1 and HIV-2 infection) in a cohort with a long follow-up duration (approximately 20 years), according to whether HIV-2 infection occurred first, the time to the development of AIDS (time to AIDS), CD4+ and CD8+ T-cell counts, and measures of viral evolution.

RESULTS

The median time to AIDS was 104 months (95% confidence interval [CI], 75 to 133) in participants with dual infection and 68 months (95% CI, 60 to 76) in participants infected with HIV-1 only (P=0.003). CD4+ T-cell levels were higher and CD8+ T-cell levels increased at a lower rate among participants with dual infection, reflecting slower disease progression. Participants with dual infection with HIV-2 infection preceding HIV-1 infection had the longest time to AIDS and highest levels of CD4+ T-cell counts. HIV-1 genetic diversity was significantly lower in participants with dual infections than in those with HIV-1 infection alone at similar time points after infection.

CONCLUSIONS

Our results suggest that HIV-1 disease progression is inhibited by concomitant HIV-2 infection and that dual infection is associated with slower disease progression. The slower rate of disease progression was most evident in participants with dual infection in whom HIV-2 infection preceded HIV-1 infection. These findings could have implications for the development of HIV-1 vaccines and therapeutics. (Funded by the Swedish International Development Cooperation Agency-Swedish Agency for Research Cooperation with Developing Countries and others.).

Chronic HIV-2 infection protects against total CD4+ cell depletion and rapid disease progression induced by SHIV89.6p challenge

OBJECTIVE

To better understand HIV-1 sexual transmission risk, we have studied the susceptibility of HIV-2-exposed, uninfected (EU) female pig-tailed macaques to intravaginal (IVAG) re-challenge with the homologous HIV-2 strain, followed by heterologous SHIV89.6p.

METHODS

Nine female macaques, previously protected by a post-exposure prophylaxis (PEP) regimen, along with one mock-treated EU animal, were re-exposed to HIV-2 by the IVAG route approximately 1.5 years later. A single follow-up challenge was performed approximately 1 year later with SHIV89.6p to assess susceptibility of chronic HIV-2-infected animals to further re-infection and pathogenic effects with a heterologous virus, somewhat mimicking HIV-1.

RESULTS

Eight of ten macaques (80%) became infected systemically with HIV-2, and plasma or cervicovaginal vRNA levels did not appreciably differ from prior historic non-PEP control macaques. Interestingly, all eight HIV-2-infected females were susceptible to SHIV89.6p infection by either intravenous (n = 4) or IVAG exposure (n = 4) after one inoculation. Plasma vRNA levels in these groups were controlled by week 8 and there were no decrease in CD4+ T cells > 50%. The remaining two HIV-2 EU macaques, inoculated intrarectally with SHIV89.6p, were unable to control virus replication and succumbed to disease by week 25 or week 61.

CONCLUSIONS

Our findings demonstrate that successful PEP regimens to prevent an initial infection do not have any lasting protective effects. The observed lack of cross-protection against SHIV89.6p transmission among chronic HIV-2-infected macaques provides modeling support for limited epidemiologic data indicating that human HIV-2 infection does not protect against HIV-1 infection, but may serve to alter overt clinical outcome.

HIV-2 derived lentiviral vectors: gene transfer in Parkinson's and Fabry disease models in vitro

Lentiviral vectors are prime candidate vectors for gene transfer into dividing and non-dividing cells, including neuronal cells and stem cells. For safety, HIV-2 lentiviral vectors may be better suited for gene transfer in humans than HIV-1 lentiviral vectors. HIV-2 vectors cross-packaged in HIV-1 cores may be even safer. Demonstration of the efficacy of these vectors in disease models will validate their usefulness. Parkinson's disease and Fabry disease provide excellent models for validation. Parkinson's disease is a focal degeneration of dopaminergic neurons in the brain with progressive loss of ability to produce the neurotransmitter dopamine. Current treatment entails administration of increasing doses of L-dopa, with attendant toxicity. We explore here the hypothesis that gene transfer of aromatic acid decarboxylase (AADC), a key enzyme in the pathway, will make neuronal cells more efficiently convert L-dopa into dopamine. Fabry disease on the other hand is a monogenic inherited disease, characterized by alpha-galactosidase A (AGA) deficiency, resulting in glycolipid accumulation in several cell types, including fibroblasts. Animal models for preclinical investigations of both of these diseases are available. We have designed monocistronic HIV-1 and HIV-2 vectors with the AADC transgene and monocistronic and bicistronic HIV-2 vectors with the AGA and puromycin resistance transgenes. They were packaged with either HIV-2 cores or HIV-1 cores (hybrid vectors). Gene transfer of AADC gene in neuronal cells imparted the ability on the transduced cells to efficiently convert L-dopa into dopamine. Similarly, the AGA vectors induced Fabry fibroblasts to produce high levels of AGA enzyme and caused rapid clearance of the glycolipids from the cells. Both monocistronic and bicistronic vectors were effective. Thus, the insertion of a second gene downstream in the bicistronic vector was not deleterious. In addition, both the self-packaged vectors and the cross-packaged hybrid vectors were effective in gene transfer.

Gene therapy of HIV-1 infection using lentiviral vectors expressing anti-HIV-1 genes

The use of vectors based on primate lentiviruses for gene therapy of human immunodeficiency virus type 1 (HIV-1) infection has many potential advantages over the previous murine retroviral vectors used for delivery of genes that inhibit replication of HIV-1. First, lentiviral vectors have the ability to transduce dividing and nondividing cells that constitute the targets of HIV-1 infection such as resting T cells, dendritic cells, and macrophages. Lentiviral vectors can also transfer genes to hematopoietic stem cells with a superior gene transfer efficiency and without affecting the repopulating capacity of these cells. Second, these vectors could be potentially mobilized in vivo by the wild-type virus to secondary target cells, thus expanding the protection to previously untransduced cells. And finally, lentiviral vector backbones have the ability to block HIV-1 replication by several mechanisms that include sequestration of the regulatory proteins Tat and Rev, competition for packaging into virions, and by inhibition of reverse transcription in heterodimeric virions with possible generation of nonfunctional recombinants between the vector and viral genomes. The inhibitory ability of lentiviral vectors can be further increased by expression of anti-HIV-1 genes. In this case, the lentiviral vector packaging system has to be modified to become resistant to the anti-HIV-1 genes expressed by the vector in order to avoid self-inhibition of the vector packaging system during vector production. This review focuses on the use of lentiviral vectors as the main agents to mediate inhibition of HIV-1 replication and discusses the different genetic intervention strategies for gene therapy of HIV-1 infection.

Inhibition of HIV type 1 replication by simultaneous infection of peripheral blood lymphocytes with human immunodeficiency virus types 1 and 2

A productive infection of peripheral blood lymphocytes by HIV-1 was severely inhibited by the simultaneous infection of these cells with HIV-2. A similar reciprocal effect on HIV-2 infection was not observed. The extent of virus replication was determined by virus-specific antigen capture assays of the supernatants of the infections. The inhibitory effect was observed with T cell-tropic, dual-tropic, as well as with primary HIV-1 isolates from different subtypes (A, B, C, E, F, and O). Infection of PBLs with different subtypes of HIV-2 (A and B) as well as with SIV(mac) resulted in the inhibition of HIV-1. However, the inhibitory effect was limited to PBLs; similar results were not observed in a T cell line. The inhibition of HIV-1 replication was independent of HIV-2 concentration; however, the infection by HIV-2 had to take place within 24 hr after PBLs were infected by HIV-1 for inhibition of HIV-1 replication to occur. The inhibition could be reversed by the addition of PHA. Analysis of HIV-1 RNA and DNA demonstrated that the inhibition was not at uptake or reverse transcription and that equal amounts of PBLs were infected by HIV-1 in single infections and coinfections. Immunocytochemical analysis of HIV-1 proteins demonstrated that equal numbers of cells were infected and that equal amounts of intracellular HIV-1 Env and Gag proteins were produced throughout the culture period. Therefore we conclude that HIV-2 can potently inhibit the productive infection of PBLs by HIV-1 and that the mechanism of this inhibition appears to prevent HIV-1 assembly or release from PBLs.

Human immunodeficiency virus type 2 lentiviral vectors: packaging signal and splice donor in expression and encapsidation

Retroviral vectors provide the means for gene transfer with long-term expression. The lentivirus subgroup of retroviruses, such as human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2), possesses a number of regulatory and accessory genes and other special elements. These features can be exploited to design vectors for transducing non-dividing as well as dividing cells with the potential for regulated transgene expression. Encapsidation of the transgene RNA in lentiviral vectors is determined by the leader sequence-based multipartite packaging signal. Embedded in the packaging signal is a major splice donor site that, this study shows, is not by itself essential for transgene expression or encapsidation. We designed HIV-2 vectors that contained all the sequence elements thought to be necessary and sufficient for vector RNA encapsidation. Unexpectedly, despite abundant expression, only a small fraction of the transgene RNA was encapsidated and the titre of the vector was low. Redesign of the vector with a mutant splice donor resulted in increased vector RNA encapsidation and yielded vectors with high titre. Inefficient encapsidation by the conventionally designed vector was not due to suboptimal Rev responsive element (RRE)-Rev function. Varying the length of RRE in the vector did not change vector RNA encapsidation, nor did the introduction of a synthetic intron into the mutant vector. The vector RNA with the intact splice donor may have been excessively spliced, decreasing the amount of packageable RNA. A titre of 10(5) transducing units (TU)/ml was readily obtained for vectors with the neo or GFP transgene, and the vector could be concentrated to a titre of 1-5x10(7) TU/ml.

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.

Cross-protection in NYVAC-HIV-1-immunized/HIV-2-challenged but not in NYVAC-HIV-2-immunized/SHIV-challenged rhesus macaques

OBJECTIVES

Immunization with attenuated poxvirus-HIV-1 recombinants followed by protein boosting had protected four of eight rhesus macaques from HIV-2SBL6669 challenge. The present study was designed to confirm this result and to conduct the reciprocal cross-protection experiment.

METHODS

Twenty-four macaques were primed with NYVAC (a genetically attenuated Copenhagen vaccinia strain) recombinants with HIV-1 and HIV-2 env and gag-pol or NYVAC vector alone and boosted with homologous, oligomeric gp160 proteins or adjuvant only. Binding and neutralizing antibodies, cytotoxic T-lymphocytes (CTL) and CD8 T cell antiviral activity (CD8AA) were evaluated. One half of each immunization and control group were intravenously challenged with SHIV(HXB2) the other half was challenged with HIV-2SBL6669,. Protective outcome was assessed by monitoring virus isolation, proviral DNA and plasma viral RNA.

RESULTS

Both immunization groups developed homologous binding antibodies; however, homologous neutralizing antibodies were only observed in NYVAC-HIV-2-immunized macaques. While no cross-reactive neutralizing antibodies were detected, both immunization groups displayed cross-reactive CTL. Significant CD8AA was observed for only one NYVAC-HIV-2-immunized macaque. Virological assessments verified that both NYVAC-HIV-1 and NYVAC-HIV-2 immunization significantly reduced viral burdens and partially protected against HIV-2 challenge, although cross-protection was not at the level that had been previously reported. Humoral antibody and/or CTL and CD8AA were associated with protection against homologous HIV-2 challenge, while cellular immune responses seemed more important for cross-protection. No significant protection was observed in the SHIV-challenged macaques, although NYVAC-HIV-1 immunization resulted in significantly lower viral burdens compared with controls.

CONCLUSIONS

Further delineation of cross-reactive mechanisms may aid in the development of a broadly protective vaccine.

Dual infection with human immunodeficiency virus type 1 and type 2: impact on HIV type 1 viral load and immune activation markers in HIV-seropositive female sex workers in Abidjan, Ivory Coast

To determine the impact of dual infection with HIV-1 and HIV-2 on HIV-1 viral load and markers of immune activation among HIV-seropositive FSWs in Abidjan, we analyzed blood samples obtained from consenting HIV-seropositive FSWs attending a confidential clinic between September 1996 and June 1997 in Abidjan. Among HIV-1 and HIV-2 dually seropositive FSWs, polymerase chain reaction (PCR) testing with HIV-1 and HIV-2 primers was used to differentiate between FSWs who were PCR positive only for HIV-1 and those positive for both HIV-1 and HIV-2 (dually infected). Of the 203 FSWs, 151 (74%) were HIV-1 seropositive only (median age, 26 years), 4 (2%) were HIV-2 seropositive, and 48 (24%) were dually seropositive (median age, 30 years). Of the 48 dually seropositive FSWs, 33 (69%) were dually infected and 15 (31%) were dually seropositive. Median CD4+ T cell counts per microliter were not significantly different among the three groups (525 for HIV-1 positive only, 502 for dually infected, and 416 for dually seropositive) (p = 0.14). Median viral load (log10 copies/ml) was not significantly different among the HIV-1-only FSWs (4.8 log10 copies/ml) compared with the 32 dually infected FSWs (4.6 log10 copies/ml) and 14 dually seropositive FSWs (4.7 log10 copies/ml; p = 0.95). Median levels of HLA-DR immune activation were increased in both CD4+ and CD8+ T cells for the dually infected (n = 27) FSWs compared with those infected with HIV-1 only (n = 123) (p = 0.019 and p = 0.01, respectively). Dual infection does not appear to influence levels of HIV-1 viral load in vivo. However, levels of HLA-DR are higher among FSWs dually infected with HIV-1 and HIV-2 than among those infected with HIV-1 only.

Potent inhibition of human immunodeficiency virus type 1 (HIV-1) gene expression and virus production by an HIV-2 tat activation-response RNA decoy

Tat activation-response region (TAR) decoys have been developed for use in gene therapy for people infected with human immunodeficiency virus type 1 (HIV-1). When a TAR RNA decoy is overexpressed, it will bind Tat, thus leaving less of this crucial protein to bind to and activate the natural transcriptional promoter of HIV-1. Previous TAR decoy constructs have used HIV-1 TAR. However, recent epidemiological and biological data began to suggest that the TAR region from the human immunodeficiency virus type 2 (HIV-2) may suppress HIV-1 transcription and hence replication. We created a vector which overexpresses TAR-2 under the control of the human U6 small nuclear RNA gene promoter and here show that the U6-TAR-2 decoy construct potently inhibits both HIV-2 and HIV-1 gene expression. Further, this decoy construct is able to markedly suppress HIV-1 replication. Thus, we have directly proven that TAR-2 can suppress HIV-1 replication and suggest that the HIV-2 TAR decoy may prove useful for combating HIV-1 infection.

Human immunodeficiency virus type 2 lentivirus vectors for gene transfer: expression and potential for helper virus-free packaging

In addition to the long-term expression of the transgene provided by all retroviral vectors, lentiviruses present the opportunity to transduce nondividing cells and potentially achieve regulated expression. The development of lentiviral vectors requires the design of transfer vectors to ferry the transgene with efficient encapsidation of the transgene RNA and with full expression capability, and of a packaging vector to provide packaging machinery in trans but without helper virus production. For both vectors, a knowledge of packaging signal is required-the signal to be included in the transfer vector but excluded from the packaging vector. Among the human lentiviruses, human immunodeficiency virus type 1 and type 2 (HIV-1 and HIV-2), we think HIV-2 is better suited for gene transfer than HIV-1. It is less pathogenic and thus safer during design and production; its desirable nuclear import and undesirable cell-cycle arrest functions are segregated on two separate genes. In HIV-1 infection, it is less likely to recombine with the resident HIV-1, and it may itself downregulate HIV-1 expression. Evidently, elements located both upstream and downstream of the splice donor site in the leader sequence participated in RNA encapsidation and these sequences appeared necessary and sufficient. Deletion of both sequence elements resulted in a dramatic curtailment of RNA encapsidation and helper virus production. This was accompanied by some but acceptable loss of gene expression capability. The helper virus-free phenotype and expression capability of the double mutant was maintained upon replacement of its 3' long terminal repeat with a minigene cassette containing a transcriptional termination signal and a drug resistance marker gene. Deletion of the splice donor site itself had a dramatic negative effect on gene expression, supporting the important role of this element in the life of RNA.