Estimating PMTCT's Impact on Heterosexual HIV Transmission: A Mathematical Modeling Analysis

Introduction

Prevention of mother-to-child HIV transmission (PMTCT) strategies include combined short-course antiretrovirals during pregnancy (Option A), triple-drug antiretroviral treament (ART) during pregnancy and breastfeeding (Option B), or lifelong ART (Option B+). The WHO also recommends ART for HIV treatment and prevention of sexual transmission of HIV. The impact of PMTCT strategies on prevention of sexual HIV transmission of HIV is not known. We estimated the population-level impact of PMTCT interventions on heterosexual HIV transmission in southwestern Uganda and KwaZulu-Natal, South Africa, two regions with different HIV prevalence and fertility rates.

Materials and Methods

We constructed and validated dynamic, stochastic, network-based HIV transmission models for each region. PMTCT Options A, B, and B+ were simulated over ten years under three scenarios: 1) current ART and PMTCT coverage, 2) current ART and high PMTCT coverage, and 3) high ART and PMTCT coverage. We compared adult HIV incidence after ten years of each intervention to Option A (and current ART) at current coverage.

Results

At current coverage, Options B and B+ reduced heterosexual HIV incidence by about 5% and 15%, respectively, in both countries. With current ART and high PMTCT coverage, Option B+ reduced HIV incidence by 35% in Uganda and 19% in South Africa, while Option B had smaller, but meaningful, reductions. The greatest reductions in HIV incidence were achieved with high ART and PMTCT coverage. In this scenario, all PMTCT strategies yielded similar results.

Discussion

Implementation of Options B/B+ reduces adult HIV incidence, with greater effect (relative to Option A at current levels) in Uganda than South Africa. These results are likely driven by Uganda’s higher fertility rates.     

Inflammatory Genital Infections Mitigate a Severe Genetic Bottleneck in Heterosexual Transmission of Subtype A and C HIV-1

The HIV-1 epidemic in sub-Saharan Africa is driven largely by heterosexual transmission of non-subtype B viruses, of which subtypes C and A are predominant. Previous studies of subtype B and subtype C transmission pairs have suggested that a single variant from the chronically infected partner can establish infection in their newly infected partner. However, in subtype A infected individuals from a sex worker cohort and subtype B individuals from STD clinics, infection was frequently established by multiple variants. This study examined over 1750 single-genome amplified viral sequences derived from epidemiologically linked subtype C and subtype A transmission pairs very early after infection. In 90% (18/20) of the pairs, HIV-1 infection is initiated by a single viral variant that is derived from the quasispecies of the transmitting partner. In addition, the virus initiating infection in individuals who were infected by someone other than their spouse was characterized to determine if genital infections mitigated the severe genetic bottleneck observed in a majority of epidemiologically linked heterosexual HIV-1 transmission events. In nearly 50% (3/7) of individuals infected by someone other than their spouse, multiple genetic variants from a single individual established infection. A statistically significant association was observed between infection by multiple genetic variants and an inflammatory genital infection in the newly infected individual. Thus, in the vast majority of HIV-1 transmission events in cohabiting heterosexual couples, a single genetic variant establishes infection. Nevertheless, this severe genetic bottleneck can be mitigated by the presence of inflammatory genital infections in the at risk partner, suggesting that this restriction on genetic diversity is imposed in large part by the mucosal barrier.     

HIV-1抗体阳性血浆中HIV-1病毒基因分型研究

为了解HIV抗体阳性血浆中的HIV-1病毒基因亚型的情况,应用逆转录PCR和DNA序列测定技术,对6份获自高危人群的抗HIV-1阳性血浆进行序列分析和基因亚型分型的研究,结果表明均属HIV-1B亚型.V3环氨基酸序列分析指出这些HIV-1B亚型病毒株与泰国HIV-1B亚型病毒株核苷酸和氨基酸序列相似;同时发现HIV-1 cDNA和氨基酸序列均相同,推测这6份标本可能来自同时感染同一株HIV病毒的感染者.本研究对了解高危人群中HIV-1流行的遗传变异和HIV-1亚型病毒株的分子流行病分析具有一定的意义.     

Using Plasma Viral Load to Guide Antiretroviral Therapy Initiation to Prevent HIV-1 Transmission

Background

Current WHO guidelines recommend antiretroviral therapy (ART) initiation at CD4 counts ≤350 cells/µL. Increasing this threshold has been proposed, with a primary goal of reducing HIV-1 infectiousness. Because the quantity of HIV-1 in plasma is the primary predictor of HIV-1 transmission, consideration of plasma viral load in ART initiation guidelines is warranted.

Methods

Using per-sex-act infectivity estimates and cross-sectional sexual behavior data from 2,484 HIV-1 infected persons with CD4 counts >350 enrolled in a study of African heterosexual HIV-1 serodiscordant couples, we calculated the number of transmissions expected and the number potentially averted under selected scenarios for ART initiation: i) CD4 count <500 cells/µL, ii) viral load ≥10,000 or ≥50,000 copies/mL and iii) universal treatment. For each scenario, we estimated the proportion of expected infections that could be averted, the proportion of infected persons initiating treatment, and the ratio of these proportions.

Results

Initiating treatment at viral load ≥50,000 copies/mL would require treating 19.8% of infected persons with CD4 counts >350 while averting 40.5% of expected transmissions (ratio 2.0); treating at viral load ≥10,0000 copies/mL had a ratio of 1.5. In contrast, initiation at CD4 count <500 would require treating 41.8%, while averting 48.4% (ratio 1.1).

Conclusion

Inclusion of viral load in ART initiation guidelines could permit targeting ART resources to HIV-1 infected persons who have a higher risk of transmitting HIV-1. Further work is needed to estimate costs and feasibility.     

Inefficient Vaginal Transmission of Tenofovir-Resistant HIV-1

Transmission of drug-resistant HIV has been postulated to be a threat to current first-line antiretroviral therapy (ART) regimens and the efficacy of several antiretroviral-based preexposure prophylaxis (PrEP) strategies being tested. Here we evaluated the effect of the common tenofovir (TFV) resistance mutation K65R on vaginal HIV transmission. Our results demonstrate that despite no overt loss of overall replication competence in vivo, this mutation results in significantly reduced mucosal transmission. When transmitted, the mutant virus eventually reverted to the wild type in 2 of 3 animals examined.     

Neamine dimers targeting the HIV-1 TAR RNA

Natural aminoglycoside antibiotics, such as neomycin, target bacterial ribosomal RNA. Neomycin also binds strongly to HIV TAR and RRE RNA through the predominant interactions of its neamine core. In the search for antiviral agents targeting multiple binding sites for aminoglycosides in RNA, we report here the synthesis of new neamine dimers and a trimer in which the neamine cores are connected by different linking chains attached at the 4'- and/or 5-positions. Inhibition of TAR-Tat complexation by these oligomers was studied via fluorimetric binding assays performed under two ionic strengths. All dimers strongly inhibit TAR-Tat association, with IC50 values 17-85 times better than the value obtained with neomycin. These results demonstrate that modifying neamine at the 4'- or the 5-position is a promising strategy in the search for antiviral agents.     

Different effects of the TAR structure on HIV-1 and HIV-2 genomic RNA translation

The 5'-untranslated region (5'-UTR) of the genomic RNA of human immunodeficiency viruses type-1 (HIV-1) and type-2 (HIV-2) is composed of highly structured RNA motifs essential for viral replication that are expected to interfere with Gag and Gag-Pol translation. Here, we have analyzed and compared the properties by which the viral 5'-UTR drives translation from the genomic RNA of both human immunodeficiency viruses. Our results showed that translation from the HIV-2 gRNA was very poor compared to that of HIV-1. This was rather due to the intrinsic structural motifs in their respective 5'-UTR without involvement of any viral protein. Further investigation pointed to a different role of TAR RNA, which was much inhibitory for HIV-2 translation. Altogether, these data highlight important structural and functional differences between these two human pathogens.     

Heterosexual Transmission of a Murine AIDS Virus

Heterosexual transmission of a murine leukemia virus mixture named LP-BM5 MuLV, which is known as the murine AIDS virus, was investigated. Our results indicated that the heterosexual transmission of LP-BM5 MuLV occurs in both directions with high frequency and that the frequencies of virus transmission in the cervix and penis are higher than those in other genital organs. The results suggested that infection by LP-BM5 MuLV via heterosexual transmission may initially take place at particular retrovirus-sensitive sites (cells) in the genital organs.Human immunodeficiency virus (HIV) infection is now pandemic. In many countries, HIV has been spread mainly by heterosexual transmission (3, 5). For the prevention of HIV infection, as well as for the development of vaccines against HIV, it is of a great importance to understand the mechanisms of the heterosexual transmission of retroviruses. Since it is difficult to investigate the mechanisms of heterosexual transmission of HIV in humans experimentally, an animal model with a retrovirus which induces an acquired immunodeficiency syndrome like human AIDS would be useful. A murine leukemia virus mixture called LP-BM5 MuLV induces a severe acquired immunodeficiency syndrome termed murine AIDS (MAIDS) in susceptible strains of mice (10). The mixture includes a replication-competent ecotropic virus, mink cell focus-inducing virus, and a replication-defective virus which has been considered to be involved in the pathogenesis of MAIDS (4). With many similarities to human AIDS patients, mice infected with the LP-BM5 MuLV mixture develop splenomegaly, systemic lymphadenopathy, and severe immunodeficiency (4, 11). We previously reported that maternal transmission of LP-BM5 MuLV occurs via mother’s milk with high frequency (12). In the present study, we demonstrate that the heterosexual transmission of LP-BM5 MuLV also occurs with high frequency via genital organs.C57BL/10 (B10) mice were purchased from Japan SLC Inc., Shizuoka, Japan. All mice were specific-pathogen free and were housed in an air-conditioned room. They were given autoclaved water and sterilized pelleted feed. An SC-1 clone chronically infected with LP-BM5 MuLV, the G6 cell line, was kindly supplied by H. C. Morse III, National Institutes of Health, Bethesda, Md. Virus was prepared from the supernatant of G6 cells as previously described (12). The virus preparation was stored at −70°C until use. B10 mice were inoculated by the intraperitoneal route with 0.3 ml of the LP-BM5 MuLV preparation. To increase the frequency of sexual contacts and to avoid pregnancy in the female mice, all male mice were sterilized by vasectomy under anesthesia with pentobarbital (Nembutal). The vasectomized male mice were mated with female mice at least 4 weeks postoperation, since sperm are usually kept alive for 2 to 3 weeks in spermiducts. Excised genital organs were crushed with plastic sticks in 1 ml of lysis buffer containing 10 mM Tris-HCl (pH 8.0), 100 mM NaCl, 1 mM EDTA, 0.5% sodium dodecyl sulfate, and proteinase K (0.5 mg/ml). Spleen cells were lysed after hemolysis with 0.83% NH₄Cl. Lysed samples were incubated at 50°C for 3 h. DNA was extracted three times with phenol-chloroform, precipitated with cold ethanol, treated with RNase and proteinase K, and dissolved in 0.1 ml of H₂O. LP-BM5 MuLV defective virus genome was detected by Southern blot hybridization combined with PCR as described previously (12). In brief, template DNAs (1 μg per tube) were added to a cocktail adjusted to final concentrations of 10 mM Tris-HCl (pH 8.3), 50 mM KCl, 1.5 mM MgCl₂, 0.01% gelatin, 200 μM deoxynucleoside triphosphate, 100 pmol of each primer (5′-CCTCTTCCTTTATCGACACT-3′ [sense] and 5′-ATTAGGGGGGGAATAGCTCG-3′ [antisense]), and 2 U of Taq DNA polymerase (Boehringer Mannheim) in a total volume of 100 μl and were subjected to 32 cycles of amplification. In each cycle of PCR, the mixture was denatured at 95°C for 1 min (5 min for the first cycle), annealed at 55°C for 3 min, and extended at 72°C for 1 min. The PCR-amplified products were subjected to gel electrophoresis (1.5% agarose) and transferred to a Hybond N+ membrane (Amersham) by the alkaline blotting method. Hybridization was achieved with a 5′ ³²P-labeled probe (5′-TGTCAAAGGGACCAGTTAAG-3′) at 45°C overnight in 6× SSC (1× SSC is 0.15 M NaCl plus 0.015 M sodium citrate)–0.5% sodium dodecyl sulfate–100 μg of salmon sperm DNA per ml. Hybridized membranes were washed twice in 2× SSC at 37°C for 10 min and then in 0.5× SSC at 45°C for 30 min. DNA derived from uterine cervices of uninfected mice was used as a negative control. The limit of sensitivity was approximately 10 copies per tube, as assessed by Southern blot analysis with plasmid DNAs (1/10 of the PCR product).Concanavalin A (ConA) was obtained from Pharmacia Fine Chemicals, Uppsala, Sweden. Responder spleen cells (2 × 10⁵) were cultured with ConA (5 μg/ml) in 96-well flat-bottomed microculture plates in 0.2 ml of culture medium at 37°C in 7.5% CO₂. The culture medium consisted of RPMI 1640 supplemented with 10% fetal calf serum, penicillin (5,000 IU/100 ml), streptomycin (5,000 μg/100 ml), nonessential amino acids, sodium pyruvate (11.0 mg/100 ml), 2-mercaptoethanol (5 × 10⁻⁵ M), and l-glutamine (29.2 mg/100 ml). On day 2, cultures were pulsed with 1 μCi of [³H]thymidine and incubated for an additional 12 to 18 h. Incorporation of [³H]thymidine into responder spleen cells was quantitated by liquid scintillation counting. Determinations were performed in triplicate; standard errors of the means were generally <5% and therefore have not been indicated.As illustrated in Fig. ​Fig.1,1, in order to investigate the heterosexual transmission of LP-BM5 MuLV from male to female mice, normal male mice were inoculated with LP-BM5 MuLV and vasectomized 1 week later. At 5 weeks after virus inoculation, they were mated with uninfected female mice. After 8 weeks of breeding, female mice were sacrificed and their vaginae, cervices uteri, corpora uteri, inguinal lymph nodes, and spleens were removed and stored at −70°C until use. In the opposite direction, to investigate virus transmission from female to male, normal female mice were inoculated with LP-BM5 MuLV and then mated with uninfected, vasectomized male mice as described above. After 8 weeks of breeding, male mice were sacrificed and their penes, prepuces, inguinal lymph nodes and spleens were removed and stored at −70°C until use. Figure ​Figure22 shows the detection by PCR of the LP-BM5 defective virus genome in genital organs and spleens that were taken from mice mated with their virus-infected counterparts. It was demonstrated that although the defective virus genome was detected in both spleens and genital organs in some male mice (2 of 17 [see Table ​Table1]),1]), as shown in Fig. ​Fig.2,2, lanes 3 and 4, the defective virus genome was detected only in the genital organs, not the spleens (Fig. ​(Fig.2,2, lanes 5 and 6), from most of the male mice. In contrast, all of the female mice were positive for defective virus genome only in the genital organs (Fig. ​(Fig.2,2, lanes 1 and 2). None of the mice examined were positive for the virus genome only in the spleens (this issue is discussed below). It should be noted here that the efficacy of PCR amplification, which was measured by experiments using the mixture of genomic DNA and plasmid DNA containing the defective virus, did not differ among the genital organs and spleens. By using the above strategy, the heterosexual transmission of LP-BM5 MuLV was investigated according to the protocol shown in Fig. ​Fig.1.1. Open in a separate windowFIG. 1Experimental design for examination of heterosexual transmission of the MAIDS virus in B10 mice. i.p., intraperitoneal.Open in a separate windowFIG. 2Detection of the LP-BM5 MuLV defective virus genome by PCR in genital organs and spleens. The template DNAs (1 μg) derived from female or male mice which were bred with LP-BM5 MuLV-infected mice were amplified by PCR. Samples were prepared from either female (lanes 1 and 2) or male (lanes 3 to 6) mice. Lanes 1, 3, and 5, spleen; lane 2, uterine cervix; lanes 4 and 6, penis (from two representative male mice). The PCR products (5 μl) were applied to a 1.5% agarose gel and analyzed by Southern blotting with a probe for the defective virus (12).

TABLE 1

Heterosexual transmission of LP-BM5 MuLV

Dynamic Motions of the HIV-1 Frameshift Site RNA

The HIV-1 frameshift site (FS) plays a critical role in viral replication. During translation, the HIV-1 FS transitions from a 3-helix to a 2-helix junction RNA secondary structure. The 2-helix junction structure contains a GGA bulge, and purine-rich bulges are common motifs in RNA secondary structure. Here, we investigate the dynamics of the HIV-1 FS 2-helix junction RNA. Interhelical motions were studied under different ionic conditions using NMR order tensor analysis of residual dipolar couplings. In 150 mM potassium, the RNA adopts a 43°(±4°) interhelical bend angle (β) and displays large amplitude, anisotropic interhelical motions characterized by a 0.52(±0.04) internal generalized degree of order (GDO_int) and distinct order tensor asymmetries for its two helices (η = 0.26(±0.04) and 0.5(±0.1)). These motions are effectively quenched by addition of 2 mM magnesium (GDO_int = 0.87(±0.06)), which promotes a near-coaxial conformation (β = 15°(±6°)) of the two helices. Base stacking in the bulge was investigated using the fluorescent purine analog 2-aminopurine. These results indicate that magnesium stabilizes extrahelical conformations of the bulge nucleotides, thereby promoting coaxial stacking of helices. These results are highly similar to previous studies of the HIV transactivation response RNA, despite a complete lack of sequence similarity between the two RNAs. Thus, the conformational space of these RNAs is largely determined by the topology of their interhelical junctions.     

Two alternating structures of the HIV-1 leader RNA

In this study we demonstrate that the HIV-1 leader RNA exists in two alternative conformations, a branched structure consisting of several well-known hairpin motifs and a more stable structure that is formed by extensive long-distance base pairing. The latter conformation was first identified as a compactly folded RNA that migrates unusually fast in nondenaturing gels. The minimally required domains for formation of this conformer were determined by mutational analysis. The poly(A) and DIS regions of the leader are the major determinants of this RNA conformation. Further biochemical characterization of this conformer revealed that both hairpins are disrupted to allow extensive long-distance base pairing. As the DIS hairpin is known to be instrumental for formation of the HIV-1 RNA dimer, the interplay between formation of the conformer and dimerization was addressed. Formation of the conformer and the RNA dimer are mutually exclusive. Consequently, the conformer must rearrange into a branched structure that exposes the dimer initiation signal (DIS) hairpin, thus triggering formation of the RNA dimer. This structural rearrangement is facilitated by the viral nucleocapsid protein NC. We propose that this structural polymorphism of the HIV-1 leader RNA acts as a molecular switch in the viral replication cycle.     

Plasma membrane signaling in HIV-1 infection

Plasma membrane is a multifunctional structure that acts as the initial barrier against infection by intracellular pathogens. The productive HIV-1 infection depends upon the initial interaction of virus and host plasma membrane. Immune cells such as CD4 + T cells and macrophages contain essential cell surface receptors and molecules such as CD4, CXCR4, CCR5 and lipid raft components that facilitate HIV-1 entry. From plasma membrane HIV-1 activates signaling pathways that prepare the grounds for viral replication. Through viral proteins HIV-1 hijacks host plasma membrane receptors such as Fas, TNFRs and DR4/DR5, which results in immune evasion and apoptosis both in infected and uninfected bystander cells. These events are hallmark in HIV-1 pathogenesis that leads towards AIDS. The interplay between HIV-1 and plasma membrane signaling has much to offer in terms of viral fitness and pathogenicity, and a better understanding of this interplay may lead to development of new therapeutic approaches. This article is part of a Special Issue entitled: Viral Membrane Proteins — Channels for Cellular Networking.     

Cell-Free (RNA) and Cell-Associated (DNA) HIV-1 and Postnatal Transmission through Breastfeeding

Introduction

Transmission through breastfeeding remains important for mother-to-child transmission (MTCT) in resource-limited settings. We quantify the relationship between cell-free (RNA) and cell-associated (DNA) shedding of HIV-1 virus in breastmilk and the risk of postnatal HIV-1 transmission in the first 6 months postpartum.

Materials and Methods

Thirty-six HIV-positive mothers who transmitted HIV-1 by breastfeeding were matched to 36 non-transmitting HIV-1 infected mothers in a case-control study nested in a cohort of HIV-infected women. RNA and DNA were quantified in the same breastmilk sample taken at 6 weeks and 6 months. Cox regression analysis assessed the association between cell-free and cell-associated virus levels and risk of postnatal HIV-1 transmission.

Results

There were higher median levels of cell-free than cell-associated HIV-1 virus (per ml) in breastmilk at 6 weeks and 6 months. Multivariably, adjusting for antenatal CD4 count and maternal plasma viral load, at 6 weeks, each 10-fold increase in cell-free or cell-associated levels (per ml) was significantly associated with HIV-1 transmission but stronger for cell-associated than cell-free levels [2.47 (95% CI 1.33–4.59) vs. aHR 1.52 (95% CI, 1.17–1.96), respectively]. At 6 months, cell-free and cell-associated levels (per ml) in breastmilk remained significantly associated with HIV-1 transmission but was stronger for cell-free than cell-associated levels [aHR 2.53 (95% CI 1.64–3.92) vs. 1.73 (95% CI 0.94–3.19), respectively].

Conclusions

The findings suggest that cell-associated virus level (per ml) is more important for early postpartum HIV-1 transmission (at 6 weeks) than cell-free virus. As cell-associated virus levels have been consistently detected in breastmilk despite antiretroviral therapy, this highlights a potential challenge for resource-limited settings to achieve the UNAIDS goal for 2015 of eliminating vertical transmission. More studies would further knowledge on mechanisms of HIV-1 transmission and help develop more effective drugs during lactation.     

Editing of HIV-1 RNA by the double-stranded RNA deaminase ADAR1 stimulates viral infection

Adenosine deaminases that act on dsRNA (ADARs) are enzymes that target double-stranded regions of RNA converting adenosines into inosines (A-to-I editing) thus contributing to genome complexity and fine regulation of gene expression. It has been described that a member of the ADAR family, ADAR1, can target viruses and affect their replication process. Here we report evidence showing that ADAR1 stimulates human immuno deficiency virus type 1 (HIV-1) replication by using both editing-dependent and editing-independent mechanisms. We show that over-expression of ADAR1 in HIV-1 producer cells increases viral protein accumulation in an editing-independent manner. Moreover, HIV-1 virions generated in the presence of over-expressed ADAR1 but not an editing-inactive ADAR1 mutant are released more efficiently and display enhanced infectivity, as demonstrated by challenge assays performed with T cell lines and primary CD4⁺ T lymphocytes. Finally, we report that ADAR1 associates with HIV-1 RNAs and edits adenosines in the 5′ untranslated region (UTR) and the Rev and Tat coding sequence. Overall these results suggest that HIV-1 has evolved mechanisms to take advantage of specific RNA editing activity of the host cell and disclose a stimulatory function of ADAR1 in the spread of HIV-1.