Richard B. Markham

Sex differences in HIV-1 viral load and progression to AIDS

BACKGROUND Plasma HIV-1 RNA measurements are used for initiation of antiretroviral treatments. Whether the viral-load association with prognosis is similar in women and men is unknown. METHODS We studied 812 specimens from 650 injection-drug users (IDUs) participating in a continuous observational study of patients based in a community clinic. HIV-1 load was measured by branched-chain DNA on samples from 527 IDUs from the baseline visit, and by reverse-transcriptase PCR and quantitative microculture on samples from 285 IDUs at a follow-up visit 3 years later. FNDINGS: Women had lower median viral-load measurements than men by branched-chain DNA (3365 vs 8907 copies/mL; p=0.001), reverse-transcriptase PCR (45416 vs 93130 copies/mL; p=0.02), and quantitative microculture (5 vs 8 infectious units per million peripheral blood mononuclear cells; p=0.015). This association remained even after adjustment for CD4 cell count, race, and drug use within the previous 6 months. Time to AIDS was statistically similar for men and women in a univariate proportional-hazards model and in a model adjusting for CD4 cell count. Proportional-hazards models showed that women with the same viral load as men had a 1.6-fold higher risk of AIDS (95% CI 1.10-2.32); or, equivalently, that women with half the viral load of men had a similar time to AIDS as men. INTERPRETATION Although a biological mechanism remains unclear, these data suggest that current recommendations for HIV-1 viral-load thresholds to initiate antiretroviral therapy should be revised downwards for women.

Lactobacilli-expressed single-chain variable fragment (scFv) specific for intercellular adhesion molecule 1 (ICAM-1) blocks cell-associated HIV-1 transmission across a cervical epithelial monolayer

The vaginal and cervical epithelia provide an initial barrier to sexually acquired HIV-1 infection in women. To study the interactions between HIV-1-infected cells or cell-free HIV-1 and the reproductive epithelium, the transmission of HIV-1 by infected cells or cell-free virus across human cervical epithelial cells was examined using a Transwell culture system. Cell-associated HIV-1 was transmitted more efficiently than cell-free virus, and monocyte-associated virus was transmitted most efficiently. Abs to ICAM-1 added to the apical side of the epithelium blocked cell-mediated transepithelial HIV-1 transmission in vitro. When used in a previously described model of vaginal HIV-1 transmission in human PBL-SCID mice, anti-murine ICAM-1 Abs (0.4 μg/10 μl) also blocked vaginal transmission of cell-associated HIV-1 in vivo. To evaluate a candidate delivery system for the use of this Ab as an anti-HIV-1 microbicide, anti-ICAM single-chain variable fragment Abs secreted by transformed lactobacilli were evaluated for their protective efficacy in the Transwell model. Like the intact Ab and Fab derived from it, the single-chain variable fragment at a concentration of 6.7 μg/100 μl was able to reduce HIV-1 transmission by 70 ± 5%. These data support the potential efficacy of an anti-ICAM Ab delivered by lactobacilli for use as an anti-HIV-1 microbicide.

Infection with Dual-Tropic Human Immunodeficiency Virus Type 1 Variants Associated with Rapid Total T Cell Decline and Disease Progression in Injection Drug Users

The characteristics of sequential human immunodeficiency virus type 1 (HIV-1) isolates from 12 seroconverters among injection drug users selected for either rapid or slow disease progression were evaluated. All 6 patients who developed AIDS within 5 years were initially infected with syncytium-inducing (SI) variants or showed a transition from non-SI-inducing (NSI) to SI variants. Detection of SI variants was associated with rapid decline of both CD8+ and CD4+ T cells. In contrast, the 6 slow progressors carried only NSI variants and maintained stable or increasing CD8+ T cell levels. The SI variants that were associated with initial infection were dual tropic, with efficient replication in primary macrophages and T cell lines. These results suggest that the ability to replicate in macrophages, rather than the SI or NSI phenotype per se, may be an important determinant of HIV-1 transmission and that dual-tropic viruses, when transmitted, may be associated with rapid progression to AIDS.

Low pH immobilizes and kills human leukocytes and prevents transmission of cell-associated HIV in a mouse model

BackgroundBoth cell-associated and cell-free HIV virions are present in semen and cervical secretions of HIV-infected individuals. Thus, topical microbicides may need to inactivate both cell-associated and cell-free HIV to prevent sexual transmission of HIV/AIDS. To determine if the mild acidity of the healthy vagina and acid buffering microbicides would prevent transmission by HIV-infected leukocytes, we measured the effect of pH on leukocyte motility, viability and intracellular pH and tested the ability of an acidic buffering microbicide (BufferGel®) to prevent the transmission of cell-associated HIV in a HuPBL-SCID mouse model.MethodsHuman lymphocyte, monocyte, and macrophage motilities were measured as a function of time and pH using various acidifying agents. Lymphocyte and macrophage motilities were measured using video microscopy. Monocyte motility was measured using video microscopy and chemotactic chambers. Peripheral blood mononuclear cell (PBMC) viability and intracellular pH were determined as a function of time and pH using fluorescent dyes. HuPBL-SCID mice were pretreated with BufferGel, saline, or a control gel and challenged with HIV-1-infected human PBMCs.ResultsProgressive motility was completely abolished in all cell types between pH 5.5 and 6.0. Concomitantly, at and below pH 5.5, the intracellular pH of PBMCs dropped precipitously to match the extracellular medium and did not recover. After acidification with hydrochloric acid to pH 4.5 for 60 min, although completely immotile, 58% of PBMCs excluded ethidium homodimer-1 (dead-cell dye). In contrast, when acidified to this pH with BufferGel, a microbicide designed to maintain vaginal acidity in the presence of semen, only 4% excluded dye at 10 min and none excluded dye after 30 min. BufferGel significantly reduced transmission of HIV-1 in HuPBL-SCID mice (1 of 12 infected) compared to saline (12 of 12 infected) and a control gel (5 of 7 infected).ConclusionThese results suggest that physiologic or microbicide-induced acid immobilization and killing of infected white blood cells may be effective in preventing sexual transmission of cell-associated HIV.

Multiple-infection and recombination in HIV-1 within a longitudinal cohort of women

BackgroundRecombination between strains of HIV-1 only occurs in individuals with multiple infections, and the incidence of recombinant forms implies that multiple infection is common. Most direct studies indicate that multiple infection is rare. We determined the rate of multiple infection in a longitudinal study of 58 HIV-1 positive participants from The Womens Interagency HIV Study with a richer sampling design than previous direct studies, and we investigated the role of recombination and sampling design on estimating the multiple infection rate.Results40% of our sample had multiple HIV-1 infections. This rate of multiple infection is statistically consistent with previous studies once differences in sampling design are taken into account. Injection drug use significantly increased the incidence of multiple infections. In general there was rapid elimination of secondary strains to undetectable levels, but in 3 cases a superinfecting strain displaced the initial infecting strain and in two cases the strains coexisted throughout the study. All but one secondary strain was detected as an inter- and/or intra-genic recombinant. Injection drug use significantly increased the rate of observed recombinants.ConclusionOur multiple infection rate is consistent with rates estimated from the frequency of recombinant forms of HIV-1. The fact that our results are also consistent with previous direct studies that had reported a much lower rate illustrates the critical role of sampling design in estimating this rate. Multiple infection and recombination significantly add to the genetic diversity of HIV-1 and its evolutionary potential, and injection drug use significantly increases both.

Differences Among HIV-1 Variants in Their Ability to Elicit Secretion of TNF-α

HIV-1 infection of human PBMC has been shown to elicit secretion of several different cytokines. TNF-α secretion induced by this virus has been of particular interest because it has been associated with the development of HIV-1 dementia and because TNF-α increases viral replication by enhancing NF-κB interaction with the viral promoter, the HIV-1 long terminal repeat. Thus, an autocrine pathway is potentially created in which HIV-1 stimulates its own replication. Conflicting reports exist, however, on the ability of HIV-1 to induce TNF-α secretion in vitro or in vivo. Using experimental protocols that controlled for potential bacterial endotoxin-induced TNF-α secretion, the current study demonstrates significant differences in TNF-α-eliciting properties among primary and laboratory obtained HIV-1. The relative TNF-α-inducing ability of different variants is conserved when tested using PBMC from different individuals. Elicitation of TNF-α secretion was not blocked by exposure of cells to zidovudine, indicating that viral integration was not required to induce secretion. Rather, the interaction between the virus and cell surface is critical for TNF-α induction, as Abs against CD4 or CCR5 blocked the induction of TNF-α synthesis by PBMC when added before virus exposure. Furthermore, the ability to induce TNF-α secretion mapped to a region of the HIV-1 env gene that includes the third hypervariable domain. Differences in the ability of different HIV-1 variants to elicit TNF-α may account for individual differences in HIV-1 disease course.

A Perspective on Cellular Immunity in the Elderly

The increased incidence of infection and malignancy in elderly individuals has prompted many studies that demonstrate that the aging immune system is impaired. Most of these studies have focused on the impairment of acquired immunity provided by lymphocytes. While defects in acquired humoral and T-cell-mediated immunity may exist, increased susceptibility to infection may result from defects in the constitutive functioning of macrophages and granulocytes. Recognition of the potential importance of defects in constitutive immunity in the elderly may provide new opportunities for therapeutic and prophylactic intervention in this population.

Diversification of Subtype E Human Immunodeficiency Virus Type 1 env in Heterosexual Seroconverters from Northern Thailand

The C2-V3 region of the human immunodeficiency virus (HIV)-1 env was determined from 15 northern Thailand seroconverters between 1993 and 1995. Similar sequences were also determined from 18 seroconverting injection drug users in Baltimore. All seroconverters from northern Thailand were infected with subtype E HIV-1 on the basis of env sequences. Intersubject viral DNA distances increased from 2.3% in asymptomatic HIV-1-infected subjects characterized between 1990 and 1992 to 7.8% in these more recent seroconverters from Thailand. On the other hand, sequences from 18 seroconverters from Baltimore had a mean intersubject distance of 13.2%. The genetic diversity within HIV-1 subtype E in seroconverters in Thailand has increased significantly but is still less than that observed in HIV-1 from seroconverters in the United States, where the epidemic of HIV-1 infection is more mature. These results suggest that continued monitoring of the molecular epidemiology of HIV-1 infection in Thailand will be important for HIV vaccine development and evaluation.

Maternal IgG1 and IgA antibody to V3 loop consensus sequence and maternal-infant HIV-1 transmission.

Maternal-infant transmission of HIV-1 occurs in 13-40% of pregnancies. Studies on transmission of maternal immunity to HIV antigens have used antigens from viruses not representative of clinical isolates and have been conflicting. Using a consensus peptide sequence based on HIV isolates found in Haiti, we found that Haitian mothers who transmitted infection to their offspring had significantly higher mean concentrations of IgG1 antibodies to the V3 loop of the primary neutralising domain of the viral envelope (gp 160) than non-transmitters (p = 0.02). Concentrations of IgA antibody to this domain were similar in transmitters and non-transmitters.

Requirement for the second coding exon of Tat in the optimal replication of macrophage-tropic HIV-1

HIV-1 Tat is essential for virus replication and is a potent transactivator of viral gene expression. Evidence suggests that Tat also influences virus infectivity and cytopathicity. Here, we find that the second coding exon of Tat contributes a novel function for the replication/infectivity of macrophage-tropic HIV-1. We show that macrophage-tropic HIV-1 which expresses the full-length two-exon form of Tat replicates better in monocyte-derived macrophages (MDM) than an otherwise isogenic virus which expresses only the one-exon form of Tat. Similarly, two-exon Tat expressing HIV-1 also replicates better than one-exon Tat expressing HIV-1 in two different models of human cells/tissue reconstituted SCID mice.