Quantitation of human immunodeficiency virus type 1 during pregnancy: relationship of viral titer to mother-to-child transmission and stability of viral load

To develop strategies to prevent mother-to-child transmission of human immunodeficiency virus type 1 (HIV-1), it is important to define the factors determining it. We examined the relationship between maternal HIV-1 titer and the occurrence of mother-to-child transmission. In addition, we quantitated HIV-1 longitudinally in mothers during pregnancy, at delivery, and up to 1 year postpartum. To examine transmission, we prospectively studied 19 mother-child pairs; in 5 pairs, HIV-1 transmission occurred. We used endpoint dilution culture of peripheral blood mononuclear cells to determine maternal viral titer and found that although 4 of 6 (67%) women with viral titers of > or = 125 HIV-1 infectious units per 10(6) cells transmitted HIV-1 to their infants, only 1 of 13 (7.6%) women with lower viral titers transmitted (P = 0.01). Twelve of the 19 mothers had HIV-1 loads determined serially 3-8 times over periods ranging from 18 to 65 weeks. Viral titers varied greatly between the 12 women, but the viral load in each woman remained stable over time. In this cohort, HIV-1 viral load remained stable during pregnancy and the greater the maternal viral burden, the more likely that transmission occurred. These two related findings suggest that determination of HIV-1 titers early in pregnancy may predict which women are at high risk of transmitting to their infants and may be used to counsel HIV-1-infected women of childbearing age. These data identify maternal viral titer as a major determinant of mother-to-child HIV-1 transmission and thereby provide the scientific rationale for therapeutic strategies designed to interrupt transmission by lowering viral load.     

Apparent enhancement of perinatal transmission of human immunodeficiency virus type 1 by high maternal anti-gp160 antibody titer

The presence of antibodies able to enhance infection in vitro in sera from human immunodeficiency virus (HIV)-1-infected patients raises the possibility that antibodies exert a deleterious activity during natural infection. The anti-HIV-1 humoral response and plasma HIV-1 RNA were measured in a cohort of 98 infected mothers, included in the French Prospective Study on Pediatric HIV Infection, 49 of whom transmitted HIV to their children. Transmission from mother to child was associated with antibody responses to the envelope gp160 (P = .009 for serum dilution of 1/400) and to a highly conserved domain of the transmembrane glycoprotein (P = .055 for serum dilution of 1/400) and with plasma HIV-1 RNA levels (P < .0001). Multivariate logistic regression indicated that a high anti-gp160 response and a high plasma virus load are independent risk factors for perinatal transmission of HIV-1 (odds ratio, 3.4; 95% confidence interval, 1.1-9.9 for anti-gp160; odds ratio, 2.8; 95% confidence interval, 1.6-5.0 for virus load).     

Horizontal transmission of human immunodeficiency virus type 1 from father to child

An unusual case of human immunodeficiency virus type 1 (HIV-1) infection in a child was studied. The child, identified as HIV-1 infected at 5 years of age, lived with his parents and a 3-year-old sister. HIV-1 infection was excluded in the mother and sister, but confirmed in the father, who was unaware of his infection and was in good health, apart from an atopic dermatitis on the face and limbs. A portion of the HIV-1 proviral envelope gene was amplified from the father's and child's peripheral blood cells, and the amplified products were cloned and sequenced. Phylogenetic analysis disclosed that the father's and child's viral sequences clustered together, and were clearly distinct from the sequence sets obtained from six epidemiologically unlinked mother-child HIV-1-infected pairs included in the analysis. HIV-1 variability was lower in the child's sequence set than in the father's, and the variability between father's and child's sequences was significantly lower than that found between epidemiologically unlinked cases (p < 0.001). An uncommon APGR motif on the tip of the V3 domain was found in both the father's and child's viral clones. These data, together with the epidemiological investigations, strongly suggest that the child acquired the infection from his father, possibly by exposure to bleeding skin lesions.     

Maternal virus load and perinatal human immunodeficiency virus type 1 subtype E transmission, Thailand. Bangkok Collaborative Perinatal HIV Transmission Study Group

To determine the rate and risk factors for human immunodeficiency virus (HIV)-1 subtype E perinatal transmission, with focus on virus load, pregnant HIV-infected women and their formula-fed infants were followed prospectively in Bangkok. Of 281 infants with known outcome, 68 were infected (transmission rate, 24.2%; 95% confidence interval, 19.3%-29.6%). Transmitting mothers had a 4.3-fold higher median plasma HIV RNA level at delivery than did nontransmitters (P<.001). No transmission occurred at <2000 copies/mL. On multivariate analysis, prematurity (adjusted odds ratio [AOR], 4.5), vaginal delivery (AOR, 2.9), low NK cell percentage (AOR, 2.4), and maternal virus load were associated with transmission. As RNA quintiles increased, the AOR for transmission increased linearly from 4.5 to 24.8. Two-thirds of transmission was attributed to virus load>10,000 copies/mL. Although risk is multifactorial, high maternal virus load at delivery strongly predicts transmission. This may have important implications for interventions designed to reduce perinatal transmission.     

Detection of human immunodeficiency virus type 1 and type 2 in the female genital tract: implications for the understanding of virus transmission

Risk of perinatal or female to male sexual transmission of HIV is likely to be associated with whether, and at what concentration, the virus is present in the cervical and vaginal secretions of the HIV-infected woman. Examining correlates of cervical and vaginal HIV shedding is, therefore, essential for the development of strategies to interrupt HIV transmission. This article presents the rationale for using detection of HIV in the female genital tract as a marker of infectivity, and briefly describes methods for detecting HIV-1 and HIV-2 in cervical or vaginal fluids. Findings from studies incorporating the measurement of HIV in the female genital tract are reviewed, placing particular emphasis on issues relevant to epidemiological studies of HIV transmission.     

Conservation of an intact vif gene of human immunodeficiency virus type 1 during maternal-fetal transmission

The human immunodeficiency virus type 1 (HIV-1) vif gene is conserved among most lentiviruses, suggesting that vif is important for natural infection. To determine whether an intact vif gene is positively selected during mother-to-infant transmission, we analyzed vif sequences from five infected mother-infant pairs following perinatal transmission. The coding potential of the vif open reading frame directly derived from uncultured peripheral blood mononuclear cell DNA was maintained in most of the 78,912 bp sequenced. We found that 123 of the 137 clones analyzed showed an 89.8% frequency of intact vif open reading frames. There was a low degree of heterogeneity of vif genes within mothers, within infants, and between epidemiologically linked mother-infant pairs. The distances between vif sequences were greater in epidemiologically unlinked individuals than in epidemiologically linked mother-infant pairs. Furthermore, the epidemiologically linked mother-infant pair vif sequences displayed similar patterns that were not seen in vif sequences from epidemiologically unlinked individuals. The functional domains, including the two cysteines at positions 114 and 133, a serine phosphorylation site at position 144, and the C-terminal basic amino acids essential for vif protein function, were highly conserved in most of the sequences. Phylogenetic analyses of 137 mother-infant pair vif sequences and 187 other available vif sequences from HIV-1 databases revealed distinct clusters for vif sequences from each mother-infant pair and for other vif sequences. Taken together, these findings suggest that vif plays an important role in HIV-1 infection and replication in mothers and their perinatally infected infants.     

Vasectomy and human immunodeficiency virus type 1 in semen

PURPOSE: Human immunodeficiency virus type 1 (HIV) is cultured more often from seminal cells than seminal plasma. Because vasectomy causes dramatic reductions in seminal cells and also eliminates secretions from proximal sites in the male reproductive tract, vasectomy may change the potential infectiousness of semen. MATERIALS AND METHODS: We used polymerase chain reaction (PCR) assays to measure HIV ribonucleic acid (RNA) in seminal plasma and HIV deoxyribonucleic acid (DNA) in seminal cells from 46 asymptomatic, seropositive men before and after vasectomy. RESULTS: HIV RNA levels in semen correlated only weakly with blood levels (r = 0.22, p = 0.03). Of 183 semen specimens assayed for cell-free HIV RNA and proviral DNA 37 (20%) were positive for HIV RNA only, 41 (22%) were positive for HIV DNA only, and 18 (10%) were positive for RNA and DNA. Thus, detection of HIV RNA in seminal plasma was not associated with detection of HIV DNA in seminal cells. HIV RNA was present in 23 of 82 specimens (28%) (mean 2.87 log copies/ml.) before vasectomy and in 38 of 121 specimens (31%) after vasectomy (mean 2.81 log copies/ml.). CONCLUSIONS: These findings suggest that direct measurement of HIV levels in semen is necessary to assess the potential for sexual transmission, most cell-free HIV in seminal plasma arises distal to the vas deferens, and vasectomy may have minimal impact on the infectiousness of HIV seropositive men on sexual partners.     

Serotypes of the human immunodeficiency virus type 1 in Madrid

BACKGROUND: HIV-1 shows high genetic variability, mainly in the genomic region codifying the envelope proteins, which are the most immunogenic. This fact explains the high heterogeneity of antibodies against HIV-1 epitopes. Both genetic and serologic diversity has allowed to classify HIV-1 variants in several subtypes (genotypes and serotypes, respectively). The clinical and epidemiological significance of infection caused by each subtype remains to be clarified. PATIENTS AND METHODS: Serum samples from 154 HIV-seropositive individuals living in Madrid were studied. Serotyping was performed using 4 peptides belonging to the V3 env region. Epidemiological and clinical variables examined in these patients were the route of infection, the year in which HIV infection occurred, the country of birth, and the rate of disease progression (rapid versus slow). RESULTS: 148 (96.2%) samples could be serotyped, and the B class was recognized in 131 (88.5%) of them. Serotype A/C was found in 9 (6.1%). Two samples (1.3%) reacted to peptide E; however, both were also reactive against the B peptide, suggesting co-infection with B and E subtypes. Six samples were EIA-reactive for HIV-1/2 but were typed as HIV-2 alone. Infection with serotypes A/C was more frequent amongst immigrants, mainly in Africans. There was not association between any subtype and the route of infection neither a different rate of disease progression. CONCLUSION: HIV-1 serotype B is the most frequently found in HIV-seropositive individuals living in Madrid, without association with the route of infection or the clinical course of the disease. Serotypes A/C and E were found sporadically, mainly among immigrants.     

Hormonal contraception, sexually transmitted diseases, and risk of heterosexual transmission of human immunodeficiency virus type 1

The beta chemokine known as 6-C-kine, secondary lymphoid-tissue chemokine (SLC), TCA4, or Exodus-2 (herein referred to as 6CK/SLC) can trigger rapid integrin-dependent arrest of lymphocytes rolling under physiological shear and is highly expressed by high endothelial venules, specialized vessels involved in lymphocyte homing from the blood into lymph nodes and Peyer's patches. We show that 6CK/SLC is an agonist for the lymphocyte chemoattractant receptor, CCR7 (EBI-1, BLR-2), previously described as a receptor for the related beta chemokine MIP-3beta (ELC or Exodus-3). Moreover, 6CK/SLC and MIP-3beta attract the same major populations of circulating lymphocytes, including naive and memory T cells > B cells (but not natural killer cells); desensitization to MIP-3beta inhibits lymphocyte chemotaxis to 6CK/SLC but not to the alpha chemokine SDF-1 (stromal cell-derived factor); and 6CK/SLC competes for MIP-3beta binding to resting mouse lymphocytes. The findings suggest that the majority of circulating lymphocytes respond to 6CK/SLC and MIP-3beta in large part through their common receptor CCR7 and that these molecules may be important mediators of physiological lymphocyte recirculation in vivo.     

Common themes of antibody maturation to simian immunodeficiency virus, simian-human immunodeficiency virus, and human immunodeficiency virus type 1 infections

Characterization of virus-specific immune responses to human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) is important to understanding the early virus-host interactions that may determine the course of virus infection and disease. Using a comprehensive panel of serological assays, we have previously demonstrated a complex and lengthy maturation of virus-specific antibody responses elicited by attenuated strains of SIV that was closely associated with the development of protective immunity. In the present study, we expand these analyses to address several questions regarding the nature of the virus-specific antibody responses to pathogenic SIV, SIV/HIV-1 (SHIV), and HIV-1 infections. The results demonstrate for the first time a common theme of antibody maturation to SIV, SHIV, and HIV-1 infections that is characterized by ongoing changes in antibody titer, conformational dependence, and antibody avidity during the first 6 to 10 months following virus infection. We demonstrate that this gradual evolution of virus-specific antibody responses is independent of the levels of virus replication and the pathogenicity of the infection viral strain. While the serological assays used in these studies were useful in discriminating between protective and nonprotective antibody responses during evaluation of vaccine efficacy with attenuated SIV, these same assays do not distinguish the clinical outcome of infection in pathogenic SIV, SHIV, or HIV-1 infections. These results likely reflect differences in the immune mechanisms involved in mediating protection from virus challenge compared to those that control an established viral infection, and they suggest that additional characteristics of both humoral and cellular responses evolve during this early immune maturation.     

Antibody neutralization-resistant primary isolates of human immunodeficiency virus type 1

Although typical primary isolates of human immunodeficiency virus type 1 (HIV-1) are relatively neutralization resistant, three human monoclonal antibodies and a small number of HIV-1(+) human sera that neutralize the majority of isolates have been described. The monoclonal antibodies (2G12, 2F5, and b12) represent specificities that a putative vaccine should aim to elicit, since in vitro neutralization has been correlated with protection against primary viruses in animal models. Furthermore, a neutralization escape mutant to one of the antibodies (b12) selected in vitro remains sensitive to neutralization by the other two (2G12 and 2F5) (H. Mo, L. Stamatatos, J. E. Ip, C. F. Barbas, P. W. H. I. Parren, D. R. Burton, J. P. Moore, and D. D. Ho, J. Virol. 71:6869-6874, 1997), supporting the notion that eliciting a combination of such specificities would be particularly advantageous. Here, however, we describe a small subset of viruses, mostly pediatric, which show a high level of neutralization resistance to all three human monoclonal antibodies and to two broadly neutralizing sera. Such viruses threaten antibody-based antiviral strategies, and the basis for their resistance should be explored.     

Differential membrane binding of the human immunodeficiency virus type 1 matrix protein

The human immunodeficiency virus type 1 matrix protein (p17MA) plays a central role at both the early and late stages of the virus life cycle. During viral assembly, the p17MA domain of Pr55gag promotes membrane association, which is essential for the formation of viral particles. When viral infection occurs, the mature p17MA dissociates from the plasma membrane and participates in the nuclear targeting process. Thus, p17MA contains a reversible membrane binding signal to govern its differential subcellular localization and biological functions. We previously identified a membrane binding signal within the amino-terminal 31 amino acids of the matrix domain of human immunodeficiency virus type 1 Gag, consisting of myristate and a highly basic region (W. Zhou, L. J. Parent, J. W. Wills, and M. D. Resh, J. Virol. 68:2556-2569, 1994). Here we show that exposure of this membrane binding signal is regulated in different Gag protein contexts. Within full-length Pr55gag, the membrane targeting signal is exposed and can direct Pr55gag as well as heterologous proteins to the plasma membrane. However, in the context of p17MA alone, this signal is hidden and unable to confer plasma membrane binding. To investigate the molecular mechanism for regulation of membrane binding, a series of deletions within p17MA was generated by sequentially removing alpha-helical regions defined by the nuclear magnetic resonance structure. Removal of the last alpha helix (amino acids 97 to 109) of p17MA was associated with enhancement of binding to biological membranes in vitro and in vivo. Liposome binding experiments indicated that the C-terminal region of p17MA exerts a negative effect on the N-terminal MA membrane targeting domain by sequestering the myristate signal. We propose that mature p17MA adopts a conformation different from that of the p17MA domain within Pr55gag and present evidence to support this hypothesis. It is likely that such a conformational change results in an N-terminal myristyl switch which governs differential membrane binding.