Various viral compartments in HIV-1-infected mothers contribute to in utero transmission of HIV-1

Perinatal HIV transmission occurs in utero or intrapartum. The mechanisms and timing of transmission are not clearly understood. To compare the genetic sequences of the V3 envelope region of infant's plasma HIV to that of the mother's plasma, peripheral blood mononuclear cells (PBMC) and vaginal secretions, and correlate with timing of transmission. All 3 infants had a positive HIV PCR in the first days of life, thus classified as in utero infections. In the first mother-infant pair, two different variants were present in the infant, one correlating with maternal PBMC virus and highly homologous to virus from vaginal secretions and the other identical to sequences in maternal plasma. In the second pair, the infant plasma virus was similar to that of maternal PBMC. In the third pair, the cord blood and infant plasma virus were highly similar to maternal vaginal virus. The presence of more than one HIV variant from the maternal blood and from the vaginal compartment in the cord blood of infants presumably infected in utero could point to more than one episode of transmission or, alternatively, to transmission of PBMC virus.

Elevated cervical white blood cell infiltrate is associated with genital HIV detection in a longitudinal cohort of antiretroviral therapy-adherent women

BACKGROUND

Identification of factors associated with the presence of human immunodeficiency virus (HIV) in female genital secretions is critical for intervention strategies targeting transmission and eliminating replication of genital virus. We sought to monitor the prevalence of genital HIV shedding in antiretroviral therapy-adherent women over time and to assess changes in the genital microenvironment.

METHODS

Levels of cell-free HIV (HIV RNA) and HIV-infected cells (HIV DNA) were monitored in peripheral blood samples and cervical and vaginal fluid samples at monthly intervals in 11 women for 1 year. Genital tract infections and fluctuations in cervical and vaginal white blood cell counts were also evaluated at each study visit.

RESULTS

Plasma HIV was undetectable at the majority of study visits; when detected, it was only at low levels. Throughout the study, genital HIV RNA and DNA were detected in each person. Combined genital HIV (RNA and DNA) was detected at 49.2% of study visits and was associated with an elevated concentration of cervical white blood cell infiltrate (odds ratio, 2.52 [95% confidence interval, 1.01-6.22]; P = .04). Infiltrate was not associated with a clinical disorder or patient-reported symptoms.

CONCLUSIONS

Despite antiretroviral therapy adherence and clinically suppressed plasma viremia, HIV was intermittently detected in genital secretions and was associated with subclinical inflammation and cells trafficking to the cervical mucosa.

Efficient methodologies for sensitive HIV-1 RNA quantitation from plasma and vaginal secretions

BACKGROUND

Quantifying HIV levels in mucosal secretions is essential to study compartmentalized expression of HIV and facilitate development of intervention strategies to prevent disease progression and transmission.

OBJECTIVES

To develop a sensitive, reliable, and cost-effective technique to quantify HIV from blood and vaginal secretions that is compatible with efficient implementation in clinical research environments.

STUDY DESIGN

A sensitive, reliable, internally-controlled real-time reverse transcriptase (RT) PCR assay, which uses the HIV-1 pol gene as a target (Hpol assay) was developed to quantify HIV levels in plasma and genital secretions, and compared to the widely used Roche Amplicor HIV-1 Monitor assay. In addition, a simplified method of sample collection and processing of genital secretions (self-collection and use of RNAlater with batch processing) was compared to provider collection of samples and immediate processing.

RESULTS

The sensitivity and reliability of HIV levels detected by the assay described herein correlate well with measurements from Roche Amplicor HIV-1 Monitor assay for both plasma and vaginal secretions (R(2)=0.9179 and R(2)=0.942, respectively). The Hpol assay reproducibly quantifies a lower limit of 5 HIV-1 RNA copies per reaction, with low-levels of inter-assay and intra-assay variation. Additionally, vaginal viral levels and detection frequency did not differ significantly between the two the collection and processing methods.

CONCLUSIONS

The methodologies developed here provide sensitive, reliable, and cost-effective quantification of HIV levels in plasma and mucosal secretions, and are compatible with efficient use in clinical research studies.

Genetic analysis of simian immunodeficiency virus expressed in milk and selectively transmitted through breastfeeding

To develop effective intervention strategies that prevent breast milk transmission of human immunodeficiency virus (HIV), we must understand the specific viral properties and mechanisms responsible for infant infection. We have used lactating rhesus macaques infected with a pathogenic simian immunodeficiency virus (SIV) stock to analyze the viral genotypes expressed in plasma and milk throughout the disease course and to identify those variants ultimately transmitted to infants through breastfeeding. In these studies we observed mother-to-infant transmission of SIV/Delta(B670) by eight females during the chronic phase of disease, and we analyzed by heteroduplex tracking assays and sequence analysis the distribution and fluctuations in viral genotypes expressed. Each female expressed multiple V1 envelope genotypes in milk near the time of transmission, while a single genotype was found in each of the infants. Variants transmitted to infants were not expressed throughout the maternal disease course but were only detected near the time of transmission. The emergence of the transmitted genotype in the dam typically occurred in plasma before milk and was coincident with increased milk viral loads. Transmitted genotypes tended to be longer and more glycosylated and had a less negative charge over the V1 region compared to viral genotypes expressed in milk but not transmitted. These observations demonstrate that specific viral genotypes are selectively transmitted to infants through breastfeeding and support the hypothesis that transmission occurs as genotypes adapt for efficient expression in milk.

The antibody response to SIV in lactating rhesus macaques

As a model of breast milk transmission of HIV, we characterized humoral immune responses in the milk and plasma of 14 female rhesus macaques with suckling infants. Total immunoglobulin levels in plasma and milk were similar in all females and could not be correlated with transmission to the infant. These females, however, had elevated milk IgG levels and decreased milk IgA levels as compared with levels in seronegative controls. SIV envelope-specific antibody responses developed similarly in all females over the first 14-28 days after inoculation; however, 2 females had significantly lower titers by 98 days after inoculation. These females, characterized as rapid disease progressors, were the only animals to transmit SIV through breast-feeding during the period of acute viremia (14-21 days after inoculation). The remaining 12 females developed similar levels of high-avidity SIV envelope-specific IgG in plasma and low, but detectable, levels of IgA in milk. Despite similar quantities of antibody in milk, transmission of SIV through breast-feeding occurred in 8 of 12 mother-baby pairs during the chronic phase of disease. These observations are comparable with those for HIV-infected women and indicate that the SIV-macaque model provides a unique resource for deciphering the functional role of antibodies in breast milk transmission of HIV.

Amniotic fluid has higher relative levels of lentivirus-specific antibodies than plasma and can contain neutralizing antibodies

BACKGROUND

The in utero transmission rate of HIV-1 is estimated to be 10-15% in the absence of interventions and breastfeeding. Natural protective mechanisms involving lentivirus-specific antibodies may therefore exist to limit in utero transmission of lentiviruses.

OBJECTIVES

HIV-1- and SIV-specific immunoglobulin G (IgG) levels in amniotic fluid samples from humans and rhesus macaques were assessed.

STUDY DESIGN

HIV-1- and SIV-specific immunoglobulin G levels, relative to total IgG concentrations in amniotic fluid samples from humans and rhesus macaques, were determined using a quantitative Western blotting procedure. Amniotic fluid from rhesus macaques was tested for the ability to neutralize SIV infection of CEMX174 cells.

RESULTS

The levels of HIV-1- and SIV-specific immunoglobulin G, relative to total IgG concentrations in amniotic fluid samples from humans and rhesus macaques, were approximately 3-10-fold higher than in plasma. The ability of antibodies in human amniotic fluid samples to neutralize viral infectivity could not be assessed, because zidovidine was present in the samples. Most amniotic fluid samples from rhesus macques not treated with antiretrovirals were able to neutralize SIV infectivity, except for a sample from a SIV positive rhesus whose infant was infected in utero.

CONCLUSIONS

Active immunity to HIV-1 resulting in virus-specific antibodies in amniotic fluid exists, and may be a natural barrier to in utero infection. This may provide hope for stimulating neutralizing antibody via vaccine design.

Mother-to-infant transmission of SIV via breast-feeding in rhesus macaques

To decipher the mechanisms involved in oral transmission of human immunodeficiency virus/simian immunodeficiency virus (HIV/SIV) through breast-feeding, we have developed an animal model using SIV-infected lactating rhesus macaques (Macaca mulatta) and their infants. Five of eight macaque infants became infected during a 10-month study course after SIV inoculation of lactating dams. In a second study, three of four chronically infected female macaques transmitted virus to their infants through breast-feeding within 4 months of birth. Transmission of virus to infants did not correlate with viral loads in either milk or plasma. Infants were infected with homogeneous virus populations, while milk samples near the time of transmission were more diverse. These studies suggest that specific viral phenotypes are selectively transmitted through breast-feeding.

Production and characterization of SIV envelope-specific rhesus monoclonal antibodies from a macaque asymptomatically infected with a live SIV vaccine

Five rhesus monoclonal antibodies (RhMAbs) were produced by rhesus EBV transformation of peripheral blood B cells from a rhesus macaque that had been asymptomatically infected with an attenuated, macrophage-tropic SIV strain, 17E-Cl. These MAbs recognized conformation-dependent epitopes on SIV gp120 and could not be mapped using synthetic peptides. All five RhMAbs were able to neutralize the vaccine strain and a heterologous isolate, SIV/DeltaB670. The RhMAbs did not cross-react with HIV-2; by contrast, four human MAbs derived from an HIV-2-infected person were broadly cross-reactive with both SIV and HIV-2 gp120s. Cross-competition analysis indicated that the five RhMAbs could be placed in two groups recognizing two nonoverlapping epitopes; while the HMAbs were placed in two additional competition groups. Binding of the three group I RhMAbs (1.7F, 3.11B, and 1.10A) as well as HMAb 17A was shown to be sensitive to specific amino acid alterations in V4 occurring in natural env variants. The results of this study demonstrate that RhEBV transformation provides a means to probe rhesus antibody responses to SIV infection at the monoclonal level. RhMAbs will allow structural and functional studies of envelope glycoprotein determinants that elicit protective immune responses against SIV.

Tracking members of the simian immunodeficiency virus deltaB670 quasispecies population in vivo at single-cell resolution

Genetically distinct lentiviruses constitute a quasispecies population that can evolve in response to selective forces. To move beyond characterization of the population as a whole to the behavior of individual members, we devised an in situ hybridization approach that uses genotype-specific probes. We used probes that detect simian immunodeficiency viruses (SIV) that differ in sequence in the V1 region of the surface envelope glycoprotein (env) gene to investigate the replication and cellular tropisms of four viral variants in the tissues of infected rhesus macaques. We found that the V1 genotypic variants replicated in spatially defined patterns and to different extents at each anatomic site. The two variants that replicated most extensively in animals with AIDS were detected in both macrophages and T lymphocytes in tissues. By extension of this approach, it will be possible to investigate the role of individual lentiviruses in a quasispecies in pathogenesis and to evaluate the effects of antiviral or immunotherapeutic treatment on select members of a quasispecies.

Pathogenesis of SIV encephalitis. Selection and replication of neurovirulent SIV

To investigate the viral and host factors that contribute to neurological disease, nine macaques were intravenously co-inoculated with SIV/DeltaB670, a primary isolate of SIV consisting of at least 21 different genotypes, and SIV/17E-Fr, a neurovirulent recombinant clone. CD4+ cell counts and antigenemia were measured throughout infection. The SIV env V1 region was amplified from brain and peripheral blood mononuclear cell DNA to compare the genotypes present in brain and blood. Seven of the 9 macaques (78%) developed typical SIV-associated neurological lesions classified as severe (4 macaques), moderate (2 macaques), or mild (1 macaque) with a mean time to euthanasia of 7 months. Macaques with severe neurological lesions progressed more rapidly, with a mean time to euthanasia of 3-6 months. SIV/17E-Fr was detected in brain homogenates from all four macaques with severe encephalitis, and in three of the four, SIV/17E-Fr was the only genotype identified in the central nervous system. Macaques with less severe or no neurological lesions usually had one of various genotypes of SIV/DeltaB670 in brain. A variety of genotypes of SIV/DeltaB670 and SIV/17E-Fr were detected in peripheral blood mononuclear cells throughout infection. Macaques with severe neurological lesions had the most precipitous declines in CD4+ cell counts, the highest levels of antigenemia, and the greatest expression of viral RNA and protein in the central nervous system. Macaca nemestrina were more likely to develop severe neurological lesions than M. mulatta or M. fascicularis (P = 0.048). This study demonstrated that neurovirulent strains within the virus swarm can selectively enter and become established in the central nervous system and that the neurological lesions that develop are correlated with the development of host immunosuppression. The species differences in severity of neurological lesions seen in this study suggest that host factors are also important in determining the outcome of lentiviral infection.

Pathogenesis of simian immunodeficiency virus encephalitis: viral determinants of neurovirulence

To examine the relationship between macrophage tropism and neurovirulence, macaques were inoculated with two recombinant hybrid viruses derived from the parent viruses SIVmac239, a lymphocyte-tropic, non-neurovirulent clone, and SIV/17E-Br, a macrophage-tropic, neurovirulent virus strain. The first recombinant, SIV/17E-Cl, contained the portion of the env gene that encodes the surface glycoprotein and a short segment of the transmembrane glycoprotein of SIV/17E-Br in the backbone of SIVmac239. Unlike SIVmac239, SIV/17E-Cl replicated productively in macrophages, demonstrating that sequences in the surface portion of env determine macrophage tropism. None of five macaques inoculated with SIV/17E-Cl developed simian immunodeficiency virus (SIV) encephalitis. The second recombinant, SIV/17E-Fr, which contained the entire env and nef genes and the 3' long terminal repeat of SIV/17E-Br in the SIVmac239 backbone, was also macrophage tropic. Six of nine macaques inoculated with SIV/17E-Fr developed SIV encephalitis ranging from mild to moderate in severity, indicating a significant (P = 0.031) difference in the neurovirulence of the two recombinants. In both groups of macaques, CD4+ cell counts declined gradually during infection and there was no significant difference in the rate of the decline between the two groups of macaques. This study demonstrated that macrophage tropism alone is not sufficient for the development of neurological disease. In addition, it showed that while sequences in the surface portion of the envelope gene determine macrophage tropism, additional sequences derived from the transmembrane portion of envelope and/or nef confer neurovirulence.

Genotypic selection of simian immunodeficiency virus in macaque infants infected transplacentally

To understand viral and host factors that contribute to transplacental transmission of human immunodeficiency virus, we developed an animal model using pregnant female macaques infected with simian immunodeficiency virus (SIV). Pregnant females were inoculated intravenously during midgestation with either a well-characterized primary isolate of SIV (SIV/DeltaB670) or a combination of SIV/DeltaB670 and the macrophage-tropic molecular clone SIV/17E-Fr. The viral genetic diversity in five infected female macaques and their in utero-infected infants was analyzed. All of the mothers harbored a genetically diverse virus population at parturition, whereas a single genotype from the maternal quasispecies was identified in the infants at birth. Only one of two variants was found in the infants: SIV/17E-Fr (two cases) or a genotype contained within the SIV/DeltaB670 quasispecies (three cases). The macrophage-tropic properties of both transmitted genotypes were suggested by productive replication in primary rhesus macrophage cultures in vitro and the clonal presence in central nervous system tissue of infected monkeys with encephalitis. These observations provide compelling evidence for both genotypic and phenotypic selection in transplacental transmission of SIV and suggest a critical role for macrophages in fetal infection in utero.

Cross-protective immune responses induced in rhesus macaques by immunization with attenuated macrophage-tropic simian immunodeficiency virus

The simian immunodeficiency virus (SIV) macaque model of AIDS has provided a valuable system with which to investigate vaccine approaches for protection against human immunodeficiency virus type 1 (HIV-1) infection. In particular, the ability of macaques persistently infected with attenuated infectious molecular clones of SIV to resist challenge with the pathogenic parental swarm has conclusively demonstrated that protective immunity can be achieved by immunization prior to exposure. The breadth of these protective responses and the immunological correlates of protection, however, have not been identified. In addition, vaccine studies have mainly employed lymphocyte-tropic strains of HIV-1 and SIV. Recent studies have implicated macrophage-tropic strains in the transmission of HIV-1 and have suggested that these virus strains should be examined in vaccine strategies. Macrophage-tropic viruses may confer additional advantages in the induction of protective immunity by replication in antigen-presenting cells. In this study, the immune response of rhesus macaques inoculated with an attenuated macrophage-tropic recombinant of SIVmac239 (SIV/17E-Cl) was evaluated with respect to protective immunity by heterologous challenge at various times after infection. Vigorous type-specific neutralizing-antibody responses restricted to SIV/17E-Cl were evident by 2 weeks postinfection. By 7 months, however, cross-reactive neutralizing antibodies emerged which neutralized not only SIV/17E-Cl but also the heterologous primary isolate SIV/DeltaB670. Challenge of SIV/17E-Cl-infected monkeys with SIV/DeltaB670 at various times postinfection demonstrated that protective responses were associated with the appearance of cross-reactive neutralizing antibodies. Furthermore, passive transfer of sera from SIV/17E-Cl-infected animals passively protected two of four naive recipients.