Analysis of envelope sequence variants suggests multiple mechanisms of mother-to-child transmission of human immunodeficiency virus type 1

Inferring the multiplicity of founder variants initiating HIV-1 infection: a systematic review and individual patient data meta-analysis

BACKGROUND

HIV-1 infections initiated by multiple founder variants are characterised by a higher viral load and a worse clinical prognosis than those initiated with single founder variants, yet little is known about the routes of exposure through which transmission of multiple founder variants is most probable. Here we used individual patient data to calculate the probability of multiple founders stratified by route of HIV exposure and study methodology.

METHODS

We conducted a systematic review and meta-analysis of studies that estimated founder variant multiplicity in HIV-1 infection, searching MEDLINE, Embase, and Global Health databases for papers published between Jan 1, 1990, and Sept 14, 2020. Eligible studies must have reported original estimates of founder variant multiplicity in people with acute or early HIV-1 infections, have clearly detailed the methods used, and reported the route of exposure. Studies were excluded if they reported data concerning people living with HIV-1 who had known or suspected superinfection, who were documented as having received pre-exposure prophylaxis, or if the transmitting partner was known to be receiving antiretroviral treatment. Individual patient data were collated from all studies, with authors contacted if these data were not publicly available. We applied logistic meta-regression to these data to estimate the probability that an HIV infection is initiated by multiple founder variants. We calculated a pooled estimate using a random effects model, subsequently stratifying this estimate across exposure routes in a univariable analysis. We then extended our model to adjust for different study methods in a multivariable analysis, recalculating estimates across the exposure routes. This study is registered with PROSPERO, CRD42020202672.

FINDINGS

We included 70 publications in our analysis, comprising 1657 individual patients. Our pooled estimate of the probability that an infection is initiated by multiple founder variants was 0·25 (95% CI 0·21-0·29), with moderate heterogeneity (Q=132·3, p<0·0001, I²=64·2%). Our multivariable analysis uncovered differences in the probability of multiple variant infection by exposure route. Relative to a baseline of male-to-female transmission, the predicted probability for female-to-male multiple variant transmission was significantly lower at 0·13 (95% CI 0·08-0·20), and the probabilities were significantly higher for transmissions in people who inject drugs (0·37 [0·24-0·53]) and men who have sex with men (0·30 [0·33-0·40]). There was no significant difference in the probability of multiple variant transmission between male-to-female transmission (0·21 [0·14-0·31]), post-partum transmission (0·18 [0·03-0·57]), pre-partum transmission (0·17 [0·08-0·33]), and intra-partum transmission (0·27 [0·14-0·45]).

INTERPRETATION

We identified that transmissions in people who inject drugs and men who have sex with men are significantly more likely to result in an infection initiated by multiple founder variants, and female-to-male infections are significantly less probable. Quantifying how the routes of HIV infection affect the transmission of multiple variants allows us to better understand how the evolution and epidemiology of HIV-1 determine clinical outcomes.

FUNDING

Medical Research Council Precision Medicine Doctoral Training Programme and a European Research Council Starting Grant.

Inactivation of HIV-1 in Polarized Infant Tonsil Epithelial Cells by Human Beta-Defensins 2 and 3 Tagged with the Protein Transduction Domain of HIV-1 Tat

Mother-to-child transmission (MTCT) of HIV-1 may occur during pregnancy, labor, and breastfeeding; however, the molecular mechanism of MTCT of virus remains poorly understood. Infant tonsil mucosal epithelium may sequester HIV-1, serving as a transient reservoir, and may play a critical role in MTCT. Innate immune proteins human beta-defensins 2 (hBD-2) and -3 may inactivate intravesicular virions. To establish delivery of hBD-2 and -3 into vesicles containing HIV-1, we tagged hBDs with the protein transduction domain (PTD) of HIV-1 Tat, which facilitates an efficient translocation of proteins across cell membranes. Our new findings showed that hBD-2 and -3 proteins tagged with PTD efficiently penetrated polarized tonsil epithelial cells by endocytosis and direct penetration. PTD-initiated internalization of hBD-2 and -3 proteins into epithelial cells led to their subsequent penetration of multivesicular bodies (MVB) and vacuoles containing HIV-1. Furthermore, PTD played a role in the fusion of vesicles containing HIV-1 with lysosomes, where virus was inactivated. PTD-initiated internalization of hBD-2 and -3 proteins into ex vivo tonsil tissue explants reduced the spread of virus from epithelial cells to CD4+ T lymphocytes, CD68+ macrophages, and CD1c+ dendritic cells, suggesting that this approach may serve as an antiviral strategy for inactivating intraepithelial HIV-1 and reducing viral MTCT.

Quasispecies characteristics in mother-to-child transmission of hepatitis B virus by next-generation sequencing

OBJECTIVES

To identify within-host quasispecies characteristics of hepatitis B virus (HBV) in mothers and children infected via mother-to-child transmission (MTCT).

METHODS

Using next-generation sequencing (NGS), we analyzed sequences within the non-overlapping pre-core/core (pre-C/C) gene in 37 mother-child pairs.

RESULTS

Phylogenetic and Highlighter analyses suggested that both a single strain and multiple distinct strains may be transmitted in MTCT of HBV. However, analysis of reassembled viral sequences revealed a relatively narrow distribution of variants in children, which was confirmed by a lower viral diversity in children than that in mothers. New closely related variants with combinations of two to five high-frequency mutations were observed in seven children with elevated ALT levels; the new variants out-competed the transmitted maternal variants to become the dominant strains in five of them. Furthermore, 30 mutations with a frequency >1% of all viruses within-host were present in those children; the mutations caused 19 amino-acid substitutions. Interestingly, almost all were located within the well-known T-cell or B-cell epitopes.

CONCLUSIONS

There are restrictive changes that occur in the early stages of chronic HBV infection through MTCT with different clinical consequences. These data might have important implications for future investigations of interrelated immunopathogenesis and therapeutic strategies.

Estimating the timing of mother-to-child transmission of the human immunodeficiency virus type 1 using a viral molecular evolution model

Background

Mother-to-child transmission (MTCT) is responsible for most pediatric HIV-1 infections worldwide. It can occur during pregnancy, labor, or breastfeeding. Numerous studies have used coalescent and molecular clock methods to understand the epidemic history of HIV-1, but the timing of vertical transmission has not been studied using these methods. Taking advantage of the constant accumulation of HIV genetic variation over time and using longitudinally sampled viral sequences, we used a coalescent approach to investigate the timing of MTCT.

Materials and Methods

Six-hundred and twenty-two clonal env sequences from the RNA and DNA viral population were longitudinally sampled from nine HIV-1 infected mother-and-child pairs [range: 277–1034 days]. For each transmission pair, timing of MTCT was determined using a coalescent-based model within a Bayesian statistical framework. Results were compared with available estimates of MTCT timing obtained with the classic biomedical approach based on serial HIV DNA detection by PCR assays.

Results

Four children were infected during pregnancy, whereas the remaining five children were infected at time of delivery. For eight out of nine pairs, results were consistent with the transmission periods assessed by standard PCR-based assay. The discordance in the remaining case was likely confused by co-infection, with simultaneous introduction of multiple maternal viral variants at the time of delivery.

Conclusions

The study provided the opportunity to validate the Bayesian coalescent approach that determines the timing of MTCT of HIV-1. It illustrates the power of population genetics approaches to reliably estimate the timing of transmission events and deepens our knowledge about the dynamics of viral evolution in HIV-infected children, accounting for the complexity of multiple transmission events.

The role of neutralizing antibodies in prevention of HIV-1 infection: what can we learn from the mother-to-child transmission context?

In most viral infections, protection through existing vaccines is linked to the presence of vaccine-induced neutralizing antibodies (NAbs). However, more than 30 years after the identification of AIDS, the design of an immunogen able to induce antibodies that would neutralize the highly diverse HIV-1 variants remains one of the most puzzling challenges of the human microbiology. The role of antibodies in protection against HIV-1 can be studied in a natural situation that is the mother-to-child transmission (MTCT) context. Indeed, at least at the end of pregnancy, maternal antibodies of the IgG class are passively transferred to the fetus protecting the neonate from new infections during the first weeks or months of life. During the last few years, strong data, presented in this review, have suggested that some NAbs might confer protection toward neonatal HIV-1 infection. In cases of transmission, it has been shown that the viral population that is transmitted from the mother to the infant is usually homogeneous, genetically restricted and resistant to the maternal HIV-1-specific antibodies. Although the breath of neutralization was not associated with protection, it has not been excluded that NAbs toward specific HIV-1 strains might be associated with a lower rate of MTCT. A better identification of the antibody specificities that could mediate protection toward MTCT of HIV-1 would provide important insights into the antibody responses that would be useful for vaccine development. The most convincing data suggesting that NAbs migh confer protection against HIV-1 infection have been obtained by experiments of passive immunization of newborn macaques with the first generation of human monoclonal broadly neutralizing antibodies (HuMoNAbs). However, these studies, which included only a few selected subtype B challenge viruses, provide data limited to protection against a very restricted number of isolates and therefore have limitations in addressing the hypervariability of HIV-1. The recent identification of highly potent second-generation cross-clade HuMoNAbs provides a new opportunity to evaluate the efficacy of passive immunization to prevent MTCT of HIV-1.

Comparative analysis of the fusion efficiency elicited by the envelope glycoprotein V1-V5 regions derived from human immunodeficiency virus type 1 transmitted perinatally

Understanding the properties of viruses preferentially establishing infection during perinatal transmission of human immunodeficiency virus type 1 (HIV-1) is critical for the development of effective measures to prevent transmission. A previous study demonstrated that the newly transmitted viruses (in infants) of chronically infected mother-infant pairs (MIPs) were fitter in terms of growth, which was imparted by their envelope (Env) glycoprotein V1-V5 regions, than those in the corresponding chronically infected mothers. In order to investigate whether the higher fitness of transmitted viruses was conferred by their higher entry efficiency directed by the V1-V5 regions during perinatal transmission, the fusogenicity of Env containing V1-V5 regions derived from transmitted and non-tranmsmitted viruses of five chronically infected MIPs and two acutely infected MIPs was analysed using two different cell-cell fusion assays. The results showed that, in one chronically infected MIP, a higher fusion efficiency was induced by the infant Env V1-V5 compared with that of the corresponding mother. Moreover, the V4-V5 regions played an important role in discriminating the transmitted and non-transmitted viruses in this pair. However, neither a consistent pattern nor significant differences in fusogenicity mediated by the V1-V5 regions between maternal and infant variants was observed in the other MIPs. This study suggests that there is no consistent and significant correlation between viral fitness selection and entry efficiency directed by the V1-V5 regions during perinatal transmission. Other factors such as the route and timing of transmission may also be involved.

Phylogenetic analysis of human immunodeficiency virus type 1 subtype C env gp120 sequences among four drug-naive families following subsequent heterosexual and vertical transmissions

To characterize phylogenetic relatedness of plasma HIV-1 RNA subtype C env gp120 viral variants capable of establishing an infection following heterosexual and subsequent vertical transmission events a 650-base pair fragment within the C2-V5 subregion was sequenced from four HIV-1-infected families each consisting of biological parent(s), index children (first), and subsequent (second) siblings. None of the family members had received antiretroviral therapy at the time of sample collection. Sequence alignment and analysis were done using Gene Doc, Clustal X, and MEGA software programs. Second siblings' sequences were homogeneous and clustered in a single branch while first siblings' sequences were more heterogeneous, clustering in separate branches, suggestive of more than one donor variants responsible for the infection or evolution from founder variant(s) could have occurred. While the directionality for heterosexual transmission could not be determined, homogeneous viral variants were a unique characteristic of maternal variants as opposed to the more heterogeneous paternal variants. Analysis of families' sequences demonstrated a localized expansion of the subtype C infection. We demonstrated that families' sequences clustered quite closely with other regional HIV-1 subtype C sequences supported by a bootstrap value of 86%, confirming the difficulty of classifying subtype C sequences on a geographic basis. Data are indicative of several mechanisms that may be involved in both vertical and heterosexual transmission. Larger studies are warranted to address the caveats of this study and build on the strengths. Our study could be the beginning of family-based HIV-1 intervention research in Zimbabwe.

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.

Genetic analysis of small ruminant lentiviruses following lactogenic transmission

Lactogenic transmission plays an important role in the biology of lentiviruses such as HIV and SIV or the small ruminant lentiviruses (SRLV). In this work we analyzed the characteristics of viruses that goats, naturally infected with two strains of SRLV, transmitted to their kids. The spectrum of viral genotypes transmitted was broader and the efficiency of transmission greater compared to their human and simian counterparts. The newly described A10 subgroup of SRLV was more efficiently transmitted than the B1 genotype. The analysis of a particular stretch of the envelope glycoprotein encompassing a potential neutralizing epitope revealed that, as in SIV, the transmitted viruses were positively charged in this region, but, in contrast to SIV, they tended to lack a glycosylation site that might protect against antibody neutralization. We conclude that the physiology of the ruminant neonatal intestine, which permits the adsorption of infected maternal cells, shaped the evolution of these particular lentiviruses that represent a valid model of lactogenic lentivirus transmission.

Intrahost and interhost variability of the HIV type 1 nef gene in Brazilian children

Many aspects of HIV-1 pathogenesis are affected by Nef protein activity, and efforts have been made to study variation in the nef gene and how that variation relates to disease outcome. We studied the genetic diversity of the nef gene in distinct clones obtained from the same patient (intrahost) and in sequences obtained from different hosts (interhost). The set of sequences analyzed was obtained from HIV-1-infected Brazilian children and contained 112 clones from 25 children (intrahost samples), as well as 55 sequences from epidemiologically unlinked children (interhost samples). We found extensive site polymorphisms and amino acid length variations, mainly in the amino terminal region of the nef gene, between the myristoylation motif (MGxxxS) and the MHC-1 downregulation motif (Rxx). Analysis of the sequences deposited in the Los Alamos HIV sequences database ( www.hiv.lanl.gov ) indicated that the most frequent motif at the MHC-1 downregulation site in the subtype B strain is R(86%)A(64%)E(82%) (n = 1040) and R(78%)T(74%)E(56%) in the subtype C strain (n = 549). Conversely, the Brazilian subtype B isolates presented the motif R(81%)T(62%)E(67%) at this site (n = 64). A detailed analysis of selective pressures identified a concentration of codons under strong positive selection in the amino terminal region of the nef gene. We also determined that different sites are under positive selection in the subtype B and subtype C viruses. The amino acid composition in the MHC-1 downregulation motif of the nef gene in our sequences may indicate a distinct adaptive pattern of HIV-1 subtype B to the Brazilian host population.

Factors associated with prevalent hepatitis C infection among HIV-infected women with no reported history of injection drug use: the Women's Interagency HIV Study (WIHS)

Although the primary mode of hepatitis C virus (HCV) transmission is exposure to blood products or injection drug use (IDU), studies have found varying independent risk factors for HCV infection among persons with no history of IDU or exposure to blood products. For HIV-infected women, sexual transmission may be another potential source of HCV infection. HIV-infected and HIV-negative women at risk for HIV enrolled in the Women's Interagency HIV Study (WIHS) during October 1994 to November 1995 and again between October 2001 and November 2002 were studied. Clinical and demographic factors associated with HCV seroprevalence were assessed in multivariate logistic regression models controlling for history of blood transfusion and IDU. Among 3636 women with HCV results, 31.5% were HCV antibody positive (HCV+) including 13.5% with no reported history of IDU or blood transfusions. Multivariate logistic regression analyses stratified on IDU showed that among women with no history of IDU, sex with an IDU male was independently associated with HCV positivity (odds ratio [OR] = 2.8, 95% confidence [CI] = 2.1, 3.8, p < 0.0001) after controlling for blood transfusion, age, HIV infection, unemployment, birth in the United States, history of hepatitis B infection, and current smoking status. Further stratification on HIV status showed that the association was significant only for the HIV+ (OR = 1.9, 95% CI = 1.3, 2.7, p = 0.0007) compared to the HIV- women (OR = 1.1, 95% CI = 0.4, 2.7) although these odds ratios were not significantly different (p = 0.25). For HIV-positive women with no reported history of IDU, sex with an IDU male was independently associated with HCV suggesting that sexual transmission may be an important mode of HCV transmission for these high-risk women.

Lack of viral selection in human immunodeficiency virus type 1 mother-to-child transmission with primary infection during late pregnancy and/or breastfeeding

Mother-to-child transmission (MTCT) of human immunodeficiency virus type 1 (HIV-1) as described for women with an established infection is, in most cases, associated with the transmission of few maternal variants. This study analysed virus variability in four cases of maternal primary infection occurring during pregnancy and/or breastfeeding. Estimated time of seroconversion was at 4 months of pregnancy for one woman (early seroconversion) and during the last months of pregnancy and/or breastfeeding for the remaining three (late seroconversion). The C2V3 envelope region was analysed in samples of mother-child pairs by molecular cloning and sequencing. Comparisons of nucleotide and amino acid sequences as well as phylogenetic analysis were performed. The results showed low variability in the virus population of both mother and child. Maximum-likelihood analysis showed that, in the early pregnancy seroconversion case, a minor viral variant with further evolution in the child was transmitted, which could indicate a selection event in MTCT or a stochastic event, whereas in the late seroconversion cases, the mother's and child's sequences were intermingled, which is compatible with the transmission of multiple viral variants from the mother's major population. These results could be explained by the less pronounced selective pressure exerted by the immune system in the early stages of the mother's infection, which could play a role in MTCT of HIV-1.

HIV-1 Transmission, Replication Fitness and Disease Progression

Upon transmission, human immunodeficiency virus type 1 (HIV-1) establishes infection of the lymphatic reservoir, leading to profound depletion of the memory CD4(+) T cell population, despite the induction of the adaptive immune response. The rapid evolution and association of viral variants having distinct characteristics with different stages of infection, the level of viral burden, and rate of disease progression suggest a role for viral variants in this process. Here, we review the literature on HIV-1 variants and disease and discuss the importance of viral fitness for transmission and disease.

HIV-1 Transmission, Replication Fitness and Disease Progression

Upon transmission, human immunodeficiency virus type 1 (HIV-1) establishes infection of the lymphatic reservoir, leading to profound depletion of the memory CD4+ T cell population despite the induction of the adaptive immune response. The rapid evolution and association of viral variants having distinct characteristics during different stages of infection, the level of viral burden, and rate of disease progression suggest a role for viral variants in this process. Here, we review the literature on HIV-1 variants and disease and discuss the importance of viral fitness for transmission and disease.

The molecular epidemiology of HIV-1 envelope diversity during HIV-1 subtype C vertical transmission in Malawian mother-infant pairs

OBJECTIVES

To study the relationship between HIV-1 subtype C genetic diversity and mother-to-child transmission and to determine if transmission of HIV-1 V1/V2 env variants occurs stochastically.

DESIGN

Case-case-control study of Malawian mother-infant pairs consisting of 32 nontransmitting women, 25 intrauterine transmitters, and 23 intrapartum transmitters in Blantyre, Malawi.

METHODS

A heteroduplex tracking assay against the highly variable HIV-1 env V1/V2 region was used to characterize the relationship between HIV-1 diversity and mother-to-child transmission. The relative abundance of the maternal env variants was quantified and categorized as transmitted or nontransmitted based on the env variants detected in the infant plasma. The V1/V2 region was sequenced from two mother-infant pairs and a phylogenetic tree was built.

RESULTS

No relationship was found between transmission and overall maternal env diversity. Infants had less diverse HIV-1 populations than their mothers, and intrauterine-infected infants had fewer V1/V2 variants and were more likely to harbor a homogeneous V1/V2 population than infants infected intrapartum. V1/V2 sequences cloned from two mother-infant transmission pairs support multiple env variant transmission when multiple variants are detected, rather than single variant transmission followed by diversification. Almost 50% of the HIV-infected infants contained V1/V2 env variants that were not detected in maternal plasma samples. Finally transmission of env variants was not related to their abundance in maternal blood.

CONCLUSION

These data suggest that the predominant mechanism(s) of HIV-1 subtype C mother-to-child transmission differs by the timing of transmission and is unlikely to be explained by a simple stochastic model.

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.

Adaptive evolution in perinatal HIV-1

The immune-viral dynamics of the transmission of HIV-1 from mother to child are poorly understood, despite 20 years of research. Here we review evidence that the maternal immune response against HIV-1 can select forms of the virus that evade immunity and when transmitted have negative consequences in the child. Moreover, recent studies indicate that when wild-type virus is transmitted, an early immune response in the child can lead to the selection of viral escape forms in the first few months of life. These data suggest that adaptive immune surveillance in both mother and child contributes to the pathogenesis of early perinatal HIV-1. These observations augment our general understanding of the processes that determine the evolution of HIV-1 as it passes from one host to another.

Simian immunodeficiency virus (SIV) envelope quasispecies transmission and evolution in infant rhesus macaques after oral challenge with uncloned SIVmac251: increased diversity is associated with neutralizing antibodies and improved survival in previously immunized animals

Background

Oral infection of infant macaques with simian immunodeficiency virus (SIV) is a useful animal model to test interventions to reduce postnatal HIV transmission via breast-feeding. We previously demonstrated that immunization of infant rhesus macaques with either modified vaccinia virus Ankara (MVA) expressing SIV Gag, Pol and Env, or live-attenuated SIVmac1A11 resulted in lower viremia and longer survival compared to unimmunized controls after oral challenge with virulent SIVmac251 (Van Rompay et al., J. Virology 77:179–190, 2003). Here we evaluate the impact of these vaccines on oral transmission and evolution of SIV envelope variants.

Results

Limiting dilution analysis of SIV RNA followed by heteroduplex mobility assays of the V1–V2 envelope (env) region revealed two major env variants in the uncloned SIVmac251 inoculum. Plasma sampled from all infants 1 week after challenge contained heterogeneous SIV env populations including one or both of the most common env variants in the virus inoculum; no consistent differences in patterns of env variants were found between vaccinated and unvaccinated infants. However, SIV env variant populations diverged in most vaccinated monkeys 3 to 5 months after challenge, in association with the development of neutralizing antibodies.

Conclusions

These patterns of viral envelope diversity, immune responses and disease course in SIV-infected infant macaques are similar to observations in HIV-infected children, and underscore the relevance of this pediatric animal model. The results also support the concept that neonatal immunization with HIV vaccines might modulate disease progression in infants infected with HIV by breast-feeding.

Diversity of the human immunodeficiency virus type 1 (HIV-1) env sequence after vertical transmission in mother-child pairs infected with HIV-1 subtype A

Although several virologic and immunologic factors associated with an increased risk of perinatal human immunodeficiency virus type 1 (HIV-1) transmission have been described, the mechanism of mother-to-child transmission is still unclear. More specifically, the question of whether selective pressures influence the transmission remains unanswered. The aim of this study was to assess the genetic diversity of the transmitted virus after in utero transmission and after peripartum transmission and to compare the viral heterogeneity in the child with the viral heterogeneity in the mother. To allow a very accurate characterization of the viral heterogeneity in a single sample, limiting-dilution sequencing of a 1016-bp fragment of the env gene was performed. Thirteen children were tested, including 6 with in utero infections and 7 with peripartum infections. Samples were taken the day after birth and at the ages of 6 and 14 weeks. A homogeneous virus population was seen in six (46.2%) infants, of whom two were infected in utero and four were infected peripartum. A more heterogeneous virus population was detected in seven infants (53.8%), four infected in utero and three infected peripartum. The phylogenetic trees of the mother-child pairs presented a whole range of different tree topologies and showed infection of the child by one or more maternal variants. In conclusion, after HIV-1 transmission from mother to child a heterogeneous virus population was detected in approximately one-half of the children examined. Heterogeneous virus populations were found after peripartum infection as well as after in utero infection. Phylogenetic tree topologies argue against selection processes as the major mechanism driving mother-to-child transmission but support the hypothesis that virus variability is mainly driven by the inoculum level and/or exposure time.

Phylogenetic and phenotypic analysis of HIV type 1 env gp120 in cases of subtype C mother-to-child transmission

Human immunodeficiency virus type 1 (HIV-1) subtype C constitutes a majority of the newly transmitted cases of HIV-1 in many developing countries. There is growing evidence suggesting that subtype C viruses may display characteristics that make them distinct from subtype B and other subtypes, and such differences may affect its transmission and pathogenesis in infected individuals. In this study, HIV-1 sequences from the C2-V4 region of the envelope gene were analyzed from four infected mother-infant pairs (MIPs) after perinatal transmission in Zambia. We found that all viral isolates from four Zambian MIPs were of the subtype C HIV-1 subgroup. All tested isolates were macrophage tropic and did not infect any tested T cell lines or form syncytia in vitro. In addition, the isolates appear to use exclusively the CCR5 coreceptor. Phylogenetic analyses clearly indicated two contrasting phylogenetic transmission patterns for the four MIPs analyzed in the present study. Three cases displayed a pattern of selective transmission of a single or a few variants, and one case was found to transmit multiple maternal HIV-1 variants to her infant. The differences in the mode and timing of transmission may account for the observed transmission pattern among four MIPs.

Virologic risk factors for vertical transmission of HIV type 1 in Puerto Rico

HIV-1 vertical transmission in Puerto Rico has decreased significantly due to the implementation of antiviral therapy. Several studies have shown that the phenotype of the HIV-1 isolates initially recovered from infected infants has generally been one that replicates rapidly, infects macrophages, and preferentially use the CCR5 coreceptor. Our hypothesis is that viral genotypic and phenotypic differences exist between HIV-1 nontransmitter and transmitter mothers. Viral DNA samples and virus isolates were analyzed from a Puerto Rican perinatal population. Heteroduplex tracking assay (HTA) was performed on DNA samples to detect env V3 evolutionary variants and the extent of heterogeneity within each sample. HIV-1 C2-V3 variants were cloned from each patient to study sequence variation among the groups. Differences in replication kinetics of viral isolates in macrophage and GHOST CCR5 cells were analyzed by use of repeated measures linear regression analysis. HTA analysis showed that only two nontransmitter patient samples showed the presence of evolutionary variants. Phylogenetic analysis between maternal-infant pairs showed that transmission of a single maternal variant occurred, with the exception of one sample pair. When evaluating amino acid sequences from cloned PCR products, nontransmitting mothers appear to have a higher number of distinct sequences than both the transmitting mothers (p = 0.0410) and the infected infants (p = 0.0315). Analysis of replication kinetics indicated that transmitters showed faster replication kinetics in GHOST CCR5 cell cultures at 12 days postinfection (p = 0.0434) and 15 days postinfection (p = 0.0181). In conclusion, viral homogeneity and rapid replication kinetics were correlated with vertical transmission.

Confirmation of vertical transmission of bovine immunodeficiency virus in naturally infected dairy cattle using the polymerase chain reaction

The purpose of this study was to determine whether bovine immunodeficiency virus (BIV) is vertically transmitted in naturally infected dairy cattle. Twenty-two dam/calf pairs from a Mississippi Agriculture and Forestry Experiment Station dairy were the study group. Blood samples were collected following delivery of calves, the peripheral blood leukocytes were purified from these samples, and the leukocyte DNA was used in polymerase chain reactions targeting the pol gene region of the BIV provirus. Southern blotting and hybridization were used to confirm the BIV specificity of the amplified fragments. BIV provirus was detected in 14 of 22 calves (64%), demonstrating vertical transmission. Eight of the calves were disqualified from the final interpretation of transplacental transfer because they may have nursed their mothers prior to blood collection, allowing the possibility of lactogenic transfer of the virus. Transplacental transmission of BIV was identified in 6 of 22 calves (27%).

The selection and evolution of viral quasispecies in HIV-1 infected children

OBJECTIVES

To analyse the diversity and divergence of the viral populations in three mother-child pairs in longitudinally obtained samples for up to 7 years.

METHODS

Peripheral blood mononuclear cells were obtained from three mothers at delivery and three to four samples were obtained from each of their children from 1.5 months up to 78 months of age. The V3 region of HIV-1 was amplified by polymerase chain reaction, cloned and sequenced. HIV-1 DNA sequence comparisons were performed by phylogenetic analysis.

RESULTS

The viral population was initially homogenous in two children but highly heterogeneous in one child. Three patterns of vertical transmission seemed to have occurred: transmission of the most prevalent maternal strain, of a minor maternal strain and of multiple maternal strains. In one child, a possible reappearance of a maternal sequence was observed at 34 months of age.

CONCLUSIONS

Children may become infected with the most prevalent maternal strain, a minor maternal variant or multiple maternal quasispecies. Maternal viral variants may reappear in children after several years of infection and could possibly be derived from a reservoir of founder quasispecies established during the children's primary HIV-1 infection.

Differential selection of specific human immunodeficiency virus type 1/JC499 variants after mucosal and parenteral inoculation of chimpanzees

Regardless of the route of transmission, it is generally accepted that the human immunodeficiency virus type 1 (HIV-1) quasispecies transmitted from an infected individual to an uninfected individual is genetically homogeneous. This finding and the observation that HIV-1 genotypes in recipients are minor variants in the donors suggest strongly that selection for specific variants occurs. However, most analyses have been limited to the V3 region of env. In addition, the exact time at which most new infections occurred was not known, making it almost impossible to analyze virus populations present in donor-recipient pairs at the time of HIV-1 transmission. To circumvent this problem, three chimpanzees were inoculated with a genetically defined stock of cell-free HIV-1/JC499 by one of three routes: intravenously or via the cervical or penile mucosa. PCR products of the C2-to-V5 region of env were amplified from both proviral DNA and virion RNA in blood samples collected soon after infection and were screened by heteroduplex analysis (HDA). Those PCR products with distinct HDA banding patterns were cloned and sequenced. In all three animals, transmitted variants encoded one of two V3-loop populations identified in the inoculum, indicating relative homogeneity in this region. However, different virus populations, defined by combinations of specific V4 and V5 sequences, were found when variants in the animal inoculated intravenously (at least 13 V4-plus-V5 combinations) were compared with those in the two animals inoculated by the mucosal routes (limited to only four V4-plus-V5 combinations). The only V4-plus-V5 population in variants found in all three chimpanzees was the major population in the inoculum, which contained viruses with more than 30 different V4-plus-V5 combinations. That the majority of the V4-plus-V5 genotypes in variants transmitted to all three animals were minor populations in the inoculum indicated that selective transmission defined by the V4-plus-V5 regions had occurred but that distinct populations were transmitted by parenteral versus mucosal routes. These results indicate that the putative homogeneity of HIV-1 variants in a newly infected individual might be an artifact of the region of the env gene evaluated and that regions other than V3 might play a major role in selective transmission.

Perinatal transmission of major, minor, and multiple maternal human immunodeficiency virus type 1 variants in utero and intrapartum

Previous studies have provided conflicting data on the presence of selective pressures in the transmission of a homogeneous maternal viral subpopulation to the infant. Therefore, the purpose of this study was to definitively characterize the human immunodeficiency virus type 1 (HIV-1) quasispecies transmitted in utero and intrapartum. HIV-1 envelope gene diversity from peripheral blood mononuclear cells and plasma was measured during gestation and at delivery in mothers who did and did not transmit HIV perinatally by using a DNA heteroduplex mobility assay. Children were defined as infected in utero or intrapartum based on the timing of the first detection of HIV. Untreated transmitting mothers (n = 19) had significantly lower HIV-1 quasispecies diversity at delivery than untreated nontransmittting mothers (n = 18) (median Shannon entropy, 0.711 [0.642 to 0.816] versus 0.853 [0.762 to 0.925], P = 0.005). Eight mothers transmitted a single major env variant to their infants in utero, and one mother transmitted a single major env variant intrapartum. Four mothers transmitted multiple HIV-1 env variants to their infants in utero, and two mothers transmitted multiple env variants intrapartum. The remaining six intrapartum- and two in utero-infected infants had a homogeneous HIV-1 env quasispecies which did not comigrate with their mothers' bands at their first positive time point. In conclusion, in utero transmitters were more likely to transmit single or multiple major maternal viral variants. In contrast, intrapartum transmitters were more likely to transmit minor HIV-1 variants. These data indicate that different selective pressures, depending on the timing of transmission, may be involved in determining the pattern of maternal HIV-1 variant transmission.

Early changes in quasispecies repertoire in HIV-infected infants: correlation with disease progression

The evolution of HIV-1 quasispecies in patients during the first year of life was investigated in 10 vertically infected infants, using heteroduplex analysis of the V3-V5 region of env. Four subjects, who showed little viral evolution during the period of the study, had rapid progression of disease and early loss of CD4(+) cells. The remaining six subjects, who were slow progressors, evolved new viral variants within 6 months, and in one case by 1 month of age. Of the four patients who were PCR positive at birth, one was infected with multiple HIV-1 variants. These results show that in HIV-infected children, multiple variants may initiate infection and early quasispecies diversification is associated with a favorable clinical outcome.

Up-regulation of CCR5 expression in the placenta is associated with human immunodeficiency virus-1 vertical transmission

The role of placenta in vertical transmission is not yet fully understood. A protective role of the placenta during gestation is suggested by the finding that caesarian sections reduce the risk of transmission of human immunodeficiency virus (HIV)-1 from mother to child three- to fourfold. Here we investigated whether the immunological milieu of the placenta might be important in HIV-1 transmission. In situ imaging of immunohistochemically stained placenta sections and reverse transcriptase-polymerase chain reaction demonstrated a fourfold increase in CCR5:CXCR4 expression ratio in placentae from transmitting women compared to placentae from nontransmitting women. This chemokine receptor repertoire was consistent with an up-regulation of interleukin-4 and interleukin-10 expression in placentae from nontransmitting placentae compared to transmitting placentae. In situ imaging demonstrated that CCR5 and CXCR4 were expressed on placental macrophages and lymphocytes but not in trophoblasts. Simultaneous immunofluorescence/ultrasensitive in situ hybridization for HIV-1 gag-pol mRNA revealed that HIV-1 infects primarily CXCR4-expressing cells in placentae from nontransmitting women whereas predominantly CCR5-expressing cells were infected in placentae from transmitting women. These data are consistent with transmission of a homogeneous population of nonsyncytium-inducing HIV-1 isolates that use CCR5 as co-receptor.

Evolution in the hypervariable region of hepatitis C virus in infants after vertical transmission

To elucidate the clonal evolution of hepatitis C virus (HCV) during mother-to-infant transmission, we prospectively analyzed HCV clones of the hypervariable region in four HCV RNA-positive infants and compared them with those of the mother. Cord blood samples from three of the four infants were positive for the HCV RNA (< or =10(3) copies/mL), and all of the four infants had the HCV RNA titer of >10(6) copies/mL within 2 mo after birth. The hypervariable region clones detected in the infants were closely related to those in the respective mothers. The results suggest the perinatal transmission of HCV. The hypervariable region clones transmitted to infants were not a single selected clone or minor clones in the mother. None of the clones specific to the low-density fraction in the mother was transmitted to the infants. Moreover, the proportion of HCV in the low-density fraction was minimal in the first few months of life, but increased several months after birth in association with the elevation of alanine aminotransferase. These results suggest that the increase of HCV in the low-density fraction reflect the evolution of immune response in infants. We also demonstrated that the emergence of quasispecies in infants precedes the infantile antibody response.

Genetic analysis of viral variants selected in transmission of human immunodeficiency viruses to newborns

Our previous studies have indicated that HIV transmission from infected mothers to infants occurs with viruses showing rapid kinetics of replication, and either resistance to maternal neutralizing antibodies or sensitivity to enhancing antibodies. The genotypic patterns that result in these and other phenotypic viral characteristics may provide clues to the selection pressures exerted during this mode of transmission. For this reason, DNA sequences of the envelope gene (env) were determined for viral isolates obtained from seropositive women who were mothers of either infected or uninfected infants. Sequences of viruses isolated early in life from the infected newborns were also determined, such that diversity both within isolates and between maternal and infant isolates could be assessed. Among isolates obtained from mothers of uninfected infants, the V3 region of env demonstrated a higher degree of heterogeneity than those from mothers of infected infants. Similar to the viruses obtained from the mothers of infected infants, the infant-derived viral sequences were relatively homogeneous. Finally, the reactivity of maternal plasma with infant-derived HIV isolates, whether via neutralizing or enhancing antibodies, appeared to predict the distribution of viral sequences in the infant isolates. These data suggest that selective pressure on HIV-1 during transmission or growth in the infected infant may be mediated by biologic and/or immunologic processes.

Human immunodeficiency viruses in the developing world

AIDS has become a major burden in developing countries. At present, more than 90% of new HIV infections are emerging in Asia and Africa. Particularly ominous is the epidemic due to HIV-1 C in southern Africa, where about 25% of adults in several countries are infected. Although most of its spread apparently occurred during the 1990s, HIV-1 C currently accounts for one-half of the infections in the world. Both HIV-2, which is less virulent than HIV-1, and HIV-1 apparently spread to the human population from nonhuman African primates during the twentieth century. HIV-1 infection is usually lethal in the absence of antiretroviral therapy, but clinical disease occurs only after an induction period of several years. Some subtypes of HIV-1, such as C, E, and A, appear to be transmitted more efficiently than HIV-1 B, which is the major subtype in the United States and Europe. Molecular evolutionary changes that include receptor affinity, mediated by the env gene, and increased transcriptional activation, mediated by changes in the LTR and the tat gene, may account for some of the changes in transmission. Current therapies are prohibitively expensive for use in adults in most developing countries, although drugs for maternal-to-infant transmission are becoming accessible. A vaccine for HIV is desperately needed for the developing world.

Molecular evidence for mother-to-child transmission of multiple variants by analysis of RNA and DNA sequences of human immunodeficiency virus type 1

We have examined the viral selection that may occur during transmission by studying the env gene sequences from four cases of mother-to-child transmission of human immunodeficiency virus type 1. The V3 region sequences were directly amplified from both plasma viral RNA and peripheral blood mononuclear cells containing proviral DNA from mothers at delivery and at the time of diagnosis for children. Transmission occurred perinatally in three cases. The similarity of the viral sequences in each infant sample contrasted with the heterogeneous viral populations in the mothers. Phylogenetic analysis indicated the transmission of one or a few closely related maternal minor virus variants. In contrast, the child virus population in the fourth case was as heterogeneous as that of his mother, and phylogenetic analysis strongly suggested the transmission of multiple maternal variants. This case of multiple transmission was confirmed by analyzing sequences obtained at three times after delivery. Strains with sequences corresponding to the syncytium-inducing phenotype were also transmitted in this fourth case, and this was associated with the rapid development of disease in the child. There was no evidence for transmission of particular viral variants from mother to infant. We have thus described a particular case of vertical human immunodeficiency virus type 1 transmission with the transmission of multiple maternal variants to the infant and a rapid, fatal outcome in the child.

Selection of appropriate HIV-1 genomic regions for single-strand conformation polymorphism analysis of the diversity, modification, and transmission of HIV-1 quasispecies

Single-strand conformation polymorphism (SSCP) analysis is a useful tool for studying viral quasispecies. Four regions within the HIV-1 genome were studied by means of SSCP analysis with the aim of determining which regions were the most informative for the study of HIV-1 transmission or for detection of changes in HIV-1 quasispecies populations. Nested polymerase chain reaction (PCR) was used to amplify V1, V2, V3 of the env gene, and the p2 region in the gag gene. In total, 114 plasma specimens from 79 individuals were tested, including serial specimens from 10 mother-infant pairs that were provided by the Women and Infants Transmission Study (WITS). HIV-1 in specimens that were PCR-positive with primer pair SK38/SK39 showed different percentages of positive signals with primer pairs for the four regions: V1, 63%; V2, 83%; V3, 88%, and p2, 100%. HIV-1 sequences in the p2 target region displayed the greatest degree of polymorphism. Analysis of serial specimens showed that the V1 target region was the most variable of the four regions studied and was the most appropriate region for monitoring changes in quasispecies populations. Of the four regions studied, p2 was the most informative for the study of HIV transmission, as shown by analysis of samples from documented cases of mother to infant HIV-1 transmission.

V3 sequence diversity of HIV-1 subtype E in infected mothers and their infants

To elucidate genetic characteristics of HIV-1 subtype E involved in vertical transmission, V3 regions of HIV-1 subtype E isolated from 17 infected mothers (M1-M17) and their infants (I1-I17) at 1 month after birth were sequenced after cloned into pCRII vectors. At least three clones of each sample were collected. All mothers were asymptomatic and had been infected through a heterosexual route. Nine infants (I9-I17) showed mild symptomatic and immunosuppression within the first year of life. The interpatient nucleotide distance of mothers and infants in this group (0.065+/-0.008) were of greater diversity than those of a nonimmunosuppression group (0.039+/-0.006) by a significant amount (Fischer's exact test, p = .003). The substitution with asparagine (N) at threonine (T) at position 13 and aspartic acid (D) at position 29 of the V3 sequence were significantly associated with nonimmunosuppression in the first year of life (F-test, p = 0.003). Either a single or multiple viral variants could transmit from mothers to their infants.

Neutralizing antibodies and complement-mediated, antibody-dependent enhancement (C'-ADE) of human immunodeficiency virus infection in its vertical transmission

PROBLEM

Mother-to-child transmission is a major route for the spread of human immunodeficiency virus (HIV) worldwide. Our understanding of its mechanisms and parameters is still limited. Among the factors possibly involved in virus passage determination are the level and quality of antiviral humoral response.

METHOD OF STUDY

Anti-HIV-1/Lai neutralizing activity in sera from 35 mother-infant pairs (in which 13 transmission cases occurred) was investigated, as was the complement-mediated antibody-dependent enhancement capacity of the same sera.

RESULTS

Neutralization titers of 640 or more were found only in four mothers of uninfected children, but this result was not significant. No significant link was obtained with the occurrence of complement-mediated, antibody-dependent enhancement.

CONCLUSIONS

As suggested by a synthesis of the literature, vertical transmission of HIV is probably the result of multiple active and/or stochastic parameters in the mother, the fetal structures, and the viral population. The precise definition of cellular mechanisms involved in in utero infection would help to better define which immune activity in the mother should be more carefully considered.

Mother-to-child transmission of a hepatitis C virus variant with an insertional mutation in its hypervariable region

BACKGROUND/AIMS

We have analyzed the molecular basis of mother-to-child transmission of hepatitis C virus.

METHODS/RESULTS

Healthy pregnant women were screened for anti-HCV antibody and babies born to hepatitis C virus carrier mothers were prospectively investigated. Among the 35 pairs studied, the hepatitis C virus genome was detectable in only one baby, who did not show any significant symptoms of hepatitis. The viral load in the blood of the mother was one of the highest of the 35, and the population of the hepatitis C virus genome was heterogeneous. Furthermore, she was found to have a mixed infection with type 1a and type 1b hepatitis C virus. However, the hepatitis C virus genome obtained from the baby was only from type 1b, less heterogeneous and composed of the clones which were detected in the blood of the mother. The selected hepatitis C virus had a 12-nucleotide insertion in the amino-terminus of the E2 hypervariable region of the genome.

CONCLUSIONS

The incidence of mother-to-child transmission of hepatitis C virus from carrier mothers was shown by this prospective study to be low. The presence of selection pressure during transmission was suggested. The biological significance of the virus with 12-nucleotide insertion has to be determined.

Intrarectal transmission of simian immunodeficiency virus in rhesus macaques: selective amplification and host responses to transient or persistent viremia

Intrarectal simian immunodeficiency virus (SIV) infection in rhesus macaques is a model for sexual transmission of primate retroviruses. Phylogenetic studies on envelope gene sequences that were present in blood following intrarectal SIV inoculation provided evidence for selective amplification of a subset of viruses present in the inoculum and defined one amino acid sequence uniquely associated with intrarectal infection. Both persistent and transient viremia states were observed after intrarectal infection. Immune responses in persistently infected animals accounted for slower rates of disease progression despite the presence of highly pathogenic viruses that were documented by transfusion studies. Transient viremia elicited protective immunity against subsequent intrarectal virus challenge but did not protect against intravenous virus challenge. Transient viremia usually but not always led to self-limiting infection. In one animal, we documented a relapse to active viremia long after the initial transient viremia. SIV transmission across mucosal barriers affects pathogenesis in the short term by limiting the types of viruses established in the host and in the longer term by establishing host responses that slow disease progression despite the presence of highly pathogenic viruses in blood.

Maintaining the integrity of human immunodeficiency virus sequence databases

Human immunodeficiency virus type 1 (HIV-1) sequences are accumulating in the literature at a rapid pace. For this ever-expanding resource to be maximally useful, it is critical that researchers strive to maintain a high level of quality assurance, both in experimental design and conduct and in analyses. Here we present detailed analyses of problematic sets of HIV-1 sequences in the database that include sequence anomalies suggestive of mislabeling or sample contamination problems. These data are examined in the context of currently available HIV-1 sequence information to provide an example of how to identify potentially flawed data. Indicators of potential problems with sequences are (i) sequences that are nearly identical that are supposed to be derived from unlinked individuals and that are markedly distinct from other sequences from the putative source or (ii) sequences that are nearly identical to those of laboratory strains. We provide an outline of methods that researchers can use to perform preliminary laboratory and computational analyses that could help identify problematic data and thus help ensure the integrity of sequence databases.

Characterization of human immunodeficiency virus type 1 p17 matrix protein motifs associated with mother-to-child transmission

In order to determine if viral selection occurs during mother-to-child transmission of human immunodeficiency virus type 1 (HIV-1), we used a direct solid-phase sequencing method to sequence the p17 matrix protein-encoding regions of viral isolates from 12 HIV-1-infected mother-and-child pairs, 4 infected infants, 4 transmitting mothers, and 22 nontransmitting mothers and compared the sequences. The blood samples were collected during the delivery period for the mothers and during the first month of life for most of the children. The p17 nucleic sequences were distributed among several clades corresponding to the HIV-1 A, B, and G subtypes. At the amino acid level, no significant differences within the known p17 functional regions were observed among the subtypes. Statistical analyses could be performed with the B subtype. Within the major p17 antibody binding site, a constant KIEEEQN motif (amino acids 103 to 109) was found in all mother-and-child isolates from the B subtype. On the other hand, 9 of 17 nontransmitting mother isolates were variable in this 103 to 109 region. Thus, this motif was significantly associated with the transmitting status (chi square, P = 0.0034). A valine residue at position 104 was significantly associated with the nontransmitting phenotype (chi square, P = 0.014), suggesting that it has a protective role during vertical transmission. The C-terminal end of p17 was globally conserved among nontransmitting mother isolates (chi square, P = 0.0037). These results might improve the understanding of the pathogenesis of HIV-1 vertical transmission and might allow the screening of seropositive mothers by a rapid molecular or peptide test.

Elucidation of an HIV-1 transmission from mother to child in west Africa by sequence analysis

A pregnant woman living in Germany went to Ghana for several months, where she received 4 blood transfusions. Her newborn child also received one blood transfusion in West Africa. After return to Germany, HIV-1 infection was detected in both of them. Serotyping with V3 peptides revealed that the sera reacted only poorly with the subtype B-specific antigens. To investigate whether the child had been infected by vertical or parenteral transmission, we amplified different proviral HIV-1 gene segments from samples obtained 1-3 years after infection. Sequence analysis of the hypervariable regions V1 and V2 of the proviral env gene was misleading, since the viral population of the mother was highly heterogeneous, whereas only one predominant viral variant was found in the child. In contrast, sequences of the gag p17 gene and the regulatory genes nef and vif were homogeneous and revealed a very high homology, suggesting that the child had been infected by the mother. This was confirmed by phylogenetic tree analysis showing that sequences of mother and child clustered together and that both were infected by HIV-1 subtype A which is common in West Africa. The results suggest that sequence analysis of the hypervariable regions V1 and V2 alone can lead to unclear results, especially if not single genomes are analysed but a mixture of quasi-species. It is recommended that investigations into HIV transmission should be based on sequence analysis of several HIV genes.

Maternal-Fetal Transmission of Human Immunodeficiency Virus

The World Health Organization estimates that by year 2000, 10 million children will be infected with human immunodeficiency virus type 1 (HIV-1) at birth and will subsequently develop AIDS. Perinatally acquired infections account for the majority of all HIV-1 cases in children, with an estimated mother-to-infant transmission rate of more than 30%. It is not clear why more than half of the children born to HIV-1-infected mothers are uninfected. Maternal transmission of HIV-1 occurs at three levels: prepartum, intrapartum, and postpartum. Several maternal parameters including advanced clinical stages of the mother, low CD4+ lymphocyte counts, maternal immune response to HIV-1, recent infection, high level of circulating HIV-1, and maternal disease progression have been implicated in an increased risk of mother-to-infant transmission of HIV-1. Viral factors influencing mother-to-infant transmission are not known. Furthermore, several other factors such as acute infection during pregnancy, presence of other sexually transmitted diseases (STD) or other chronic infections, vaginal bleeding, disruption of placental integrity, premature rupture of membrane (PROM), and preterm PROM have been associated with mother-to-infant transmission of HIV-1. In addition, tobacco and cigarette smoking during pregnancy have been shown to triple the rate of maternal transmission of HIV-1. The AIDS Clinical Trial Group (ACTG) suggested that zidovudine (ZDV) can reduce therate of mother-to-infant transmission of HIV-1 if administered to HIV-1-infected pregnant women with CD4 counts greater than 200. Moreover, this study failed to take into consideration several factors that may influence maternal transmission of HIV-1. However, the molecular mechanisms involved in mother-to-infant transmission of HIV-1 are not understood, which makes it more difficult to define strategies for effective treatment and prevention of HIV-1 infection in children. Several groups are engaged in the understanding of the molecular and biological properties of HIV-1 influencing mother-to-infant transmission. Results from my and several other laboratories suggest that the minor genotypes, subtypes, or variants of HIV-1 found in a genetically heterogeneous virus population of infected mothers are transmitted to their infants. The minor HIV-1 genotype predominates initially as a homogeneous population in the infant and then becomes diverse as the infant matures. Furthermore, transmission of a major or multiple HIV-1 genotypes from mother to infant has been reported. Taken together, these results strongly suggest that there are differences among the molecular and biological properties of the maternal variants that are transmitted to the infants and the maternal variants that are not transmitted to the infants. The understanding of the molecular and biological properties of the transmitted viruses will enable researchers to target a particular subtype in the mothers that is transmitted to the infants. Copyright 1996 S. Karger AG, Basel

Dried blood spots collected on filter paper: an international resource for the diagnosis and genetic characterization of human immunodeficiency virus type-1

The collection of dried blood spots (DBS) on filter paper provides a powerful approach for the development of large-scale, population-based screening programs. DBS methods are particularly valuable in developing countries and isolated rural regions where resources are limited. Large numbers of field specimens can be economically collected and shipped to centralized reference laboratories for genetic and (or) serological analysis. Alternatively, the dried blood can be stored and used as an archival resource to rapidly establish the frequency and distribution of newly recognized mutations, confirm patient identity or track the origins and emergence of newly identified pathogens. In this report, we describe how PCR-based technologies are beginning to interface with international screening programmes for the diagnosis and genetic characterization of human immunodeficiency virus type 1 (HIV-1). In particular, we review recent progress using DBS specimens to resolve the HIV-1 infection status of neonates, monitor the genetic evolution of HIV-1 during early infancy and establish a sentinel surveillance system for the systematic monitoring of HIV-1 genetic variation in Asia.

Mother-to-child transmission of human immunodeficiency virus type 1

A great deal of progress has been made in our understanding of mother-to-child transmission of HIV-1. Standardization of case definitions and transmission rate calculation methodologies, and a broader array of diagnostic options for detection of infant HIV-1 infection, will enhance our ability to evaluate and compare cohorts worldwide. In the next decade, several intervention studies should be completed. Carefully designed intervention studies have the potential both to determine which interventions are effective as well as to add to our understanding of vertical transmission of HIV-1. Regional differences in vertical transmission rates reflect a variety of viral, host, and obstetric factors. Intervention strategies will probably need to be regionally designed, taking into consideration these factors. Further research on timing and correlates of vertical transmission is necessary to determine the extent to which specific clinical trials can be extrapolated to public health policy.

Convergent evolution within the V3 loop domain of human immunodeficiency virus type 1 in association with disease progression

Phylogenetic analysis was used to study in vivo genetic variation of the V3 region of human immunodeficiency virus type 1 in relation to disease progression in six infants with vertically acquired human immunodeficiency virus type 1 infection. Nucleotide sequences from each infant formed a monophyletic group with similar average branch lengths separating the sets of sequences. In contrast to the star-shaped phylogeny characteristic of interinfant viral evolution, the shape of the phylogeny formed by sequences from the infants who developed AIDS tended to be linear. A computer program, DISTRATE, was written to analyze changes in DNA distance values over time. For the six infants, the rate of divergence from the initial variant was inversely correlated with CD4 cell counts averaged over the first 11 to 15 months of life (r = -0.87, P = 0.024). To uncover evolutionary relationships that might be dictated by protein structure and function, tree-building methods were applied to inferred amino acid sequences. Trees constructed from the full-length protein fragment (92 amino acids) showed that viruses from each infant formed a monophyletic group. Unexpectedly, V3 loop protein sequences (35 amino acids) that were found at later time points from the two infants who developed AIDS clustered together. Furthermore, these sequences uniquely shared amino acids that have been shown to confer a T-cell line tropic phenotype. The evolutionary pattern suggests that viruses from these infants with AIDS acquired similar and possibly more virulent phenotypes.