Characterization of mother-infant HIV type 1 gag p17 sequences associated with perinatal transmission

Features of Maternal HIV-1 Associated with Lack of Vertical Transmission

HIV-1 is transmitted from mother-to-child (vertical transmission) at an estimated rate of approximately 30% without any antiretroviral therapy (ART). However, administration of ART during pregnancy considerably diminishes the rate of mother-to-child transmission of HIV-1, which has become a standard of perinatal care in HIV-infected pregnant females in developed countries. Moreover, a majority of children born to HIV-infected mothers are uninfected without any ART. In addition, characteristics of HIV-1 and/or cellular factors in the mothers may play a role in influencing or preventing vertical transmission. Several studies, including from our laboratory have characterized the properties of HIV-1 from infected mothers that transmitted HIV-1 to their infants (transmitting mothers) and compared with those mothers that failed to transmit HIV-1 to their infants (non-transmitting mothers) in the absence of ART. One of the striking differences observed was that the non-transmitting mothers harbored a less heterogeneous HIV-1 population than transmitting mothers in the analyzed HIV-1 regions of p17 gag, env V3, vif and vpr. The other significant and distinctive findings were that the functional domains of HIV-1 vif and vpr proteins were less conserved in non-transmitting mothers compared with transmitting mothers. Furthermore, there were differences seen in two important motifs of HIV-1 Gag p17, including conservation of QVSQNY motif and variation in KIEEEQN motif in non-transmitting mothers compared with transmitting mothers. Several of these distinguishing properties of HIV-1 in non-transmitting mothers provide insights in developing strategies for preventing HIV-1 vertical transmission.

Molecular mechanisms of HIV-1 infection in neonatal target cells

HIV-1-infected neonates and infants have a higher viral load and progress to symptomatic AIDS more rapidly than their own infected mothers, as well as other infected adults, with differences in clinical manifestations, recurrent bacterial infections and CNS disorders. Two major reasons have been attributed to this differential HIV pathogenesis and disease; the relative immaturity of the neonate’s immune system and it’s inability to contain the highly replicating and mutating HIV-1, and the more efficient replication of HIV-1 in neonatal cells than in adult target cells. In this context, it has been demonstrated that HIV-1 replicates more efficiently in neonatal (cord) blood monocytes/macrophages and T lymphocytes – including naive and memory T lymphocytes – compared with adult blood cells. We have also determined the mechanisms of the differential HIV-1 replication in cord versus adult blood monocytes/macrophages and T lymphocytes (naive and memory), finding that it was influenced at the level of HIV-1 gene expression. The increased HIV-1 gene expression in neonatal versus adult target cells was regulated by differential expression of host factors, transcription factors (NF-κB, E2F, HAT-1, TFIIE, Cdk9 and Cyclin T1), signal transducers (STAT3 and STAT5A) and cytokines (IL-1β, IL-6 and IL-10). We also showed that nuclear extracts from cord cells interacted with HIV-1 long terminal repeat cis-acting sequences, including NF-κB, NFAT, AP1 and NF-IL6, to a greater extent when compared with adult peripheral blood mononuclear cell nuclear extracts. Additionally, shRNA of retroviral origin for STAT3 and IL-6 downregulated both their own gene expression as well as that of HIV-1, indicating that these factors influenced the differential expression of HIV-1 genes in cord cells compared with adult cells. In addition, HIV-1 integration plays an important role in differential HIV-1 replication and gene expression in neonatal versus adult cells by integrating into more actively transcribed genes in neonates compared with adults. We characterized 468 HIV-1 integration sites within cord and adult blood T lymphocytes and monocytes/macrophages, including genes coding for cellular components, and those involved with maintenance of the intracellular environment, enzyme regulation, cellular metabolism, catalytic activity and cation transport, as well as several potential transcription factor binding sites at the sites of integration. Additionally, the genes at the integration sites, transcription factors and transcription binding sites were expressed at higher levels in cord than adult target cells. In summary, the increased HIV-1 gene expression and replication in neonatal target cells due to differential expression of host factors all contribute to an increased viral load and faster disease progression in neonates and infants when compared with similar situations in adult patients. Based on these findings, it may be possible to identify new viral and host targets for use in developing strategies for the treatment and prevention of HIV-1.

Viral linkage in HIV-1 seroconverters and their partners in an HIV-1 prevention clinical trial

BACKGROUND

Characterization of viruses in HIV-1 transmission pairs will help identify biological determinants of infectiousness and evaluate candidate interventions to reduce transmission. Although HIV-1 sequencing is frequently used to substantiate linkage between newly HIV-1 infected individuals and their sexual partners in epidemiologic and forensic studies, viral sequencing is seldom applied in HIV-1 prevention trials. The Partners in Prevention HSV/HIV Transmission Study (ClinicalTrials.gov #NCT00194519) was a prospective randomized placebo-controlled trial that enrolled serodiscordant heterosexual couples to determine the efficacy of genital herpes suppression in reducing HIV-1 transmission; as part of the study analysis, HIV-1 sequences were examined for genetic linkage between seroconverters and their enrolled partners.

METHODOLOGY/PRINCIPAL FINDINGS

We obtained partial consensus HIV-1 env and gag sequences from blood plasma for 151 transmission pairs and performed deep sequencing of env in some cases. We analyzed sequences with phylogenetic techniques and developed a Bayesian algorithm to evaluate the probability of linkage. For linkage, we required monophyletic clustering between enrolled partners' sequences and a Bayesian posterior probability of ≥ 50%. Adjudicators classified each seroconversion, finding 108 (71.5%) linked, 40 (26.5%) unlinked, and 3 (2.0%) indeterminate transmissions, with linkage determined by consensus env sequencing in 91 (84%). Male seroconverters had a higher frequency of unlinked transmissions than female seroconverters. The likelihood of transmission from the enrolled partner was related to time on study, with increasing numbers of unlinked transmissions occurring after longer observation periods. Finally, baseline viral load was found to be significantly higher among linked transmitters.

CONCLUSIONS/SIGNIFICANCE

In this first use of HIV-1 sequencing to establish endpoints in a large clinical trial, more than one-fourth of transmissions were unlinked to the enrolled partner, illustrating the relevance of these methods in the design of future HIV-1 prevention trials in serodiscordant couples. A hierarchy of sequencing techniques, analysis methods, and expert adjudication contributed to the linkage determination process.

Molecular mechanisms of HIV-1 mother-to-child transmission and infection in neonatal target cells

HIV-1 mother-to-child transmission (MTCT) occurs mainly at three stages, including prepartum, intrapartum and postpartum. Several maternal factors, including low CD4+ lymphocyte counts, high viral load, immune response, advanced disease status, smoking and abusing drugs have been implicated in an increased risk of HIV-1 MTCT. While use of antiretroviral therapy (ART) during pregnancy has significantly reduced the rate of MTCT, selective transmission of ART resistant mutants has been reported. Based on HIV-1 sequence comparison, the maternal HIV-1 minor genotypes with R5 phenotypes are predominantly transmitted to their infants and initially maintained in the infants with the same properties. Several HIV-1 structural, regulatory and accessory genes were highly conserved following MTCT. In addition, HIV-1 sequences from non-transmitting mothers are less heterogeneous compared with transmitting mothers, suggesting that a higher level of viral heterogeneity influences MTCT. Analysis of the immunologically relevant epitopes showed that variants evolved to escape the immune response that influenced HIV-1 MTCT. Several cytotoxic T-lymphocyte (CTL) epitopes were identified in various HIV-1 genes that were conserved in HIV-1 mother-infant sequences, suggesting a role in MTCT. We have shown that HIV-1 replicates more efficiently in neonatal T-lymphocytes and monocytes/macrophages compared with adult cells, and this differential replication is influenced at the level of HIV-1 gene expression, which was due to differential expression of host factors, including transcriptional activators, signal transducers and cytokines in neonatal than adult cells. In addition, HIV-1 integration occurs in more actively transcribed genes in neonatal compared with adult cells, which may influence HIV-1 gene expression. The increased HIV-1 gene expression and replication in neonatal target cells contribute to a higher viral load and more rapid disease progression in neonates/infants than adults. These findings may identify targets, viral and host, for developing strategies for HIV-1 prevention and treatment.

Role of placenta in the vertical transmission of human immunodeficiency virus

OBJECTIVE

Review the role and mechanism of in utero placental transmission of HIV-1.

STUDY DESIGN

A thorough review based on a literature search for publications relevant to this subject was performed using relevant search terms. Articles that describe the genetic and pathophysiology of vertical transmission have been acknowledged. The articles pertinent to the topic were selected to support the discussion.

RESULTS

Vertical transmission may occur through CD4+ endothelial tissues or CD4+ Hofbauer cells. Trophoblasts and villi have CD4 receptors, which make them potential candidates for HIV infection. Placental cytokines and chemokines influence HIV replication in trophoblasts. Genetic analysis of HIV-1 sequences verify the interaction of HIV-1 and placental tissue. The vertical transmission of HIV-1 characterized by selection of genotype variant that escape the mother's immune system.

CONCLUSION

Placental transmission of HIV-1 is a complex incompletely understood process which requires advanced studies. The available literature provides information with regards to the interactions of placental cells with HIV.

THE VERTICAL TRANSMISSION OF HUMAN IMMUNODEFICIENCY VIRUS TYPE 1: Molecular and Biological Properties of the Virus

The vertical (mother-to-infant) transmission of human immunodeficiency virus type 1 (HIV-1 ) occurs at an estimated rate of more than 30% and is the major cause of AIDS in children. Numerous maternal parameters, including advanced dinical stages, low CD4+ lymphocte counts, high viral load, immune response, and disease progression have been implicated in an increased risk of vertical transmission. While the use of antiretroviral therapy (ART) during pregnancy has been shown to reduce the risk of vertical transmission, selective transmission of ART-resistant mutants has also been documented. Elucidation of the molecular mechanisms of vertical transmission might provide relevant information for the development of effective strategies for prevention and treatment. By using HIV-1 infected mother-infant pairs as a transmitter-recipient model, the minor genotypes of HIV-1 with macrophage-tropic and non-syncytium-inducing phenotypes (R5 viruses) in infected mothers were found to be transmitted to their infants and were initially maintained in the infants with the same properties. In addition, the transmission of major and multiple genotypes has been suggested. Furthermore, HIV-1 sequences found in non-transmitting mothers (mothers who failed to transmit HIV-1 to their infants in the absence of ART) were less heterogeneous than those from transmitting mothers, suggesting that viral heterogeneity may play an important role in vertical transmission. In the analysis of other regions of the HIV-1 genome, we have shown a high conservation of intact and functional gag p17, vif, vpr, vpu, tat, and nef open reading frames following mother-to-infant transmission. Moreover the accessory genes, vif and vpr, were less functionally conserved in the isolates of non-transmitting mothers than transmitting mothers and their infants. We, therefore, should target the properties of transmitted viruses to develop new and more effective strategies for the prevention and treatment of HIV-1 infection.

Mutations generated in human immunodeficiency virus type 1 long terminal repeat during vertical transmission correlate with viral gene expression

We determined the effect of mutations generated in HIV-1 LTR on viral gene expression in six mother-infant pairs following vertical transmission. We show that the functional domains critical for LTR function, the promoter (TATAA), enhancers (three SpI and two NFkappaB sites), the modulatory region (two AP-I sites, two NFAT, one NF-IL6 site, one Ets-1, and one USF-1) and the TAR region were generally conserved among mother-infant pairs, although we observed several patient and pair specific mutations in these important domains. We then determined the promoter activity of our mother-infant LTR sequences by measuring CAT gene expression, which was driven by these LTRs and found that most of these HIV-1 LTRs derived from 6 mother-infant pairs were functional. However, mutations in the important transcription factor binding sites, including TATAA, SpI, NFkappaB, AP-I, NFAT, NF-IL6, Ets-1, USF-1 and TAR resulted in reduced LTR driven CAT gene expression. Taken together, conservation of functional domains in the LTR during vertical transmission supports the notion that a functional LTR is critical in viral replication and pathogenesis and mutations generated during the course of infection correlated with HIV-1 gene expression.

Genetic characterization of HIV type 1 long terminal repeat following vertical transmission

Human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) sequences were characterized from six mother-infant pairs following vertical transmission. The LTR sequences exhibited a low degree of heterogeneity within mothers, within infants, and between epidemiologically linked mother-infant pairs. However, LTR sequences were more heterogeneous between epidemiologically unlinked individuals compared with linked mother-infant pairs. These data were further supported by low estimates of genetic diversity and clustering of each mother-infant pair's sequences into a separate subtree as well as the presence of common signature sequences between mother-infant pairs. The functional domains essential for LTR (promoter) function, including the promoter (TATAA), enhancers (three Sp-I and two NF-kappaB), the modulatory regions (two AP-I sites, two NFAT, one NF-IL6 site, one Ets-1, and one USF-1), and the TAR region were generally conserved among mother-infant pairs. Taken together, limited heterogeneity and conservation of functional domains in the LTR following vertical transmission support the notion that a functional LTR is critical in viral replication and pathogenesis in HIV-1-infected mothers and their infected infants.

Derivation of primary sequences and secondary structures of rev responsive element from HIV-1 infected mothers and infants following vertical transmission

We have characterized the primary RRE sequences of HIV-1, including in vivo genetic variation and functional motifs required for Rev-RRE interactions as well as evaluated the RNA secondary structures of RRE derived from five mother-infant pairs following vertical transmission. Multiple (157) RRE sequences derived from mother-infant pairs showed that primary nucleotide sequences of RRE were highly conserved with a low degree of viral heterogeneity following vertical transmission. We found that the RRE sequences from mothers and infants folded and retained all the essential stem-loop formation required for Rev-RRE interactions. More importantly, a primary 9-nucleotide (5'-CACTATGGG-3') RRE sequence in the stem-loop B that is required for optimal Rev recognition and must be presented as a stem-bulge-stem structure was highly conserved in most of the sequences. The domains required for RRE-host protein interactions were also conserved in most of the RRE sequences. Taken together, the primary RRE sequences in the context of secondary structures were maintained and the Rev-RRE interaction domains were conserved following vertical transmission, which is consistent with a crucial role of RRE in HIV-1 pathogenesis.

Characterization of HIV-1 envelope gp41 genetic diversity and functional domains following perinatal transmission

Background

HIV-1 envelope gp41 is a transmembrane protein that promotes fusion of the virus with the plasma membrane of the host cells required for virus entry. In addition, gp41 is an important target for the immune response and development of antiviral and vaccine strategies, especially when targeting the highly variable envelope gp120 has not met with resounding success. Mutations in gp41 may affect HIV-1 entry, replication, pathogenesis, and transmission. We, therefore, characterized the molecular properties of gp41, including genetic diversity, functional motifs, and evolutionary dynamics from five mother-infant pairs following perinatal transmission.

Results

The gp41 open reading frame (ORF) was maintained with a frequency of 84.17% in five mother-infant pairs' sequences following perinatal transmission. There was a low degree of viral heterogeneity and estimates of genetic diversity in gp41 sequences. Both mother and infant gp41 sequences were under positive selection pressure, as determined by ratios of non-synonymous to synonymous substitutions. Phylogenetic analysis of 157 mother-infant gp41 sequences revealed distinct clusters for each mother-infant pair, suggesting that the epidemiologically linked mother-infant pairs were evolutionarily closer to each other as compared with epidemiologically unlinked sequences. The functional domains of gp41, including fusion peptide, heptad repeats, glycosylation sites and lentiviral lytic peptides were mostly conserved in gp41 sequences analyzed in this study. The CTL recognition epitopes and motifs recognized by fusion inhibitors were also conserved in the five mother-infant pairs.

Conclusion

The maintenance of an intact envelope gp41 ORF with conserved functional domains and a low degree of genetic variability as well as positive selection pressure for adaptive evolution following perinatal transmission is consistent with an indispensable role of envelope gp41 in HIV-1 replication and pathogenesis.

Molecular characterization of the HIV-1 gag nucleocapsid gene associated with vertical transmission

BACKGROUND

The human immunodeficiency virus type 1 (HIV-1) nucleocapsid (NC) plays a pivotal role in the viral lifecycle: including encapsulating the viral genome, aiding in strand transfer during reverse transcription, and packaging two copies of the viral genome into progeny virions. Another gag gene product, p6, plays an integral role in successful viral budding from the plasma membrane and inclusion of the accessory protein Vpr within newly budding virions. In this study, we have characterized the gag NC and p6 genes from six mother-infant pairs following vertical transmission by performing phylogenetic analysis and by analyzing the degree of genetic diversity, evolutionary dynamics, and conservation of functional domains.

RESULTS

Phylogenetic analysis of 168 gag NC and p6 genes sequences revealed six separate subtrees that corresponded to each mother-infant pair, suggesting that epidemiologically linked individuals were closer to each other than epidemiologically unlinked individuals. A high frequency (92.8%) of intact open reading frames of NC and p6 with patient and pair specific sequence motifs were conserved in mother-infant pairs' sequences. Nucleotide and amino acid distances showed a lower degree of viral heterogeneity, and a low degree of estimates of genetic diversity was also found in NC and p6 sequences. The NC and p6 sequences from both mothers and infants were found to be under positive selection pressure. The two important functional motifs within NC, the zinc-finger motifs, were highly conserved in most of the sequences, as were the gag p6 Vpr binding, AIP1 and late binding domains. Several CTL recognition epitopes identified within the NC and p6 genes were found to be mostly conserved in 6 mother-infant pairs' sequences.

CONCLUSION

These data suggest that the gag NC and p6 open reading frames and functional domains were conserved in mother-infant pairs' sequences following vertical transmission, which confirms the critical role of these gene products in the viral lifecycle.

Evaluations of HIV type 1 rev gene diversity and functional domains following perinatal transmission

The human immunodeficiency virus type 1 (HIV-1) rev exons 1 and 2 sequences were analyzed from six mother-infant pairs following perinatal transmission. The rev open reading frame was maintained with a frequency of 93.96% in six mother-infant pairs' sequences. There was a low degree of viral heterogeneity and estimates of genetic diversity in mother-infant pairs' rev sequences. However, the distances of rev sequences between epidemiologically unlinked individuals were greater than in epidemiologically linked mother-infant pairs. Furthermore, phylogenetic parameters revealed that the epidemiologically linked mother-infant pairs were closer evolutionarily to each other as compared with epidemiologically unlinked mother-infant pairs. Both mothers and infants were under positive selection pressure as determined by the ratios of nonsynonymous to synonymous substitutions. The functional domains required for Rev activity, including nuclear export of RNA, RNA binding domain, and nuclear import signals, were conserved in all mother-infant pairs' sequences. The conservation of functional domains of rev and a low degree of heterogeneity following vertical transmission are consistent with an indispensable role of rev in the HIV-1 life cycle.

Conservation of functional domains and limited heterogeneity of HIV-1 reverse transcriptase gene following vertical transmission

BACKGROUND

The reverse transcriptase (RT) enzyme of human immunodeficiency virus type 1 (HIV-1) plays a crucial role in the life cycle of the virus by converting the single stranded RNA genome into double stranded DNA that integrates into the host chromosome. In addition, RT is also responsible for the generation of mutations throughout the viral genome, including in its own sequences and is thus responsible for the generation of quasi-species in HIV-1-infected individuals. We therefore characterized the molecular properties of RT, including the conservation of functional motifs, degree of genetic diversity, and evolutionary dynamics from five mother-infant pairs following vertical transmission.

RESULTS

The RT open reading frame was maintained with a frequency of 87.2% in five mother-infant pairs' sequences following vertical transmission. There was a low degree of viral heterogeneity and estimates of genetic diversity in mother-infant pairs' sequences. Both mothers and infants RT sequences were under positive selection pressure, as determined by the ratios of non-synonymous to synonymous substitutions. Phylogenetic analysis of 132 mother-infant RT sequences revealed distinct clusters for each mother-infant pair, suggesting that the epidemiologically linked mother-infant pairs were evolutionarily closer to each other as compared with epidemiologically unlinked mother-infant pairs. The functional domains of RT which are responsible for reverse transcription, DNA polymerization and RNase H activity were mostly conserved in the RT sequences analyzed in this study. Specifically, the active sites and domains required for primer binding, template binding, primer and template positioning and nucleotide recruitment were conserved in all mother-infant pairs' sequences.

CONCLUSION

The maintenance of an intact RT open reading frame, conservation of functional domains for RT activity, preservation of several amino acid motifs in epidemiologically linked mother-infant pairs, and a low degree of genetic variability following vertical transmission is consistent with an indispensable role of RT in HIV-1 replication in infected mother-infant pairs.

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.

Evaluation of genetic diversity of human immunodeficiency virus type 1 NEF gene associated with vertical transmission

The NEF gene is conserved among members of human and simian immunodeficiency viruses and may play an important role in viral pathogenesis. To determine the evolutionary dynamics and conservation of functionality of the human immunodeficiency virus type 1 (HIV-1) NEF gene during maternal-fetal transmission, we analyzed NEF sequences from seven mother-infant pairs following perinatal transmission, including a mother with infected twin infants. The NEF open reading frame was maintained in mother-infant isolates with a frequency of 86.2% following vertical transmission. While there was a low degree of viral heterogeneity and estimates of genetic diversity and high population growth rates of NEF sequences from mother-infant isolates, the infants' NEF sequences were slightly higher with respect to these parameters compared with the mothers' sequences. Both the mothers' and infants' NEF sequences were under positive selection pressure, as determined by a new method of Nielsen and Yang [Genetics 148:929-936;1998]. Based on genetic distance and phylogenetic parameters, the epidemiologically linked NEF sequences from mother-infant pairs were closer to each other compared with epidemiologically unlinked sequences from individuals. The functional domains essential for Nef activity, including membrane binding, CD4 and MHC-I downmodulation, T cell activation and interaction with factors of the cellular protein trafficking machinery, were conserved in most of the sequences from mother-infant pairs. The maintenance of intact NEF open reading frames with conserved functional domains and a low degree of genetic variability following vertical transmission supports the notion that NEF plays an important role in HIV-1 infection and replication in mothers and their perinatally infected infants.

Flt3 ligand and conjugation to IL-1beta peptide as adjuvants for a type 1, T-cell response to an HIV p17 gag vaccine

The adjuvant activity of Flt3 ligand (Flt3L) and conjugation to an interleukin (IL)-1beta bioactive fragment were compared, either alone or in combination, for their ability to induce T- and B-cell responses to the HGP-30 peptide sequence (amino acids 86-115 of human immunodeficiency virus (HIV) gag p17). The efficiency of HGP-30/IL-1beta conjugation, Flt3L administration or both as adjuvants was examined and all were found to augment similar levels of delayed type hypersensitivity (DTH) responses. In contrast, significant antigen (Ag)-specific types 1 and 2 T-cell ELISPOT responses were induced only by the combination of adjuvants. Further, in vitro sensitization with HGP-30 selectively increased Ag-specific, type 1 T-cell and cytotoxic T lymphocyte (CTL) responses to HGP-30-derived nonapeptide epitopes, while type 2 responses declined as measured in the ELISPOT assay. No serum antibodies to HGP-30 were induced unless HGP-30 was conjugated to keyhole-limpet hemocyanin. This suggests that a combination adjuvant strategy using Flt3L and conjugation to a biologically active IL-1beta fragment may be used to preferentially increase type 1 T-cell and CTL responses to HIV-1 gag antigenic epitopes.

Genetic characterization of HIV type 1 gag p17 matrix genes in isolates from infected mothers lacking perinatal transmission

The gag p17 matrix sequences of human immunodeficiency virus type 1 (HIV-1) were analyzed from three nontransmitting mothers (mothers who failed to transmit HIV-1 to their infants in the absence of antiretroviral therapy), including multiple deliveries in the case of mother 3. There was a low degree of heterogeneity of gag p17 matrix sequences in nontransmitting mothers compared with our previously analyzed mother-infant pairs' sequences. Whereas most of the functional domains essential for p17 matrix function were generally conserved, the polymerization site was less conserved. Several amino acid motifs, including KIEEEQN (positions 103-109) at the major antibody-binding site, were variable and the C-terminal 6-mer QVSQNY, a lysine or glutamine at position 15, an alanine at position 54, a lysine at position 76, a valine at position 104, and an aspartic acid at positions 102 and 121 were conserved in nontransmitting mothers' sequences compared with transmitting mothers' sequences. Phylogenetic analyses of 82 p17 matrix sequences revealed distinct clusters for each nontransmitting mother. Some of these motifs in gag p17 matrix sequences that are present in nontransmitting mothers and absent in transmitting mothers could be used as new targets for the development of preventive strategies for perinatal transmission.

Molecular characterization of HIV type 1 vpu genes from mothers and infants after perinatal transmission

We compared 162 vpu sequences of human immunodeficiency virus type 1 (HIV-1) in peripheral blood mononuclear cell DNA of 6 infected mother-infant pairs after perinatal transmission, and found a 90.12% frequency of intact vpu open reading frames. The heterogeneity of vpu genes between epidemiologically linked mother-infant pairs was lower compared with epidemiologically unlinked individuals. However, the variability of vpu genes was higher than that seen for other HIV-1 genes, including vif, vpr, tat, and gag p17 from the same mother-infant pairs. Moreover, the infants' sequences displayed patterns similar to those seen in their mothers. The functional domains essential for Vpu activity, including efficient release of virus particles from infected cells and CD4 degradation, were conserved in most of the sequences. In a phylogenetic analysis, the 162 sequences from 6 mother-infant pairs formed distinct clusters for each mother-infant pair sequences and grouped with subtype B sequences. These data support the importance of vpu in HIV-1 replication of mother-infant isolates that are involved in perinatal transmission.

Low conservation of functional domains of HIV type 1 vif and vpr genes in infected mothers correlates with lack of vertical transmission

Human immunodeficiency virus type 1 (HIV-1) vif and vpr sequences were analyzed from four nontransmitting mothers (infected mothers who failed to transmit HIV-1 to their infants mainly in the absence of anti-retroviral therapy), including a mother with multiple deliveries, and compared with the vif and vpr sequences of five and six previously analyzed transmitting mothers, respectively. In contrast to a high functional conservation of vif and vpr genes in transmitting mother isolates, we found that there was a low degree of conservation of functional domains of these genes in nontransmitting (NT) mother isolates. For vif sequences, NT-2 contained stop codons and no initiation codons, whereas NT-1 sequences carried a substitution of a highly conserved tyrosine to histidine at position 30. In addition, NT-3 and NT-4 sequences contained additional substitutions, including asparagine at position 22, lysine at position 77 and histidine at position 110, that were absent in transmitting mother and consensus subtype B sequences. Similarly, the vpr sequences of NT-2 contained stop codons and no initiation codons, NT-4 contained a substitution of serine in place of alanine at position 30, some NT-1 sequences substituted arginine in place of glycine at position 75, and NT-3 sequences presented a deletion in the C terminus that was absent in transmitting mother and consensus subtype B sequences and is essential for Vpr function. Furthermore, vif and vpr sequences of nontransmitting mothers were less heterogeneous compared with transmitting mother sequences. In conclusion, a low degree of conservation of functional domains and heterogeneity of HIV-1 vif and vpr genes in these infected mothers correlates with lack of vertical transmission.

Characterization of HIV type 1 tat sequences associated with perinatal transmission

Human immunodeficiency virus type 1 (HIV-1) tat exon I sequences were analyzed from six mother-infant pairs after perinatal transmission. The tat open reading frame was maintained in 140 of the 154 clones analyzed, with a 90.9% frequency of intact tat open reading frames. In addition, a low degree of heterogeneity was observed in tat sequences within mothers, within infants, and between epidemiologically linked mother-infant pairs. However, the distances of tat sequences between epidemiologically unlinked individuals were greater than in epidemiologically linked mother-infant pairs. The infant sequences showed amino acid sequence patterns similar to those present in their respective mothers. The functional domains required for Tat function, including amino-terminal, cysteine-rich, core and basic regions, which constitute domains for activation and RNA binding, were highly conserved in most of the sequences. Phylogenetic analysis of 154 mother-infant tat sequences showed that they formed distinct clusters for each mother-infant pair and grouped with subtype B sequence. These findings suggest that an intact and functional tat gene is conserved in HIV-1 mother-infant isolates that are involved in perinatal transmission.

Vertical human immunodeficiency virus type 1--HIV-1--transmission--a review

Several factors appear to affect vertical HIV-1 transmission, dependent mainly on characteristics of the mother (extent of immunodeficiency, co-infections, risk behaviour, nutritional status, immune response, genetical make-up), but also of the virus (phenotype, tropism) and, possibly, of the child (genetical make-up). This complex situation is compounded by the fact that the virus may have the whole gestation period, apart from variable periods between membrane rupture and birth and the breast-feeding period, to pass from the mother to the infant. It seems probable that an extensive interplay of all factors occurs, and that some factors may be more important during specific periods and other factors in other periods. Factors predominant in protection against in utero transmission may be less important for peri-natal transmission, and probably quite different from those that predominantly affect transmission by mothers milk. For instance, cytotoxic T lymphocytes will probably be unable to exert any effect during breast-feeding, while neutralizing antibodies will be unable to protect transmission by HIV transmitted through infected cells. Furthermore, some responses may be capable of controlling transmission of determined virus types, while being inadequate for controlling others. As occurrence of mixed infections and recombination of HIV-1 types is a known fact, it does not appear possible to prevent vertical HIV-1 transmission by reinforcing just one of the factors, and probably a general strategy including all known factors must be used. Recent reports have brought information on vertical HIV-1 transmission in a variety of research fields, which will have to be considered in conjunction as background for specific studies.

Limited heterogeneity of HIV type 1 in infected mothers correlates with lack of vertical transmission

The human immunodeficiency virus type 1 (HIV-1) envelope V3 region sequences of peripheral blood mononuclear cell DNA were analyzed from three nontransmitting mothers (infected mothers who failed to transmit HIV-1 to their infants in the absence of antiretroviral therapy), including one mother with two deliveries, and compared with the sequences of seven previously analyzed transmitting mothers. The coding potential of the envelope open reading frame, including several patient-specific amino acid motifs and previously described molecular features across the V3 region, were highly conserved. There was a low degree of heterogeneity within the sequences of each nontransmitting mother compared with the sequences of transmitting mothers. In addition, the estimates of genetic diversity of nontransmitting mother sequences were significantly lower compared with transmitting mother sequences. Phylogenetic analysis showed that the sequences of each nontransmitting mother formed distinct clusters that were well discriminated from each other and the sequences of seven transmitting mothers. In conclusion, a low degree of HIV-1 genetic heterogeneity in these infected mothers correlates with lack of vertical transmission; this finding may be useful in developing strategies for further prevention of maternal-fetal transmission.