Presence of maternal antibodies to human immunodeficiency virus 1 envelope glycoprotein gp120 epitopes correlates with the uninfected status of children born to seropositive mothers

Leveraging antigenic seniority for maternal vaccination to prevent mother-to-child transmission of HIV-1

The development of a maternal HIV vaccine to synergize with current antiretroviral drug prophylaxis can overcome implementation challenges and further reduce mother-to-child transmission (MTCT) of HIV. Both the epitope-specificity and autologous neutralization capacity of maternal HIV envelope (Env)-specific antibodies have been implicated in decreased risk of MTCT of HIV. Our goal was to determine if heterologous HIV Env immunization of SHIV.C.CH505-infected, ART-suppressed female rhesus macaques (RMs) could boost autologous Env-specific antibodies. SHIV.C.CH505-infected female RMs (n = 12), began a daily ART regimen at 12 weeks post-infection (wpi), which was continued for 12 weeks. Starting 2 weeks after ART initiation, RMs received 3 monthly immunizations with HIV b.63521/1086.C gp120 or placebo (n = 6/group) vaccine with adjuvant STR8S-C. Compared to the placebo-immunized animals, Env-vaccinated, SHIV-infected RMs exhibited enhanced IgG binding, avidity, and ADCC responses against the vaccine immunogens and the autologous SHIV.C.CH505 Env. Notably, the Env-specific memory B cells elicited by heterologous vaccination were dominated by cells that recognized the SHIV.C.CH505 Env, the antigen of primary exposure. Thus, vaccination of SHIV-infected, ART-suppressed RMs with heterologous HIV Envs can augment multiple components of the antibody response against the Env antigen of primary exposure, suggesting antigenic seniority. Our results suggest that a universal maternal HIV vaccination regimen can be developed to leverage antigenic seniority in targeting the maternal autologous virus pool.

Systematic comparison of HIV-1 Envelope-specific IgG responses induced by different vaccination regimens: Can we steer IgG recognition towards regions of viral vulnerability?

Immunogens and vaccination regimens can influence patterns of immune-epitope recognition, steering them towards or away from epitopes of potential viral vulnerability. HIV-1 envelope (Env)-specific antibodies targeting variable region 2 (V2) or 3 (V3) correlated with protection during the RV144 trial, however, it was suggested that the immunodominant V3 region might divert antibody responses away from other relevant sites. We mapped IgG responses against linear Env epitopes in five clinical HIV vaccine trials, revealing a specific pattern of Env targeting for each regimen. Notable V2 responses were only induced in trials administering CRF01_AE based immunogens, but targeting of V3 was seen in all trials, with the soluble, trimeric CN54gp140 protein eliciting robust V3 recognition. Strong V3 targeting was linked to greater overall response, increased number of total recognised antigenic regions, and where present, stronger V2 recognition. Hence, strong induction of V3-specific antibodies did not negatively impact the targeting of other linear epitopes in this study, suggesting that the induction of antibodies against V3 and other regions of potential viral vulnerability need not be necessarily mutually exclusive.

Understanding Viral and Immune Interplay During Vertical Transmission of HIV: Implications for Cure

Despite the significant progress that has been made to eliminate vertical HIV infection, more than 150,000 children were infected with HIV in 2019, emphasizing the continued need for sustainable HIV treatment strategies and ideally a cure for children. Mother-to-child-transmission (MTCT) remains the most important route of pediatric HIV acquisition and, in absence of prevention measures, transmission rates range from 15% to 45% via three distinct routes: in utero, intrapartum, and in the postnatal period through breastfeeding. The exact mechanisms and biological basis of these different routes of transmission are not yet fully understood. Some infants escape infection despite significant virus exposure, while others do not, suggesting possible maternal or fetal immune protective factors including the presence of HIV-specific antibodies. Here we summarize the unique aspects of HIV MTCT including the immunopathogenesis of the different routes of transmission, and how transmission in the antenatal or postnatal periods may affect early life immune responses and HIV persistence. A more refined understanding of the complex interaction between viral, maternal, and fetal/infant factors may enhance the pursuit of strategies to achieve an HIV cure for pediatric populations.

Preventive HIV Vaccines-Leveraging on Lessons from the Past to Pave the Way Forward

Almost four decades on, since the 1980’s, with hundreds of HIV vaccine candidates tested in both non-human primates and humans, and several HIV vaccines trials later, an efficacious HIV vaccine continues to evade us. The enormous worldwide genetic diversity of HIV, combined with HIV’s inherent recombination and high mutation rates, has hampered the development of an effective vaccine. Despite the advent of antiretrovirals as pre-exposure prophylaxis and preventative treatment, which have shown to be effective, HIV infections continue to proliferate, highlighting the great need for a vaccine. Here, we provide a brief history for the HIV vaccine field, with the most recent disappointments and advancements. We also provide an update on current passive immunity trials, testing proof of the concept of the most clinically advanced broadly neutralizing monoclonal antibodies for HIV prevention. Finally, we include mucosal immunity, the importance of vaccine-elicited immune responses and the challenges thereof in the most vulnerable environment–the female genital tract and the rectal surfaces of the gastrointestinal tract for heterosexual and men who have sex with men transmissions, respectively.

Maternal Intervention to Prevent Mother-to-Child Transmission of HIV: Moving Beyond Antiretroviral Therapy

Widespread availability of antiretroviral therapy among pregnant women living with HIV has greatly reduced the rate of mother-to-child transmission (MTCT) of HIV across the globe. However, while Joint United Nations Programme on HIV/AIDS has set targets to reduce the annual number of new pediatric HIV infections to fewer than 40,000 in 2018 and fewer than 20,000 in 2020, progress towards these targets has plateaued at an unacceptably high global estimate of greater than 160,000 children newly infected with HIV in 2018. Moreover, it has become clear that expansion of maternal antiretroviral therapy alone will not be sufficient to close the remaining gap and eliminate MTCT of HIV. Additional strategies such as maternal or infant passive and/or active immunization that synergize with maternal antiretroviral therapy will be required to end the pediatric HIV epidemic. In this review, we outline the landscape of existing maternal interventions and emerging maternal immune-based approaches to prevent MTCT of HIV.

Broadly Neutralizing Antibodies for HIV Prevention

In the last decade, over a dozen potent broadly neutralizing antibodies (bnAbs) to several HIV envelope protein epitopes have been identified, and their in vitro neutralization profiles have been defined. Many have demonstrated prevention efficacy in preclinical trials and favorable safety and pharmacokinetic profiles in early human clinical trials. The first human prevention efficacy trials using 10 sequential, every-two-month administrations of a single anti-HIV bnAb are anticipated to conclude in 2020. Combinations of complementary bnAbs and multi-specific bnAbs exhibit improved breadth and potency over most individual antibodies and are entering advanced clinical development. Genetic engineering of the Fc regions has markedly improved bnAb half-life, increased mucosal tissue concentrations of antibodies (especially in the genital tract), and enhanced immunomodulatory and Fc effector functionality, all of which improve antibodies' preventative and therapeutic potential. Human-derived monoclonal antibodies are likely to enter the realm of primary care prevention and therapy for viral infections in the near future.

Maternal Envelope gp41 Ectodomain-Specific Antibodies Are Associated With Increased Mother-to-Child Transmission of Human Immunodeficiency Virus-1

Mother-to-child transmission of human immunodeficiency virus (HIV) occurs in the setting of maternal and passively acquired antibodies, providing a unique window into immune correlates of HIV risk. We compared plasma antibody binding to HIV antigens between 51 nontransmitting mother-infant pairs and 21 transmitting mother-infant pairs. Plasma antibody binding to a variety of gp41 ectodomain-containing antigens was associated with increased odds of transmission. Understanding the reasons why gp41 ectodomain-targeting antibodies are associated with transmission risk will be important in determining whether they can directly enhance infection or whether their presence reflects a redirecting of the humoral response away from targeting more protective epitopes.

Induction of Neutralizing Responses against Autologous Virus in Maternal HIV Vaccine Trials

A maternal vaccine capable of boosting neutralizing antibody (NAb) responses directed against circulating viruses in HIV-infected pregnant women could effectively decrease mother-to-child transmission of HIV. However, it is not known if an HIV envelope (Env) vaccine administered to infected pregnant women could enhance autologous virus neutralization and thereby reduce this risk of vertical HIV transmission. Here, we assessed autologous virus NAb responses in maternal plasma samples obtained from AIDS Vaccine Evaluation Group (AVEG) protocols 104 and 102, representing historical phase I safety and immunogenicity trials of recombinant HIV Env subunit vaccines administered to HIV-infected pregnant women (ClinicalTrials registration no. NCT00001041). Maternal HIV Env-specific plasma binding and neutralizing antibody responses were characterized before and after vaccination in 15 AVEG 104 (n = 10 vaccine recipients, n = 5 placebo recipients) and 2 AVEG 102 (n = 1 vaccine recipient, n = 1 placebo recipient) participants. Single-genome amplification (SGA) was used to obtain HIV env gene sequences of autologous maternal viruses for pseudovirus production and neutralization sensitivity testing in pre- and postvaccination plasma of HIV-infected pregnant vaccine recipients (n = 6 gp120, n = 1 gp160) and placebo recipients (n = 3). We detected an increase in Env subunit MN gp120-specific IgG binding in the group of vaccine recipients between the first immunization visit and the last visit at delivery (P = 0.027, 2-sided Wilcoxon test). While no difference was observed in the levels of autologous virus neutralization potency between groups, in both groups maternal plasma collected at delivery more effectively neutralized autologous viruses from early pregnancy than late pregnancy. Immunization strategies capable of further enhancing these autologous virus NAb responses in pregnant women will be important to block vertical transmission of HIV.IMPORTANCE Maternal antiretroviral therapy (ART) has effectively reduced but not eliminated the burden of mother-to-child transmission of HIV across the globe, as an estimated 160,000 children were newly infected with HIV in 2018. Thus, additional preventive strategies beyond ART will be required to close the remaining gap and end the pediatric HIV epidemic. A maternal active immunization strategy that synergizes with maternal ART could further reduce infant HIV infections. In this study, we found that two historic HIV Env vaccines did not enhance the ability of HIV-infected pregnant women to neutralize autologous viruses. Therefore, next-generation maternal HIV vaccine candidates must employ alternate approaches to achieve potent neutralizing antibody and perhaps nonneutralizing antibody responses to effectively impede vertical virus transmission. Moreover, these approaches must reflect the broad diversity of HIV strains and widespread availability of ART worldwide.

Induction of Identical IgG HIV-1 Envelope Epitope Recognition Patterns After Initial HIVIS-DNA/MVA-CMDR Immunization and a Late MVA-CMDR Boost

In the RV144 trial, to date the only HIV-1 vaccine efficacy trial demonstrating a modestly reduced risk of HIV-1 acquisition, antibody responses toward the HIV Envelope protein (Env) variable (V) 2 and V3 regions were shown to be correlated with a reduced risk of infection. These potentially protective antibody responses, in parallel with the vaccine efficacy, however, waned quickly. Dissecting vaccine-induced IgG recognition of antigenic regions and their variants within the HIV-1 Env from different vaccine trials will aid in designing future HIV-1 immunogens and vaccination schedules. We, therefore, analyzed the IgG response toward linear HIV-1 Env epitopes elicited by a multi-clade, multigene HIVIS-DNA priming, and heterologous recombinant modified vaccinia virus Ankara (MVA-CMDR) boosting regimen (HIVIS03) and assessed whether a late MVA-CMDR boost 3 years after completion of the initial vaccination schedule (HIVIS06) restored antibody responses toward these epitopes. Here we report that vaccination schedule in the HIVIS03 trial elicited IgG responses against linear epitopes within the V2 and V3 tip as well as against the gp41 immunodominant region in a high proportion of vaccinees. Antibodies against the V2 and gp41 Env regions were restricted to variants with close homology to the MVA-CMDR immunogen sequence, while V3 responses were more cross-reactive. Boosting with a late third MVA-CMDR after 3 years effectively restored waned IgG responses to linear Env epitopes and induced targeting of identical antigenic regions and variants comparable to the previous combined HIVIS-DNA/MVA-CMDR regimen. Our findings support the notion that anti-HIV-1 Env responses, associated with a reduced risk of infection in RV144, could be maintained by regular boosting with a single dose of MVA-CMDR.

Pediatric HIV-1 Acquisition and Lifelong Consequences of Infant Infection

Increased availability of antiretroviral therapy to pregnant and breastfeeding women in resource-limited areas has proven remarkably successful at reducing HIV vertical transmission rates over the past several decades. Yet, still more than 170,000 children are infected annually due to failures in therapy implementation, monitoring, and adherence. Mother-to-child transmission (MTCT) of HIV-1 can occur at one of several distinct stages of infant development - intrauterine, intrapartum, and postpartum. The heterogeneity of the maternal-fetal interface at each of these modes of transmission poses a challenge for the implementation of immune interventions to prevent all modes of HIV MTCT. However, using mother-infant human cohorts and nonhuman primate models of infant simian immunodeficiency virus (SIV) acquisition, investigators have made important observation about the biology of pediatric HIV infection and have identified unique protective immune factors for each mode of transmission. Knowledge of immune factors protective against HIV MTCT will be critical to the development of targeted immune therapies to prevent infant HIV acquisition and to bring an end to the pediatric AIDS epidemic.

Human T-lymphotropic virus type I and breastfeeding; systematic review and meta-analysis of the literature

Background: The human T-cell lymphotropic virus type-I (HTLV-I) is the first identified pathogenic human retrovirus. Breastfeeding has been reported to be the predominant route of vertical transmission of HTLV-I. The objective of this systematic review was to pool and evaluate the data on the transmission of HTLV-I with different infant-feeding practices on children born to HTLV-I-positive mothers. We conducted a systematic review of comparison of HTLV-I transmission risk to breastfed and bottle-fed babies. Methods: We searched the following databases: MEDLINE, SID, Magiran, and Cochrane Library. The search strategy was limited to articles in English. Initial screening identified 254 citations; of these, 96 potentially relevant articles were identified. After reviewing the 96 full-text articles in detail, 7 reports met the inclusion criteria for this review. Results: Pooled odds ratio (OR) and risk difference (RD) of HTLV-I transmission in the breastfed group compared to the bottle-fed infants were [OR = 3.48, 95% confidence interval (CI): 1.58-7.64, P = 0.0020, Cochran's Q = 27.7, P = 0.0010, and I² = 67.5%] and (RD = 17.1%, 95% CI: 7.5%-26.7%, P < 0.0001, Cochran's Q = 106, P < 0.0001, and I² = 91.5%). So, we have evidence to support that exclusive breast feeding more than 6 months in comparison to bottle feeding highly increases transmission rate of HTLV-I infection. We have also enough evidence to support that exclusive breast feeding up to 6 months compared to bottle feeding does not increase transmission rate of HTLV-I infection (pooled OR = 0.912, CI: 0.45-1.80; OR: 3.83, CI: 1.80-8.10, respectively). Conclusion: The current meta-analysis showed that short period (less than 6 months) of breastfeeding did not increase risk of HTLV-I infection transmission from mother to child among breastfeeders and more than 6 months of breastfeeding significantly increased the risk of HTLV-I infection. However, our meta-analysis shows that refraining from breastfeeding can decrease the risk of vertical HTLV-I transmission.

Maternal HIV-1 Env Vaccination for Systemic and Breast Milk Immunity To Prevent Oral SHIV Acquisition in Infant Macaques

Without novel strategies to prevent mother-to-child HIV-1 transmission, more than 5% of HIV-1-exposed infants will continue to acquire HIV-1, most through breastfeeding. This study of rhesus macaque dam-and-infant pairs is the first preclinical study to investigate the protective role of transplacentally transferred HIV-1 vaccine-elicited antibodies and HIV-1 vaccine-elicited breast milk antibody responses in infant oral virus acquisition. It revealed highly variable placental transfer of potentially protective antibodies and emphasized the importance of pregnancy immunization timing to reach peak antibody levels prior to delivery. While there was no discernible impact of maternal immunization on late infant oral virus acquisition, we observed a strong correlation between the percentage of activated CD4⁺ T cells in infant peripheral blood and a reduced number of challenges to infection. This finding highlights an important consideration for future studies evaluating alternative strategies to further reduce the vertical HIV-1 transmission risk.

Mother-to-child transmission (MTCT) of human immunodeficiency virus type 1 (HIV-1) contributes to an estimated 150,000 new infections annually. Maternal vaccination has proven safe and effective at mitigating the impact of other neonatal pathogens and is one avenue toward generating the potentially protective immune responses necessary to inhibit HIV-1 infection of infants through breastfeeding. In the present study, we tested the efficacy of a maternal vaccine regimen consisting of a modified vaccinia virus Ankara (MVA) 1086.C gp120 prime-combined intramuscular-intranasal gp120 boost administered during pregnancy and postpartum to confer passive protection on infant rhesus macaques against weekly oral exposure to subtype C simian-human immunodeficiency virus 1157ipd3N4 (SHIV1157ipd3N4) starting 6 weeks after birth. Despite eliciting a robust systemic envelope (Env)-specific IgG response, as well as durable milk IgA responses, the maternal vaccine did not have a discernible impact on infant oral SHIV acquisition. This study revealed considerable variation in vaccine-elicited IgG placental transfer and a swift decline of both Env-specific antibodies (Abs) and functional Ab responses in the infants prior to the first challenge, illustrating the importance of pregnancy immunization timing to elicit optimal systemic Ab levels at birth. Interestingly, the strongest correlation to the number of challenges required to infect the infants was the percentage of activated CD4⁺ T cells in the infant peripheral blood at the time of the first challenge. These findings suggest that, in addition to maternal immunization, interventions that limit the activation of target cells that contribute to susceptibility to oral HIV-1 acquisition independently of vaccination may be required to reduce infant HIV-1 acquisition via breastfeeding.

IMPORTANCE Without novel strategies to prevent mother-to-child HIV-1 transmission, more than 5% of HIV-1-exposed infants will continue to acquire HIV-1, most through breastfeeding. This study of rhesus macaque dam-and-infant pairs is the first preclinical study to investigate the protective role of transplacentally transferred HIV-1 vaccine-elicited antibodies and HIV-1 vaccine-elicited breast milk antibody responses in infant oral virus acquisition. It revealed highly variable placental transfer of potentially protective antibodies and emphasized the importance of pregnancy immunization timing to reach peak antibody levels prior to delivery. While there was no discernible impact of maternal immunization on late infant oral virus acquisition, we observed a strong correlation between the percentage of activated CD4⁺ T cells in infant peripheral blood and a reduced number of challenges to infection. This finding highlights an important consideration for future studies evaluating alternative strategies to further reduce the vertical HIV-1 transmission risk.

Maternal Binding and Neutralizing IgG Responses Targeting the C-Terminal Region of the V3 Loop Are Predictive of Reduced Peripartum HIV-1 Transmission Risk

The development of an effective maternal HIV-1 vaccine that could synergize with antiretroviral therapy (ART) to eliminate pediatric HIV-1 infection will require the characterization of maternal immune responses capable of blocking transmission of autologous HIV to the infant. We previously determined that maternal plasma antibody binding to linear epitopes within the variable loop 3 (V3) region of HIV envelope (Env) and neutralizing responses against easy-to-neutralize tier 1 viruses were associated with reduced risk of peripartum HIV infection in the historic U.S. Woman and Infant Transmission Study (WITS) cohort. Here, we defined the fine specificity and function of the potentially protective maternal V3-specific IgG antibodies associated with reduced peripartum HIV transmission risk in this cohort. The V3-specific IgG binding that predicted low risk of mother-to-child-transmission (MTCT) was dependent on the C-terminal flank of the V3 crown and particularly on amino acid position 317, a residue that has also been associated with breakthrough transmission in the RV144 vaccine trial. Remarkably, the fine specificity of potentially protective maternal plasma V3-specific tier 1 virus-neutralizing responses was dependent on the same region in the V3 loop. Our findings suggest that MTCT risk is associated with neutralizing maternal IgG that targets amino acid residues in the C-terminal region of the V3 loop crown, suggesting the importance of the region in immunogen design for maternal vaccines to prevent MTCT.IMPORTANCE Efforts to curb HIV-1 transmission in pediatric populations by antiretroviral therapy (ART) have been highly successful in both developed and developing countries. However, more than 150,000 infants continue to be infected each year, likely due to a combination of late maternal HIV diagnosis, lack of ART access or adherence, and drug-resistant viral strains. Defining the fine specificity of maternal humoral responses that partially protect against MTCT of HIV is required to inform the development of a maternal HIV vaccine that will enhance these responses during pregnancy. In this study, we identified amino acid residues targeted by potentially protective maternal V3-specific IgG binding and neutralizing responses, localizing the potentially protective response in the C-terminal region of the V3 loop crown. Our findings have important implications for the design of maternal vaccination strategies that could synergize with ART during pregnancy to achieve the elimination of pediatric HIV infections.

Antibodies for prevention of mother-to-child transmission of HIV-1

PURPOSE OF REVIEW

Although antiretroviral (ARV) prophylaxis can reduce mother-to-child transmission (MTCT) of HIV-1 to less than 2%, one-quarter of a million infants continue to be infected with HIV-1 annually. ARV prophylaxis alone will fail to eliminate infant HIV-1 infection because of issues of maternal adherence, toxicities, ARV-resistant virus strains, and acute maternal infection. Effective maternal and/or infant immunization will likely be required to achieve the goal of an HIV-free generation.

RECENT FINDINGS

This article describes recent studies of antibody responses that protect against vertical HIV-1 transmission. Studies have shown that maternal neutralization breadth is not a critical factor in MTCT, yet the ability of maternal plasma to neutralize autologous virus variants may be important in infant protection. There is also new evidence that infants mount robust and durable antibody responses to HIV-1 envelope following vaccination and can develop broad neutralization during infection. Finally, passive immunization of infants with highly potent and broad neutralizing antibodies may be an effective strategy to protect infants against infection with postnatally transmitted variants.

SUMMARY

Defining the characteristics of maternal and infant antibody responses that protect against MTCT will inform development of effective passive and active immunization strategies that will likely be required to eliminate pediatric HIV-1.

Maternal HIV-1 envelope-specific antibody responses and reduced risk of perinatal transmission

Despite the wide availability of antiretroviral drugs, more than 250,000 infants are vertically infected with HIV-1 annually, emphasizing the need for additional interventions to eliminate pediatric HIV-1 infections. Here, we aimed to define humoral immune correlates of risk of mother-to-child transmission (MTCT) of HIV-1, including responses associated with protection in the RV144 vaccine trial. Eighty-three untreated, HIV-1-transmitting mothers and 165 propensity score-matched nontransmitting mothers were selected from the Women and Infants Transmission Study (WITS) of US nonbreastfeeding, HIV-1-infected mothers. In a multivariable logistic regression model, the magnitude of the maternal IgG responses specific for the third variable loop (V3) of the HIV-1 envelope was predictive of a reduced risk of MTCT. Neutralizing Ab responses against easy-to-neutralize (tier 1) HIV-1 strains also predicted a reduced risk of peripartum transmission in secondary analyses. Moreover, recombinant maternal V3-specific IgG mAbs mediated neutralization of autologous HIV-1 isolates. Thus, common V3-specific Ab responses in maternal plasma predicted a reduced risk of MTCT and mediated autologous virus neutralization, suggesting that boosting these maternal Ab responses may further reduce HIV-1 MTCT.

Safety and efficacy of HIV hyperimmune globulin for prevention of mother-to-child HIV transmission in HIV-1-infected pregnant women and their infants in Kampala, Uganda (HIVIGLOB/NVP STUDY)

BACKGROUND

This phase III, randomized, clinical trial compared single-dose nevirapine (sdNVP) plus HIV hyperimmune globulin (HIVIGLOB) with sdNVP alone for preventing maternal-to-child transmission of HIV. Primary objectives were to determine rates of HIV infection among infants and to assess the safety of HIVIGLOB in combination with sdNVP in HIV-infected Ugandan pregnant women and their infants.

METHODS

Mother-infant pairs were randomized to receive 200 mg of nevirapine to women in labor and 2 mg/kg NVP to newborns within 72 hours after birth (sdNVP arm) or to receive sdNVP plus a single intravenous 240-mL dose of HIVIGLOB given to women at 36- to 38-week gestation and a single intravenous 24-mL dose to newborns within 18 hours of birth (HIVIGLOB/sdNVP arm). Risk of HIV infection was determined using Kaplan-Meier and risk ratio estimates at birth, 2, 6, 14 weeks, 6, and 12 months of age.

RESULTS

Intent-to-treat analysis included 198 HIVIGLOB/sdNVP and 294 sdNVP mother-infant pairs. At 6 months of age, the primary endpoint, there was no statistically significant difference in HIV transmission in the HIVIGLOB/sdNVP arm vs. the sdNVP arm [18.7% vs. 15.0%; risk ratio = 1.240 (95% confidence interval: 0.833 to 1.846); P = 0.290]. Similarly, the proportion of serious adverse events in the HIVIGLOB/sdNVP and sdNVP arms, respectively, for mothers (18.9% vs. 19.3%; P = 0.91) and infants (62.6% vs. 59.5%; P = 0.51) was not significantly different.

CONCLUSIONS

Giving mother-infant pairs an infusion of peripartum HIV hyperimmune globulin in addition to sdNVP for preventing maternal-to-child transmission was as safe as sdNVP alone but was no more effective than sdNVP alone in preventing HIV transmission.

Human immunodeficiency virus type 1 mother-to-child transmission and prevention: successes and controversies

The World Health Organization (WHO) and United Nations Programme on HIV/AIDS (UNAIDS) estimated that an additional 370 000 new human immunodeficiency virus type 1 (HIV-1) infections occurred in children in 2009, mainly through mother-to-child transmission (MTCT). Intrapartum transmission contributes to approximately 20-25% of infections, in utero transmission to 5-10% and postnatal transmission to an additional 10-15% of cases. MTCT accounts for only a few hundred infected newborns in those countries in which services are established for voluntary counselling and testing of pregnant women, and a supply of antiretroviral drugs is available throughout pregnancy with recommendations for elective Caesarean section and avoidance of breastfeeding. The single-dose nevirapine regimen has provided the momentum to initiate MTCT programmes in many resource-limited countries; however, regimens using a combination of antiretroviral drugs are needed also to effectively reduce transmission via breastfeeding.

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.

Molecular analysis and phylogenetic characterization of HIV in Iran

The rate of human immunodeficiency virus type 1 (HIV-1) infection in Iran has increased dramatically in the last few years. While the earliest cases were found in hemophiliacs, intravenous drug users are now fueling the outbreak. In this study, both the 122 clones of HIV-1 gag p17 and the 131 clones of env V1-V5 region were obtained from 61 HIV-1 seropositives belonging to these two groups in Iran. HIV-1 subtyping and phylogenetic analysis was done by heteroduplex mobility assays (HMA) and multiple clone sequencing. The result indicated all hemophiliacs are infected with HIV-1 subtype B and all intravenous drug users are infected with HIV-1 subtype A. Since intravenous drug abuse is the major transmission route in Iran, HIV-1 subtype A is likely to be the dominant viral subtype circulating in the country. The analysis of genetic distances showed subtype B viruses in Iran to be twice as heterogeneous as the subtype A viruses. In conclusion, this first molecular study of HIV-1 genotypes in Iran suggests two parallel outbreaks in distinct high-risk populations and may offer clues to the origin and spread of infection in Iran.

Immunoprophylaxis against mother-to-child transmission of HIV-1

The authors discuss a new study in PLoS Medicine that examines whether human anti-HIV monoclonal antibodies might be useful in South Africa for preventing mother-to-child transmission of subtype C HIV viruses.

Impact of the placental cytokine-chemokine balance on regulation of cell-cell contact-induced human immunodeficiency virus type 1 translocation across a trophoblastic barrier in vitro

Cells constituting the placental barrier secrete soluble factors that may participate in controlling human immunodeficiency virus type 1 (HIV-1) transmission from the mother to the fetus. In this study, we asked whether placental soluble factors (PSF) could limit cell-cell contact inducing HIV-1 production that occurs after inoculation of HIV-1-infected peripheral blood mononuclear cells (HIV-1+ PBMCs) onto trophoblast-derived BeWo cells grown as tight and polarized barriers in a two-chamber system. The activity of recombinant chemokines and cytokines expressed by placental tissue and of factors secreted by either early or term placentae of HIV-1-negative women, was analyzed. We identified chemokines (RANTES and MIP-1beta) and cytokines (tumor necrosis factor alpha and interleukin-8) that decreased and increased, respectively, viral production in trophoblast barrier cells inoculated with HIV-1+ PBMCs. Unexpectedly, factors secreted by either early or term placentae of HIV-1-negative women enhanced viral production. Nevertheless, the same PSF did not favor infection of trophoblastic barriers with cell-free HIV-1 and strongly reduced viral production in PBMCs infected with cell-free HIV-1. Moreover, PSF contained chemokines (RANTES and MIP-1beta) and a cytokine, leukemia inhibitory factor, exhibiting a strong anti-HIV-1 activity in our model of cell-to-cell infection. Together these data suggested that at the maternal interface the global activity of PSF is related to the synergistic action of several soluble factors with a balance in favor of an enhancing activity on the passage of viruses across the trophoblast barrier. This could explain the presence of viral sequences in trophoblasts in all placentae of HIV-1-infected women.

Maternal plasma viral load and neutralizing/enhancing antibodies in vertical transmission of HIV: a non-randomized prospective study

Background

We examined the association and interaction between maternal viral load and antibodies in vertical transmission of HIV in a non-randomized prospective study of 43 HIV-1 infected pregnant women who attended the San Juan City Hospital, Puerto Rico, and their 45 newborn infants. The women and infants received antiretroviral therapy.

Methods

A nested PCR assay of the HIV-1 envelope V3 region and infant PBMC culture were performed to determine HIV status of the infants. Maternal and infant plasma were tested for HIV neutralization or enhancement in monocyte-derived macrophages.

Results

Twelve (26.7%) infants were positive by the HIV V3 PCR assay and 3 of the 12 were also positive by culture. There was a trend of agreement between high maternal viral load and HIV transmission by multivariate analysis (OR = 2.5, CI = 0.92, p = 0.0681). Both maternal and infant plasma significantly (p = 0.001 for both) reduced HIV replication at 10^-1 dilution compared with HIV negative plasma. Infant plasma neutralized HIV (p = 0.001) at 10^-2 dilution but maternal plasma lost neutralizing effect at this dilution. At 10^-3 dilution both maternal and infant plasma increased virus replication above that obtained with HIV negative plasma but only the increase by maternal plasma was statistically significant (p = 0.005). There were good agreements in enhancing activity in plasma between mother-infant pairs, but there was no significant association between HIV enhancement by maternal plasma and vertical transmission.

Conclusion

Although not statistically significant, the trend of association between maternal viral load and maternal-infant transmission of HIV supports the finding that viral load is a predictor of maternal-infant transmission. Both maternal and infant plasma neutralized HIV at low dilution and enhanced virus replication at high dilution. The antiretroviral treatments that the women received and the small sample size may have contributed to the lack of association between HIV enhancement by maternal plasma and vertical transmission.

Immunoprophylaxis to Prevent Mother-to-Child Transmission of HIV-1

Antiretroviral therapy can profoundly reduce the risk of mother-to-child transmission (MTCT) of HIV, but the drugs have a relatively short half-life and should thus be administered throughout breast-feeding to optimally prevent postnatal infection of the infant. The potential toxicities and the development of resistance may limit the long-term efficacy of antiretroviral prophylaxis, and a safe and effective active/passive immunoprophylaxis regimen, begun at birth, and potentially overlapping with interpartum or neonatal chemoprophylaxis, would pose an attractive alternative. This review draws on data presented at the Ghent Workshop on prevention of breast milk transmission and on selected issues from a workshop specifically relating to immunoprophylaxis held in Seattle in October 2002. This purpose of this review is to address the scientific rationale for the development of passive (antibody) and active (vaccine) immunization strategies for prevention of MTCT. Data regarding currently or imminently available passive and active immunoprophylaxis products are reviewed for their potential use in neonatal trials within the coming 1-2 years.

Parasitic infection and the polarized Th2 immune response can alter a vaccine-induced immune response

The AIDS epidemic in the Developing World represents a major global crisis. It is imperative that we develop an effective vaccine. Vaccines are economically the most efficient means of controlling viral infections. However, the development of a vaccine against HIV-1 has been a formidable task, and in developing countries chronic parasitic infection adds another level of complexity to AIDS vaccine development. Helminthic and protozoan infections, common in developing countries, can result in a constant state of immune activation that is characterized by a dominant Th2 type of cytokine profile, high IgE levels, and eosinophilia. Such an immune profile may have an adverse impact on the efficacy of vaccines, in particular, an HIV-1 vaccine. Indeed, the CD8 cellular immune response and the corresponding Th1 type cytokines that enhance the CD8 cellular immune response are important for clearing many viral infections. It is believed that an antigen specific CD8 cellular immune response will be an important component of an HIV-1 vaccine.

Phase I/II trial of HIV-1 hyperimmune globulin for the prevention of HIV-1 vertical transmission in Uganda

OBJECTIVES

To assess the safety, tolerance, pharmacokinetics, and virologic and immunologic changes associated with the use of Ugandan HIV hyperimmune globulin (HIVIGLOB) in HIV infected pregnant Ugandan women and their infants.

DESIGN

A prospective, phase I/II, three-arm dose escalation trial of HIVIGLOB.

METHODS

HIVIGLOB was prepared from discarded HIV infected units of blood collected from the National Blood Bank in Kampala. From June 1996 to April 1997, 31 HIV positive pregnant women were enrolled with HIVIGLOB infusions given at 37 weeks gestation and within 16 h of birth for infants. The first 10 mother-infant pairs were infused at a dose of 50 mg/kg, followed by 11 pairs at 200 mg/kg, and 10 pairs at 400 mg/kg. Study participants were followed for 30 months.

RESULTS

Thirty-one women and 29 infants were infused with HIVIGLOB. The infusions were safe and well tolerated by the women and their infants at all doses. There were no significant changes in virologic or immunologic parameters after HIVIGLOB infusion. Pharmacokinetic properties of this product were similar to other immune globulin products with a median half-life of 28 days in women and 30 days in infants.

CONCLUSION

An HIV immune globulin product derived from HIV infected Ugandan donors is safe, well tolerated, and has pharmacokinetic properties consistent with other immunoglobulin products. Data suggest that a 400 mg/kg dose of HIVIGLOB would be the most appropriate dose for a subsequent efficacy trial of HIVIGLOB for the prevention of mother to child HIV transmission.

Anti-HIV activity of a glycoprotein from first trimester placental tissue

Human Immunodeficiency Virus-1 (HIV-1) transmission from a mother to the offspring during pregnancy is highly complex and a variable process in part due to the presence of several anti-HIV factors. In this study, we report an early pregnancy-associated protein (early pregnancy associated protein-1, Epap-1) with an apparent molecular weight of 90 kDa in placental tissue of pregnant women during the first trimester. Epap-1 was isolated and purified using Sambucus nigra agarose lectin affinity chromatography. Epap-1 strongly inhibits HIV-1(MN), HIV-1(91US056), HIV-1(VB-7) replication in vitro while it exhibits low activity with HIV-1(VB-66) strain. The molecular analysis of action of Epap-1 shows that it affects HIV-CD4 binding through inhibition of CD4-gp120 interaction.

Comparison of two different preparations of HIV immune globulin for efficiency of neutralization of HIV type 1 primary isolates

The objective of this study was to compare the virus-neutralizing ability of two different preparations of HIV immune globulin (HIVIG) isolated from human plasma units that were selected according to two different criteria. The first preparation, designated NYBC-HIVIG, was isolated from plasmas with high neutralizing antibody titers against HIV-1. The second preparation, designated NABI-HIVIG, was isolated from plasma with high titers of antibody to the HIV-1 p24 antigen. A panel of primary HIV-1 isolates was phenotypically characterized by their ability to induce syncytia in CEM-SS cells. Neutralization of this panel of primary isolates by the two HIVIG preparations was assessed in HeLa-MAGI-CCR5 cells, utilizing a luminescence-based assay. In addition, the reactivities of these two preparations with a panel of HIV-1 gp120 proteins, V3 loop peptides, and HIV-1 p24 antigen were determined. Both HIVIG preparations were shown to neutralize all virus isolates tested. However, doses of NABI-HIVIG required for 50% virus neutralization were 2.2- to 4.4- fold (mean, 3.2-fold) higher than the required doses of NYBC-HIVIG. Comparative antigen-binding assays showed that, although NABI-HIVIG possessed higher titers of antibody to HIV-1 p24, NYBC-HIVIG generally contained higher titers of antibody to HIV-1 gp120 and V3 peptides. These experiments show that the criteria used for selection of source plasmas for isolation of HIVIG can influence the effective concentration of virus-neutralizing antibody present in the final immunoglobulin preparation, and may determine the doses required for clinical efficacy.

HIV type 1 chemokine receptor usage in mother-to-child transmission

To investigate the role of the HIV-1 phenotype in mother-to-child HIV-1 transmission, we evaluated coreceptor usage and replication kinetics in chemokine receptor-expressing U87MG.CD4 cells of primary isolates from 32 HIV-1-infected mothers of Italian origin, none under preventive antiretroviral therapy, and from their infected infants. Five of 15 mothers of infected children and 2 of 17 mothers of uninfected children harbored viruses able to use CXCR4 as coreceptor. However, all isolates used CCR5, alone or in association with CXCR4. The replicative capacity in coreceptor-expressing cells of the viral isolates did not differ between the two groups of mothers. All mothers with an R5 virus transmitted a virus with the same coreceptor usage, whereas those four with a multitropic virus transmitted such a virus in one case. Although the presence of a mixed viral population was documented in the mothers, we did not observe transmission solely of X4 viruses. Interestingly, the only child infected with a multitropic virus carried a defective CCR5 allele. Analysis of the env V3 region of the provirus from this child revealed infection with multiple viral variants with a predominance of R5-type over X4-type sequences. These findings show that CCR5 usage of a viral isolate is not a discriminating risk factor for vertical transmission. Furthermore, X4 viruses can be transmitted to the newborn, although less frequently. In particular, we document the transmission of multiple viral variants with different coreceptor usage in a Delta32 CCR5 heterozygous child, and demonstrate that the heterozygous genotype per se does not contribute to the restriction of R5-type virus spread.

Leukemia inhibitory factor inhibits HIV-1 replication and is upregulated in placentae from nontransmitting women

The placenta may play a critical role in inhibiting vertical transmission of HIV-1. Here we demonstrate that leukemia inhibitory factor (LIF) is a potent endogenous HIV-1-suppressive factor produced locally in placentae. In vitro, LIF exerted a potent, gp130-LIFRbeta-dependent, HIV coreceptor-independent inhibition of HIV-1 replication with IC50 values between 0.1 pg/ml and 0.7 pg/ml, depending on the HIV-1 isolate. LIF also inhibited HIV-1 in placenta and thymus tissues grown in ex vivo organ culture. The level of LIF mRNA and the incidence of LIF protein-expressing cells were significantly greater in placentae from HIV-1-infected women who did not transmit HIV-1 to their fetuses compared with women who transmitted the infection, but they were not significantly different from placentae of uninfected mothers. These findings demonstrate a novel pathway for endogenous HIV suppression that may prove to be an effective immune therapy for HIV infection.

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.

HIV-1 DNA vaccines and chemokines

DNA vaccines have a demonstrated ability to induce humoral and cellular immune responses in animal models and humans. The technology, although it dates back to the 1950's, has had an insurgence of interest within the past few years following concurrent research papers. The basic technology is being applied broadly to viral, bacterial and parasitic infections. It has also been demonstrated that genes delivered via plasmid expression vectors result in expression of functional proteins in the inoculated host. Further, injection of plasmids encoding cytokine, chemokine or co-stimulatory molecules, also referred to as immunomodulatory plasmids can lead to the further expansion of this technology to include directed immunology. We have been developing DNA technology specifically with a focus as a vaccine against HIV-1 infection. We report that such vaccines can stimulate immune responses in a variety of relevant animal systems including humoral and cellular responses as well as the production of beta-chemokines. We describe that the beta-chemokines can both modulate the immune response induced by DNA vaccines and be modulated by the DNA vaccines in the murine and chimpanzee models as well as in humans.

Emerging recombinant human immunodeficiency viruses: uneven representation of the envelope V3 region

OBJECTIVE

To determine whether the envelope V3 region from HIV-1 subtypes A, C or D had the same probability of being present in intersubtype recombinant genomes.

MATERIALS AND METHODS

The envelope C2-C5 and the gag p24-p7 regions from one hundred infants infected perinatally in Tanzania were compared using phylogenetic and recombination analysis. Exact binomial and Fisher's exact tests were used to assess if various genomic regions were more likely to be overrepresented in intersubtype recombinants.

RESULTS

Of one hundred HIV-1 positive infants analyzed, twenty-two (22%) showed exclusively subtype A sequence in gag and env. Subtype C accounted for twenty-two infants (22%) whereas nineteen infants (19%) were infected by HIV-1 subtype D. Intersubtype recombinant genomes accounted for thirty-seven infections (37%). The V3 region from subtype A was found in all fifteen A-D recombinants (P = 0.00003) and the V3 region from subtype C was found in all twelve C-D recombinants (P = 0.0002). Conversely, subtype D gag sequences were preferentially represented in the gag of A-D recombinants (P = 0.0003) as well as C-D recombinants (P = 0.002). In A-D recombinants, the V3 region of subtype A was generally surrounded by subtype A C3-C5 sequences. In contrast, the V3 region from subtype C was surrounded by subtype D C3-C5 sequences in C-D recombinants. Significant differences were not found in the number of subtype A or subtype C sequences in A-C recombinants.

CONCLUSION

We have shown that several recombinant HIV-1 viruses have been generated and efficiently transmitted to infants in Tanzania. The recombination patterns showed that the V3 region of subtypes A or C was always selected in A-D and C-D recombinants. This selection suggests that the fitness of subtype D-V3 in perinatal transmission may be reduced with respect to V3 from subtype A and/or subtype C. The elevated number of recombinants transmitted perinatally suggests that co-infection or super-infection by two HIV-1 subtypes is not uncommon in this population.

Role of maternal humoral immunity in vertical transmission of HIV-1 subtype E in Thailand

The significance of the maternal humoral immune response in relation to vertical transmission of HIV-1 was investigated in 123 mothers infected with subtype E from Thailand. Antibody binding titers to HIV-1 env domains (monomeric gp120, the CD4/gp120 binding site [BS], V3 loop, and gp41) and antibody-mediated neutralization of primary and T-cell line-adapted (TCLA) subtypes B and E HIV-1 isolates were investigated. No correlation between maternal anti HIV-1 antibodies at delivery and vertical transmission of HIV-1 subtype E was found. However, a trend to higher titer antibody-mediated cross-neutralization of a heterologous subtype B TCLA isolate, HIV-1MN, was observed in nontransmitting mothers postpartum. The HIV-1-specific antibody titers in these infected mothers increased significantly from delivery to 6 months postpartum (p < .05), but this was only partially attributable to hemodilution and an additional factor or factors appear to affect humoral immunity to HIV-1 during late pregnancy.

Frequent detection of escape from cytotoxic T-lymphocyte recognition in perinatal human immunodeficiency virus (HIV) type 1 transmission: the ariel project for the prevention of transmission of HIV from mother to infant

Host immunologic factors, including human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes (CTL), are thought to contribute to the control of HIV type 1 (HIV-1) replication and thus delay disease progression in infected individuals. Host immunologic factors are also likely to influence perinatal transmission of HIV-1 from infected mother to infant. In this study, the potential role of CTL in modulating HIV-1 transmission from mother to infant was examined in 11 HIV-1-infected mothers, 3 of whom transmitted virus to their offspring. Frequencies of HIV-1-specific human leukocyte antigen class I-restricted CTL responses and viral epitope amino acid sequence variation were determined in the mothers and their infected infants. Maternal HIV-1-specific CTL clones were derived from each of the HIV-1-infected pregnant women. Amino acid substitutions within the targeted CTL epitopes were more frequently identified in transmitting mothers than in nontransmitting mothers, and immune escape from CTL recognition was detected in all three transmitting mothers but in only one of eight nontransmitting mothers. The majority of viral sequences obtained from the HIV-1-infected infant blood samples were susceptible to maternal CTL. These findings demonstrate that epitope amino acid sequence variation and escape from CTL recognition occur more frequently in mothers that transmit HIV-1 to their infants than in those who do not. However, the transmitted virus can be a CTL susceptible form, suggesting inadequate in vivo immune control.

Enhancement of cellular immune response in HIV-1 seropositive individuals: A DNA-based trial

A DNA-based vaccine containing HIV-1 Env and Rev genes was tested for safety and host immune response in 15 HIV-infected asymptomatic patients with CD4-positive lymphocyte counts >/=500/microl of blood and receiving no antiviral therapy. Successive groups of patients received three doses of vaccine at 30, 100, or 300 microg at 10-week intervals in a dose-escalation trial. Some changes were noted in cytotoxic T-lymphocyte activity against gp160-bearing targets. Importantly, enhanced specific lymphocyte proliferative activity against HIV-1 envelope was observed in multiple patients. Three of three patients in the 300-microg dose group also developed increased MIP-1alpha levels which were detectable in their serum. Interestingly patients in the lowest dose group showed no overall changes in the immune parameters measured. The majority of patients who exhibited increases in any immune parameters were contained within the 300 microg, which was the highest dose group. These studies support further investigation of this technology for the production of antigen-specific immune responses in humans.

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.

How to prolong the effects of combination therapy for HIV

Infection with HIV leads to AIDS and death in about 90% of patients within ten years. The first generation of anti-HIV drugs inhibited the viral enzyme reverse transcriptase (RT); but long-term studies have revealed side-effects and a high rate of emergence of drug-resistant HIV mutants. The more recent combination of two anti-RT drugs and a protease inhibitor appears to be more promising: approximately 75% of AIDS patients benefit. However, increasing numbers of treatment failures from toxicity and drug-resistant mutants are emerging. Passive immunotherapy (PIT) is a non-toxic form of treatment based on the neutralization of HIV with antibody-rich plasma from healthy HIV-positive individuals. Studies show it can benefit AIDS patients. Here, we suggest that, in combination with anti-HIV drugs, PIT could reduce some of the toxicity of the latter and limit the emergence of drug-resistant HIV strains. In addition, regular plasma donation seems to be beneficial to the donors.

Increased immune response elicited by DNA vaccination with a synthetic gp120 sequence with optimized codon usage

DNA vaccination elicits humoral and cellular immune responses and has been shown to confer protection against several viral, bacterial, and parasitic pathogens. Here we report that optimized codon usage of an injected DNA sequence considerably increases both humoral and cellular immune responses. We recently generated a synthetic human immunodeficiency virus type 1 gp120 sequence in which most wild-type codons were replaced with codons from highly expressed human genes (syngp120). In vitro expression of syngp120 is considerably increased in comparison to that of the respective wild-type sequence. In BALB/c mice, DNA immunization with syngp120 resulted in significantly increased antibody titers and cytotoxic T-lymphocyte reactivity, suggesting a direct correlation between expression levels and the immune response. Moreover, syngp120 is characterized by rev-independent expression and a low risk of recombination with viral sequences. Thus, synthetic genes with optimized codon usage represent a novel strategy to increase the efficacy and safety of DNA vaccination.

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

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

Pharmacokinetics of hyperimmune anti-human immunodeficiency virus immunoglobulin in persons with AIDS

Hyperimmune anti-human immunodeficiency virus immunoglobulin (HIVIG) is an intravenous immunoglobulin prepared from HIV-infected asymptomatic donors with a CD4 cell count greater than 400 cells/microl and a high titer of antibody to HIV-1 p24 protein. Twelve persons with AIDS received four doses of HMG (two at 50 mg/kg of body weight and then two at 200 mg/kg) every 28 days. Pharmacokinetics were evaluated by measurement of anti-p24 antibody. HIVIG was well tolerated, and all participants completed the study. Three subjects who were not receiving Pneumocystis carinii pneumonia (PCP) prophylaxis developed PCP. The mean value for HIVIG clearance was 3.02 ml/kg/day at 50 mg/kg and 3.65 ml/kg/day at 200 mg/kg (P = 0.027); the mean trough antibody titers (reciprocal units) were 1,442 and 4,428, respectively. This study indicates that high titers of anti-p24 antibody can be maintained with a monthly administration schedule of HIVIG and that short-term safety is acceptable. Comparisons to evaluate the therapeutic potential of HIVIG are justified.

Failure of Neutralizing gp120 Monoclonal Antibodies to Prevent HIV Infection of Choriocarcinoma-Derived Trophoblasts

Although placental trophoblasts, the only fetal cells in direct contact with infectious maternal blood, can be infected with HIV, the precise cause for the low transmission rate of virus across the placental barrier is unknown. One of the most common conjectures is that maternal anti-HIV antibodies (Abs) contribute to the protection of the fetus. This hypothesis has been tested in vitro by infecting the CD4-negative placental trophoblast line, BeWo, with HIV-1(IIIB) in the presence of serial dilutions of neutralizing monoclonal Abs against the V3 loop (No. 694) or CD4-binding conformational domain (No. 588). The results, based on measurement of p24 production from virus-exposed cells, reveal that the titers of Abs, adequate in preventing the infection of control MT-4 T lymphocytes, were less effective in protecting trophoblasts. Furthermore, PCR analysis of HIV DNA formed after a single round of infection has shown no significant decrease in the number of viral copies in Ab-protected BeWo cells. An anti-HIV serum from a pregnant woman did also have no effect. Although our in vitro observations do not necessarily apply to the in vivo situation, the results suggest that the humoral immune response sustained by neutralizing Abs may be able to protect T lymphocytes, but not placental trophoblasts. The findings are consistent with recent clinical studies demonstrating a lack of correlation between the presence of neutralizing anti-HIV Abs in pregnant women and HIV transmission in utero. Copyright 1997 S. Karger AG, Basel

Protection of chimpanzees from high-dose heterologous HIV-1 challenge by DNA vaccination

Novel approaches for the generation of more effective vaccines for HIV-1 are of significant importance. In this report we analyze the immunogenicity and efficacy of an HIV-1 DNA vaccine encoding env, rev and gag/pol in a chimpanzee model system. The immunized animals developed specific cellular and humoral immune responses. Animals were challenged with a heterologous chimpanzee titered stock of HIV-1 SF2 virus and followed for 48 weeks after challenge. Polymerase chain reaction coupled with reverse transcription (RT-PCR) results indicated infection in the control animal, whereas those animals vaccinated with the DNA constructs were protected from the establishment of infection. These studies serve as an important benchmark for the use of DNA vaccine technology for the production of protective immune responses.

Worldwide prevention of vertical human immunodeficiency virus (HIV) transmission

Most human immunodeficiency virus (HIV) infected children acquire the infection by perinatal transmission. Strategies for the prevention of perinatal HIV transmission mainly focus on conditions that prevail in industrialized countries, although most of these children are born in areas with less privileged circumstances. This review takes these circumstances into consideration when addressing six potential strategies to reduce perinatal HIV transmission.

Paediatric HIV infection

By the year 2000 there will be six million pregnant women and five to ten million children infected with HIV-1. Intervention strategies have been planned and in some instances already started. A timely and cost-effective strategy needs to take into account that most HIV-1 infected individuals reside in developing countries. Further studies are needed on immunological and virological factors affecting HIV-1 transmission from mother to child, on differential disease progression in affected children, and on transient infection.

A human monoclonal antibody to HIV-1 gp41 with neutralizing activity against diverse laboratory isolates

A potential component that may be useful for passive immunotherapy for HIV-1 is human monoclonal antibodies (HumAbs) possessing potent anti-HIV-1 activity that is directed against conserved regions of the envelope glycoprotein. Such antibodies would, in principle, have the ability to neutralize diverse isolates of HIV-1. To develop such reagents, hybridomas were derived by initial Epstein Barr virus transformation of peripheral blood mononuclear cells (PBMCs) from an asymptomatic HIV-1 seropositive donor followed by fusion with heteromyelomas, and secreted anti-HIV-1 antibodies were further characterized. The specificity of one HumAb, designated as clone 3, was determined by enzyme-linked immunosorbent assay (ELISA) and Western blotting analyses that indicated reactivity to the transmembrane envelope glyco-protein gp41. Synthetic pentadecapeptides overlapping by 10 amino acids were utilized for epitope mapping of clone 3; a decapeptide GCSGKLICTT in the transmembrane gp41 was identified as the epitope. Clone 3 bound to SupT1 cells infected with HTLV-IIIB in fluorescent activated cell sorting analysis. In addition, in vitro biological assays demonstrated that clone 3 possessed neutralization reactivity against diverse laboratory isolates as well as an AZT-resistant isolate. Therefore, clone 3 reactivity defines a conserved neutralizable site on the HIV-1 transmembrane glycoprotein. Clone 3 and the conserved immunogenic epitope on gp41 could be useful in passive and active immunotherapy for the acquired immunodeficiency syndrome (AIDS).

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