Safety and pharmacokinetics of hyperimmune anti-human immunodeficiency virus (HIV) immunoglobulin administered to HIV-infected pregnant women and their newborns. Pediatric AIDS Clinical Trials Group Protocol 185 Pharmacokinetic Study Group

Antibodies and Antibody Derivatives: New Partners in HIV Eradication Strategies

Promptly after primoinfection, HIV generates a pool of infected cells carrying transcriptionally silent integrated proviral DNA, the HIV-1 reservoir. These cells are not cleared by combined antiretroviral therapy (cART), and persist lifelong in treated HIV-infected individuals. Defining clinical strategies to eradicate the HIV reservoir and cure HIV-infected individuals is a major research field that requires a deep understanding of the mechanisms of seeding, maintenance and destruction of latently infected cells. Although CTL responses have been classically associated with the control of HIV replication, and hence with the size of HIV reservoir, broadly neutralizing antibodies (bNAbs) have emerged as new players in HIV cure strategies. Several reasons support this potential role: (i) over the last years a number of bNAbs with high potency and ability to cope with the extreme variability of HIV have been identified; (ii) antibodies not only block HIV replication but mediate effector functions that may contribute to the removal of infected cells and to boost immune responses against HIV; (iii) a series of new technologies have allowed for the in vitro design of improved antibodies with increased antiviral and effector functions. Recent studies in non-human primate models and in HIV-infected individuals have shown that treatment with recombinant bNAbs isolated from HIV-infected individuals is safe and may have a beneficial effect both on the seeding of the HIV reservoir and on the inhibition of HIV replication. These promising data and the development of antibody technology have paved the way for treating HIV infection with engineered monoclonal antibodies with high potency of neutralization, wide coverage of HIV diversity, extended plasma half-life in vivo and improved effector functions. The exciting effects of these newly designed antibodies in vivo, either alone or in combination with other cure strategies (latency reversing agents or therapeutic vaccines), open a new hope in HIV eradication.

Use of human immunoglobulins as an anti-infective treatment: the experience so far and their possible re-emerging role

INTRODUCTION

Pooled human immunoglobulins (IGs) are prepared from plasma obtained from healthy donors as a concentrated antibody-containing solution. In addition, high-titer IGs (hyperimmune) against a specific pathogen can be obtained from vaccinated or convalescing donors. Currently, IGs can be used for the treatment of a variety of infections for which no specific therapy exists or that remain difficult to treat. Moreover, the recent pathogen outbreaks for which there is no approved treatment have renewed attention to the role of convalescent plasma and IGs. Areas covered: In this review, a historical perspective of the use of sera and IGs in humans as anti-infective agents (any viral, bacterial, parasitic infection), excluding immunodeficient patients, is presented from early development to the latest clinical studies. A Medline search was conducted to examine the peer-reviewed literature, with no date limits. Expert commentary: Human pooled plasma-derived IG products benefit from the polyclonal response of every individual donor and from the interindividual variability in such response. The trend to increased availability of vaccines for infectious diseases also opens new potential applications of hyperimmune IGs for emerging or re-emerging infectious diseases (e.g.: Ebola, Zika, Dengue), for the prevention and treatment in the general population, healthcare personnel and caregivers.

Transient neonatal liver disease after maternal antenatal intravenous Ig infusions in gestational alloimmune liver disease associated with neonatal haemochromatosis

OBJECTIVES

Neonatal haemochromatosis is a rare gestational disease that results in severe foetal liver disease with extrahepatic iron overload, sparing the reticuloendothelial system. Recurrence can be prevented with intravenous immunoglobulin (IVIG) infusions during pregnancy, supporting an alloimmune aetiology. The aim of the study was to assess the effect of antenatal treatment with IVIG infusion on the outcome of pregnancies in women with a history of documented neonatal haemochromatosis likely owing to gestational alloimmune disease and to analyse IVIG tolerance.

METHODS

From 2004 to 2012, 8 pregnant women were treated with IVIG at 1 g/kg body weight weekly from 18 weeks' gestation until birth in a prospective multicentre study.

RESULTS

All 8 neonates born to the treated women survived. Five developed mild neonatal liver disease with hepatomegaly (n = 1), hyperechogenic liver (n = 2), abnormal liver function tests (n = 1), raised serum ferritin (n = 3) and α-fetoprotein (n = 5) levels, or mild iron overload on liver magnetic resonance imaging (n = 1). Ferritin and α-fetoprotein levels normalised before 14 days and 2 months, respectively. A per-mother-basis analysis comparing outcomes of treated (n = 8) and untreated (n = 9) gestations showed a significant improvement in the survival of neonates with gestational IVIG therapy (survival 8/8 vs 0/9, P < 0.001). Adverse effects of IVIG infusion occurred in 5 mothers leading to discontinuation of treatment in 1 case. Preterm neonates born before 37 weeks' gestation had a decreased risk of neonatal liver disease (P = 0.04).

CONCLUSIONS

Antenatal treatment with IVIG infusion in women at risk for gestational alloimmune disease recurrence improves the outcome of pregnancies despite mild signs of transient neonatal liver disease.

A critical question for HIV vaccine development: which antibodies to induce?

A vaccine against HIV-1 must prevent infection against genetically diverse virus strains. Two approaches are currently being pursued to elicit antibody-mediated protection: vaccines that induce potent and broadly reactive neutralizing antibodies (bnAbs) or vaccines that induce "conventional antibodies," which are less potent and broadly neutralizing in comparison. Although bnAbs may provide the greatest level of protection, their structural and genetic characteristics make their elicitation through vaccination a major challenge. In contrast, conventional HIV-1 antibodies have been induced by vaccination and correlated with reduced HIV-1 infection in a phase III vaccine trial. Here, I present evidence that both approaches should be pursued with equal vigor.

HIV-1 envelope glycoprotein signatures that correlate with the development of cross-reactive neutralizing activity

BACKGROUND

Current HIV-1 envelope glycoprotein (Env) vaccines are unable to induce cross-reactive neutralizing antibodies. However, such antibodies are elicited in 10-30% of HIV-1 infected individuals, but it is unknown why these antibodies are induced in some individuals and not in others. We hypothesized that the Envs of early HIV-1 variants in individuals who develop cross-reactive neutralizing activity (CrNA) might have unique characteristics that support the induction of CrNA.

RESULTS

We retrospectively generated and analyzed env sequences of early HIV-1 clonal variants from 31 individuals with diverse levels of CrNA 2-4 years post-seroconversion. These sequences revealed a number of Env signatures that coincided with CrNA development. These included a statistically shorter variable region 1 and a lower probability of glycosylation as implied by a high ratio of NXS versus NXT glycosylation motifs. Furthermore, lower probability of glycosylation at position 332, which is involved in the epitopes of many broadly reactive neutralizing antibodies, was associated with the induction of CrNA. Finally, Sequence Harmony identified a number of amino acid changes associated with the development of CrNA. These residues mapped to various Env subdomains, but in particular to the first and fourth variable region as well as the underlying α2 helix of the third constant region.

CONCLUSIONS

These findings imply that the development of CrNA might depend on specific characteristics of early Env. Env signatures that correlate with the induction of CrNA might be relevant for the design of effective HIV-1 vaccines.

The Thai Phase III HIV Type 1 Vaccine trial (RV144) regimen induces antibodies that target conserved regions within the V2 loop of gp120

The Thai Phase III clinical trial (RV144) showed modest efficacy in preventing HIV-1 acquisition. Plasma collected from HIV-1-uninfected trial participants completing all injections with ALVAC-HIV (vCP1521) prime and AIDSVAX B/E boost were tested for antibody responses against HIV-1 gp120 envelope (Env). Peptide microarray analysis from six HIV-1 subtypes and group M consensus showed that vaccination induced antibody responses to the second variable (V2) loop of gp120 of multiple subtypes. We further evaluated V2 responses by ELISA and surface plasmon resonance using cyclic (Cyc) and linear V2 loop peptides. Thirty-one of 32 vaccine recipients tested (97%) had antibody responses against Cyc V2 at 2 weeks postimmunization with a reciprocal geometric mean titer (GMT) of 1100 (range: 200-3200). The frequency of detecting plasma V2 antibodies declined to 19% at 28 weeks post-last injection (GMT: 110, range: 100-200). Antibody responses targeted the mid-region of the V2 loop that contains conserved epitopes and has the amino acid sequence KQKVHALFYKLDIVPI (HXB2 Numbering sequence 169-184). Valine at position 172 was critical for antibody binding. The frequency of V3 responses at 2 weeks postimmunization was modest (18/32, 56%) with a GMT of 185 (range: 100-800). In contrast, naturally infected HIV-1 individuals had a lower frequency of antibody responses to V2 (10/20, 50%; p=0.003) and a higher frequency of responses to V3 (19/20, 95%), with GMTs of 400 (range: 100-3200) and 3570 (range: 200-12,800), respectively. RV144 vaccination induced antibodies that targeted a region of the V2 loop that contains conserved epitopes. Early HIV-1 transmission events involve V2 loop interactions, raising the possibility that anti-V2 antibodies in RV144 may have contributed to viral inhibition.

Cross-clade HIV-1 neutralizing antibodies induced with V3-scaffold protein immunogens following priming with gp120 DNA

The V3 epitope is a known target for HIV-1 neutralizing antibodies (NAbs), and V3-scaffold fusion proteins used as boosting immunogens after gp120 DNA priming were previously shown to induce NAbs in rabbits. Here, we evaluated whether the breadth and potency of the NAb response could be improved when boosted with rationally designed V3-scaffold immunogens. Rabbits were primed with codon-optimized clade C gp120 DNA and boosted with one of five V3-cholera toxin B fusion proteins (V3-CTBs) or with double combinations of these. The inserts in these immunogens were designed to display V3 epitopes shared by the majority of global HIV-1 isolates. Double combinations of V3-CTB immunogens generally induced more broad and potent NAbs than did boosts with single V3-CTB immunogens, with the most potent and broad NAbs elicited with the V3-CTB carrying the consensus V3 of clade C (V3(C)-CTB), or with double combinations of V3-CTB immunogens that included V3(C)-CTB. Neutralization of tier 1 and 2 pseudoviruses from clades AG, B, and C and of peripheral blood mononuclear cell (PBMC)-grown primary viruses from clades A, AG, and B was achieved, demonstrating that priming with gp120 DNA followed by boosts with V3-scaffold immunogens effectively elicits cross-clade NAbs. Focusing on the V3 region is a first step in designing a vaccine targeting protective epitopes, a strategy with potential advantages over the use of Env, a molecule that evolved to protect the virus by poorly inducing NAbs and by shielding the epitopes that are most critical for infectivity.

Longer V1V2 region with increased number of potential N-linked glycosylation sites in the HIV-1 envelope glycoprotein protects against HIV-specific neutralizing antibodies

Human immunodeficiency virus type 1 (HIV-1) has the ability to adapt to the host environment by escaping from host immune responses. We previously observed that escape from humoral immunity, both at the individual and at a population level, coincided with longer variable loops and an increased number of potential N-linked glycosylation sites (PNGS) in the viral envelope glycoprotein (Env) and, in particular, in variable regions 1 and 2 (V1V2). Here, we provide several lines of evidence for the role of V1V2 in the resistance of HIV-1 to neutralizing antibodies. First, we determined that the increasing neutralization resistance of a reference panel of tier-categorized neutralization-sensitive and -resistant HIV-1 variants coincided with a longer V1V2 loop containing more PNGS. Second, an exchange of the different variable regions of Env from a neutralization-sensitive HIV-1 variant into a neutralization-resistant escape variant from the same individual revealed that the V1V2 loop is a strong determinant for sensitivity to autologous-serum neutralization. Third, exchange of the V1V2 loop of neutralization-sensitive HIV-1 variants from historical seroconverters with the V1V2 loop of neutralization-resistant HIV-1 variants from contemporary seroconverters decreased the neutralization sensitivity to CD4-binding site-directed antibodies. Overall, we demonstrate that an increase in the length of the V1V2 loop and/or the number of PNGS in that same region of the HIV-1 envelope glycoprotein is directly involved in the protection of HIV-1 against HIV-specific neutralizing antibodies, possibly by shielding underlying epitopes in the envelope glycoprotein from antibody recognition.

Activity of broadly neutralizing antibodies, including PG9, PG16, and VRC01, against recently transmitted subtype B HIV-1 variants from early and late in the epidemic

For the development of a neutralizing antibody-based human immunodeficiency virus type 1 (HIV-1) vaccine, it is important to characterize which antibody specificities are most effective against currently circulating HIV-1 variants. We recently reported that HIV-1 has become more resistant to antibody neutralization over the course of the epidemic, and we here explore whether this increased neutralization resistance is also observed for the newly identified broadly neutralizing antibodies (BrNAbs) PG9, PG16, and VRC01. Furthermore, we performed a comprehensive analysis of the neutralizing sensitivity of currently circulating recently transmitted subtype B viruses to the currently most known BrNAbs. Virus variants isolated less than 6 months after seroconversion from individuals who seroconverted between 2003 and 2006 (n = 21) were significantly more resistant to neutralization by VRC01 than viruses from individuals who seroconverted between 1985 and 1989 (n = 14). In addition, viruses from contemporary seroconverters tended to be more resistant to neutralization by PG16, which coincided with the presence of more mutations at positions in the viral envelope that may potentially influence neutralization by this antibody. Despite this increased neutralization resistance, all recently transmitted viruses from contemporary seroconverters were sensitive to at least one BrNAb at concentrations of ≤5 μg/ml, with PG9, PG16, and VRC01 showing the greatest breadth of neutralization at lower concentrations. These results suggest that a vaccine capable of eliciting multiple BrNAb specificities will be necessary for protection of the population against HIV-1 infection.

Clinical experience with therapeutic AIDS vaccines

Recently, there has been a renewed interest in therapeutic vaccination as an adjunct or alternative to current treatment options for HIV. The first immunotherapeutic trial relevant to this topic was published in 1983. Since then, several dozen therapeutic vaccine trials have been carried out. The results have consistently shown that although in vitro-measured HIV-specific immune responses were evident as a result of vaccination, clinical improvement has been seldom observed. The instances of apparent clinical benefit however, were invariably associated with the usage of vaccines that acted in accord with the principles of allo- or autoimmunization. The majority of these vaccines were derived from the blood of HIV carriers or a cell culture and therefore inherently contained host-cell antigens unrelated to HIV. These observations raise the issue of whether this clinically successful approach has been unduly neglected. Most commercial vaccines on the market today are made the old-fashioned way, but very little support or attention has been given to the development of such vaccines for AIDS therapy. The current strategy, biased toward vaccines which have shown little evidence of clinical efficacy, is shortsighted and needs to be revised.

Polyvalent HIV-1 Env vaccine formulations delivered by the DNA priming plus protein boosting approach are effective in generating neutralizing antibodies against primary human immunodeficiency virus type 1 isolates from subtypes A, B, C, D and E

A major challenge in developing an HIV-1 vaccine is to identify immunogens and their delivery methods that can elicit broad neutralizing antibodies against primary isolates of different genetic subtypes. Recently, we demonstrated that priming with DNA vaccines expressing primary HIV-1 envelope glycoprotein (Env) followed by recombinant Env protein boosting was successful in generating positive neutralizing antibody responses against a clade B primary HIV-1 isolate, JR-FL, that was not easily neutralized. In the current study, we examined whether the DNA priming plus recombinant protein boosting approach delivering a polyvalent primary Env formulation was able to generate neutralizing antibodies against primary HIV-1 viral isolates from various genetic subtypes. New Zealand White rabbits were first immunized with DNA vaccines expressing one, three or eight primary HIV-1 gp120 antigens delivered by a gene gun followed by recombinant gp120 protein boosting. Neutralizing antibody responses were examined by two independently executed neutralization assays: the first one was a single round infection neutralization assay against a panel of 10 primary HIV-1 isolates of subtypes A, B, C and E and the second one used the PhenoSense assay against a panel of 12 pseudovirues expressing primary HIV-1 Env antigens from subtypes A, B, C, D and E as well as 2 pseudoviruses expressing the Env antigens from MN and NL4-3 viruses. Rabbit sera immunized with the DNA priming plus protein boosting approach, but not DNA vaccine alone or Env protein alone, were capable of neutralizing 7 of 10 viruses in the first assay and 12 of 14 viruses in the second assay. More importantly, sera immunized with the polyvalent Env antigens were able to neutralize a significantly higher percentage of viruses than the sera immunized with the monovalent antigens. Our results suggest that DNA priming followed by recombinant Env protein boosting can be used to deliver polyvalent Env-antigen-based HIV-1 vaccines to elicit neutralizing antibody responses against viruses with diverse genetic sequence variations.

HIV-1 envelope pseudotyped viral vectors and infectious molecular clones expressing the same envelope glycoprotein have a similar neutralization phenotype, but culture in peripheral blood mononuclear cells is associated with decreased neutralization sensitivity

Recombinant lentiviral vectors pseudotyped with heterologous HIV-1 envelope glycoproteins allow rapid and accurate measurement of antibody-mediated HIV-1 neutralization. However, the neutralization phenotypes of envelope pseudoviruses have not been directly compared to isogenic replication competent HIV-1. We produced pseudoviruses expressing three different HIV-1 envelope glycoproteins and subcloned the same three env genes into a replication competent NL4-3 molecular clone. For each of the antibodies tested, the neutralization dose-response curves of pseudoviruses and corresponding replication competent viruses were similar. Thus, envelope pseudoviruses can be used to study the anti-HIV-1 neutralizing antibody response. A single passage of replication competent virus derived from 293T cells through peripheral blood mononuclear cells (PBMC) caused a substantial decrease in sensitivity to neutralizing antibodies. This was associated with an increase in average virion envelope glycoprotein content of the PBMC-derived virus. Replication competent HIV-1 and isogenic envelope pseudoviruses have similar neutralization characteristics, but passage into PBMC is associated with decreased sensitivity to neutralization.

Human retroviruses in leukaemia and AIDS: reflections on their discovery, biology and epidemiology

The study of retroviruses has had a profound impact by unveiling an unusual form of viral replication: the multiplication of RNA viruses via a proviral DNA, for which Jan Svoboda provided the experimental model over forty years ago. In 1970 Temin, Mizutani and Baltimore discovered that this group of viruses contains a unique enzyme catalysing the synthesis of a DNA copy of the viral RNA: reverse transcriptase (RT). The discovery of RT has itself had an enormous impact on molecular biology in general, but also stimulated many premature claims of its detection in human disease. Claims by Gallo's laboratory that the cytoplasm of human leukaemia cells contained RT proved to be unfounded, as did his report in collaboration with Weiss that myeloid leukaemia contained HL23 virus, this organism proving not to be human but a laboratory contaminant of three monkey viruses. Conclusive demonstration of a retroviral involvement in human leukaemia was first provided in 1981 by Hinuma and his associates, showing that adult T-cell leukaemia (ATL), a rare form of leukaemia endemic to south-west Japan, is caused by a new retrovirus (ATLV). Other publications in December 1980 and through 1981 claimed the discovery of a new human T-cell leukaemia virus involved in mycosis fungoides (MF) and Sézary's syndrome (SS). This virus was termed HTLV by Gallo. The nucleotide sequence of ATLV is strongly conserved, that of my 1983 isolate from a black British ATL patient being practically identical with the Japanese virus isolates. After AIDS was recognised in 1981 by Gottlieb and coworkers as a new human disease, several papers were published by Gallo and his associates during 1983-4, invoking the oncovirus responsible for adult T-cell leukaemia as the cause of AIDS. In 1983 the French scientist Barré-Sinoussi and her colleagues succeeded in isolating a new agent in the disease, a lentivirus, which they named LAV. The French immunologist Klatzmann and his colleagues discovered that LAV killed CD4+ T-cells, furnishing an explanation for the pathogenesis of AIDS and providing a mechanism for how AIDS developed. For some time Gallo continued to suggest leukaemia virus involvement, claiming that his independent isolate of the AIDS virus, termed HTLV-III, was closely related to HTLV-I (the Japanese ATLV). Although this created considerable confusion among researchers for a period, the relationship was eventually disproved. Unlike ATLV, whose nucleic acid sequence is very stable, the AIDS virus (now termed HIV by international agreement) is extraordinarily unstable, the sequences of independent HIV isolates being quite unique: this made it possible to establish conclusively that both HTLV-III and another independent isolate CBL-1, from Weiss' laboratory, were actually LAV isolates from the French laboratory. It has been shown by Hayami and his associates that only African primates are infected with similar lentiviruses to HIV which explains why AIDS started in Africa. Further research has clarified the origin of HIV-1 to be a chimpanzee lentivirus and HIV-2 to be the sooty mangabey lentivirus, which began to spread in humans perhaps no more than fifty years ago. The infection has spread rapidly, primarily through sexual intercourse, but also by transmission through blood and its products as well as contaminated needles and syringes. Sexual intercourse has now spread the virus around the World; and there are probably some 70 million infected. 90% of those infected with HIV develop the deadly disease of AIDS within ten years of infection: the death toll from the disease has been enormous. By contrast, HTLV-1 has been infecting man in isolated areas probably for hundreds of years; but it has not spread widely. HTLV causes leukaemia in only less than 1% of those infected. The prime mode of transmission of HTLV-1 is between mother and neonate; infections can be reduced by stopping breast-feeding by infected mothers. The isolation of HIV enabled screening tests to be developed for contaminated blood. However, due to the peculiar biology of HIV infection, unfortunately all efforts to develop an effective vaccine have so far failed.

Antibody-based therapies as anti-infective agents

Antibody-based therapies are effective against a wide variety of pathogens. Historically, antibody-based therapies were largely abandoned with the advent of antimicrobial chemotherapy, due to the toxicity associated with the administration of heterologous immune sera. As a class, antibody-based therapies have significant advantages and disadvantages relative to conventional antimicrobial chemotherapy. Advantages include versatility, specificity, and antimicrobial activities not available in antibiotic drugs, such as toxin and viral neutralisation, opsonisation, complement activation and the enhancement of host immune function. Disadvantages include expense, the necessity for early and accurate diagnosis prior to use, and the complex logistics necessary for therapeutic use. Advances in antibody technology have minimised some of the disadvantages associated with antibody therapy. In recent years, the therapy of infectious diseases has been complicated by the emergence of new pathogens, the spread of antibiotic-resistant strains and the relative inefficacy of antimicrobial chemotherapy in immunocompromised hosts. This has led to renewed interest in the utilisation of antibody-based therapies as anti-infectives. Many opportunities for developing antibody-based drugs now exist in areas where the available antimicrobial therapies are inadequate.

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

BACKGROUND

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

OBJECTIVES

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

STUDY DESIGN

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

RESULTS

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

CONCLUSIONS

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

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.

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.

Human immunodeficiency virus type 1 neutralization measured by flow cytometric quantitation of single-round infection of primary human T cells

There is currently intensive research on the design of novel human immunodeficiency virus type 1 (HIV-1) vaccine immunogens that can elicit potent neutralizing antibodies. A prerequisite for comparing and optimizing these strategies is the ability to precisely measure neutralizing antibody responses. To this end, we sought to develop an assay that directly quantifies single-round HIV-1 infection of peripheral blood mononuclear cells (PBMC). Initial experiments demonstrated that essentially all productively infected PBMC could be identified by flow cytometric detection of intracellular p24 antigen (p24-Ag). After infection of PBMC with HIV-1, p24(+) lymphocytes could be distinguished beginning 1 day postinfection, and the majority of CD8(-) T cells were p24-Ag positive by 3 to 4 days postinfection. To directly quantify first-round infection, we included a protease inhibitor in PBMC cultures. The resulting 2-day assay was highly sensitive and specific for the detection of HIV-1-infected PBMC. Serial dilutions of virus stocks demonstrated that the number of target cells infected was directly related to the amount of infectious virus input into the assay. In neutralization assays, the flow cytometric enumeration of first-round infection of PBMC provided quantitative data on the number of target cells infected and on the inactivation of infectious virus due to reaction with antibody. We also used this single-round assay to compare the percentage of cells expressing p24-Ag to the number of copies of HIV-1 gag per 100 PBMC. The precision and reproducibility of this assay will facilitate the measurement of HIV-1 neutralization, particularly incrementally improved neutralizing antibody responses generated by new candidate vaccines.

A phase I trial with two human monoclonal antibodies (hMAb 2F5, 2G12) against HIV-1

OBJECTIVE

To study the safety, immunogenicity and pharmacokinetics of two intravenously administered human monoclonal antibodies (hMAb 2F5, 2G12) against HIV-1 in humans.

DESIGN

Open label clinical phase I trial.

SETTING

Primary institutional care.

PATIENTS

Seven HIV-1-infected healthy volunteers with > or = 500 x 10(6)CD4 cells/l and < or = 10,000 HIV-1 RNA copies/ml, not treated with highly active antiretroviral therapy (HAART), entered and finished the study.

INTERVENTIONS

and main outcome measures: Eight separate infusions of the hMAb were administered over a 4-week period (total dose 14 g). The safety was assessed by physical examination, blood chemistry, complete blood cell count and recording adverse events. 2F5 and 2G12 plasma levels were determined prior to and at the end of each infusion and during the follow-up period of 22 weeks.

RESULTS

No clinical or laboratory abnormalities were observed throughout the study. The median distribution half-life (t(1/2 alpha)) of 2F5 and 2G12 was 1.02 (range, 0.77-1.47) days and 2.49 (range, 0.92-4.59) days, respectively. The elimination half-life (t(1/2 beta)) was calculated to be 7.94 (range, 3.46-8.31) days for 2F5 and 16.48 (range, 12.84-24.85) days for 2G12. The median plasma concentration immediately after the first infusion was 216 microg/ml (range, 158-409 microg/ml) for 2F5 and 238 microg/ml (range, 197-402 microg/ml) for 2G12. Multiple infusions resulted in maximum plasma concentrations of 374 microg/ml (range, 304-700 microg/ml) and 605 microg/ml (range, 479-897 microg/ml) for 2F5 and 2G12, respectively.

CONCLUSIONS

This study showed that the hMAb 2F5 and 2G12 are safe and well tolerated by HIV-1-infected subjects.

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.

Immunoglobulin G3 from polyclonal human immunodeficiency virus (HIV) immune globulin is more potent than other subclasses in neutralizing HIV type 1

Passive antibody prophylaxis against human immunodeficiency virus type 1 (HIV-1) has been accomplished in primates, suggesting that this strategy may prove useful in humans. While antibody specificity is crucial for neutralization, other antibody characteristics, such as subclass, have not been explored. Our objective was to compare the efficiencies of immunoglobulin G (IgG) subclasses from polyclonal human HIV immune globulin (HIVIG) in the neutralization of HIV-1 strains differing in coreceptor tropism. IgG1, IgG2, and IgG3 were enriched from HIVIG by using protein A-Sepharose. All three subclasses bound major HIV-1 proteins, as shown by Western blot assay and enzyme-linked immunosorbent assay. In HIV-1 fusion assays using X4, R5, or X4R5 envelope-expressing effector cells, IgG3 more efficiently blocked fusion. In neutralization assays with cell-free viruses using X4 (LAI, IIIB), R5 (BaL), and X4R5 (DH123), a similar hierarchy of neutralization was found: IgG3 > IgG1 > IgG2. IgG3 has a longer, more flexible hinge region than the other subclasses. To test whether this is important, IgG1 and IgG3 were digested with pepsin to generate F(ab')(2) fragments or with papain to generate Fab fragments. IgG3 F(ab')(2) fragments were still more efficient in neutralization than F(ab')(2) of IgG1. However, Fab fragments of IgG3 and IgG1 demonstrated equivalent neutralization capacities and the IgG3 advantage was lost. These results suggest that the IgG3 hinge region confers enhanced HIV-neutralizing ability. Enrichment and stabilization of IgG3 may therefore lead to improved HIVIG preparations. The results of this study have implications for the improvement of passive immunization with polyclonal or monoclonal antibodies and suggest that HIV-1 vaccines which induce high-titer IgG3 responses could be advantageous.

Passive infusion of immune serum into simian immunodeficiency virus-infected rhesus macaques undergoing a rapid disease course has minimal effect on plasma viremia

Antibody responses are often considered to play only a limited role in controlling viremia during chronic infections with human or simian immunodeficiency virus (SIV). We investigated this by determining the effect of passively infused antibody on plasma viremia in infected rhesus macaques. The emphasis of the study was to understand the mechanism(s) underlying any observed effects. We infused serum immunoglobulins (SIVIG) purified from SIV(mac)251-infected macaques into other SIV(mac)251-infected macaques. The rapid progressor recipients had high viral loads but negligible titers of antibodies to SIV. Thus, we could significantly increase antibody titers with exogenous SIVIG. Despite restoring anti-SIV titers to levels typical of macaques with a normal disease course, SIVIG had only a modest effect on plasma SIV RNA and cell-associated viral load; the maximum, transient, reduction was threefold. The decrease in plasma RNA commenced within 1-2 h of SIVIG infusion, the nadir was at 12 h, and then a rebound occurred. A two- to threefold drop in cell-associated viral RNA was simultaneous with the decrease in plasma RNA. The kinetics of the viremia changes are inconsistent with neutralization of new cycles of infection. More likely, perhaps unexpectedly, is that infused antibodies killed SIV-infected cells, via an effector mechanism such as antibody-dependent cellular cytotoxicity.

A step ahead. Infant protection through maternal immunization

The concept of maternal immunization to prevent infectious diseases during a period of increased vulnerability in infants is not new and is supported by historical experience and carefully conducted studies of various viral and bacterial vaccines. Candidate vaccines should be minimally reactogenic, immunogenic, and safe for maternal immunization to be considered as a disease prevention strategy. The possibilities increase as more potential candidate vaccines for use during pregnancy become available, including conjugate meningococcal vaccines, parainfluenza virus type 3 purified subunit vaccines, herpes simplex virus, cytomegalovirus, and HIV vaccines. Additional research on the safety and efficacy of maternal immunization must continue to effect the development of infectious diseases in neonates and infants.

Monocyte-macrophage system as targets for immunomodulation by intravenous immunoglobulin

Pooled human intravenous immunoglobulin (IVIg) has been used successfully to treat or ameliorate the clinical manifestations of humoral immune deficiencies, haematological disorders, HIV infection and many other diseases states. However, the mechanism of action of IVIg remains unclear. Several mechanisms of action of IVIg have been proposed. These include Fcy receptor blockade, accelerated clearance of endogenous pathogenic auto-antibodies, inhibition of components of the complement cascade, neutralization of super-antigens and bacterial toxins as well as anti-cytokine and anti-idiotype effects. A major contributor to host immunity and immune surveillance against infection, tissue or cell damage and malignancy is the monocyte/macrophage system. Monocyte-directed inflammation is a desirable consequence of microbiological or malignant challenge. However, monocyte hyperactivity may contribute to certain pathological conditions. These include the systemic inflammatory response syndrome (SIRS), septic shock, other dysregulated inflammatory disorders and auto-immunity. Novel therapies that can suppress the hyperactive state or correct monocyte/macrophage dysfunction without compromising normal host cell-mediated immunity are desirable. In this review, we discuss the immunomodulatory effects of IVIg focussing particularly upon the monocyte/macrophage system in pertinent disease states.

Protection of macaques against vaginal transmission of a pathogenic HIV-1/SIV chimeric virus by passive infusion of neutralizing antibodies

The development of the human immunodeficiency virus-1 (HIV-1)/simian immunodeficiency virus (SIV) chimeric virus macaque model (SHIV) permits the in vivo evaluation of anti-HIV-1 envelope glycoprotein immune responses. Using this model, others, and we have shown that passively infused antibody can protect against an intravenous challenge. However, HIV-1 is most often transmitted across mucosal surfaces and the intravenous challenge model may not accurately predict the role of antibody in protection against mucosal exposure. After controlling the macaque estrous cycle with progesterone, anti-HIV-1 neutralizing monoclonal antibodies 2F5 and 2G12, and HIV immune globulin were tested. Whereas all five control monkeys displayed high plasma viremia and rapid CD4 cell decline, 14 antibody-treated macaques were either completely protected against infection or against pathogenic manifestations of SHIV-infection. Infusion of all three antibodies together provided the greatest amount of protection, but a single monoclonal antibody, with modest virus neutralizing activity, was also protective. Compared with our previous intravenous challenge study with the same virus and antibodies, the data indicated that greater protection was achieved after vaginal challenge. This study demonstrates that antibodies can affect transmission and subsequent disease course after vaginal SHIV-challenge; the data begin to define the type of antibody response that could play a role in protection against mucosal transmission of HIV-1.

Interventions aimed at decreasing the risk of mother-to-child transmission of HIV infection

BACKGROUND

At the end of 1998 over 33 million people were infected with the human immunodeficiency virus (HIV) and over one million children had been infected from their mothers.

OBJECTIVES

The objective of this review was to assess what interventions may be effective in decreasing the risk of mother-to-child transmission of HIV infection as well as their effect on neonatal and maternal mortality and morbidity.

SEARCH STRATEGY

The Cochrane Pregnancy and Childbirth Group trials register and the Cochrane Controlled Trials Register were searched.

SELECTION CRITERIA

Randomised trials comparing any intervention aimed at decreasing the risk of mother-to-child transmission of HIV infection compared with placebo or no treatment, or any two or more interventions aimed at decreasing the risk of mother-to-child transmission of HIV infection.

DATA COLLECTION AND ANALYSIS

Trial quality assessments and data extraction were undertaken by the reviewer.

MAIN RESULTS

Zidovudine Four trials comparing zidovudine with placebo involving 1585 participants were included. Compared with placebo, there was a significant reduction in the risk of mother-to-child transmission with any zidovudine (relative risk (RR) 0.54, 95% confidence interval (CI) 0.42-0.69). There is no evidence that 'long course therapy' is superior to 'short course therapy'. Nevirapine One trial compared intrapartum and postnatal nevirapine with intrapartum and postnatal zidovudine in 626 women, the majority of whom breast fed their infants. Compared with zidovudine, there was a significant reduction in the risk of mother-to-child transmission of HIV with nevirapine (RR 0.58, 95% CI 0.40-0.83). No trials are available comparing nevirapine with placebo. Caesarean section One trial comparing elective caesarean section with anticipation of vaginal delivery involving 436 participants was included. Compared with vaginal delivery, there was a significant reduction in the risk of mother-to-child transmission of HIV infection with caesarean section (RR 0.17, 95% CI 0.05-0.55). Immunoglobulin One trial comparing hyperimmune immunoglobulin plus zidovudine with non-specific immunoglobulin plus zidovudine involving 501 participants was included. The addition of hyperimmune immunoglobulin to zidovudine does not appear to have any additional effect on the risk of mother-to-child transmission (RR 0.67, 95% CI 0.29-1.55).

REVIEWER'S CONCLUSIONS

Zidovudine, nevirapine and delivery by elective caesarean section appear to be very effective in decreasing the risk of mother-to-child transmission of HIV infection.

Risk factors for perinatal transmission of human immunodeficiency virus type 1 in women treated with zidovudine. Pediatric AIDS Clinical Trials Group Study 185 Team

BACKGROUND

Maternal, obstetrical, and infant-related factors associated with the risk of perinatal transmission of human immunodeficiency virus type 1 (HIV-1) were identified before the widespread use of zidovudine therapy in pregnant women. The risk factors for transmission when women and infants receive zidovudine are not well characterized.

METHODS

We examined the effects of maternal, obstetrical, and infant-related characteristics and maternal virologic and immunologic variables on the risk of perinatal transmission of HIV-1 among 480 women and their infants, all of whom received zidovudine. The women and infants were participating in a phase 3 trial of passive immunoprophylaxis for the prevention of perinatal transmission.

RESULTS

In univariate analyses, the risk of perinatal transmission was associated with each of the following: decreased maternal CD4+ lymphocyte counts at base line; decreased maternal HIV p24 antibody levels at base line and delivery; increased maternal HIV-1 titer at base line and delivery; increased maternal HIV-1 RNA levels at base line and delivery; and the presence of chorioamnionitis at delivery. In multivariate analyses, the only independent risk factor was the maternal HIV-1 RNA level at base line (odds ratio for transmission, 2.4 per log increase in the number of copies; 95 percent confidence interval, 1.2 to 4.7; P=0.02) and at delivery (odds ratio, 3.4; 95 percent confidence interval, 1.7 to 6.8; P=0.001). There was no perinatal transmission of HIV-1 among the 84 women who had HIV-1 levels below the limit of detection (500 copies per milliliter) at base line or the 107 women who had undetectable levels at delivery.

CONCLUSIONS

Among pregnant women and their infants, all treated with zidovudine, the maternal plasma HIV-1 RNA level was the best predictor of the risk of perinatal transmission of HIV-1. Antiretroviral therapy that reduces the HIV-1 RNA level to below 500 copies per milliliter appears to minimize the risk of perinatal transmission as well as improve the health of the women.

Protection of Macaques against pathogenic simian/human immunodeficiency virus 89.6PD by passive transfer of neutralizing antibodies

The role of antibody in protection against human immunodeficiency virus (HIV-1) has been difficult to study in animal models because most primary HIV-1 strains do not infect nonhuman primates. Using a chimeric simian/human immunodeficiency virus (SHIV) based on the envelope of a primary isolate (HIV-89.6), we performed passive-transfer experiments in rhesus macaques to study the role of anti-envelope antibodies in protection. Based on prior in vitro data showing neutralization synergy by antibody combinations, we evaluated HIV immune globulin (HIVIG), and human monoclonal antibodies (MAbs) 2F5 and 2G12 given alone, compared with the double combination 2F5/2G12 and the triple combination HIVIG/2F5/2G12. Antibodies were administered 24 h prior to intravenous challenge with the pathogenic SHIV-89.6PD. Six control monkeys displayed high plasma viremia, rapid CD4(+)-cell decline, and clinical AIDS within 14 weeks. Of six animals given HIVIG/2F5/2G12, three were completely protected; the remaining three animals became SHIV infected but displayed reduced plasma viremia and near normal CD4(+)-cell counts. One of three monkeys given 2F5/2G12 exhibited only transient evidence of infection; the other two had marked reductions in viral load. All monkeys that received HIVIG, 2F5, or 2G12 alone became infected and developed high-level plasma viremia. However, compared to controls, monkeys that received HIVIG or MAb 2G12 displayed a less profound drop in CD4(+) T cells and a more benign clinical course. These data indicate a general correlation between in vitro neutralization and protection and suggest that a vaccine that elicits neutralizing antibody should have a protective effect against HIV-1 infection or disease.

Maternal immunization against viral disease

The protective effect of maternal antibody against many viral diseases has been recognized. The use of maternal immunization has been considered as a means to augment this protection in the young infant against disease. Advantages of maternal immunization include the fact that young infants are most susceptible to infections but least responsive to vaccines, that pregnant women are accessible to medical care and respond well to vaccines, that IgG antibodies cross the placenta well during the third trimester, and that immunization of the pregnant woman has the potential to benefit both the mother and the infant. Disadvantages include the potential inhibition of an infant's response to active immunization or natural infection and liability issues with pharmaceutical companies and physicians. Immunization of pregnant women with viral vaccines for poliovirus, influenza viruses, and rubella has been described and maternal vaccination with these vaccines has been found to be safe for both the mother and the fetus. An open-label study of post-partum women immunized with the purified fusion protein of RSV (PFP-2, Wyeth-Lederle Pediatrics and Vaccines, Inc., Pearl River, NY) demonstrated that the vaccine was non-reactogenic and immunogenic; RSV-specific antibody was detected in breast milk. Immunization of pregnant women with purified protein or subunit vaccines could be considered against neonatal viral pathogens, such as respiratory syncytial virus, parainfluenza viruses, herpes group viruses, and human immunodeficiency virus. Further studies are needed to define the safety and efficacy of maternal immunization.

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.

CD4-immunoglobulin G2 protects Hu-PBL-SCID mice against challenge by primary human immunodeficiency virus type 1 isolates

CD4-immunoglobulin G2 (IgG2) is a fusion protein comprising human IgG2 in which the Fv portions of both heavy and light chains have been replaced by the V1 and V2 domains of human CD4. Previous studies found that CD4-IgG2 potently neutralizes a broad range of primary human immunodeficiency virus type 1 (HIV-1) isolates in vitro and ex vivo. The current report demonstrates that CD4-IgG2 protects against infection by primary isolates of HIV-1 in vivo, using the hu-PBL-SCID mouse model. Passive administration of 10 mg of CD4-IgG2 per kg of body weight protected all animals against subsequent challenge with 10 mouse infectious doses of the laboratory-adapted T-cell-tropic isolate HIV-1(LAI), while 50 mg of CD4-IgG2 per kg protected four of five mice against the primary isolates HIV-1(JR-CSF) and HIV-1(AD6). In contrast, a polyclonal HIV-1 Ig fraction exhibited partial protection against HIV-1(LAI) at 150 mg/kg but no significant protection against the primary HIV-1 isolates. The results demonstrate that CD4-IgG2 effectively neutralizes primary HIV-1 isolates in vivo and can prevent the initiation of infection by these viruses.

Direct HIV cytopathicity cannot account for CD4 decline in AIDS in the presence of homeostasis: a worst-case dynamic analysis

The central paradox of HIV pathogenesis is that the viral burden, either free or cellular, seems too low to deplete the CD4 population by direct killing. Until recently, little data could be used to compare direct and indirect pathogenic theories critically. Clinical trials with potent new antiviral agents have measured important kinetic parameters of HIV infection, including viral and infected cell half-lives. This has led to the construction of explicit models of direct killing. Using a worst-case dynamic analysis, we show that such cytopathic models are untenable. Rates of infected cell removal are orders of magnitude too low to suppress steady state CD4 counts significantly in the face of lymphocyte replenishment, especially in early infection. Furthermore, the direct cytopathic models, as proposed, predict an extremely variable disease course across the broad range of observed viral burdens (five orders of magnitude), which is inconsistent with the relatively small differences in disease progression observed between patients. In contrast, immunologic theories of pathogenesis, such as homeostatic dysregulation based on immune activation, do not suffer from these difficulties and are more consistent with the natural history of HIV infection.

Perinatal transmission of HIV and diagnosis of HIV infection in infants: a review

Paediatric HIV infection has become a major burden on families, communities and health services worldwide. The vast majority of children now acquire HIV as a result of mother to infant (vertical) transmission. Recent major advances have occurred following the greater understanding of the risk factors for perinatal transmission and the role of antiretroviral therapy in preventing transmission. Now that interruption of vertical transmission is possible, early identification of HIV-infected pregnant women is critical. As of June 1997, HIV infection has been diagnosed in 37 children under 15 yrs of age in the Republic of Ireland; 32 as a result of maternal to infant transmission. The exact timing of HIV transmission during pregnancy is unclear but it is estimated that 60-70 per cent of infants may be infected at the time of delivery with approximately 30 per cent infected earlier in gestation. Vertical transmission rates vary from 15-40 per cent in different global areas. Antenatal and perinatal zidovudine treatment can reduce this rate by 60-70 per cent. Risk factors for the vertical transmission of HIV-1 are multifactorial. These factors include maternal disease status, in particular maternal viral load, route of delivery, duration of membrane rupture, presence of obstetric complications and infant feeding practices. Definitive diagnosis of HIV infection in infancy has been difficult in the past. Direct viral detection methods now allow the reliable diagnosis of HIV infection in the first few months of life. The most effective intervention to reduce perinatal HIV infection will be the better identification of HIV positive pregnant women with the subsequent introduction of measures to interrupt vertical transmission of HIV.

Passive immunization with a human monoclonal antibody protects hu-PBL-SCID mice against challenge by primary isolates of HIV-1

How well antibodies can protect against disease due to HIV-1 infection remains a pivotal but unresolved issue with important implications for vaccine design and the use of prophylactic antibody to prevent infection after accidental exposure to the virus and to interrupt transmission of virus from mother to child. Strong doubts about the possible utility of antibodies in vivo have been raised because of the relative resistance of primary viruses to antibody neutralization in vitro. Primary viruses are likely to be close to the viruses transmitted during natural infection in humans. Vaccine studies have been of little value in assessing antibody efficacy in vivo because none of the strategies described to date have elicited significant neutralizing antibody responses to primary viruses. Passive immunization studies are similarly hindered by the paucity of reagents able to neutralize primary viruses effectively and a single study has suggested some benefit. Here we describe experiments to explore the ability of passive antibody to protect against primary virus challenge in hu-PBL-SCID mice. In this model, severe combined immunodeficient (SCID) mice are populated with human peripheral blood mononuclear cells (PBMCs) and infected with HIV-1. We find that the potent neutralizing human monoclonal antibody IgG1b12 at high dose is able to completely protect even when given several hours after viral challenge. The results are encouraging for antibody-based postexposure prophylaxis and support the notion that antibody induction could contribute to an effective vaccine.

Potent and synergistic neutralization of human immunodeficiency virus (HIV) type 1 primary isolates by hyperimmune anti-HIV immunoglobulin combined with monoclonal antibodies 2F5 and 2G12

Three antibody reagents that neutralize primary human immunodeficiency virus type 1 (HIV-1) isolates were tested for magnitude and breadth of neutralization when used alone or in double or triple combinations. Hyperimmune anti-HIV immunoglobulin (HIVIG) is derived from the plasma of HIV-1-infected donors, and monoclonal antibodies (MAbs) 2F5 and 2G12 bind to distinct regions of the HIV-1 envelope glycoprotein. The antibodies were initially tested against a panel of 15 clade B HIV-1 isolates, using a single concentration that is achievable in vivo (HIVIG, 2,500 microg/ml; MAbs, 25 microg/ml). Individual antibody reagents neutralized many of the viruses tested, but antibody potency varied substantially among the viruses. The virus neutralization produced by double combinations of HIVIG plus 2F5 or 2G12, the two MAbs together, or the triple combination of HIVIG, 2F5, and 2G12 was generally equal to or greater than that predicted by the effect of individual antibodies. Overall, the triple combination displayed the greatest magnitude and breadth of neutralization. Synergistic neutralization was evaluated by analyzing data from dose-response curves of each individual antibody reagent compared to the triple combination and was demonstrated against each of four viruses tested. Therefore, combinations of polyclonal and monoclonal anti-HIV antibodies can produce additive or synergistic neutralization of primary HIV-1 isolates. Passive immunotherapy for treatment or prophylaxis of HIV-1 should consider mixtures of potent neutralizing antibody reagents to expand the magnitude and breadth of virus neutralization.

A vaccine for HIV type 1: the antibody perspective

Antibodies that bind well to the envelope spikes of immunodeficiency viruses such as HIV type 1 (HIV-1) and simian immunodeficiency virus (SIV) can offer protection or benefit if present at appropriate concentrations before viral exposure. The challenge in antibody-based HIV-1 vaccine design is to elicit such antibodies to the viruses involved in transmission in humans (primary viruses). At least two major obstacles exist. The first is that very little of the envelope spike surface of primary viruses appears accessible for antibody binding (low antigenicity), probably because of oligomerization of the constituent proteins and a high degree of glycosylation of one of the proteins. The second is that the mature oligomer constituting the spikes appears to stimulate only weak antibody responses (low immunogenicity). Viral variation is another possible obstacle that appears to present fewer problems than anticipated. Vaccine design should focus on presentation of an intact mature oligomer, increasing the immunogenicity of the oligomer and learning from the antibodies available that potently neutralize primary viruses.

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.