Antibodies to the putative SIV infection-enhancing domain diminish beneficial effects of an SIV gp160 vaccine in rhesus macaques

Association of complement C3d receptor 2 genotypes with the acquisition of HIV infection in a trial of recombinant glycoprotein 120 vaccine

OBJECTIVES

Complement C3d receptor 2 (CR2) is the main receptor for complement protein C3d and plays an important role in adaptive immune responses. CR2 genetic variants are associated with susceptibility to systemic lupus erythematosus as well as to HIV-1 infection. In addition, CR2 function can be subverted by HIV-1 for an efficient entry into target cells; in a process known as antibody-dependent enhancement of viral infection. We sought to determine the association between CR2 gene variants with HIV-1 acquisition after vaccination with recombinant gp120 protein (Vax004 clinical trial).

DESIGN AND METHODS

This is a retrospective cross-sectional study, comprising male volunteers of European ancestry including infected (n = 273) and uninfected (n = 402) vaccinees and placebo, who were genotyped for three single nucleotide polymorphisms (SNPs) in the CR2 gene region.

RESULTS

An interaction was observed between the baseline sexual behavior and the SNP rs3813946 for higher risk of infection in vacinees (interaction term P = 0.02). This SNP was associated with increased susceptibility to HIV-1 infection after vaccination in volunteers with low behavioral risk odds ratio (95% confidence interval): 5.5 (1.4-21.7) P = 0.006 but not vaccinees with high behavioral risk or volunteers given placebo (P = 0.7). Moreover, CR2 genotype was strongly associated with the rate of HIV-1 acquisition after vaccination in low-risk volunteers [hazard odds ratio (95% confidence interval): 3.3 (1.6-7.0), P = 0.001].

CONCLUSION

The current study suggests that CR2 may play a role in HIV-1 acquisition after vaccination with rgp120 proteins.

Protease Inhibitors as Ad-hoc Antibiotics

Background:

Proteases are important enzymes that can degrade proteins and are found in animals, plants, bacteria, fungi and viruses. The action of proteases can be controlled by Protease Inhibitors (PIs), chemical or proteinaceous in nature that can block the active site of protease. Since the step catalyzed by proteases may play important role in life cycle of microbes, hindering the action of proteases by PIs may act as therapeutic intervention for microbial infection.

Material and Methods:

A thorough study was performed and wide range of literature was surveyed to confirm our results of PIs showing antibacterial activity.

Results:

PIs have shown to be effective drugs against bacterial pathogens, pathogenic viruses- Human Immunodeficiency Virus (HIV), Herpes virus, Hepatitis Virus. PIs have recently been investigated for controlling protozoan parasites. Clinical value of proteases and their inhibitors has been studied inHelicobacter pyloriwhich is the etiologic agent of gastritis.

Conclusion:

This review is intended to highlight the role of PIs in the Battle against Microbial Pathogens.

[Thermodynamic analysis of dimerization inhibitors binding to HIV protease monomers]

Here, we describe the analysis of kinetic and thermodynamic parameters for binding of peptide and nonpeptide dimerization inhibitors to immobilized HIV protease (HIVp) monomers by using surface plasmon resonance. Molecular interactions were investigated at different inhibitors concentrations (0-80 microM) and temperatures (15-35 degrees C). The kinetic, equilibrium and thermodynamic parameters have been determined. It was found that both inhibitors were characterized by similar interaction parameters. The complex formation is entropically driven process for both inhibitors. The entropic term(-TdeltaS) had the value about -20 kcal/mol while the enthalpic term (deltaH) had the positive value about 14 kcal/mol and counteracted the complex formation.

Extensive complement-dependent enhancement of HIV-1 by autologous non-neutralising antibodies at early stages of infection

BACKGROUND

Non-neutralising antibodies to the envelope glycoprotein are elicited during acute HIV-1 infection and are abundant throughout the course of disease progression. Although these antibodies appear to have negligible effects on HIV-1 infection when assayed in standard neutralisation assays, they have the potential to exert either inhibitory or enhancing effects through interactions with complement and/or Fc receptors. Here we report that non-neutralising antibodies produced early in response to HIV-1 infection can enhance viral infectivity.

RESULTS

We investigated this complement-mediated antibody-dependent enhancement (C'-ADE) of early HIV infection by carrying out longitudinal studies with primary viruses and autologous sera derived sequentially from recently infected individuals, using a T cell line naturally expressing the complement receptor 2 (CR2; CD21). The C'-ADE was consistently observed and in some cases achieved infection-enhancing levels of greater than 350-fold, converting a low-level infection to a highly destructive one. C'-ADE activity declined as a neutralising response to the early virus emerged, but later virus isolates that had escaped the neutralising response demonstrated an increased capacity for enhanced infection by autologous antibodies. Moreover, sera with autologous enhancing activity were capable of C'ADE of heterologous viral isolates, suggesting the targeting of conserved epitopes on the envelope glycoprotein. Ectopic expression of CR2 on cell lines expressing HIV-1 receptors was sufficient to render them sensitive to C'ADE.

CONCLUSIONS

Taken together, these results suggest that non-neutralising antibodies to the HIV-1 envelope that arise during acute infection are not 'passive', but in concert with complement and complement receptors may have consequences for HIV-1 dissemination and pathogenesis.

Adherence in people living with HIV/AIDS, mental illness, and chemical dependency: a review of the literature

Adherence to antiretroviral medications is central to reducing morbidity and mortality among people living with HIV/AIDS. Relatively few studies published to date address HIV adherence among special populations. The purpose of this article is to review the existing literature on HIV antiretroviral adherence, with an emphasis on studies among the triply diagnosed population of people living with HIV/AIDS, mental illness, and chemical dependency. In order to reflect the most current information available, data from conference proceedings, federally funded studies in progress, and the academic literature are presented for consideration.

Mechanisms and results of the antibody-dependent enhancement of viral infections and role in the pathogenesis of coxsackievirus B-induced diseases

The mechanisms of the antibody-dependent enhancement (ADE) of viral infection are presented, particularly within the Picornaviridae family. The ADE of infection has been described in both human and animal models, worsens viral infections and compromises vaccine safety. The ADE of coxsackievirus B infection can also be implied in the pathogenesis of diseases like chronic dilated cardiomyopathy or insulin-dependent type 1 diabetes.

Traitors of the immune system-enhancing antibodies in HIV infection: their possible implication in HIV vaccine development

Considering recent HIV vaccine failures, the authors believe that it would be most important to find new targets for vaccine-induced immunity, and to analyze the data from previous trials, using an innovative approach. In their review article, the authors briefly summarize the significance of the antibody-dependent enhancement of infection in different viral diseases and discuss role of these types of antibodies as the obstacles for vaccine development. Findings which indicate that complement-mediated antibody-dependent enhancement (C-ADE) is present also in HIV-infected patients, are summarized. Previous results of the authors, suggesting that C-ADE plays a very important role in the progression of HIV infection are described. Data reflecting that enhancing antibodies may develop even in vaccinated animals and human volunteers, and may be responsible for the paradoxical results obtained in some subgroups of vaccinees are discussed. Finally, based on their hypothesis, the authors offer some suggestions for the future development of vaccines.

Mechanism for complement-mediated, antibody-dependent enhancement of human immunodeficiency virus type 1 infection in MT2 cells is enhanced entry through CD4, CD21, and CXCR4 chemokine receptors

Some antibodies neutralize Human Immunodeficiency Virus (HIV). However, antibody to HIV and complement can enhance HIV replication if cells express both complement receptors and CD4, a phenomenon described as complement-mediated, antibody-dependent enhancement (C'ADE). Although increased binding of opsonized virions has been reported, the mechanism by which C'ADE enhances HIV replication remains unproven. In this study, real-time polymerase chain reaction to detect HIV cDNA indicates that complement and anti-HIV antibodies enhance HIV entry 8- to 30- fold with similar increases in integrated provirus. Thus, complement increases HIV replication through a mechanism of enhanced entry. To further refine the mechanism of C'ADE, chemokine receptor antagonists were employed. JM2987, a CXCR4 chemokine receptor antagonist, blocked HIV infection and C'ADE; thus CD4, complement receptors, and CXCR4 chemokine receptors are required for enhanced entry of HIV into MT2 cells. Finally, anti-HIV immunoglobulin enhanced replication of not only group M clade B HIV but also group M clade D and group O isolates. These data demonstrate that antibodies mediating C'ADE of HIV infection are broadly reactive.

Role of invariant Thr80 in human immunodeficiency virus type 1 protease structure, function, and viral infectivity

Sequence variability associated with human immunodeficiency virus type 1 (HIV-1) is useful for inferring structural and/or functional constraints at specific residues within the viral protease. Positions that are invariant even in the presence of drug selection define critically important residues for protease function. While the importance of conserved active-site residues is easily understood, the role of other invariant residues is not. This work focuses on invariant Thr80 at the apex of the P1 loop of HIV-1, HIV-2, and simian immunodeficiency virus protease. In a previous study, we postulated, on the basis of a molecular dynamics simulation of the unliganded protease, that Thr80 may play a role in the mobility of the flaps of protease. In the present study, both experimental and computational methods were used to study the role of Thr80 in HIV protease. Three protease variants (T80V, T80N, and T80S) were examined for changes in structure, dynamics, enzymatic activity, affinity for protease inhibitors, and viral infectivity. While all three variants were structurally similar to the wild type, only T80S was functionally similar. Both T80V and T80N had decreased the affinity for saquinavir. T80V significantly decreased the ability of the enzyme to cleave a peptide substrate but maintained infectivity, while T80N abolished both activity and viral infectivity. Additionally, T80N decreased the conformational flexibility of the flap region, as observed by simulations of molecular dynamics. Taken together, these data indicate that HIV-1 protease functions best when residue 80 is a small polar residue and that mutations to other amino acids significantly impair enzyme function, possibly by affecting the flexibility of the flap domain.

Evaluation of live feline immunodeficiency virus vaccines with modified antigenic properties

Live-attenuated viruses have typically been generated from pathogenic viruses by genetic modifications that modified their replicative capacity. The present study investigated whether modification of the antigenic properties of live-attenuated viruses might improve upon the protection that such vaccines afford against lentivirus infection. In a previous study, random amino acid substitutions were introduced into the transmembrane envelope glycoprotein of the feline immunodeficiency virus (FIV), within a highly conserved domain (principal immunodominant domain) bearing immunodominant B-cell epitopes. Amongst a wide set of mutants, mutations that modified antibody specificity without abolishing infectivity ex vivo were selected. In the present study, two such mutants, TN14 and TN92, were evaluated for their replicative capacities and pathogenic properties in vivo in comparison with the parental virus, FIV 34TF10. No significant differences in viral load were observed between mutant and parental viruses. After 1 year of infection, all animals were subjected to a heterologous intraclade superinfection with a primary strain of FIV. Whilst both parental and modified viruses protected cats from high viral loads after superinfection, the TN92 virus afforded a higher degree of protection (P=0·0079). Such improvement in protection might correlate with a decrease in the immunogenicity of a B-cell epitope potentially involved in antibody enhancement of infection.

Structural and thermodynamic basis for the binding of TMC114, a next-generation human immunodeficiency virus type 1 protease inhibitor

TMC114, a newly designed human immunodeficiency virus type 1 (HIV-1) protease inhibitor, is extremely potent against both wild-type (wt) and multidrug-resistant (MDR) viruses in vitro as well as in vivo. Although chemically similar to amprenavir (APV), the potency of TMC114 is substantially greater. To examine the basis for this potency, we solved crystal structures of TMC114 complexed with wt HIV-1 protease and TMC114 and APV complexed with an MDR (L63P, V82T, and I84V) protease variant. In addition, we determined the corresponding binding thermodynamics by isothermal titration calorimetry. TMC114 binds approximately 2 orders of magnitude more tightly to the wt enzyme (K(d) = 4.5 x 10(-12) M) than APV (K(d) = 3.9 x 10(-10) M). Our X-ray data (resolution ranging from 2.2 to 1.2 A) reveal strong interactions between the bis-tetrahydrofuranyl urethane moiety of TMC114 and main-chain atoms of D29 and D30. These interactions appear largely responsible for TMC114's very favorable binding enthalpy to the wt protease (-12.1 kcal/mol). However, TMC114 binding to the MDR HIV-1 protease is reduced by a factor of 13.3, whereas the APV binding constant is reduced only by a factor of 5.1. However, even with the reduction in binding affinity to the MDR HIV protease, TMC114 still binds with an affinity that is more than 1.5 orders of magnitude tighter than the first-generation inhibitors. Both APV and TMC114 fit predominantly within the substrate envelope, a property that may be associated with decreased susceptibility to drug-resistant mutations relative to that of first-generation inhibitors. Overall, TMC114's potency against MDR viruses is likely a combination of its extremely high affinity and close fit within the substrate envelope.

Gp120-alum boosting of a Gag-Pol-Env DNA/MVA AIDS vaccine: poorer control of a pathogenic viral challenge

Envelope protein immunogens may improve DNA or live-vectored HIV vaccines by complementing antiviral cellular responses with Env antibodies. We tested this concept by administering two immunizations of alum-adjuvanted HIV-1 89.6 gp120 to macaques being primed at weeks 0 and 8 with SHIV 89.6 Gag-Pol-Env DNA and boosted at week 24 with SHIV-89.6 Gag-Pol-Env recombinant modified vaccinia Ankara (MVA). Three hundred micrograms of gp120 was delivered with the second DNA prime and the MVA booster. Eight months after vaccination, all animals were challenged intrarectally with the related, yet serologically distinct, SHIV-89.6P. The gp120 immunizations raised binding, but not neutralizing antibody for the challenge virus, and allowed testing of whether gp120 vaccines that fail to raise neutralizing antibody can improve protection. Following the second gp120 immunization, the plus-gp120 group showed >10 times higher levels of binding antibody than the minus-gp120 group. These levels fell and were overall similar in both groups at the time of challenge. Following the second challenge, both groups had similar temporal patterns and heights of binding and neutralizing antibodies. However, the plus-gp120 group had less consistent control of viremia and higher levels of plasma viral RNA for the first year postchallenge. Assays for complement-dependent enhancing antibody revealed a trend toward higher levels of activity in the plus-gp120 group. This trend did not reach significance in our animal groups of 8. We conclude that gp120 inoculations that fail to raise neutralizing antibody do not improve the efficacy of Gag-Pol-Env DNA/MVA vaccines.

Parameters driving the selection of nelfinavir-resistant human immunodeficiency virus type 1 variants

We investigated the parameters driving nelfinavir resistance, along the D30N and L90M evolutionary pathways. The advantage of the D30N mutant was mostly due to its resistance level, while the L90M mutation allowed preservation of infectivity coupled with minimal resistance. Emergence of secondary mutations further increased the selective advantage of viruses harboring D30N.

Inhibitory activity of synthetic peptide antibiotics on feline immunodeficiency virus infectivity in vitro

Natural peptide antibiotics are part of host innate immunity against a wide range of microbes, including some viruses. Synthetic peptides modeled after natural peptide antibiotics interfere with microbial membranes and are termed peptidyl membrane-interactive molecules (peptidyl-MIM [Demegen Inc, Pittsburgh, Pa.]). Sixteen peptidyl-MIM candidates were tested for activity against feline immunodeficiency virus (FIV) on infected CrFK cells. Three of them (D4E1, DC1, and D1D6) showed potent anti-FIV activity in chronically infected CrFK cells as measured by decreased reverse transcriptase (RT) activity, having 50% inhibitory concentrations of 0.46, 0.75, and 0.94 micro M, respectively, which were approximately 10 times lower than their direct cytotoxic concentrations. Treatment of chronically infected CrFK cells with 2 micro M D4E1 for 3 days completely reversed virus-induced cytopathic effect. Immunofluorescence revealed reduced p26 staining in these cells. Treatment of chronically infected CrFK cells with 2 micro M D4E1 suppressed virus production ( approximately 50%) for up to 7 days, The virions from the D4E1-treated culture had impaired infectivity, as measured by the 50% tissue culture infectious dose and nested PCR analysis of proviral DNA. However, these noninfectious virions were able to bind and internalize, suggesting a defect at some postentry step. After chronically infected CrFK cells were treated with D4E1 for 24 h, increased cell-associated mature p26 Gag and decreased extracellular virus-associated p26 Gag were observed by Western blot analysis, suggesting that virus assembly and/or release may be blocked by D4E1 treatment, whereas virus binding, penetration, RNA synthesis, and protein synthesis appear to be unaffected. Synthetic peptide antibiotics may be useful tools in the search for antiviral drugs having a wide therapeutic window for host cells.

Consequences and Determinants of Adherence to Antiretroviral Medication: Results from Adult Aids Clinical Trials Group Protocol 370

Objectives

(1) To document rates and patterns of adherence from enrollment until week 24 of an AIDS clinical trial; (2) to examine the association of adherence to clinical end-points including plasma HIV-1 RNA level and CD4 cell count; and (3) to identify predictors of adherence from clinical, behavioural, psychosocial and demographic factors.

Design

Sub-study of a multicentre, randomised, open-label, comparison-controlled trial; 21 collaborating units of the Adult AIDS Clinical Trials Group. Observational, prospective analysis.

Methods

Ninety-three subjects with baseline plasma HIV-1 RNA levels >500 copies/ml, who completed clinical assessment, plasma HIV-1 RNA titres and CD4 cell counts at study entry, weeks 2, 4 and every 4 weeks thereafter until week 24. All patients were antiretroviral-experienced but were naive to non-nucleoside reverse transcriptase inhibitors and protease inhibitors. Self-reported adherence to antiretroviral therapies prescribed as part of the trial was assessed every 4 weeks from trial, week 4 until week 24.

Results

Average adherence was high, with 63% of subjects reporting >95% adherence across the trial. However, there was a significant decline in adherence over time on trial. After controlling for potential confounding variables, patients who were less than 95% adherent to medications were 3.5-times more likely to have treatment failure (HIV-1 RNA >50 copies/ml) than subjects with adherence rates of 95–100%. The strongest predictor of adherence was adverse clinical events (for example, dermatological, gastrointestinal symptoms): patients with adverse events were 12.8-times less likely to have 95–100% adherence. Other clinical, demographic, psychosocial and behavioural factors were also significant predictors of adherence.

Conclusions

Adherence influences virological outcome even in AIDS clinical trials where overall adherence rates are high and should therefore be monitored in future trials. Intervention may be warranted to enhance adherence for subjects who have early toxicities, express concern about taking medications as directed, and for women and minorities.

Interference between D30N and L90M in selection and development of protease inhibitor-resistant human immunodeficiency virus type 1

We studied the evolutionary relationships between the two protease inhibitor (PI) resistance mutations, D30N and L90M, of human immunodeficiency virus type 1 (HIV-1). The former is highly specific for nelfinavir resistance, while the latter is associated with resistance to several PIs, including nelfinavir. Among patients with nelfinavir treatment failure, we found that D30N acquisition was strongly suppressed when L90M preexisted. Thus, D30N/L90M double mutations not only were detected in a very limited number of patients but also accounted for a minor fraction within each patient. In the disease course, the D30N and L90M clones readily evolved independently of each other, and later the D30N/L90M double mutants emerged. The double mutants appeared to originate from the D30N lineage but not from the L90M lineage, or were strongly associated with the former. However, their evolutionary pathways appeared to be highly complex and to still have something in common, as they always contained several additional polymorphisms, including L63P and N88D, as common signatures. These results suggest that D30N and L90M are mutually exclusive during the evolutionary process. Supporting this notion, the D30N/L90M mutation was also quite rare in a large clinical database. Recombinant viruses with the relevant mutations were generated and compared for the ability to process p55gag and p160pol precursor proteins as well as for their infectivity. L90M caused little impairment of the cleavage activities, but D30N was detrimental, although significant residual activity was observed. In contrast, D30N/L90M demonstrated severe impairment. Thus, the concept of mutual antagonism of the two mutations was substantiated biochemically and functionally.

Primary and recombinant HIV type 1 strains resistant to protease inhibitors are pathogenic in mature human lymphoid tissues

Preserved peripheral CD4+ T cell counts despite virologic failure in patients undergoing protease inhibitor (PI)-containing antiviral regimens are a frequent occurrence in human immunodeficiency virus (HIV) disease. One hypothesis to explain the relative sparing of CD4+ T cells is that HIV strains exhibiting PI resistance concomitantly are attenuated in terms of cytopathicity for mature T cells. To test this hypothesis, we used a three-dimensional human tonsil histoculture microenvironment to assess the pathogenic potential of a panel of primary and recombinant HIV-1 strains derived from patients experiencing PI failure. All the viruses tested replicated efficiently in these cultures and, in some cases, better than comparable wild-type viral isolates. Furthermore, the PI-resistant strains depleted CD4+ T cells potently and comparably with wild-type isolates in these ex vivo lymphoid tissues. These results demonstrate that PI-resistant viruses are not inherently less pathogenic for mature T cells. Therefore, the sustained peripheral lymphocyte counts in patients with selective virologic failure may be due to specific defects in viral replication in other cell compartments or to an undefined host adaptation to viral infection during PI therapy.

Inhibition of murine AIDS by alternate administration of azidothymidine and fludarabine monophosphate

Anti-HIV-1 combination therapies, including protease and reverse transcriptase inhibitors, can reduce plasma viremia to undetectable levels within the first 2 weeks of treatment. This reduction is followed by a slower decline that primarily results from the presence of viral reservoirs such as CD4+ memory cells, dendritic cells, and macrophages. For this reason, we evaluated a new drug combination therapy that includes a lympholytic drug: (2-fluoro-ara-AMP, fludarabine) to eliminate cells already infected and an antiviral drug (azidothymidine [AZT]) to protect cells not yet infected. We used C57BL/6 mice infected with the retroviral complex LP-BM5, which developed severe immunodeficiency (i.e., murine AIDS), to select the most effective fludarabine regimen to inhibit disease progression, and then to evaluate the efficacy and toxicity of the fludarabine and AZT combinations. The results obtained show that intraperitoneal administration of fludarabine at 3 mg/mouse twice a day for 4 weeks is the most effective regimen in reducing splenomegaly, lymphadenopathy, hypergammaglobulinemia, and proviral DNA content in spleen and lymph nodes and in restoring the architecture of lymph nodes. Subsequently, we evaluated the combined or sequential administration of fludarabine and AZT. The data reported in this paper show that the sequential administration of the two drugs provides additive antiviral effects that reduce spleen and lymph node weights to normal values and proviral DNA content by approximately 95% in all infected organs; the phenotypes of blood T and B cells moved toward control values, although the number of B cells was significantly reduced by fludarabine treatment. Finally, we evaluated the outcome of the disease after suspension or continuation of different treatment regimens. In all treatment groups, the disease progressed and increased proviral DNA content was found in infected organs, but animals receiving the sequential administration of fludarabine and AZT were less affected than those receiving only fludarabine or the simultaneous administration of both. The results obtained suggest that fludarabine could be part of a new therapeutic approach aiming at eradicating HIV from those cells that have been already infected and that are not protected by highly active antiretroviral therapy (HAART).

Strong correlation between the complement-mediated antibody-dependent enhancement of HIV-1 infection and plasma viral load

OBJECTIVE

We have previously demonstrated that complement-mediated antibody-dependent enhancement (C-ADE) of HIV-1 infection correlates with accelerated immunosuppression and disease progression in HIV-1-infected individuals. In the present work the relationship between C-ADE and plasma HIV-1 RNA concentrations was studied to determine the effect of C-ADE on viral replication.

METHODS

Three studies were performed: (a) C-ADE and HIV-1 RNA concentrations were determined in the serum and plasma aliquots taken at the same time from 98 HIV patients, mostly in the advanced stage of the disease; (b) the above two parameters as well as HIV enzyme-linked immunosorbent assay (ELISA)-reactive antibodies (Abbott HIV 1/2 test), and p24 antigen levels (Abbott antigen test; Abbott, Delkenheim, Germany) were determined in four seroconversion panels purchased from the Boston Biomedica firm; (c) changes of HIV-1 RNA concentration and C-ADE during a 17 month follow-up period were determined in 18 HIV-infected patients. C-ADE was measured by the method previously established in our laboratories. The results were expressed by an enhancement/neutralization index (E/NI). HIV-1 RNA levels were determined with the Amplicor monitor kit (Roche, Basel, Switzerland), and in some experiments with the nucleic acid sequence based amplification (Organon Teknika, Turnhout, Belgium) kits.

RESULTS

(a) We found a highly significant (P<0.0001) positive correlation between E/NI values reflecting the extent of HIV-1 infection enhancement and plasma HIV-1 RNA levels. Both E/NI and HIV-1 RNA levels negatively correlated to the CD4 cell counts. (b) C-ADE was first detected just before, or concomitantly with, seroconversion in 4/4 seroconversion panels. (c) Both E/NI values and HIV-1 RNA levels significantly (P<0.001) increased during a 17 month observation period in 18 HIV-infected patients.

CONCLUSION

We found strong association between the extent of the complement-mediated antibody-dependent enhancement of HIV-1 infection and the plasma viral load in HIV patients. On the basis of these findings, C-ADE correlates with HIV replication in vivo, and potentially contributes to the progression of HIV disease.

The rabbit study: ritonavir and saquinavir in combination in saquinavir-experienced and previously untreated patients

Thirteen protease inhibitor-naive patients with HIV-1 infection, and 12 patients with a median of 58 months prior treatment with saquinavir (SQV) monotherapy, were treated with SQV (400 mg twice daily) and ritonavir (RIT, 500 mg twice daily) in a study designed to assess the effect of prior treatment with SQV monotherapy on the antiretroviral activity of RIT-SQV combination therapy. Median baseline viral load and CD4+ cell counts were 155,000 and 262,000 copies/ml and 333 and 225 cells/mm3 in the naive and experienced groups, respectively. Mean viral load changes at 24 weeks were -1.63 and -0.27 log copies/ml in the naive and SQV-experienced groups, respectively (intent-to-treat analysis). Baseline genotype by point mutation assay and sequencing in the SQV-experienced group was highly predictive of virological response. Eight of 11 SQV-experienced patients had evidence of phenotypic resistance to RIT at baseline, despite previous treatment with SQV only. There was strong correlation between phenotypic resistance to RIT and the presence of the L90M mutation. We conclude that prolonged prior treatment with saquinavir monotherapy may produce cross-resistance to ritonavir and reduce the subsequent response to ritonavir-saquinavir in combination. In this study, both phenotypic resistance to ritonavir and presence of the L90M mutation predicted the viral load response to ritonavir-saquinavir.

The HIV type 1 protease inhibitor saquinavir can select for multiple mutations that confer increasing resistance

Previous use of the HIV-1 protease inhibitor saquinavir resulted in the infrequent appearance of mutations in the HIV-1 protease gene associated with resistance. We have examined the ability of saquinavir to select for resistance mutations. In multiple selections of HIV-1 in cell culture with saquinavir, similar patterns of mutations were reproducibly observed and the number of mutations increased with increasing selective pressure. In a small number of subjects who showed an antiviral response when saquinavir was added to their therapeutic regimen, similar mutations were detected in viral genomic RNA in vivo after 30 to 40 weeks of therapy. These results indicate that saquinavir can select for resistance mutations and suggest that the infrequent appearance of these mutations in vivo is the result of low drug exposure. These results also predict that the use of higher levels of saquinavir will lead to an even greater frequency of resistance mutations in patients who fail therapy.

Characterization of human immunodeficiency virus type 1 resistant to modified cyclodextrin sulphate (mCDS71) in vitro

Drug resistance of human immunodeficiency virus type 1 (HIV) to modified cyclodextrin sulphate (mCDS71) has been analysed with respect to both the in vitro appearance of resistance to the compound and the mechanism of the acquisition of resistance. Resistant strains could be obtained in all three strains (NL432, KK-1 and A018) tested after serial passages in MT-4 cells with a gradual increase of the concentration of mCDS71. Cross-resistance both to mCDS71 and dextran sulphate 8000 was observed. As a result of sequencing analysis of the gp120 V3-C5 region of resistant strains, the mechanism of resistance can be explained in several ways: (i) substitution of sugar chain-binding amino acids, N and S; (ii) three to five amino acid deletion in V4 loop; and (iii) several mutations in V3 and V4 regions. The real cause of the resistance may be a combination of these three mechanisms. The results suggest that the target of mCDS71 is relatively widely distributed on the viral surface glycoprotein.

Simian immunodeficiency virus as a model of human HIV disease

Because of strong clinical, pathological, virological and immunological analogies with HIV infection of humans, infection of macaques with SIV provides a valuable model for exploring crucial issues related to both the pathogenesis and prevention of HIV infection. The model has offered a unique setting for the preclinical evaluation of drugs, vaccines and gene-therapies against HIV, and has helped to identify many virus and host determinants of lentiviral disease. For instance, the importance of an intact nef gene for efficient lentivirus replication and disease induction, and the protective ability of live attenuated, nef-deleted viruses have been first demonstrated in macaques using molecular clones of SIV. More recently, the development of chimeric HIV-SIV vectors able to establish infection and induce disease in macaques has provided new opportunities for the evaluation of vaccination strategies based upon HIV antigens. The aim of this review is to describe the natural course of SIV infection in macaques and to outline how this model has contributed to our understanding of the complex interaction between lentiviruses and host immune system.

Functional and molecular characterization of human monoclonal antibody reactive with the immunodominant region of HIV type 1 glycoprotein 41

The immunoreactivity, functional activity, and molecular features of a human monoclonal antibody (HMAb), F240, from an HIV-1-infected individual have been studied. Flow cytometric analysis demonstrated that F240 is reactive with cells infected with a broad range of laboratory isolates but not with uninfected cells. Reactivity of F240 is greatly enhanced by preincubation of infected cells with soluble CD4, and to a much lesser extent, with F105, an HMAb reactive with the CD4-binding site of gp120. This enhancement is temperature dependent, with maximum enhancement observed at 37 degrees C, and suggests that the F240 epitope may be more accessible after gp120 has bound to CD4 in vivo. Immunoblot analysis reveals antigen specificity of F240 for gp41 or its precursor gp160. F240 specificity is mapped to the immunodominant region of the gp41 ectodomain by Pepscan analysis. This epitope has been implicated in eliciting nonprotective antibodies that enhance infection in the presence of complement. Consistent with this, F240 failed to neutralize laboratory isolates and enhanced viral infection in a complement-dependent manner. The F240 VH demonstrates extensive somatic mutations compared with the product of its closest homologous germline gene VH3-3.11. Most amino acid substitutions occur in CDR2, characteristic of an antigen-driven response, and in FR3, a phenomenon observed in other anti-HIV-1 envelope HMAbs. Primary structure analysis of the F240 heavy chain revealed strong homology in the CDR domains to an HMAb (3D6) reactive with the same gp41 region, which suggests that these HMAbs could define a potential human antibody clonotype.

Characterization of V3 loop-Pseudomonas exotoxin chimeras. Candidate vaccines for human immunodeficiency virus-1

To develop a candidate vaccine for human immunodeficiency virus, type 1 (HIV-1), chimeric proteins were constructed by inserting sequences derived from the V3 loop of gp120 into a nontoxic form of Pseudomonas exotoxin (PE). Inserts of 14 or 26 amino acids, constrained by a disulfide bond, were introduced between domains II and III of PE. V3 loop-toxin proteins expressed in Escherichia coli and corresponding to either MN (subtype B) or Thai (subtype E) strains, were recognized by strain-specific monoclonal anti-gp120 antibodies. When loop sequences were introduced into an enzymatically active form of the toxin, there was no loss of toxin-mediated cell killing, suggesting that these sequences were co-transported to the cytosol. Sera from rabbits injected with nontoxic PE-V3 loop chimeras were reactive for strain-specific gp120s in Western blots, immunocapture assays, enzyme-linked immunosorbent assays, and neutralized HIV-1 infectivity. Since toxin vectors were designed to receive oligonucleotide duplexes encoding any V3 loop sequence, this approach should allow for the production of V3 loop-toxin chimeras corresponding to multiple HIV isolates.

Inactivation of a common epitope responsible for the induction of antibody-dependent enhancement of HIV

BACKGROUND

The primary antigenic domain responsible for complement-mediated antibody-dependent enhancement (C'-ADE) of HIV and simian immunodeficiency virus resides in the principal immunodominant sequence of the transmembrane protein.

OBJECTIVE

To identify whether there are amino-acid residues common to the epitopes of the known enhancing human monoclonal antibodies (MAb), and to provide a structural model for this functional region present on the HIV envelope. Since our model predicts that this region is involved in the association of gp120 with gp41, this association was monitored for each mutant.

DESIGN

The binding of enhancing human MAb to point and deletion mutations within the enhancing domain was analyzed by two methods. The first analyzed binding to mutants expressed in COS cells: the second quantified the binding of four enhancing human MAb to each mutant gp160 versus wild-type control by enzyme-linked immunosorbent assay (ELISA).

METHODS

Site-directed mutagenesis was used to produce specific deletions and point mutants, which were expressed in COS cells. Binding of MAb 50-69 and V3-loop MAb 5F7 were visualized in the wild-type and each of the mutant constructs by immunohistochemistry. Quantitative evaluation of enhancing human MAb binding to each mutant versus wild-type was performed by ELISA. A model for the enhancing domain and its relationship to gp120 association with gp41 was provided by molecular dynamics and ligand docking methods.

RESULTS

All available enhancing human MAb known to bind to the principal immunodominant region of gp41 were unable to bind to deletions involving the disulfide loop, which in our molecular model provided the primary association site between gp120 and gp41. Point mutations in the loop blocked this association, but had a quantitatively smaller effect on the binding of the enhancing human MAb. A conservative W596Y mutation completely blocked the binding of all human MAb, but had no effect on gp120-gp41 association.

CONCLUSIONS

A variety of mutations within the primary C'-ADE domain inhibit binding of enhancing human MAb as well as blocking the association of gp120 and gp41. A conservative W596Y mutation blocks binding of all enhancing human MAb with retention of gp120-gp41 association. These data are important to the design of vaccines in which the primary enhancing epitope is disarmed to prevent the subsequent induction of an amnestic response that could lead to viral enhancement of infection. The retention of the gp120-gp41 association is postulated to yield an immunogen similar to natural infection for both subunit and genetic vaccines.

Defensins purified from human granulocytes bind C1q and activate the classical complement pathway like the transmembrane glycoprotein gp41 of HIV-1

The transmembrane glycoprotein gp41 of HIV-1 contains a C1q binding domain (HIVenv 583-610) and activates the human complement system through the classical pathway. Based on structural and functional similarities between human defensins (human neutrophil peptide, HNP 1-3) and synthetic peptides representing the env 583-610 region of HIV-1, we found it interesting to investigate the C1q binding and complement activating ability of human defensins. Human defensins were purified and characterized by size exclusion chromatography, ultrafiltration, gel electrophoresis and HPLC. The complement activating ability of the purified peptides was assessed in a solid-phase immunoassay. Defensins, fixed to an ELISA plate, were able to bind the C1q subcomponent of the first complement component (C1), triggering the classical pathway of complement activation which led to C4b binding to the plate. Reduction and subsequent alkylation of disulfide bridges of defensins greatly decreased the C1q binding ability but complement activation (C4b binding) remained high. Further acetylation of the reduced defensin peptide resulted in a molecule which bound very little or no C1q but still activated the complement cascade. These phenomena indicate that defensins interact with the complement system via C1q-dependent and C1q-independent mechanisms, and extend the number of functional similarities between defensins and gp41 of HIV-1 to include C1q binding and complement activation.

Anti-major histocompatibility complex antibody responses to simian B cells do not protect macaques against SIVmac infection

Macaques have been protected against infection with human cell-grown SIVmac by immunization with antigens encoded by the human major histocompatibility complex (MHC). Here, we investigated the efficacy of alloimmunization with simian B cells expressing high levels of MHC class I and class II molecules to confer protection against systemic challenge with simian-grown SIVmac. Eight rhesus macaques were vaccinated with glutaraldehyde-fixed and beta-propiolactone-inactivated herpesvirus papio-transformed B cells. Four of the macaques received 5 doses, the others 10. Animals were challenged with rhesus macaque spleen-derived cell-free SIVmac. Allogeneic B cells elicited antibody responses to rhesus MHC class I and II but failed to protect animals against infection. Anti-MHC class I antibodies were restricted in specificity and failed to recognize MHC class I from some B lymphoblastoid cell lines (B-LCLs) including a B-LCL from the animal in whose cells the challenge virus was grown. Vaccinated animals responded to self-MHC class I antigens but not to self-MHC class II antigens from peripheral blood mononuclear cells (PBMCs). Animals that underwent the shorter immunization regimen had transiently enhanced PBMC-associated virus loads after challenge, whereas the average virus-infected cell load was reduced in animals that underwent the more extensive immunization. These results suggest that antibody responses to allogeneic MHC molecules do not protect against infection with immunodeficiency lentiviruses.

Two parallel routes of the complement-mediated antibody-dependent enhancement of HIV-1 infection

OBJECTIVE

To study the mechanism of the complement-mediated antibody-dependent enhancement (C'-ADE) of HIV infection which may play a significant role in the progression of HIV-disease.

METHODS

In vitro complement activating and complement-mediated HIV-infection enhancing abilities of three human anti-gp41 monoclonal antibodies (MAb) were tested. C'-ADE was estimated using HIV-1IIIB and CR2 (CD21)-carrying MT-4 target cells. Normal human serum (NHS), purified C1q, C1q-deficient (C1qD) and C2-deficient (C2D) human sera were applied as complement sources.

RESULTS

All MAb mediated increased C1q binding to solid-phase gp41. All MAb had a marked dose-dependent and strictly complement-mediated HIV-infection enhancing effect. Mixtures of the MAb with purified C1q also significantly increased HIV-1 infection. C1qD serum had a markedly lower enhancing effect than NHS, which could be raised to normal level by addition of purified C1q. Pretreatment of the target cells with anti-CR2 antibodies only partially inhibited the enhancing effect of the MAb plus normal human serum.

CONCLUSION

These novel findings indicate that besides the well-known facilitation of entry of HIV-1 by the interaction between virus-bound C3 fragments and CR2 present on the target cells, fixation of C1q to intact virions also results in an enhanced productive HIV-1 infection in the MT-4 cell cultures.

Passive immunization of rhesus macaques against SIV infection and disease

To evaluate the role of humoral immunity against simian immunodeficiency virus (SIV), we tested whether passive immunization with plasma from SIVmac251 vaccine-protected or healthy infected animals would protect rhesus monkeys against intravenous infection with ten 50% animal infectious doses of the cell-free homologous virus. The challenge dose of this SIVmac251 virus stock had previously caused persistent infection in all (21 of 21) nonimmunized controls. A plasma pool was obtained from a donor that had been immunized with an inactivated whole SIVmac251 vaccine produced in human T cells. This plasma pool contained low levels of SIVmac binding and neutralizing antibody but had a high titer of antibodies recognizing human cell proteins. Given 4 or 18 hr before intravenous challenge, this plasma completely protected three of eight recipients from infection and delayed virus detection in one recipient. The five unprotected animals had only a transient or undetectable p27 antigenemia and low virus load in their PBMCs, and all survived at least 7 months after infection. By contrast, no protection was observed in 6 monkeys given inactivated, pooled plasma or purified immunoglobulin (Ig) from healthy SIVmac251-infected animals. This plasma pool and the Ig preparation contained high levels of SIV-binding and neutralizing antibody but no reactivity to human cellular components. Five of the six recipients had persistent antigenemia after challenge and four died acutely from simian AIDS in 4-7 months. These studies suggest that passive transfer of antibody to human cellular antigens can confer protection against SIVmac whereas passive transfer of neutralizing antibodies without human cellular antibodies does not protect against the homologous virus and may enhance infection.