Immunization of chimpanzees confers protection against challenge with human immunodeficiency virus

Safety and immunogenicity of a recombinant HIV type 1 glycoprotein 160 boosted by a V3 synthetic peptide in HIV-negative volunteers

The safety and the immunogenicity of a recombinant hybrid envelope glycoprotein MN/LAI (rgp160) followed by booster injections of a V3 (MN) linear peptide were evaluated in HIV-negative adults at low risk for HIV infection. Volunteers received either rgp160 in alum at 0, 1, and 6 months (group A), rgp160 at 0 and 1 months followed by V3 at 3 and 6 months formulated in alum (group B), or in Freund's incomplete adjuvant (FIA) (group C). Local and systemic reactions were mild to moderate and resolved within the first 72 hr after immunization. No significant biological changes (routine tests and autoantibodies) were observed. One month after the last injection in either group, neutralizing antibodies (NAs) against the HIV-1 MN isolate were detected in 4 of 5 (A), 7 of 10 (B), and 10 of 10 (C) subjects with significantly higher geometric mean titers in the latter group. Four of nine sera with the highest NA titers against MN weakly cross-neutralized the HIV-1 SF2 isolate; none had NA against the HIV-1 LAI strain or against a North American primary isolate. Specific lymphocyte T cell proliferation to rgp160 was detected in 92% of the subjects after the second injection of rgp160 and in 80% of them 12 months after the first injection. A weak and short-lived envelope-specific CD(4+)-mediated cytotoxic lymphocyte activity was detected at certain time points in few subjects. This prime-boost vaccine approach using rgp160 followed by a V3 peptide was safe in humans, and was able to elicit high levels of neutralizing antibodies and a strong and persistent T cell lymphoproliferative response to rgp160 and to V3. However, the neutralization response was restricted to the homologous HIV-1 strain and little env-specific cytotoxic activity was induced.

Heteroduplex mobility assay and phylogenetic analysis of V3 region sequences of human immunodeficiency virus type 1 isolates from Gulu, northern Uganda. The Italian-Ugandan Cooperation AIDS Program

We analyzed peripheral blood mononuclear cells from 19 asymptomatic seropositive pregnant women from the district of Gulu in northern Uganda. A 700-bp fragment of the human immunodeficiency virus type 1 (HIV-1) env gene, including the V3-V5 region, was successfully amplified by PCR from 10 samples (52.6%) and was subsequently subjected to both a heteroduplex mobility assay for genetic screening and subtyping and DNA sequence analysis (approximately 300 bp) for nucleotide comparison and phylogenetic studies. The results show the presence of HIV-1 A and D subtypes (or clades) in this rural area, with the prevalence of the A subtype (8 of 10) being greater than that of the D (2 of 10) subtype, which is unlike what was previously reported for Uganda. By pairwise comparison analysis, the percentage of sequence divergence among samples within each subtype is low (the average intrasubtype divergence is 15.8%), but it is significantly higher between the two subtypes (the average intersubtype divergence is 23%). At the amino acid level, the two HIV-1 subtypes show distinct tetramers at the apex of the V3 loop and, in particular, GPGQ in clade A and GPGR in clade D. In addition, 10 of the 19 viral samples (52.6%) have been isolated in vitro. Nine of the samples have been classified as rapid/high, which reflects a high in vitro replication capacity for the HIV-1 field isolates from this country, even for those obtained from seropositive asymptomatic individuals. These observations, despite being made on the basis of a limited sample size, show a modest degree of genetic divergence among samples isolated in the last 4 years in this country by comparison with those based on the 1990 data on HIV-1 isolates from Kampala. The results reported here are, therefore, extremely relevant for Uganda, which is one of the selected World Health Organization field sites for future HIV-1 vaccine evaluation programs.

Vaccine-induced protection of chimpanzees against infection by a heterologous human immunodeficiency virus type 1

The extraordinary genetic diversity of human immunodeficiency virus type 1 (HIV-1) is a major problem to overcome in the development of an effective vaccine. In the most reliable animal model of HIV-1 infection, chimpanzees were immunized with various combinations of HIV-1 antigens, which were derived primarily from the surface glycoprotein, gp160, of HIV-1 strains LAI and MN. The immunogens also included a live recombinant canarypox virus expressing a gp160-MN protein. In one experiment, two chimpanzees were immunized multiple times; one animal received antigens derived only from HIV-1LAI, and the second animal received antigens from both HIV-1LAI and HIV-1MN. In another experiment, four chimpanzees were immunized in parallel a total of five times over 18 months; two animals received purified gp160 and V3-MN peptides, whereas the other two animals received the recombinant canarypox virus and gp160. At 3 months after the final booster, all immunized and naive control chimpanzees were challenged by intravenous inoculation of HIV-1SF2; therefore, the study represented an intrasubtype B heterologous virus challenge. Virologic and serologic follow-up showed that the controls and the two chimpanzees immunized with the live recombinant canarypox virus became infected, whereas the other animals that were immunized with gp160 and V3-MN peptides were protected from infection. Evaluation of both cellular and humoral HIV-specific immune responses at the time of infectious HIV-1 challenge identified the following as possible correlates of protection: antibody titers to the V3 loop of MN and neutralizing antibody titers to HIV-1MN or HIV-1LAI, but not to HIV-1SF2. The results of this study indicate that vaccine-mediated protection against intravenous infection with heterologous HIV-1 strains of the same subtype is possible with some immunogens.

Highly attenuated HIV type 2 recombinant poxviruses, but not HIV-2 recombinant Salmonella vaccines, induce long-lasting protection in rhesus macaques

Immunization schemes employing priming with vector-based vaccine candidates followed by subunit booster administrations have been explored and shown to have merit in the human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus systems. In this study, we have assessed the priming capacity of highly attenuated poxvirus vector (NYVAC and ALVAC)-based HIV-2 recombinants, as well as Salmonella typhimurium HIV-2 recombinants in rhesus macaques. ALVAC- and NYVAC-based vaccine candidates expressing the HIV-2 gag, pol, and env genes or NYVAC-based recombinants expressing either gp160 or gp120 were used to immunize rhesus macaques in combination protocols with alum-adjuvanted HIV-2 rgp160. Following intravenous challenge exposure with 100 infectious doses of the HIV-2SBL6669 parental virus genotype mixture, seven of eight animals were protected from infection. The seven protected animals were rechallenged 6 months postprimary challenge, without additional booster inoculations, with the same dose of the HIV-2SBL6669 parental virus. Five of the seven animals remained protected against HIV-2 infection at 6 months following the second challenge. In contrast, oral immunization with recombinant Salmonella expressing the HIV-2 gag and the gp120 portion of the envelope either alone or in combination with alum-adjuvanted rgp160 failed to confer protection. These results suggest that the NYVAC- and ALVAC-based recombinants may confer long-lasting protection and that these two highly attenuated poxvirus vaccine vectors may represent promising candidates for developing an acquired immunodeficiency syndrome vaccine.

Induction of potent humoral and cell-mediated immune responses following direct injection of DNA encoding the HIV type 1 env and rev gene products

DNA vaccines have the potential of giving rise to a potent cell-mediated immune response by inducing intracellular synthesis and subsequent antigenic presentation of encoded antigens. We have tested a DNA vaccine specific for human immunodeficiency virus type 1 (HIV-1) by the injection of animals with expression plasmids encoding the HIV-1 envelope protein and the Rev regulatory protein. Injection of both plasmids into mice, rabbits, or macaques was found to induce high levels of specific antibodies capable of efficiently inhibiting both HIV-1 infection and envelope-mediated cell fusion. A readily detectable delayed-type hypersensitivity (DTH) response was demonstrable in injected mice and lymphocytes derived from these proliferated in response to an HIV-1 envelope V3 loop-specific peptide. Interestingly, the injected mice or macaques also developed a strong cytotoxic T lymphocyte (CTL) response against target cells pulsed with the V3 peptide. Taken together, these data demonstrate that injection of HIV-1 gene expression plasmids can induce potent humoral and cell-mediated immune responses and suggest that DNA vaccines may prove to be significantly beneficial as a means of immunizing against HIV-1.

Presence of neutralizing antibodies to heterologous human immunodeficiency virus type 1 isolates in sera of infected individuals is not predictive of rate of disease progression

These studies were undertaken to examine whether the presence of human immunodeficiency virus type 1 (HIV-1)-neutralizing antibodies in sera of infected individuals would alter the rate of disease progression. HIV-1-infected individuals (n = 87) were initially examined for neutralizing activity in vitro against both laboratory and tissue culture-adapted clinical heterologous HIV-1 isolates. The neutralizing activities of sera were determined by a 90% or greater reduction in HIV-1 p24 levels in vitro. In a cross-sectional analysis of all infected individuals, we observed that sera from asymptomatic individuals neutralized a significantly greater number of heterologous HIV-1 isolates than sera from symptomatic patients. Patients who could be followed up longitudinally (n = 24) were then studied to determine the impact of neutralizing antibodies on the rate of disease progression. We observed no significant difference between the numbers of HIV-1 isolates neutralized in vitro by sera from patients who remained clinically stable and by those from patients who progressed rapidly. Our data indicated that the presence or absence of neutralizing antibodies to heterologous HIV-1 isolates was not associated with the rate of disease progression.

Yeast retrotransposon particles as antigen delivery systems

The development of technologies to produce recombinant proteins for use in the pharmaceutical industry has made substantial advances, in particular in the area of generating antigens containing multiple copies of important immunological regions. One such antigen-carrier system is based on the ability of a protein encoded by the yeast retrotransposon, Ty, to self-assemble into virus-like particles. Ty-fusion proteins retain this ability to form particles, and a range of hybrid VLPs carrying a variety of heterologous antigens have been produced and shown to induce potent immune responses. In particular, hybrid VLPs carrying the core protein p24 of HIV (p24-VLPs) have been shown to induce antibody and T-cell proliferative responses in both experimental animals and human volunteers, and immunization of rabbits with VLPs carrying the principal neutralizing determinant of HIV (V3-VLPs) resulted in the induction of neutralizing antibody responses and T-cell proliferation. Further studies with V3-VLPs have shown that this particulate antigen stimulates enhanced V3-specific lymphoproliferative responses as compared to whole recombinant gp120 or to V3 peptide conjugated to albumin. The V3-VLPs also induce potent CTL responses following immunization of mice in the absence of adjuvant. These responses are MHC class I restricted and are mediated by CD8-positive cells. These observations therefore demonstrate that hybrid Ty-VLPs induce both humoral and cellular immune responses against HIV and suggest that these immunogens may be important in combatting AIDS and other infections.

Neutralising epitopes of simian immunodeficiency virus envelope glycoprotein

Monoclonal and polyclonal antibodies with weak SIV neutralising activity bind to the V2 and V4 regions of gp120 or bind to the amino acids DWNND in gp41. Antibodies with the most potent neutralising activity recognise conformation-dependent epitopes involving the V3 and V4 regions of gp120. Monoclonal antibodies that map to the V3 region of SIVmac failed to neutralise. However, one antibody to SIV AGM neutralised but only in the presence of soluble CD4.

Neutralizing monoclonal antibody against a external envelope glycoprotein (gp110) of SIVmac251

Three monoclonal antibodies (M318T, M56S and M815) against an external envelope glycoprotein (gp110) of simian immunodeficiency virus (SIV) mac251 were obtained by immunizing BALB/c mice with recombinant gp110 (rgp110). All three monoclonal antibodies reacted with the surface of cells infected with SIVmac251 but not with that of uninfected counterparts. The binding activity of these monoclonal antibodies against native gp110 was confirmed by means of Western blotting. One of them, M318T neutralized SIVmac251 infection both by cell-free and cell-associated viruses. M318T cross-reacted with human immunodeficiency virus type 2 strains (HIV-2 GH1 and ROD isolates) and SIVmac239 isolates. However, the antibody did not cross-neutralize these viral strains. Epitope mapping revealed that the neutralizing epitope recognized by M318T was localized at 8 residues between amino acids 178 and 185 (KRDKTKEY) in gp110, corresponding to the V2 region of human immunodeficiency virus type 1 (HIV-1). Because some antibodies against the V2 region of HIV-1 reportedly neutralize virus infection by interfering with CD4-gp120 interaction, we tested the activity of M318T against the binding of CD4-gp110. However, M318T did not inhibit CD4-gp110 interaction, suggesting the involvement of another unknown mechanism of M318T-mediated neutralization. In analogy with the V2 region of HIV-1, the V2 region of SIV contains a type specific neutralizing epitope recognized by M318T. Although some amino acid sequence in the epitope was conserved for the isolates of SIV and HIV-2 and there was cross-reactivity of the antibody against the strains, neutralization by M318T was associated with a single amino acid (182 T) in the epitope.

Characterization of neutralization epitopes in the V2 region of human immunodeficiency virus type 1 gp120: role of glycosylation in the correct folding of the V1/V2 domain

A number of monoclonal antibodies (MAbs) with various levels of neutralizing activity that recognize epitopes in the V1/V2 domain of LAI-related gp120s have been described. These include rodent antibodies directed against linear and conformational epitopes and a chimpanzee MAb, C108G, with extremely potent neutralizing activity directed against a glycan-dependent epitope. A fusion glycoprotein expression system that expressed the isolated V1/V2 domain of gp120 in native form was used to analyze the structural characteristics of these epitopes. A number of MAbs (C108G, G3-4, 684-238, SC258, 11/68b, 38/66a, 38/66c, 38/62c, and CRA3) that did not bind with high affinity to peptides immunoprecipitated a fusion glycoprotein expressing the V1/V2 domain of HXB2 gp120 in the absence of other human immunodeficiency virus sequences, establishing that their epitopes were fully specified within this region. Biochemical analyses indicated that in the majority of V1/V2 fusion molecules only five of the six glycosylation signals in the V1/V2 domain were utilized, and the glycoforms were found to be differentially recognized by particular MAbs. Both C108G and MAbs directed against conformational epitopes reacted with large fractions of the fully glycosylated molecules but with only small fractions of the incompletely glycosylated molecules. Mutational analysis of the V1 and V2 glycosylation signals indicated that in most cases the unutilized site was located either at position 156 or at position 160, suggesting the occurrence of competition for glycan addition at these neighboring positions. Mutation of glycosylation site 160 destroyed the C108G epitope but increased the fraction of the molecules that presented the conformational epitopes, while mutation of the highly conserved glycosylation site at position 156 greatly diminished the expression of the conformational epitopes and increased expression of the C108G epitope. Similar heterogeneity in glycosylation was also observed when the HXB2 V1/V2 fusion glycoprotein was expressed without most of the gp70 carrier protein, and thus, this appeared to be an intrinsic property of the V1/V2 domain. Heterogeneity in expression of conformational and glycan-dependent epitopes was also observed for the natural viral env precursor, gPr160, but not for gp120. These results suggested that the closely spaced glycosylation sites 156 and 160 are often alternatively utilized and that the pattern of glycosylation at these positions affects the formation of the conformational structures needed for both expression of native epitopes in this region and processing of gPr160 to mature env products.

Synthetic peptides representing sequences within gp41 of HIV as immunogens for murine T- and B-cell responses

Within the gp41 glycoprotein of the human immunodeficiency virus type 1 (HIV-1) there is a relatively conserved region which appears accessible to the immune system during the course of HIV infection and is recognised by antibody from virtually all patients with AIDS. This region has also been shown to function as a target for human T cells. We have examined synthetic peptides spanning this sequence, between residues 572 and 604, with a view to evaluating their potential as immunogens. Peptides 572GIKQLQARILAVERYLKDQQ591 and 579RILAVERYLKDQQLLGGIWGCSGK601 were good immunogens in two different strains of mice while peptide 576LQARILAVERYLKDQQ591 was an inferior immunogen, and peptide 593LGIWGCSGKLIC604 was non-immunogenic unless coupled to a carrier protein. For both antibody and T cell responses it was apparent that sequences that could function as determinants within one peptide could not do so in the context of a different peptide immunogen. It follows that by judicious choice of immunogen sequence it may be possible to direct the immune response towards a desired fine specificity. Unwanted responses by CD4+ T cells isolated from certain peptide-primed animals were also observed. These T cells showed an unusual reactivity in that they were incapable of recognising their determinant AVERYLKDQQ if it was extended at the C-terminal end with the native sequence and as such would not be expected to recognise the native molecule unless processing created the identical C-terminus.

Can live attenuated virus work as post-exposure treatment?

Simple mathematical models for the competition between different virus variants in the presence of a crossreactive immune response show that, contrary to expectation, selection can favour variants that induce low viral loads. Here, Sebastian Bonhoeffer and Martin Nowak suggest that such 'competitively superior', but 'less pathogenic', mutants may be a possibility for post-exposure treatment of persistent virus infections.

Human immunodeficiency virus type 1-neutralizing antibodies raised to a glycoprotein 41 peptide expressed on the surface of a plant virus

An oligonucleotide encoding the amino acids 731-752 of the gp41 envelope protein of the human immunodeficiency virus type 1 strain IIIB, which is known to induce cross-reactive neutralizing antibodies in humans, was inserted into a full-length clone of the RNA encoding the coat proteins of cowpea mosaic virus (RNA 2 of CPMV). When transfected together with RNA 1 of CPMV, transcribed RNA 2 was able to replicate in plants and form infectious virions (CPMV-HIV). Purified virions were injected subcutaneously with alum adjuvant into adult C57/BL6 mice to determine their ability to stimulate ELISA and neutralizing antibody specific for HIV-1. Antisera to CPMV-HIV obtained after only two injections gave a strong ELISA response (mean of 1:25,800) using the free gp41 peptide as antigen, showing that the gp41 peptide incorporated into the chimera was immunogenic. The same antisera gave 97% neutralization of HIV-1 IIIB at 1:100 dilution, with a highly uniform response in all (six of six) animals tested. A third injection barely increased the neutralization titer. Normal mouse serum had no neutralizing activity. Antisera also strongly neutralized the HIV-1 strains RF and SF2. ELISA and neutralizing activity to HIV-1 IIIB declined after the second injection and were undetectable after 7 weeks, but were restimulated to the same level after the third injection. Neutralization was marginally more stable after the third injection. Antibody specific for CPMV epitopes was equally short lived. A bonus of this system was unexpected neutralizing activity specifically stimulated by unmodified CPMV virions, although this amounted to no more than 10% of the neutralizing activity stimulated by the CPMV-HIV chimera.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of adjuvants on immunogenicity of MN recombinant glycoprotein 120 in guinea pigs

The immunogenicity of recombinant gp120 from the MN strain of HIV-1, a candidate HIV-1 vaccine, was evaluated in guinea pigs using adjuvant formulations with different physical and chemical properties. The adjuvants tested included Freund's adjuvant (FA), alum, and the novel adjuvant QS-21. These studies demonstrated that QS-21 provides a number of advantages compared to the two other adjuvants tested. QS-21 formulations accelerated the production of antibodies to MN rgp120 and elicited complete seroconversion after a single immunization. QS-21 shifted the antigen dose-response curve for antibody production by as much as three orders of magnitude, enabling a more economical use of antigen. Antibody titers to MN rgp120 and to the principal neutralizing determinant in the V3 domain were higher in animals receiving QS-21 formulations than in animals immunized with the other adjuvants, and correlated well with higher virus neutralization titers in an in vitro assay. These results support the testing of QS-21 in future clinical trials of candidate HIV-1 vaccines.

Regions required for CD4 binding in the external glycoprotein gp120 of simian immunodeficiency virus

The external domain of the envelope glycoprotein, gp120, of simian immunodeficiency virus (SIV) has been expressed as a mature secreted product using recombinant baculoviruses and the expressed protein, which has an observed molecular mass of 110 kDa, was purified by monoclonal antibody (MAb) affinity chromatography. N-terminal sequence analysis showed a signal sequence cleavage identity similar to that of the gp120s of both human immunodeficiency virus type 1 (HIV-1) and HIV type 2. The expressed molecule bound to soluble CD4 with an affinity that was approximately 10-fold lower than that of gp120 from HIV-1. A screening of the ability of SIV envelope MAbs to inhibit CD4 binding revealed two groups of inhibitory MAbs. One group is dependent on conformation, while the second group maps to a discrete epitope near the amino terminus. The particular role of the V3 loop region of the molecule in CD4 binding was investigated by the construction of an SIV-HIV hybrid in which the V3 loop of SIV was precisely replaced with the equivalent domain from HIV-1 MN. The hybrid glycoprotein bound HIV-1 V3 loop MAbs and not SIV V3 MAbs but continued to bind conformational SIV MAbs and soluble CD4 as well as the parent molecule.

Nonclassical mucosal antibodies predominate in genital secretions of HIV-1 infected chimpanzees

To identify mucosal immunity in HIV-infected chimpanzees, IgG, IgA, and IgM from plasma, saliva, rectal swabs, vaginal washes, semen, and urethral washes were tested from four male and three female HIV-1IIIB infected chimpanzees. The level of HIV infections in the seven chimpanzees were classified as high, intermediate and low depending on the number of HIV-1 infected cells per 10(7) peripheral blood mononuclear cells (PBMC). One male chimpanzee had a relatively high viral load, two males and two females had moderate viral loads and one male and one female had low levels of infection. All seven animals had plasma antibody. The principal finding was that nonclassical mucosal antibodies of the IgG isotype were the predominant antibody in the saliva, rectal swabs, vaginal washes, semen, and urethral washes of infected animals. All plasma and mucosal samples were negative for IgM antibodies. The results show that HIV-1 specific IgG responses and not sIgA predominate at mucosal surfaces of HIV-1IIIB infected chimpanzees. A trend was observed in which high viral loads correlated with high plasma IgG, IgA and sIgA titers. An overall correlation between relatively high virus loads and high amounts of mucosal IgG was also found.

Effect of anti-V3 antibodies on cell-free and cell-to-cell human immunodeficiency virus transmission

The present study was undertaken to compare the effects of a type-specific (HIV-1 MN) anti-V3 antibody on in vitro human immunodeficiency virus (HIV) infection of peripheral blood mononuclear cells in systems of cell-free versus cell-to-cell transmission of virus. Anti-V3 antibody completely prevented HIV-1 infection when cell-free virus was the sole mechanism of infection. A significant reduction of the neutralizing activity of the anti-V3 antibody was observed when infectivity was dependent on both cell-free and cell-to-cell mechanisms of infection. Furthermore, when cell-to-cell transfer of virions was the primary mechanism of HIV-1 infection, inhibition of HIV-1 infection was not observed. Therefore, a potent neutralizing antibody with a single epitope specificity failed to effectively control dissemination of a persistent HIV-1 infection in a system characterized predominantly by cell-to-cell transfer of virus.

Primary isolates of human immunodeficiency virus type 1 are relatively resistant to neutralization by monoclonal antibodies to gp120, and their neutralization is not predicted by studies with monomeric gp120

A panel of anti-gp120 human monoclonal antibodies (HuMAbs), CD4-IgG, and sera from people infected with human immunodeficiency virus type 1 (HIV-1) was tested for neutralization of nine primary HIV-1 isolates, one molecularly cloned primary strain (JR-CSF), and two strains (IIIB and MN) adapted for growth in transformed T-cell lines. All the viruses were grown in mitogen-stimulated peripheral blood mononuclear cells and were tested for their ability to infect these cells in the presence and absence of the reagents mentioned above. In general, the primary isolates were relatively resistant to neutralization by the MAbs tested, compared with the T-cell line-adapted strains. However, one HuMAb, IgG1b12, was able to neutralize most of the primary isolates at concentrations of < or = 1 microgram/ml. Usually, the inability of a HuMAb to neutralize a primary isolate was not due merely to the absence of the antibody epitope from the virus; the majority of the HuMAbs bound with high affinity to monomeric gp120 molecules derived from various strains but neutralized the viruses inefficiently. We infer therefore that the mechanism of resistance of primary isolates to most neutralizing antibodies is complex, and we suggest that it involves an inaccessibility of antibody binding sites in the context of the native glycoprotein complex on the virion. Such a mechanism would parallel that which was previously postulated for soluble CD4 resistance. We conclude that studies of HIV-1 neutralization that rely on strains adapted to growth in transformed T-cell lines yield the misleading impression that HIV-1 is readily neutralized. The more relevant primary HIV-1 isolates are relatively resistant to neutralization, although these isolates can be potently neutralized by a subset of human polyclonal or monoclonal antibodies.

Neutralization of primary human immunodeficiency virus type 1 isolates by the broadly reactive anti-V3 monoclonal antibody, 447-52D

Human monoclonal antibody 447-52D binds to the V3 determinant of the human immunodeficiency virus type 1 (HIV-1) gp120 external glycoprotein. Its binding requires the expression of the GPxR sequence at the center of the V3 domain. HIV-1 variants that are adapted to replication in T-lymphoid cell lines and express this sequence motif are efficiently neutralized by the antibody (M. K. Gorny, A. J. Conley, S. Karwowska, A. Buchbinder, J.-Y. Xu, E. A. Emini, S. Koenig, and S. Zolla-Pazner, J. Virol. 66:7538-7542, 1992). In the present study, the antiviral activity of 447-52D was further defined with regard to its ability to mediate neutralization of primary HIV-1 clinical isolates. Again, the antibody was found to potently neutralize those isolates that expressed the binding sequence. We confirmed that this determinant is commonly expressed by virus isolates belonging to the subtype (clade) B sequence classification. As such, 447-52D may be useful for prophylactic and immunotherapeutic intervention. In addition, the study demonstrated that neutralization of primary HIV-1 isolates is possible if mediated by an appropriate antibody.

Immunoreactivity of chimeric proteins carrying the HIV-1 epitope IGPGRAF. Correlation between predicted conformation and antigenicity

Sera from HIV-1 infected individuals were examined for their reactivity to the principal neutralizing domain, IGPGRAF sequence, of the V3-loop of HIV-1. Four hybrid proteins carrying this sequence inserted in four different outer loops of a protein that makes up the capsid of an insect virus were used as antigen in a Western blot assay for this survey. All the four antigens showed different activity: sera that recognise all antigens to sera that reacted with only one of them. Competition experiments indicated that the antibodies recognised these proteins with different affinity. Molecular modelling of the hybrid proteins predicted that the inserted sequence adopted different conformations in each position. Comparison of predicted most stable conformations for IGPGRAF indicated that there is a close relationship between conformational similarity to a V3-loop reference structure and the degree of reactivity with sera.

Fine analysis of humoral antibody response to envelope glycoprotein of SIV in infected and vaccinated macaques

To characterize the serological response to SIV envelope, induced by vaccination with different envelope immunogens or by SIV infection, plasma samples from 11 cynomolgus macaques infected with simian immunodeficiency virus (SIV) and from 16 macaques vaccinated with three different recombinant envelope proteins were analyzed by (1) ELISA, using a variety of antigens including overlapping peptides encompassing the entire sequence of the envelope protein of SIV, and (2) competition assays, using neutralizing monoclonal antibodies to SIV gp120. Seven regions of SIV envelope were predicted to be antigenic. Peptides representing four of these, in the second and third variable regions (V2 and V3) and the fourth constant (C4) region of gp120 and the Gnann region of gp41, were recognized by the majority of sera from infected and vaccinated animals. Additional antigenic regions were identified in the first and fourth variable domains (V1 and V4) and the carboxy terminus (C5) of gp120 and in three additional regions of gp41. Most infected and vaccinated animals made antibodies that competed with the binding of the three conformational MAbs. Among the vaccinated groups, antibodies induced by vaccination with precursor glycoproteins (gp140 or gp160) recognized several additional gp120 epitopes when compared with antibodies induced by external glycoprotein gp130. Sera from infected animals showed a more restricted gp120 response (17 of 46 peptides recognized) compared to animals vaccinated with precursor glycoproteins (31 peptides recognized). The converse was true for antibodies to gp41. Sera from animals vaccinated with recombinant gp140, produced in insect cells, were the only group that failed to compete with the binding of conformational MAbs. Finally, the development of antibodies to specific epitopes of gp120 and gp41 revealed differences between long-term survivors and nonsurvivors, implying that responses to specific epitopes may be important in conferring resistance to disease progression.

Nef and Gag synthetic peptide priming of antibody responses to HIV type 1 antigens in mice and primates

T epitope mapping in human immunodeficiency virus proteins provides a useful tool for AIDS vaccine design. We have previously shown that four peptides selected from the Gag polyprotein of HIV-1 were able to prime mice for in vitro lymphoproliferative responses. These responses were shown to be MHC restricted, and a pool of these peptides was able to prime mice for a subsequent humoral response to HIV-1 Gag proteins. Here we show that two of these Gag peptides are able to prime the anti-HIV-1 IgG response to heat-inactivated HIV-1 in B10Sc.Cr mice. Furthermore, we extended this study in the nonhuman primate model, and show efficient priming of the IgG response to heat-inactivated HIV-1 using the pool of four Gag peptides in baboons. Further mapping of "nonself" peptides is extended to the HIV-1 Nef protein. Three potential Nef T epitopes located at positions 137-145, 98-107, and 81-95 are also shown to prime the IgG response to HIV-1 in the mouse model, although T cell proliferation to recall peptides in vitro was not detectable. Although they have not yet been defined as major helper T epitopes in humans, using classic in vitro stimulation assays, the fact that most of them are able to prime IgG responses in animals without detectable in vitro proliferative responses does not rule out their functional helper capacity in humans.

Vaccine-induced neutralizing antibodies directed in part to the simian immunodeficiency virus (SIV) V2 domain were unable to protect rhesus monkeys from SIV experimental challenge

The potential of the simian immunodeficiency virus (SIV) variable 2 (V2) domain as an effective region to boost SIV-neutralizing antibodies and to protect against live SIV challenge was tested in rhesus macaques. In this study, two rhesus macaques were primed with vaccinia virus recombinants expressing the surface glycoprotein gp140 of SIVmac and were given booster injections with the SIVmac V2 domain presented by a highly immunogenic carrier, the hepatitis B surface antigen (HBsAg). The two vaccinated macaques exhibited SIV-neutralizing antibodies after primer injections that were enhanced by the V2/HBsAg injections. Part of these SIV-neutralizing antibodies were directed specifically to the V2 region, as shown by neutralization-blocking experiments. However, despite having consistent SIV-neutralizing antibody titers, animals were not protected against homologous challenge with BK28, the molecular clone of SIVmac251. No SIV envelope-specific cellular cytotoxic response was detected throughout the immunization protocol, suggesting that neutralizing antibodies directed to SIV envelope gp140 and especially to the V2 domain were unable on their own to protect against SIV challenge. Furthermore, the vaccinees seemed to have higher viral loads than control animals after challenge, raising the question of whether neutralizing antibodies induced by vaccination and directed to the SIV envelope selected viral escape mutants, as shown previously in SIV-infected macaques. This mechanism is certainly worthy of intensive investigation and raises some concern for SIV envelope-targeted immunization.

A simian immunodeficiency virus envelope V3 cytotoxic T-lymphocyte epitope in rhesus monkeys and its restricting major histocompatibility complex class I molecule Mamu-A*02

The use of the simian immunodeficiency virus (SIV) macaque model for assessing human immunodeficiency virus vaccine strategies will be facilitated by the characterization of predominant SIV cytotoxic T-lymphocyte (CTL) epitopes and their restricting major histocompatibility complex (MHC) class I molecules in macaque species. We now define a rhesus monkey SIVmac CTL epitope in the third hypervariable region of the envelope glycoprotein of the virus. This epitope, YNLTMKCR, contains the first two amino acids of a cysteine-cysteine loop which is the SIVmac analog of the human immunodeficiency virus type 1 V3 loop. We also employed one-dimensional isoelectric focusing to characterize the MHC class I molecule of the rhesus monkey that binds this SIVmac envelope peptide fragment. Cloning and sequencing the cDNA encoding this rhesus monkey MHC class I molecule demonstrates that it is a newly described HLA-A homolog, Mamu-A*02. This viral CTL epitope and its restricting MHC class I molecule will facilitate the use of the SIVmac rhesus monkey model for studies of envelope-based vaccine strategies and for exploring AIDS immunopathogenesis.

Enhanced activation of human T cell clones specific for virus-like particles expressing the HIV V3 loop in the presence of HIV V3 loop-specific polyclonal antibodies

Recombinant virus-like particles (VLP), formed by the yeast Ty p1 protein, carrying the HIV gp120 V3 loop on their surface (V3-VLP) have been tested in vitro for immunogenicity and antigenicity by using VLP p1-specific human CD4+ T cell lines and clones. VLP-specific human T cell lines and clones were generated from normal individuals, indicating that VLP-specific precursor cells present in the peripheral lymphocyte pool can be induced to expand clonally upon antigen challenge in vitro, in the absence of previous immunization. It was also shown that V3-specific polyclonal antibodies enhance V3-VLP-induced activation of VLP-specific T cell clones. Antibody-dependent potentiation has been shown previously in other antigen systems, and it depends on enhanced uptake of complexed antigen by Fc receptor-positive antigen-presenting cells. Since in this case antigen is internalized by presenting cells as a complex, it can be inferred that a similar event of antibody-mediated antigen uptake can take place with V3-specific B cells, resulting in presentation by the B cells of T helper epitopes derived from processing of the VLP p1 moiety. This suggests that T helper cells specific for the carrier VLP p1 protein can be activated to provide help to V3-specific B cells in the presence of the appropriate antigen construct.

The induction of in vivo superinfection and recombination using feline immunodeficiency virus as the model

This study investigated the hypothesis that under certain conditions, superinfection of cats with feline immunodeficiency virus (FIV), may occur. One FIV isolate (T91) was used to inoculate three FIV and FeLV-free cats. Blood from an FIV-infected cat (N), which contained two variants and differed from T91 by at least 5% in nucleotide sequence in the env gene, was inoculated into a fourth cat. Both T91 and blood from N were inoculated simultaneously into a fifth cat. After 22 weeks, two of the three cats initially infected with T91 were challenged with blood from N. At 30 weeks following initial infection, peripheral blood mononuclear cells were obtained from all cats, DNA was extracted, and a segment of the env gene was PCR amplified, cloned and sequenced. Nucleotide sequence analysis of the cloned PCR product showed that virus strains used in initial infection were recovered from cats not challenged with a second variant. Challenge of cats with the blood of N following initial infection with T91 resulted in superinfection occurring in one cat and recombination occurring in the other. Furthermore, the use of blood as a source of challenge, in cats where superinfection and simultaneous infections were attempted, may have induced the appearance of variants which more closely resembled the most heterologous strain present in the infectious source.

Immunization with a soluble CD4-gp120 complex preferentially induces neutralizing anti-human immunodeficiency virus type 1 antibodies directed to conformation-dependent epitopes of gp120

Preservation of the conformation of recombinant gp120 in an adjuvant, enabling it to elicit conformation-dependent, epitope-specific, broadly neutralizing antibodies, may be critical for the development of any gp120-based human immunodeficiency virus type 1 (HIV-1) vaccine. It was hypothesized that recombinant gp120 complexed with recombinant CD4 could stabilize the conformation-dependent neutralizing epitopes and effectively deliver them to the immune system. Therefore, a soluble CD4-gp120 complex in Syntex adjuvant formulation was tested with mice for its ability to induce neutralizing anti-gp120 antibody responses. Seventeen monoclonal antibodies (MAbs) were generated and characterized. Immunochemical studies, neutralization assays, and mapping studies with gp120 mutants indicated that the 17 MAbs fell into three groups. Four of them were directed to what is probably a conformational epitope involving the C1 domain and did not possess virus-neutralizing activities. Another four MAbs bound to V3 peptide 302-321 and exhibited cross-reactive gp120 binding and relatively weak virus-neutralizing activities. These MAbs were very sensitive to amino acid substitutions, not only in the V3 regions but also in the base of the V1/V2 loop, implying a conformational constraint on the epitope. The last group of nine MAbs recognized conformation-dependent epitopes near the CD4 binding site of gp120 and inhibited the gp120-soluble CD4 interaction. Four of these nine MAbs showed broadly neutralizing activities against multiple laboratory-adapted strains of HIV-1, three of them neutralized only HIVIIIB, and the two lower-affinity MAbs did not neutralize any strain tested. Collectively, the results from this study indicate that immunization with the CD4-gp120 complex can elicit antibodies to conformationally sensitive gp120 epitopes, with some of the antibodies having broadly neutralizing activities. We suggest that immunization with CD4-gp120 complexes may be worth evaluating further for the development of an AIDS vaccine.

Major histocompatibility complex class I-associated vaccine protection from simian immunodeficiency virus-infected peripheral blood cells

To evaluate the effectiveness of vaccine protection from infected cells from another individual of the same species, vaccinated rhesus macaques (Macaca mulatta) were challenged with peripheral blood mononuclear cells from another animal diagnosed with acquired immune deficiency syndrome (AIDS). Half of the simian immunodeficiency virus (SIV)-vaccinated animals challenged were protected, whereas unprotected vaccinates progressed as rapidly to AIDS. Protection was unrelated to either total antibody titers to human cells, used in the production of the vaccine, to HLA antibodies or to virus neutralizing activity. However, analysis of the serotype of each animal revealed that all animals protected against cell-associated virus challenge were those which were SIV vaccinated and which shared a particular major histocompatibility complex (MHC) class I allele (Mamu-A26) with the donor of the infected cells. Cytotoxic T lymphocytes (CTL) specific for SIV envelope protein were detected in three of four protected animals vs. one of four unprotected animals, suggesting a possible role of MHC class I-restricted CTL in protection from infected blood cells. These findings have possible implications for the design of vaccines for intracellular pathogens such as human immunodeficiency virus (HIV).

Recognition properties of a panel of human recombinant Fab fragments to the CD4 binding site of gp120 that show differing abilities to neutralize human immunodeficiency virus type 1

Six recombinant human Fab fragments that were derived from the same human immunodeficiency virus type 1 (HIV-1)-infected individual and are directed against the CD4 binding site (CD4bs) of the gp120 envelope glycoprotein were studied. A range of neutralizing activity against the HIV-1 (HXBc2) isolate was observed, with Fab b12 exhibiting the greatest potency among the Fabs tested. The neutralizing potency of Fab b12 was better than that of monoclonal whole antibodies directed against the third variable (V3) region of gp120. To explore the basis for the efficient neutralizing activity of b12, the recognition of a panel of HIV-1 gp120 mutants by the six Fabs was studied. The patterns of sensitivity to particular gp120 amino acid changes were similar for all six Fabs to those seen for anti-CD4bs monoclonal antibodies derived from HIV-1-infected individuals by conventional means. In addition, recognition by Fab b12 demonstrated an atypical sensitivity to changes in the V1 and V2 variable regions. Next, the binding of the Fabs to monomeric gp120 and to the envelope glycoprotein complex was examined. Neither the binding properties of the b12 Fab to monomeric gp120 nor the ability of the Fab to compete with soluble CD4 for monomeric gp120 binding appeared to account for the greater neutralizing potency. However, both quantitative and qualitative differences between the binding of b12 and that of less potent Fabs to the cell surface envelope glycoprotein complex were observed. Relative to less potently neutralizing Fabs, Fab b12 exhibited a higher affinity for a subpopulation of cell surface envelope glycoproteins, the conformation of which was best approximated by the mature gp120 glycoprotein. Apparently, subtle differences in the gp120 epitope recognized allow some members of the group of anti-CD4bs antibodies to bind to the functionally relevant envelope glycoprotein complex and to neutralize virus more efficiently.

Serum neutralization of feline immunodeficiency virus is markedly dependent on passage history of the virus and host system

Sera from feline immunodeficiency virus (FIV)-infected cats exhibited extremely low levels of neutralizing antibodies against virus passaged a few times in vitro (low passage), when residual infectivity was assayed in the CD3+ CD4- CD8- MBM lymphoid cell line or mitogen-activated peripheral blood mononuclear cells. By sharp contrast, elevated titers of highly efficient neutralizing activity against FIV were measured, by use of high-passage virus, in assays on either the fibroblastoid CrFK or MBM cell line. However, high-passage virus behaved the same as low-passage virus after one in vivo passage in a specific-pathogen-free cat and reisolation. Subneutralizing concentrations of infected cat sera enhanced the production of low-passage virus by MBM cells, an effect not seen with high-passage virus in CrFK cells. These qualitative and quantitative discrepancies could not be attributed to differences in the amount of immunoreactive viral material, to the amount of infectious virus present in the viral stocks, or to the presence of anti-cell antibodies. The observed effects were most likely due to the different passage history of the viral preparations used. The observation that neutralizing antibodies detected with high-passage virus were broadly cross-reactive in assays with CrFK cells but isolate specific in MBM cells suggests also that the cell substrate can influence the result of FIV neutralization assays. This possibility could not be tested directly because FIV adapted to grow in CrFK cells had little infectivity for lymphoid cells and vice versa. In vitro exposure to infected cat sera had little or no effect on the ability of in vivo-passaged FIV to infect cats. These data reveal no obvious relationship between titers against high-passage virus and ability to block infectivity of FIV in cats and suggest caution in the use of such assays to measure vaccine efficacy. In conclusion, by contrast with what has been previously reported for the use of CrFK cells and high-passage virus, both natural and experimental infections of cats with FIV generate poor neutralizing antibody responses with regard to in vivo protection.

A novel, glycan-dependent epitope in the V2 domain of human immunodeficiency virus type 1 gp120 is recognized by a highly potent, neutralizing chimpanzee monoclonal antibody

An anti-gp120 monoclonal antibody (MAb), C108G (gamma 1, kappa), was isolated from a chimpanzee that had been infected with strain IIIB of human immunodeficiency virus type 1 (HIV-1IIIB) and subsequently immunized with the recombinant glycoprotein rgp160MN. This MAb is specific for the IIIB strain of HIV-1 and related clones and exhibits very potent neutralization of these viruses; e.g., 100% neutralization of approximately 8 x 10(3) infectious units of HXB2 was achieved with 125 ng of C108G per ml. Commensurate with this potent neutralizing activity, the apparent affinity of C108G for rgp160LAI was very high, i.e., approximately 3 x 10(10) liters/mol. The C108G epitope was not destroyed by reduction of gp120 disulfide bonds but was profoundly disrupted by removal of N-linked sugars from gp120. Despite the importance of a glycan(s) in forming the C108G epitope, specific binding of C108G to synthetic peptides overlapping in amino acids 162 to 169 of the V2 region was detected, albeit with an affinity approximately 2,000-fold lower than that of C108G's binding to glycosylated envelope protein. This epitope mapping correlated with results of competition assays using MAbs of known epitope specificities. To our knowledge, this is the first description of an anti-V2 MAb raised in response to HIV-1 infection. Its potent neutralizing activity and epitope specificity indicate that the V2 domain of gp120 may be an effective target of the protective immune response and, therefore, potentially an important component of HIV vaccines.

Neutralization of divergent human immunodeficiency virus type 1 variants and primary isolates by IAM-41-2F5, an anti-gp41 human monoclonal antibody

The antiviral characteristics of monoclonal antibody IAM-41-2F5 (2F5) were determined in cell culture. The antibody had been previously shown to bind a specific sequence, ELDKWA, within the external domain of the gp41 envelope glycoprotein human immunodeficiency virus type 1 (HIV-1). Selection by 2F5 of recombinant phage from an epitope library confirmed the identification of the antibody's binding determinant. The antibody was found to be capable of neutralizing a broad range of lymphoid cell culture-adapted HIV-1 variants as well as HIV-1 primary isolates. Sequence analysis of the latter showed that neutralization was related to the presence of the antibody binding site. From kinetic measurements using an epitope-containing peptide or gp41, the half-time of dissociation for 2F5 was determined to be 122 min for the peptide and 156 min for gp41. The region of gp41 expressing this sequence exhibits greater conservation among HIV-1 isolates than do the variable domains of gp120.

Epitope mapping and topology of baculovirus-expressed HIV-1 gp160 determined with a panel of murine monoclonal antibodies

To define protein folding patterns of HIV-1 Env subunit vaccines, we have isolated a set of 30 monoclonal antibodies (MAbs) from BALB/c mice immunized with a recombinant gp160 vaccine (rgp160) expressed in a baculovirus system. This article describes epitope mapping for the MAb panel and topology of the epitopes for rgp160 and a recombinant gp120 (rgp120) also expressed in a baculovirus system. The following results are reported: (1) rgp160 harbors a minimum of 4 antigenic domains, 3 mapping to the C1, C2, and C3/V4 regions of gp120 and 1 mapping to the cytoplasmic tail of gp41; (2) there are at least 3 adjacent or overlapping epitopes in each antigenic domain; (3) a minimum of 14 independent epitopes were mapped, all of which are continuous sites; (4) each of the epitopes is exposed on rgp160 without prior manipulation of the protein; and (5) by contrast, 6 of the 8 epitopes mapping to the C1, C2, and C3/V4 regions are not exposed on rgp120, but become exposed when the protein is denatured. Taken together, these results show that rgp160 and rgp120 are folded differently, illustrating the use of this MAb panel to compare epitope topographies of recombination HIV-1 Env proteins. This MAb panel may aid in the refinement of HIV-1 Env subunit vaccines.

Studies of the conformation-dependent neutralizing epitopes of simian immunodeficiency virus envelope protein

It has been shown previously that the major neutralizing epitopes in simian immunodeficiency virus (SIV) are discontinuous and conformation dependent and that the V3 loop, in contrast to that of human immunodeficiency virus (HIV) type 1, does not by itself elicit neutralizing antibodies (K. Javaherian et al., Proc. Natl. Acad. Sci. USA 89:1418-1422, 1992). We now present data showing that on the basis of fractionation of infected macaque sera, protease digestion of the envelope, and binding properties of two neutralizing monoclonal antibodies to SIV and SIV-HIV chimeric envelope proteins, changes in V3 can disrupt the conformation-dependent neutralization region. The chimeric protein did not produce significant neutralizing antibodies against either SIV or HIV. We also report that neutralizing antibodies elicited by recombinant SIV envelope proteins of mac251 and B670 isolates cross-neutralize. Finally, we show that deglycosylation of the SIV envelope results in a molecule which binds neither soluble CD4 nor the neutralizing monoclonal antibodies being investigated here and does not elicit sera with a significant neutralizing titer.

Effect of sialic acid removal on the antibody response to the third variable domain of human immunodeficiency virus type-1 envelope glycoprotein

The gp160 envelope glycoprotein of human immunodeficiency virus type-1 (HIV-1) is an essential component of current vaccine trials. The glycans of gp160, part of which are highly sialylated, have been shown to influence gp160 immunogenicity. Here, using a panel of synthetic V3 peptides, we characterized the anti-V3 antibodies generated in rabbits immunized by desialylated recombinant gp160LAI. Amino acid residues flanking the GPGR tip of V3 were necessary for the recognition by anti-V3 antibodies raised against either the native or desialylated gp160. Both types of antibodies reacted to V3 peptides of MN and SF2 strains and with a North American/European V3 consensus peptide, while anti-desialylated gp160LAI antibodies reacted in addition to the V3 of CDC4, WMJ2 and NY5 strains. Yet, the V3 peptides did not significantly differ in their secondary structure, as determined by circular dichroism. The titer and avidity for V3MN of anti-desialylated gp160LAI antibodies were significantly lower than those of anti-native gp160LAI, which likely accounts for the inability of anti-desialylated gp160LAI sera to neutralize HIV-1MN-induced syncytia. These results indicate that V3 immunogenicity may be influenced by subtle directed changes in the gp160 glycosylation pattern.

Incomplete protection, but suppression of virus burden, elicited by subunit simian immunodeficiency virus vaccines

We compared the efficacy of immunization with either simian immunodeficiency virus (SIV) Env glycoprotein (Env), Env plus Gag proteins (Gag-Env), or whole inactivated virus (WIV), with or without recombinant live vaccinia vector (VV) priming, in protecting 23 rhesus macaques (six vaccine and two control groups) from challenge with SIVmac251 clone BK28. Vaccination elicited high titers of syncytium-inhibiting and anti-Env (gp120/gp160) antibodies in all vaccinated macaques and anti-Gag (p27) antibodies in groups immunized with WIV or Gag-Env. Only WIV-immunized macaques developed anticell (HuT78) antibodies. After homologous low-dose intravenous virus challenge, we used frequency of virus isolation, provirus burden, and change in antibody titers to define four levels of resistance to SIV infection as follows. (i) No infection ("sterilizing" immunity) was induced only in WIV-immunized animals. (ii) Abortive infection (strong immunity) was defined when virus or provirus were detected early in the postchallenge period but not thereafter and no evidence of virus or provirus was detected in terminal tissues. This response was observed in two animals (one VV-Env and one Gag-Env). (iii) Suppression of infection (incomplete or partial immunity) described a gradient of virus suppression manifested by termination of viremia, declining postchallenge antibody titers, and low levels (composite mean = 9.1 copies per 10(6) cells) of provirus detectable in peripheral blood mononuclear cells or lymphoid tissues at termination (40 weeks postchallenge). This response occurred in the majority (8 of 12) of subunit-vaccinated animals. (iv) Active infection (no immunity) was characterized by persistent virus isolation from blood mononuclear cells, increasing viral antibody titers postchallenge, and high levels (composite mean = 198 copies per 10(6) cells) of provirus in terminal tissues and blood. Active infection developed in all controls and two of three VV-Gag-Env-immunized animals. The results of this study restate the protective effect of inactivated whole virus vaccines produced in heterologous cells but more importantly demonstrate that a gradient of suppression of challenge virus growth, reflecting partial resistance to SIV infection, is induced by subunit vaccination. The latter finding may be pertinent to studies with human immunodeficiency virus vaccines, in which it is plausible that vaccination may elicit significant suppression of virus infection and pathogenicity rather than sterilizing immunity.

Cross-reactivity between autoimmune anti-U1 snRNP antibodies and neutralizing epitopes of HIV-1 gp120/41

We report extensive amino acid sequence homology between HIV-1 gp120/41, and > 33% of a U1 RNA-associated splicing protein, 70K. The latter is a target of autoimmune anti-RNP antibodies in mixed connective tissue disease (MCTD). The homologies, involving dominant epitopes of 70K and neutralizing epitopes of gp120/41, are the basis for mutual antibody cross-reactivity. A key finding is that the epitope GRAFVTIG in the V3 loop of gp120 (strain IIIB) is homologous to the functionally essential U1 RNA-binding site of 70K. ELISA data reveal a mean reactivity of anti-RNP antibodies to V3 IIIB that is as high as that of HIV sera. V3 MN, containing the framework sequence G-AF-T, also cross-reacts with anti-RNP antibodies, as do hydrophilic epitopes in gp41 homologous to the COOH end of 70K. Further, there is strong cross-reactivity between HIV sera and 70K in Western blots. In contrast, antibodies from a related autoimmune disorder, Sjögren's syndrome (SS), are neither V3 nor gp41 selective. We conclude that the substantial cross-reactivities reported here are due to conserved, antigenically dominant B cell epitopes having homologous counterparts in 70K and gp120/41. Because antibody production in both MCTD and HIV-1 infection is T cell dependent, the results imply that common T cell clones are also activated in these two disease paradigms. Further exploration of the mechanisms that activate these clones, and that control their divergent fates in MCTD and AIDS, may provide new insights into immune dysregulation in HIV infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of mutants of human immunodeficiency virus type 1 that have escaped neutralization by a monoclonal antibody to the gp120 V2 loop

The biologically cloned human immunodeficiency virus type 1 (HIV-1) RF isolate is sensitive to neutralization by the murine monoclonal antibody (MAb) G3-4 to a conformationally sensitive epitope in the V2 loop of HIV-1 gp120. To assess how variation in the V2 amino acid sequence affects neutralization by this MAb, we cultured RF in the presence of G3-4 to select neutralization escape mutants. Three such mutants resistant to G3-4 neutralization were generated from three independent experiments. Solubilized gp120 from each of these escape mutants had a reduced affinity for G3-4 and also for two other V2 MAbs that were able to bind the wild-type RF gp120. PCR sequencing of the entire gp120 of the wild-type RF virus and the escape mutants showed that amino acid substitutions had occurred only at two positions, Y177H and L179P, both in V2. Experimental introduction of the Y177H substitution into the RF V2 loop in the context of the NL4-3 molecular clone re-created the G3-4-resistant phenotype. The L179P mutant was not viable. Thus, our findings confirm that the HIV-1 V2 loop contains the conformationally sensitive neutralization epitope recognized by G3-4 and that a single amino acid substitution within this region can result in escape variants that arise from immune selection pressure.

Production of long-lived neutralizing antibodies to HIV-1 IIIB in mice with a vaccinia recombinant virus-infected cell vaccine expressing gp160

A formaldehyde-fixed cell vaccine in adjuvant (syngeneic cells infected with a vaccinia virus recombinant expressing gp160: vacc-gp160) stimulated only nonneutralizing antibody when used on its own in four strains of mice, but a similar nonfixed cell vaccine stimulated neutralizing antibodies up to a titer of 1/320 in C57BL/6 (H-2b) mice previously infected with live vacc-gp160. Synthesis of ELISA antibodies to rgp120 or rgp160 did not correspond closely to the synthesis of neutralizing antibodies and should not therefore be used to monitor the production of neutralizing antibody. The ELISA antibody response produced by boosting with the cell vaccine made with the vaccinia virus expressing gp160 under the control of a T7 promoter (vacc-gp160-PT7) was as high as that in mice given an approximately 10-fold higher dose of purified rgp160. The ELISA antibody response to the cell vaccine made with vacc-gp160-PT7 was better than that in which gp160 was expressed under the vaccinia early/late promoter (vacc-gp160-P7.5). Nearly all mice (92%; 11 of 12) primed by infection with vacc-gp160 produced comparable levels of neutralizing antibodies after a single boost with rgp160, vacc-gp160-PT7-infected cells, or vacc-gp160-P7.5-infected cells. Neutralization titers peaked at around day 22 after boost, and declined by day 29. A second boost with the same vacc-gp160-infected cells gave increased neutralizing titers in all (eight of eight) mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of inactivated whole HIV-2 vaccines with various adjuvants in cynomolgus monkeys

Twenty-one cynomolgus monkeys were immunized with whole inactivated HIV-2 preparations administered with various adjuvants (incomplete Freund's adjuvant, Alum, Ribi, MDP, or Iscoms) and challenged with 10 or 100 MID50 of a homologous monkey-cell grown, cell-free HIV-2. Seven animals were completely protected against infection, three showed reduced virus replication. The vaccines elicited neutralizing and ADCC antibodies; the titers did not correlate with protection. Immunization with a whole inactivated vaccine can protect primates from intravenous challenge with a monkey-cell grown cell-free human immunodeficiency virus type 2.

Chimpanzees in AIDS research: a biomedical and bioethical perspective

The present article represents a consensus view of the appropriate utilization of chimpanzees in AIDS research arrived at as a result of a meeting of a group of scientists involved in AIDS research with chimpanzees and bioethicists. The paper considers which types of studies are scientifically justifiable in this species, the conditions under which such studies should be carried out, and the conditions which should be encouraged for post-experimental retirement of these animals.