Identification and characterization of sera from HIV-infected individuals with broad cross-neutralizing activity against group M (env clade A-H) and group O primary HIV-1 isolates

Three families of CD4-induced antibodies are associated with the capacity of plasma from people living with HIV to mediate ADCC in the presence of CD4-mimetics

CD4-mimetics (CD4mcs) are small molecule compounds that mimic the interaction of the CD4 receptor with HIV-1 envelope glycoproteins (Env). Env from primary viruses normally samples a "closed" conformation that occludes epitopes recognized by CD4-induced (CD4i) non-neutralizing antibodies (nnAbs). CD4mcs induce conformational changes on Env resulting in the exposure of these otherwise inaccessible epitopes. Here, we evaluated the capacity of plasma from a cohort of 50 people living with HIV to recognize HIV-1-infected cells and eliminate them by antibody-dependent cellular cytotoxicity (ADCC) in the presence of a potent indoline CD4mc. We observed a marked heterogeneity among plasma samples. By measuring the levels of different families of CD4i Abs, we found that the levels of anti-cluster A, anti-coreceptor binding site, and anti-gp41 cluster I antibodies are responsible for plasma-mediated ADCC in the presence of CD4mc.

IMPORTANCE

There are several reasons that make it difficult to target the HIV reservoir. One of them is the capacity of infected cells to prevent the recognition of HIV-1 envelope glycoproteins (Env) by commonly elicited antibodies in people living with HIV. Small CD4-mimetic compounds expose otherwise occluded Env epitopes, thus enabling their recognition by non-neutralizing antibodies (nnAbs). A better understanding of the contribution of these antibodies to eliminate infected cells in the presence of CD4mc could lead to the development of therapeutic cure strategies.

Applying Flow Virometry to Study the HIV Envelope Glycoprotein and Differences Across HIV Model Systems

The HIV envelope glycoprotein (Env) is a trimeric protein that facilitates viral binding and fusion with target cells. As the sole viral protein on the HIV surface, Env is important both for immune responses to HIV and in vaccine designs. Targeting Env in clinical applications is challenging due to its heavy glycosylation, high genetic variability, conformational camouflage, and its low abundance on virions. Thus, there is a critical need to better understand this protein. Flow virometry (FV) is a useful methodology for phenotyping the virion surface in a high-throughput, single virion manner. To demonstrate the utility of FV to characterize Env, we stained HIV virions with a panel of 85 monoclonal antibodies targeting different regions of Env. A broad range of antibodies yielded robust staining of Env, with V3 antibodies showing the highest quantitative staining. A subset of antibodies tested in parallel on viruses produced in CD4+ T cell lines, HEK293T cells, and primary cells showed that the cellular model of virus production can impact Env detection. Finally, in addition to being able to highlight Env heterogeneity on virions, we show FV can sensitively detect differences in Env conformation when soluble CD4 is added to virions before staining.

V1/V2 Neutralizing Epitope is Conserved in Divergent Non-M Groups of HIV-1

Supplemental Digital Content is Available in the Text.

Background:

Highly potent broadly neutralizing monoclonal antibodies (bNAbs) have been obtained from individuals infected by HIV-1 group M variants. We analyzed the cross-group neutralization potency of these bNAbs toward non-M primary isolates (PI).

Material and Methods:

The sensitivity to neutralization was analyzed in a neutralization assay using TZM-bl cells. Twenty-three bNAbs were used, including reagents targeting the CD4-binding site, the N160 glycan-V1/V2 site, the N332 glycan-V3 site, the membrane proximal external region of gp41, and complex epitopes spanning both env subunits. Two bispecific antibodies that combine the inhibitory activity of an anti-CD4 with that of PG9 or PG16 bNAbs were included in the study (PG9-iMab and PG16-iMab).

Results:

Cross-group neutralization was observed only with the bNAbs targeting the N160 glycan-V1/V2 site. Four group O PIs, 1 group N PI, and the group P PI were neutralized by PG9 and/or PG16 or PGT145 at low concentrations (0.04–9.39 μg/mL). None of the non-M PIs was neutralized by the bNAbs targeting other regions at the highest concentration tested, except 10E8 that neutralized weakly 2 group N PIs and 35O22 that neutralized 1 group O PI. The bispecific bNAbs neutralized very efficiently all the non-M PIs with IC₅₀ below 1 μg/mL, except 2 group O strains.

Conclusion:

The N160 glycan-V1/V2 site is the most conserved neutralizing site within the 4 groups of HIV-1. This makes it an interesting target for the development of HIV vaccine immunogens. The corresponding bNAbs may be useful for immunotherapeutic strategies in patients infected by non-M variants.

Detection of HIV-1 neutralizing antibodies in a human CD4⁺/CXCR4⁺/CCR5⁺ T-lymphoblastoid cell assay system

Sensitive assays are needed to meaningfully assess low levels of neutralizing antibodies (NAbs) that may be important for protection against the acquisition of HIV-1 infection in vaccine recipients. The current assay of choice uses a non-lymphoid cell line (TZM-bl) that may lack sensitivity owing to over expression of CD4 and CCR5. We used transfection of a human CD4+/CXCR4+/α4β7+ T-lymphoblastoid cell line (A3.01) with a CMV IE promoter-driven CCR5neo vector to stably express CCR5. The resulting line, designated A3R5, is permissive to a wide range of CCR5-tropic circulating strains of HIV-1, including HIV-1 molecular clones containing a Tat-inducible Renilla luciferase reporter gene and expressing multiple Env subtypes. Flow cytometric analysis found CCR5 surface expression on A3R5 cells to be markedly less than TZM-bl but similar to CD3.8 stimulated PBMC. More importantly, neutralization mediated by a diverse panel of monoclonal antibodies, HIV-1 positive polyclonal sera and sCD4 was consistently greater in A3R5 compared to TZM-bl cells. The A3R5 cell line provides a novel approach to guide the development and qualification of promising new HIV-1 vaccine immunogens.

The N276 glycosylation site is required for HIV-1 neutralization by the CD4 binding site specific HJ16 monoclonal antibody

Immunogen design for HIV-1 vaccines could be based on epitope identification of naturally occurring neutralizing antibodies in infected patients. A tier 2 neutralizing monoclonal antibody (mAb), HJ16 recognizes a new epitope in the CD4 binding site (CD4bs) region that only partially overlaps with the b12 epitope. We aimed to identify the critical binding site by resistance induction in a sensitive primary CRF02_AG strain. In four independent dose-escalation studies, the N276D mutation was consistently the only alteration found and it was confirmed to be responsible for resistance to HJ16 by site-directed mutagenesis in envelopes (envs) of the homologous CRF02_AG, as well as of a subtype A and a subtype C primary isolate. This mutation removes an N-linked glycosylation site. The effect of N276D was very selective, as it failed to confer resistance to a range of other entry inhibitors. Remarkably, sensitivity to the CD4bs VRC01 and VRC03 mAbs was increased in the N276D mutated viruses. These data indicate that binding of the CD4bs specific HJ16 mAb critically depends on the interaction with the N276-glycan, thus indicating that HJ16 is the first glycan dependent CD4bs-specific mAb.

Cross-group neutralization of HIV-1 and evidence for conservation of the PG9/PG16 epitopes within divergent groups

OBJECTIVE

HIV-1 has been classified into four groups: M, N, O and P. The aim of this study was to revisit the cross-group neutralization using a highly diverse panel of primary isolates.

DESIGN

The panel of viruses included nine HIV-1 group O primary isolates, one recombinant M/O primary isolate, one group N primary isolates, one group P primary isolate, two group M (subtype B) primary isolates and the HIV-1 group M adapted strain MN.

METHODS

All the viruses were tested for neutralization in TZM-bl cells, using sera issued from patients infected by viruses of group M (n = 11), O (n = 12) and P (n = 1), and a panel of nine human monoclonal broadly neutralizing antibodies (HuMo bNAbs).

RESULTS

Although the primary isolates displayed a wide spectrum of sensitivity to neutralization by the human sera, cross-group neutralization was clearly observed. In contrast, the bNAbs did not show any cross-group neutralization, except PG9 and PG16. Interestingly, the group N prototype strain YBF30 was highly sensitive to neutralization by PG9 (IC50: 0.28 μg/ml) and PG16 (IC50: < 0.12 μg/ml). The interaction between PG9 and key residues of YBF30 was confirmed by molecular modeling.

CONCLUSION

The conservation of the PG9 and PG16 epitopes within groups M and N provides an argument for their relevance as components of a potentially efficient HIV vaccine immunogen.

Genome-wide association study on the development of cross-reactive neutralizing antibodies in HIV-1 infected individuals

Broadly neutralizing antibodies may protect against HIV-1 acquisition. In natural infection, only 10–30% of patients have cross-reactive neutralizing humoral immunity which may relate to viral and or host factors. To explore the role of host genetic markers in the formation of cross-reactive neutralizing activity (CrNA) in HIV-1 infected individuals, we performed a genome-wide association study (GWAS), in participants of the Amsterdam Cohort Studies with known CrNA in their sera. Single-nucleotide polymorphisms (SNPs) with the strongest P-values are located in the major histocompatibility complex (MHC) region, close to MICA (P = 7.68×10⁻⁷), HLA-B (P = 6.96×10⁻⁶) and in the coding region of HCP5 (P = 1.34×10⁻⁵). However, none of the signals reached genome-wide significance. Our findings underline the potential involvement of genes close or within the MHC region with the development of CrNA.

Neutralization sensitivity of HIV-1 subtype B' clinical isolates from former plasma donors in China

BACKGROUND

HIV-1 subtype B' isolates have been predominantly circulating in China. Their intra- and inter-subtype neutralization sensitivity to autologous and heterologous plasmas has not been well studied.

RESULTS

Twelve HIV-1 B' clinical isolates obtained from patients were tested for their intra- and inter-subtype neutralization sensitivity to the neutralization antibodies in the plasmas from patients infected by HIV-1 B' and CRF07_BC subtypes, respectively. We found that the plasmas from the HIV-1 B'-infected patients could potently neutralize heterologous viruses of subtype B' with mean ID50 titer (1/x) of about 67, but they were not effective in neutralizing autologous viruses of subtype B' with mean ID50 titer (1/x) of about 8. The plasmas from HIV-1 CRF07_BC-infected patients exhibited weak inter-subtype neutralization activity against subtype B' viruses with ID50 titer (1/x) is about 22. The neutralization sensitivity of HIV-1 B' isolates was inversely correlated with the neutralizing activity of plasmas from HIV-1 B'-infected patients (Spearman's r = -0.657, P = 0.020), and with the number of potential N-glycosylation site (PNGS) in V1-V5 region (Spearman's r = -0.493, P = 0.034), but positively correlated with the viral load (Spearman's r = 0.629, P = 0.028). It had no correlation with the length of V1-V5 regions or the CD4+ T cell count. Virus AH259V has low intra-subtype neutralization sensitivity, it can be neutralized by 17b (IC50: 10μg/ml) and 447-52D (IC50: 1.6μg/ml), and the neutralizing antibodies (nAbs) in plasma AH259P are effective in neutralizing infection by the primary HIV-1 isolates with different subtypes with ID50 titers (1/x) in the range of 32-396.

CONCLUSIONS

These findings suggest that the HIV-1 subtype B' viruses may mutate under the immune pressure, thus becoming resistant to the autologous nAbs, possibly by changing the number of PNGS in the V1-V5 region of the viral gp120. Some of primary HIV-1 isolates are able to induce both intra- and inter-subtype cross-neutralizing antibody responses.

B-lymphocyte dysfunction in chronic HIV-1 infection does not prevent cross-clade neutralization breadth

Aberrant expression of regulatory receptors programmed death-1 (PD-1) and B- and T-lymphocyte attenuator (BTLA) is linked with dysregulation and exhaustion of T lymphocytes during chronic human immunodeficiency virus type 1 (HIV-1) infection; however, less is known about whether a similar process impacts B-lymphocyte function during HIV-1 infection. We reasoned that disruption of the peripheral B cell compartment might be associated with decreased neutralizing antibody activity. Expression of markers that indicate dysregulation (BTLA and PD-1), immune activation (CD95), and proliferation (Ki-67) was evaluated in B cells from HIV-1-infected viremic and aviremic subjects and healthy subjects, in conjunction with immunoglobulin production and CD4 T cell count. Viral load and cross-clade neutralizing activity in plasma from viremic subjects were also assessed. Dysregulation of B lymphocytes was indicated by a marked disruption of peripheral B cell subsets, increased levels of PD-1 expression, and decreased levels of BTLA expression in viremic subjects compared to aviremic subjects and healthy controls. PD-1 and BTLA were correlated in a divergent fashion with immune activation, CD4 T cell count, and the total plasma IgG level, a functional correlate of B cell dysfunction. Within viremic subjects, the total IgG level correlated directly with cross-clade neutralizing activity in plasma. The findings demonstrate that even in chronically infected subjects in which B lymphocytes display multiple indications of dysfunction, antibodies that mediate cross-clade neutralization breadth continue to circulate in plasma.

Superinfection by discordant subtypes of HIV-1 does not enhance the neutralizing antibody response against autologous virus

Recent studies have demonstrated that both the potency and breadth of the humoral anti-HIV-1 immune response in generating neutralizing antibodies (nAbs) against heterologous viruses are significantly enhanced after superinfection by discordant HIV-1 subtypes, suggesting that repeated exposure of the immune system to highly diverse HIV-1 antigens can significantly improve anti-HIV-1 immunity. Thus, we investigated whether sequential plasma from these subjects superinfected with discordant HIV-1 subtypes, who exhibit broad nAbs against heterologous viruses, also neutralize their discordant early autologous viruses with increasing potency. Comparing the neutralization capacities of sequential plasma obtained before and after superinfection of 4 subjects to those of matched plasma obtained from 4 singly infected control subjects, no difference in the increase in neutralization capacity was observed between the two groups (p = 0.328). Overall, a higher increase in neutralization over time was detected in the singly infected patients (mean change in IC₅₀ titer from first to last plasma sample: 183.4) compared to the superinfected study subjects (mean change in IC₅₀ titer from first to last plasma sample: 66.5). Analysis of the Breadth-Potency Scores confirmed that there was no significant difference in the increase in superinfected and singly infected study subjects (p = 0.234). These studies suggest that while superinfection by discordant subtypes induces antibodies with enhanced neutralizing breadth and potency against heterologous viruses, the potency to neutralize their autologous viruses is not better than those seen in singly infected patients.

Broadly cross-neutralizing antibodies in HIV-1 patients with undetectable viremia

Several recent studies have identified HIV-infected patients able to produce a broad neutralizing response, and the detailed analyses of their sera have provided valuable information to improve future vaccine design. All these studies have excluded patients on antiretroviral treatment and with undetectable viral loads, who have an improved B cell profile compared to untreated patients. To better understand the induction of neutralizing antibodies in patients on antiretroviral treatment with undetectable viremia, we have screened 508 serum samples from 364 patients (173 treated and 191 untreated) for a broadly neutralizing antibody (bNAb) response using a new strategy based on the use of recombinant viruses. Sera able to neutralize a minipanel of 6 recombinant viruses, including envelopes from 5 different subtypes, were found in both groups. After IgG purification, we were able to confirm the presence of IgG-associated broadly neutralizing activity in 3.7% (7 of 191) of untreated patients with detectable viremia and 1.7% (3 of 174) of aviremic patients receiving antiretroviral treatment. We thus confirm the possibility of induction of a broad IgG-associated neutralizing response in patients on antiretroviral treatment, despite having undetectable viremia. This observation is in stark contrast to the data obtained from long-term nonprogressors, whose little neutralizing activity has been attributed to the low levels of viral replication.

Breadth of human immunodeficiency virus-specific neutralizing activity in sera: clustering analysis and association with clinical variables

Induction of antibodies that neutralize a broad range of human immunodeficiency virus type 1 (HIV-1) isolates is a major goal of vaccine development. To study natural examples of broad neutralization, we analyzed sera from 103 HIV-1-infected subjects. Among progressor patients, 20% of sera neutralized more than 75% of a panel of 20 diverse viral isolates. Little activity was observed in sera from long-term nonprogressors (elite controllers). Breadth of neutralization was correlated with viral load, but not with CD4 count, history of past antiretroviral use, age, gender, race/ethnicity, or route of exposure. Clustering analysis of sera by a novel method identified a statistically robust subgrouping of sera that demonstrated broad and potent neutralization activity.

HIV type 1 subtype A envelope genetic evolution in a slow progressing individual with consistent broadly neutralizing antibodies

Studies of viruses taken from individuals with broad cross-neutralizing antibodies against primary isolates may reveal novel antibody specificities and their associated epitopes that could be useful for immunogen design. We report on the Env antigenic variability of a slow progressing HIV-1 subtype A-infected donor with consistent broad cross-neutralizing antibodies during the second decade of disease progression after vertical transmission. The Env evolution is characterized by a genetic shift to variants with altered V1-V5 loop sequences, marked by consecutive changes in V1, V4-V5, and C3 and largely conserved V2 and V3 loop sequences. Major V1 Env sequence expansion, variation by a duplication event, and cumulative addition of cysteine residues and potential N-glycosylation sites over time may contribute to escape from antibody pressure directed to Env receptor domains by changing the exposure of neutralization-sensitive epitopes. Conservation of functional epitopes may correlate with the continued presence of broad cross-neutralizing antibodies.

Frequency and phenotype of human immunodeficiency virus envelope-specific B cells from patients with broadly cross-neutralizing antibodies

Induction of broadly cross-reactive neutralizing antibodies (NAb) is an important goal for a prophylactic human immunodeficiency virus type 1 (HIV-1) vaccine. Some HIV-infected patients make a NAb response that reacts with diverse strains of HIV-1, but most candidate vaccines have induced NAb only against a subset of highly sensitive isolates. To better understand the nature of broad NAb responses that arise during natural infection, we screened patients for sera able to neutralize diverse HIV strains and explored the frequency and phenotype of their peripheral Envelope-specific B cells. We screened 113 HIV-infected patients of various clinical statuses for the prevalence of broad NAb. Sera able to neutralize at least four of five viral isolates were found in over one-third of progressors and slow progressors, but much less frequently in aviremic long-term nonprogressors. Most Env-specific antibody-secreting B cells were CD27(hi) CD38(hi) plasmablasts, and the total plasmablast frequency was higher in HIV-infected patients than in uninfected donors. We found that 0.0031% of B cells and 0.047% of plasmablasts secreted Env-specific immunoglobulin G (IgG) in an enzyme-linked immunospot (ELISPOT) assay. We developed a novel staining protocol to label HIV-specific B cells with Env gp140 protein. A total of 0.09% of B cells were found to be Env-specific by this method, a frequency far higher than that indicated by ELISPOT assay. gp140-labeled B cells were predominantly CD27(+) and surface IgG(+). These data describe the breadth and titer of serum NAb and the frequency and phenotype of HIV-specific B cells in a cohort of patients with broad cross-neutralizing antibody responses that are potential goals for vaccines for HIV.

Human immunodeficiency virus type 1 superinfection occurs despite relatively robust neutralizing antibody responses

Superinfection by a second human immunodeficiency virus type 1 (HIV-1) strain indicates that gaps in protective immunity occur during natural infection. To define the role of HIV-1-specific neutralizing antibodies (NAbs) in this setting, we examined NAb responses in 6 women who became superinfected between approximately 1 to 5 years following initial infection compared to 18 women with similar risk factors who did not. Although superinfected individuals had less NAb breadth than matched controls at approximately 1 year postinfection, no significant differences in the breadth or potency of NAb responses were observed just prior to the second infection. In fact, four of the six subjects had relatively broad and potent NAb responses prior to infection by the second strain. To more specifically examine the specificity of the NAbs against the superinfecting virus, these variants were cloned from five of the six individuals. The superinfecting variants did not appear to be inherently neutralization resistant, as measured against a pool of plasma from unrelated HIV-infected individuals. Moreover, the superinfected individuals were able to mount autologous NAb responses to these variants following reinfection. In addition, most superinfected individuals had NAbs that could neutralize their second viral strains prior to their reinfection, suggesting that the level of NAbs elicited during natural infection was not sufficient to block infection. These data indicate that preventing infection by vaccination will likely require broader and more potent NAb responses than those found in HIV-1-infected individuals.

Development of the 1st International Reference Panel for HIV-1 RNA genotypes for use in nucleic acid-based techniques

Twenty-eight laboratories from 16 countries participated in a collaborative study to evaluate an HIV-1 RNA Genotype Reference Panel for use with nucleic acid-based tests (NAT). The Reference Panel consisted of 11 coded samples representing different HIV-1 genotypes (subtypes A-D, AE, F, G, AA-GH, groups N and O) as well as a negative diluent control. Each laboratory assayed the eleven panel members concurrently with the 1st International Standard for HIV-1 RNA (NIBSC Code 97/656) on at least three separate occasions and the data collated and analysed at NIBSC. Twenty-nine sets of data from NAT were received, 19 from quantitative and 10 from qualitative assays, with six different commercial assays and five "in-house" assays represented. The results showed that viruses from subtypes A-D and recombinant virus AE [CRF01_AE] were detected consistently, but that some assays had difficulty with the detection and quantification of viruses from subtypes F and G, a mixed recombinant virus AA-GH and a representative of group N. Furthermore, most assays failed to detect the group O representative. The study illustrated the limitations of some molecular assays particularly in detection of certain non-B genotypes which are important viruses in the global AIDS pandemic and illustrated the value of a well-characterised genotype panel. The panel has been established by the World Health Organisation's Expert Committee on Biological Standardisation as the 1st International Reference Panel HIV-1 RNA Genotypes (code 01/466).

Inhibition of replication of primary HIV-1 isolates in huPBL-NOD/Scid mice by antibodies from HIV-1 infected patients

Although a limited number of HIV-infected patients have broadly neutralizing antibodies, it has not been examined whether these antibodies can protect against infection with primary virus in vivo. Here we screened the plasma of 23 HIV-1-infected patients for broadly neutralizing antibodies. Purified antibodies from subjects with broad and more narrow responses were administered to huPBL-NOD/Scid mice that were subsequently challenged with primary viruses of clade A, B and CRF01_AE. Although we observed a lack of correlation between the data from the in vitro neutralization assay and the results from the passive immunization experiments, we report for the first time that antibodies from HIV-infected persons can inhibit replication of primary virus isolates in an animal model.

Dissecting the neutralizing antibody specificities of broadly neutralizing sera from human immunodeficiency virus type 1-infected donors

Attempts to elicit broadly neutralizing antibody responses by human immunodeficiency virus type 1 (HIV-1) vaccine antigens have been met with limited success. To better understand the requirements for cross-neutralization of HIV-1, we have characterized the neutralizing antibody specificities present in the sera of three asymptomatic individuals exhibiting broad neutralization. Two individuals were infected with clade B viruses and the third with a clade A virus. The broadly neutralizing activity could be exclusively assigned to the protein A-reactive immunoglobulin G (IgG) fraction of all three donor sera. Neutralization inhibition assays performed with a panel of linear peptides corresponding to the third hypervariable (V3) loop of gp120 failed to inhibit serum neutralization of a panel of HIV-1 viruses. The sera also failed to neutralize chimeric simian immunodeficiency virus (SIV) and HIV-2 viruses displaying highly conserved gp41-neutralizing epitopes, suggesting that antibodies directed against these epitopes likely do not account for the broad neutralizing activity observed. Polyclonal IgG was fractionated on recombinant monomeric clade B gp120, and the neutralization capacities of the gp120-depleted samples were compared to that of the original polyclonal IgG. We found that the gp120-binding antibody population mediated neutralization of some isolates, but not all. Overall, the data suggest that broad neutralization results from more than one specificity in the sera but that the number of these specificities is likely small. The most likely epitope recognized by the monomeric gp120 binding neutralizing fraction is the CD4 binding site, although other epitopes, such as the glycan shield, cannot be excluded.

Cross-clade CD8 T-cell responses to HIV(IIIB) and Chinese B' and C/B' viruses in North American and Chinese HIV-seropositive donors

HIV variation presents an obstacle to a global AIDS vaccine. Viral diversity and host variations in MHC expression both affect vaccine responses. Whether CD8 T cells from HIV-infected donors in 1 part of the world cross-recognize isolates from other regions will provide guidance about whether country-specific vaccines are needed. We compared recognition of HIV(IIIB) and representative B' (Thai B) and recombinant C/B' virus strains endemic in China by CD8 T cells from 7 HIV-infected North American donors and 4 Chinese donors. IFN-gamma production in response to HIV(IIIB) or the Chinese viruses was comparable. Although 1.6 +/- 0.8% of American donor CD8 T cells produced IFN-gamma above the background level in response to IIIB virus, 1.5 +/- 0.8% responded to B' virus, and 1.4 +/- 0.7% responded to C/B' virus. Responses to adherent cells infected with vaccinia viruses expressing B' and C/B' virus gag and env were also comparable in magnitude with responses to IIIB virus. Cytolysis of CD4 T cells infected with B' virus was comparable with lysis of cells infected with IIIB virus, but lysis of the more divergent C/B' virus was somewhat reduced. T cells, selected for IFN-gamma production to IIIB virus, also efficiently lysed cells infected with Chinese viruses. Therefore, cross-clade CD8 T-cell responses to IIIB virus and prevalent Chinese viral strains are common.

Neutralization and infectivity characteristics of envelope glycoproteins from human immunodeficiency virus type 1 infected donors whose sera exhibit broadly cross-reactive neutralizing activity

In this study, we tested the hypothesis that donors with broadly cross-reactive HIV-1 neutralizing (BCN) sera are infected with viruses encoding envelope glycoproteins (Envs) with unusual immunogenic properties. Cloned env genes were from samples of donors previously identified as having BCN antibodies (BCN donors) and from other donors not known to have such antibodies (non-BCN donors). Neutralization properties of viruses pseudotyped with BCN and non-BCN Envs were determined using BCN, non-BCN sera and broadly cross-neutralizing monoclonal antibodies (Mabs). BCN sera neutralized with higher frequency and geometric mean titers than non-BCN sera. Viruses pseudotyped with BCN Envs were mostly resistant to neutralization by anti-gp120 Mabs but tended to be more sensitive to the anti-gp41 Mabs, 2F5 and 4E10 than non-BCN Env-pseudotyped viruses. Sequence analysis of clones obtained from sequential samples of two BCN donors revealed respective 2F5 epitope mutations T662A and K665T. The K665T mutation evolved as the predominant genotype in the respective donor, consistent with an escape mutation event. The A662T mutation reduced sensitivity to 4E10, as well as 2F5 and homologous sera, consistent with neutralization escape mutation and targeting of the 2F5 epitope region by the serum. Our study suggests that viruses infecting these BCN donors encoded Envs that may have been unusually competent for induction of antibodies against the membrane proximal epitope region (MPER) of gp41, and these Envs may be useful vaccine components.

Antibodies that are cross-reactive for human immunodeficiency virus type 1 clade a and clade B v3 domains are common in patient sera from Cameroon, but their neutralization activity is usually restricted by epitope masking

Sera from human immunodeficiency virus type 1 (HIV-1)-infected North American patients recognized a fusion protein expressing a V3 loop from a clade B primary isolate virus (JR-CSF) but not from a clade A primary isolate virus (92UG037.8), while most sera from Cameroonian patients recognized both fusion proteins. Competition studies of consensus V3 peptides demonstrated that the majority of the cross-reactive Cameroonian sera contained cross-reactive antibodies that reacted strongly with both V3 sequences. V3-specific antibodies purified from all six cross-reactive sera examined had potent neutralizing activity for virus pseudotyped with envelope proteins (Env) from SF162, a neutralization-sensitive clade B primary isolate. For four of these samples, neutralization of SF162 pseudotypes was blocked by both the clade A and clade B V3 fusion proteins, indicating that this activity was mediated by cross-reactive antibodies. In contrast, the V3-reactive antibodies from only one of these six sera had significant neutralizing activity against viruses pseudotyped with Envs from typically resistant clade B (JR-FL) or clade A (92UG037.8) primary isolates. However, the V3-reactive antibodies from these cross-reactive Cameroonian sera did neutralize virus pseudotyped with chimeric Envs containing the 92UG037.8 or JR-FL V3 sequence in Env backbones that did not express V1/V2 domain masking of V3 epitopes. These data indicated that Cameroonian sera frequently contain cross-clade reactive V3-directed antibodies and indicated that the typical inability of such antibodies to neutralize typical, resistant primary isolate Env pseudotypes was primarily due to indirect masking effects rather than to the absence of the target epitopes.

Dichotomy in cross-clade reactivity and neutralization by HIV-1 sera: Implications for active and passive immunotherapy

The identification of broadly reactive and cross-clade neutralizing antibodies will facilitate the development of a more universally effective vaccine for human immunodeficiency virus (HIV). Antibodies in sera from individuals infected with Clade B HIV bind native primary viral isolates, and virus binding correlates with neutralization and stable clinical disease. In this study, we quantified cross-clade antibody reactivity and neutralization by Clades B and C sera. Primary viral isolates were captured by serum IgG bound to anti-human IgG and quantitated as p24 released by lysis of captured virus. Neutralization was determined using PHA-stimulated PBMC. Clade B antibodies reacted more frequently with Clade B R5 virus, but positive sera captured quantitatively more X4 virus than R5 and R5X4 virus. Clade B sera reacted less frequently and captured less Clade C virus than Clade B virus. Antibodies in Clade C sera captured Clades B and C isolates with equal frequency and quantity. There was no difference in neutralization of Clade B virus by either group of sera; however, Clade C sera neutralized Clade C virus, whereas Clade B sera were ineffective against Clade C virus. Thus, there are distinct differences in cross-clade reactivity of and neutralization by antibodies induced in response to Clade C infection compared to Clade B infection. Understanding antibody responses to native virions after Clade C infection and cross clade antibody behavior has implications for understanding pathogenesis and vaccine development.

Comprehensive cross-clade neutralization analysis of a panel of anti-human immunodeficiency virus type 1 monoclonal antibodies

Broadly neutralizing monoclonal antibodies (MAbs) are potentially important tools in human immunodeficiency virus type 1 (HIV-1) vaccine design. A few rare MAbs have been intensively studied, but we still have a limited appreciation of their neutralization breadth. Using a pseudovirus assay, we evaluated MAbs from clade B-infected donors and a clade B HIV(+) plasma against 93 viruses from diverse backgrounds. Anti-gp120 MAbs exhibited greater activity against clade B than non-B viruses, whereas anti-gp41 MAbs exhibited broad interclade activity. Unexpectedly, MAb 4E10 (directed against the C terminus of the gp41 ectodomain) neutralized all 90 viruses with moderate potency. MAb 2F5 (directed against an epitope adjacent to that of 4E10) neutralized 67% of isolates, but none from clade C. Anti-gp120 MAb b12 (directed against an epitope overlapping the CD4 binding site) neutralized 50% of viruses, including some from almost every clade. 2G12 (directed against a high-mannose epitope on gp120) neutralized 41% of the viruses, but none from clades C or E. MAbs to the gp120 V3 loop, including 447-52D, neutralized a subset of clade B viruses (up to 45%) but infrequently neutralized other clades ( Collapse

Key Words Collapse

MESH Headings

• AIDS Vaccines/immunology
• Antibodies, Monoclonal/immunology
• HIV Antibodies/immunology
• HIV Envelope Protein gp120/immunology
• HIV Envelope Protein gp41/immunology
• HIV-1/immunology
• Humans
• Neutralization Tests
• Protein Conformation

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Grants

• R01 HL059725 NHLBI NIH HHS
• R37 AI033292 NIAID NIH HHS
• R01 AI033292 NIAID NIH HHS
• HL 59725 NHLBI NIH HHS
• P30 AI027742 NIAID NIH HHS
• AI 27742 NIAID NIH HHS
• AI33292 NIAID NIH HHS
• R01 AI093278 NIAID NIH HHS

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Affiliation(s)

James M Binley IMM2, Department of Immunology, The Scripps Research Institute, 10550 N. Torrey Pines Rd., La Jolla, CA 92037, USA
Terri Wrin
Bette Korber
Michael B Zwick
Meng Wang
Colombe Chappey
Gabriela Stiegler
Renate Kunert
Susan Zolla-Pazner
Hermann Katinger
Christos J Petropoulos
Dennis R Burton

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The first generation of candidate HIV-1 vaccines can induce antibodies able to neutralize primary isolates in assays with extended incubation phases

Quantification of human immunodeficiency virus type 1 (HIV-1) neutralizing antibodies is considered to be an important parameter in evaluating candidate vaccines. Most previous studies have failed to detect vaccine-induced antibodies against primary isolates, which are more resistant to antibody mediated neutralization compared with laboratory isolates, in neutralization assays. In this study, sera from a prime boost vaccination strategy of a phase I clinical trial were tested against six clade B primary HIV-1 isolates and single isolates of clades C and F. These sera produced statistically significant neutralization against primary isolates MN, SF13, SF162 and Han 2 but not the most resistant subtype B isolates (92US077 and 93US143) nor the subtype C and F isolates. These data suggest that the sera from vaccinated volunteers have subtype-specific neutralizing antibodies against primary HIV-1 isolates. We recommend using assays with extended incubation phases to monitor current HIV vaccine efficacy trials.

Broadly cross-reactive HIV neutralizing human monoclonal antibody Fab selected by sequential antigen panning of a phage display library

Identification of broadly cross-reactive human monoclonal antibodies (mAbs) has major implications for development of vaccines, inhibitors and research tools. Here we describe a sequential antigen panning (SAP) methodology that may facilitate the selection of such antibodies. An HIV-specific antibody Fab (m18) was selected from a human Fab phage-display library by SAP against several recombinant soluble HIV envelope glycoproteins (Envs) and Env-sCD4 complexes. This Fab bound to a variety of recombinant soluble Envs (gp140s) from primary HIV isolates representing different clades, and inhibited cell fusion and virus entry mediated by Envs of primary HIV isolates. The methodology and the results may have implications for development of HIV vaccines and inhibitors, as well as for identification of antibodies to conserved epitopes on rapidly mutating viruses and cells.

Induction of primary virus-cross-reactive human immunodeficiency virus type 1-neutralizing antibodies in small animals by using an alphavirus-derived in vivo expression system

We have studied the induction of neutralizing antibodies by in vivo expression of the human immunodeficiency virus type 1 (HIV-1) envelope by using a Venezuelan equine encephalitis virus (VEE) replicon system with mice and rabbits. The HIV-1 envelope, clone R2, has broad sensitivity to cross-reactive neutralization and was obtained from a donor with broadly cross-reactive, primary virus-neutralizing antibodies (donor of reference serum, HIV-1-neutralizing serum 2 [HNS2]). It was expressed as gp160, as secreted gp140, and as gp160deltaCT with the cytoplasmic tail deleted. gp140 was expressed in vitro at a high level and was predominantly uncleaved oligomer. gp160deltaCT was released by cells in the form of membrane-bound vesicles. gp160deltaCT induced stronger neutralizing responses than the other forms. Use of a helper plasmid for replicon particle packaging, in which the VEE envelope gene comprised a wild-type rather than a host range-adapted sequence, also enhanced immunogenicity. Neutralizing activity fractionated with immunoglobulin G. This activity was cross-reactive among a panel of five nonhomologous primary clade B strains and a Chinese clade C strain and minimally reactive against a Chinese clade E (circulating recombinant form 1) strain. The comparative neutralization of these strains by immune mouse sera was similar to the relative neutralizing effects of HNS2, and responses induced in rabbits were similar to those induced in mice. Together, these results demonstrate that neutralizing antibody responses can be induced in mice within 2 to 3 months that are similar in potency and cross-reactivity to those found in the chronically infected, long-term nonprogressive donor of HNS2. These findings support the expectation that induction of highly cross-reactive HIV-1 primary virus-neutralizing activity by vaccination may be realized.

Inter-subtype cross-neutralizing antibodies recognize epitopes on cell-associated HIV-1 virions

HIV-1 infected individuals with cross-neutralizing antibodies against primary HIV-1 isolates belonging to Group M (envA-H) and O, are identified. To investigate the neutralization-kinetics of primary isolates with these antibodies, different neutralization assay conditions are compared. Each set is summarized as a/b/c where a is the time in hours for which antibody is incubated with virus, b is the time in hours allowed for virus to absorb to cells, c is the total culture period in days, from the cells' first exposure to virus, before antigen production (peripheral blood mononuclear cells) or number of fluorescent cells (GHOST) are measured. In HIV-infected individuals, neutralizing antibodies can be detected against a wide range of primary isolates (Group M; A-H and Group O) in PBMC-assays with short incubation phases (1/2/7 or 1/24/7). If cultures are extended (1/2/14 or 1/24/14), however, neutralization can be lost. In kinetic experiments, neutralization can even be seen without pre-incubation (a=0 hr). This study shows that neutralization of primary HIV isolates by cross-reactive antibodies can continue after the virus has bound to its target cell. This neutralization, however, is not an all or nothing loss in virus infectivity. Most often it leads only to a reduction in viral replication rates.

Evidence for antibody-mediated enhancement of simian immunodeficiency virus (SIV) Gag antigen processing and cross presentation in SIV-infected rhesus macaques

By using the dominant simian immunodeficiency virus (SIV) Gag Mamu-A01 restricted major histocompatibility complex (MHC) class I epitope p11CM, we demonstrate antibody-mediated enhanced MHC class I cross presentation of SIV Gag. In vitro restimulation of peripheral blood mononuclear cells from SIV-infected rhesus macaques with recombinant full-length SIV Gag p55 plus p55 affinity-purified immunoglobulin G (p55 Gag/p55-IgG) led to the generation of markedly higher frequencies of p11CM specific precursor cytotoxic T lymphocytes (p-CTLs) compared with restimulation with (i) SIV Gag p55 alone or (ii) optimal concentrations of the p11CM peptide alone. These results, along with the finding that CD4 depletion abrogated the enhancement, suggest a prominent role for CD4(+) T cells. Testing for p-CTLs against other Mamu-A01-restricted SIV Gag epitopes suggested that this mechanism favored recognition of the dominant p11CM peptide, potentially further skewing of the CTL response. The p-CTL enhancing effect was also decreased or abrogated by pepsin digestion of the p55-specific IgG or by the addition of monoclonal antibodies to Fc receptor (FcR) II/III, suggesting that the effect was dependent on FcR-mediated uptake of the immune-complexed antigen. Finally, incubation of antigen-presenting cells with SIV Gag p55 immune complexes in the presence of lactacystin or of bafilomycin indicated that the mechanism of antibody-mediated enhancement of cross presentation required both the proteasomal and the endosomal pathways. These data demonstrate for the first time the cross presentation of antigens via immune complexes in lentiviral infection and indicate a heretofore-unrecognized role for antibodies in modulating the magnitude and potentially also the breadth of MHC class I-restricted antigen processing and presentation and CTL responses.

Neutralization titres and vertical HIV-1 transmission

Replication of the human immunodeficiency virus type 1 (HIV-1) isolate MN in CEM cells was less neutralized by the plasma from the mothers of infected children (MIC) in comparison with the plasma from the mothers of uninfected children (MUC). Significantly higher neutralization titres were observed for the sera from MUCs compared with MICs, and only the sera from MUC showed 100% neutralization of the HIV-1 MN strain. We suggest that a simple neutralization assay as described here could be useful in prognostic analyses.

Immunoglobulin G (IgG) and IgA, but also nonantibody factors, account for in vitro neutralization of human immunodeficiency virus (HIV) type 1 primary isolates by serum and plasma of HIV-infected patients

The factors present in serum and plasma samples of human immunodeficiency virus (HIV)-infected patients that are responsible for the neutralization of four HIV type 1 (HIV-1) primary isolates in vitro have been analyzed. Purification of immunoglobulins (Ig) by affinity chromatography showed that the activities were mostly attributable to IgG and less frequently to IgA. For two samples, we have shown that the high-level and broad-spectrum inhibitory activity was essentially caused by non-Ig factors interfering with the measurement of antibody-specific neutralizing activity.

Potent broad cross-neutralizing sera inhibit attachment of primary HIV-1 isolates (groups M and O) to peripheral blood mononuclear cells

Gp160-directed antibody-mediated neutralization is thought to function by at least two different mechanisms that impair virus entry into the host cell: inhibition of virus attachment and inhibition of virus-cell membrane fusion. Previously, the neutralization spectra of sera derived from human immunodeficiency virus type 1 (HIV-1) infected patients were determined using 17 primary isolates belonging to HIV-1 group M (env clades A-H) and group O. The sera could be categorized as potent broad cross-neutralizing, limited cross-neutralizing, and nonneutralizing sera. The aim of this study was to examine whether the neutralizing capacity of polyclonal human sera correlates with their capacity to inhibit the attachment of infectious virions to the surface of peripheral blood mononuclear cells. A 100% correlation was found between the broad cross-neutralizing capacity and the ability to inhibit binding of primary isolates belonging to different genetic clades and groups to peripheral blood mononuclear cells. These results may indicate that broad cross-neutralizing antibodies are directed against those conserved regions on gp120 that interact with the cell receptor(s) and that those antibodies can therefore interfere with the binding of virus to the host cell.