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 sitedirected 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

Characterization of neutralizing profiles in HIV-1 infected patients from whom the HJ16, HGN194 and HK20 mAbs were obtained

Several new human monoclonal antibodies (mAbs) with a neutralizing potential across different subtypes have recently been described. Three mAbs, HJ16, HGN194 and HK20, were obtained from patients within the HIV-1 cohort of the Institute of Tropical Medicine (ITM). Our aim was to generate immunization antibodies equivalent to those seen in plasma. Here, we describe the selection and characterization of patient plasma and their mAbs, using a range of neutralization assays, including several peripheral blood mononuclear cell (PBMC) based assays and replicating primary viruses as well as cell line based assays and pseudoviruses (PV). The principal criterion for selection of patient plasma was the activity in an ‘extended incubation phase’ PBMC assay. Neutralizing Abs, derived from their memory B cells, were then selected by ELISA with envelope proteins as solid phase. MAbs were subsequently tested in a high-throughput HOS-PV assay to assess functional neutralization. The present study indicates that the strong profiles in the patients' plasma were not solely due to antibodies represented by the newly isolated mAbs. Although results from the various assays were divergent, they by and large indicate that neutralizing Abs to other epitopes of the HIV-1 envelope are present in the plasma and synergy between Abs may be important. Thus, the spectrum of the obtained mAbs does not cover the range of cross-reactivity seen in plasma in these carefully selected patients irrespective of which neutralization assay is used. Nevertheless, these mAbs are relevant for immunogen discovery because they bind to the recombinant glycoproteins to which the immune response needs to be targeted in vivo. Our observations illustrate the remaining challenges required for successful immunogen design and development

Analysis of Memory B Cell Responses and Isolation of Novel Monoclonal Antibodies with Neutralizing Breadth from HIV-1-Infected Individuals

BACKGROUND: The isolation of human monoclonal antibodies (mAbs) that neutralize a broad spectrum of primary HIV-1 isolates and the characterization of the human neutralizing antibody B cell response to HIV-1 infection are important goals that are central to the design of an effective antibody-based vaccine. METHODS AND FINDINGS: We immortalized IgG(+) memory B cells from individuals infected with diverse clades of HIV-1 and selected on the basis of plasma neutralization profiles that were cross-clade and relatively potent. Culture supernatants were screened using various recombinant forms of the envelope glycoproteins (Env) in multiple parallel assays. We isolated 58 mAbs that were mapped to different Env surfaces, most of which showed neutralizing activity. One mAb in particular (HJ16) specific for a novel epitope proximal to the CD4 binding site on gp120 selectively neutralized a multi-clade panel of Tier-2 HIV-1 pseudoviruses, and demonstrated reactivity that was comparable in breadth, but distinct in neutralization specificity, to that of the other CD4 binding site-specific neutralizing mAb b12. A second mAb (HGN194) bound a conserved epitope in the V3 crown and neutralized all Tier-1 and a proportion of Tier-2 pseudoviruses tested, irrespective of clade. A third mAb (HK20) with broad neutralizing activity, particularly as a Fab fragment, recognized a highly conserved epitope in the HR-1 region of gp41, but showed striking assay-dependent selectivity in its activity. CONCLUSIONS: This study reveals that by using appropriate screening methods, a large proportion of memory B cells can be isolated that produce mAbs with HIV-1 neutralizing activity. Three of these mAbs show unusual breadth of neutralization and therefore add to the current panel of HIV-1 neutralizing antibodies with potential for passive protection and template-based vaccine design

Analysis of memory B cell responses and isolation of novel monoclonal antibodies with neutralizing breadth from HIV-1-infected individuals

Background The isolation of human monoclonal antibodies (mAbs) that neutralize a broad spectrum of primary HIV-1 isolates and the characterization of the human neutralizing antibody B cell response to HIV-1 infection are important goals that are central to the design of an effective antibody-based vaccine. Methods and Findings We immortalized IgG+ memory B cells from individuals infected with diverse clades of HIV-1 and selected on the basis of plasma neutralization profiles that were cross-clade and relatively potent. Culture supernatants were screened using various recombinant forms of the envelope glycoproteins (Env) in multiple parallel assays. We isolated 58 mAbs that were mapped to different Env surfaces, most of which showed neutralizing activity. One mAb in particular (HJ16) specific for a novel epitope proximal to the CD4 binding site on gp120 selectively neutralized a multi-clade panel of Tier-2 HIV-1 pseudoviruses, and demonstrated reactivity that was comparable in breadth, but distinct in neutralization specificity, to that of the other CD4 binding site-specific neutralizing mAb b12. A second mAb (HGN194) bound a conserved epitope in the V3 crown and neutralized all Tier-1 and a proportion of Tier-2 pseudoviruses tested, irrespective of clade. A third mAb (HK20) with broad neutralizing activity, particularly as a Fab fragment, recognized a highly conserved epitope in the HR-1 region of gp41, but showed striking assay-dependent selectivity in its activity. Conclusions This study reveals that by using appropriate screening methods, a large proportion of memory B cells can be isolated that produce mAbs with HIV-1 neutralizing activity. Three of these mAbs show unusual breadth of neutralization and therefore add to the current panel of HIV-1 neutralizing antibodies with potential for passive protection and template-based vaccine design

Characterization of Neutralizing Profiles in HIV-1 Infected Patients from whom the HJ16, HGN194 and HK20 mAbs were Obtained

Several new human monoclonal antibodies (mAbs) with a neutralizing potential across different subtypes have recently been described. Three mAbs, HJ16, HGN194 and HK20, were obtained from patients within the HIV-1 cohort of the Institute of Tropical Medicine (ITM). Our aim was to generate immunization antibodies equivalent to those seen in plasma. Here, we describe the selection and characterization of patient plasma and their mAbs, using a range of neutralization assays, including several peripheral blood mononuclear cell (PBMC) based assays and replicating primary viruses as well as cell line based assays and pseudoviruses (PV). The principal criterion for selection of patient plasma was the activity in an ‘extended incubation phase’ PBMC assay. Neutralizing Abs, derived from their memory B cells, were then selected by ELISA with envelope proteins as solid phase. MAbs were subsequently tested in a high-throughput HOS-PV assay to assess functional neutralization. The present study indicates that the strong profiles in the patients' plasma were not solely due to antibodies represented by the newly isolated mAbs. Although results from the various assays were divergent, they by and large indicate that neutralizing Abs to other epitopes of the HIV-1 envelope are present in the plasma and synergy between Abs may be important. Thus, the spectrum of the obtained mAbs does not cover the range of cross-reactivity seen in plasma in these carefully selected patients irrespective of which neutralization assay is used. Nevertheless, these mAbs are relevant for immunogen discovery because they bind to the recombinant glycoproteins to which the immune response needs to be targeted in vivo. Our observations illustrate the remaining challenges required for successful immunogen design and development

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

Long-term persistence of HIV-1 vaccine-induced CD4+CD45RA-CD62L-CCR7- memory T-helper cells.

OBJECTIVE: To determine in chimpanzees if candidate HIV-1 subunit protein vaccines were capable of eliciting long-lasting T-cell memory responses in the absence of viral infection, and to determine the specific characteristics of these responses. DESIGN: A longitudinal study of cell-mediated immune responses induced in three chimpanzees following immunization with subunit envelope glycoproteins of either HIV-1 or herpes simplex virus (HSV)-2. Following these pre-clinical observations, four human volunteers who had been immunized 7 years previously with the same HIV-1 vaccine candidate donated blood for assessment of immune responses. METHODS: Responses were monitored by protein and peptide based ELISpot assays, lymphocyte proliferation, and intracellular cytokine staining. Humoral responses were assessed by enzyme-linked immunosorbent assay and virus neutralization assays. RESULTS: Although antigen (Ag)-specific CD4 T-cell responses persisted for at least 5 years in chimpanzees, CD8 T-cell responses were discordant and declined within 2 years. Detailed cellular analyses revealed that strong Th1 in addition to Th2 type responses were induced by AS2/gp120 and persisted, whereas CD8 T-cell memory declined in peripheral blood. The specificity of both Th and cytotoxic T-lymphocyte responses revealed that the majority of responses were directed to conserved epitopes. The remarkable persistence of Ag-specific CD4 T-cell memory was characterized as a population of the CD45RA-CD62L-CCR7- "effector phenotype" producing the cytokines IFNgamma, IL-2 and IL-4 upon epitope-specific recognition. Importantly, results in chimpanzees were confirmed in peripheral blood of one of four human volunteers studied more than 7 years after immunization. CONCLUSION: These studies demonstrate that epitope-specific Th1 and Th2 cytokine-dependent Th responses can be induced and maintained for longer than 5 years by immunization with subunit proteins of HIV-1

Neutralization profile of HJ patient plasma and HJ16 mAb against VI1090 virus in various assays.

a<p>The extended incubation PBMC assay was performed with the infectious virus VI1090.</p>b<p>Both infectious virus (IV) and pseudovirus (PV) were used in the TZMbl assay, whereas only PV was used in the GHOST and HOS assays.</p>c<p>HJ plasma used at 1∶20.</p>d<p>mAb used at 50 µg/ml.</p>e<p>% Reduction in virus titer.</p>f<p>% Reduction in luciferase activity.</p

Positioning in yellow of N276-bound glycans (yellow spheres) in solved structures for sCD4, PGV04, b12 and VRC01.

<p>The blue highlight indicate the footprint of the cognate ligand and the red spheres the other glycans. A N276 glycan on gp120 structures. In blue are shown the footprints of CD4 (pdb accession n° 1gc1) and the CD4bs-specific antibodies PGV04 (pdb n°: 3se9), b12 (pdb n°: 3dnl), and VRC01 (pdb n°: 3ngb). In each structure the N276-bound glycan is highlighted in yellow, other, surrounding glycans in red.<b> B.</b> Detail of the molecular interaction between the residues tyrosine 28 and threonine 30 of the VRC01 light chain with N-acetyl-glucosamine of the N276-bound glycan (3ngb). Figures were made with PyMOL.</p

Neutralization profile of HJ patient plasma and HJ16 mAb in the 24 h/1 h/14d^a extended incubation PBMC assay.

a<p>In this assay virus and plasma or mAb are incubated during 24 hours, followed by an absorption time of 1 hour during which the mAb/virus mixture is co-incubated with donor PBMC. After washing the PBMC cultures are maintained for 14 days.</p>b<p>% Neutralization obtained with 1∶20 plasma dilution or 50 µg/ml mAb during the incubation phase.</p>c<p>≥80% reduction in virus titer is highlighted, E = enhancement of infection.</p