HIV-specific Neutralizing Antibodies Research Articles

Immunogenicity of 2 therapeutic mosaic HIV-1 vaccine strategies in individuals with HIV-1 on antiretroviral therapy

Mosaic HIV-1 vaccines have been shown to elicit robust humoral and cellular immune responses in people living with HIV-1 (PLWH), that had started antiretroviral therapy (ART) during acute infection. We evaluated the safety and immunogenicity of 2 mosaic vaccine regimens in virologically suppressed individuals that had initiated ART during the chronic phase of infection, exemplifying the majority of PLWH. In this double-blind, placebo-controlled phase 1 trial (IPCAVD013/HTX1002) 25 ART-suppressed PLWH were randomized to receive Ad26.Mos4.HIV/MVA-Mosaic (Ad26/MVA) (n = 10) or Ad26.Mos4.HIV/Ad26.Mos4.HIV plus adjuvanted gp140 protein (Ad26/Ad26+gp140) (n = 9) or placebo (n = 6). Primary endpoints included safety and tolerability and secondary endpoints included HIV-specific binding and neutralizing antibody titers and HIV-specific T cell responses. Both vaccine regimens were well tolerated with pain/tenderness at the injection site and fatigue, myalgia/chills and headache as the most commonly reported solicited local and grade 3 systemic adverse events, respectively. In the Ad26/Ad26+gp140 group, Env-specific IFN-γ T cell responses showed a median 12-fold increase while responses to Gag and Pol increased 1.8 and 2.4-fold, respectively. The breadth of T cell responses to individual peptide subpools increased from 11.0 pre-vaccination to 26.0 in the Ad26/Ad26+gp140 group and from 10.0 to 14.5 in the Ad26/MVA group. Ad26/Ad26+gp140 vaccination increased binding antibody titers against vaccine-matched clade C Env 5.5-fold as well as augmented neutralizing antibody titers against Clade C pseudovirus by 7.2-fold. Both vaccine regimens were immunogenic, while the addition of the protein boost resulted in additional T cell and augmented binding and neutralizing antibody titers. These data suggest that the Ad26/Ad26+gp140 regimen should be tested further.

HIV-1 Env Does Not Enable the Development of Protective Broadly Neutralizing Antibodies in an Experimental Autoimmune Encephalomyelitis Mouse Model.

Recent studies showed that immunological tolerance may restrict the development of Env-specific autoreactive broadly neutralizing antibodies. This evidence is consistent with the finding that Env immunization of a systemic lupus erythematosus (SLE) murine model produced antibodies that neutralize tier 2 HIV-1 strains. In this study, we address the possibility of eliciting neutralizing anti-Env antibodies in other autoimmune diseases such as multiple sclerosis (MS). While, as reported for SLE, we showed for the first time that a small number of HIV-1 negative, relapsing remitting MS patients exhibited antibodies with neutralizing properties, our attempts at inducing those antibodies in a EAE mouse model of MS failed. The success in eliciting Env-specific neutralizing antibodies might be related to the specific characteristics of the autoimmune disease, or it might rely in improving the vaccination design. Studies using mouse models are useful to gain insight in how HIV-specific neutralizing antibody responses are regulated in order to develop a protective HIV-1 vaccine.

Glycan-dependent HIV-specific neutralizing antibodies bind to cells of uninfected individuals.

A number of highly potent and broadly neutralizing antibodies (bNAbs) against the human immunodeficiency virus (HIV) have recently been shown to prevent transmission of the virus, suppress viral replication, and delay plasma viral rebound following discontinuation of antiretroviral therapy in animal models and infected humans. However, the degree and extent to which such bNAbs interact with primary lymphocytes have not been fully delineated. Here, we show that certain glycan-dependent bNAbs, such as PGT121 and PGT151, bind to B, activated T, and natural killer (NK) cells of HIV-infected and -uninfected individuals. Binding of these bNAbs, particularly PGT121 and PGT151, to activated CD4+ and CD8+ T cells was mediated by complex-type glycans and was abrogated by enzymatic inhibition of N-linked glycosylation. In addition, a short-term incubation of PGT151 and primary NK cells led to degranulation and cellular death. Our data suggest that the propensity of certain bNAbs to bind uninfected/bystander cells has the potential for unexpected outcomes in passive-transfer studies and underscore the importance of antibody screening against primary lymphocytes.

Longing for HIV protection.

Antibodies that potently neutralize highly diverse HIV-1 variants offer great potential for therapy and prevention. Passive administration of HIV-specific neutralizing antibodies genetically modified to have a long serum half-life has now been shown to confer long-lasting protection from infection in the rhesus macaque model.

Superinfection Drives HIV Neutralizing Antibody Responses from Several B Cell Lineages that Contribute to a Polyclonal Repertoire

SUMMARYEliciting broad and potent HIV-specific neutralizing antibody responses represents the holy grail of HIV vaccine efforts. Data from singly infected individuals with broad and potent plasma neutralizing activity targeting one epitope have guided our understanding of how these responses develop. However, far less is known about responses developed by super-infected individuals who acquire two distinct HIV strains. Here, we isolated HIV-specific mAbs from a superinfected individual with a broad plasma response. In this superinfection case, neutralizing activity resulted from multiple distinct B cell lineages that arose in response to either the initial or the superinfecting virus, including an antibody that targets the N332 supersite. This nAb, QA013.2, was specific to the superinfecting virus and was associated with eventual reemergence of the initial infecting virus. The complex dynamic between viruses in superinfection may drive development of a unique collection of polyclonal nAbs that present a higher barrier to escape than monoclonal responses.

B-106 Characterizing the basis for the broad and potent HIV-specific neutralizing antibody response of infants

In the past few years, many new broad and potent HIV-specific monoclonal antibodies (Mabs) have been isolated from HIV-infected adults. However, because the breadth of these antibodies was acquired over many years, it will be challenging to elicit such Nabs with a vaccine. We found that HIV-infected infants often develop broad and potent HIV-specific Nab responses. Among 28 infants we identified 20 with cross clade Nab responses within the first two years of their infection, including a subset that neutralized Tier 2–3 variants from multiple clades. In some infants, there was evidence of cross clade breadth within the first year[LINE SEPARATOR]of their infection. To characterize these infant antibody responses, we isolated single B cells from sample from an infant with a cross clade Nab response at 336 days PI. We used a combination of sorting for B cells that bound envelope trimer as well as functional screening of cultured B cells for neutralizing activity to identify B cells of interest. Among those B cells identified through functional screening, there are 10 where we have rescued matched VH and VL chains. Six of these Mabs demonstrate some HIV-specific Tier 2 neutralizing activity and one Mab demonstrates potency similar to VRC01 for some viruses tested. In preliminary analysis using a small virus panel, these antibodies show distinct patterns of neutralization and no single Mab isolated to-date recapitulates the full breadth of the original plasma. None of the Mabs share a common VH or VL chain, suggesting that the broad antibody activity in this infant may be due to a polyclonal response.

Multiple factors affect immunogenicity of DNA plasmid HIV vaccines in human clinical trials

Plasmid DNA vaccines have been licensed for use in domesticated animals because of their excellent immunogenicity, but none have yet been licensed for use in humans. Here we report a retrospective analysis of 1218 healthy human volunteers enrolled in 10 phase I clinical trials in which DNA plasmids encoding HIV antigens were administered. Elicited T-cell immune responses were quantified by validated intracellular cytokine staining (ICS) stimulated with HIV peptide pools. HIV-specific binding and neutralizing antibody activities were also analyzed using validated assays. Results showed that, in the absence of adjuvants and boosting with alternative vaccines, DNA vaccines elicited CD8+ and CD4+ T-cell responses in an average of 13.3% (95% CI: 9.8–17.8%) and 37.7% (95% CI: 31.9–43.8%) of vaccine recipients, respectively. Three vaccinations (vs. 2) improved the proportion of subjects with antigen-specific CD8+ responses (p=0.02), as did increased DNA dosage (p=0.007). Furthermore, female gender and participants having a lower body mass index were independently associated with higher CD4+ T-cell response rate (p=0.001 and p=0.008, respectively). These vaccines elicited minimal neutralizing and binding antibody responses. These findings of the immunogenicity of HIV DNA vaccines in humans can provide guidance for future clinical trials.

HIV-1 neutralizing antibody response and viral genetic diversity characterized with next generation sequencing

To better understand the dynamics of HIV-specific neutralizing antibody (NAb), we examined associations between viral genetic diversity and the NAb response against a multi-subtype panel of heterologous viruses in a well-characterized, therapy-naïve primary infection cohort. Using next generation sequencing (NGS), we computed sequence-based measures of diversity within HIV-1 env, gag and pol, and compared them to NAb breadth and potency as calculated by a neutralization score. Contemporaneous env diversity and the neutralization score were positively correlated (p=0.0033), as were the neutralization score and estimated duration of infection (EDI) (p=0.0038), and env diversity and EDI (p=0.0005). Neither early env diversity nor baseline viral load correlated with future NAb breadth and potency (p>0.05). Taken together, it is unlikely that neutralizing capability in our cohort was conditioned on viral diversity, but rather that env evolution was driven by the level of NAb selective pressure.

Live Adenovirus Type 4 Recombinants Induce Durable Neutralizing Antibody Responses to Influenza H5 with High Levels of Somatic Hypermutation in Humans

OA16.01 Background: Induction of durable antibody responses capable of neutralizing diverse HIV-1 isolates is the most important goal in HIV vaccinology. Broad and potent HIV Env-specific antibodies isolated from humans are characterized by binding to conserved sites on Env and by high levels of hypermutation. Live virus recombinant vectors may provide prolonged exposure to transgene-encoded antigen and may more potently drive affinity maturation than non-replicating vectors. We report results of a small Phase 1 trial of mucosal immunization with live adenovirus type 4 encoding influenza H5 HA (Ad4-H5-Vtn) as a model antigen. We explored its ability to induce durable, broad neutralizing antibody responses through upper respiratory tract application. Methods: Live Ad4-H5Vtn (103-108 viral particles (VP)) was administered by tonsillar swab or by nasal spray in a dose escalation study. Controls received (1010 VP) as enteric-coated capsules. Neutralizing antibodies were measured by a pseudotype HA lentiviral vector system. B cells were isolated using fluorescent HA probes. Immunoglobulin genes were cloned for mutation analysis, and re-expressed to measure neutralization potency and breadth. Results: The vaccine was well tolerated and symptoms were consistent with mild URI. Tonsillar and nasal immunizations were the most immunogenic routes inducing neutralizing antibody responses at day 60 (ID50=809 and 666 respectively) which rose during the first 6 months. B cells that expanded early were specific for both H1 and H5 and were directed to the conserved stalk, with H5 HA-monospecific cells expanding by 6 months. The median level of hypermutation was 3.6% compared to germline at week 4 and 7.4% at weeks 34–52. However, some antibodies contained 13–34% mutation and neutralized group 1 and 2 viruses. Conclusions: A single dose of live recombinant Ad4-H5 can induce highly mutated antibodies, suggesting that mucosal administration is a promising platform for the induction of HIV-specific neutralizing antibodies.

Longer V1V2 Region with Increased Number of Potential N-Linked Glycosylation Sites in the HIV-1 Envelope Glycoprotein Protects against HIV-Specific Neutralizing Antibodies

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

143 HIV Transmission: The Role of Neutralizing Antibodies

At present, it is unknown whether the presence of HIV-specific neutralizing antibodies (NAbs) provides any protection from infection in individuals naturally exposed to HIV. Although here is evidence that select NAbs can protect in the SHIV/macaque model, these studies were limited to analysis of a few select neutralization sensitive challenge strains that are not representative of circulating HIV. We have examined whether NAbs, when present at the levels found in natural HIV-infection, can reduce the risk of HIV acquisition using two cohorts: 1) HIV positive high-risk women who continue to be exposed to new source partners and 2) breastfeeding infants of HIV positive mothers, who may have HIV NAbs through passive transfer. Both of these settings provide a situation in which the individual has pre-existing HIV-specific antibodies at the time of exposure to HIV. Among high-risk women, those who became superinfected by a second partner did not show evidence of notably weak or narrow NAb responses at the time of superinfection compared to women who did not become superinfected. In infants, the presence of broad potent neutralizing antibodies did not impact of their risk of HIV acquisition after birth. Together, these studies suggest that neutralizing antibodies that are elicited by a natural HIV infection are not of sufficient breadth or potency to protect against diverse circulating strains of HIV-1.

Roles of HIV neutralizing antibodies in the control of HIV infection

Neutralizing antibodies specific for HIV can bind to the virus and inhibit HIV entry into host cells.The targets of HIV-specific neutralizing antibodies are the sites associated with receptor binding or membrane fusion on the envelop proteins of HIV.Relevant studies have provided theoretical basis for developing anti-HIV medicines and microbicides.The neutralization is sensitive to the conformation of related proteins.On the other hand, HIV has a latent ability to escape from antibodies neutralization.Therefore, the rational design of antigen to induce broad-spectrum neutralizing antibodies is necessary for the development of successful vaccines.This paper introduces HIV invasion mechanism as well as the relationship of HIV neutralizing antibodies with entry-related crucial proteins,targets and anti-HIV vaccines. Key words: HIV; Infections; Neutralizing antibodies

Correlations Between HIV-1 Clades and HIV-1 Antibody Neutralization Sensitivity: Significant for Vaccine Development?

The correlates of protection against HIV-1 infection or disease progression are still unknown which causes an immense challenge for HIV-1 vaccine design. Existing effective vaccines against other viruses generate antibodies that either block the initial infection or contribute to the eradication of the virus before it can cause disease. For HIV-1, a protective vaccine capable of eliciting protective neutralizing antibodies does not exist and the difficulties for the generation of such a vaccine are multiple. Conserved elements on the viral envelope glycoprotein, the target of HIV-specific neutralizing antibodies, seem to be poorly immunogenic and attempts to generate an immunogen that can elicit broadly reactive neutralizing antibodies have remained largely without success. In addition, the envelope of HIV-1 is highly variable with respect to amino acid sequence, length of the variable loops, and glycosylation pattern. To cope with the high sequence variation, vaccine-elicited clade-specific neutralizing antibodies have been suggested as an attractive alternative and recent studies have revealed some evidence for the existence of HIV-1 clade-specific humoral immune responses. Here, we will review these recent findings and hypothesize on the nature of clade-specific humoral immunity also in light of their relevance for HIV-1 vaccine development.

P04-53 LB. Potent and broad HIV-specific neutralizing antibodies in infants are not associated with prevention of mother to infant HIV transmission

Background Infants of women infected with HIV-1 are born with antibodies specific for the virus. In the non-human primate model, neutralizing antibodies (NAb) protect from SHIV/ SIV transmission, implying a role for such a response in candidate HIV vaccines. The setting of mother to child HIV transmission provides an opportunity to examine whether NAb provide protection from HIV infection in exposed humans.

Is an HIV vaccine possible?

The road to the discovery of a vaccine for HIV has been arduous and will continue to be difficult over the ensuing twenty years. Most vaccines are developed by inducing neutralizing antibodies against the target pathogen or by using attenuated strains of the particular pathogen to engender a variety of protective immune responses. Unfortunately, simple methods of generating anti-HIV antibodies have already failed in a phase III clinical trial. While attenuated SIV variants work well against homologous challenges in non-human primates, the potential for reversion to a more pathogenic virus and recombination with challenge viruses will preclude the use of attenuated HIV in the field. It has been exceedingly frustrating to vaccinate for HIV-specific neutralizing antibodies given the enormous diversity of the Envelope (Env) glycoprotein and its well-developed glycan shield. However, there are several antibodies that will neutralize many different strains of HIV and inducing these types of antibodies in vaccinees remains the goal of a vigorous effort to develop a vaccine for HIV based on neutralizing antibodies. Given the difficulty in generating broadly reactive neutralizing antibodies, the HIV vaccine field has turned its attention to inducing T cell responses against the virus using a variety of vectors. Unfortunately, the results from Merck's phase IIb STEP trial proved to be disappointing. Vaccinees received Adenovirus type 5 (Ad5) expressing Gag, Pol, and Nef of HIV. This vaccine regimen failed to either prevent infection or reduce the level of HIV replication after challenge. These results mirrored those in non-human primate testing of Ad5 using rigorous SIV challenge models. This review will focus on recent developments in HIV vaccine development. We will deal largely with attempts to develop a T cell-based vaccine using the non-human primate SIV challenge model.

Autologous Neutralizing Humoral Immunity and Evolution of the Viral Envelope in the Course of Subtype B Human Immunodeficiency Virus Type 1 Infection

Most human immunodeficiency virus type 1 (HIV-1)-infected individuals develop an HIV-specific neutralizing antibody (NAb) response that selects for escape variants of the virus. Here, we studied autologous NAb responses in five typical CCR5-using progressors in relation to viral NAb escape and molecular changes in the viral envelope (Env) in the period from seroconversion until after AIDS diagnosis. In sera from three patients, high-titer neutralizing activity was observed against the earliest autologous virus variants, followed by declining humoral immune responses against subsequent viral escape variants. Autologous neutralizing activity was undetectable in sera from two patients. Patients with high-titer neutralizing activity in serum showed the strongest positive selection pressure on Env early in infection. In the initial phase of infection, gp160 length and the number of potential N-linked glycosylation sites (PNGS) increased in viruses from all patients. Over the course of infection, positive selection pressure declined as the NAb response subsided, coinciding with reversions of changes in gp160 length and the number of PNGS. A number of identical amino acid changes were observed over the course of infection in the viral quasispecies of different patients. Our results indicate that although neutralizing autologous humoral immunity may have a limited effect on the disease course, it is an important selection pressure in virus evolution early in infection, while declining HIV-specific humoral immunity in later stages may coincide with reversion of NAb-driven changes in Env.

Mucosal HIV‐Binding Antibody and Neutralizing Activity in High‐Risk HIV‐Uninfected Female Participants in a Trial of HIV‐Vaccine Efficacy

This study investigated gp120-binding antibody and neutralizing activity, at the gingival- and cervical-mucosal levels, in response to a bivalent gp120 candidate vaccine. Women who met the study's inclusion criteria for documented high-risk behaviors participated in a nested substudy of the multicenter phase 3 trial of human immunodeficiency virus (HIV)-vaccine efficacy, VAX004. Gingival, cervicovaginal lavage, and plasma specimens were collected at 6-month intervals for 3 years. Binding-antibody and neutralizing-activity assays quantified the presence of anti-HIV activity in mucosal specimens. Vaccine recipients were more likely than placebo recipients to have IgG binding antibodies in all 3 compartments tested and to have only IgA binding antibody in plasma (P<.0001). The relationship between vaccine and cervicovaginal IgG achieved significance (odds ratio [OR], 6.6 [P=.01]) but was weakened by the presence of cervicovaginal leukocytes. There was no relationship between immunization and the presence of neutralizing activity, in either bivariate or multivariate modeling (OR, 6.0 [P=.29]). Vaccination is associated with the presence of both gp120-binding IgG in all compartments and plasma IgA but not with neutralizing activity. There is a role for the measurement of mucosal immunity in response to candidate vaccines and, in particular, for a determination of HIV-specific neutralizing antibodies.

Advances in methods for the production, purification, and characterization of HIV-1 Gag–Env pseudovirion vaccines

HIV pseudovirion or virus-like particle vaccines represent a promising approach for eliciting humoral and cellular immune responses. Pseudovirions present the envelope glycoprotein complex in its authentic trimeric form, and thus have the potential to generate neutralizing antibodies against relevant virion-associated epitopes that may be lacking in protein subunit vaccines. The development of pseudovirion particles as a viable vaccine approach for progression to clinical testing has been limited by a number of factors, including shedding of particle-associated gp120, practical limitations to large-scale production and purification, and the generation of antibodies against cellular proteins incorporated on the particle surface that confound the analysis of HIV-specific neutralizing antibody responses. Here, we review methods that address each of these challenges, with a focus on production methods for generating non-infectious Gag–Env pseudovirions. Mammalian cell lines that inducibly express HIV Gag and Env can overcome production limitations, and produce pseudovirions that retain gp120 following purification. Baculovirus production systems have the potential to provide higher quantities of particles, but cleavage of gp160 remains a current limitation. Anti-cellular antibody responses can be diminished by adsorption with cell lysates or whole cells. These technical advances should facilitate the further development of pseudovirion vaccine approaches in preclinical testing and future clinical trials.

Non-Neutralizing Antibodies and Vaccine-Induced Protection Against HIV

HIV-specific neutralizing antibodies are crucial for sterilizing immunity but have been difficult to elicit using current vaccine approaches. By contrast, non-neutralizing antibodies that mediate other effector functions are readily induced. Recent data suggest these antibodies may play a significant role in viral load reduction and/or clearance. The interval between viral entry across a mucosal barrier and development of systemic infection provides a timeframe during which these antibodies may impact the outcome of infection. Here we discuss various effector mechanisms mediated by non-neutralizing antibodies and summarize evidence of their contribution to protective efficacy. We suggest that non-neutralizing antibody components be incorporated into vaccine strategies, and predict that further exploration of this area of research will prove fruitful for HIV vaccine development.

Excellent Safety and Tolerability of the Human Immunodeficiency Virus Type 1 pGA2/JS2 Plasmid DNA Priming Vector Vaccine in HIV Type 1 Uninfected Adults

A vaccine consisting of DNA priming followed by recombinant modified vaccinia Ankara (rMVA) boosting has achieved long-term control of a pathogenic challenge with a chimera of simian and human immunodeficiency viruses (SHIV-89.6P) in rhesus macaques. Based on these results, clade B HIV-1 DNA and rMVA immunogens have been developed for trials in humans. We conducted a first-time in humans phase I safety trial using the pGA2/JS2 (JS2) HIV-1 DNA priming vector expressing Gag, Pol, Env, Tat, Rev, and Vpu. Thirty HIV-uninfected adults were vaccinated with 0.3 or 3 mg of JS2 DNA, or a saline placebo, by intramuscular injection at months 0 and 2. Both doses of DNA were safe and well-tolerated with no differences between the control, 0.3 mg, or 3 mg groups (n = 6, 12, and 12, respectively) through 12 months of postvaccination follow- up. A chromium-release assay using fresh peripheral blood mononuclear cells (PBMCs) and a validated IFN-gamma ELISpot assay with frozen PBMCs failed to detect CD4(+) or CD8(+) HIV-1-specific T cell responses. HIV-specific neutralizing antibodies were also not detected. The vaccine is being further developed as a priming vector for a combined DNA plus rMVA prime/boost HIV vaccination regimen.