Broadly neutralizing antibodies against HIV-1 and concepts for application

HIV diagnosis during acute infection: implications of long-acting preexposure prophylaxis and other evolving challenges

PURPOSE OF REVIEW

Tests for HIV may perform differently in some circumstances such as with preexposure prophylaxis (PrEP) or other HIV prevention agents. Testing algorithms may not account for this, with a risk of false negative or positive HIV results. In this review we have explored the challenges of HIV testing in these special circumstances.

RECENT FINDINGS

Long-acting injectable PrEP using cabotegravir or lenacapavir has been studied in large randomized controlled trials (HPTN083/084 and PURPOSE1/2 respectively). Injectable PrEP was significantly more efficacious than oral PrEP, but infections still occurred risking the emergence of HIV drug-resistance. HIV diagnostic test results were atypical in those receiving injectable PrEP, with low or undetectable HIV viral loads, delayed or diminished antibody, and HIV detection assays reverting from reactive to unreactive; so-called long acting early viral inhibition (LEVI) syndrome. In these cases, missed or delayed HIV diagnoses could be reduced with the use of HIV nucleic acid amplification tests in addition to routine testing, but this remains unfeasible in many settings.

SUMMARY

Finding HIV testing strategies that are affordable and practical in low- and middle-income countries that can accurately diagnose HIV in the context of HIV prevention is of high importance, but more research is needed in this area.

Virologic effects of broadly neutralizing antibodies VRC01LS and VRC07-523LS on chronic HIV-1 infection

BACKGROUNDHIV-1-specific broadly neutralizing monoclonal antibodies (bNAbs) have emerged as promising interventions with the potential to effectively treat and prevent HIV-1 infections. We conducted a phase I clinical trial evaluating the potent CD4-binding site-specific (CD4bs-specific) bNAbs VRC01LS and VRC07-523LS in people with HIV-1 (PWH) not receiving antiretroviral therapy (ART).METHODSParticipants received a single intravenous 40 mg/kg dose of either VRC01LS (n = 7) or VRC07-523LS (n = 9) and did not initiate ART for a minimum of 14 days. The primary study objective was to evaluate safety and tolerability; the secondary study objectives were to evaluate pharmacokinetics (PK) and the impact of administered bNAbs on viral loads (VL) and CD4+ T cell counts in the absence of ART.RESULTSThis trial enrolled 16 PWH aged 20 to 57 years. Both bNAbs were safe and well tolerated. Mild local reactogenicity was only reported in participants who received VRC07-523LS, while both bNAbs were associated with mild systemic symptoms. Maximum serum concentrations (Cmax) following VRC01LS or VRC07-523LS were 1,566 ± 316 and 1,295 ± 376 μg/mL, respectively. VRC07-523LS administration significantly decreased VL in 8 out of 9 participants, with an average decline of 1.7 ± 0.8 log10 copies/mL within 14 days after administration. In contrast, VRC01LS administration resulted in a smaller average decline (0.8 ± 0.8 log10 copies/mL), and 3 out of 7 participants showedno change in VL. Postinfusion maximum decline in VL correlated with post hoc baseline in vitro viral susceptibility results for both bNAbs.CONCLUSIONThe results of this trial support inclusion of potent CD4bs-specific bNAbs, such as VRC07-523LS, into next-generation treatment regimens for HIV-1.TRIAL REGISTRATIONClinicalTrials.gov NCT02840474.FUNDINGNational Institute of Allergy and Infectious Diseases (NIAID)/NIH (grants UM1 AI068634, UM1 AI068636, UM1 AI106701, UM1AI069424, UM1AI069501, UM1AI69415, UM1AI069534, UM1AI69494); the Intramural Research Program of the NIAID/NIH; National Center for Advancing Translational Sciences/NIH (grants UM1TR004548, UL1TR001881, and UL1TR001878); and the National Cancer Institute/NIH (contract 75N91019D00024).

SERINC5 counters retroviruses and non-retroviruses

SERINC5 (serine incorporator 5), a member of the serine incorporator family, has been identified as a retrovirus restriction factor that inhibits the fusion of virions with the plasma membrane, thus blocking the release of the viral core into target cells and subsequently attenuating viral infectivity. Several viruses, such as human immunodeficiency virus (HIV), murine leukemia virus (MLV), and equine infectious anemia virus (EIAV), have evolved mechanisms to antagonize the host protein SERINC5 through HIV Nef, MLV glycosylated Gag, and the EIAV S2 protein. These viral proteins degrade SERINC5 on the cell surface through the endolysosomal system. In addition to its direct antiviral ability, SERINC5 also modulates immunity to inhibit the replication of retroviruses and nonretroviruses. This review summarizes the interaction between SERINC5 and viral replication, providing a promising avenue for fighting viral diseases.

Current methods for detecting and assessing HIV-1 antibody resistance

Antiretroviral therapy is the standard treatment for HIV, but it requires daily use and can cause side effects. Despite being available for decades, there are still 1.5 million new infections and 700,000 deaths each year, highlighting the need for better therapies. Broadly neutralizing antibodies (bNAbs), which are highly active against HIV-1, represent a promising new approach and clinical trials have demonstrated the potential of bNAbs in the treatment and prevention of HIV-1 infection. However, HIV-1 antibody resistance (HIVAR) due to variants in the HIV-1 envelope glycoproteins (HIV-1 Env) is not well understood yet and poses a critical problem for the clinical use of bNAbs in treatment. HIVAR also plays an important role in the future development of an HIV-1 vaccine, which will require elicitation of bNAbs to which the circulating strains are sensitive. In recent years, a variety of methods have been developed to detect, characterize and predict HIVAR. Structural analysis of antibody-HIV-1 Env complexes has provided insight into viral residues critical for neutralization, while testing of viruses for antibody susceptibility has verified the impact of some of these residues. In addition, in vitro viral neutralization and adaption assays have shaped our understanding of bNAb susceptibility based on the envelope sequence. Furthermore, in vivo studies in animal models have revealed the rapid emergence of escape variants to mono- or combined bNAb treatments. Finally, similar variants were found in the first clinical trials testing bNAbs for the treatment of HIV-1-infected patients. These structural, in vitro, in vivo and clinical studies have led to the identification and validation of HIVAR for almost all available bNAbs. However, defined assays for the detection of HIVAR in patients are still lacking and for some novel, highly potent and broad-spectrum bNAbs, HIVAR have not been clearly defined. Here, we review currently available approaches for the detection, characterization and prediction of HIVAR.

Neutralizing antibodies elicited in macaques recognize V3 residues on altered conformations of HIV-1 Env trimer

Eliciting broadly neutralizing antibodies that protect against diverse HIV-1 strains is a primary goal of AIDS vaccine research. We characterized Ab1456 and Ab1271, two heterologously-neutralizing antibodies elicited in non-human primates by priming with an engineered V3-targeting SOSIP Env immunogen and boosting with increasingly native-like SOSIP Envs derived from different strain backgrounds. Structures of Env trimers in complex with these antibodies revealed V3 targeting, but on conformational states of Env distinct from the typical closed, prefusion trimeric SOSIP structure. Env trimers bound by Ab1456 adopted conformations resembling CD4-bound open Env states in the absence of soluble CD4, whereas trimers bound by Ab1271 exhibited a trimer apex-altered conformation to accommodate antibody binding. The finding that elicited antibodies cross-neutralized by targeting altered, non-closed, prefusion Env trimer conformations provides important information about Env dynamics that is relevant for HIV-1 vaccine design aimed at raising antibodies to desired epitopes on closed pre-fusion Env trimers.

Trade-off between the antiviral and vaccinal effects of antibody therapy in the humoral response to HIV

Antibody therapy for HIV-1 infection exerts two broad effects: a drug-like, antiviral effect, which rapidly lowers the viral load, and a vaccinal effect, which may control the viral load long-term by improving the immune response. Here, we elucidate a trade-off between these two effects as they pertain to the humoral response, which may compromise antibody therapy aimed at eliciting long-term HIV-1 remission. We developed a multi-scale computational model that combined within-host viral dynamics and stochastic simulations of the germinal centre (GC) reaction, enabling simultaneous quantification of the antiviral and vaccinal effects of antibody therapy. The model predicted that increasing antibody dosage or antibody-antigen affinity increased immune complex formation and enhanced GC output. Beyond a point, however, a strong antiviral effect reduced antigen levels substantially, extinguishing GCs and limiting the humoral response. We found signatures of this trade-off in clinical studies. Accounting for the trade-off could be important in optimizing antibody therapy for HIV-1 remission.

The CH1 domain influences the expression and antigen sensing of the HIV-specific CH31 IgM-BCR and IgG-BCR

How different classes of the B cell antigen receptor (BCR) sense viral antigens used in vaccination protocols is poorly understood. Here, we study antigen binding and sensing of human Ramos B cells expressing a BCR of either the IgM or IgG1 class with specificity for the CD4-binding-site of the envelope (Env) protein of the HIV-1. Both BCRs carry an identical antigen binding site derived from the broad neutralizing antibody (bnAb) CH31. We find a five times higher expression of the IgG1-BCR in comparison to the IgM-BCR on the surface of transfected Ramos B cells. The two BCR classes also differ from each other in their interaction with cognate HIV Env antigens in that the IgG1-BCR and IgM-BCR bind preferentially to polyvalent and monovalent antigens, respectively. By generating an IgM/IgG1 chimeric BCR, we found that the class-specific BCR expression and antigen-sensing behavior can be transferred with the CH1γ domain from the IgG1-BCR to the IgM-BCR. Thus, the class of CH1 domain has an impact on BCR assembly and expression as well as on antigen sensing.

Preference for novel biomedical HIV pre-exposure prophylaxis methods among adolescent girls and young women in Kampala, Uganda: a mixed methods study

Background

Novel HIV pre-exposure prophylaxis (PrEP) methods including a potential future HIV vaccine, will increase prevention options for adolescent girls and young women (AGYW) at high risk of HIV infection in Eastern and Southern Africa, yet data on AGYW's preferences for various PrEP methods is limited. We investigated preferences for five biomedical PrEP methods (oral, injectable, vaginal ring, implant, HIV vaccine) among 14-24-years-old AGYW in Kampala, Uganda.

Methods

From January to December 2019, we conducted a mixed methods study including 265 high-risk AGYW. After receiving two education sessions on the five PrEP methods, participants were asked about their "most preferred PrEP method." Multinomial logistic regression (oral PrEP as reference category) was used to determine participant characteristics associated with method preference. Results are presented as adjusted relative risk ratios (aRRR) with 95% confidence intervals (CI). In-depth interviews were conducted with 20 selected participants to examine reasons influencing PrEP preferences and suggestions for method improvements. Transcripts were analyzed thematically.

Results

Participants preferred methods were: HIV vaccine (34.7%), oral PrEP (25.7%), injectable PrEP (24.9%), PrEP implant (13.6%), and vaginal ring (1.1%). Preference for injectable PrEP increased with every year of age (aRRR 1.22; 95% CI 1.04-1.44) and among participants with chlamydia or gonorrhoea (aRRR 2.53; 95% CI 1.08-5.90), while it was lower among participants having sexual partner(s) living with HIV or of unknown HIV status (aRRR 0.30; 95% CI 0.10-0.91). Preference for PrEP implants also increased with age (aRRR 1.42; 95% CI 1.14-1.77) and was strong among participants having ≥10 sexual partners in the past 3 months (aRRR 3.14; 95% CI 1.16-8.55), while it was lower among those with sexual partner(s) living with HIV or of unknown HIV status (aRRR 0.25; 95% CI 0.07-0.92). PrEP method preference was influenced by product attributes and prior experiences with similar product forms commonly used in health care.

Conclusion

AGYW have varied preferences for biomedical PrEP method and those with higher sexual behavioral risk prefer long-acting methods. As we anticipate more available PrEP options, oral PrEP use should be supported among AGYW, especially for those with sexual partners living with HIV or of unknown HIV status.

Next-generation bNAbs for HIV-1 cure strategies

Despite the ability to suppress viral replication using anti-retroviral therapy (ART), HIV-1 remains a global public health problem. Curative strategies for HIV-1 have to target and eradicate latently infected cells across the body, i.e. the viral reservoir. Broadly neutralizing antibodies (bNAbs) targeting the HIV-1 envelope glycoprotein (Env) have the capacity to neutralize virions and bind to infected cells to initiate elimination of these cells. To improve the efficacy of bNAbs in terms of viral suppression and viral reservoir eradication, next generation antibodies (Abs) are being developed that address the current limitations of Ab treatment efficacy; (1) low antigen (Env) density on (reactivated) HIV-1 infected cells, (2) high viral genetic diversity, (3) exhaustion of immune cells and (4) short half-life of Abs. In this review we summarize and discuss preclinical and clinical studies in which anti-HIV-1 Abs demonstrated potent viral control, and describe the development of engineered Abs that could address the limitations described above. Next generation Abs with optimized effector function, avidity, effector cell recruitment and immune cell activation have the potential to contribute to an HIV-1 cure or durable control.

Probabilities of developing HIV-1 bNAb sequence features in uninfected and chronically infected individuals

HIV-1 broadly neutralizing antibodies (bNAbs) are able to suppress viremia and prevent infection. Their induction by vaccination is therefore a major goal. However, in contrast to antibodies that neutralize other pathogens, HIV-1-specific bNAbs frequently carry uncommon molecular characteristics that might prevent their induction. Here, we perform unbiased sequence analyses of B cell receptor repertoires from 57 uninfected and 46 chronically HIV-1- or HCV-infected individuals and learn probabilistic models to predict the likelihood of bNAb development. We formally show that lower probabilities for bNAbs are predictive of higher HIV-1 neutralization activity. Moreover, ranking bNAbs by their probabilities allows to identify highly potent antibodies with superior generation probabilities as preferential targets for vaccination approaches. Importantly, we find equal bNAb probabilities across infected and uninfected individuals. This implies that chronic infection is not a prerequisite for the generation of bNAbs, fostering the hope that HIV-1 vaccines can induce bNAb development in uninfected people.

Mapping the neutralizing specificity of human anti-HIV serum by deep mutational scanning

Understanding the specificities of human serum antibodies that broadly neutralize HIV can inform prevention and treatment strategies. Here, we describe a deep mutational scanning system that can measure the effects of combinations of mutations to HIV envelope (Env) on neutralization by antibodies and polyclonal serum. We first show that this system can accurately map how all functionally tolerated mutations to Env affect neutralization by monoclonal antibodies. We then comprehensively map Env mutations that affect neutralization by a set of human polyclonal sera that neutralize diverse strains of HIV and target the site engaging the host receptor CD4. The neutralizing activities of these sera target different epitopes, with most sera having specificities reminiscent of individual characterized monoclonal antibodies, but one serum targeting two epitopes within the CD4-binding site. Mapping the specificity of the neutralizing activity in polyclonal human serum will aid in assessing anti-HIV immune responses to inform prevention strategies.

Complement contributes to antibody-mediated protection against repeated SHIV challenge

The first clinical efficacy trials of a broadly neutralizing antibody (bNAb) resulted in less benefit than expected and suggested that improvements are needed to prevent HIV infection. While considerable effort has focused on optimizing neutralization breadth and potency, it remains unclear whether augmenting the effector functions elicited by broadly neutralizing antibodies (bNAbs) may also improve their clinical potential. Among these effector functions, complement-mediated activities, which can culminate in the lysis of virions or infected cells, have been the least well studied. Here, functionally modified variants of the second-generation bNAb 10-1074 with ablated and enhanced complement activation profiles were used to examine the role of complement-associated effector functions. When administered prophylactically against simian-HIV challenge in rhesus macaques, more bNAb was required to prevent plasma viremia when complement activity was eliminated. Conversely, less bNAb was required to protect animals from plasma viremia when complement activity was enhanced. These results suggest that complement-mediated effector functions contribute to in vivo antiviral activity, and that their engineering may contribute to the further improvements in the efficacy of antibody-mediated prevention strategies.

Conserved multiepitope vaccine constructs: A potent HIV-1 therapeutic vaccine in clinical trials

Despite the success of Antiretroviral Therapy (ART) in preventing HIV-1-associated clinical progression to AIDS, it is unable to eliminate the viral reservoirs and eradicate the HIV-1 infection. Therapeutic vaccination is an alternative approach to alter the HIV-1 infection course. It can induce effective HIV-1-specific immunity to control viremia and eliminate the need for lifelong ART. Immunological data from spontaneous HIV-1 controllers have shown that cross-reactive T-cell responses are the key immune mechanism in HIV-1 control. Directing these responses toward preferred HIV-1 epitopes is a promising strategy in therapeutic vaccine settings. Designing novel immunogens based on the HIV-1 conserved regions containing a wide range of critical T- and B-cell epitopes of the main viral antigens (conserved multiepitope approaches) supplies broad coverage of global diversity in HIV-1 strains and Human Leukocyte Antigen (HLA) alleles. It can also prevent immune induction to undesirable decoy epitopes theoretically. The efficacy of different novel HIV-1 immunogens based on the conserved and/or functional protective site of HIV-1 proteome has been evaluated in multiple clinical trials. Most of these immunogens were generally safe and able to induce potent HIV-1-specific immunity. However, despite these findings, several candidates have demonstrated limited efficacy in viral replication control. In this study, we used the PubMed and ClinicalTrial.gov databases to review the rationale of designing curative HIV-1 vaccine immunogens based on the conserved favorable site of the virus. Most of these studies evaluate the efficacy of vaccine candidates in combination with other therapeutics and/or with new formulations and immunization protocols. This review briefly describes the design of conserved multiepitope constructs and outlines the results of these vaccine candidates in the recent clinical pipeline.

Mapping the neutralizing specificity of human anti-HIV serum by deep mutational scanning

Understanding the specificities of human serum antibodies that broadly neutralize HIV can inform prevention and treatment strategies. Here we describe a deep mutational scanning system that can measure the effects of combinations of mutations to HIV envelope (Env) on neutralization by antibodies and polyclonal serum. We first show that this system can accurately map how all functionally tolerated mutations to Env affect neutralization by monoclonal antibodies. We then comprehensively map Env mutations that affect neutralization by a set of human polyclonal sera known to target the CD4-binding site that neutralize diverse strains of HIV. The neutralizing activities of these sera target different epitopes, with most sera having specificities reminiscent of individual characterized monoclonal antibodies, but one sera targeting two epitopes within the CD4 binding site. Mapping the specificity of the neutralizing activity in polyclonal human serum will aid in assessing anti-HIV immune responses to inform prevention strategies.

4-phenylquinoline-8-amine induces HIV-1 reactivation and apoptosis in latently HIV-1 infected cells

Combinational antiretroviral therapy (cART) dramatically suppresses the viral load to undetectable levels in human immunodeficiency virus (HIV)-infected patients. However, HIV-1 reservoirs in CD4+T cells and myeloid cells, which can evade cART and host antiviral immune systems, are still significant obstacles to HIV-1 eradication. The "Shock and Kill" approach using latently-reversing agents (LRAs) is therefore currently developing strategies for effective HIV-1 reactivation from latency and inducing cell death. Here, we performed small-molecular chemical library screening with monocytic HIV-1 latently-infected model cells, THP-1 Nluc #225, and identified 4-phenylquinoline-8-amine (PQA) as a novel LRA candidate. PQA induced efficient HIV-1 reactivation in combination with PKC agonists including Prostratin and showed a similar tendency for HIV-1 activation in primary HIV-1 reservoirs. Furthermore, PQA induced killing of HIV-1 latently-infected cells. RNA-sequencing analysis revealed PQA had different functional mechanisms from PKC agonists, and oxidative stress-inducible genes including DDIT3 or CTSD were only involved in PQA-mediated cell death. In summary, PQA is a potential LRA lead compound that exerts novel functions related to HIV-1 activation and apoptosis-mediated cell death to eliminate HIV-1 reservoirs.

Monoclonal Antibodies as Long-Acting Products: What Are We Learning From Human Immunodeficiency Virus (HIV) and Coronavirus Disease 2019 (COVID-19)?

Broadly neutralizing antibodies directed against human immunodeficiency virus (HIV) offer promise as long-acting agents for prevention and treatment of HIV. Progress and challenges are discussed. Lessons may be learned from the development of monoclonal antibodies to treat and prevent COVID-19.

A naturally arising broad and potent CD4-binding site antibody with low somatic mutation

The induction of broadly neutralizing antibodies (bNAbs) is a potential strategy for a vaccine against HIV-1. However, most bNAbs exhibit features such as unusually high somatic hypermutation, including insertions and deletions, which make their induction challenging. VRC01-class bNAbs not only exhibit extraordinary breadth and potency but also rank among the most highly somatically mutated bNAbs. Here, we describe a VRC01-class antibody isolated from a viremic controller, BG24, that is much less mutated than most relatives of its class while achieving comparable breadth and potency. A 3.8-Å x-ray crystal structure of a BG24-BG505 Env trimer complex revealed conserved contacts at the gp120 interface characteristic of the VRC01-class Abs, despite lacking common CDR3 sequence motifs. The existence of moderately mutated CD4-binding site (CD4bs) bNAbs such as BG24 provides a simpler blueprint for CD4bs antibody induction by a vaccine, raising the prospect that such an induction might be feasible with a germline-targeting approach.

Design of a Bispecific HIV Entry Inhibitor Targeting the Cell Receptor CD4 and Viral Fusion Protein Gp41

Given the high variability and drug-resistance problem by human immunodeficiency virus type 1 (HIV-1), the development of bispecific or multi-specific inhibitors targeting different steps of HIV entry is highly appreciated. We previously generated a very potent short-peptide-based HIV fusion inhibitor 2P23. In this study, we designed and characterized a bifunctional inhibitor termed 2P23-iMab by genetically conjugating 2P23 to the single-chain variable fragment (scFv) of ibalizumab (iMab), a newly approved antibody drug targeting the cell receptor CD4. As anticipated, 2P23-iMab could bind to the cell membrane through CD4 anchoring and inhibit HIV-1 infection as well as viral Env-mediated cell-cell fusion efficiently. When tested against a large panel of HIV-1 pseudoviruses with different subtypes and phenotypes, 2P23-iMab exhibited dramatically improved inhibitory activity than the parental inhibitors; especially, it potently inhibited the viruses not being susceptible to iMab. Moreover, 2P23-iMab had a dramatically increased potency in inhibiting two panels of HIV-1 mutants that are resistant to T-20 or 2P23 and the infections of HIV-2 and simian immunodeficiency virus (SIV). In conclusion, our studies have provided new insights into the design of novel bispecific HIV entry inhibitors with highly potent and broad-spectrum antiviral activity.