Antibody responses to the HIV-1 envelope high mannose patch

The Question of HIV Vaccine: Why Is a Solution Not Yet Available?

Ever since its discovery, human immunodeficiency virus type 1 (HIV-1) infection has remained a significant public health concern. The number of HIV-1 seropositive individuals currently stands at 40.1 million, yet definitive treatment for the virus is still unavailable on the market. Vaccination has proven to be a potent tool in combating infectious diseases, as evidenced by its success against other pathogens. However, despite ongoing efforts and research, the unique viral characteristics have prevented the development of an effective anti-HIV-1 vaccine. In this review, we aim to provide an historical overview of the various approaches attempted to create an effective anti-HIV-1 vaccine. Our objective is to explore the reasons why specific methods have failed to induce a protective immune response and to analyze the different modalities of immunogen presentation. This trial is registered with NCT05414786, NCT05471076, NCT04224701, and NCT01937455.

A HIV-1 Gp41 Peptide-Liposome Vaccine Elicits Neutralizing Epitope-Targeted Antibody Responses in Healthy Individuals

Background

HIV-1 vaccine development is a global health priority. Broadly neutralizing antibodies (bnAbs) which target the HIV-1 gp41 membrane-proximal external region (MPER) have some of the highest neutralization breadth. An MPER peptide-liposome vaccine has been found to expand bnAb precursors in monkeys.

Methods

The HVTN133 phase 1 clinical trial (NCT03934541) studied the MPER-peptide liposome immunogen in 24 HIV-1 seronegative individuals. Participants were recruited between 15 July 2019 and 18 October 2019 and were randomized in a dose-escalation design to either 500 mcg or 2000 mcg of the MPER-peptide liposome or placebo. Four intramuscular injections were planned at months 0, 2, 6, and 12.

Results

The trial was stopped prematurely due to an anaphylaxis reaction in one participant ultimately attributed to vaccine-associated polyethylene glycol. The immunogen induced robust immune responses, including MPER+ serum and blood CD4+ T-cell responses in 95% and 100% of vaccinees, respectively, and 35% (7/20) of vaccine recipients had blood IgG memory B cells with MPER-bnAb binding phenotype. Affinity purification of plasma MPER+ IgG demonstrated tier 2 HIV-1 neutralizing activity in two of five participants after 3 immunizations.

Conclusions

MPER-peptide liposomes induced gp41 serum neutralizing epitope-targeted antibodies and memory B-cell responses in humans despite the early termination of the study. These results suggest that the MPER region is a promising target for a candidate HIV vaccine.

Genetic signatures in the highly virulent subtype B HIV-1 conferring immune escape to V1/V2 and V3 broadly neutralizing antibodies

HIV-1 is considered to become less susceptible to existing neutralizing antibodies over time. Our study on the virulent B (VB) HIV-1 identified genetic signatures responsible for immune escape from broadly neutralizing antibodies (bNAbs) targeting V1/V2 and V3 glycan epitopes. We found that the absence of N295 and N332 glycans in the high mannose patch, which are crucial for neutralization by V3 glycan bNAbs and are typically conserved in subtype B HIV-1, is a notable feature in more than half of the VB variants. Neutralization assays confirmed that the loss of these two glycans in VB HIV-1 leads to escape from V3 glycan bNAbs. Additionally, all VB variants we investigated have an insertion in V2, contributing to immune escape from V1/V2 bNAbs PG9 and PG16. These findings suggest potential co-evolution of HIV-1 virulence and antigenicity, underscoring the need to monitor both the pathogenicity and neutralization susceptibility of newly emerged HIV-1 strains.

Eliminating the HIV tissue reservoir: current strategies and challenges

BACKGROUND

Acquired immunodeficiency syndrome (AIDS) is still one of the most widespread and harmful infectious diseases in the world. The presence of reservoirs housing the human immunodeficiency virus (HIV) represents a significant impediment to the development of clinically applicable treatments on a large scale. The viral load in the blood can be effectively reduced to undetectable levels through antiretroviral therapy (ART), and a higher concentration of HIV is sequestered in various tissues throughout the body, forming the tissue reservoir - the source of viremia after interruption treatment.

METHODS

We take the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) as a guideline for this review. In June 2023, we used the Pubmed, Embase, and Scopus databases to search the relevant literature published in the last decade.

RESULTS

Here we review the current strategies and treatments for eliminating the HIV tissue reservoirs: early and intensive therapy, gene therapy (including ribozyme, RNA interference, RNA aptamer, zinc finger enzyme, transcriptional activator-like effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeats/associated nuclease 9 (CRISPR/Cas9)), 'Shock and Kill', 'Block and lock', immunotherapy (including therapeutic vaccines, broadly neutralising antibodies (bNAbs), chimeric antigen receptor T-cell immunotherapy (CAR-T)), and haematopoietic stem cell transplantation (HSCT).

CONCLUSION

The existence of an HIV reservoir is the main obstacle to the complete cure of AIDS. Choosing the appropriate strategy to deplete the HIV reservoir and achieve a functional cure for AIDS is the focus and difficulty of current research. So far, there has been a lot of research and progress in reducing the HIV reservoir, but in general, the current research is still very preliminary. Much research is still needed to properly assess the reliability, effectiveness, and necessity of these strategies.

Antigen pressure from two founder viruses induces multiple insertions at a single antibody position to generate broadly neutralizing HIV antibodies

Vaccination strategies aimed at maturing broadly neutralizing antibodies (bnAbs) from naïve precursors are hindered by unusual features that characterize these Abs, including insertions and deletions (indels). Longitudinal studies of natural HIV infection cases shed light on the complex processes underlying bnAb development and have suggested a role for superinfection as a potential enhancer of neutralization breadth. Here we describe the development of a potent bnAb lineage that was elicited by two founder viruses to inform vaccine design. The V3-glycan targeting bnAb lineage (PC39-1) was isolated from subtype C-infected IAVI Protocol C elite neutralizer, donor PC39, and is defined by the presence of multiple independent insertions in CDRH1 that range from 1-11 amino acids in length. Memory B cell members of this lineage are predominantly atypical in phenotype yet also span the class-switched and antibody-secreting cell compartments. Development of neutralization breadth occurred concomitantly with extensive recombination between founder viruses before each virus separated into two distinct population "arms" that evolved independently to escape the PC39-1 lineage. Ab crystal structures show an extended CDRH1 that can help stabilize the CDRH3. Overall, these findings suggest that early exposure of the humoral system to multiple related Env molecules could promote the induction of bnAbs by focusing Ab responses to conserved epitopes.

An HIV-1/HIV-2 Chimeric Envelope Glycoprotein Generates Binding and Neutralising Antibodies against HIV-1 and HIV-2 Isolates

The development of immunogens that elicit broadly reactive neutralising antibodies (bNAbs) is the highest priority for an HIV vaccine. We have shown that a prime-boost vaccination strategy with vaccinia virus expressing the envelope glycoprotein gp120 of HIV-2 and a polypeptide comprising the envelope regions C2, V3 and C3 elicits bNAbs against HIV-2. We hypothesised that a chimeric envelope gp120 containing the C2, V3 and C3 regions of HIV-2 and the remaining parts of HIV-1 would elicit a neutralising response against HIV-1 and HIV-2. This chimeric envelope was synthesised and expressed in vaccinia virus. Balb/c mice primed with the recombinant vaccinia virus and boosted with an HIV-2 C2V3C3 polypeptide or monomeric gp120 from a CRF01_AG HIV-1 isolate produced antibodies that neutralised >60% (serum dilution 1:40) of a primary HIV-2 isolate. Four out of nine mice also produced antibodies that neutralised at least one HIV-1 isolate. Neutralising epitope specificity was assessed using a panel of HIV-1 TRO.11 pseudoviruses with key neutralising epitopes disrupted by alanine substitution (N160A in V2; N278A in the CD4 binding site region; N332A in the high mannose patch). The neutralisation of the mutant pseudoviruses was reduced or abolished in one mouse, suggesting that neutralising antibodies target the three major neutralising epitopes in the HIV-1 envelope gp120. These results provide proof of concept for chimeric HIV-1/HIV-2 envelope glycoproteins as vaccine immunogens that can direct the antibody response against neutralising epitopes in the HIV-1 and HIV-2 surface glycoproteins.

Strategies for HIV-1 vaccines that induce broadly neutralizing antibodies

After nearly four decades of research, a safe and effective HIV-1 vaccine remains elusive. There are many reasons why the development of a potent and durable HIV-1 vaccine is challenging, including the extraordinary genetic diversity of HIV-1 and its complex mechanisms of immune evasion. HIV-1 envelope glycoproteins are poorly recognized by the immune system, which means that potent broadly neutralizing antibodies (bnAbs) are only infrequently induced in the setting of HIV-1 infection or through vaccination. Thus, the biology of HIV-1-host interactions necessitates novel strategies for vaccine development to be designed to activate and expand rare bnAb-producing B cell lineages and to select for the acquisition of critical improbable bnAb mutations. Here we discuss strategies for the induction of potent and broad HIV-1 bnAbs and outline the steps that may be necessary for ultimate success.

The HIV Env Glycoprotein Conformational States on Cells and Viruses

The HIV Env glycoprotein is the surface glycoprotein responsible for viral entry into CD4+ immune cells. During infection, Env also serves as a primary target for antibody responses, which are robust but unable to control virus replication. Immune evasion by HIV-1 Env appears to employ complex mechanisms to regulate what antigenic states are presented to the immune system. Immunodominant features appear to be distinct from epitopes that interfere with Env functions in mediating infection. Further, cell-cell transmission studies indicate that vulnerable conformational states are additionally hidden from recognition on infected cells, even though the presence of Env at the cell surface is required for viral infection through the virological synapse. Cell-cell infection studies support that Env on infected cells is presented in distinct conformations from that on virus particles. Here we review data regarding the regulation of conformational states of Env and assess how regulated sorting of Env within the infected cell may underlie mechanisms to distinguish Env on the surface of virus particles versus Env on the surface of infected cells. These mechanisms may allow infected cells to avoid opsonization, providing cell-to-cell infection by HIV with a selective advantage during evolution within an infected individual. Understanding how distinct Env conformations are presented on cells versus viruses may be essential to designing effective vaccine approaches and therapeutic strategies to clear infected cell reservoirs.

Epitope convergence of broadly HIV-1 neutralizing IgA and IgG antibody lineages in a viremic controller

Decrypting the B cell ontogeny of HIV-1 broadly neutralizing antibodies (bNAbs) is paramount for vaccine design. Here, we characterized IgA and IgG bNAbs of three distinct B cell lineages in a viremic controller, two of which comprised only IgG⁺ or IgA⁺ blood memory B cells; the third combined both IgG and IgA clonal variants. 7-269 bNAb in the IgA-only lineage displayed the highest neutralizing capacity despite limited somatic mutation, and delayed viral rebound in humanized mice. bNAbs in all three lineages targeted the N332 glycan supersite. The 2.8-Å resolution cryo-EM structure of 7-269-BG505 SOSIP.664 complex showed a similar pose as 2G12, on an epitope mainly composed of sugar residues comprising the N332 and N295 glycans. Binding and cryo-EM structural analyses showed that antibodies from the two other lineages interact mostly with glycans N332 and N386. Hence, multiple B cell lineages of IgG and IgA bNAbs focused on a unique HIV-1 site of vulnerability can codevelop in HIV-1 viremic controllers.

Algal and Cyanobacterial Lectins and Their Antimicrobial Properties

Lectins are proteins with a remarkably high affinity and specificity for carbohydrates. Many organisms naturally produce them, including animals, plants, fungi, protists, bacteria, archaea, and viruses. The present report focuses on lectins produced by marine or freshwater organisms, in particular algae and cyanobacteria. We explore their structure, function, classification, and antimicrobial properties. Furthermore, we look at the expression of lectins in heterologous systems and the current research on the preclinical and clinical evaluation of these fascinating molecules. The further development of these molecules might positively impact human health, particularly the prevention or treatment of diseases caused by pathogens such as human immunodeficiency virus, influenza, and severe acute respiratory coronaviruses, among others.

Strategies for induction of HIV-1 envelope-reactive broadly neutralizing antibodies

INTRODUCTION

A primary focus of HIV-1 vaccine development is the activation of B cell receptors for naïve or precursor broadly neutralizing antibodies (bnAbs), followed by expansion and maturation of bnAb B cell lineage intermediates leading to highly affinity-matured bnAbs. HIV-1 envelope (Env) encodes epitopes for bnAbs of different specificities. Design of immunogens to induce bnAb precursors of different specificities and mature them into bnAb status is a goal for HIV-1 vaccine development. We review vaccine strategies for bnAb lineages development and highlight the immunological barriers that these strategies must overcome to generate bnAbs.

METHODS

We provide perspectives based on published research articles and reviews.

DISCUSSION

The recent Antibody Mediated Protection (AMP) trial that tested the protective efficacy of one HIV-1 Env bnAb specificity demonstrated that relatively high levels of long-lasting serum titers of multiple specificities of bnAbs will be required for protection from HIV-1 transmission. Current vaccine efforts for induction of bnAb lineages are focused on immunogens designed to expand naïve HIV-1 bnAb precursor B cells following the recent success of vaccine-induction of bnAb precursor B cells in macaques and humans. BnAb precursor B cells serve as templates for priming-immunogen design. However, design of boosting immunogens for bnAb maturation requires knowledge of the optimal immunogen design and immunological environment for bnAb B cell lineage affinity maturation. BnAb lineages acquire rare genetic changes as mutations during B cell maturation. Moreover, the immunological environment that supports bnAb development during HIV-1 infection is perturbed with an altered B cell repertoire and dysfunctional immunoregulatory controls, suggesting that in normal settings, bnAb development will be disfavoured. Thus, strategies for vaccine induction of bnAbs must circumvent immunological barriers for bnAb development that normally constrain bnAb B cell affinity maturation.

CONCLUSIONS

A fully protective HIV-1 vaccine needs to induce durable high titers of bnAbs that can be generated by a sequential set of Env immunogens for expansion and maturation of bnAb B cell lineages in a permitted immunological environment. Moreover, multiple specificities of bnAbs will be required to be sufficiently broad to prevent the escape of HIV-1 strains during transmission.

A Structural Update of Neutralizing Epitopes on the HIV Envelope, a Moving Target

Antibodies that can neutralize diverse HIV-1 strains develop in ~10–20% of HIV-1 infected individuals, and their elicitation is a goal of vaccine design. Such antibodies can also serve as therapeutics for those who have already been infected with the virus. Structural characterizations of broadly reactive antibodies in complex with the HIV-1 spike indicate that there are a limited number of sites of vulnerability on the spike. Analysis of their structures can help reveal commonalities that would be useful in vaccine design and provide insights on combinations of antibodies that can be used to minimize the incidence of viral resistance mutations. In this review, we give an update on recent structures determined of the spike in complex with broadly neutralizing antibodies in the context of all epitopes on the HIV-1 spike identified to date.

Carbohydrate-Based Macromolecular Biomaterials

Carbohydrates are the most abundant and one of the most important biomacromolecules in Nature. Except for energy-related compounds, carbohydrates can be roughly divided into two categories: Carbohydrates as matter and carbohydrates as information. As matter, carbohydrates are abundantly present in the extracellular matrix of animals and cell walls of various plants, bacteria, fungi, etc., serving as scaffolds. Some commonly found polysaccharides are featured as biocompatible materials with controllable rigidity and functionality, forming polymeric biomaterials which are widely used in drug delivery, tissue engineering, etc. As information, carbohydrates are usually referred to the glycans from glycoproteins, glycolipids, and proteoglycans, which bind to proteins or other carbohydrates, thereby meditating the cell-cell and cell-matrix interactions. These glycans could be simplified as synthetic glycopolymers, glycolipids, and glycoproteins, which could be afforded through polymerization, multistep synthesis, or a semisynthetic strategy. The information role of carbohydrates can be demonstrated not only as targeting reagents but also as immune antigens and adjuvants. The latter are also included in this review as they are always in a macromolecular formulation. In this review, we intend to provide a relatively comprehensive summary of carbohydrate-based macromolecular biomaterials since 2010 while emphasizing the fundamental understanding to guide the rational design of biomaterials. Carbohydrate-based macromolecules on the basis of their resources and chemical structures will be discussed, including naturally occurring polysaccharides, naturally derived synthetic polysaccharides, glycopolymers/glycodendrimers, supramolecular glycopolymers, and synthetic glycolipids/glycoproteins. Multiscale structure-function relationships in several major application areas, including delivery systems, tissue engineering, and immunology, will be detailed. We hope this review will provide valuable information for the development of carbohydrate-based macromolecular biomaterials and build a bridge between the carbohydrates as matter and the carbohydrates as information to promote new biomaterial design in the near future.

Carbohydrate-containing nanoparticles as vaccine adjuvants

Introduction: Adjuvants are essential to vaccines for immunopotentiation in the elicitation of protective immunity. However, classical and widely used aluminum-based adjuvants have limited capacity to induce cellular response. There are increasing needs for appropriate adjuvants with improved profiles for vaccine development toward emerging pathogens. Carbohydrate-containing nanoparticles (NPs) with immunomodulatory activity and particulate nanocarriers for effective antigen presentation are capable of eliciting a more balanced humoral and cellular immune response.Areas covered: We reviewed several carbohydrates with immunomodulatory properties. They include chitosan, β-glucan, mannan, and saponins, which have been used in vaccine formulations. The mode of action, the preparation methods, characterization of these carbohydrate-containing NPs and the corresponding vaccines are presented.Expert opinion: Several carbohydrate-containing NPs have entered the clinical stage or have been used in licensed vaccines for human use. Saponin-containing NPs are being evaluated in a vaccine against SARS-CoV-2, the pathogen causing the on-going worldwide pandemic. Vaccines with carbohydrate-containing NPs are in different stages of development, from preclinical studies to late-stage clinical trials. A better understanding of the mode of action for carbohydrate-containing NPs as vaccine carriers and as immunostimulators will likely contribute to the design and development of new generation vaccines against cancer and infectious diseases.

Fab-dimerized glycan-reactive antibodies are a structural category of natural antibodies

Natural antibodies (Abs) can target host glycans on the surface of pathogens. We studied the evolution of glycan-reactive B cells of rhesus macaques and humans using glycosylated HIV-1 envelope (Env) as a model antigen. 2G12 is a broadly neutralizing Ab (bnAb) that targets a conserved glycan patch on Env of geographically diverse HIV-1 strains using a unique heavy-chain (VH) domain-swapped architecture that results in fragment antigen-binding (Fab) dimerization. Here, we describe HIV-1 Env Fab-dimerized glycan (FDG)-reactive bnAbs without VH-swapped domains from simian-human immunodeficiency virus (SHIV)-infected macaques. FDG Abs also recognized cell-surface glycans on diverse pathogens, including yeast and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike. FDG precursors were expanded by glycan-bearing immunogens in macaques and were abundant in HIV-1-naive humans. Moreover, FDG precursors were predominately mutated IgM+IgD+CD27+, thus suggesting that they originated from a pool of antigen-experienced IgM+ or marginal zone B cells.

The Importance of Glycans of Viral and Host Proteins in Enveloped Virus Infection

Animal viruses are parasites of animal cells that have characteristics such as heredity and replication. Viruses can be divided into non-enveloped and enveloped viruses if a lipid bilayer membrane surrounds them or not. All the membrane proteins of enveloped viruses that function in attachment to target cells or membrane fusion are modified by glycosylation. Glycosylation is one of the most common post-translational modifications of proteins and plays an important role in many biological behaviors, such as protein folding and stabilization, virus attachment to target cell receptors and inhibition of antibody neutralization. Glycans of the host receptors can also regulate the attachment of the viruses and then influence the virus entry. With the development of glycosylation research technology, the research and development of novel virus vaccines and antiviral drugs based on glycan have received increasing attention. Here, we review the effects of host glycans and viral proteins on biological behaviors of viruses, and the opportunities for prevention and treatment of viral infectious diseases.

Using the antibody-antigen binding interface to train image-based deep neural networks for antibody-epitope classification

High-throughput B-cell sequencing has opened up new avenues for investigating complex mechanisms underlying our adaptive immune response. These technological advances drive data generation and the need to mine and analyze the information contained in these large datasets, in particular the identification of therapeutic antibodies (Abs) or those associated with disease exposure and protection. Here, we describe our efforts to use artificial intelligence (AI)-based image-analyses for prospective classification of Abs based solely on sequence information. We hypothesized that Abs recognizing the same part of an antigen share a limited set of features at the binding interface, and that the binding site regions of these Abs share share common structure and physicochemical property patterns that can serve as a "fingerprint" to recognize uncharacterized Abs. We combined large-scale sequence-based protein-structure predictions to generate ensembles of 3-D Ab models, reduced the Ab binding interface to a 2-D image (fingerprint), used pre-trained convolutional neural networks to extract features, and trained deep neural networks (DNNs) to classify Abs. We evaluated this approach using Ab sequences derived from human HIV and Ebola viral infections to differentiate between two Abs, Abs belonging to specific B-cell family lineages, and Abs with different epitope preferences. In addition, we explored a different type of DNN method to detect one class of Abs from a larger pool of Abs. Testing on Ab sets that had been kept aside during model training, we achieved average prediction accuracies ranging from 71-96% depending on the complexity of the classification task. The high level of accuracies reached during these classification tests suggests that the DNN models were able to learn a series of structural patterns shared by Abs belonging to the same class. The developed methodology provides a means to apply AI-based image recognition techniques to analyze high-throughput B-cell sequencing datasets (repertoires) for Ab classification.

The Impact of Sustained Immunization Regimens on the Antibody Response to Oligomannose Glycans

The high mannose patch (HMP) of the HIV envelope protein (Env) is the structure most frequently targeted by broadly neutralizing antibodies; therefore, many researchers have attempted to use mimics of this region as a vaccine immunogen. In our previous efforts, vaccinating rabbits with evolved HMP mimic glycopeptides containing Man₉ resulted in an overall antibody response targeting the glycan core and linker rather than the full glycan or Manα1→2Man tips of Man₉ glycans. A possible reason could be processing of our immunogen by host serum mannosidases. We sought to test whether more prolonged dosing could increase the antibody response to intact glycans, possibly by increasing the availability of intact Man₉ to germinal centers. Here, we describe a study investigating the impact of immunization regimen on antibody response by testing immunogen delivery through bolus, an exponential series of mini doses, or a continuously infusing mini-osmotic pump. Our results indicate that, with our glycopeptide immunogens, standard bolus immunization elicited the strongest HIV Env-binding antibody response, even though higher overall titers to the glycopeptide were elicited by the exponential and pump regimens. Antibody selectivity for intact glycan was, if anything, slightly better in the bolus-immunized animals.

Targeted selection of HIV-specific antibody mutations by engineering B cell maturation

INTRODUCTION

A major goal of HIV-1 vaccine development is the design of immunogens that induce broadly neutralizing antibodies (bnAbs). However, vaccination of humans has not resulted in the induction of affinity-matured and potent HIV-1 bnAbs. To devise effective vaccine strategies, we previously determined the maturation pathway of select HIV-1 bnAbs from acute infection through neutralizing antibody development. During their evolution, bnAbs acquire an abundance of improbable amino acid substitutions as a result of nucleotide mutations at variable region sequences rarely targeted by activation-induced cytidine deaminase, the enzyme responsible for antibody mutation. A subset of improbable mutations is essential for broad neutralization activity, and their acquisition represents a key roadblock to bnAb development.

RATIONALE

Current bnAb lineage-based vaccine strategies can initiate bnAb lineage development in animal models but have not specifically elicited the improbable mutations required for neutralization breadth. Induction of bnAbs requires vaccine strategies that specifically engage bnAb precursors and subsequently select for improbable mutations required for broadly neutralizing activity. We hypothesized that vaccination with immunogens that bind with moderate to high affinity to bnAb B cell precursors, and with higher affinity to precursors that have acquired improbable mutations, could initiate bnAb B cell lineages and select for key improbable mutations required for bnAb development.

RESULTS

We elicited serum neutralizing HIV-1 antibodies in human bnAb precursor knock-in mice and wild-type macaques vaccinated with immunogens designed to select for improbable mutations. We designed two HIV-1 envelope immunogens that bound precursor B cells of either a CD4 binding site or V3-glycan bnAb lineage. In vitro, these immunogens bound more strongly to bnAb precursors once the precursor acquired the desired improbable mutations. Vaccination of macaques with the CD4 binding site–targeting immunogen induced CD4 binding site serum neutralizing antibodies. Antibody sequences elicited in human bnAb precursor knock-in mice encoded functional improbable mutations critical for bnAb development. In bnAb precursor knock-in mice, we isolated a vaccine-elicited monoclonal antibody bearing functional improbable mutations that was capable of neutralizing multiple HIV-1 global isolates. Structures of a bnAb precursor, a bnAb, and the vaccine-elicited antibody revealed the precise roles that acquired improbable mutations played in recognizing the HIV-1 envelope. Thus, our immunogens elicited antibody responses in macaques and knock-in mice that exhibited the mutational patterns, structural characteristics, or neutralization profiles of nascent broadly neutralizing antibodies.

CONCLUSION

Our study represents a proof of concept for targeted selection of improbable mutations to guide antibody affinity maturation. Moreover, this study demonstrates a rational strategy for sequential immunogen design to circumvent the difficult roadblocks in HIV-1 bnAb induction by vaccination. We show that immunogens should exhibit differences in affinity across antibody maturation stages where improbable mutations are necessary for the desired antibody function. This strategy of selection of specific antibody nucleotides by immunogen design can be applied to B cell lineages targeting other pathogens where guided affinity maturation is needed for a protective antibody response.