HIV Vaccine Candidates Research Articles

The therapeutic HIV Env C5/gp41 vaccine candidate Vacc-C5 induces specific T cell regulation in a phase I/II clinical study

BackgroundLevels of non-neutralising antibodies (AB) to the C5 domain of HIV Env gp120 are inversely related to progression of HIV infection. In this phase I/II clinical study we investigated safety of Vacc-C5, a peptide-based therapeutic vaccine candidate corresponding to C5/gp41732–744 as well as the effects on pre-existing AB levels to C5/gp41732–744, immune activation and T cell responses including exploratory assessments of Vacc-C5-induced T cell regulation. Our hypothesis was that exposure of the C5 peptide motif may have detrimental effects due to several of its HLA-like features and that enhancement of non-neutralising anti-C5 AB by vaccination could reduce C5 exposure and thereby chronic immune activation.MethodsThirty-six HIV patients on effective antiretroviral therapy were randomised to one of three dose levels of Vacc-C5 administered intramuscularly with Alhydrogel or intradermally with GM-CSF as adjuvant through initial immunisation and two booster periods over 26 weeks. Vacc-C5-specific AB were measured by ELISA and T cell responses by both IFN-γ ELISPOT and proliferative assays analysed by flow cytometry. Immune regulation was assessed by functional blockade of the two inhibitory cytokines IL-10 and TGF-β in parallel cultures. Non-parametric statistical tests were applied.ResultsVacc-C5 was found safe and well tolerated in all patients. Only marginal changes in humoral and cellular responses were induced, without any effect on immune activation. Overall, anti-Vacc-C5 AB levels seemed to decrease compared to pre-existing levels. Whereas Vacc-C5-specific CD8+ T cell proliferative responses increased after the first booster period (p = 0.020; CD4+, p = 0.057), they were reduced after the second. In contrast, Vacc-C5-induced T cell regulation increased after completed vaccination (p ≤ 0.027) and was lower at baseline in the few AB responders identified (p = 0.027).ConclusionsThe therapeutic HIV vaccine candidate Vacc-C5 safely induced only marginal immune responses, whereas Vacc-C5-induced T cell regulation markedly increased. Our data support further attention on immune regulation during therapeutic HIV vaccination studies.Trial registrationNCT01627678.

Conjugated anionic PEG-citrate G2 dendrimer with multi-epitopic HIV-1 vaccine candidate enhance the cellular immune responses in mice

Multi-epitope vaccines might cause immunity against multiple antigenic targets. Four immunodominant epitopes of HIV-1 genome were used to construct a polytope vaccine, formulated by dendrimer. Two regimens of polytopes mixture with dendrimer were utilized to immunize BALB/c mice. Adjuvants were also used to boost immune responses. The conjugated polytope could arouse significant cellular immune responses (P < 0.05) and Th1 response showed higher intensity compared to Th2 (P < 0.05). Our study depicted that conjugated dendrimer with multi-epitopic rHIVtop4 would efficiently induce cell-mediated immune responses and might be considered as promising delivery system for vaccines formulation.

Construction, Selection and Immunogenicity of Recombinant Fowlpox Candidate Vaccine Co-expressing HIV-1 gag and gp145.

An HIV candidate vaccine for the Chinese population was designed by constructing a recombinant fowlpox virus expressing HIV-1 gag and HIV gp145 proteins via homologous recombination and plaque screening using enhanced green fluorescent protein (EGFP) as the reporter gene. EGFP in the recombinant was then knocked out with the Cre/Loxp system yielding rFPVHg-Hp, which was identified at the genomic, transcriptional and translational levels. The immunogenicity of rFPVHg-Hp was analyzed by measuring levels of HIV-specific antibodies and IFN-γ-secreting splenocytes by enzyme-linked immunosorbent assay and IFN enzyme-linked immune spot test in the BALB/c mouse model. Results showed that rFPV could not stimulate HIV-1 specific antibodies or IFN-γ-secreting cells by a single immunization. Meanwhile, in the prime-boost strategy, HIV-p24 antibodies (P<0.01) and IFN-γ-secreting cells (P<0.05) were induced strongly by the candidate vaccine after the boost immunization. Thus, both humoral and cellular immunity could be elicited by the candidate vaccine in a prime-boost immunization strategy. This study provides a foundation for future preclinical studies on the HIV rFPVHg-Hp candidate vaccine.

IMMUNOGENS DESIGNED FOR TARGETING NEUTRALIZING EPITOPES OF HIV-1 ENVELOPE GLYCOPROTEIN

BackgroundDue to its unique challenge of establishing lifelong reservoirs a successful HIV-1 vaccine must elicit protective antibodies responses at the portals of entry. Broadly neutralising antibodies (bnAb) have been demonstrated...

The quest for an antibody-based HIV vaccine.

Despite major advances in our understanding of the biology of HIV-1 infection, and advances in antiretroviral therapy to treat the disease, there were 2.1 million new cases of HIV-1 infection in 2015, and 36.7 million people living with AIDS ( http://www.unaids.org/en/resources/fact-sheet ). Thus, a vaccine that can prevent HIV-infection remains a global priority. Thirty-three years after the discovery of HIV-1(1), and the demonstration it was the cause of AIDS(2) and after 6 HIV-1 vaccine efficacy trials (–8), no HIV-1 candidate vaccine has shown enough efficacy to be approved for clinical use. Of several vaccine concepts tested in efficacy trials, only one, the RV144 pox virus prime, protein boost (ALVAC/AIDSVAX B/E) vaccine, showed a low level of vaccine protection with an estimated 31% vaccine efficacy (8). Candidate vaccines have sought to elicit both antibody and T-cell responses, but to fully prevent the acquisition of infection, a major focus has been on the induction of protective antibody responses (9, 10). Hence, the focus of this issue of Immunologic Reviews is “Antibodies and Immunity to HIV”. Animal models have demonstrated that passive administration of HIV-1-- neutralizing antibodies can fully protect against infection, but the induction of such antibodies via immunization remains a major scientific challenge. With recent advances in the isolation and characterization of broadly neutralizing antibodies (bnAbs) from HIV-1-infected subjects, in elucidating structures of the HIV-1 envelope glycoprotein (Env), in defining novel approaches to immunogen design, and in improved understanding of the immunological pathways leading to bNAb elicitation, the challenge developing an HIV-1 vaccine appears to be more tractable. The articles in this issue highlight both major areas of HIV-1 vaccine development progress and remaining obstacles, and provide context for the renewed optimism that a highly effective vaccine, while not imminent, is possible.

Identification and specificity of broadly neutralizing antibodies against HIV.

SummaryBeginning in 2009, studies of the humoral responses of HIV‐positive individuals have led to the identification of scores, if not hundreds, of antibodies that are both broadly reactive and potently neutralizing. This development has provided renewed impetus toward an HIV vaccine and led directly to the development of novel immunogens. Advances in identification of donors with the most potent and broad anti‐HIV serum neutralizing responses were crucial in this effort. Equally, development of methods for the rapid generation of human antibodies from these donors was pivotal. Primarily these methods comprise single B‐cell culture coupled to high‐throughput neutralization screening and flow cytometry‐based sorting of single B cells using HIV envelope protein baits. In this review, the advantages and disadvantages of these methodologies are discussed in the context of the specificities targeted by individual antibodies and the need for further improvements to evaluate HIV vaccine candidates.

The rectal mucosa and condomless receptive anal intercourse in HIV-negative MSM: implications for HIV transmission and prevention.

Most HIV transmissions among men who have sex with men (MSM), the group that accounted for 67% of new US infections in 2014, occur via exposure to the rectal mucosa. However, it is unclear how the act of condomless receptive anal intercourse (CRAI) may alter the mucosal immune environment in HIV negative MSM. Here, we performed a comprehensive characterization of the rectal mucosal immune environment for the phenotype and production of pro-inflammatory cytokines by CD4 and CD8 T cells, global transcriptomic analyses, and the composition of microbiota in HIV negative MSM. Our results show that compared to men who had never engaged in anal intercourse, the rectal mucosa of MSM engaging in CRAI has a distinct phenotype characterized by higher levels of Th17 cells, greater CD8+ T cell proliferation and production of pro-inflammatory cytokines, molecular signatures associated with mucosal injury and repair likely mediated by innate immune cells, and a microbiota enriched for the Prevotellaceae family. These data provide a high-resolution model of the immunological, molecular, and microbiological perturbations induced by CRAI, will have direct utility in understanding rectal HIV transmission among MSM, and will enhance the design of future biomedical prevention interventions, including candidate HIV vaccines.

Lessons from HIV-1 vaccine efficacy trials

Only four HIV-1 vaccine concepts have been tested in six efficacy trials with no product licensed to date. Several scientific and programmatic lessons can be learned from these studies generating new hypotheses and guiding future steps. RV144 [ALVAC-HIV (canarypox vector) and AIDSVAX B/E (bivalent gp120 HIV-1 subtype B and CRF01_AE)] remains the only efficacy trial that demonstrated a modest vaccine efficacy, which led to the identification of immune correlates of risk. Progress on subtype-specific, ALVAC (canarypox vector) and gp120 vaccine prime-boost approaches has been slow, but we are finally close to the launch of an efficacy study in Africa in 2016. The quest of a globally effective HIV-1 vaccine has led to the development of new approaches. Efficacy studies of combinations of Adenovirus type 26 (Ad26)/Modified Vaccinia Ankara (MVA)/gp140 vaccines with mosaic designs will enter efficacy studies mid-2017 and cytomegalovirus (CMV)-vectored vaccines begin Phase I studies at the same time. Future HIV-1 vaccine efficacy trials face practical challenges as effective nonvaccine prevention programs are projected to decrease HIV-1 incidence. An HIV-1 vaccine is urgently needed. Increased industry involvement, mobilization of resources, expansion of a robust pipeline of new concepts, and robust preclinical challenge studies will be essential to accelerate efficacy testing of next generation HIV-1 vaccine candidates.

Stabilizing Protein Motifs with a Genetically Encoded Metal-Ion Chelator

The N-peptide of HIV gp41 forms a trimeric coiled-coil intermediate during host cell-viral fusion. Stable mimics of this coiled coil could potentially serve as HIV vaccine candidates or inhibitors of viral entry. Therefore, a variety of approaches have been investigated to maintain the N-peptide in its trimeric helical conformation. Here, we utilize a genetic method to incorporate the metal chelating noncanonical amino acid (2,2'-bipyridin-5-yl)alanine (BpyAla) into IZN17, an established trimeric coiled-coil gp41 model. Wedemonstrate that BpyAla-IZN17 acquires Fe(II) during expression in Escherichia coli, resulting in the formation of a highly stable IZN17 helical trimer with a Tm > 95°C. Removal of Fe(II) results in a 27°C decrease in thermal stability. Replacement of Fe(II) with Zn(II) also affords a Tm > 90°C. Thus, the genetic introduction of BpyAla into polypeptide provides astraightforward method for stabilizing coiled-coilstructural motifs in recombinantly engineered proteins.

P4 Preclinical evaluation of an mRNA-based therapeutic HIV vaccine candidate combining rationally selected antigenic sequences and potent adjuvant signals (HTI-TriMix)

P4 Preclinical evaluation of an mRNA-based therapeutic HIV vaccine candidate combining rationally selected antigenic sequences and potent adjuvant signals (HTI-TriMix)

Synthesis of multivalent glycopeptide conjugates that mimic an HIV epitope

Recently, we reported a directed evolution method which enabled us to discover sequences of glycopeptides that bind with picomolar affinity to HIV antibody 2G12 and are of interest as HIV vaccine candidates. In this manuscript, we describe the syntheses of several of these large (∼11–12 kDa) glycopeptides by a combination of fast flow peptide synthesis and click chemistry. We also discuss the optimization of their attachment to carrier protein CRM197, affording antigenic and immunogenic conjugates ready for animal vaccination.

Induction of Heterologous Tier 2 HIV-1-Neutralizing and Cross-Reactive V1/V2-Specific Antibodies in Rabbits by Prime-Boost Immunization.

Poxvirus prime-protein boost used in the RV144 trial remains the only immunization strategy shown to elicit a modest level of protection against HIV-1 acquisition in humans. Although neutralizing antibodies (NAb) were generated, they were against sensitive viruses, not the more resistant "tier 2" isolates that dominate circulating strains. Instead, risk reduction correlated with antibodies recognizing epitopes in the V1/V2 region of HIV-1 envelope glycoprotein (Env). Here, we examined whether tier 2 virus NAb and V1/V2-specific non-NAb could be elicited by a poxvirus prime-gp120 boost strategy in a rabbit model. We studied two clade B Envs that differ in multiple parameters, including tissue origin, neutralization sensitivity, and presence of the N197 (N7) glycan that was previously shown to modulate the exposure of conserved epitopes on Env. We demonstrate that immunized rabbits generated cross-reactive neutralizing activities against >50% of the tier 2 global HIV-1 isolates tested. Some of these activities were directed against the CD4 binding site (CD4bs). These rabbits also generated antibodies that recognized protein scaffolds bearing V1/V2 sequences from diverse HIV-1 isolates and mediated antibody-dependent cellular cytotoxicity. However, there are subtle differences in the specificities and the response rates of V1/V2-specific antibodies between animals immunized with different Envs, with or without the N7 glycan. These findings demonstrate that antibody responses that have been correlated with protection against HIV-1 acquisition in humans can be elicited in a preclinical model by a poxvirus prime-gp120 boost strategy and that improvements may be achievable by optimizing the nature of the priming and boosting immunogens. The only vaccine approach shown to elicit any protective efficacy against HIV-1 acquisition is based on a poxvirus prime-protein boost regimen (RV144 Thai trial). Reduction of risk was associated with nonneutralizing antibodies targeting the V1/V2 loops of the envelope protein gp120. However, the modest efficacy (31.2%) achieved in this trial highlights the need to examine approaches and factors that may improve vaccine-induced responses, including cross-reactive neutralizing activities. We show here that rabbits immunized with a novel recombinant vaccinia virus prime-gp120 protein boost regimen generated antibodies that recognize protein scaffolds bearing V1/V2 sequences from diverse HIV-1 isolates and mediated antibody-dependent cellular cytotoxicity. Importantly, immunized rabbits also showed neutralizing activities against heterologous tier 2 HIV-1 isolates. These findings may inform the design of prime-boost immunization approaches and help improve the protective efficacy of candidate HIV-1 vaccines.

Adenovirus-based HIV-1 vaccine candidates tested in efficacy trials elicit CD8+ T cells with limited breadth of HIV-1 inhibition.

The ability of HIV-1 vaccine candidates MRKAd5, VRC DNA/Ad5 and ALVAC/AIDSVAX to elicit CD8 T cells with direct antiviral function was assessed and compared with HIV-1-infected volunteers. Adenovirus serotype 5 (Ad5)-based regimens MRKAd5 and VRC DNA/Ad5, designed to elicit HIV-1-specific T cells, are immunogenic but failed to prevent infection or impact on viral loads in volunteers infected subsequently. Failure may be due in part to a lack of CD8 T cells with effective antiviral functions. An in-vitro viral inhibition assay tested the ability of bispecific antibody expanded CD8 T cells from peripheral blood mononuclear cells to inhibit replication of a multiclade panel of HIV-1 isolates in autologous CD4 T cells. HIV-1 proteins recognized by CD8 T cells were assessed by IFNγ enzyme-linked immunospot assay. Ad5-based regimens elicited CD8 T cells that inhibited replication of HIV-1 IIIB isolate with more limited inhibition of other isolates. IIIB isolate Gag and Pol genes have high sequence identities (>96%) to vector HIV-1 gene inserts, and these were the predominant HIV-1 proteins recognized by CD8 T cells. Virus inhibition breadth was greater in antiretroviral naïve HIV-1-infected volunteers naturally controlling viremia (plasma viral load < 10 000/ml). HIV-1-inhibitory CD8 T cells were not elicited by the ALVAC/AIDSVAX regimen. The Ad5-based regimens, although immunogenic, elicited CD8 T cells with limited HIV-1-inhibition breadth. Effective T-cell-based vaccines should presumably elicit broader HIV-1-inhibition profiles. The viral inhibition assay can be used in vaccine design and to prioritize promising candidates with greater inhibition breadth for further clinical trials.

Immunological Characterization of Plant-Based HIV-1 Gag/Dgp41 Virus-Like Particles.

It is widely anticipated that a prophylactic vaccine may be needed to control the HIV/AIDS epidemic worldwide. Despite over two decades of research, a vaccine against HIV-1 remains elusive, although a recent clinical trial has shown promising results. Recent studies have focused on highly conserved domains within HIV-1 such as the membrane proximal external region (MPER) of the envelope glycoprotein, gp41. MPER has been shown to play critical roles in mucosal transmission of HIV-1, though this peptide is poorly immunogenic on its own. Here we provide evidence that plant-produced HIV-1 enveloped virus-like particles (VLPs) consisting of Gag and a deconstructed form of gp41 comprising the MPER, transmembrane, and cytoplasmic domains (Dgp41) provides an effective platform to display MPER for use as an HIV vaccine candidate. Prime-boost strategies combining systemic and mucosal priming with systemic boosting using two different vaccine candidates (VLPs and CTB-MPR—a fusion of MPER and the B-subunit of cholera toxin) were investigated in BALB/c mice. Serum antibody responses against both the Gag and gp41 antigens were elicited when systemically primed with VLPs. These responses could be recalled following systemic boosting with VLPs. In addition, mucosal priming with VLPs allowed for a boosting response against Gag and gp41 when boosted with either candidate. Importantly, the VLPs also induced Gag-specific CD4 and CD8 T-cell responses. This report on the immunogenicity of plant-based Gag/Dgp41 VLPs may represent an important milestone on the road towards a broadly efficacious and inexpensive subunit vaccine against HIV-1.

P-D7 Structural mimicry of the antigen binding modes of rhesus macaque and human anti-gp120 V3 antibodies

Background: Nonhuman primates (NHPs), such as rhesus macaques, are currently the best preclinical models for studying HIV vaccines. The details of how NHP Abs can mimic human Abs will be useful in evaluating NHP Ab responses to HIV vaccine candidates. The extensive knowledge of the antigen binding modes of anti-V3 Abs allows a structural comparison of NHP and human Ab binding modes. Methods: We have crystallized and determined the epitope complex structures of rhesus macaque anti-V3 monoclonal Abs (mAbs) 2.10A (encoded by a VH5 family gene and derived from an animal infected with SHIV SF162P4) and P2A10 and P2E3 (encoded by VH3 family genes and from an animal infected with SHIV SF162P3N). These structures were compared to the Ab-epitope interactions of human anti-V3 mAbs encoded by the equivalent human genes. Results: Human anti-V3 mAbs preferentially use VH5, VH1 and VH3 family genes with the antigen binding sites resembling either a cradle or ladle, respectively, as previously described. Similarly, rhesus macaque mAb 2.10A utilizes the cradle-binding mode while mAbs P2A10 and P2E3 use the ladle-binding mode. Additionally, the amino acids encoded by both human and macaque VH3 and VH5 family germline genes are critical for shaping the antigen binding sites. Thus, key elements in the antigen-Ab interactions are preserved between human and rhesus macaque mAbs. Conclusions: The antigen binding modes of human and rhesus macaque mAbs targeting HIV-1 gp120 V3 epitopes were found to be structurally extremely similar at the atomic level.

Contrasting Adult and Infant Immune Responses to HIV Infection and Vaccination.

Extensive studies have demonstrated that infant immune responses are distinct from those of adults. Despite these differences, infant immunization can elicit protective immune responses at levels comparable to or, in some cases, higher than adult immune responses to many vaccines. To date, only a few HIV vaccine candidates have been tested in infant populations, and none of them evaluated vaccine efficacy. Recent exciting studies showing that HIV-infected infants can develop broad neutralizing antibody responses and that some HIV vaccine regimens can elicit high levels of potentially protective antibodies in infants provide support for the development and testing of HIV vaccines in pediatric populations. In this review, we discuss the differences in adult and infant immune responses in the setting of HIV infection and vaccination.

Affinity Maturation of a Potent Family of HIV Antibodies Is Primarily Focused on Accommodating or Avoiding Glycans

The high-mannose patch on the HIV-1 envelope (Env) glycoprotein is the epicenter for binding of the potent broadly neutralizing PGT121 family of antibodies, but strategies for generating such antibodies by vaccination have not been defined. We generated structures of inferred antibody intermediates by X-ray crystallography and electron microscopy to elucidate the molecular events that occurred during evolution of this family. Binding analyses revealed that affinity maturation was primarily focused on avoiding, accommodating, or binding the N137 glycan. The overall antibody approach angle to Env was defined very early in the maturation process, yet some variation evolved in the PGT121 family branches that led to differences in glycan specificities in their respective epitopes. Furthermore, we determined a crystal structure of the recombinant BG505 SOSIP.664 HIV-1 trimer with a PGT121 family member at 3.0 Å that, in concert with these antibody intermediate structures, provides insights to advance design of HIV vaccine candidates.

All systems go for HIV vaccine development

Systematically mapping diverse antibody effector functions induced by candidate HIV vaccines moves toward pinpointing a protective strategy.

Are Clade Specific HIV Vaccines a Necessity? An Analysis Based on Mathematical Models

As HIV-1 envelope immune responses are critical to vaccine related protection, most candidate HIV vaccines entering efficacy trials are based upon a clade specific design. This need for clade specific vaccine prototypes markedly reduces the implementation of potentially effective HIV vaccines. We utilized a mathematical model to determine the effectiveness of immediate roll-out of a non-clade matched vaccine with reduced efficacy compared to constructing clade specific vaccines, which would take considerable time to manufacture and test in safety and efficacy trials. We simulated the HIV epidemic in San Francisco (SF) and South Africa (SA) and projected effectiveness of three vaccination strategies: i) immediate intervention with a 20–40% vaccine efficacy (VE) non-matched vaccine, ii) delayed intervention by developing a 50% VE clade-specific vaccine, and iii) immediate intervention with a non-matched vaccine replaced by a clade-specific vaccine when developed. Immediate vaccination with a non-clade matched vaccine, even with reduced efficacy, would prevent thousands of new infections in SF and millions in SA over 30years. Vaccination with 50% VE delayed for five years needs six and 12years in SA to break-even with immediate 20 and 30% VE vaccination, respectively, while not able to surpass the impact of immediate 40% VE vaccination over 30years. Replacing a 30% VE with a 50% VE vaccine after 5years reduces the HIV acquisition by 5% compared to delayed vaccination. The immediate use of an HIV vaccine with reduced VE in high risk communities appears desirable over a short time line but higher VE should be the pursued to achieve strong long-term impact. Our analysis illustrates the importance of developing surrogate markers (correlates of protection) to allow bridging types of immunogenicity studies to support more rapid assessment of clade specific vaccines.

Conserved Role of an N-Linked Glycan on the Surface Antigen of Human Immunodeficiency Virus Type 1 Modulating Virus Sensitivity to Broadly Neutralizing Antibodies against the Receptor and Coreceptor Binding Sites.

HIV-1 establishes persistent infection in part due to its ability to evade host immune responses. Occlusion by glycans contributes to masking conserved sites that are targets for some broadly neutralizing antibodies (bNAbs). Previous work has shown that removal of a highly conserved potential N-linked glycan (PNLG) site at amino acid residue 197 (N7) on the surface antigen gp120 of HIV-1 increases neutralization sensitivity of the mutant virus to CD4 binding site (CD4bs)-directed antibodies compared to its wild-type (WT) counterpart. However, it is not clear if the role of the N7 glycan is conserved among diverse HIV-1 isolates and if other glycans in the conserved regions of HIV-1 Env display similar functions. In this work, we examined the role of PNLGs in the conserved region of HIV-1 Env, particularly the role of the N7 glycan in a panel of HIV-1 strains representing different clades, tissue origins, coreceptor usages, and neutralization sensitivities. We demonstrate that the absence of the N7 glycan increases the sensitivity of diverse HIV-1 isolates to CD4bs- and V3 loop-directed antibodies, indicating that the N7 glycan plays a conserved role masking these conserved epitopes. However, the effect of the N7 glycan on virus sensitivity to neutralizing antibodies directed against the V2 loop epitope is isolate dependent. These findings indicate that the N7 glycan plays an important and conserved role modulating the structure, stability, or accessibility of bNAb epitopes in the CD4bs and coreceptor binding region, thus representing a potential target for the design of immunogens and therapeutics. N-linked glycans on the HIV-1 envelope protein have been postulated to contribute to viral escape from host immune responses. However, the role of specific glycans in the conserved regions of HIV-1 Env in modulating epitope recognition by broadly neutralizing antibodies has not been well defined. We show here that a single N-linked glycan plays a unique and conserved role among conserved glycans on HIV-1 gp120 in modulating the exposure or the stability of the receptor and coreceptor binding site without affecting the integrity of the Env in mediating viral infection or the ability of the mutant gp120 to bind to CD4. The observation that the antigenicity of the receptor and coreceptor binding sites can be modulated by a single glycan indicates that select glycan modification offers a potential strategy for the design of HIV-1 vaccine candidates.