Scientific Publications

The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env) trimer, a membrane-fusing machine, mediates virus entry into host cells and is the sole virus-specific target for neutralizing antibodies. Binding the receptors, CD4 and CCR5/CXCR4, triggers Env conformational changes from the metastable unliganded state to the fusion-active state. We used cryo-electron microscopy to obtain a 6-Å structure of the membrane-bound, heavily glycosylated HIV-1 Env trimer in its uncleaved and unliganded state. The spatial organization of secondary structure elements reveals that the unliganded conformations of both glycoprotein (gp)120 and gp41 subunits differ from those induced by receptor binding. The gp120 trimer association domains, which contribute to interprotomer contacts in the unliganded Env trimer, undergo rearrangement upon CD4 binding. In the unliganded Env, intersubunit interactions maintain the gp41 ectodomain helical bundles in a 'spring-loaded' conformation distinct from the extended helical coils of the fusion-active state. Quaternary structure regulates the virus-neutralizing potency of antibodies targeting the conserved CD4-binding site on gp120. The Env trimer architecture provides mechanistic insights into the metastability of the unliganded state, receptor-induced conformational changes, and quaternary structure-based strategies for immune evasion.

HIV epidemics in sub-Saharan Africa are generalized, but high-risk subgroups exist within these epidemics. A recent study among fisher-folk communities (FFC) in Uganda showed high HIV prevalence (28.8%) and incidence (4.9/100 person-years). However, those findings may not reflect population-wide HIV rates in FFC since the study population was selected for high-risk behaviour.

This paper used qualitative methods to explore experiences of men who have sex with men and female sex workers in Nairobi and Mtwapa, Kenya, who used oral pre-exposure prophylaxis (PrEP) for HIV prevention as part of a four-month trial of safety, acceptability and adherence. Fifty-one of 72 volunteers who took part in a randomized, placebo-controlled, blinded trial that compared daily and intermittent dosage of PrEP underwent qualitative assessments after completing the trial. Analyses identified three themes: (i) acceptability of PrEP was high, i.e. side effects were experienced early in the study but diminished over time, however characteristics of pills could improve comfort and use; (ii) social impacts such as stigma, rumors, and relationship difficulties due to being perceived as HIV positive were prevalent; (iii) adherence was challenged by complexities of daily life, in particular post-coital dosing adherence suffered from alcohol use around time of sex, mobile populations, and transactional sex work. These themes resonated across dosing regimens and gender, and while most participants favored the intermittent dosing schedule, those in the intermittent group noted particular challenges in adhering to the post-coital dose. Culturally appropriate and consistent counseling addressing these issues may be critical for PrEP effectiveness.

HIV-1 uses a diverse N-linked-glycan shield to evade recognition by antibody. Select human antibodies, such as the clonally related PG9 and PG16, recognize glycopeptide epitopes in the HIV-1 V1-V2 region and penetrate this shield, but their ability to accommodate diverse glycans is unclear. Here we report the structure of antibody PG16 bound to a scaffolded V1-V2, showing an epitope comprising both high mannose-type and complex-type N-linked glycans. We combined structure, NMR and mutagenesis analyses to characterize glycan recognition by PG9 and PG16. Three PG16-specific residues, arginine, serine and histidine (RSH), were critical for binding sialic acid on complex-type glycans, and introduction of these residues into PG9 produced a chimeric antibody with enhanced HIV-1 neutralization. Although HIV-1-glycan diversity facilitates evasion, antibody somatic diversity can overcome this and can provide clues to guide the design of modified antibodies with enhanced neutralization.

A substantial proportion of the broadly neutralizing antibodies (bnAbs) identified in certain HIV-infected donors recognize glycan-dependent epitopes on HIV-1 gp120. Here we elucidate how the bnAb PGT 135 binds its Asn332 glycan-dependent epitope from its 3.1-Å crystal structure with gp120, CD4 and Fab 17b. PGT 135 interacts with glycans at Asn332, Asn392 and Asn386, using long CDR loops H1 and H3 to penetrate the glycan shield and access the gp120 protein surface. EM reveals that PGT 135 can accommodate the conformational and chemical diversity of gp120 glycans by altering its angle of engagement. Combined structural studies of PGT 135, PGT 128 and 2G12 show that this Asn332-dependent antigenic region is highly accessible and much more extensive than initially appreciated, which allows for multiple binding modes and varied angles of approach; thereby it represents a supersite of vulnerability for antibody neutralization.

Abs that bind the functional envelope glycoprotein (Env) spike are considered critical for a broadly effective prophylactic HIV-1 vaccine. The difficulty in eliciting such Abs by vaccination is partially attributed to the immunodominance of hydrophilic, surface-exposed variable protein regions of Env. However, little is known about the potential for competition between B cells that recognize distinct and distal epitopes on Env during protein subunit vaccination. In this study, we address this basic question at the level of Ab-secreting cells and serum IgG using a pair of isogenic soluble Env trimers, designated wildtype and gV3, which differ only in their potential to activate B cell responses against the highly immunogenic V3 region of Env. Immunization of mice with gV3 resulted in a markedly lower Ag-specific response compared with that induced by wildtype Env and could be explained by a loss of V3-directed reactivities. There was no redistribution of the response to other regions of Env in gV3-inoculated mice, suggesting that the epitope-specific Ab-secreting cell responses measured after boost are independently regulated rather than dictated by direct or indirect competition between B cells recognizing different structural elements of Env. This information is relevant for ongoing efforts in Env immunogen design to focus responses on conserved neutralizing determinants and for our general understanding of B cell responses to large-protein Ags that display numerous B cell epitopes.

A shield of glycans coats the viral-envelope proteins of HIV. Recent work shows how broadly neutralizing antibodies can recognize this shield despite structural variation in these ‘self’ carbohydrate structures.

The development of a preventive vaccine to neutralize the highly variable and antigenically diverse human immunodeficiency virus type 1 (HIV-1) has been an indomitable goal. The recent discovery of a number of cross-neutralizing and potent monoclonal antibodies from elite neutralizers has provided important insights in this field. Neutralizing antibodies (NAbs) are useful in identifying neutralizing epitopes of vaccine utility and for understanding the mechanism of potent and broad cross-neutralization thus providing a modality of preventive and therapeutic value. In this article we review the current understanding on the potential use of broadly neutralizing antibodies (bNAbs) in their full-length IgG structure, engineered domain antibody or bispecific versions towards preventive and therapeutic applications. The potential implications of NAbs are discussed in the light of the recent developments as key components in vaccination against HIV-1. The development of a vaccine immunogen which elicits bNAbs and confers protective immunity remains a real challenge.

HIV-discordant heterosexual couples are faced with the dual challenge of preventing sexual HIV transmission and unplanned pregnancies with the attendant risk of perinatal HIV transmission. Our aim was to examine uptake of two long-acting reversible contraceptive (LARC) methods--intrauterine devices (IUD) and hormonal implants--among HIV-discordant couples in Rwanda and Zambia.

The role of men who have sex with men (MSM) in the African HIV epidemic is gaining recognition yet capacity to address the HIV prevention needs of this group is limited. HIV testing and counselling is not only a critical entry point for biomedical HIV prevention interventions, such as pre-exposure prophylaxis, rectal microbicides and early treatment initiation, but is also an opportunity for focused risk reduction counselling that can support individuals living in difficult circumstances. For prevention efforts to succeed, however, MSM need to access services and they will only do so if these are non-judgmental, informative, focused on their needs, and of clear benefit. This study aimed to understand Kenyan providers' attitudes towards and experiences with counselling MSM in a research clinic targeting this group for HIV prevention. We used in-depth interviews to explore values, attitudes and cognitive and social constructs of 13 counsellors and 3 clinicians providing services to MSM at this clinic. Service providers felt that despite their growing experience, more targeted training would have been helpful to improve their effectiveness in MSM-specific risk reduction counselling. They wanted greater familiarity with MSM in Kenya to better understand the root causes of MSM risk-taking (e.g., poverty, sex work, substance abuse, misconceptions about transmission, stigma, and sexual desire) and felt frustrated at the perceived intractability of some of their clients' issues. In addition, they identified training needs on how to question men about specific risk behaviours, improved strategies for negotiating risk reduction with counselling clients, and improved support supervision from senior counsellors. This paper describes the themes arising from these interviews and makes practical recommendations on training and support supervision systems for nascent MSM HIV prevention programmes in Africa.

Results from recent HIV-1 vaccine studies have indicated that high serum antibody (Ab) titers may not be necessary for Ab-mediated protection, and that Abs localized to mucosal sites might be critical for preventing infection. Enzyme-linked immunosorbent assay (ELISA) has been used for decades as the gold standard for Ab measurement, though recently, highly sensitive microsphere-based assays have become available, with potential utility for improved detection of Abs. In this study, we assessed the Bio-Plex(®) Suspension Array System for the detection of simian immunodeficiency virus (SIV)-specific Abs in rhesus macaques (RMs) chronically infected with SIV, whose serum or mucosal SIV-specific Ab titers were negative by ELISA. We developed a SIVmac239-specific 4-plex bead array for the simultaneous detection of Abs binding to Env, Gag, Pol, and Nef. The 4-plex assay was used to quantify SIV-specific serum IgG and rectal swab IgA titers from control (SIV-naive) and SIVmac239-infected RMs. The Bio-Plex assay specifically detected anti-SIV Abs in specimens from SIV-infected animals for all four analytes when compared to SIV-naive control samples (p≤0.04). Furthermore, in 70% of Env and 79% of Gag ELISA-negative serum samples, specific Ab was detected using the Bio-Plex assay. Similarly, 71% of Env and 48% of Gag ELISA-negative rectal swab samples were identified as positive using the Bio-Plex assay. Importantly, assay specificity (i.e., probability of true positives) was comparable to ELISA (94%-100%). The results reported here indicate that microsphere-based methods provide a substantial improvement over ELISA for the detection of Ab responses, aid in detecting specific Abs when analyzing samples containing low levels of Abs, such as during the early stages of a vaccine trial, and may be valuable in attempts to link protective efficacy of vaccines with induced Ab responses.

Syphilis continues to be a common sexually transmitted infection, despite the availability of inexpensive and effective treatment. Infection in human immunodeficiency virus (HIV)-discordant couples is important because syphilis increases the risk of HIV acquisition. Current US treatment guidelines recommend 1 dose of benzathine penicillin for early syphilis, irrespective of HIV status, but data from coinfected patients are limited.

Vaccines are among the greatest successes in the history of public health. However, past strategies for vaccine development are unlikely to succeed in the future against major global diseases such as AIDS, tuberculosis, and malaria. For such diseases, the correlates of protection are poorly defined and the pathogens evade immune detection and/or exhibit extensive genetic variability. Recent advances have heralded in a new era of vaccine discovery. However, translation of these advances into vaccines remains impeded by lack of understanding of key vaccinology principles in humans. We review these advances toward vaccine discovery and suggest that for accelerating successful vaccine development, new human immunology-based clinical research initiatives be implemented with the goal of elucidating and more effectively generating vaccine-induced protective immune responses.