Po-Ying Chan-Hui

Broad and Potent Neutralizing Antibodies from an African Donor Reveal a New HIV-1 Vaccine Target

Anti-HIV Antibodies One of the top priorities for an HIV vaccine is the ability to elicit a broadly neutralizing antibody response, which should provide the best protection against infection. In the 25 years since the discovery of HIV, very few broadly neutralizing antibodies have been identified, and those that do exist were discovered nearly two decades ago. Using a high-throughput culture system, Walker et al. (p. 285; published online 3 September) now identify two additional broadly neutralizing antibodies isolated from a clade A HIV-infected African donor. These antibodies exhibit great potency and, in contrast to other known broadly neutralizing antibodies, are able to neutralize a wide range of viruses from many different clades. The antibodies recognize a motif in the trimerized viral envelope protein that is found in conserved regions of the variable loops of the gp120 subunit. Identification of this motif provides an intriguing new target for vaccine development. High-throughput screening has revealed two new broadly neutralizing antibodies from a clade A–infected donor in Africa. Broadly neutralizing antibodies (bNAbs), which develop over time in some HIV-1–infected individuals, define critical epitopes for HIV vaccine design. Using a systematic approach, we have examined neutralization breadth in the sera of about 1800 HIV-1–infected individuals, primarily infected with non–clade B viruses, and have selected donors for monoclonal antibody (mAb) generation. We then used a high-throughput neutralization screen of antibody-containing culture supernatants from about 30,000 activated memory B cells from a clade A–infected African donor to isolate two potent mAbs that target a broadly neutralizing epitope. This epitope is preferentially expressed on trimeric Envelope protein and spans conserved regions of variable loops of the gp120 subunit. The results provide a framework for the design of new vaccine candidates for the elicitation of bNAb responses.

Broad neutralization coverage of HIV by multiple highly potent antibodies

Broadly neutralizing antibodies against highly variable viral pathogens are much sought after to treat or protect against global circulating viruses. Here we probed the neutralizing antibody repertoires of four human immunodeficiency virus (HIV)-infected donors with remarkably broad and potent neutralizing responses and rescued 17 new monoclonal antibodies that neutralize broadly across clades. Many of the new monoclonal antibodies are almost tenfold more potent than the recently described PG9, PG16 and VRC01 broadly neutralizing monoclonal antibodies and 100-fold more potent than the original prototype HIV broadly neutralizing monoclonal antibodies. The monoclonal antibodies largely recapitulate the neutralization breadth found in the corresponding donor serum and many recognize novel epitopes on envelope (Env) glycoprotein gp120, illuminating new targets for vaccine design. Analysis of neutralization by the full complement of anti-HIV broadly neutralizing monoclonal antibodies now available reveals that certain combinations of antibodies should offer markedly more favourable coverage of the enormous diversity of global circulating viruses than others and these combinations might be sought in active or passive immunization regimes. Overall, the isolation of multiple HIV broadly neutralizing monoclonal antibodies from several donors that, in aggregate, provide broad coverage at low concentrations is a highly positive indicator for the eventual design of an effective antibody-based HIV vaccine.

Highly potent HIV-specific antibody neutralization in vitro translates into effective protection against mucosal SHIV challenge in vivo

Most animal studies using passive administration of HIV broadly neutralizing monoclonal antibodies (bnMAbs) have associated protection against high-dose mucosal viral challenge with relatively high serum concentrations of antibody. We recently identified several bnMAbs remarkable for their in vitro potency against HIV. Of these bnMAbs, PGT121 is one of the most broad and potent antibodies isolated to date and shows 10- to 100-fold higher neutralizing activity than previously characterized bnMAbs. To evaluate the protective potency of PGT121 in vivo, we performed a protection study in rhesus macaques. Animals were i.v. administered 5 mg/kg, 1 mg/kg, or 0.2 mg/kg PGT121 24 h before being vaginally challenged with a single high dose of chimeric simian-human immunodeficiency virus (SHIV)SF162P3. Sterilizing immunity was achieved in all animals administered 5 mg/kg and 1 mg/kg and three of five animals administered 0.2 mg/kg PGT121, with corresponding average antibody serum concentrations of 95 µg/mL, 15 µg/mL, and 1.8 µg/mL, respectively. The results suggest that a protective serum concentration for PGT121 is in the single-digit µg/mL for SHIVSF162P3, showing that PGT121 can mediate sterilizing immunity at serum concentrations that are significantly lower than those observed in previous studies and that may be achievable through vaccination with the development of a suitable immunogen.

Broadly Neutralizing HIV Antibodies Define a Glycan-Dependent Epitope on the Prefusion Conformation of gp41 on Cleaved Envelope Trimers

Broadly neutralizing HIV antibodies are much sought after (a) to guide vaccine design, both as templates and as indicators of the authenticity of vaccine candidates, (b) to assist in structural studies, and (c) to serve as potential therapeutics. However, the number of targets on the viral envelope spike for such antibodies has been limited. Here, we describe a set of human monoclonal antibodies that define what is, to the best of our knowledge, a previously undefined target on HIV Env. The antibodies recognize a glycan-dependent epitope on the prefusion conformation of gp41 and unambiguously distinguish cleaved from uncleaved Env trimers, an important property given increasing evidence that cleavage is required for vaccine candidates that seek to mimic the functional HIV envelope spike. The availability of this set of antibodies expands the number of vaccine targets on HIV and provides reagents to characterize the native envelope spike.

HIV Envelope Glycoform Heterogeneity and Localized Diversity Govern the Initiation and Maturation of a V2 Apex Broadly Neutralizing Antibody Lineage

SUMMARY Understanding how broadly neutralizing antibodies (bnAbs) to HIV envelope (Env) develop during natural infection can help guide the rational design of an HIV vaccine. Here, we described a bnAb lineage targeting the Env V2 apex and the Ab‐Env co‐evolution that led to development of neutralization breadth. The lineage Abs bore an anionic heavy chain complementarity‐determining region 3 (CDRH3) of 25 amino acids, among the shortest known for this class of Abs, and achieved breadth with only 10% nucleotide somatic hypermutation and no insertions or deletions. The data suggested a role for Env glycoform heterogeneity in the activation of the lineage germline B cell. Finally, we showed that localized diversity at key V2 epitope residues drove bnAb maturation toward breadth, mirroring the Env evolution pattern described for another donor who developed V2‐apex targeting bnAbs. Overall, these findings suggest potential strategies for vaccine approaches based on germline‐targeting and serial immunogen design. HIGHLIGHTSIsolation of PCT64, a PGT145‐like, 25‐aa CDRH3 HIV Env V2 apex bnAb lineageEnv glycoform heterogeneity plays a role in the lineage precursor B cell activationLocalized diversity at key V2 epitope residues drove bnAb maturation toward breadthEnv evolution pattern is similar to CAP256, another V2 apex broad neutralizer Understanding the molecular basis of HIV Env‐specific broadly neutralizing antibodies (bnAbs) development is key for vaccine design. Landais et al. find that glycan heterogeneity played a role in the activation of V2 apex PCT64 bnAbs precursor and that viral evolution was similar to CAP256, another donor with V2 apex bnAbs.

Efficacy of Broadly Neutralizing Monoclonal Antibody PG16 in HIV-infected Humanized Mice

Highly potent broadly neutralizing human monoclonal antibodies hold promise for HIV prophylaxis and treatment. We used the SCID-hu Thy/Liv and BLT humanized mouse models to study the efficacy of these antibodies, primarily PG16, against HIV-1 clades A, B, and C. PG16 targets a conserved epitope in the V1/V2 region of gp120 common to 70-80% of HIV-1 isolates from multiple clades and has extremely potent in vitro activity against HIVJR-CSF. PG16 was highly efficacious in SCID-hu mice as a single intraperitoneal administration the day before inoculation of R5-tropic HIV directly into their Thy/Liv implants and demonstrated even greater efficacy if PG16 administration was continued after Thy/Liv implant HIV inoculation. However, PG16 as monotherapy had no activity in humanized mice with established R5-tropic HIV infection. These results provide evidence of tissue penetration of the antibodies, which could aid in their ability to prevent infection if virus crosses the mucosal barrier.

Immunological considerations for developing antibody therapeutics for Influenza A

Influenza infection can give rise to serious illness leading to complications and hospitalization of patients. The efficacy of current standard of care is very limited and provides little relief for patients hospitalized with serious flu. Human monoclonal antibodies (mAb) against influenza are being developed as new treatment options for this patient population. When developing antibody therapeutics, it is important to consider all possible immunologic effects of the antibodies on viral infection and disease progression including those other than the postulated therapeutic mechanisms. An area of concern is the potential of antibody-dependent enhancement (ADE) of illness. ADE of viral infections has been extensively described for Dengue virus (DENV) but not for influenza. Recently, preliminary results from clinical viral challenge studies of anti-HA-stalk mAbs suggested the possibility of enhanced viral shedding, raising concerns for ADE when utilizing mAbs as therapeutic intervention for influenza although viral shedding was not enhanced in the clinical viral challenge of anti-M2 mAb TCN-032. We herein discuss the known mechanisms of ADE and their relevance to developing mAbs such as anti-HA and anti-M2 for influenza disease.

Abstract P2-16-01: Discovery of fully human monoclonal antibodies as therapeutic candidates for the treatment of HER2-negative breast cancer

Unlike HER2-positive breast cancer, there are limited treatment options for patients diagnosed with triple negative and endocrine resistant HER2-negative breast cancer, and as such HER2-negative breast cancer represents a significant unmet medical need. The goal of this work is to use Theraclone’s proprietary I-STAR platform to mine the memory B cell immune repertoire of breast cancer patients for the discovery of therapeutically relevant monoclonal antibodies (mAbs) and targets that may be exploited as candidates for treatment of HER2-negative breast cancer. Matched serum and PBMC samples were collected from breast cancer patients at multiple clinical sites. The selected patient populations included, but were not limited to, patients who were treatment naive, those who had received immunotherapy or adjuvant chemotherapy, and patients who had an exceptional clinical response to treatment and/or disease. Serum antibody binding to a diverse panel of 5 well characterized breast cancer-derived cell lines of luminal and basal sub-types was determined. Utilizing this approach, patients with a robust serological profile across multiple breast cancer cell lines were identified and prioritized for memory B cell repertoire analysis via the I-STAR platform. Using a high throughput and miniaturized, multiplex flow cytometry assay, the secreted IgG antibodies from over 85,000 individually enriched and expanded B cell clones were screened for binding to the tumor cell line panel and a large number of positive B cell clones were identified. The screening hits can be binned into several unique binding profiles, many of which were confirmed to be shared across multiple patient samples. Deep sequence analysis of the variable regions of the antibodies produced by the B cell clones demonstrated that several of the screening hits were derived from clonally related B cells; the majority of the screening hits represented antibodies derived from unique B cell clones. A representative set of these antibodies was expressed recombinantly for further in vitro characterization. Citation Format: Christy Boozer, Paul Algate, Aurelio Bonavia, Mark Branum, Po-Ying Chan-Hui, Alison Fitch, Brad Greenfield, Claire Sutherland, Kristine Swiderek. Discovery of fully human monoclonal antibodies as therapeutic candidates for the treatment of HER2-negative breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P2-16-01.