Newly defined biomarker may accelerate clinical trials for vaccines to prevent HIV-1 infection – the Antibody Mediated Prevention (AMP) trials

A new biomarker appears to be an effective surrogate endpoint to reliably predict the ability of broadly neutralizing monoclonal antibodies to prevent acquisition of HIV-1. Broadly neutralizing antibodies (bnAbs) are defined by their ability to neutralize multiple genetically distinct viral strains.
Published in Healthcare & Nursing

Contributed by the study authors and the HIV Vaccine Trials Network communications team.

Findings from Gilbert et al., in the August 22, 2022 Nature Medicine issue, build on the proof-of-concept Antibody Mediated Prevention (AMP) trials first published in March 2021 showing that a broadly neutralizing antibody (or bnAb) called VRC01 was effective in preventing the acquisition of some – but not all – HIV strains. Seventy percent of strains circulating in regions where the studies were conducted – sub-Saharan Africa, the U.S., and South America – were resistant to VRC01, and the original report noted no statistical difference between the VRC01 arms and the placebo arm in overall prevention of HIV acquisition.
“A single HIV-1 broadly neutralizing monoclonal antibody, such as VRC01, will not be sufficient to provide high protection against HIV-1 acquisition because many strains are resistant,” said Dr. Peter Gilbert, one of the paper’s co-first authors. “Therefore, bnAb cocktails will be needed, and although there is a rich pipeline of these antibodies under development, we first needed a biomarker that would enable us to compare cocktails and select the best candidates to advance to efficacy trials.”

Dr. Gilbert and co-first author Dr. Yunda Huang are researchers with the HIV Vaccine Trials Network (HVTN), based at Fred Hutchinson Cancer Center in Seattle. The study was conducted with collaborators from the HIV Prevention Trials Network (HPTN).
Gilbert said a useful biomarker must also be validated as a surrogate endpoint to reliably predict the prevention efficacy level of an HIV-1 bnAb cocktail. This would permit expedited approval of different cocktails without requiring long and expensive efficacy trials. According to results from this study, the newly defined biomarker, called PT80, appears to meet those requirements, which predicts the 80% neutralizing antibody titer of a bnAb recipient’s blood sample at a given time to a given virus.
“In other words, PT80 quantifies the ‘killing power’ of a bnAb in a blood sample at a given time point against a specific HIV-1 strain,” said Dr. Larry Corey, AMP Protocol Chair and Principal Investigator, HVTN Leadership Operations Center. “Our study showed that PT80 is likely to be highly successful as the sought-after biomarker and surrogate endpoint for future monoclonal antibody studies.” 
The HVTN and HPTN expect to leverage these study results in planning and seeking approval for an AMP-sequel, large-scale efficacy study.
“This research sought to provide validation data for the PT80 biomarker for the specific HIV-1 bnAb VRC01, but our team will further study validation of this biomarker for non-VRC01 cocktails,” said senior author Myron Cohen, M.D., AMP Protocol Chair, HPTN Principal Investigator, and Director of the Institute for Global Health and Infectious Diseases at the University of North Carolina at Chapel Hill. “One of our priorities is the study of novel candidate HIV-1 vaccine regimens that, through iterative refinement, will identify those that induce antibodies to broadly neutralize most strains of HIV-1 for at least six to 12 months post-vaccination. This study predicts that such a vaccine would be effective at preventing HIV-1 acquisition.”
In the primary AMP trials paper, a biomarker called IC80 was able to measure the susceptibility of an exposing virus to the monoclonal antibody given in the trial. This assay is done in a test tube with the infecting strain. But IC80 contains no information about the quantity of bnAb in an individual’s blood sample. PT80 allows analysis of bnAb concentrations measured over time.
This study:
●    Codified HVTN/HPTN’s use of PT80 as a primary study endpoint for Phase 1 clinical studies of HIV-1 bnAb cocktails for ranking and selecting bnAb regimens.
●    Showed similar results for the PT80 biomarker in two diverse contexts: 1) sub-Saharan African women in a subtype C HIV-1 epidemic, and 2) men who have sex with men and transgender persons in Peru, Brazil, Switzerland and the U.S. in a predominantly subtype B HIV-1 epidemic. This replication in two study and virus populations strengthens the generalizable use of this biomarker.
●    Partially validated results from nonhuman primate studies showing that the PT80 biomarker is related to prevention efficacy in a similar way for VRC01 recipients in the AMP trials as for nonhuman primate recipients of bnAbs in virus challenge models. This indicates that previous nonhuman primate studies of VRC01 and other bnAbs did not over-promise in what level of protection could be achieved with VRC01 in the AMP efficacy trial.
●    Confirmed that PT80 is a very good predictor of neutralizing antibody titer. Neutralizing antibody titer has been successfully used as a surrogate endpoint for approval and use of vaccines against many different pathogens. Through the COVID-19 Prevention Network, sponsored by the National Institute of Allergy and Infectious Diseases (NIAID), HVTN scientists have shown that neutralizing antibody titer is supported to be a useful surrogate endpoint for occurrence of symptomatic COVID-19 in all five COVID-19 vaccine efficacy trials that have been analyzed. The researchers anticipate that PT80 developed in this study will have similar utility in the HIV-1 prevention field.

“Our modeling predicts that currently available triple cocktail HIV-1 bnAbs, administered every four to six months, would have high prevention efficacy of approximately 90%, which, once verified in an efficacy trial, is promising for regulatory approval as a new modality for HIV-1 prevention,” Huang said. “Communities generally favor diversity in HIV prevention options, recognizing that one option doesn’t work for everyone. For example, some people prefer a bnAb over antiretroviral-based prevention, such as PrEP, due to potential advantages in safety and side effects.”
The two AMP studies (HVTN 704/HPTN 085 and HVTN 703/HPTN 081) opened in 2016 and successfully enrolled 4,623 participants. The studies are sponsored and funded by NIAID, part of the National Institutes of Health, and were conducted jointly by the HIV Vaccine Trials Network (HVTN) and HIV Prevention Trials Network (HPTN). The NIAID Vaccine Research Center (VRC) isolated VRC01 in 2010 from the blood of a person living with HIV and subsequently manufactured the antibody for the AMP studies. Data from the AMP studies were first reported at a press conference hosted by the 4th International HIV Research for Prevention Conference (HIVR4P) on Jan. 26, 2021. The New England Journal of Medicine published these results in March 2021.
There are still more than 1.7 million new cases per year of HIV globally; more than 75 million people have acquired HIV and more than 32 million people have died from AIDS-related illnesses since the pandemic began. The need for a safe and effective preventive HIV vaccine and other HIV prevention technologies remains as urgent as ever.

REFERENCE: Gilbert, P.B., Huang, Y., deCamp, A.C. et al. Neutralization titer biomarker for antibody-mediated prevention of HIV-1 acquisition. Nat Med (2022).


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About the HIV Vaccine Trials Network (HVTN)
The HIV Vaccine Trials Network (HVTN) is the world’s largest publicly funded international collaboration facilitating the evaluation of vaccines to prevent HIV/AIDS. The HVTN helps advance the fields of vaccinology, social and behavioral sciences, statistics, and immunology, as well as tuberculosis and COVID-19 vaccines. The HVTN’s mission is to fully characterize the safety, statistics, and immunology, as well as tuberculosis and COVID-19 vaccines. The HVTN’s mission is to fully characterize the safety, immunogenicity, and efficacy of HIV vaccine candidates with the goal of developing a safe, effective vaccine as rapidly as possible for prevention of HIV globally. Funding is provided by public and private sources. The National Institute of Allergy and Infectious Diseases (NIAID) at the U.S. National Institutes of Health, is the primary funder and sponsor of the majority of trials conducted by the HVTN. The Network’s clinical research sites are located at leading research institutions in over 16 countries on four continents. Internationally renowned researchers in HIV vaccines and prevention lead these units and contribute to the Network’s scientific agenda. The Network’s headquarters are the Fred Hutchinson Cancer Center in Seattle, Washington.

About Fred Hutchinson Cancer Center
Fred Hutchinson Cancer Center (Fred Hutch) is an independent, nonprofit, unified adult cancer care and research center that is clinically integrated with UW Medicine, a world leader in clinical care, research and learning. Fred Hutchinson Cancer Center was created in April 2022 by the merger of long-time partners, Fred Hutchinson Cancer Research Center and Seattle Cancer Care Alliance. Together, our fully integrated research and clinical care teams seek to discover new cures for the world’s deadliest diseases and make life beyond cancer a reality.
The first National Cancer Institute-designated cancer center in the Pacific Northwest, Fred Hutch’s global leadership in bone marrow transplantation, HIV/AIDS, immunotherapy and COVID-19 has confirmed our reputation as one of the world’s leading cancer, infectious disease and biomedical research centers. Based in Seattle, Fred Hutch operates eight clinical care sites that provide medical oncology, infusion, radiation, proton therapy and related services, and has network affiliations with hospitals in five states. 

 About the HPTN
The HIV Prevention Trials Network (HPTN) is a worldwide collaborative clinical trials network that brings together investigators, ethicists, community members, and other partners to develop and test the safety and efficacy of interventions designed to prevent the acquisition and transmission of HIV. The U.S. National Institute of Allergy and Infectious Diseases, the U.S. National Institute of Mental Health, Office of The Director, the U.S. National Institute on Drug Abuse, and the Eunice Kennedy Shriver National Institute of Child Health and Human Development, all part of the U.S. National Institutes of Health, co-fund the HPTN. The HPTN has collaborated with more than 85 clinical research sites in 19 countries to evaluate new HIV prevention interventions and strategies in populations with a disproportionate HIV burden. The HPTN research agenda – more than 50 trials ongoing or completed with over 161,000 participants enrolled and evaluated – is focused primarily on discovering new HIV prevention tools and evaluating integrated strategies, including biomedical interventions combined with behavioral risk reduction interventions and structural interventions. For more information, visit 

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