This week the NIH-funded HIV Vaccine Trials Network (HVTN) and HIV Prevention Trials Network (HPTN) announced the launch of the HVTN 704/HPTN 085 trial, also known as "AMP" (Antibody-Mediated Prevention). The Phase IIb trial is designed to measure the safety and effectiveness of an intravenous infusion of the broadly neutralizing antibody VRC01 for HIV prevention. The infusion will be delivered to participants every eight weeks over the course of a year and a half (participants are also followed for 20 weeks after their last infusion).
AMP consists of two parallel trials conducted collaboratively by the the HVTN and HPTN. The trial that just initiated (HVTN 704/HPTN 085) has 24 sites across Brazil, Peru and the US and plans to recruit 2,700 men and transgender people who have sex with men. The other study, HVTN 703/HPTN 081, will be initiated later this year and will enroll 1,500 women at 15 sites across Botswana, Kenya, Malawi, Mozambique, South Africa, Tanzania and Zimbabwe.
For the past several years, scientists have been working with potent antibodies that neutralize many different strains of HIV. These broadly neutralizing antibodies, or bNAbs, include VRC01. Antibodies are substances made by the immune system; these bNAbs have been isolated from people living with HIV. Researchers have purified the bNAbs and modified them to make them even more effective against HIV. The antibodies in trials like AMP are delivered via infusion -- meaning intravenous administration. The approach of delivering an immune defense directly is called passive immunization, and it stands in contrast to vaccination or immunizations that teach the body how to mount an immune defense itself, via a vaccine. In the AMP trial study visits are expected to take approximately 90 minutes and participants are scheduled to come to the clinic every eight weeks.
Many scientists in the field say that the point of bNAb trials isn't to identify a new strategy for widespread use. Instead, a positive result could lead to more focused vaccine development efforts. Other researchers say that more potent antibodies that could protect in smaller, more easily-administered doses, could perhaps make it to market one day. For this to happen, all agree that the dosage (the amount delivered to a person) would need to come down from where it is in the AMP trial, and the half-life (a measure of the time that protective levels of antibody stay in the blood) would need to go up.
The AMP trials will contribute significantly to the field's understanding of how to fight HIV. AVAC and other advocates have urged that the trial sponsors and implementers ensure consistency in the messaging about and expectations for VRC01 -- especially given that other, more potent antibodies may be ready for additional testing by the time the AMP trials are over, alone or in combination. (This is a common conundrum in research: first-in-class products break new ground but may not be the optimal choices for introduction.)
Extensive and continuous stakeholder engagement is essential to ensure that passive immunization trials and product development plans are clearly articulated.
The AMP trials are among the first prevention efficacy trials to start in the "post-PrEP-approval" era, raising an issue that's challenging prevention stakeholders everywhere: the need to define the standard of prevention in trials to include daily oral PrEP, which is now recommended by the WHO for all people at substantial risk of HIV. People who participate in efficacy trials are, by definition, at substantial risk of acquiring HIV and therefore there is an ethical imperative to include PrEP. The question is how -- and how to design trials that can answer questions about new products, even as incidence may go down due to PrEP use.
The AMP trial that launched this week has this to say about its approach to PrEP:
Volunteers in the AMP Studies will be referred to available local programs where they may obtain the oral medication Truvada [TDF/FTC] to take daily for HIV prevention, a highly effective practice called pre-exposure prophylaxis (PrEP). Volunteers' access to PrEP will expand as more host countries approve Truvada for PrEP and develop the infrastructure to support its use.
The prevention standard of care is defined as, "condoms and lubricant, counseling on how to reduce behaviors that increase risk for infection, and counseling and referral for antiretrovirals to take immediately following suspected exposure to HIV (post-exposure prophylaxis)."
ACT UP New York member and long-time activist Luis Santiago responded, "Should Truvada/PrEP be more than just an 'option'? Should it be actually provided in the studies in the control arm? Are we back to the ethical discussion of the 1990s?"
These questions, which were a key part of the prevention advocacy agenda years ago, still apply today -- how does the field ensure that trials are not responsive to context but help to shape it? There is precedent for this, as the HVTN ensured access to antiretroviral therapy for individuals who seroconverted in vaccine trials before ART was widely available in Africa, and subsequently ensured access to voluntary medical male circumcision (VMMC) in its vaccine trial in South Africa before there was national policy on that strategy.
The reality of HIV prevention programming is rapidly evolving. In just the past four months, three of the AMP trial host countries (Kenya, Peru, South Africa) joined the US in approved TDF/FTC for daily oral PrEP, joining the USA in this decision. This leaves six AMP countries that have not: Botswana, Brazil, Malawi, Mozambique, Tanzania and Zimbabwe. But approval doesn't mean access, and these countries may or may not have programs set up to which AMP participants can be easily and effectively referred. In that case, it's up to the trial site to sort out provision of this key service.
At the end of the day, everyone is after the same thing -- access to new options that can prevent HIV today and in the future, whether that's a pill in hand for a young woman at risk today or a vaccine or antibody for the generations to come.
John Mascola of the Vaccine Research Center (VRC) that isolated the VRC01 antibody recently presented on the use of antibodies for both prevention and treatment, which provides helpful background and context for these recent developments, Harnessing Antibodies for HIV Prevention and Treatment.
Additional study info can be found in AVAC's prevention research and development database (PxRD) and at ampstudy.org.