The world needs an HIV vaccine if it ever hopes to beat a virus that still infects over 1 million people a year and contributes to hundreds of thousands of deaths.
Despite 20 years of failures in major HIV vaccine trials — four this decade alone — researchers say recent scientific advances have likely, hopefully, put them on the right track to develop a highly effective vaccine against the insidious virus.
But probably not until the 2030s.
“An effective vaccine is really the only way to provide long-term immunity against HIV, and that’s what we need,” Dr. Julie McElrath, the director of the vaccine and infectious disease division at the Fred Hutchinson Cancer Center in Seattle, said Monday at the Conference on Retroviruses and Opportunistic Infections in Denver.
All current HIV vaccine action is in the laboratory, animal studies or very early human trials.
Researchers at the retrovirus conference presented favorable results from two HIV vaccine studies. One found that a modification to the simian version of HIV spurred production of what are known as broadly neutralizing antibodies against the virus in monkeys. Another showed promise in the effort to coax the immune system’s B cells to make the powerful antibodies in humans.
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“These trials illustrate as a proof of concept that we can train the immune system. But we need to further optimize it and test it in clinical trials,” Karlijn van der Straten, a Ph.D. student at the Academic Medical Center at Amsterdam University, who presented the human study, said at a news conference Monday.
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Still, the scrappy scientists in this field face a towering challenge. HIV is perhaps the most complex pathogen ever known.
“The whole field has learned from the past,” said William Schief, who leads Moderna’s HIV vaccine efforts. “We’ve learned strategies that don’t work.”
The cost has already been immense. Nearly $17 billion was spent worldwide on HIV -vaccine research from 2000 to 2021. Nearly $1 billion more is spent annually, according to the Joint United Nations Program on HIV/AIDS and the nonprofit HIV group AVAC.
“Maintaining the funding for HIV vaccines right now is really important,” said Dr. Nina Russell, who directs HIV research at the Bill & Melinda Gates Foundation. She pointed to the field’s own “progress and the excitement” and to how “HIV vaccine science and scientists continue to drive innovation and science that benefits other infectious diseases and global health in general.”
Case in point: Covid. Thanks to HIV research, the mRNA vaccine technology was already available in 2020 to speed a coronavirus vaccine to market.
Why the HIV vaccine efficacy trials failed
In strong contrast to Covid, the HIV vaccine endeavor has spanned four decades. Only one of the nine HIV vaccine trials have shown efficacy: a trial conducted in Thailand and published in 2009 that reported a modest 31% reduction in HIV risk.
HIV vaccine researchers subsequently spent years seeking to retool and improve that vaccine strategy, leading to a series of trials that launched in the late 2010s — only to fail.
Researchers have concluded those latest trials were doomed because, aside from prompting an anti-HIV response based in immune cells, they only drove the immune system to produce what are known as non-neutralizing antibodies. Those weapons just weren’t strong enough for such a fearsome foe.
Preventing HIV through vaccination remains a daunting challenge because the immune system doesn’t naturally mount an effective defense against the virus, as it does with so many other vaccine-preventable infections, including Covid. An HIV vaccine must coax from the body a supercharged immune response with no natural equivalent.
That path to victory is based on a crucial caveat: A small proportion of people with HIV do produce what are known as broadly neutralizing antibodies against the virus. They attack HIV in multiple ways and can neutralize a swath of variants of the virus.
Those antibodies don’t do much apparent good for people who develop them naturally, because they typically don’t arise until years into infection. HIV establishes a permanent reservoir in the body within about a week after infection, one that their immune response can’t eliminate. So HIV-positive people with such antibodies still require antiretroviral treatment to remain healthy.
Researchers believe that broadly neutralizing antibodies could prevent HIV from ever seeding an infection, provided the defense was ready in advance of exposure. A pair of major efficacy trials, published in 2021, demonstrated that infusions of cloned versions of one such antibody did, indeed, protect people who were exposed to certain HIV strains that are susceptible to that antibody.
However, globally, those particular strains of the virus comprise only a small subset of all circulating HIV. That means researchers can’t simply prompt a vaccine to produce that one antibody and expect it to be effective. Importantly, from this study they got a sense of what antibody level would be required to prevent infection.
It’s a high benchmark, but at least investigators now have a clearer sense of the challenge before them.
Also frustrating the HIV vaccine quest is that the virus mutates like mad. Whatever spot on the surface of the virus that antibodies target might be prone to change through mutation, thus allowing the virus to evade their attack. Consequently, researchers search for targets on the virus’ surface that aren’t highly subject to mutation.
Experts also believe warding off the mutation threat will require targeting multiple sites on the virus. So researchers are seeking to develop a portfolio of immune system prompts that would spur production of an array of broadly neutralizing antibodies.
Prompting the development of such antibodies requires a complex, step-by step process of coaxing the infection-fighting B cells, getting them to multiply and then guiding their maturation into potent broadly neutralizing antibody-producing factories.
HIV vaccine development “in a better place”
Dr. Carl Dieffenbach, the head of the AIDS division at the National Institute of Allergy and Infectious Diseases, said numerous recent technological advances — including mRNA, better animal models of HIV infection and high-tech imaging technology — have improved researchers’ precision in designing, and speed in producing, new proteins to spur anti-HIV immune responses.
Global collaboration among major players is also flourishing, researchers said. There are several early-stage human clinical trials of HIV-vaccine components underway.
Three mRNA-based early human trials of such components have been launched since 2022. Among them, they have been led or otherwise funded by the global vaccine research nonprofit group IAVI, Fred Hutch, Moderna, Scripps Research, the Gates Foundation, the National Institutes of Health, the U.S. Agency for International Development, and university teams. More such trials are in the works.
On Friday, Science magazine reported concerning recent findings that among the three mRNA trials, a substantial proportion of participants — 7% to 18%, IAVI said in a statement — experienced skin-related symptoms following injections, including hives, itching and welts.
IAVI said in its statement that it and partners are investigating the HIV trials’ skin-related outcomes, most of which were “mild or moderate and managed with simple allergy medications.”
Researchers have shown success in one of those mRNA trials in executing a particular step in the B-cell cultivation process.
That vaccine component also generated “helper” CD4 cells primed to combat HIV. The immune cells are expected to operate like an orchestra conductor for the immune system, coordinating a response by sending instructions to B cells and scaling up other facets of an assault on HIV.
A complementary strategy under investigation seeks to promote the development of “killer” CD8 cells that might be primed to kill off any immune cells that the antibodies failed to save from infection.
Crucially, investigators believe they are now much better able to discern top vaccine component candidates from the duds. They plan to spend the coming years developing such components so that when they do assemble the most promising among them into a multi-pronged vaccine, they can be much more confident of ultimate success in a trial.
“An HIV vaccine could end HIV,” McElrath said at the Denver conference. “So I say, ‘Let’s just get on with it.”
Dr. Mark Feinberg, president and CEO of IAVI, suggested that the first trial to test effectiveness of the vaccine might not launch until 2030 or later.
Even so, he was bullish.
“The field of HIV vaccine development is in a better place now than it’s ever been,” he said.
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