Major Blow as Experimental HIV Vaccine Fails in Late Clinical Trial : ScienceAlert


The decades-long quest to develop an HIV vaccine has taken another major blow, with the ‘last true candidate in development’ failing to prevent infections any better than a placebo in late-stage clinical trials.

The multinational Mosaico study, which began in 2019 and involved more than 3,900 volunteers, investigated a four-shot HIV vaccine for cisgender and transgender men who have sex with cisgender and/or transgender men.

As the U.S. National Institute of Allergy and Infectious Diseases (NIAID) reported last week, the trial was halted after a scheduled data review by the study’s independent data and safety review committee determined that the vaccine was safe, but ineffective.

“For our research partners and others who have spent decades developing vaccines to end the HIV/AIDS pandemic, these results are disappointing,” said lead researcher Susan Buchbinder, an HIV researcher at the University of California, San Francisco. in a statement.

“While HIV remains a unique challenge for vaccine development, the HIV research community remains fully committed to doing just that, and each study brings us one step closer to this realization.”

The vaccine was developed by Janssen, Johnson & Johnson’s vaccine division, which was testing the same vaccine delivery system as their now widely used COVID-19 vaccine.

Despite decades of research, only one vaccine candidate has so far shown even marginal efficacy in preventing HIV infection. Ccompleted in the early 2000s, it is the largest HIV vaccine trial to date. Researchers hoped to improve those results with an HIV vaccine that offered broad protection.

To do that, the Mosaico study and other parallel studies examined vaccines based on “mosaic” immunogens – fragments of genetic material from multiple HIV subtypes – which are designed to train the body’s immune system to fight the wide range of identify global HIV strains. .

This was thought to be a promising strategy against HIV, a notorious virus that mutates quickly and, in fact, is many steps ahead of vaccine development. It also protects itself from recognition by antibodies with a heavily sugared protein coat.

When the trial got underway, Buchbinder said it was “an important step toward developing a safe and effective HIV vaccine for people around the world.”

That feeling still rings true, even as the trial draws to a close. Experts say the way the trial valued participants’ choice removed barriers to accessing preventive medication and will bring lasting benefits to those most vulnerable to HIV.

Volunteers did not participate in the study until they were offered and refused antiretroviral drugs that can prevent HIV infection. These preventive drugs, called HIV pre-exposure prophylaxis (PrEP), are taken daily. Those who chose PrEP were matched with services that provided the drugs, and trial participants who later changed their mind and wanted to take PrEP could do so, too.

“One thing we clearly learned from study participants is that people want a choice, and a vaccine will be an important option for those who don’t want PrEP,” Buchbinder said.

“The ethical and community-friendly design and conduct of this study helped build trust in communities that may not be inclined to trust research institutions,” added Mitchell Warren, executive director of the AIDS Vaccine Advocacy Coalition.

Other efforts to develop HIV vaccines are continuing. Three mRNA HIV vaccines are currently being tested in a phase I clinical trial, investigating whether the vaccines are safe and can stimulate an immune response.

“Finding an HIV vaccine has proven to be a huge scientific challenge,” immunologist and former NIAID director Anthony Fauci said in a statement last year.

“With the success of safe and highly effective COVID-19 vaccines, we have a great opportunity to learn whether mRNA technology can achieve similar results against HIV infection.”

The problem is that phase I safety trials are a long way from phase III trials that provide data on whether a new vaccine (or drug) is effective or not, so it will be many years before we see another candidate late stage of research.

As Warren told health reporter Helen Branswell at Stat News, the latest trial results are a “hard reminder” of the challenges of developing an HIV vaccine.

At least five experimental HIV vaccines, tested in nine trials, have failed efficacy trials, Warren said. He suspects the problem is not in the vaccine delivery systems — which have worked against COVID-19 — but in the immune targets that HIV vaccines are trying to hit.

“Our challenge is figuring out exactly what the target is,” Warren told Branswell. “We have the vehicles. We don’t even know which passengers to put in the vehicles.’

A tough job against a shape-shifting virus.

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