About 37 million people worldwide live with HIV, the human immunodeficiency virus. While treatments are available to prevent or treat HIV infections, there is no vaccine for it. Many approaches are currently being developed: some are preventative to be used by people at risk of getting the disease and some are aimed at ridding the virus hiding in cells.
The goal of a vaccine is to give our immune system the right weapons to defeat the virus. Unfortunately, HIV is extremely adaptable – it can change components and become unrecognizable. Due to this, many efforts to produce a vaccine have encountered limitations. The most famous example of this was the “RV HIV trial”, which showed a reduced rate of HIV infection by 31.2 percent compared to a placebo. The vaccine was safe and well-tolerated, but it was, unfortunately, only moderately effective.
“RV144 was not a public health success, but was highly important for the scientific endeavour. Immune analyses after the trial revealed signals that correlated with protection or lack of protection, which laid the foundation to develop improved approaches,” Dr Jill Gilmour, executive director for Human Immunology at the International AIDS Vaccine Initiative (IAVI), told IFLScience. “Coupled with new scientific discoveries, the pipeline today is more diverse and robust, increasing the chances for success to achieve effective vaccines and related immune-based interventions to stop HIV infection and AIDS.”
While the search for an effective treatment has been an uphill struggle, several approaches are now coming to fruition. Earlier this year, it was announced that the phase I human testing of one of these vaccines would take place in 2019.
This particular vaccine targets a fusion peptide on the surface of the virus. Peptides are short chains of amino acids (the components of proteins), and HIV uses them to enter cells. The vaccine aims to stop this action and prevent the virus from infecting cells. So far, it has been effective across a promising 31 percent of HIV strains out of 208 tested. Tests conducted in animals have shown that the vaccine is effective across multiple species and it is believed it will be effective in humans as well. The 2019 trial will assess side-effects and safety limitations for the vaccine.
A different approach was recently reported in Science Advances. In the study, researchers injected animal models with antigens that are designed to stimulate the production of precursor antibodies. These will eventually develop in bNAbs, or “broadly neutralizing antibodies”, which will bind to the virus and envelope it in order to stop it from infecting other cells. It has been recently announced by IAVI that the first vaccine candidate aimed at eliciting bNABs is going into clinical trial. This is the first of its kind. There is currently a vaccine in a phase II efficacy trial that will run until 2022 and a phase III study (comparison between treatments) of RV144 that started in 2016 and will run until mid-2021.
“The development of an effective HIV vaccine has been challenging in light of the nature of the virus and its interaction with the human immune system; no person has ever naturally recovered from an HIV infection, and there are no correlates that signal what immune responses are needed to block or clear HIV,” Dr Gilmour explained. “An HIV vaccine remains an essential tool to halt the spread of HIV and end AIDS. The number of new HIV infections has hardly decreased over the last 5 years, and could increase if prevention efforts are not scaled up substantially.”