Why HIV jab is elusive
The red ribbon is the universal symbol of awareness and support for people living with HIV.
What you need to know:
- Antibodies have been the heroes of Covid-19 immunity.
- HIV has a spherical shield around it as its most powerful weapon.
Before the Covid-19 pandemic, the largest and longest-running puzzle in infectious disease was how to develop a HIV vaccine. Thirty-eight years after the discovery of HIV, you could fill encyclopedias with all scientists have learned about this skillful shape-shifter that affects some 38 million people. Yet a vaccine has been elusive.
Confronted by the most dangerous microbial enemy yet, scientists came up with, not a vaccine, one of medicine’s biggest prizes, but antibodies. Yet while that could be crucial to one of virology’s new Holy Grails, unlike for Sars-CoV-2 (the Covid-19-causing virus), a HIV vaccine could still be elusive.
Part of this disparity probably has to do with Sars-CoV-2’s comparative simplicity. Antibodies have been the heroes of Covid-19 immunity. Swarming through your bloodstream are 10 billion B cells, each carrying a slightly different antibody.
Immune system
These amazingly eclectic Y-shaped molecules, produced by random shuffling of DNA, act first like an army of sentinels. When one latches onto a foreign protein, it starts making copies of itself and spitting out thousands of others per second. Ideally, they latch onto a part of the virus and interfere with its ability to infect cells, a process called neutralisation.
SARS-CoV-2 makes little attempt to hide its spike protein — that now famous grappling hook — and, for all the concerns about variants, it can’t readily change the spike’s structure. Give someone a vaccine encoding for the spike protein and, in two weeks, they’ll have swarms of neutralising antibodies coursing through their veins, an army waiting to fire: The RBD is just there as a ready target.
HIV has a spherical shield around it — the envelope— as its most powerful weapon, which doesn’t have an equivalent of RBD. It’s studded with a forest of glycans, vibrating sugars that form a defensive canopy around the virus. Worse, the envelope can mutate so rapidly that even if the immune system finds an antibody that neutralises some strains, others within the same person will evolve their way around it. The antibody then becomes useless.
Mr Onyango, a life scientist, is a Global Fellow at Moving Worlds Institute. [email protected]
