The Hunt for the AIDS Vaccine - questions and answers
Why did scientists originally think that it would only take two years to develop a vaccine for AIDS?
Scientists had previously been quite successful at making good vaccines once the biology of a virus was understood. Dr Robert Gallo thought that we understood the HIV virus, and it was easy to make, so he thought a vaccine should follow shortly. He and many other scientists just hadn’t anticipated the guile of the virus.
How does HIV evolve and change?
HIV makes an estimated 10-20 mistakes every time it copies itself. Most of the mutations will prevent the virus from replicating, but enough will survive and go on to replicate, allowing the process to continue and propagating increased variation.
Is HIV the only virus that evolves in this way?
No. Every living thing evolves due to mutation and selection. HIV demonstrates evolution speeded up. It replicates very often and mutates at a high rate resulting in very fast evolution.
What are killer T cells and how do they work?
Killer T cells, also known as Cytotoxic T-lymphocytes, are cells produced by the immune system which recognise virally infected cells and kill them. They recognise that a cell is infected with a virus, by the HLA-viral peptide complex presented on the infected cell surface.
What was different about the Nairobi sex workers’ T cells that made them successful at destroying infected cells, compared to most people with HIV that go on to get AIDS?
This is a bit of a mystery, but it is thought that these workers may have had a better HLA presentation system, probably due to their not being familiar to the local HIV. For example, many Nairobi prostitutes are Ugandan. It is thought that if you are local to the area of HIV then the HIV will have “learnt” how to avoid your HLA, as in it would have mutated the epitope which the HLA recognises so that it no longer stimulates killer T cells. If you have foreign HLA (e.g. from Uganda) then the virus may not have seen your HLA before and so its peptides are recognised by HLA and the cell can be killed.
If a vaccine using killer T cells was developed, could people keep getting re-vaccinated as the virus changed?
The idea of a killer T cell vaccine is to kill off enough of the virus on initial infection so that the immune system can keep it under control – if not rid the body entirely of the virus. The vaccines could be tailored to local strains of HIV but keeping track of all the possible variations and making appropriate vaccines would be very difficult.
Are there more people like Bob Massie who have HIV but are still healthy?
Yes. Bruce Walker is trying to find as many as he can. He estimates that there are a few thousand people like this in the US. There are many reasons why infected people might not progress to AIDS. The genetics of the virus and/or the person play an important part, but scientists couldn’t explain why Bob is still healthy using the usual reasons. That’s why he is so important to study.
It is feared that if a live vaccine was given to humans, it could mutate and cause infection. Did this happen to the monkeys that were given the live vaccine?
No. The live attenuated vaccine that Ron Desrosiers gave the monkeys offered better protection than any other HIV vaccine. The fears arose when Ruth Ruprecht asked what would happen if mothers given the live attenuated virus passed it on to their infants who have immature immune systems. She carried out experiments on infant monkeys, and found that when given the same live attenuated vaccine as the adult monkeys, they went on to progress to disease.
Will there ever be a vaccine for AIDS?
We don’t know.
