A fresh effort to find a vaccine for HIV is beginning at laboratories in a London hospital and two centres in Africa.
Scientists are recruiting 64 healthy adult volunteers for the trial, which is expected to take up to two years.
The work will be split equally between London, the Rwandan capital Kigali and Nairobi in Kenya.
This early trial is being run by the International Aids Vaccine Initiative (IAVI), a non-profit organization.
The principal investigator, Dr Jill Gilmour, who has worked at the laboratory at Chelsea and Westminster Hospital since its founding in 2001, says she is optimistic that the Aids virus can eventually be tackled with a vaccine.
The virus is now 30 years old, and the search for a vaccine has proved elusive so far.
However, an American-backed trial in Thailand found in 2009 that a combination of two vaccine prototypes was 30% effective in preventing HIV infection.
Follow-up trials are being planned with the aim of improving those initial results.
In the IAVI trial, volunteers who are free of HIV and not at risk of catching the infection will receive a combination of two vaccines.
One of them is derived from a weakened version of Sendai, a flu-like virus that infects rodents. It will be administered through nasal drops.
This is because in the early stages of infection, both HIV and Sendai affect the mucosal tissues, which are found in the nose and also in the genital area.
Dr Gilmour said: "I believe it's not if, it's when we will have an effective HIV vaccine. There is now strong scientific data to support that position.
"We will get there but vaccine development takes time. It's not for the faint-hearted.
"Bear in mind that with polio, it was 45 years from discovering the virus to getting an effective vaccine.
"HIV is a formidable beast with sneaky tricks. It changes every time it divides, so it's highly variable. And it can integrate into your own cells, so your immune system can't see it."
The trial is early work known as Phase I, meaning that the aim is to ensure the vaccine is safe and induces an immune response.
Dr Gilmour added: "Delivering the vaccine into the nose has public health benefits, because we're not using needles.
"If we see strong immune responses, we go into the larger second phase of testing whether the vaccine is effective in reducing transmission or lowering the load of the virus.
"The Sendai product is modified from a virus which affects rodents, including hamsters. From our perspective, it's a bonus that this virus has lived in the human environment without causing us harm."
The IAVI laboratory at Chelsea and Westminster handles almost 100,000 blood samples a year and has supported more than 20 other vaccine trials.
Its work includes sending test kits to sub-Saharan African countries at the heart of the Aids epidemic, carefully tracking the thousands of blood samples that it holds and ships elsewhere, and ensuring the data and paperwork from trials is rigorously monitored, so the results from different sets of tests can be pooled.