Biology Reference
In-Depth Information
These original studies are now considered to be foundational in understanding the
epidemiology of HIV, and the risk factors associated with its spread (Bandewar et al.
2010
). Since 1998, researchers from the universities of Oxford, Nairobi and
Manitoba (Canada) have been collaborating on a project to develop a vaccine against
HIV based on the immunological protection mechanisms found in these sex work-
ers. The partnership currently includes the UK Medical Research Council, the
International AIDS Vaccine Initiative
18
and the Uganda Virus Research Institute.
An early study which followed 424 sex workers between 1985 and 1994 estab-
lished that a small proportion of highly exposed individuals have a natural pro-
tective immunity, which means that they seem to be resistant to HIV infection
(Fowke et al.
1996
). Subsequent studies aimed to clarify the nature of the wom-
en's immune response, as this 'has significant implications for vaccine design'
(Rowland-Jones et al.
1998a
). A 1998 study established that the Nairobi women's
resistance could not be accounted for by various mechanisms suggested so far
(Fowke et al.
1998
).
An immunological evaluation in a further study established that the HIV-
resistant women possessed high levels of a type of white blood cell known as cyto-
toxic T lymphocytes, or killer T-cells, which showed an HIV-1 specific response.
The women's killer T-cells were able to target particular proteins produced by
the HIV virus quickly, before the virus could take hold, and this protected them
against HIV-1 infection (Fowke et al.
2000
). This provided the researchers with a
new understanding, on which subsequent vaccine development was based (Bower
1998
; Rowland-Jones et al.
1998b
; Kaul et al.
2001a
).
Vaccine trials started in 2001 and proceeded through Phase I and II clinical trials.
19
However, in 2004 it was announced by the Oxford-Nairobi team at an international
AIDS vaccine conference in Switzerland that the vaccine had failed to offer sufficient
protection against HIV infection.
20
A study conducted in Nairobi between 1996 and 2000 noted that 11 of the
women who had been classified as HIV-1-resistant had seroconverted.
21
This
18
Founded in 1996, the International AIDS Vaccine Initiative (IAVI) is a global not-for-profit,
public-private partnership, with a mission to ensure the development of preventive AIDS vac-
cines that are not only safe and effective, but also accessible to all people
http://www.iavi.org/
19
Phase I trials are the earliest human tests in the life of a new drug. They involve few peo-
ple and check for safety, side effects and efficacy. This information is used to establish the dose
which will be used in the next stage of testing. Phase II trials are carried out in larger groups of
volunteers, to establish more about efficacy, dosage and side effects.
20
Initial analysis showed that although the vaccine was safe and well tolerated, only 20% of
the volunteer participants had shown a potentially protective stimulated T-cell response after
receiving the vaccine, and even that response was at a lower rate than desired (Okwemba
2004
;
Waldholz
2004
).
21
After initial exposure to any agent, it takes time for antibodies to develop. At some point after
initial HIV infection, seroconversion occurs. (Usually this takes a few weeks to a few months.)
This means there is now a detectable level of antibodies to HIV in the blood, and a person will
test (sero)positive for HIV.
