Calling all poz-neg couples
Why do some people remain HIV negative despite regular exposure to HIV, asks
Dr Sarah Fidler
There is little doubt repeated high level exposure to HIV will lead to transmission
of infection in the vast majority. The type and frequency of exposure as well
as the ‘dose’ of exposing virus all play an important role in
determining the risk of infection. Receipt of contaminated blood products
in a transfusion will lead to almost 100 per cent viral transmission while
low-level sexual exposure with someone on antiretroviral therapy with an ‘undetectable’
viral load under 50 copies remains relatively low (0.005-0.03 per cent per
exposure).
However, some rare individuals, despite repeated exposure, remain uninfected.
This may reflect chance alone and with continued exposure they too will become
infected. Scientific investigation into genetic and immune factors that may
potentially offer some protection may be important to help us understand how
HIV is passed from one person to another and how to protect people from ever
getting infected.
For HIV to enter a cell and infect it, two separate receptors are required:
CD4 and a chemokine receptor, usually CCR5. A rare genetic mutation in one
of the CCR5 chemokine receptor genes in under one per cent of Caucasians can
prevent infection with HIV, which uses CCR5 to enter into the cell. There
are other variants of HIV however that use other chemokine genes to enter
cells and there may be other yet unidentified genes that could also confer
similar protection.
Immune responses, if present naturally in the absence of actual infection,
which is unusual for viral infections, could be involved in protecting against
infection.
To date there is controversial scientific information that such ‘protective’
immune responses exist naturally in people who are exposed to HIV yet remain
uninfected. Some scientists have failed to find naturally occurring strong
HIV-specific immune responses in people who have reported exposure to HIV
but remain uninfected. Others have detected low-level responses not present
in unexposed volunteers.
Understanding the mechanisms involved in HIV protection and transmission are
critical for future successful preventative vaccine design. We are funded
by the American National Institute of Health to study of the science that
may be involved in protection from HIV infection with the goal of generating
a successful vaccine. This project is now recruiting in London at St Mary’s
Hospital and in Kampala, Uganda.
We will study rare individuals who remain HIV negative but have been in a
relationship where one partner is HIV positive and the other remains HIV negative
for more than a year and report a past exposure to their partners’ HIV
virus. We do not under any circumstances support continued unprotected sex
to continue for the purposes of this study.
We would like to study both partners to find out if there has been any HIV-specific
immunity or genetic factors that may have contributed towards protection in
the HIV negative partner.
We are also looking for couples together for at least a year where both partners
have tested negative for HIV with no known exposure to virus. For both groups
of couples we would ask you to volunteer to attend the clinical trials unit
four times a year to give a blood sample and undergo HIV testing and answer
some questions about your sex lives. Participants will be reimbursed for their
time and transport.
• For further information contact:
Kristin Kuldanek 020 7886 6047
