Facts and Issues [International Conference on AIDS (11th: 1996: Vancouver, Canada)]

Vaccine development for HIV has been fraught with difficulties and the original optimism
surrounding their development has been much reduced. Several experimental vaccines are
still being tested in humans although, in general, large-scale trials have still not started. Some
observers feel a vaccine is unlikely to be available for many more years.
Vaccine development is also problematic because HIV infects some of the very cells (helper
T cells and macrophages) that a vaccine needs to activate. Some researchers fear a vaccine
could actually enhance the infectivity of the virus or the progress of the disease.
Despite these formidable difficulties, researchers are continuing to develop vaccines against
HIV. At least 14 projects were under way in the USA in 1995.
Gene Therapy
Gene therapy (also called recombinant DNA technology) for HIV infection is still at the early
stages of development, with a few products in phase I clinical trials. It needs to cross many
technical and conceptual hurdles before it can be used successfully for the treatment of HIV.
Gene therapy can involve injecting a gene directly into the body or packaging it with an inactivated biological vector (carrier), such as a retrovirus, prior to injection or mixing with cells
outside the bodyThe genes enter the T-cells, to either increase the body's capacity to recognise and destroy HIV, or alter the T-cells themselves to make them resistant to HIV infection.
Gene therapy can also be used to carry non-genetic materials into cells, such as interleukin-2.
The most advanced therapy Retrovector" by Viagene, has a retroviral vector which encodes
the HIV genes env and rev. Fibroblasts (a type of cell) are taken from the patient and treated
with the therapyThe fibroblasts are then reintroduced back into the same patient to boost
the anti-HIV immune response.
Other technologies include the use of ribozymes (pieces of RNA that can "cut" other
RNA, such as HIV RNA) which are also known as "molecular scissors." CD4 cells are taken
from a patient's white blood cells and treated with a viral vector containing the HIV double
ribozyme gene (University of California at San Diego).These treated CD4 cells are then
infused back into the same patient.The purpose of this therapy is to shield CD4 cells from
infection or block HIV replication in those that are already infected.
Cell GeneSys has taken a different approach to gene therapy modifying killerT-cells to
express HIV-specific receptors, enabling the cells to recognise and destroy HIV-infected
cells. Another approach involves inserting the REVM I 0 gene into stem cells to make them
resistant to HIV (Systemix).
Opportunistic Infections
People with AIDS suffer from one or more of a variety of opportunistic infections or cancers
that take advantage of the weakened immune system to become established. Some of these
infections and cancers can be prevented and treated, their symptoms ameliorated, and the
patient's life prolonged.
Although a range of organisms are constantly present in the environment, or even in an
individual's body they do not often cause illnesses as they are rapidly destroyed by or held
in check by the body's immune system.The body's defenses eventually break down as HIV
destroys the immune system. Many latent infections reactivate, and what were previously
mild infections become life-threatening.