Important note: Information in this article was accurate in May 2000. The state of the art may have changed since the publication date.
Mistakenly cast as "suppressor" cells in the early 1980s, CD8+ cells were largely viewed as useless for the fight against HIV and other infections. Worse, the high levels of CD8+ cells that occurred as a result of HIV infection were seen as a bad thing. Researchers who have a more sophisticated understanding of immunology now know better. In fact, different research teams have found that CD8+ cells play an important role in controlling the following infections in animals as well as humans:
CD8+ cells also appear to be critical in helping monkeys control infection by SIV (simian immunodeficiency virus). In people, CD8+ cells also play a major role in fighting HIV. These cells either directly kill virus-infected cells or release chemicals that stop those cells from producing new viruses. According to some studies, CD8+ cells are so important that when their levels fall below a certain level, the risk of death increases.
The CD8+ antiviral defense system in people with HIV/AIDS (PHAs) becomes less efficient over time for a number of reasons:
HAART helps the immune system begin to recover from the damage caused by HIV. Therapy that significantly reduces viral load allows the immune system to begin repairing itself. Unfortunately, in people whose viral loads fall below detectable levels, the immune system seems to "forget" how to fight HIV. Indeed, CD8+ cells that are specifically programmed to attack HIV disappear from the blood. As well, when people stop taking anti-HIV drugs their viral load soars, a fact that demonstrates the inability of their immune system to control HIV.
In order to help the immune systems of people with a weakened CD8+ response to HIV, researchers are conducting studies during which PHAs take short breaks, or holidays, from therapy. These researchers hope that the temporary increase in viral load that occurs during these breaks will encourage CD8+ cells to "remember" how to attack HIV. Drug holidays are also referred to as Structured (or strategic) Treatment Interruptions.
Researchers are also conducting experiments on monkeys infected with SIV by giving them vaccines to boost immunity against that virus. If successful, these vaccines could possibly be modified for use in PHAs as a means to boost their immunity to HIV.
Another way to increase the number of CD8+ cells is to grow huge numbers of them - usually around a billion cells - outside the body then infuse (administer intravenously) them into PHAs. One problem with this approach is about 90% of these cells usually die within 48 hours of infusion. Researchers aren't certain why this happens and are busy studying ways of making CD8+ cells more robust.
Later in this issue, we will report developments in the field of CD8+ infusion research.
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