Can someone be immune to HIV infection? As our last column observed, research recently has shifted its answer from “No!” to “Hmm, maybe.” Budding research now suggests that some people have a modest form of immunity to HIV infection, or they at least are able to fight infection very effectively. However, this characteristic is not common and is not spread evenly throughout the human population. What is it, who has it, and how did they get it?
To get inside the T4 (or CD4) cell, the AIDS virus must bind onto the cell’s CD4 molecule, plus onto another protein such as “CCR5 receptor” or “fusin.” If the proteins aren’t there to bind to, the virus has a hard time causing disease.
Some people don’t make these proteins, as the result of what is actually a genetic “defect,” so they would be resistant to infection. We each carry two copies of every gene, one from our mother and one from our father. In the case of CCR5, for example, Steve O’Brien of the National Cancer Institute found that about 20% of European-Americans carry one defective CCR5 gene, so they don’t make a normal amount of that protein on their T4 cells. If infected, they take a very long time for HIV to cause disease. Both genes are defective for about 1% of European-Americans, and they would seem to be actually immune, because they don’t make any CCR5 at all. Having or not having the genetic characteristic doesn’t seem to make any difference in a person’s overall health.
The characteristic is not universally spread through the population. The defective genes are much less common among African-Americans and Asian-Americans, and it’s extremely rare among native Africans and Asians. However, there may be other characteristics, not yet identified, which accomplish similar forms of resistance for them.
What does this mean, practically speaking? First, there is no test commercially available which would tell people if they have resistance/ immunity, so everyone should assume that they don’t have it and make safe choices accordingly.
Second, this research offers yet another possible path to help manage HIV infection. Can this characteristic be imitated so that immune destruction is blocked? For example, can substances be artificially introduced to bind to the CCR5 receptors so that HIV present doesn’t have access to them? Indeed, researchers have found a protein that does just that, at least in the test tube. Also, Naval Medical Research Institute scientists recently announced that in the lab they can stop the T4/CD4 cell from making CCR5.
As is so often the case with HIV/AIDS research, there may be applications far beyond this disease. Other diseases also may depend on such mechanisms for progression, and scientific understanding developed for AIDS may have enormous usefulness for all of medicine.
— Sandy Bartlett
ASA Community Education/Information Coordinator
This article appears in June 13 • 1997 and June 13 • 1997 (Cover).