[3] Crohn's resistance was a result of the absence of a receptor, which prevent the HIV from infecting CD4 present on the exterior of the white blood cells.
[5] In early 2000, researchers discovered a small group of sex workers in Nairobi, Kenya, who were estimated to have sexual contact with 60 to 70 HIV positive clients a year without signs of infection.
[7] Later, however, some sex workers were discovered to have contracted the virus, leading Oxford University researcher Sarah Rowland-Jones to believe continual exposure is a requirement for maintaining immunity.
[citation needed] Cytotoxic T-lymphocytes (CTLs) provide a protective reaction against HIV when consistent exposure to the virus is present.
This resistance is not due to the primate's ability to control the virus in a manner that is substantially more effective than humans, but rather because of the lack of tissues created within the body that typically progress HIV to AIDS.
One method of genetic modification is through the manipulation of hematopoietic stem cells, which replaces HIV genes with engineered particles that attach to chromosomes.
Another method used by the Kiem lab was the release of zinc finger nuclease (ZFN), which identifies specific sections of DNA to cause a break in the double helix.