HIV infects “command and control” cells of the immune system.
During the period you are HIV+, the body is engaged in fight with the virus. The virus is infecting as many T Lymphocytes it can and the body is trying to replace them. Treatment against HIV helps tilt the odds in the body’s favor, making it harder for the virus to replicate inside the cells and infect other cells. The treatment, however, cannot eliminate the virus from the body.
AIDS occurs when you have so few T Lymphocytes that you can no longer fight off other infections, such as TB, pneumonias, and so on. AIDS is defined when the person’s laboratory count of CD4 cells (T lymphocytes) is under 200.
It’s possible to go in and out of AIDS. If a person starts treatment and boosts CD4 count to above 200, then the person no longer clinically has AIDS, but remains HIV+
There are a few genetic mutations that impacts progression from HIV seropositivity to AIDS. If you have a homozygous CCR5 mutation, you are immune to HIV. If you have a heterozygous CCR5 mutation, the progression takes a slower course. A CXCR1 mutation results in a much more rapid progression to AIDS.