Roughly 70% of the immune system (the T-cells) is found in the gut.
HIV requires two receptors to infect and kill the T-cells and 1 in 300 Americans and 1 in 100 Europeans have a natural immunity to HIV due to a mutation in one of the receptors. These people can become infected with HIV but will survive without any medications.
There have been about 3 functional cures for HIV already, but they're very expensive treatments costing over $300,000.
From: Cured: How the Berlin Patients Defeated HIV and forever changed medical science