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
I'm waiting for Theresa May to apologize to the great people of the USA for failing to protect an American in that London attack.