They did several experiments for HIV drugs. The details are fuzzy, but if I remember correctly, they create a replica of the HIV virus that is totally harmless, but has the same outer cell layer (and reacts to the same chemicals as the real HIV would), and then infect you with that. This allows them to test the interactions with drugs, without giving people real HIV.
After the tests, you receive a certificate saying you are forever HIV positive according to some tests, but that it is a false positive, and using test X it can be verified that you're not really HIV positive. This was important for future medical operations and getting into certain countries that ban HIV-positive people.
Needless to say, you got a lot of money to do these fake HIV experiments.