They didn’t give them HIV. They gave them a virus genetically designed to be similar enough to HIV that the antibodies produced would also fight the HIV virus.
They also give half the volunteers a placebo instead of a real vaccine. The problem is that, as many on FR have guessed, even the chance of having the real vaccine tends to increase the rate for risky behavior It's not unusual for these tests to produce an increase in HIV rates for both the vaccine group and the placebo group. It's hard to protect people if their priorities do not include protection.
and the result????????????????