This story is doing the rounds at the moment, so I thought I'd add my two cents worth. A German man happened to have both HIV and leukaemia. After failing first-line chemotherapy for his leukaemia, he was booked for a bone marrow transplant. His astute doctor remembered that a rare few people have a mutation in the gene for CCR5, a receptor found on our immune cells. Most stains of HIV bind to the CCR5 receptor and thereby trick the cell into letting them inside. However, those few people with two 'defective' copies of the gene have the serendipitous effect of not allowing HIV in, and are thus 'immune' to the disease.
What the doctor did was to specifically seek out a matching donor for his patient who also had these mutations in his CCR5 gene. The result: almost 2 years after the transplant, HIV is undetectable in the patient's body. It may still be 'hiding' somewhere there, but even if this is the case, the man has been 'functionally cured' at the very least.
This is very promising news, although it doesn't mean that a cure (or 'vaccination') is around the corner. Bone marrow transplantations arguably carry a greater risk to the patient than HIV does, and so repeating this feat on a routine basis isn't feasible. However, it does suggest that if we could alter people's CCR5 receptors artificially, we would make them immune to HIV. The way to do this, of course, is via gene therapy. That takes time to develop and test, so we're a long way off. But this finding is nonetheless certainly good news.
There's a really good article on the matter here.