Human immunodeficiency virus--can it mutate?

Yes: Hiv mutates in response to HIV therapy. If you're being treated without a complete response (partial suppression), the virus can mutate so it can replicate in the presence of the drugs. This usually happens in people who don't take their medications properly. They can then transmit the mutant virus to others. Spontaneous mutation (mutation independent of therapy) has not been a big problem.