Despite tremendous efforts to develop HIV vaccines eliciting virus-specific T-cell responses, whether this strategy can really result in HIV control remains unknown. It is important to determine what T-cell responses are responsible for primary HIV control. Recently, encouraging HIV vaccine trials indicated that vaccine induction of highly effective cytotoxic T lymphocytes (CTLs) may result in viral containment in a macaque AIDS model. CTLs exerting strong suppressive effect on viral replication frequently select for escape mutations at the cost of viral fitness. Thus, analysis of CTL-induced viral polymorphisms would contribute to determination of effective CTLs that may be essential for HIV control.