The invention relates to peptides comprising part or all of a conserved element within a Center-of-Tree (COT) sequence derived from a family of polypeptides encoded by naturally occurring variants of HIV. The invention also relates to immunogenic compositions and vaccines comprising said peptides. The invention also relates to methods for the identification of HIV controller patients based on the detection of the T cells of the patient to mount a cytotoxic T cell response against said peptides and to methods for the identification of immunogenic peptides within a family of variant polypeptides.