Abstract: Disclosed is an immunogen in sterile form suitable for administration to a human subject, the immunogen comprising: at least a portion of the gag protein of HIV, said gag protein being from an HIV clade or having a consensus sequence for one or more HIV clades, and comprising at least parts of p17 and p24; and a synthetic polypeptide comprising a plurality of amino acid sequences, each sequence comprising a human CTL epitope of an HIV protein, and wherein a plurality of HIV proteins are represented in the synthetic polypeptide, said CTL epitopes being selected to stimulate an immune response to one or more HIV clades of interest.