Abstract: The invention provides methods and compositions for expanding cells that are not abundant or are difficult to obtain in pure form in culture, are in short supply (e.g., human cells), or have brief lifetimes in culture, using fusion polypeptide. The fusion polypeptide has a first region containing a translocation carrier moiety having the function of a transport polypeptide amino acid sequence from, e.g., herpesviral VP22, HIV TAT, Antp HD, Arg repeats, or a cationic polymer, or from homologues or fragments thereof, and a second region with a polypeptide having cell immortalization activity, a polypeptide having telomerase-specific activity, or a polypeptide having telomerase gene activation activity. The resulting cells of the invention are suitable for use in cell therapy.