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 having the transport function of herpesviral VP22 protein or human immunodeficiency virus (HIV) TAT protein, 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.
