This invention relates to novel protein transduction domains (PTDs) derived from secretory leukocyte protease inhibitor (SLPI). SLPI-derived PTDs are able to deliver cargo moieties in vivo and in vitro into the cytoplasm and nucleus of a host cell. The invention also relates to a transduction complex comprising one or more SLPI-derived PTDs linked or fused to one or more cargo moieties, which may comprise, for example, proteins, nucleic acids, lipids, carbohydrates, small molecules and other chemical compounds. The invention also relates to the manufacture of SLPI-derived PTDs, complexes comprising them； compositions comprising SLPI-derived PTDs or complexes； and utilization of SLPI-derived PTDs or complexes comprising them for therapeutic, diagnostic and research methods involving delivery of heterologous molecules across cellular membranes, and especially, across nuclear membranes.
