A composition comprising recombinant, intact minicells that contain a therapeutic nucleic acid molecule is disclosed. Methods for purifying a preparation of such minicells also are disclosed. Additionally, a genetic transformation method is disclosed, which comprises (i) making recombinant, intact minicells available that contain a plasmid comprised of a first nucleic acid segment, and (ii) bringing the minicells into contact with mammalian cells that are engulfing-competent, such that the minicells are engulfed by the mammalian cells, which thereafter produce an expression product of the first nucleic acid segment.
