A very direct method to indroduce foreign DNA to a cell, microinjection consists of taking a glass micropipette and squirting DNA directly into the nucleus of a cell with the aid of a micromanipulator. The process is more arduous than most. All the cells treated in this manner will at least show transient expression of the foreign DNA. If you're lucky (1% to 30% of the time), the cell will become a stable clone, meaning when it reproduces the foreign DNA will come along for the ride.