Abstract: Terminal differentiated cells are proliferated by introducing a cyclin and a cyclin dependent kinase into the nucleus of terminal differentiated cells, and then cultivating or holding the cells. A method for proliferating terminal differentiated cells comprising adding a nucleotide sequence coding for a nuclear localization signal to at least one of a cyclin gene and a cyclin dependent kinase gene, and introducing each of the genes to terminal differentiated cells in vitro, and then cultivating the cells, or introducing each of the genes directly to terminal differentiated cells in vivo is provided. The cyclin is a cyclin that can activate CDK4 or CDK6, and the cyclin dependent kinase is a cyclin dependent kinase that is activated by D-type cyclin. The invention also provides a recombinant vector used for such a method or a pharmaceutical composition comprising the vector.