In collaboration with Dr. Melissa Rosenfeld, a colleague in the Laboratory of Gene Transfer, we are constructing human artificial chromosomes (HAC) that may provide the ideal gene delivery system. The HAC vector would not integrate into endogenous chromosomes, eliminating the possibility of insertional mutagenesis. It can, in theory, accept unlimited sizes of DNA, so large genes and long stretches of surrounding regulatory sequences can be transferred. Design features of the vectors such as centromeres, telomeres, and replication origins should facilitate the stable maintenance and correct segregation of the vector in human cells.