A human artificial chromosome (HAC) is a microchromosome that can act as a new chromosome in a population of human cells. That is, instead of 46 chromosomes, the cell could have 47 with the 47th being very small, roughly 6-10 megabases in size, and able to carry new genes introduced by human researchers. They are useful in expression studies as gene transfer vectors and are a tool for elucidating human chromosome function. Grown in HT1080 cells, they are mitotically and cytogenetically stable for up to six months.
HACs carrying a functional kinetochore were considered as a promising system for gene delivery and expression with a potential to overcome many problems caused by the use of viral-based gene transfer systems. HACs avoid the limited cloning capacity, lack of copy number control and insertional mutagenesis due to integration into host chromosomes that plague viral vectors.
