text: A 2009 study has shown additional benefits of HACs, namely their ability to stably contain extremely large genomic fragments. Researchers incorporated the 2.4Mb dystrophin gene, in which a mutation is a key causal element of Duchenne muscular dystrophy. The resulting HAC was mitotically stable, and correctly expressed dystrophin in chimeric mice. Previous attempts at correctly expressing dystrophin have failed. Due to its large size, it has never before been successfully integrated into a vector.
  In 2010, a refined human artificial chromosome called 21HAC was reported. 21HAC is based on a stripped copy of human chromosome 21, producing a chromosome 5Mb in length. Truncation of chromosome 21 resulted in a human artificial chromosome that was mitotically stable. 21HAC was also able to be transferred into cells from a variety of species (mice, chickens, humans). Using 21HAC, researchers were able to insert a herpes simplex virus thymidine kinase coding gene into tumor cells. This "suicide gene" is required to activate many antiviral medications. These targeted tumor cells were successfully, and selectively, terminated by the antiviral drug ganciclovir in a population including healthy cells. This research opens a variety of opportunities for using HACs in gene therapy.
  In 2011, researchers formed a human artificial chromosome by truncating chromosome 14. Genetic material was then introduced using the Cre-Lox recombination system. This particular study focused on changes in expression levels by leaving portions of the existing genomic DNA. By leaving existing telomeric and sub-telomeric sequences, researchers were able to amplify expression levels of genes coding for erythropoietin production over 1000-fold. This work also has large gene therapy implications, as erythropoietin controls red blood cell formation.
  HACs have been used to create transgenic animals for use as animal models of human disease and for production of therapeutic products.