Researchers at Case Western Reserve University and Athersys Inc., both in Cleveland, report constructing the first wholly synthetic, self-replicating, human “microchromosomes,” which are one-fifth to one-tenth the size of normal human chromosomes. Although the team hasn't yet found an efficient way of transplanting microchromosomes’ self-assembling components into new cells--a crucial step before researchers can exploit them fully--human artificial chromosomes could eventually be used to study chromosomal functions and to ferry “repair genes” into target cells in gene therapy.