For example, one team has begun using adenoviruses to initiate angiogenesis. Members of that same team grew frustrated with that virus as a vector for cystic fibrosis, because its high initial transfection was thwarted by short-term expression. Just as the viral vector field continues to expand, the newer field of nonviral vectors continues to develop. These chromosomes are enormous. He notes that the artificial chromosomes can be built as either circular or linear systems.
Some disadvantages exist, too.
Some centromere functions remain unknown, Willard reported. Researchers inserting human artificial chromosomes into mouse cells produced the artificial chromosomes at high efficiency, but the human centromere failed to function. The first nonviral vector's single biggest failing is its low efficiency, Philip Felgner , Gene Therapy Systems Inc. chief science officer, admitted. We definitely have plenty of room to improve these kinds of systems. Felgner posits that adding ligands to the PNA could improve both efficiency and targeting of this vector.