The vector that would be the best choice for cystic fibrosis gene therapy is adeno-associated virus for it has valuable reasons. First, it is huge enough to carry the gene, second, it will infect the right type of tissue, third, it will not cause an immune response and lastly, it infects the particular cells that divide irregularly. Therefore, this vector will definitely treat cystic fibrosis for it can target affected cells, which is a great help in the normal functioning of an organ.