The first big breakthrough in solving this problem was when it was found that one virus, the adeno-associated virus (AAV), preferentially inserts into a particular (safe) place on human chromosome 19.

• 解决这一问题的第一个大突破，是发现一种病毒，即腺病毒相关病毒(AAV)，会有选择地插进人类第19号染色体的一个特殊（安全）位置。