This document discusses gene therapy, which involves using genes to treat or prevent diseases. It describes genetic diseases like Wilson's disease that result from mutations in DNA replication. It then compares different vector methods for delivering genes - viruses have advantages of targeting and entering cells but immune and capacity issues, while plasmids and virosomes can carry more genes without immune blocking but have cell targeting and entry challenges. The document also outlines in vivo and ex vivo delivery methods and discusses ongoing challenges like immune response, commercial viability, and potential gene disruption, as well as some successes in cancer treatment, immune deficiencies and other diseases.