Pros of viral vectors in gene therapy?

They work!: For gene therapy to work, material must be transported into cells, such as new genes to insert , or proteins that cleave (break apart) chains or delete genes. Since viruses are capable of entering cells (that is how they infect them) and are able to integrate their own genes into the dna inside the cell, they can be effective in gene therapy. But the virus must be or be made harmless first.