When Using Vectors to Produce Proteins for Gene Therapy, What

When using vectors to produce proteins for gene therapy, what are some of the problems that may occur and how has medical science overcome these problems?

A) Virus vectors used may actually cause disease and therefore medical technicians have removed those segments.
B) RNA added via vectors to a human may cause a toxic response and so a buffer is added to the vector.
C) Proteins injected using vectors get degraded too quickly and therefore protective segments have been added to the proteins.
D) cDNA produced by vectors active an immune response, tags are therefore added to help the body identify them as self.