Which of the following is a major disadvantage of using a vector based on adeno-associated virus (AAV)rather than an adenovirus or a retrovirus?

A) The DNA of the AAV vectors integrates into specific location in the genome.
B) The virus is toxic to human cells.
C) It infects cells of the immune system, causing a strong immune response.
D) The immune system reacts very strongly to the AAV proteins.
E) The small genome can only tolerate an insert of 4.5kb.