Which of the Following Remains a Problem of Gene Therapy

Which of the following remains a problem of gene therapy?

A) To date, there has not been a case of gene therapy curing a disease.
B) We have yet to develop a vector for delivering the gene.
C) Patients mount immune responses to the transferred gene and vectors.
D) We do not have the ability to use somatic gene therapy at this time.
E) We can only alter germ-line cells at this time.