Problem: What was the major set-back for two of three patients in the first gene-therapy treatment of X-linked SCID (caused by the lack of the common gamma receptor chain, γc)? Group of answer choices The viral vector did not integrate into the genome of the stem cells Gene therapy activated Epstein Barr virus, leading to Burkitt's lymphoma. The viral vectors inserted next to an oncogene and induced the development of leukemia. The gene-therapy failed to restore immunity and the two patients died of infection.