Jesse Gelsinger died from what was essentially a massive and systemic allergic reaction to the adenovirus vector, not from some unexpected regaining of pathogenicity by the replication-defective virus. This provides the profound benefit of stable transformation. The major obstacle to using retrovirus vectors such as MMLV is that they only infect rapidly dividing cells. An MMLV-based vector was recently responsible for one of gene therapy's few validated successes. The suspension of many such protocols pending investigation of Jesse Gelsinger's death was not listed as a factor in these percentages.
Adenoviruses are DNA-containing viruses typical of the common cold.
Despite their immunogenic properties, they are considered valuable vectors for several reasons. Lack of integration is a disadvantage for those diseases described above, in which long-term genetic repair is envisioned as the sole solution. In such cases, repeated treatments would be required. These viruses, known as AAVs, are small DNA viruses that cause no known diseases in humans. In addition, these viruses can achieve stable integration of the gene of interest into the treated cells and can target nondividing cells.