Viral Vectors in Gene Therapy
What viral vectors are, which virus families carry gene therapies, what trials and FDA labels show about benefits and risks, and why a vector is not the same as a treatment.
Content last updated . This page has not been medically reviewed.
Features that differ between vectors
- Replication. The ELEVIDYS label states its AAV vector genome contains no viral genes and cannot replicate. [7] VYJUVEK's label describes a replication-defective, non-integrating herpes-based vector. [8] IMLYGIC is different: it is described as an oncolytic (tumor-attacking) viral therapy. [9]
- Integration into the genome. Retrovirus-type vectors can insert into DNA. In an early trial for a severe inherited immune disease, two patients developed uncontrolled growth of T cells linked to vector insertion near a cancer-related gene. [15] Current labels for two lentiviral products carry boxed warnings for blood cancers (see safety below).
- Cargo and target. Which tissue gets the gene depends on the vector type, the way it is given, and elements in the gene construct. The HEMGENIX label describes a liver-specific promoter. [5] See Targeted Delivery and Tissue Specificity.
What human evidence shows
Evidence labels apply to a specific product in a specific disease, not to "viral vectors" in general.- LUXTURNA, inherited retinal disease (approved medicine; established for a narrow group). In an open-label randomized phase 3 trial at two US sites, 31 people were assigned to treatment or control. Mean change on a mobility test was 1.8 light levels with treatment versus 0.2 in controls after one year. [16] The trial was small and open-label, and the outcome was functional vision in a specific test.
- ELEVIDYS, Duchenne muscular dystrophy (approved medicine; mixed). In the phase 3 EMBARK trial (63 treated, 62 placebo), the primary endpoint, change in a motor function score at week 52, was not met. Some secondary endpoints numerically favored treatment without statistical significance. [17] Seven treated children (11.1%) had treatment-related serious adverse events. [17] A later FDA action added a boxed warning for liver injury and limited the indication to people who can still walk. [18]
These two examples show why "gene therapy works" is too broad: one is a clear functional gain in a rare eye disease, the other a missed primary endpoint with an approved but restricted label. Learn how to read such differences in Mechanism vs Demonstrated Benefit.
Frequently asked questions
Is a viral vector the same as an infection?
No. The FDA describes vectors as viruses modified to remove their ability to cause infectious disease. [1] The product can still cause reactions, so labels list monitoring and warnings. [4]
Which viral vector is most used?
A review calls AAV the leading platform for gene delivery. [14] Lentiviral, adenoviral and herpes-based vectors are used for other products. [11][10][8]
Do viral-vector gene therapies permanently change my DNA?
It depends on the product. The VYJUVEK label calls its vector non-integrating [8], while lentiviral products insert genes into a patient's own cells outside the body. [11] AAV labels describe a theoretical or possible integration risk. [4][5]
Are all approved vector therapies proven for every patient with the condition?
No. Approval applies to a stated indication. For example, the ELEVIDYS indication was limited to people with Duchenne muscular dystrophy who are ambulatory. [18]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
How to read the evidence labels
Labels used on this page: approved medicine (with the regulator and indication), established, promising but limited, mixed, insufficient evidence.
What a vector is
The US Food and Drug Administration (FDA) explains that viruses naturally deliver genetic material into cells, so some gene therapy products are built from viruses that were modified to remove their ability to cause infectious disease. [1] MedlinePlus describes gene therapy as an approach that treats or prevents disease by correcting the underlying genetic problem. [2] For the general idea of gene addition, see Gene Addition and Gene Therapy Explained.The main vector families
| Vector family | Approved examples (FDA, as read) | How it is given |
|---|---|---|
| Adeno-associated virus (AAV) | LUXTURNA, ZOLGENSMA, HEMGENIX, ELEVIDYS, KEBILIDI | Subretinal injection for LUXTURNA [3]; intravenous infusion for ZOLGENSMA [4]; vector types per the HEMGENIX, KEBILIDI and ELEVIDYS labels [5][6][7] |
| Herpes simplex virus type 1 | VYJUVEK, IMLYGIC | Topical gel on wounds for VYJUVEK [8]; injection into skin lesions for IMLYGIC [9] |
| Adenovirus | ADSTILADRIN | Instilled into the bladder [10] |
| Lentivirus (used outside the body on a patient's own stem cells) | ZYNTEGLO, SKYSONA, LYFGENIA | Cells are modified in the lab and returned [11][12][13] |
A review in a major drug-discovery journal calls AAV vectors the leading platform for gene delivery. [14] The FDA also describes a separate route in which a patient's own cells are modified, often with a viral vector, and then returned. [1]
Risks and who should not use it
- Liver injury. ZOLGENSMA's label reports acute liver failure with fatal outcomes. [4] ELEVIDYS's label reports life-threatening and fatal acute liver failure. [7]
- Blood cancers. SKYSONA's label reports myelodysplastic syndrome and acute myeloid leukemia, with cases diagnosed from 14 months to 10 years after treatment. [11] LYFGENIA's label also reports hematologic malignancy. [12]
- Possible tumors from integration. The ZOLGENSMA label lists a theoretical tumor risk from AAV integration [4], and the HEMGENIX label says liver cancer may develop through integration of vector DNA. [5]
- Procedure risks. LUXTURNA's label warns of a permanent decline in visual acuity after subretinal injection. [3]
- Exposure of others. VYJUVEK's label advises close contacts to avoid touching treated wounds and dressings. [8]
Immune reactions are a separate major issue: see Immune Responses to Gene Therapy and Delivery Vehicles.
Safety note
References
- US FDA, What is Gene Therapy?. Read 2026-10-22.
- MedlinePlus Genetics, What is gene therapy?. Read 2026-10-22.
- US FDA prescribing information, LUXTURNA (label data via openFDA). Read 2026-10-22.
- US FDA prescribing information, ZOLGENSMA (label data via openFDA). Read 2026-10-22.
- US FDA prescribing information, HEMGENIX (label data via openFDA). Read 2026-10-22.
- US FDA prescribing information, KEBILIDI (label data via openFDA). Read 2026-10-22.
- US FDA prescribing information, ELEVIDYS (label data via openFDA). Read 2026-10-22.
- US FDA prescribing information, VYJUVEK (label data via openFDA). Read 2026-10-22.
- US FDA prescribing information, IMLYGIC (label data via openFDA). Read 2026-10-22.
- US FDA prescribing information, ADSTILADRIN (label data via openFDA). Read 2026-10-22.
- US FDA prescribing information, SKYSONA (label data via openFDA). Read 2026-10-22.
- US FDA prescribing information, LYFGENIA (label data via openFDA). Read 2026-10-22.
- US FDA prescribing information, ZYNTEGLO (label data via openFDA). Read 2026-10-22.
- Wang D, Tai PWL, Gao G. Adeno-associated virus vector as a platform for gene therapy delivery. Nat Rev Drug Discov 2019. PubMed 30710128. Read 2026-10-22.
- Hacein-Bey-Abina S et al. LMO2-associated clonal T cell proliferation in two patients after gene therapy for SCID-X1. Science 2003. PubMed 14564000. Read 2026-10-22.
- Russell S et al. Efficacy and safety of voretigene neparvovec (AAV2-hRPE65v2) in patients with RPE65-mediated inherited retinal dystrophy: a randomised, controlled, open-label, phase 3 trial. Lancet 2017. PubMed 28712537. Read 2026-10-22.
- Mendell JR et al. AAV gene therapy for Duchenne muscular dystrophy: the EMBARK phase 3 randomized trial. Nat Med 2025. PubMed 39385046. Read 2026-10-22.
- US FDA, ELEVIDYS product page. Read 2026-10-22.