Approved treatment — Japan (Delytact, malignant glioma, conditional and time-limited approval in 2021), U.S. and EU (Imlygic, melanoma, 2015) Sources: Nature Medicine 2022 phase 2 paper, Journal of Clinical Oncology 2015 phase 3 paper, manufacturer and European Medicines Agency documents
Oncolytic virus therapy is an immunotherapy that uses a virus modified to grow mainly inside cancer cells: the virus bursts the cancer cells and, in the process, wakes up the body's immune system. In Japan, the brain tumor (malignant glioma) treatment Delytact (G47Δ) was approved in 2021; in its phase 2 trial, 16 of 19 patients (84.2%) were alive one year after starting treatment. In the U.S. and Europe, the melanoma treatment Imlygic (T-VEC) is in use.
What is oncolytic virus therapy?
An oncolytic virus is a "tumor-dissolving virus." Doctors take a common virus, such as the one that causes cold sores, and change its genes so that it can hardly multiply in normal cells but grows well inside cancer cells. Many cancer cells have weakened antiviral defenses, and the treatment takes advantage of this.
Because it uses a genetically modified virus, it broadly belongs to gene therapy, and because it triggers an immune response, it is also classed as immunotherapy. Most of these drugs are injected directly into the tumor rather than into a vein.
Two ways the virus attacks cancer
- Direct destruction: the virus multiplies inside a cancer cell until the cell bursts. New viruses released from the burst cell move to neighboring cancer cells and repeat the process.
- Waking the immune system: when cancer cells burst, cancer markers (antigens) are exposed. Immune cells learn these markers, which helps them attack cancer cells elsewhere in the body, including tumors that were not injected. Some drugs are designed to produce immune-boosting substances (such as GM-CSF) to strengthen this effect.
Japan's Delytact is a "triple-mutated" herpes simplex virus type 1 with changes in three genes, developed by Professor Tomoki Todo's team at the Institute of Medical Science, The University of Tokyo. It is designed for added safety: it cannot multiply in normal brain cells and grows only in cancer cells.
Which drugs are approved, and where?
| Drug | Country and year | Cancer | How it is given |
|---|---|---|---|
| Delytact (teserpaturev, G47Δ) | Japan, June 2021 (conditional and time-limited approval) | Malignant glioma (including glioblastoma) | Injected directly into the brain tumor, up to 6 doses |
| Imlygic (talimogene laherparepvec, T-VEC) | U.S. 2015, European Union December 2015 | Melanoma that cannot be removed by surgery (EU: stage IIIB–IVM1a without bone, brain, lung or other organ spread) | Injected into skin and lymph node tumors every 2 weeks |
| Oncorine (H101) | China, 2005 | Head and neck cancers such as nasopharyngeal carcinoma (with chemotherapy) | Injected directly into the tumor |
Sources: Daiichi Sankyo approval and launch releases (2021), European Medicines Agency Imlygic EPAR, Liang M. Current Cancer Drug Targets 2018. Approved uses differ by country; your care team decides whether you are eligible.
Japan's "conditional and time-limited approval" applies to regenerative medicine products: when a small trial shows expected benefit, the product can be used early, and full approval is confirmed with additional post-marketing data. Delytact also received SAKIGAKE designation and orphan designation from Japan's Ministry of Health, Labour and Welfare.
Results in patients
| Trial | Patients | Reported results |
|---|---|---|
| Delytact phase 2 (Japan, single arm) | 19 patients with residual or recurrent glioblastoma after radiotherapy and temozolomide | 1-year survival from start of treatment 84.2% (16 of 19); median survival 20.2 months from treatment start and 28.8 months from first surgery |
| Imlygic phase 3 OPTiM (international, randomized) | 436 patients with unresectable stage IIIB–IV melanoma | Response lasting 6 months or more 16.3% (vs 2.1% with GM-CSF injection); overall response 26.4% (vs 5.7%); median survival 23.3 months (vs 18.9 months) |
Sources: Todo T et al., Nature Medicine 2022 / Andtbacka RHI et al., Journal of Clinical Oncology 2015. The survival difference for Imlygic was at the edge of statistical significance (P=0.051); the effect was larger in stage IIIB, IIIC and IVM1a disease and in previously untreated patients.
Glioblastoma is a brain tumor with few options after recurrence, so the 84.2% one-year survival reported in the Japanese phase 2 trial became the key evidence for approval. Imlygic showed a higher durable response rate than the control in a randomized phase 3 trial and was approved in the U.S. and Europe.
How is treatment given?
For Delytact, a neurosurgeon uses imaging to guide a 1 mL injection directly into the brain tumor. The first and second doses are given 5–14 days apart, then every 4 weeks, for up to 6 doses. It may only be used at institutions where an experienced neurosurgeon can monitor and manage the patient, and at launch (November 2021) it was supplied first to the hospitals that took part in the trial. The Japanese National Health Insurance price was announced as 1,431,918 yen per 1 mL vial.
Imlygic is injected into melanoma in the skin or lymph nodes every 2 weeks; in the trial, treatment lasted up to 18 months. Your care team will explain how to look after the injection site during treatment.
Side effects and management
- In the Delytact phase 2 trial, the most common side effect was fever (17 of 19 patients), followed by vomiting, nausea, and decreases in lymphocytes and white blood cells. The care team checks body temperature and blood tests along the way.
- In the Imlygic phase 3 trial, common side effects were flu-like symptoms such as fatigue, chills and fever, and pain at the injection site. The only grade 3–4 side effect seen in 2% or more of patients was cellulitis (2.1%), and there were no treatment-related deaths.
- Because this treatment uses a virus, your care team checks your immune status and other factors before deciding whether to use it.
Questions for your doctor
- Is an oncolytic virus therapy approved, or is there a clinical trial, for my cancer type and stage?
- Is my tumor in a location and of a size that allow direct injection?
- Can it be used together with, or after, the chemotherapy or immunotherapy I am receiving now?
- What infection-control steps should my family follow during treatment?
Frequently asked questions
Has oncolytic virus therapy been shown to work in people?
Yes. In a Japanese phase 2 trial, 16 of 19 patients (84.2%) with residual or recurrent glioblastoma were alive one year after starting treatment, and in a melanoma phase 3 trial the rate of responses lasting 6 months or more was 16.3%, higher than 2.1% in the control group. These results led to approvals in Japan, the U.S. and Europe.
Is it safe to put a virus into the body?
Approved drugs use viruses whose genes have been changed so they can hardly multiply in normal cells. The most common side effects in trials were flu-like symptoms such as fever, fatigue and chills, and there were no treatment-related deaths in the melanoma phase 3 trial.
Who can receive Delytact in Japan?
It is approved in Japan for malignant glioma, and the pivotal trial enrolled patients with glioblastoma that remained or recurred after radiotherapy and temozolomide. It is given at designated institutions with an experienced neurosurgeon.
Is an oncolytic virus the same as gene therapy?
Because it uses a genetically modified virus, it belongs to gene therapy in a broad sense, but it is distinctive in that it multiplies inside cancer cells, bursts them and wakes the immune system. In Japan it was approved as a regenerative medicine product.
Related: Nucleic acid medicine and aptamers: start by separating the terms · Glioblastoma Photodynamic Therapy in Japan: Insurance and Survival · CAR-NK vs CAR-T · Nucleic Acid Medicine & Aptamers guide
Sources
- Todo T, Ito H, Ino Y et al. Intratumoral oncolytic herpes virus G47Δ for residual or recurrent glioblastoma: a phase 2 trial. Nature Medicine 2022;28:1630–1639
doi.org/10.1038/s41591-022-01897-x
Checked: 2026-10-20 - Daiichi Sankyo — DELYTACT Oncolytic Virus G47Δ Approved in Japan for Treatment of Patients with Malignant Glioma (2021-06-11)
daiichisankyo.com
Checked: 2026-10-20 - Daiichi Sankyo — Launch of DELYTACT in Japan (2021-11-01)
daiichisankyo.com
Checked: 2026-10-20 - Andtbacka RHI, Kaufman HL, Collichio F et al. Talimogene Laherparepvec Improves Durable Response Rate in Patients With Advanced Melanoma. Journal of Clinical Oncology 2015;33(25):2780–2788
doi.org/10.1200/JCO.2014.58.3377
Checked: 2026-10-20 - European Medicines Agency — Imlygic (talimogene laherparepvec) EPAR
ema.europa.eu
Checked: 2026-10-20 - Cancer Research Institute — Oncolytic Virus Therapy
cancerresearch.org
Checked: 2026-10-20 - Liang M. Oncorine, the World First Oncolytic Virus Medicine and its Update in China. Current Cancer Drug Targets 2018;18(2):171–176
doi.org/10.2174/1568009618666171129221503
Checked: 2026-10-20
Written by the FTH editorial team. Sources checked 2026-10-20 · Medical review: not applicable
This article is general information based on public sources and does not replace diagnosis or treatment. Please discuss treatment decisions with your medical team.
