When viruses become cancer therapies: 5 UK companies advancing the science
Viruses are normally something medicine tries to keep out of the body, but a small group of biotechnology companies are deliberately putting them into cancer patients.
This approach is known as oncolytic virotherapy. It uses viruses that can preferentially infect and destroy cancer cells while potentially stimulating the immune system to recognise and attack the tumour.
Although it sounds like a distinctly modern branch of biotechnology, surprisingly, its origins stretch back more than a century.
When infections appeared to make cancers disappear
One of the earliest observations was published in 1904, when physician George Dock described a woman with leukaemia who had experienced a temporary remission during a presumed influenza infection in 1896.
By the 1950s, researchers were testing the idea deliberately, administering naturally occurring viruses to people with cancer and observing whether they could damage tumours. In a 1956 study involving women with cervical cancer, wild-type adenoviruses produced varying degrees of tumour necrosis, although no significant tumour regression was seen.
These early experiments also exposed the limitations of the approach, because researchers had relatively little control over where a virus replicated, how dangerous it might be to healthy tissue or how quickly the immune system would clear it.
As molecular biology and genetic engineering developed, researchers no longer had to rely entirely on naturally occurring viruses and could begin designing or selecting viruses with properties suited to cancer therapy.
How does an oncolytic virus work?
Cancer cells differ from healthy cells in ways that extend beyond uncontrolled growth. During tumour development, pathways involved in apoptosis, interferon signalling and antiviral defence can become disrupted, creating weaknesses that an appropriately selected or engineered virus may be able to exploit.
An oncolytic virus can therefore be designed or selected to replicate efficiently in cancer cells while being restricted in healthy tissue. Once inside a susceptible tumour cell, it copies itself until the cell is damaged or destroyed, releasing more viral particles that can potentially spread through the tumour.
Direct killing is only part of the effect. When infected cancer cells die, they release tumour antigens alongside viral material and inflammatory signals, which can attract antigen-presenting cells and T cells and help expose a tumour that may previously have been poorly recognised by the immune system.
Modern oncolytic viruses can also be "armed" with additional genes, allowing them to produce cytokines, antibodies or other therapeutic molecules inside the tumour and turning the virus into both a treatment and a delivery vehicle.
From experimental idea to approved medicine
China approved the oncolytic adenovirus H101 in 2005, but a major international milestone came a decade later with talimogene laherparepvec, better known as T-VEC or Imlygic, which became the first oncolytic virus approved by the US Food and Drug Administration.
Developed from herpes simplex virus type 1, T-VEC was engineered to preferentially replicate in tumour tissue and produce GM-CSF, an immune-stimulating protein. The FDA approved it for certain melanoma lesions in 2015.
The therapy also has a strong UK connection. T-VEC originated as OncoVEX GM-CSF at BioVex, which grew out of UK research into engineered herpes viruses before being acquired by Amgen in 2011, while several of the people involved later returned to the field through Replimune.
In August 2026, the FDA granted accelerated approval to TUDRIQEV, developed by Replimune, in combination with nivolumab for adults with unresectable advanced cutaneous melanoma whose disease had progressed following anti-PD-1 treatment.
The approval followed a protracted regulatory review, including two earlier complete response letters from the FDA, and remains conditional on confirmation of clinical benefit in the ongoing Phase III IGNYTE-3 trial.
Even with those milestones, substantial technical challenges remain, particularly when treatment needs to reach disease beyond an accessible tumour. Viruses administered through the bloodstream must survive immune clearance, reach the right tissues, penetrate tumour architecture and remain active within an environment that can itself suppress immune responses.
The five companies below, all based in the UK or with substantial UK operations, are developing the next generation of oncolytic viruses and approaching those problems in very different ways.
1. Replimune: building on the first generation of HSV therapies
Few companies have a more direct connection to the history of modern oncolytic virotherapy than Replimune, a US-headquartered company with manufacturing and laboratory operations at Milton Park in Oxfordshire.
The company was founded in 2015 by a team including Robert Coffin and Philip Astley-Sparke, both closely associated with the earlier development of BioVex and T-VEC.
Its RPx platform is built around engineered HSV-1, with its most advanced therapy, vusolimogene oderparepvec-wtpg, marketed as TUDRIQEV, combining a modified herpes virus backbone with GM-CSF and a fusogenic protein intended to increase tumour-cell killing and immune activation.
Its 2026 accelerated approval creates a direct line from earlier UK work on T-VEC to one of the newest approved oncolytic therapies, while the ongoing confirmatory trial will determine how firmly that position is established.
View Replimune on Benchscope →
2. Theolytics: searching millions of viruses for the right one
Where much of the field begins with a particular virus and engineers it step by step, Oxford-based Theolytics has built its approach around searching a much larger pool of biological possibilities.
The company says its Adenovo platform contains around 100 million adenovirus variants, which can be subjected to biological selection pressures to identify candidates with characteristics suited to a particular cancer.
Its lead candidate, THEO-260, is being developed for platinum-resistant ovarian cancer and has been selected with stroma-rich tumours in mind, including environments containing cancer-associated fibroblasts that can contribute to immune exclusion and treatment resistance.
THEO-260 is now being evaluated through both intravenous and intraperitoneal clinical studies, allowing the programme to test different routes of delivery while also exploring how selected viral properties perform in a difficult tumour environment.
View Theolytics on Benchscope →
3. Akamis Bio: turning tumours into drug factories
Akamis Bio, a US-headquartered company formerly known as the Oxfordshire biotech PsiOxus Therapeutics, is developing oncolytic viruses that not only replicate within tumours but also produce additional therapeutic proteins once they get there.
Its T-SIGn platform uses replication-competent chimeric group B adenoviruses designed for intravenous administration and selective replication in epithelial-derived solid tumours.
The lead programme, NG-350A, carries the genetic instructions for a CD40 agonist antibody, with the aim of producing the immune-stimulating molecule locally inside infected tumour tissue rather than circulating it throughout the body.
NG-350A is being evaluated in the Phase Ib FORTRESS study in mismatch repair-proficient locally advanced rectal cancer alongside chemoradiotherapy, while Akamis is also developing viruses carrying other immune-modulating payloads, including programmes based around direct T-cell engagement.
The underlying approach effectively turns infected tumour tissue into a temporary site of drug production as well as viral replication.
View Akamis Bio on Benchscope →
4. VacV Biotherapeutics: getting viruses to metastatic disease
For oncolytic virotherapy to treat widespread cancer rather than individual accessible lesions, one of the most important problems to solve is delivery through the bloodstream.
VacV Biotherapeutics, spun out of research at Barts Cancer Institute, Queen Mary University of London, is developing modified vaccinia viruses with systemic delivery in mind.
Its candidates use a genetically modified Lister strain of vaccinia virus, combining gene deletions intended to improve tumour specificity with additional payloads designed to enhance viral spread, reduce early clearance and remodel the immunosuppressive tumour microenvironment.
The company's current preclinical pipeline includes programmes in pancreatic cancer, glioblastoma and colorectal cancer with liver metastases, where systemic administration could potentially allow the virus to reach disease at several locations rather than requiring each tumour to be injected individually.
Achieving that reliably remains one of the central technical challenges for the wider field.
View VacV Biotherapeutics on Benchscope →
5. PsiVac: changing one nucleotide to change where a virus replicates
London-based PsiVac is approaching tumour selectivity through a comparatively subtle alteration to adenovirus biology.
Its lead programme, Ixovex-1, contains a single point mutation in the adenovirus E1B region, which changes how E1B RNA is spliced and alters the balance of viral proteins produced inside infected cells.
Preclinical research showed that this change allowed the virus to retain much of its replication ability in cancer cells while substantially restricting replication in normal cells, demonstrating how detailed knowledge of viral biology can be used to tune an oncolytic virus without extensively rewriting its genome.
Ixovex-1 is now in a Phase I/II study at The Royal Marsden, where intratumoural treatment is being evaluated both as a single agent and in combination with the checkpoint inhibitor pembrolizumab in patients with locally advanced, unresectable or metastatic solid tumours.
The combination reflects growing interest in using viral infection to alter the tumour environment and potentially improve responses to established immunotherapies.
Where does oncolytic virotherapy go next?
More than 120 years separate the first reports of cancer regression during viral illness from today's engineered oncolytic therapies, and the questions facing researchers have become steadily more sophisticated.
The earliest experiments asked whether viruses could kill tumours at all, while the first generation of engineered therapies focused on making that effect safer and more selective. Today's developers are trying to deliver viruses through the bloodstream, penetrate difficult tumour microenvironments, combine them with checkpoint inhibitors and use viral genomes to manufacture additional medicines inside tumours.
Clinical progress has been slower than some of the field's early enthusiasm suggested, and systemic delivery, immune clearance, manufacturing and reproducible efficacy across different tumour types remain substantial hurdles.
What has changed is that the field now has approved products demonstrating that the concept can work in patients, while increasingly sophisticated platforms are expanding what an oncolytic virus might actually do once it reaches a tumour.
For the companies working on that problem in the UK, the ability of a virus to kill a cancer cell may increasingly be only the starting point.
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