Pioneering Ex Vivo Viral Vector-based Gene Therapy Transforms Boy with Hunter Syndrome

LONDON, UK – November 24, 2025– A three-year-old boy with the rare genetic condition, Hunter Syndrome (Mucopolysaccharidosis type II or MPS II), is showing “dramatic improvements” after receiving a world-first ex vivo viral vector gene therapy manufactured by a specialist team at Great Ormond Street Hospital (GOSH).

The pioneering treatment, which uses a viral vector to deliver a healthy gene copy, was administered to Ollie Chu at Royal Manchester Children’s Hospital (RMCH) as part of a pivotal clinical trial.

Hunter Syndrome is a life-threatening, progressive condition caused by a missing enzyme, leading to the toxic buildup of sugars in the body. Current treatment requires lifelong, weekly enzyme replacement infusions.

Viral Vector Gene Therapy Manufacturing

The gene therapy product was manufactured at GOSH’s specialist Cell and Gene Therapy Manufacturing Facility. This ex vivo process involves:

• Collection: White blood cells are removed from the patient.

• Isolation & Transduction: Stem cells are isolated, and a viral vector carrying the corrective gene is used to genetically modify these cells.

• Quality Control & Infusion: The corrected cells are checked, certified, and infused back into the patient.

Dr. Karen Buckland, Lead Scientist for GOSH’s Cell and Gene Therapy Service, confirmed the manufacturing reliability: “For over 20 years, GOSH has developed a robust method for inserting genes into patients’ stem cells and are pleased to be able to work alongside the teams in Manchester to provide the viral vector gene modified cell product for all five patients with Hunter syndrome.”

Promising Progress and Safer Treatment with Viral Vector Technology

Several months after receiving the gene therapy, Ollie has fully recovered, with his parents reporting “dramatic improvements” in his physical and cognitive development.

Professor Rob Wynn, Consultant Paediatric Haematologist at RMCH and joint study lead, highlighted the advantages of using the patient’s own cells and a viral vector:

“Gene therapy is not only safer and more effective, but it enables us to use the child’s own cells which cuts out the need to find a donor and means we can produce more enzyme for the patient.”

This successful application of viral vector gene therapy to modify blood cells for treating this disease opens up exciting prospects for applying this principle to many other conditions. Ollie is the first of five young children in the trial, with GOSH currently manufacturing the third batch of the viral vector product.