Gene therapy given green light in Europe

A gene therapy for children with a rare but life-threatening genetic disorder that severely weakens the immune system has been recommended for approval by the European Medicines Agency.

Strimvelis has been developed by Italian scientists in conjunction with GlaxoSmithKline and is aimed at children with ADA-SCID (adenosine deaminase deficiency, severe combined immunodeficiency), where a single genetic defect prevents the development of a robust immune system. Children with ADA-SCID are susceptible to multiple infections and without treatment they rarely live beyond two years of age. The condition is sometimes known as 'bubble boy disease' due to children with the condition sometimes having to live in plastic, germ-free chambers.

Patients with ADA-SCID can also suffer serious liver and kidney problems, growth problems and hearing loss. There are believed to be around 350 children worldwide who have been born with the condition.

At present, ADA-SCID sufferers often undergo bone-marrow transplants, which may offer them a good chance at survival. The success of such transplants depends on how good the donor match is, and around one in four babies with a well-matched family member will be effectively cured. This option is not possible for all candidates, however, and so Strimvelis is primarily intended for those who lack a suitable transplant donor.

The treatment involves taking the patients own stem cells and inserting a working copy of the gene that produces adenosine deaminase, needed for the production of white blood cells. The cells are then injected back into the patient in order to correct the root cause of ADA-SCID. Since the manipulated cells are the patient's own, problems traditionally associated with transplant procedures such as host rejection and increased infection due to immunosuppressive therapy are avoided.

However, due to the very short shelf life of stem cells, the procedure must take place within a short time frame, meaning that the procedure is only currently available in the Milan hospital where it was first developed.

Other barriers to currently accessing the drug are likely to include cost. The first gene therapy, Glybera, intended to treat rare genetic blood disorders, was notorious for its high price tag set at $1 million per patient to administer (reported in BioNews 782). While GlaxoSmithKline has not indicated a price for Strimvelis just yet, Reuters reports that a source close to the company has said that it would cost 'very significantly less than $1million'.

Success rates for the treatment have been promising. Of the 22 children treated with the therapy in the past 14 years, doctors report that all are still alive, with most not needing any further treatment.

Strimvelis was designated as an orphan medicinal product in 2005, providing medicine developers with additional incentives such as fee reductions for scientific advice and the possibility of gaining extended market exclusivity.

GlaxoSmithKline has other gene therapies under development with Italian researchers, including a treatment for metachromatic leukodystrophy and Wiskott-Aldrich syndrome.

Now that the European Medicines Agency has recommended approval of the drug, the European Commission will to take the final decision on whether it should be marketed for clinical use across the European Union.