ON AUGUST 3rd the British pharmaceutical company GSK said that it would charge €594,000 ($665,000) for a gene-therapy cure for ADA-SCID—a severe immune disorder that is usually fatal in the first few years of life. A child born with ADA-SCID is unable to fight off everyday infections; Strimvelis has cured this in each of the 18 children it has been tested on over 15 years. Gene therapies work by delivering correct versions of DNA, usually using a virus as a vector. Once DNA is inside the cell, it produces the protein that was missing and the fault is fixed. Scientists have been trying to develop gene therapies for decades. Early work hit the buffers due to a series of unexpected cancers, the death of a young man during a trial, and some disappointing results.

Much progress has been made since then and according to analysts at Datamonitor Healthcare the number of gene therapies in development has doubled since 2012. Last week, America’s Food and Drug Administration (FDA) handed out “breakthrough” designations—intended to hasten the approval of important new treatments—to two gene therapies. One, made by Pfizer, a giant drugmaker, and Spark Therapeutics, a biotech company, is for haemophilia B, a rare bleeding disorder. The new drug to cure ADA-SCID was developed by scientists at the San Raffaele Telethon Institute for Gene Therapy, in Milan, with support from a charitable foundation. Given that the costs of developing Strimvelis were not paid by GSK, the pharmaceutical company that has bought the licence to sell this treatment, one might ask why its price is so high.

One reason is that the process of making the drug is particularly labour-intensive because it is tailored to each patient (rather than being made once and pulled off the shelf). Stem cells are extracted from a patient’s bone marrow and over five days are painstakingly mingled with the virus that will introduce the correct version of the gene they need. After this, corrected stem cells are infused back into the patient. Another reason the therapy is costly is that it has been difficult to take a complex and experimental therapy and turn it into a reliable product of guaranteed quality that drug regulators will allow to be sold. GSK will also incur ongoing costs, as it must follow up with patients on this novel therapy for years. On top of all this, GSK will be selling into a tiny market. Annually, just 15 patients are diagnosed with the disorder across Europe.

Pharma supporters will also point out that the price of Strimvelis is significantly lower than that of another therapy, Glybera, which was the first to be sold in Europe (for a genetic condition that causes a dangerously high amount of fat to build up in the blood system). At $1m, it was bought only once since it was introduced in 2012 and has been a commercial failure. The lesson from this, and one that loomed large in the pricing of Strimvelis, was that it is possible to charge too much—even for a cure. Drug companies are also trying to argue that the cost of cures for diseases need to be set against the overall benefit to the health-care system. The cost of treating ADA-SCID with an enzyme-replacement therapy can run into many hundreds of thousands of dollars a year. Nonetheless, with growing numbers of costly therapies of different kinds expected to arrive in the near future, there are worries about how health-care systems will afford them all. It isn’t all doom and gloom, however. Over time the cost of making these therapies will decline: patents will run out and labour-intensive parts of the process will be automated. It may also become possible to develop off-the shelf treatments one day. The process of industrialising gene therapies is only just beginning.