David Vetter was born on 21 September 1971 via caesarean section in an operating theatre that had been deep-cleaned for three days prior to his birth.

He died aged 12 after an infection by a latent virus undetectable in a bone marrow transplant from his sister.

Born with adenosine deaminase deficient severe combined immunodeficiency (ADA-SCID), a rare genetic disorder characterised by the deficient production of proteins involved in the development of T and B cells, he lived his entire life inside a complex containment system designed to separate him from the world – a ‘bubble baby’.

The cost of his care and treatment was around $1.3m.

Forty years later, in January 2018, the NHS approved Strimvelis, the first gene therapy for ADA-SCID and the first ex vivo gene therapy approved in Europe.

Strimvelis uses a retrovirus to insert a functional copy of the gene mutated in ADA-SCID into stem cells from the patient-derived from their bone marrow.

It was made through collaboration between GSK and the San Raffaele Hospital in Milan, Italy.

Costing €594,000, Strimvelis can only be made in the San Raffaele Hospital and has a half-life of six hours once made, meaning these highly susceptible patients must travel to Milan for treatment.

Because it was made using a retroviral vector, there is a small risk of those receiving it developing leukaemia.

Knowledge about its safety profile is complicated by the pre-treatment profile of bone marrow transplant and the small number of patients Strimvelis has been tested on 24 so far, some of which have been followed for 18 years.

Although the therapy is a clinical success, GSK conducted a strategic review of its rare disease unit and in April licensed the drug to Orchard Therapeutics, a rare disease biotech now set to float on NASDAQ before the end of the year.

The following figure shows the licensing deals in the gene therapy market between 2006 and 2017.

In its prospectus, Orchard estimates the incidence of patients able to be treated by its pipeline products as 1,000–2,000 per annum, stating this is a market of $2bn globally – an average price of $1m per product.

The company will be the 52nd biotech to go public in 2018 and the fourth to do so at a ‘unicorn’ valuation – a valuation exceeding $1bn.

It does so at a time when the US biotech index is highly volatile and there remain significant concerns about the pricing of pharmaceutical products.

Orchard’s most promising pipeline candidate is OTL-101, a follow-on to Strimvelis.

OTL-101 is made using viral vectors that have a reduced likelihood of leukaemia, and (crucially) the product can be frozen, meaning patients may not have to travel to Milan for treatment.

GSK was unable to profit from Strimvelis; later this year Orchard will see whether OTL-101 goes some way to justifying its valuation.

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