Syncona has dialed up its bet on gene therapy startup Freeline Therapeutics. The life science investor committed £85 million ($112 million) to Freeline’s £88 million series B round, thereby maintaining a big stake in a biotech that is working to redefine the treatment of hemophilia B and Fabry disease.

Freeline got started late in 2015 with gene therapy technology from London university UCL and a £25 million series A commitment from Syncona. The startup went on to buy an adeno-associated virus (AAV) manufacturing platform and tap Syncona for more cash, bringing the total size of the investor’s series A outlay up to £33.5 million.

Now, Syncona has doubled down on its bet, committing £85 million to Freeline to see it through a period in which it will test hemophilia B and Fabry disease gene therapies in humans while building out its manufacturing capabilities. UCL Technology Fund contributed £3.4 million to the B round.

The series B commitment is tranched. Following the first tranche, Syncona owns 80% of Freeline and values its stake at £63.5 million. As Freeline progresses, Syncona will make more of the series B cash available and, if all goes to plan, see the value of its stake grow. Syncona’s willingness to bet big on Freeline has enabled it to remain the sole institutional investor alongside the UCL fund.

That willingness stems from the scientific pedigree underpinning Freeline and how it has built upon it over the past few years. Syncona and UCL Business founded Freeline to advance an AAV gene therapy platform developed by Amit Nathwani, M.D., Ph.D., a UCL professor who took up the CSO role at the startup.

By the time Freeline came into existence, Nathwani had already tested the gene therapy vector in 10 hemophilia B patients. Factor IX expression increased to 5.1% of the normal value in the six patients who received the high dose. That is a smaller improvement than Pfizer and Spark Therapeutics’ gene therapy achieved late last year. But Freeline has had considerable time and money to improve the candidate since Nathwani validated its potential in the first half of the decade.  

Freeline also faces competition for its other initial target indication, Fabry disease. Notably, Avrobio posted early clinical data on a lentiviral Fabry gene therapy last year, and went on to raise $60 million in a B round in February. Freeline’s approach uses an AAV vector, which it thinks will result in the durable production of therapeutic proteins by the liver.