LONDON – The gene therapy buzz goes on, with Freeline Therapeutics Ltd. closing an £88.4 million (US$116.5 million) series B round to fund clinical development of treatments for hemophilia B and Fabry disease, and to add other programs using its proprietary adeno-associated viral (AAV) vector to the portfolio.

£85 million of the funding comes from London-listed biotech investment firm Syncona Ltd., an evergreen fund that is making big investments in cell and gene therapy start-ups. The balance is from UCL Technology Fund, the venture arm of University College London (UCL), where Freeline's technology originated.

The company is built around the research of its scientific founder, Amit Nathwani, professor of hematology at UCL, who fixed several hitches encountered in early attempts to use AAV vectors and reported the first unequivocal evidence of successful gene therapy for hemophilia B.

In a landmark paper published in December 2011, Nathwani and colleagues described devising an expression cassette that mediates a high level of expression of the blood clotting protein factor IX and selecting the AAV8 serotype to minimize the possibility of pre-existing immunity to the virus.

That choice of AAV8 is also handy because it has a strong tropism for the liver, enabling vectors to be administered via the peripheral vein.

A follow-up article in November 2014 showed a single intravenous dose of vector administered to 10 patients with severe hemophilia B resulted in a dose dependent increase of circulating factor IX, to a level between 1 percent and 6 percent of normal levels. That effect was maintained over a median of 3.2 years, making this the first study to show sustainable expression of the clotting factor.

In the highest dose group, there was a consistent increase in levels of factor IX, resulting in a reduction of more than 90 percent in both bleeding episodes and the need for prophylaxis with factor IX replacement therapy.

During the follow-up of three years, no late toxic effects from the therapy were reported.

In advance of publication of the follow-up data, in March 2014, Syncona activated its philosophy of finding key opinion leaders with clinical experience to form gene therapy companies and had its first meeting with Nathwani.

That led onto the formation of Stevenage-based Freeline in December 2015, with a £25 million series A from Syncona.

The money has been invested to further optimize the proprietary AAV delivery vector, CEO Anne Prener told BioWorld. "I'm very excited about achieving this level of funding. It has taken three years to get to where we are today and this is going to push the hemophilia B program further into development and towards launch."

The phase I/II study began in the U.K. earlier in the year, testing three dose levels, with two to three patients per cohort. The end points will be safety, ensuring there are no dose-limiting adverse events and the activity level of the product.

"We aim to get all patients to a curative level," Prener said. First results are expected within the next 12 months.

Prener said the most important element of the improvements Freeline has made over the construct used in the earlier study is in the viral capsid, which is now capable of high and sustainable liver transduction. She declined to comment on how it compares to competitor products but said the performance has been validated in vitro and in vivo.

Freeline is running behind Uniqure NV of Amsterdam, which is preparing to start a phase III trial of its AAV5-mediated hemophilia B gene therapy, AMT-061 later this year.

The predecessor product, AMT-060 has been tested in 10 patients in a phase I/II trial, with data showing the product was safe, with no loss of efficacy up to 18 months post-treatment.

Also in the works, Spark Therapeutics Inc.'s SPK-9001, has all but completed a phase I/II study. Last month, Spark reported data at the Federation of Hemophilia meeting in Glasgow, Scotland, showing bleeding episodes were reduced by 98 percent for all 15 participants in the trial. All have discontinued routine Factor IX infusions.

Spark expects to hand over the program to its partner Pfizer Inc. this summer, along with a batch of drug substance, enabling Pfizer to begin a phase III trial.

In August 2016 another AAV8-vectored hemophilia B program, BAX335, developed by Prener's previous employer, Baxalta Inc., was dropped following the $32 billion acquisition of Baxalta by Shire plc.

Shire's explanation was an inconsistent level of factor IX expression, both between patients and over time. The company is however taking forward another Baxalta-originated program, BAX 880 (now SHP654) in the treatment of hemophilia A.

Prener said an important part of Freeline's approach to clinical development is to make gene therapy more controllable. "Patients want predictability; they want to know what improvement they will get," she said.

After hemophilia

Following after hemophilia B, Freeline will apply its vector technology to Fabry disease and then to other monogenic disorders where there is high unmet medical need that can be addressed by using gene therapy to generate proteins in the liver.

"We will then move into diseases where gene therapy has not been used so far, building on the fact that our capsid promotes high expression levels," Prener said. The first area will be inflammatory disorders, however, Prener said there is no decision yet what indication Freeline will focus on.

In addition to optimizing the delivery capabilities, Freeline has devoted considerable resources to manufacturing, acquiring an AAV manufacturing platform from Rentschler Biotechnologie GmbH, of Munich, Germany, in August 2015.

Freeline is using this as the base to develop chemistry, manufacturing and controls (CMC) and is working with the U.K. Cell and Gene Therapy Catapult to develop manufacturing technology and produce supplies for clinical studies.

Armed with the new funding, Freeline also is increasing its headcount and expects to grow from 70 staff now to around 100 by the end of the year. Prener said a key aspect will be to build the CMC development team in Munich.