Pfizer said today it has acquired an exclusive option to acquire Vivet Therapeutics, in an up-to-€605 million ($687 million) deal through which the pharma giant has taken an immediate 15% equity interest in rare disease gene therapy developer.

Based in Paris, privately-held Vivet specializes in developing gene therapies for inherited liver disorders with high unmet medical need. Pfizer has agreed to co-develop Vivet’s lead candidate VTX-801, a gene therapy for Wilson disease.

VTX-801 is a gene therapy designed to treat Wilson disease, caused by mutations in the gene encoding the ATP7B protein. The mutations reduce the ability of the liver and other tissues to regulate copper levels causing severe hepatic damage, neurologic symptoms, and potentially death.

VTX-801 has been granted the orphan drug designations of the FDA and the European Commission.

According to Vivet, VTX-801 has been demonstrated in preclinical models—the focus of two presentations by the company at last year’s American Society of Gene and Cell Therapy (ASGCT) Annual Meeting, held in Chicago.

“VTX-801 could provide a potentially transformative therapeutic option for patients with Wilson disease by directly addressing the underlying cause of the disease,” Seng Cheng, senior vice president and CSO of Pfizer’s rare disease research unit, said in a statement.

VTX-801 also bolsters Pfizer’s rare disease pipeline, which is led by Tafamidis meglumine—for which the pharma giant in January filed NDAs with the FDA for two forms of the drug, meglumine salt and free acid, in the same indication of transthyretin amyloid cardiomyopathy.

Pfizer paid approximately €45 million ($51 million) upfront, and agreed to pay up to €560 million ($635.8 million), including its option exercise payment, and subject to certain clinical, regulatory, and commercial milestones.

Pfizer can exercise its option to acquire 100% of Vivet following the company’s delivery of Phase I/II clinical trial data for VTX-801.

As part of the transaction, Pfizer senior executive Monika Vnuk, MD, vice president, worldwide business development, will join Vivet’s Board of Directors.

Other terms of the transaction were not disclosed.

“We welcome Pfizer as a shareholder and partner that can help us advance our efforts to develop therapies for patients burdened with inherited liver disorders,” added Jean-Phillippe Combal, co-founder & CEO of Vivet. “This investment demonstrates the clear value of Vivet’s innovative approaches to gene therapy.”

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