Spark Therapeutics, the for-profit, Philadelphia gene therapy developer, said Wednesday that Swiss drugmaker Novartis has agreed to pay Spark $105 million, plus up to $65 million pending European regulatory approvals and early sales, to sell Spark's Luxturna hereditary-blindness gene-mutation therapy outside the U.S.

Luxturna was approved by the U.S. Food and Drug Administration last month "as a one-time gene therapy to restore functional vision" in people with a genetic retina deterioration condition that affects a few thousand people worldwide. Spark has proposed selling the treatment at a price of around $425,000 per eye.

"Gene therapy is a promising new avenue to potentially address this unmet need," Shreeram Aradhye, chief medical office at Novartis, said in a statement. Spark will continue to develop Luxturna for use by U.S. patients, the company said.

After burning through over $400 million in investor capital since the company went public in 2015, Spark has lately traded in the $50 to 60 a share range, down from the $80s last September. The company's market value now totals around $2 billion, a strong vote of confidence that shareholders expect sales will multiply.