Spruce’s successful FDA talks plant seeds for Q4 filing of ultra-rare disease drug

Biotech Spruce’s successful FDA talks plant seeds for Q4 filing of ultra-rare disease drug By Nick Paul Taylor Aug 24, 2026 9:57am FDA Spruce Biosciences enzyme rare diseases Spruce Biosciences has taken another step toward filing for FDA approval of its ultra-rare disease drug candidate, ticking off some of the manufacturing tasks needed to submit the long-awaited application. The planned filing will cover the use of tralesinidase alfa enzyme replacement therapy (TA-ERT) for the treatment of Sanfilippo syndrome type B (MPS IIIB). Allievex licensed TA-ERT from BioMarin in 2019, only to stop (PDF) operating after running into a barrier at the FDA.

When the agency’s position shifted, Spruce salvaged the asset, reenergizing its faltering strategy and securing a near-term shot at winning approval. Spruce’s route to the regulator has been longer than expected, with an FDA request for manufacturing data delaying the filing from the first quarter to the fourth quarter of 2026. The asset has advanced smoothly since that setback.

The biotech updated investors on Monday, revealing that two meetings with the FDA supported its plans to seek approval in the fourth quarter. FDA officials found Spruce’s drug substance and drug product analytical comparability strategies reasonable to support a filing, the company said. The feedback follows the transfer of production to a leading global biologics manufacturer.

Spruce’s manufacturing update represents progress in an area of uncertainty for analysts. In an Aug. 14 note to investors, Guggenheim Securities analysts said that, while they believe Spruce’s clinical data are “adequately derisked,” risks related to manufacturing “remain hard to quantify.” Spruce is evaluating larger bioreactors, as well as a second supplier, to meet future demand, the analysts said at the time.

The biotech shared the manufacturing update alongside the news that it is aligned with the FDA on the overall content and format of the planned submission. Both parties are aligned on the structure of the integrated efficacy and safety summaries, Spruce said. TA-ERT could be the first FDA-approved therapy for MPS IIIB.

The autosomal recessive disorder is rare, affecting an estimated one in 200,000 newborns, but the opportunity for “significant pricing power” led Guggenheim analysts to predict peak sales north of $300 million. With intellectual property protection extending to 2038, the analysts see TA-ERT sales empowering Spruce to bolster its pipeline. FDA Spruce Biosciences enzyme rare diseases contract manufacturing Biotech