Spruce Aligns With FDA On TA-ERT Filing, Setting Up Q4 MPS IIIB Submission

Spruce Biosciences said it has cleared another regulatory step toward an FDA filing for tralesinidase alfa enzyme replacement therapy, or TA-ERT, in Sanfilippo syndrome type B. The company said two meetings with the FDA supported its plan to submit the application in the fourth quarter of 2026 after an earlier manufacturing-related delay.

The latest update is centered on chemistry, manufacturing and controls rather than new clinical data. Spruce said FDA officials found its drug substance and drug product analytical comparability strategies reasonable to support a filing, and the company said it is also aligned with the agency on the overall content and format of the planned submission, including the structure of integrated efficacy and safety summaries.

The Road Here

Spruce inherited an asset with a long and uneven route to the agency. Allievex licensed TA-ERT from BioMarin in 2019 but later stopped operating after hitting a barrier at the FDA. When the agency’s position shifted, Spruce took over the program.

The company had expected to file in the first quarter, but an FDA request for manufacturing data pushed the timing to the fourth quarter of 2026. Monday’s update suggests that the company has made progress on the issue that had become the main source of uncertainty around the submission.

That matters because Guggenheim Securities had written on Aug. 14 that Spruce’s clinical data appeared “adequately de-risked,” while manufacturing risks remained hard to quantify. The FDA feedback now narrows that uncertainty, even if it does not remove execution risk until the filing is accepted.

The Commercial Picture

TA-ERT is being developed for MPS IIIB, a rare autosomal recessive disorder that Fierce Biotech said affects an estimated one in 200,000 newborns. If approved, the therapy could be the first FDA-approved treatment for the disease.

Fierce Biotech also reported that Guggenheim analysts see the program as having “significant pricing power,” forecast peak sales north of $300 million and view intellectual property protection extending to 2038 as a basis for future pipeline expansion.

Spruce is also evaluating larger bioreactors and a second supplier to meet future demand, according to the analyst note cited in the report. That is an early sign that the company is preparing not just for submission, but for the manufacturing scale questions that can follow approval in rare disease markets where commercial opportunity depends on reliably serving a small patient population.

The signal here is that for late-stage rare disease programs, regulatory progress often turns less on new efficacy arguments than on whether a company can show a stable, transferable manufacturing package. Spruce’s update does not resolve the approval decision, but it does move TA-ERT from a delayed filing story toward a filing-readiness story.