Tralesinidase alfa's BLA for MPS IIIB tests whether six-year surrogate endpoint data is sufficient for accelerated approval in a disease with no approved therapy

Bull

A complete BLA submission accepted for review by FDA, with the agency affirming that the integrated clinical and natural history dataset with CSF heparan sulfate non-reducing end as surrogate endpoint meets the accelerated approval evidentiary bar, would validate six years of data as sufficient and open a clear path to first-ever approval in MPS IIIB. Acceptance would de-risk the thesis substantially, confirm the regulatory strategy, and position Spruce for a potential commercial launch with no approved competition in the indication.

Bear

FDA could issue a Refuse to File letter or request substantial additional data, questioning whether the integrated natural history comparator constitutes an adequate and well-controlled study or whether CSF heparan sulfate normalization is sufficiently validated as a surrogate endpoint reasonably likely to predict clinical benefit. A second failure mode is that the agency accepts the filing but raises Chemistry, Manufacturing, and Controls deficiencies around the intracerebroventricular delivery approach, extending the review timeline materially.