Taysha reaffirms FDA BLA pathway for TSHA-102 Rett syndrome gene therapy

Taysha Gene Therapies has reaffirmed alignment with the US Food and Drug Administration on the pathway to a Biologics License Application for TSHA-102, its AAV9-based intrathecal gene therapy for Rett syndrome, following a breakthrough therapy Type B multidisciplinary meeting with the agency. The Dallas-based company said the FDA has confirmed agreement on pivotal trial design, endpoints, and the possibility of submitting for approval based on a six-month interim analysis from the REVEAL pivotal trial.

Alongside the regulatory update, Taysha reported first-quarter 2026 financial results, posting a net loss of $42.4 million, or $0.12 per share, compared with a net loss of $21.5 million, or $0.08 per share, in the same period a year earlier. Research and development expenditure nearly doubled to $33.8 million, driven primarily by the initiation of a BLA-enabling process performance qualification (PPQ) manufacturing campaign and higher clinical costs from the REVEAL and ASPIRE trials. The company held $276.6 million in cash and cash equivalents as of 31 March 2026, and expects that balance to fund planned operating expenses into 2028.

Clinical and manufacturing progress

The REVEAL pivotal trial is evaluating a single intrathecal administration of high-dose TSHA-102 (1×10¹⁵ total vector genomes) in 15 females aged 6 to under 22 years with Rett syndrome in the developmental plateau population. The primary endpoint measures response rate defined as gain or regain of at least one of 28 natural history-defined developmental milestones, with each patient serving as her own control and assessments reviewed by independent, blinded central raters. Taysha said dosing is on track to complete in Q2 2026, with a longer-term safety and efficacy data readout from Part A of the Phase 1/2 trial — covering all 12 patients with at least 12 months of follow-up — also expected in the second quarter.

The complementary ASPIRE trial, designed to support broad labelling for patients aged two years and older, is enrolling three females aged 2 to under 4 years across multiple sites. A minimum of three months of ASPIRE safety data is planned for inclusion in the BLA submission, with efficacy in younger patients to be extrapolated from REVEAL data. The company also initiated the BLA-enabling PPQ campaign using the commercial manufacturing process in April 2026, following FDA endorsement of the proposed strategy after a Type C meeting in January; campaign completion is targeted for Q4 2026.

Sean Nolan, chairman and chief executive, said the development strategy was "grounded in the rigour of our natural history analysis and Part A data collection and evaluation, with trial design, endpoints and statistical analyses developed based on discussions with the FDA."

Market context and competitive landscape

Rett syndrome, caused by mutations in the X-linked MECP2 gene, affects an estimated 15,000 to 20,000 patients across the US, EU, and UK, predominantly females, and currently has no approved disease-modifying therapy addressing the genetic root cause. That unmet need has attracted growing interest from gene therapy developers: Neurogene and AveXis-lineage programmes have historically targeted the same indication, and the competitive intensity around MECP2 restoration strategies has been a feature of the rare CNS gene therapy space for several years. TSHA-102's use of a miRNA-responsive auto-regulatory element to avoid MECP2 overexpression — which can itself cause toxicity — is central to Taysha's differentiation argument, and the preclinical data supporting this design is set to be presented at the American Society of Gene and Cell Therapy annual meeting on 14 May 2026.

The scale-up in R&D spend also reflects a broader dynamic in the gene therapy sector: CMC readiness and manufacturing process validation have become critical gating factors for BLA submissions following several high-profile FDA complete response letters citing manufacturing deficiencies. Taysha's decision to front-load the PPQ campaign in parallel with clinical enrolment rather than sequentially positions it to avoid that particular bottleneck, provided the interim efficacy data supports a filing.