Why Is Taysha Gene Therapies Stock Trading Higher On Thursday?

Taysha Gene Therapies Inc. (NASDAQ:TSHA) on Wednesday announced details of its planned pivotal Part B trial design for TSHA-102 following written alignment from the U.S. Food and Drug Administration (FDA).

• Single-arm, open-label trial with patients serving as their control (intend N=15).
• Enrollment of females in the developmental plateau population of Rett syndrome (≥ 6 years).
• The primary endpoint will assess developmental milestone gain or regain.
• The safety of TSHA-102 will be evaluated in females in the pre-developmental plateau population of Rett syndrome (2-6 years), with efficacy data extrapolated from the developmental plateau population.
• The 12-month primary analysis and the company intends to perform a 6-month interim analysis.
• The FDA advised the company to submit the pivotal Part B trial protocol and the associated SAP as an amendment to its IND application, eliminating the need for a formal end-of-phase meeting.

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Additionally, the company revealed clinical data from Part A of the REVEAL Phase 1/2 adolescent/adult and pediatric trials evaluating TSHA-102 in Rett syndrome, a rare genetic neurological and developmental disorder that causes a progressive loss of motor skills and language. 

Efficacy data based on May 19, 2025, data cutoff included 10 females with Rett syndrome aged 6-21 years (high dose, N=6; low dose, N=4) treated with the high dose (1×1015 total vg) or low dose (5.7×1014 total vg) of TSHA-102.

• 100% of pediatric, adolescent, and adult patients gained ≥ one defined developmental milestone across the core functional domains of fine motor, gross motor, and communication post-TSHA-102, with a ~0% likelihood of being achieved without treatment based on natural history data.
  • 22 developmental milestones were achieved across the 10 patients, as determined by multiple independent central raters.
  • Developmental milestones were achieved early post-TSHA-102, and new gains/regains were demonstrated over time (e.g., speaking in phrases with meaning, finger feeding, walking with support).
  • The dose cohort achieved a 100% responder rate 25% faster than the low-dose cohort, supporting the accelerated functional benefit observed with the high-dose.
• The high-dose cohort outperformed the low-dose cohort across multiple outcome measures six months post-treatment, with dose-dependent effects deepening over time ≥ nine months post-treatment.

Safety data based on May 20, 2025, data cutoff showed:

• High and low doses of TSHA-102 have been generally well tolerated, with no treatment-related serious adverse events (SAEs) or dose-limiting toxicities (DLTs).
• All treatment-emergent AEs related to TSHA-102 were mild to moderate in severity.

Taysha Gene Therapies expects to submit the pivotal Part B trial protocol and associated SAP to amend the IND application in the current quarter.

• Pivotal Part B trial site activation and trial initiation activities are anticipated in the third quarter of 2025.

Taysha Gene Therapies also priced an underwritten public offering of 46.9 million shares at $2.75 per share and pre-funded warrants to purchase 25.9 million shares at $2.749 per pre-funded warrant, raising $200 million in gross proceeds.

Price Action: TSHA stock is up 9% at $2.66 at the last check on Thursday.

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