CRISPR Therapeutics

CTX611 (SRSD107)

In Development

A long-acting, double-stranded siRNA that targets Factor XI (FXI) messenger RNA to inhibit FXI protein expression, aiming to provide anticoagulant and antithrombotic protection with less bleeding risk than existing anticoagulants, potentially dosed as infrequently as semi-annually. Co-developed with Sirius Therapeutics (50/50 cost and profit share; CRISPR leads U.S. commercialization, Sirius leads Greater China) across a range of thromboembolic indications including atrial fibrillation, venous thromboembolism, and stroke prevention.

Latest update Sep 15, 2026

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Current status

Phase 2 trial for prevention of venous thromboembolism in total knee arthroplasty patients dosed its first patient in September 2025, comparing CTX611 with enoxaparin. Phase 1 data showed peak FXI activity reductions >93% and aPTT increases >2x, sustained up to 6 months. Topline Phase 2 data expected in H2 2026, including high-level VTE-rate comparisons per the September 14, 2026 Morgan Stanley comments; CRISPR will lead global Phase 3 development outside Greater China.

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Specifications2

Target
Factor XI (FXI), long-acting siRNA
Phase 1 Effect
FXI activity down >93%

aPTT up >2x (6-mo durability)

Announced next steps from CRISPR Therapeutics that mention CTX611 (SRSD107).

  1. H2 2026

    CTX611 (SRSD107) Phase 2 topline data

    Report topline Phase 2 data for CTX611 (SRSD107), the long-acting Factor XI siRNA co-developed with Sirius Therapeutics, in patients undergoing total knee arthroplasty versus enoxaparin. Kulkarni said at Morgan Stanley on September 14, 2026 that the year-end update should include high-level venous-thromboembolism rate comparisons, with more detailed bleeding information later, and that CRISPR will lead Phase 3 development and potential commercialization outside Greater China. No Phase 2 readout has been published as of September 15, 2026.

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