Freeline Therapeutics Holdings plc operates as a clinical-stage systemic adeno-associated virus (AAV)-based gene therapy company. Its advanced product candidate is FLT180a, a gene therapy product candidate that is being evaluated in a Phase 1/2 dose-finding clinical trials in adult males for the treatment of patients with moderate or severe hemophilia B. The company's products also include FLT190, which is in dose-escalating Phase 1/2 clinical trials for the treatment of Fabry disease; FLT201, a liver-directed gene therapy product candidate to treat type 1 Gaucher disease; and FLT210, a liver-directed gene therapy product candidate for the treatment of hemophilia A. In addition, it has research programs in various indications for systemic gene therapy. The company was founded in 2015 and is headquartered in Stevenage, the United Kingdom.