Freeline Therapeutics Holdings plc is a clinical-stage biotechnology company. The Company is developing transformative adeno-associated virus (AAV) vector-mediated gene therapies for patients suffering from chronic debilitating diseases. It uses its rationally designed AAV vector and capsid (AAVS3), along with novel promoters and transgenes, to deliver a functional copy of a therapeutic gene into human liver cells, thereby expressing a persistent functional level of the missing or dysfunctional protein into a patient’s bloodstream. It is advancing FLT201, a differentiated gene therapy candidate that delivers a novel transgene, in a Phase 1/2 clinical trial in people with Gaucher disease type 1. Therapeutic AAV vectors consist of two main components: the capsid and the expression cassette (that contains the gene and the promoter). It has additional programs in research, including one focused on GBA1-linked Parkinson’s disease that leverages the same novel transgene as FLT201.