Freeline Therapeutics Holdings plc announced that it will deliver one oral and three e-poster presentations at the 17 Annual WORLDSymposium™ taking place virtually from February 8 to February 12, 2021, highlighting data from its gene therapy programs in Gaucher and Fabry diseases. Presentation highlights from the platform presentation and e-poster titled, FLT201: An AAV-Mediated Gene Therapy for Type 1 Gaucher Disease Designed to Target Difficult to Reach Tissues, presented by Dr. Corbau, include: In wild-type mice, FLT201 resulted in robust GCase expression in the liver and sustained GCase secretion into the plasma, with enhanced and sustained GCase uptake observed in key tissues involved in Gaucher disease including spleen, bone marrow and lung, as compared with velaglucerase alfa, a standard-of-care ERT for Gaucher disease. The data demonstrate that GCasevar85 secreted from the liver was taken up by macrophages in the spleen and trafficked to lysosomes. In Gba-deficient mice, restoration of GCase activity after FLT201 injection was observed in difficult-to-reach tissues as shown by decreased levels of disease causing substrate, lyso-Gb1, increased concentrations of plasma GCase and reduced activated macrophages and inflammation in the lung. In addition, dose-dependent reductions of lyso-Gb1 were observed in all tissues analyzed including bone marrow and lung. In vitro studies demonstrated that GCasevar 85 was taken up by human peripheral blood mononuclear cells (PBMCs) and macrophages at levels comparable to those seen with ERT. FLT201 treatment in rhesus macaques was well-tolerated with rapid and robust increases in plasma GCase levels. Based on these results, Freeline believes that administration of FLT201 to patients with Gaucher disease can lead to continuous production of GCasevar85 in hepatocytes, in turn resulting in the steady presence of GCase in plasma, and improved penetration in Gaucher target tissues as compared with ERT, with potential improved outcomes in hard-to-reach tissues such as bone marrow and lung. Freeline currently expects to initiate first-in-human dose finding studies of FLT201 in late 2021. Presentation highlights from an e-poster titled Generation of ß-Glucocerebrosidase Variants with Increased Half-Life in Human Plasma for Liver Directed AAV Gene Therapy Aimed at the Treatment of Gaucher Disease Type 1, presented by Fabrizio Comper, Scientific Director, Freeline, include preclinical data on the generation and characterization of GCasevar85, which is part of the Company’s development candidate for Gaucher disease, FLT201:Human GCase enzyme is a protein known for its short half-life in human plasma. To provide an improved solution to Type 1 Gaucher patients, It addressed the short half-life of the GCase protein by designing, through protein engineering efforts, 86 GCase variants that were engineered and assessed for stability and sustained activity at neutral and acidic pH. Variant 85 showed the highest level of GCase activity when transduced using AAVS3 in Huh7 cells, with more than an 80-fold increase in activity over wild-type GCase, and was chosen as the lead development construct. GCasevar85 showed increased stability in different physiological media compared with ERT, without differing in its fundamental enzymatic parameter KM. The higher stability translated into a substantially higher level of GCase activity in plasma and target organs of mice transduced with a very low dose of AAV vector (6x1010 vg/kg), including in difficult to treat organs such as lung and bone marrow. Presentation highlights from an e-poster titled Development of a GLA NAb Assay with a Fully-Human, Neutralizing IgG4 Positive Control to Characterize Antibody Response in Fabry Disease Patients, presented by Sujata Ravi, Scientist, Freeline, include data on the development of a NAb assay for the characterization and monitoring of NAbs in patients with Fabry disease who are receiving ERT or gene therapy: A custom in vitro phage display library against the enzyme a-galactosidase A (GLA) was used to screen and develop a unique GLA neutralizing IgG4 antibody, which is not described in the literature or commercially available. A semi-quantitative GLA NAb assay was developed to determine the titer of GLA NAbs in Fabry patient serum, enabling further characterization and monitoring of Fabry patients receiving ERT or gene therapy. Early development and qualification data suggest that the assay performance is acceptable and accurate in detecting NAbs in Fabry disease samples. These results support further development and validation as a robust, standardized assay for use in gene therapy trials, which may overcome the limitations associated with available assays that lack positive controls and show intra-lab variability.