Phase 1-2 Trial of AAVS3 Gene Therapy in Patients with Hemophilia B

BACKGROUND

FLT180a (verbrinacogene setparvovec) is a liver-directed adeno-associated virus (AAV) gene therapy that uses a synthetic capsid and a gain-of-function protein to normalize factor IX levels in patients with hemophilia B.

METHODS

In this multicenter, open-label, phase 1-2 trial, we assessed the safety and efficacy of varying doses of FLT180a in patients with severe or moderately severe hemophilia B (factor IX level, ≤2% of normal value). All the patients received glucocorticoids with or without tacrolimus for immunosuppression to decrease the risk of vector-related immune responses. After 26 weeks, patients were enrolled in a long-term follow-up study. The primary end points were safety and efficacy, as assessed by factor IX levels at week 26.

RESULTS

Ten patients received one of four FLT180a doses of vector genomes (vg) per kilogram of body weight: 3.84×10¹¹ vg, 6.40×10¹¹ vg, 8.32×10¹¹ vg, or 1.28×10¹² vg. After receiving the infusion, all the patients had dose-dependent increases in factor IX levels. At a median follow-up of 27.2 months (range, 19.1 to 42.4), sustained factor IX activity was observed in all the patients except one, who resumed factor IX prophylaxis. As of the data-cutoff date (September 20, 2021), five patients had normal factor IX levels (range, 51 to 78%), three patients had levels from 23 to 43%, and one had a level of 260%. Of the reported adverse events, approximately 10% were related to FLT180a and 24% to immunosuppression. Increases in liver aminotransferase levels were the most common FLT180a-related adverse events. Late increases in aminotransferase levels occurred in patients who had received prolonged tacrolimus beyond the glucocorticoid taper. A serious adverse event of arteriovenous fistula thrombosis occurred in the patient with high factor IX levels.

CONCLUSIONS

Sustained factor IX levels in the normal range were observed with low doses of FLT180a but necessitated immunosuppression with glucocorticoids with or without tacrolimus. (Funded by Freeline Therapeutics; ClinicalTrials.gov numbers, NCT03369444 and NCT03641703; EudraCT numbers, 2017-000852-24 and 2017-005080-40.).

Loss of attentional stimulus selection after extrastriate cortical lesions in macaques

Many objects in natural visual scenes compete for attention. To identify the neural mechanisms necessary for visual attention, we made restricted lesions, affecting different quadrants of the visual field but leaving one quadrant intact, in extrastriate cortical areas V4 and TEO of two monkeys. Monkeys were trained to discriminate the orientation of a target grating surrounded by distracters. As distracter contrast increased, performance deteriorated in quadrants affected by V4 and TEO lesions, but not in the normal quadrant. Performance in affected quadrants was restored by increasing the contrast of the target relative to distracters. Thus, without V4 and TEO, visual attention is 'captured' by strong stimuli, regardless of their behavioral relevance.