Global First-in-Neonate Use

In September 2026, the first exploratory clinical data from a neonate was published online in preprint form for GC801, an engineered IdeS protease developed by Genecradle Therapeutics, used to lower the pre-existing anti-AAV9 antibody barrier prior to AAV9 gene therapy in a newborn with infantile-onset Pompe disease (IOPD).

Image source: medRxiv preprint

This study was an investigator-initiated trial (IIT) led by the Department of Pediatrics/Neonatology at the PLA General Hospital, with participation from the Department of Ultrasound at its Seventh Medical Center, among others. GC301 and GC801 were developed and supplied by Genecradle Therapeutics. The study marks the first application of a domestically developed engineered IdeS enzyme in China to clear pre-existing antibodies prior to AAV gene therapy, providing an important reference and perspective for overcoming the pre-existing anti-AAV antibody barrier and expanding the eligible population for AAV gene therapy. It also brings new hope to patients who would otherwise be excluded from gene therapy due to pre-existing anti-AAV antibodies.

Research Highlight 1: Breaking the Bottleneck — Responding to Urgent Clinical Need

Infantile-onset Pompe disease (IOPD) is a rapidly progressive, multisystem, life-threatening genetic disorder caused by mutations in the GAA gene that lead to acid alpha-glucosidase deficiency. Glycogen accumulates abnormally in tissues including cardiac muscle, skeletal muscle, and respiratory muscles, resulting in impaired cellular function and multi-organ dysfunction. AAV-mediated GAA gene therapy offers new possibilities for early intervention, but its clinical application faces a critical bottleneck: a substantial proportion of patients have pre-existing anti-AAV neutralizing antibodies, and neonates may additionally be affected by maternally derived antibodies, leading to rapid clearance of the vector and exclusion from AAV gene therapy. It has been reported that maternally derived pre-existing anti-AAV antibodies can gradually decline over 3–6 months after birth, but IOPD progresses extremely rapidly and gravely endangers life — these infants cannot wait out this natural decline period. There is therefore an urgent clinical need for an approach that can rapidly lower the pre-existing antibody barrier and buy a time window for AAV gene therapy.

Research Highlight 2: Mechanism of Action of GC801

GC801 is an IgG-degrading enzyme. By cleaving the IgG hinge region, it depletes total IgG — including pre-existing anti-AAV9 antibodies — thereby attenuating the neutralization and clearance of the AAV9 vector by pre-existing anti-AAV9 antibodies. This makes somatic cell transduction and sustained GAA expression possible, creating a window for GC301 transduction.

Research Highlight 3: Good Drug Safety Profile and Benefit to the Subject

Plasma enzyme activity rose significantly and steadily.

This study showed that in a newborn with IOPD who had high-titer pre-existing anti-AAV9 antibodies, a single pretreatment dose of 0.2 mg/kg GC801 successfully reduced AAV neutralizing antibody titers to below the upper limit compatible with gene therapy intervention, creating a window for subsequent GC301 transduction.

Before treatment, the patient's baseline plasma GAA activity was only 0.52–0.56 mmol/L/16h, and the patient had not received enzyme replacement therapy (ERT). After GC301 infusion, GAA activity rose progressively: it reached 9.67 mmol/L/16h on day 28 and climbed to 19.38 mmol/L/16h on day 84, falling within the healthy adult reference range (11.21–52.14, median 18.17). This confirmed successful AAV9-mediated transgene expression (successful delivery of GC301). Throughout 90 days of follow-up, no adverse events attributable to GC801 were observed.

This preliminarily suggests that GC801 may be able to secure a gene therapy window for such children who would otherwise be excluded due to pre-existing anti-AAV9 antibodies.

A Window of Hope

Infantile-onset Pompe disease is a rare disease that progresses extremely rapidly and is highly dangerous. Without early intervention, it often endangers life in infancy. AAV9-mediated GAA gene therapy brings new possibilities for "early detection, early treatment." But a substantial proportion of patients are born with anti-AAV9 neutralizing antibodies, and neonates may additionally be affected by maternally derived antibodies. These antibodies cause the therapeutic vector to be rapidly cleared as soon as it enters the body, shutting these patients out of the door of AAV gene therapy. The goal of GC801 is to rapidly lower this "pre-existing antibody barrier" and buy a valuable time window for AAV9 gene therapy. This study preliminarily suggests that in newborns with IOPD, using GC801 to clear pre-existing anti-AAV9 antibodies prior to GC301 gene therapy is feasible. This brings new hope to patients who cannot receive AAV gene therapy due to pre-existing antibodies, and provides an important reference and a fresh perspective for other gene therapy strategies that need to cross the "pre-existing anti-AAV antibody barrier."