GC801-enabled AAV gene therapy in a neonate with Pompe disease

Gene therapy holds the promise of curing diseases by fixing broken genetic instructions inside a person's cells. One of the most successful tools for delivering these new instructions is a harmless virus called adeno-associated virus, or AAV. Scientists strip the virus of its ability to cause illness and replace its genetic cargo with a healthy gene, turning it into a microscopic delivery truck. However, this approach faces a significant hurdle: many people already carry natural defenses against these viruses. Because AAV is common in the environment, the human immune system often recognizes it as an invader and attacks it before it can deliver its cure. This pre-existing immunity acts like a shield, neutralizing the treatment and leaving patients with no options. This is especially difficult for newborns, whose immune systems may have inherited these defenses from their mothers, blocking life-saving treatments before they even begin.

A new report describes a breakthrough in overcoming this barrier for a newborn baby suffering from a severe form of Pompe disease. This rare condition prevents the body from breaking down a specific type of sugar, leading to a dangerous buildup that causes the heart and muscles to fail. The standard treatment involves gene therapy using an AAV9 vector, a specific type of delivery truck designed to target the heart and muscles. Yet, when doctors screened this infant, they found high levels of antibodies that would have immediately destroyed the therapy. Instead of giving up, the medical team used a specialized enzyme to temporarily disarm the baby's immune defenses, creating a brief window of opportunity for the gene therapy to work.

The infant, born with a genetic defect that left the body unable to produce the enzyme acid alpha-glucosidase, showed signs of severe distress shortly after birth. The baby's heart was enlarged and beating too slowly, and blood tests revealed massive damage to heart and muscle tissue. While the medical team at the Chinese People's Liberation Army General Hospital was prepared to administer the gene therapy, a routine check revealed a high concentration of antibodies against the AAV9 virus. These antibodies, present at levels of 1 to 4,174 for binding and 1 to 672 for neutralizing activity, meant the virus would be destroyed instantly if injected. To solve this, the team turned to a new tool called GC801, an engineered version of a bacterial enzyme known as IdeS. This enzyme acts like a pair of molecular scissors that specifically cuts the hinge region of IgG antibodies, the most common type of antibody in the blood, rendering them harmless without affecting other parts of the immune system.

On the day of the procedure, the newborn received a single intravenous dose of GC801 at 0.2 milligrams per kilogram of body weight. The effect was rapid and precise. Within 24 hours, the level of IgG antibodies in the baby's blood dropped from 6.25 grams per liter to 2.41 grams per liter. By 48 hours, the level had fallen further to 1.82 grams per liter, and by the fifth day, it reached a low point of 0.72 grams per liter. During this time, the other types of antibodies, IgA and IgM, remained unchanged, showing that the treatment targeted only the specific defenses blocking the gene therapy. This drop created a safe window where the immune system could no longer recognize or attack the incoming virus.

Once the antibody levels were low enough, the team administered the gene therapy, known as GC301, which carried the healthy gene for acid alpha-glucosidase. Because the immune system was temporarily disarmed, the virus successfully entered the baby's cells and began producing the missing enzyme. By day 84 after the gene therapy infusion, the baby's blood showed a robust increase in the activity of the missing enzyme, rising to 19.38 millimoles per liter per 16 hours. This level fell within the normal range observed in healthy adults, indicating that the gene therapy had successfully taken hold. The treatment did not cause any new side effects beyond those expected from the underlying disease, and the baby's immune system remained stable throughout the process.

To protect the infant from infection while the antibody levels were low, doctors administered a dose of intravenous immunoglobulin on the seventh day. This provided a temporary supply of healthy antibodies from donors, raising the baby's IgG levels back to a safe range of 3.04 grams per liter by day 14. As the weeks passed, the baby's own immune system began to produce new antibodies against the AAV9 virus again, a normal response to the gene therapy. However, the timing of this response matched what is seen in other patients who received the therapy without the enzyme preconditioning, suggesting that the enzyme did not alter how the body eventually learned to recognize the virus. The enzyme itself disappeared from the blood within two weeks, and no new antibodies formed against the enzyme itself, other than a brief, temporary rise that coincided with the donor immunoglobulin treatment.

This case demonstrates that it is possible to safely lower pre-existing immune defenses in a newborn to allow gene therapy to work. The use of GC801 provided a clean, targeted way to remove the specific antibodies that would have blocked the treatment, without broadly suppressing the immune system or requiring complex procedures like blood washing. The success of this single case suggests that this approach could open the door for treating other infants who are currently excluded from gene therapy due to high levels of natural antibodies. While this report focuses on the safety and immediate biological effects rather than long-term disease outcomes, the ability to deliver the gene successfully in a high-risk neonate marks a significant step forward in making these powerful treatments accessible to the youngest and most vulnerable patients.