What is gene therapy?
Gene therapy is a potential treatment option that replaces a disease-causing mutated gene by introducing a healthy copy into cells, enabling them to produce functioning proteins. A modified virus that does not cause disease is used to deliver the healthy gene to the cells. Viruses such as adeno-associated virus (AAV) and lentivirus are good candidates for delivering the healthy copy of a gene. The goal of gene therapy is to enable the body to steadily produce functioning proteins without the need for repeated administration.
Gene therapy for Gaucher disease
Gaucher disease is a genetic condition caused by mutations in the GBA gene. This gene carries the information necessary to make beta-glucocerebrosidase, an enzyme that breaks down a fat molecule called glucocerebroside. Mutations result in low levels or the complete absence of beta-glucocerebrosidase enzymes, causing glucocerebroside to accumulate in different organs in the body and leading to the symptoms of Gaucher disease.
Two types of treatments are currently available to manage the disease: enzyme replacement therapy and substrate reduction therapy. Both of these treatments help manage the condition and have to be administered or taken routinely to be effective but neither provide a long-lasting solution.
There are three gene therapy candidates for Gaucher disease that are currently being evaluated, and are at the pre-clinical testing stage. They are FLT200, AVR-RD-02, and AAV9-GBA.
FLT-200 is a gene therapy candidate for type 1 Gaucher disease and is designed to increase the production of beta-glucocerebrosidase in the liver. Developed by Freeline Therapeutics, FLT-200 uses a modified AAV vector to deliver human GBA directly to the liver. A single injection of FLT-200 resulted in a steady increase in beta-glucocerebrosidase levels in the blood of a mouse model of Gaucher disease, according to a poster presented at the 15th Annual World Symposium in February 2019. The researchers also reported that the enzyme was taken up by organs and tissues affected by Gaucher disease, such as the spleen, lungs, and bone marrow.
AVR-RD-02 is a lentiviral-based gene therapy candidate developed by Avrobio. The therapy involves collecting a patient’s blood stem cells, which are then modified by AVR-RD-02 in the laboratory to carry a healthy copy of the GBA gene. The modified stem cells are then injected back into the patient.
A preclinical study in a mouse model of Gaucher disease has shown steady levels and activity of beta-glucocerebrosidase in the spleen, liver, and bone marrow of mice treated with AVR-RD-02. A reduction in spleen size was also noted (an enlarged spleen is a symptom of Gaucher disease).
The company is planning a Phase 1/2 clinical study to evaluate the safety and efficacy of AVR-RD-02 in patients with type 1 Gaucher disease. The study aims to recruit eight to 16 patients, ages 16 to 35.
A multinational research team led by scientists from University College London designed AAV9-GBA and conducted a study in mouse and monkey models of Gaucher disease to generate a steady production of beta-glucocerebrosidase. In both models, AAV9-GBA was delivered directly into the brain of a fetus in utero. The treated mice lived for at least 18 weeks after birth while the non-treated ones survived for 15 days.
Moreover, AAV9-GBA was able to restore beta-glucocerebrosidase activity in the brain, alleviate inflammation, and block neurodegeneration. Similar results were observed in the monkey model of Gaucher disease. Researchers are preparing to test AAV9-GBA in humans.
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