NEW YORK – Long-term data from the Phase I/II/III CAMPSIITE trial of Regenxbio's RGX-121 in patients with mucopolysaccharidosis type II (MPS II) has reinforced the investigational gene therapy's benefit in this setting as well as the company's regulatory plans for the treatment.
In light of the latest readout from the CAMPSIITE trial, Rockville, Maryland-based Regenxbio on Tuesday said it is on track to initiate a rolling biologics license application (BLA) submission to the US Food and Drug Administration in the third quarter seeking accelerated approval for RGX-121 as a treatment for MPS II.
MPS II, also known as Hunter syndrome, is a rare, X-linked recessive disease due to abnormalities in the lysosomal enzyme iduronate-2-sulfatase (I2S). This I2S deficiency causes glycosaminoglycans such as heparan sulfate to accumulate in tissues, which leads to cellular, tissue, and organ dysfunction. The condition, when severe, can cause developmental delay in infants by 18 to 24 months.
Regenxbio has developed RGX-121 as an adeno-associated virus-based one-time gene therapy for boys with MPS II. The firm designed the therapy to deliver the IDS gene to the central nervous system and express I2S beyond the blood-brain barrier.
Regenxbio reported earlier this year that CAMPSIITE had met its primary endpoint with statistical significance. More recently, at the Society for the Study of Inborn Errors of Metabolism (SSIEM) Annual Symposium, the firm shared long-term data from this study, which showed that 80 percent of patients on RGX-121 did not have to take standard enzyme replacement therapy for up to 18 months. Moreover, patients on the pivotal dose of RGX-121 experienced an 85 percent median reduction in the key biomarker heparan sulfate (HS) D2S6 in CSF. The gene therapy appeared to bring HS D2S6, a biomarker of brain disease activity, down to around normal levels and maintained that reduction for up to two years.
In its planned BLA seeking accelerated approval, Regenxbio said it will use CSF D2S6 as a surrogate endpoint that is reasonably likely to predict clinical benefit. The firm expects the FDA to evaluate the BLA under priority review in 2025.