Regenxbio said on Monday the U.S. FDA has placed its experimental gene therapy for a rare inherited disorder on clinical hold after spinal scans found abnormalities in five study participants, sending its shares down more than 24% in premarket trading.
The therapy, RGX-121, was being developed as a one-time treatment for Hunter Syndrome, also known as MPS II, which can cause progressive damage to the brain and other organs and tissues.
The spinal scans identified a small lump or fluid-filled mass in the patients who received the treatment, RGX-121, about three to six years ago, the biotech said.
The setback adds to Regenxbio’s regulatory troubles after the U.S. Food and Drug Administration declined to approve RGX-121 earlier this year over concerns about the trial design and supporting evidence.
RGX-121 was also subject to the health regulator’s previous clinical hold on the company’s two gene therapy programs.
The therapy uses a harmless virus known as AAV9 vector to deliver the gene needed to produce the missing enzyme in patients with Hunter syndrome.
Current treatment options include Takeda Pharmaceutical’s Elaprase, a weekly infusion that treats the physical effects of Hunter syndrome, and Denali Therapeutics’ Avlayah, approved in March, to treat neurological symptoms in certain children.
Regenxbio said the five patients remained asymptomatic and were clinically stable or showed improvements in cognitive and behavioral assessments. Trial investigators deemed the findings to be non-serious and radiologists believed they were likely benign.
The company said it does not expect to resubmit its application for the treatment’s approval in the near term.
It, along with partner NS Pharma, will review additional imaging and longer-term follow-up data and await the FDA’s full clinical hold letter before deciding the next steps for RGX-121.
