FDA Places RGX-121 on Clinical Hold
The US Food and Drug Administration has placed Regenxbio’s experimental gene therapy RGX-121 on clinical hold.
The company announced the decision on Monday.
The FDA action follows spinal scans that showed abnormalities in five patients who received the treatment.
Regenxbio shares fell more than 24 percent in premarket trading after the announcement.
Spinal Abnormalities Found in Five Patients
The patients received RGX-121 between three and six years ago.
Follow-up scans found a small lump or fluid-filled mass in their spinal areas.
Regenxbio said none of the five patients had symptoms linked to the findings.
The company also said the patients remained clinically stable or showed improvements in cognitive and behavioral assessments.
Trial investigators classified the findings as non-serious.
Radiologists also considered the abnormalities likely benign.
RGX-121 Targets Hunter Syndrome
RGX-121 is designed as a one-time treatment for Hunter syndrome.
The rare inherited disorder is also known as mucopolysaccharidosis type II, or MPS II.
The condition can cause progressive damage to the brain and other organs.
Regenxbio developed RGX-121 to address the underlying enzyme deficiency.
The therapy uses an AAV9 viral vector to deliver the gene needed to produce the missing enzyme.
FDA Has Raised Earlier Concerns
The latest RGX-121 clinical hold adds to Regenxbio’s regulatory challenges.
Earlier this year, the FDA declined to approve the therapy.
The agency raised concerns about the study design and the evidence supporting the application.
RGX-121 had also faced a previous clinical hold involving two of Regenxbio’s gene therapy programs.
The latest findings could therefore create another major obstacle for the company.
Regenxbio Delays Potential Resubmission
Regenxbio said it does not expect to resubmit RGX-121 for approval in the near future.
The company will continue reviewing available medical data.
It will work with its partner, NS Pharma, during that process.
The companies plan to examine additional imaging and longer-term follow-up information.
They will also wait for the FDA to provide its full clinical hold letter.
Company to Review Next Steps
The FDA’s full letter should provide more details about the concerns behind the clinical hold.
Regenxbio can then determine how to respond.
The company may need additional analysis or further information before regulators allow the program to continue.
For now, the future of RGX-121 remains uncertain.
Other Hunter Syndrome Treatments Available
Patients with Hunter syndrome already have treatment options.
Takeda Pharmaceutical’s Elaprase provides a weekly infusion that addresses the physical effects of the disease.
Denali Therapeutics’ Avlayah received approval in March for certain neurological symptoms in children.
RGX-121 aimed to offer a different approach by delivering a functional gene through a one-time treatment.
The FDA’s latest action could delay that potential treatment option.
What Happens Next?
Regenxbio and NS Pharma will continue reviewing the five patients and their imaging results.
The company says the patients remain stable and have not developed symptoms from the findings.
However, the FDA’s clinical hold means the regulator wants further information before the program can move forward.
The biotech will now wait for the agency’s detailed letter before deciding its next steps for RGX-121.
