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# Clinical Hold Lifted on ‘Bubble Boy’ Therapy
- URL: https://www.fdaweb.com/clinical-hold-lifted-on-bubble-boy-therapy/
- Published: 2021-02-02T12:00:00.000Z
- Updated: 2026-09-14T16:45:01.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5148575

FDA has lifted a clinical hold on Mustang Bio’s lentiviral gene therapy MB-107 and a pivotal Phase 2 clinical trial after reviewing a “comprehensive” CMC package that the company says was submitted in late December. Mustang says it will proceed with its plans to initiate the pivotal Phase 2 trial in newly diagnosed X-linked severe combined immunodeficiency (XSCID), also known as "Bubble Boy Disease," patients.

The same lentiviral vector used in MB-107 is currently being assessed in a Phase 1/2 clinical trial for XSCID in newly diagnosed infants under the age of two at St. Jude Children’s Research Hospital, University of California San Francisco Benioff Children’s Hospital, and Seattle Children’s Hospital. Additionally, it is being assessed in a Phase 1/2 clinical trial at the National Institute of Allergy and Infectious Diseases in XSCID patients who have been previously treated with hematopoietic stem cell transplantation and for whom re-treatment is indicated.

XSCID is a rare genetic disorder that is characterized by the absence or lack of function of key immune cells, resulting in a severely compromised immune system and death by one year of age if untreated. Patients with XSCID have no T-cells or natural killer-cells, the company says. “Although their B-cells are normal in number, they are not functional,” it says, adding that patients are usually affected by severe bacterial, viral or fungal infections early in life and often present with interstitial lung disease, chronic diarrhea and failure to thrive.