Mustang Bio gets Orphan Drug Designation for MB-207 in XSCID in previously transplanted patients

The lentiviral gene-therapy method employed in MB-207 was co-developed by scientists at the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, and St. Jude Children’s Research Hospital (St. Jude). MB-207 has been studied at NIAID since 2012 and continues to be assessed in a NIAID-supported Phase 1/2 clinical trial for XSCID in patients over the age of two who have received prior HSCT. Mustang expects to file an investigational new drug application (IND) with the FDA to initiate a multi-center pivotal Phase 2 clinical trial of MB-207 in this patient population in the fourth quarter of 2020.

X-linked severe combined immunodeficiency (XSCID) is a rare genetic disorder that occurs in approximately 1 per 225,000 births. It is characterized by the absence or lack of function of key immune cells, resulting in a severely compromised immune system and death by 1 year of age if untreated. Patients with XSCID have no T-cells or natural killer cells. Although their B-cells are normal in number, they are not functional. As a result, XSCID 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. Among patients who receive HSCT, many are unable to establish adequate T-cell immunity or lose T-cell immunity over time. Further, approximately two-thirds of patients who receive HSCT lack sufficient B-cell immunity and need lifelong immunoglobulin replacement therapy.

The specific genetic disorder that causes XSCID is a mutation in the gene coding for the common gamma chain (γc), a protein that is shared by the receptors for at least six interleukins. These interleukins and their receptors are critical for the development and differentiation of immune cells. The gene coding for γc is known as IL-2 receptor gamma, or IL2RG. Because IL2RG is located on the X-chromosome, XSCID is inherited in an X-linked recessive pattern, resulting in almost all patients being male.

Mustang Bio gets Orphan Drug Designation for MB-107 in XSCID

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 (St. Jude), UCSF Benioff Children’s Hospital in San Francisco and Seattle Children’s Hospital. In May 2020, Mustang submitted an investigational new drug application (IND) to the FDA to initiate a multi-center Phase 2 clinical trial of MB-107 in newly diagnosed infants with XSCID who are between two months to two years of age. The trial is expected to enroll 10 patients who, together with 15 patients enrolled in the current multi-center trial led by St. Jude, will be compared with 25 matched historical control patients who have undergone hematopoietic stem cell transplantation (HSCT). The primary efficacy endpoint will be event-free survival. The initiation of this trial is expected early in the fourth quarter of 2020. Mustang is targeting topline data from this trial in the second half of 2022.

Another Phase 1/2 clinical trial for XSCID in patients over the age of two years, who have received prior HSCT, is underway at the National Institutes of Health, and Mustang expects to file an IND to the FDA to initiate a multi-center Phase 2 clinical trial in this population in the fourth quarter of 2020. This product candidate for XSCID in patients over the age of two years, who have received prior HSCT, is designated MB-207. The FDA granted a Rare Pediatric Disease Designation to MB-207 in August 2020.

X-linked severe combined immunodeficiency is a rare genetic disorder that occurs in approximately 1 per 225,000 births. It 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. Although their B-cells are normal in number, they are not functional. As a result, XSCID 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.

The specific genetic disorder that causes XSCID is a mutation in the gene coding for the common gamma chain (γc), a protein that is shared by the receptors for at least six interleukins. These interleukins and their receptors are critical for the development and differentiation of immune cells. The gene coding for γc is known as IL-2 receptor gamma, or IL2RG. Because IL2RG is located on the X-chromosome, XSCID is inherited in an X-linked recessive pattern, resulting in almost all patients being male.