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Mustang Bio Gallops On Gene Therapy Trial Results For Bubble Boy Disease

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Shares of Mustang Bio Inc. (MBIO) soared more than 349 percent to $11.96 in extended trading on Wednesday, following encouraging results of the company's MB-107, an investigational lentiviral gene therapy for the treatment of bubble boy disease.

The data comes from a phase I/II clinical trial of MB-107, and was published in the New England Journal of Medicine.

MB-107, a safety modified lentiviral (LV) vector, was developed by St. Jude Children's Research Hospital, and licensed to Mustang Bio last August.

What Is Bubble Boy Disease?

Bubble boy disease, also referred to as severe combined immunodeficiency (SCID), is an extremely rare, life-threatening genetic disorder, caused by a severe defect in key immune cells - i.e., both T- & B-lymphocytes - resulting in a severely compromised immune system and death by one year of age if untreated. In patients with bubble boy disease, the body produces very few T cells (CD3+, CD4+ CD8+) and Natural Killer (NK) cells. The level of immunoglobulin, especially IgM, is also very low.

The two most common types of SCID are the classical X-linked SCID (XSCID) that occurs in males, and ADA-SCID caused due to adenosine deaminase (ADA) deficiency.

The term bubble boy disease was coined in the 1970s after David Vetter who was born with X-linked severe combined immunodeficiency (XSCID) in 1971, had to live in a germ-free environment in a sterile plastic bubble from birth until he died at age 12.

Trial Results

The phase I/II clinical trial involved 10 newly diagnosed infants under two years old with XSCID, and the published data covers eight infants with XSCID who were treated at St. Jude and at UCSF Benioff Children's Hospital with MB-107 and followed for a median of 16.4 months.

According to the trial results, in seven of the eight cases, normalization of CD3+, CD4+ and CD4+ naïve T-cell and natural killer ("NK") cell numbers occurred within three to four months after treatment. The eighth infant had insufficient T cells initially, but normalization of T cells occurred following an unconditioned boost of gene-corrected cells, and the patient is progressing favorably.

All patients cleared previous infections and are growing normally. Seven of the eight infants treated have developed normal IgM levels to date. Most patients were discharged from the hospital within one month.

Approved Therapies

The standard treatment which is known to cure the bubble boy disease is a bone marrow transplant, also known as stem cell transplant.

Strimvelis, developed by GlaxoSmithKline (GSK), which is now under the aegis of Orchard Therapeutics plc (ORTX), is the first gene therapy to treat bubble boy disease. Approved in 2016 in the European Union, it is indicated for the treatment of children with severe combined immunodeficiency due to adenosine deaminase deficiency, or ADA-SCID, for whom no matching bone marrow donor is available. This therapy is not approved in the U.S. yet.

Last October, the FDA approved Revcovi in the U.S. for the treatment of adenosine deaminase severe combined immune deficiency (ADA-SCID) in pediatric and adult patients. Developed by Italy's Leadiant Biosciences, Revcovi is an enzyme replacement therapy.

Market Potential

Severe combined immunodeficiency is said to affect at least 1 in 50,000 to 100,000 newborns.

The use of Strimvelis, a one-time treatment for ADA-SCID, which has a price tag of $714,000, has been limited. During 2018, Strimvelis brought home sales of only $2.1 million for Orchard Therapeutics.

What's Next?

Commenting on the encouraging results, Martina Sersch, Chief Medical Officer of Mustang, said, "We are extremely encouraged by the Phase 1/2 clinical data published in the New England Journal of Medicine. They underscore the potential of MB-107 as a novel approach and potentially curative treatment option for newly diagnosed infants with XSCID. We are excited to continue working with St. Jude to evaluate MB-107 in this clinical trial, and we look forward to transferring the IND to Mustang by the end of this year".

MBIO closed Wednesday's trading at $2.66, down 5.34%. In after-hours, the stock was up 349% to $11.96.

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