Mustang Bio Ignites Bullish Retail Buzz As FDA Grants Orphan Status To Brain Cancer Drug

The company is advancing a novel combination of its CAR-T drug MB-101 and oncolytic virus MB-108, with both treatments currently enrolling patients in Phase 1 trials.
Illustration depicting tumour infiltrating lymphocyte (TIL) therapy for cancer treatment. During TIL therapy, T-cells (blue) that recognise tumour cells (red) are obtained from a patient. | Image source: Getty Images
Illustration depicting tumour infiltrating lymphocyte (TIL) therapy for cancer treatment. During TIL therapy, T-cells (blue) that recognise tumour cells (red) are obtained from a patient. | Image source: Getty Images
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Deepti Sri·Stocktwits
Published Jul 07, 2025 | 10:29 PM GMT-04
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Mustang Bio generated increased retail chatter on Monday after the company said that the FDA had awarded Orphan Drug Designation to its experimental CAR-T drug MB-101 for the treatment of astrocytomas and glioblastoma (GBM), two types of fast-growing brain tumors.

The treatment, which targets the IL13Ra2 protein, is currently being studied in a Phase 1 trial. 

In early results published in Nature Medicine, MB-101 was well-tolerated, with 50% of patients seeing stable disease or better. 

Among them, two had partial responses, and two others achieved complete responses lasting 7.5 months and more than five and a half years.

Mustang is also looking at a combo approach, pairing MB-101 with MB-108, an HSV-1-based oncolytic virus, in a regimen it calls MB-109. 

Preclinical studies suggest that MB-108 may help modify the tumor microenvironment, essentially turning "cold" tumors into "hot" ones to improve efficiency of MB-101 CAR-T cells.

MB-108 already has Orphan Drug status for malignant glioma, and Mustang says the combination could allow MB-101 to move more effectively through the tumor, activate in the right spots, and target cancer cells more precisely.

Both MB-101 and MB-108 are still enrolling patients in Phase 1 studies, including one at City of Hope, the other at The University of Alabama at Birmingham. 

However, moving the MB-109 program forward will depend on whether the company can secure more funding or land a partnership deal.

Orphan Drug status gives MB-101 access to several FDA benefits, including seven years of market exclusivity if approved, tax breaks on clinical trial costs, and waived fees, which are all part of a program designed to support treatments for rare conditions affecting fewer than 200,000 people in the U.S.

On Stocktwits, retail sentiment for Mustang Bio was ‘extremely bullish’ amid a 105,200% surge in 24-hour message volume.

One user on Stocktwits suggested that shares of $MBIO could climb to the $15–$20 range if the company secures a partnership, noting the stock “has life” and is poised to grow, especially for those who bought in below $1.20.

Another user speculated that a partnership or buyout by a larger pharmaceutical company could be in play, calling the day’s FDA designation “great news” for Mustang Bio.

The stock has declined 68% so far in 2025.

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