Mustang Bio Announces First Patient Treated in Its Multicenter Phase 1/2 Clinical Trial of a First-in-Class CD20-targeted, Autologous CAR T Cell Therapy 

Mustang Bio, Inc. recently announced the first patient has been treated in its multicenter, open-label, non-randomized Phase 1/2 clinical trial evaluating the safety and efficacy of MB-106, Mustang’s first-in-class CD20-targeted, autologous CAR T cell therapy for the treatment of relapsed or refractory B-cell non-Hodgkin lymphomas (B-NHL) and chronic lymphocytic leukemia (CLL). The patient did not experience cytokine release syndrome (CRS) or immune effector cell-associated neurotoxicity syndrome (ICANS). MB-106 is being developed in a collaboration between Mustang and Fred Hutchinson Cancer Center (Fred Hutch). The multicenter trial under Mustang’s Investigational New Drug Application (IND) builds upon the initial, ongoing Phase 1/2 clinical trial taking place at Fred Hutch in a single-center study under Fred Hutch’s IND.

Manuel Litchman, MD, President and Chief Executive Officer of Mustang, said “The first clinical trial under Mustang’s IND is an important milestone in the ongoing development and evaluation of MB-106. Data presented at several prestigious medical meetings earlier this year from the initial, ongoing Phase 1/2 clinical trial at Fred Hutch show that MB-106 continues to demonstrate high efficacy and a favorable safety profile across patients with a wide range of hematologic malignancies. We look forward to providing updates on our multicenter MB-106 clinical trial as it progresses and anticipate reporting efficacy data in the fourth quarter of this year.”

Interim data from 28 patients treated in the initial, ongoing Phase 1/2 investigator-sponsored clinical trial at Fred Hutch continue to support MB-106 as a viable CAR T cell therapy for B-NHLs and CLL. As of September 9, 2022, the interim data show:

• An overall response rate of 96% and complete response (CR) rate of 75% in a wide range of hematologic malignancies including follicular lymphoma (FL), CLL, diffuse large B-cell lymphoma, and Waldenstrom macroglobulinemia
• 12 patients have experienced CR for more than 12 months (10 ongoing); four patients with CR for more than 2 years and the longest patient with CR is at 33 months
• 6 patients with partial response (PR) improved to CR and all remain in ongoing CR
• All three patients previously treated with CD19 CAR T cell therapy have responded to treatment with MB-106
• A favorable safety profile for MB-106 as an outpatient therapy remains with no CRS or ICANS ≥ Grade 3
• CAR-T persistence results in deepening responses following initial 28-day assessments

“We are excited to broaden the evaluation of MB-106 with this multicenter clinical trial under Mustang’s IND. To date, the data from the initial, ongoing clinical trial at Fred Hutch continue to demonstrate a high rate of complete and durable responses,” said Mazyar Shadman, MD, MPH, Study Chair, Associate Professor and physician at Fred Hutch and University of Washington. “In addition, MB-106 has shown potential to treat patients in an outpatient setting and provide another immunotherapy option for patients treated previously with CD19-directed CAR T cell therapy.”

The six-center Phase 1/2 clinical trial is a three-arm study targeting CLL and B-NHL including FL, diffuse large B-cell lymphoma and mantle cell lymphoma. Included in the eligibility criteria are patients who have relapsed after treatment with CD19 CAR-T cell therapy. Additionally, the FL arm will evaluate other indolent histologies including Waldenstrom macroglobulinemia, a rare type of B-NHL for which the US FDA recently granted MB-106 Orphan Drug Designation. Since the Mustang-sponsored multicenter clinical trial is using the same lentiviral vector as the Fred Hutch-sponsored single-center trial, the FDA has allowed dose escalation to begin at a higher dose than what was originally conducted at Fred Hutch.

An estimated 287 patients are anticipated to be enrolled in the trial. All patients must have evidence of CD20 expression in both phases of the clinical trial. In Phase 1, escalating MB-106 dose levels will be tested independently in each arm using a 3+3 design. Patients will be enrolled in one of three arms, based on their primary diagnosis.

A total of up to 18 patients are anticipated to be treated in each Phase 1 arm, including six patients at the maximum tolerated dose, prior to proceeding to the Phase 2 portion of the study for each respective arm, where a total of up to 71 patients will participate in each independent arm. Safety of each dose level will be reviewed for each arm until the maximum tolerated dose has been reached and the recommended Phase 2 dose (RP2D) has been established for each arm. An assessment of the safety and tolerability of the dose will be made by the Safety Review Committee based on the data from the 28-day dose-limiting toxicity observation period.

In Phase 2, specific arms of relapsed or refractory CD20-positive B-cell NHL or CLL patients will be treated with MB-106 at the respective RP2D for each arm. Each arm will initially include up to 20 patients. Based on the results of the interim analysis, up to an additional 51 patients may be added to each of the arms.

Additional information about the trial can be found on clinicaltrials.gov using the identifier NCT05360238.

CD20 is a membrane-embedded surface molecule which plays a role in the differentiation of B-cells into plasma cells. The CAR T was developed by Mustang’s research collaborator, Fred Hutch, in the laboratories of the late Oliver Press, MD, PhD, and Brian Till, MD, Associate Professor in the Clinical Research Division at Fred Hutch, and was exclusively licensed to Mustang in 2017. The lentiviral vector drug substance used to transduce patients’ cells to create the MB-106 drug product produced at Fred Hutch has been optimized as a third-generation CAR derived from a fully human antibody. MB-106 is currently in a Phase 1/2 open-label, dose-escalation trial at Fred Hutch in patients with B-NHLs and CLL. The same lentiviral vector drug substance produced at Fred Hutch will be used to transduce patients’ cells to create the MB-106 drug product produced at Mustang Bio’s Worcester, MA, cell processing facility for administration in the multicenter Phase 1/2 clinical trial under Mustang Bio’s IND. It should be noted that Mustang Bio has introduced minor improvements to its cell processing to facilitate eventual commercial launch of the product. In addition, prior to commercial launch, Mustang Bio will replace the Fred Hutch lentiviral vector drug substance with vector produced at a commercial manufacturer. Additional information on these trials can be found at http://www.clinicaltrials.gov using the identifier NCT05360238 for the Mustang multicenter trial and NCT03277729 for the ongoing trial at Fred Hutch.

Mustang Bio, Inc. is a clinical-stage biopharmaceutical company focused on translating today’s medical breakthroughs in cell and gene therapies into potential cures for hematologic cancers, solid tumors and rare genetic diseases. Mustang aims to acquire rights to these technologies by licensing or otherwise acquiring an ownership interest, to fund research and development, and to outlicense or bring the technologies to market. Mustang has partnered with top medical institutions to advance the development of CAR T therapies across multiple cancers, as well as lentiviral gene therapies for severe combined immunodeficiency.  For more information, visit www.mustangbio.com.