Mustang Bio Announces Updated Results From Waldenstrom Macroglobulinemia Cohort of Ongoing Phase 1/2 Clinical Trial of MB-106, CD20-Targeted Autologous CAR T Therapy

Mustang Bio, Inc. recently announced that updated data from the ongoing Phase 1/2 clinical trial of MB-106, a CD20-targeted, autologous CAR T cell therapy, show a favorable safety and efficacy profile in patients with Waldenstrom macroglobulinemia (WM), a rare form of blood cancer. MB-106 is being developed in a collaboration between Mustang and Fred Hutchinson Cancer Center (Fred Hutch) to treat patients with relapsed or refractory B-cell non-Hodgkin lymphomas (B-NHLs) and chronic lymphocytic leukemia (CLL).

The updated results from the single-institution Phase 1/2 clinical trial were presented during a poster session at the European Hematology Association 2023 Hybrid Congress (EHA2023) by Mazyar Shadman, MD, MPH, Associate Professor and physician at Fred Hutch and University of Washington.

“As we continue to evaluate MB-106 in this single-institution study, we’re encouraged by its potential to become an outpatient treatment option for WM and other B-cell malignancies, including indolent and aggressive non-Hodgkin lymphomas,” said Dr. Shadman. “We have observed ongoing responses to MB-106 with improvements in the quality of response over time, along with a favorable safety profile.”

All six patients in the study were previously treated with Bruton’s tyrosine kinase inhibitors (BTKi), and their disease continued to progress while on BTKi’s. Overall, 83% (5/6) of the patients treated with MB-106 responded to treatment, including 2 complete responses, 1 very good partial response, 1 partial response, and 1 minor response. In addition, 1 patient experienced stable disease. One of the patients who achieved a complete response has remained in remission for 22 months, with an immunoglobulin M (IgM) level that decreased rapidly to the normal range after treatment with MB-106 and has remained normal since. No patient has started additional anti-WM treatment after being treated with MB-106. From a safety perspective, cytokine release syndrome (CRS) occurred in five patients: two patients with grade 1 and three patients with grade 2. One patient experienced grade 1 immune effector cell-associated neurotoxicity syndrome (ICANS). No grade 3 or 4 CRS or grade 2, 3 or 4 ICANS has been observed.

Manuel Litchman, MD, President and Chief Executive Officer of Mustang, commented “MB-106 has the potential to fill a significant unmet need, as there are currently no CAR T treatments for WM approved by the US FDA. The MB-106 data from the Phase 1/2 clinical trial taking place at Fred Hutch continue to be encouraging for WM and other B-NHLs. The positive data from this study and the FDA Orphan Drug Designation MB-106 received for WM support the treatment of patients with WM in the Phase 1 portion of our multicenter Phase 1/2 clinical trial which is underway and also support a fast-to-market Phase 2 strategy for this indication. We plan to report initial clinical data from the multicenter program shortly.”

For more information on the clinical trials, please visit www.clinicaltrials.gov using the identifier NCT05360238 for the multicenter trial and NCT03277729 for the ongoing trial at Fred Hutch.

Scientists at Fred Hutch played a role in developing these discoveries, and Fred Hutch and certain of its scientists may benefit financially from this work in the future.

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, and 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 is being 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 that is now open to enrollment 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 the trials can be found at http://www.clinicaltrials.gov using the identifier NCT05360238 for the multicenter trial and NCT03277729 for the ongoing trial at Fred Hutch. Mustang Bio has entered into an Asset Purchase Agreement pursuant to which it has agreed to sell, subject to the satisfaction of certain conditions, its leasehold interest in its cell processing facility and expects to enter into a manufacturing services agreement with the prospective purchaser to provide for the continued production of the MB-106 drug product. For additional information, please refer to the Current Report on Form 8-K filed by Mustang Bio with the U.S. Securities and Exchange Commission (SEC) on May 22, 2023.

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 difficult-to-treat cancers 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. Mustang’s common stock is registered under the Securities Exchange Act of 1934, as amended, and Mustang files periodic reports with the SEC. Mustang was founded by Fortress Biotech, Inc. (Nasdaq: FBIO). For more information, visit www.mustangbio.com.