Mustang Bio’s CAR-T MB-106 Achieves Responses in 9 of 10 Patients With Waldenstrom Macroglobulinemia

Mustang Bio’s and Fred Hutchinson Cancer Center (Fred Hutch)’s MB-106, an investigational CD20-directed autologous chimeric antigen receptor (CAR) T-cell therapy being evaluated in a single-center phase 1/2 clinical trial (NCT03277729) at Fred Hutch, demonstrated an overall response rate of 90% in the trial’s Waldenstrom macroglobulinemia (WM) cohort, which treated 10 patients in total.¹ The data were presented at the European Hematology Association (EHA) 2024 Congress, held June 13 to 16, both virtually and in Madrid, Spain.

The responses seen in the 9 patients included 3 complete responses (CRs), 2 very good partial responses, and 4 partial responses. The patient who did not respond showed stable disease. Mustang highlighted that 1 of the patients who achieved a CR has maintained their remission for 31 months and also pointed out that this patient had shown a rapid reduction in immunoglobulin M to the normal range, where it has since remained, after being treated with the CAR-T. The company noted that 1 of the patients has begun receiving another antiWM treatment after having received MB-106. It also stated that the trial allowed for outpatient treatment and that it had demonstrated feasibility in this regard.

In terms of safety, 9 of the 10 patients experienced cases of cytokine release syndrome ranging from grade 1 (n = 5) to grade 2 (n = 4) in severity. Immune effector cell-associated neurotoxicity syndrome occurred in only 1 patient, and the case was considered grade 1.

The group of 10 patients was heavily pretreated, having received a median of 9 prior lines of treatment. Prior lines of treatment included a Bruton's tyrosine kinase inhibitor (BTKi) for all patients and all patients’ disease had been refractory the BTKi.

“We are very encouraged by the safety and efficacy data generated in WM, along with improvements in the quality of responses over time, which demonstrates MB-106 CAR T-cell expansion and persistence,” Brian Till, MD, an associate professor and physician at Fred Hutch and University of Washington, said in a statement.¹

Analysts noted that Mustang’s stock had jumped by 347% in tandem with the announcement of these results by the company on June 17, 2024.² Active trading of the stock ($MBIO) also rose.

“This news brings with it heavy trading of MBIO stock today,” William White, an InvestorPlace writer, stated.² “That has more than 567 million shares changing hands as of this writing. This is well above its daily average trading volume of about 3.3 million shares.”

Notably, a few months ago, Mustang Bio announced that it would be pursuing the clinical evaluation of MB-106 in autoimmune disease.³ At the time of the announcement the company did not disclose any specific autoimmune diseases that it intends to target, but stated that it hopes to initiate a phase 1 investigator-sponsored clinical trial in Q4 of 2024. Along with Fred Hutch, the company is currently planning the trial, which will be considered a proof-of-concept study.

“Mustang is leveraging its expertise in developing cell therapies to explore a new frontier in patient care,” Manuel Litchman, MD, the president and chief executive officer of Mustang, said in a March 2024 statement.³ “MB-106’s observed safety profile, encouraging efficacy data, and our robust manufacturing capabilities have the potential to translate to improved outcomes for patients with autoimmune diseases. We believe an investigator-sponsored clinical trial is the fastest and most cost-effective way to embark on this program and aim to enroll the first patient in a phase 1 trial in the fourth quarter of this year to demonstrate clinical proof-of-concept. We are in discussions with Fred Hutch to determine the autoimmune indication(s) we plan to pursue in the first trial and look forward to sharing more details in the near future.”

REFERENCES
1. Mustang Bio announces favorable efficacy and safety data from complete waldenstrom macroglobulinemia cohort of phase 1/2 clinical trial of MB-106, CD20-targeted autologous CAR-T therapy. News release. Mustang Bio, Inc. June 17, 2024. Accessed June 18, 2024. https://ir.mustangbio.com/news-events/press-releases/detail/180/mustang-bio-announces-favorable-efficacy-and-safety-data
2. Why is Mustang Bio (MBIO) stock up 347% today?. News Article. William White, InvestorPlace. June 17, 2024. Accessed June 18, 2024. https://investorplace.com/2024/06/why-is-mustang-bio-mbio-stock-up-347-today/
3. Mustang Bio announces vision for CAR t-cell therapy platform expansion into autoimmune diseases. News release. Mustang Bio, Inc. March 28, 2024. Accessed June 18, 2024. https://ir.mustangbio.com/news-events/press-releases/detail/177/mustang-bio-announces-vision-for-car-t-cell-therapy