DT-DEC01, a cell therapy under development, may be a potential treatment for all individuals with Duchenne muscular dystrophy (DMD), regardless of their genetic mutation, age, or whether they are still able to walk, according to findings presented by Maria Siemionow, MD, PhD, DSc, at the 2025 Muscular Dystrophy Association Clinical & Scientific Conference.
About the treatment
DT-DEC01 works by combining healthy donor muscle cells with the patient’s own muscle cells. These fusion-blended cells, known as chimeric cells, can then produce normal dystrophin—the protein needed to maintain muscle strength, which individuals with DMD lack.
Unlike other treatments, the therapy does not require immune-suppressing medications because the body does not recognize the donor cells as foreign. The chimeric cells “tweak the immune system in such a way—it’s almost like a Trojan horse approach where the [donor] cells . . . are presented to the recipient in the context of ‘self’. So, the recipient is not rejecting the cells but considering them as ‘self,’ ” explained Dr. Siemionow, professor and director of microsurgery research at the University of Illinois at Chicago.
In addition to delivering dystrophin, the therapy also reduces inflammation, slows further muscle damage, and replaces scar-like tissue that forms as the disease progresses with healthier muscle tissue, according to her presentation.
“The therapy represents a universal therapy for all Duchenne patients regardless of gene mutation, age, or ambulatory stage,” Dr. Siemionow said. “It can be used as a standalone or as a . . . complimentary [therapy] . . . where redosing is not possible or sensitization occurs.”
About the study
The study presented by Dr. Siemionow tested DT-DEC01 in three boys with DMD, ages 15, 11, and 16, each with a different genetic mutation (exon 48-50 deletion, exon 52 deletion, and a nonsense mutation, respectively). Treatment was administered as a single injection into the bone without immune-suppressing drugs.
Researchers monitored side effects, as well as changes in muscle strength, heart and lung function, and daily activity levels over two years.
Safety findings
There were no serious side effects, adverse events, or immune reactions related to the therapy in any of the patients during the two-year study period, according to researchers.
Dr. Siemionow emphasized the significance of this, stating, “The long-term clinical, safety, and functional improvements are particularly significant in older, nonambulatory patients — a population with no current satisfactory treatment options.”
Efficacy findings
All three patients experienced improvements in various aspects of muscle function, heart and lung health, and daily movement.
Patient One (age 15, exon 48-50 deletion):
- Heart function improved by 12% over 18 months.
- Muscle strength improved in multiple areas: deltoid (round part of shoulder; 53%), biceps (23%), inner thighs (46%), and back of the lower leg (33%) over various time points.
- Arm movement increased significantly (185% in 1 year) but stabilized at 9% at 18 months.
- Breathing function improved by 28% in 1 year, stabilizing at 17% over two years.
- Upper body mobility increased 5% over 18 months and remained stable through two years.
- Grip strength improved by 6% within 6 months and remained stable over two years.
Patient Two (age 11, exon 52 deletion):
- Heart function improved by 17% in 1 year.
- Muscle strength improved in the deltoid (19%), biceps (51%), inner thighs (4%), and back of the lower leg (20%) over various time points.
- Arm movement increased dramatically, improving 93% in 1 year, 360% in 18 months, and 1150% in 2 years.
- Breathing function improved by 71% at 18 months, stabilizing at 59% through two years.
- Upper body mobility improved 15% in 1 year, stabilizing at 5% by 18 months.
- Grip strength improved by 22% over 2 years.
Patient Three (age 16, nonsense mutation):
- Heart function improved by 11% in 1 year.
- Muscle strength improved in the deltoid (49%), biceps (29%), inner thighs (31% in 3 months), and back of the lower leg (78% in 1 year).
- Arm movement remained mostly unchanged after 1 year.
- Breathing function increased 900% in 1 month, stabilizing at 850% over 1 year.
- Upper body mobility improved by 12% in 3 months, stabilizing at 6% over 1 year.
- Grip strength improved by 34% over 1 year.
Dr. Siemionow also highlighted the significance of these results, particularly for older patients. “Improvements in systemic functional tests such as echocardiography (heart function) and spirometry (breathing) are specifically encouraging at this advanced stage of the disease where with disease progression, typically the cardiovascular declines rather than improving, which we have observed,” she said.
Future studies
Development of DT-DEC01 is expected to move forward with additional clinical trials to further evaluate its safety and effectiveness.
“These results are promising and support continuation of assessment of the therapy’s safety and efficacy under a phase 1/2 clinical trial that we have received clinical trial application approval from [European Union for],” Dr. Siemionow said.
