Safety and Tolerability of Wharton's Jelly-Derived Mesenchymal Stem Cells for Patients With Duchenne Muscular Dystrophy: A Phase 1 Clinical Study

Major Points and Findings:

Among published studies, this small Korean trial comes closest to the kind of cells used at our clinic. Donor umbilical cord (Wharton’s jelly) mesenchymal stem cells were given through a vein to boys with Duchenne muscular dystrophy (DMD). The study was a regulated phase 1 trial, approved by the Korean Ministry of Food and Drug Safety and run at Samsung Medical Center in Seoul.

Six boys were enrolled, each given a single infusion, and followed for 12 weeks. There were no serious adverse events and no dose-limiting toxicity. Functional tests at 12 weeks showed no significant change, and on average walking ability and motor scores declined. The authors state that the results were insufficient to show efficacy. There was no control group.

Aim:

To determine the safety, tolerability and dose of EN001, an allogeneic early-passage Wharton’s jelly-derived mesenchymal stem cell product, in children with DMD. Efficacy was exploratory only.

Methods:

The trial used an open-label dose escalation (“3+3”) design. Three boys received the low dose, and a safety review committee examined their data before three more received the high dose. Dose-limiting toxicity was defined as any adverse event of grade 3 or higher within 2 weeks of the infusion.

Seven boys were screened and six enrolled between January and October 2022. Inclusion criteria:

• Male, aged 2 to 18 years
• A confirmed DMD mutation and clinical signs of DMD (proximal weakness, waddling gait, Gowers’ sign)
• On a stable dose of systemic corticosteroids expected to stay the same throughout

Boys were excluded for a left ventricular ejection fraction below 50% on echocardiography, need for respiratory assistance or tracheostomy ventilation, gene therapy or ataluren within the previous 24 weeks, or clinically significant abnormal screening blood tests.

The participants were aged 10.0 to 15.8 years and all were still walking, with baseline six-minute walk distances of 231 to 346 metres and North Star Ambulatory Assessment (NSAA) scores of 8 to 28 out of 34. Five were on deflazacort and one on prednisolone.

One batch of cells from a single donated umbilical cord was expanded for three passages (about 20 days) in medium containing 10% fetal bovine serum, then frozen in liquid nitrogen at 5 million cells per 10 mL bag. Release tests covered sterility, mycoplasma, endotoxin, cell count, viability and surface markers (positive for CD44, CD73, CD90, CD105, CD166 and negative for CD11b, CD14, CD19, CD34, CD45, HLA-DR).

The low dose was 500,000 cells per kg. The high dose was 2.5 million cells per kg, the dose that had worked in the mdx mouse. In practice the high-dose boys received 140 to 201 mL of cell suspension.

Bags were thawed in a 37°C water bath and infused intravenously within 10 minutes. Premedication was at the investigator’s discretion and consisted of hydrocortisone 1 to 2 mg/kg, lorazepam 0.1 mg/kg, ondansetron and chlorpheniramine. Vital signs, oxygen saturation and ECG were monitored throughout.

Adverse events and serum creatine kinase (CK) were recorded at each of seven visits. Spirometry, dynamometer strength of knee extensors and elbow flexors, NSAA and the six-minute walk test were done at baseline and week 12. Interim data to 36 weeks are in the supplement. Follow-up to 5 years is planned.

Results:

Safety: There were 18 adverse events in 12 weeks, 6 in the low-dose group and 12 in the high-dose group. Every boy had at least one. All were grade 1 and none was serious.

• Infusion-site redness, pain and swelling occurred in 2 of 3 boys in the high-dose group and in none in the low-dose group. These settled within a day.
• Headache in 3 boys (1 low dose, 2 high dose). One boy was bothered by the smell of the product for about a day.
• Others were dyspepsia, chest pain and tenderness (one boy each, low dose), bone pain (one boy, high dose), SARS-CoV-2 infection in 2 boys and a cold in 2.
• No fever, blood pressure change, rash, breathing difficulty or shock during any infusion.
• Three more grade 1 events appeared by 36 weeks (21 in total). No delayed events were attributed to the cells.
• Echocardiograms in four boys at 6 to 12 months were normal.

Motor function: Mean NSAA score fell by 3.33 points in the low-dose group and by 3.00 points in the high-dose group over 12 weeks. Individual scores went from 18 to 15, 25 to 17, 18 to 19, 8 to 5, 28 to 22, and 14 to 14. One boy gained a point, one stayed the same and four declined, one of them by 8 points.

Six-minute walk distance fell by an average of 13.8 metres (low dose) and 47.4 metres (high dose). One boy of six walked further than at baseline.

Knee extensor strength fell by 0.70 lb in the low-dose group and rose by 0.88 lb in the high-dose group. Four of six boys had some increase. Elbow flexor strength declined slightly through 36 weeks.

Breathing: Percent-predicted forced vital capacity rose by 6.67% (low dose) and 1.00% (high dose), neither statistically significant. One boy could not do the week-12 test because of bone pain. Inspiratory and expiratory pressures did not change.

CK: Levels trended down to week 12, without statistical significance, and returned to baseline afterwards in all boys. CK rose sharply in some boys while they had COVID-19. The authors state they could not tell whether the dip was a treatment effect or normal fluctuation.

Conclusions:

The authors conclude that a single intravenous dose of these cells was safe and well tolerated in six boys with DMD, and that efficacy could only be established by larger, randomised trials with repeated dosing. They have registered a multicentre, randomised, double-blind, placebo-controlled phase 1/2 trial (NCT06328725).

The limitations they state are a single dose, a very small sample, 12 weeks of follow-up where most DMD trials run 1 to 2 years, and COVID-19 infections that disturbed the measurements. In addition, there was no control group and boys aged 10 to 15 would be expected to decline anyway, so the functional results cannot show whether the cells made a difference in either direction.

Background Information:

The authors do not claim the cells turn into muscle. Based on their mouse work, they propose that the cells release protective factors: XCL1 (lymphotactin), which they report protects muscle cells from programmed cell death, and MMP-1, which they report reduces muscle scarring. They argue that cells at passage 3 are more potent and less prone to ageing in culture than the later-passage cells used in many products, which is why their dose is lower than in other MSC trials.

The authors note that transient fever is the most common side effect of cell infusions and attribute it partly to the carrier fluid. They used their own xeno-free formulation and recorded no fever in the six boys. With so few participants, no conclusion can be drawn from this observation.

The cells were supplied by ENCell Co., Ltd., the developer of the product. The paper states that the sponsor had no role in interpreting the data or writing the report, and the authors declared no conflicts of interest. Funding came from Korean government health research grants and Samsung Medical Center.