First-In-Human Application of Human Umbilical Cord-Derived Extracellular Vesicles in Tethered Spinal Cord Release Surgery

Major Points and Findings:

The paper is a case report of one child. A 2-year-old girl with spina bifida had surgery in Germany to release a tethered spinal cord, and during the operation the surgeons applied extracellular vesicles (EVs) harvested from umbilical cord mesenchymal stromal cells directly onto her spinal cord. EVs are not cells. They are tiny membrane-wrapped packages that cells release, thought to carry much of the anti-inflammatory and anti-scarring signal that mesenchymal stromal cells produce.

The product could be applied, and no adverse event occurred in six months. No benefit was shown, and the girl’s leg function was unchanged. A single case without a comparison cannot establish more, as the authors state repeatedly. We include the report because it describes the first human use of an umbilical cord cell-derived product placed intrathecally in a child with spina bifida. It also addresses tethering and scarring of the cord after the original repair, a problem many families face later.

Aim:

To test whether applying umbilical cord MSC-derived EVs (UC-MSC-EVs) onto the spinal cord during tethered cord release surgery is technically feasible, with the longer-term hope of reducing scarring inside the dura and further nerve damage.

Methods:

The girl’s open neural tube defect was diagnosed before birth. It was closed by microsurgery on the day she was delivered by caesarean section at the University Hospital Leipzig, and she needed a ventriculo-peritoneal shunt at 6 weeks of age. Routine MRI at one year showed three problems at the repair site, namely a growing dermoid inclusion tumour inside the cord, a tethered cord, and a fluid cavity (syringomyelia) extending through the lumbar and thoracic cord. Her motor function had not deteriorated and remained at functional level L3. The team judged the risk of future deterioration to be high and recommended surgery.

The treatment was given outside a clinical trial, as an “individual healing attempt” (single named-patient use). It was reviewed by the internal review board of the University Hospital Salzburg, and the parents gave written consent for the experimental intrathecal application.

Product: The EVs were manufactured under Good Manufacturing Practice at the Paracelsus Medical University in Salzburg, Austria, which holds a licence to produce MSC-EVs for phase 1 to 3 trials.

• Source: umbilical cord MSCs from a single donor, banked as master and working cell banks and tested to European Pharmacopoeia standards.
• Cells were grown with 5% pooled human platelet lysate and no animal-derived substances. At harvest they were at passage 8, about 17 population doublings.
• EVs were collected from serum-free medium after 24 hours, concentrated by tangential flow filtration through a 100 kDa filter, sterile filtered at 0.22 micrometres and stored at -80°C in 2 mL vials.
• The batch used contained 6.5 × 10¹⁰ particles per mL with a mean diameter of 130.7 nm and 0.768 mg of protein per mL. It carried the expected EV markers (CD9, CD63, CD81) and MSC markers (CD29, CD44, CD49e, CD73), and was negative for HLA-ABC and HLA-DR. The cytokines IL-1 beta, IL-6, IL-8, IL-10 and TNF-alpha were not detected. Endotoxin was 0.83 IU/mL. Biological activity was confirmed with a CD73 enzyme assay.

Operation: Surgery was performed prone with continuous neurophysiological monitoring. The surgeons found severe tethering from dermoid tissue inside the neural tube and an adjacent lipoma attached to the dural sac, and removed both. The EVs were then applied in these steps:

• 1.0 mL of EV fluid was applied to the open placode and into the syrinx cavity
• the placode was closed with 8-0 sutures
• 0.5 mL was applied onto the sutured placode
• 0.5 mL was placed in the dural sac as it was closed watertight

The total intrathecal volume was 2.0 mL, roughly 1.3 × 10¹¹ particles by our calculation from the stated concentration.

Results:

• Monitoring showed no worsening during surgery. Motor responses were present in all segments, including the sphincter, and direct stimulation showed working motor nerve roots down to S2.
• The postoperative course was uneventful and the girl went home after 7 days.
• MRI on day 5 showed a good release of the cord, no swelling of the cord and a smaller syrinx.
• No adverse events occurred in six months of follow-up.
• Motor function did not change and remained at level L3. The neuropaediatric examination at six months noted slightly improved sensation and temperature regulation in both legs.

The abstract says the neurological deficit “remained unchanged”. The case description in the body adds the slight sensory improvement. Both agree that movement did not improve.

Conclusions:

The authors conclude that direct application of UC-MSC-EVs during spina bifida surgery is feasible and should be tested in animal models and in phase I/II trials. Whether it brings any lasting neurological benefit “needs to be studied thoroughly in randomised controlled trials”.

The authors list several limitations:

• There was no control and no randomisation. The good MRI result and stable function are what successful untethering surgery alone can produce. The authors write that it is impossible to draw any definitive conclusion about benefit.
• The appropriate dose is unknown. The amount was based on earlier experimental work and given once. Whether more, or repeated dosing by another route, would be better or riskier is not known.
• Six months of follow-up is too short. Scarring and re-tethering develop over years, and delayed adverse effects cannot be excluded.
• Response may vary. Donor, passage number and isolation method on the manufacturing side, and immune status on the patient side, could all change the effect. No immune reaction was seen in this child, but a theoretical risk remains.

The authors declare no conflicts of interest.

Background Information:

Tethering: After spina bifida repair, scar tissue can anchor the cord to the dura. As the child grows the cord is stretched, and function can be lost. The paper quotes follow-up of the MOMS trial showing symptomatic tethered cord needing surgery in as many as 27% of children repaired before birth and 15% of those repaired after birth, with inclusion cysts in the placode also more common after prenatal repair (11% against 3%). In a Danish series, 45 of 166 patients needed untethering, most often for progressive spinal deformity (40%), worsening walking (38%) or worsening bladder or bowel function (32%). Untethering itself carries about a 15% risk of re-tethering from new scarring. There is currently no treatment that prevents this scarring other than careful surgical technique.

Rationale for EVs: Laboratory and animal studies cited by the authors show MSC-derived EVs dampening inflammation and scarring after spinal cord injury and acting on microglia, the immune cells of the nervous system. The same group’s UC-MSC-EVs had been used once before in a person, in the inner ear during cochlear implant surgery, with a satisfactory safety profile.