Neural stem cell transplantation in progressive multiple sclerosis: STEMS study long-term outcomes

Background To evaluate the long-term safety and potential neuroprotective effects of human fetal neural precursor cell transplantation in individuals with progressive multiple sclerosis.Methods This retrospective observational study assessed long-term follow-up data (median 5.7 years) from participants in a first-in-human phase I trial (NCT03269071) investigating neural cell transplantation in progressive multiple sclerosis. Clinical and radiological available data were collected and compared to baseline values and reference populations.Results Long-term follow-up data were available for 11 of 12 patients. No serious adverse events related to cell transplantation occurred, confirming long-term safety. Although physical disability progressed over time, cognition remained stable compared to baseline. Five patients developed new T2-hyperintense brain lesions without associated contrast enhancement. Long-term gray matter atrophy rates were lower than those observed during the initial two years post-transplantation. Rates of gray and white matter atrophy approximated those of age-matched healthy individuals and patients with early-stage multiple sclerosis, with a trend for a lower atrophy rate compared to a control cohort with progressive disease. These structural findings were consistent with stable levels of circulating biomarkers of neurodegeneration.Conclusions The findings support the long-term safety of fetal neural cell transplantation in progressive multiple sclerosis. Although exploratory in nature, the stability of cognitive function, reduced brain atrophy, and consistent biomarker profiles support the hypothesis of a possible neuroprotective effect that warrants further investigation in a controlled clinical trial setting.