Neural Stem Cell Transplantation in Multiple Sclerosis Patients

This is a prospective, monocentric, national, therapeutic exploratory, phase I, not randomized, open label, not controlled, single dose escalation clinical trial. Each subject will participate in the study for approximately 96 weeks. Participation will include a screening evaluation between -28 and -7 days before the Advance Therapy Investigational Medicinal Products (ATIMP) administration. A follow-up with clinical visits will be performed from 1 to 96 weeks. The protocol will consist of a total of four treatment cohorts (TCs), labeled from A to D, each receiving a single escalating dose of allogenic fetal-derived human Neural Stem Cells (hNSCs) injected intrathecally, as it follows: * TC-A: 0.7x10\^6 ± 10% cells/kg of body weight; * TC-B: 1.4x10\^6 ± 10% cells/kg of body weight; * TC-C: 2.8x10\^6 ± 10% cells/kg of body weight; * TC-D: 5.7x10\^6 ± 10% cells/kg of body weight. The intrathecal injection of hNSCs will be performed in a hospitalized setting. The trial will start with TC-A and will go through the subsequent enrolment of patients to be included in TCs from B to D. Each cohort will consist of three patients at minimum. In case of safety issue the number in each TC will be increased to six patients. After the inclusion of the first patient of the TC the investigators will wait at least 14 days to treat the second patient. The same interval time will be used for all the following patient within the same TC. After the inclusion of all the planned patients within a TC and with no Dose Limiting Toxicity (DLT) within the TC, the investigators will wait at least 3 months before switching to the upper TC. In case of 1 DLT within the TC, the cohort will be extended to six patients. If another DLT will be observed, the current dosage will be considered excessive and the immediate lower dosage will be considered the Maximum Tolerated Dose (MTD). The safety monitoring board will review all safety date in the case of evaluated Adverse Event (AE) ≥ 3 "possibly related to human Neural Stem Cells" by investigators and in any case before the shifts between TCs. This approach will be repeated for every TC up to the end of the study. At the end of the total follow-up, a long term follow up is planned for all enrolled and treated patients in the study, in accordance with the national applicable laws and the international guidelines.