Inclusion Criteria:
Inclusion criteria are similar in the phase 1a (RESSTORE 1a, Toxicity study) and in the phase 1b (RESSTORE 1b, Dose-effect study).
* Male or female \> 18-year-old
* Hemispheric ischemic stroke (\> 1.5 cm on 2 imaging slices) (i.e. non "lacunar" stroke) Admitted to the stroke unit within the first 24h after stroke onset
* Patient must be included within 1st and 2nd day after stroke onset (signature of informed consent and randomization) (i.e. between 24 hours and 48 hours from stroke onset) and must be able to receive investigation treatment within the first week.
* NIHSS \> or equal to 7 including motor score (upper, lower limbs and hand) \> or equal to 3
* No decompressive craniectomy procedure planned or performed
* Patient able to follow a rehabilitation program
* Modified Rankin scale = 0 before stroke onset
* Obtained signed informed consent from patient or legally acceptable representative
* Negative pregnancy test for women of child-bearing age.
Non Inclusion Criteria:
Non-inclusion criteria are similar in the phase 1a (RESSTORE 1a, Toxicity study) and the phase 1b (RESSTORE 1b, Dose-effect study).
* Contraindication for MRI
* Coma (score of 2 or more on item 1a of the NIHSS related to awareness)
* Evidence on neuroimaging (CT or MRI) of a brain tumour, cerebral oedema with midline shift and a clinically significant compression of ventricles, cerebellar or brainstem infarction, or subarachnoid haemorrhage, or intracerebral parenchymal hematoma (petechial small haemorrhages are NOT a non-inclusion criteria)
* Severe leucoariosis
* Previous stroke
* Active endocarditis, pneumonia, AIDS, active hepatic disease due to HBV or HCV (a controlled infection is NOT a non-inclusion criteria)
* Active inflammatory and/or auto-immune diseases (such as Crohn disease, lupus, rheumatoid polyarthritis, renal or liver immune pathology)
* History of cancer
* Pre-existing dementia
* A health status, any clinical condition (eg, short life expectancy, and coexisting disease) or other characteristic that precludes appropriate diagnosis, treatment, or follow-up in the trial
* Surgical or endovascular procedure planned in the following 3 months
* Pregnancy / Breast feeding (women of childbearing age should have a negative pregnancy test prior to inclusion)
* Patients who are participating in another therapeutic trial or who have previously participated in a biotherapy trial
* Non-membership to a social security scheme
* Inability or unwillingness of the individual or their legal guardian/representa tive to provide written informed consent, according to national regulations.
