This is a multicenter, doble blind, placebo controlled clinical trial to asses de safety and efficacy of intravenous administration of alogenic adipose tissue-derived mesenchymal stem cells in the first four days from acute ischemic stroke.

Two spanish hospitals with teams experienced in stroke management will participate in this study, recruiting a total of 30 patients between them both. After confirming that patients fulfill the inclusion criteria and none of the exclusion criteria, informed consent will be signed and randomization will take place (1:1). There are two different groups of treatment; the first group will be treated with intravenous alogenic adipose tissue-derived stem cells (at a concentration of one million cells per kg) within the first four days from stroke onset, the second group will be treated will an intravenous placebo solution. Follow-up will last for 24 months during which safety issues such as adverse events and neurological and systemic complications will be assessed at 24 hours, 7 days and 3, 6, 12,18 and 24 months after treatment. Neurological disability using the modified Rankin Scale and National Institute of Health Stroke Scale will also be registered in every scheduled visit. Biochemical markers of tissue repair (GM-CSF, BDNF, VEGF, TGF-1, GFAP, MBP, MMP-3) as well as extracellular vesicles will be extracted on baseline visit as well as 7 days and 3 months after treatment.

Inclusion Criteria:

• Ischemic stroke patients > 18 years old
• Patients must be able to be treated within the first 4 days (+/- 1) from acute stroke symptoms onset. If the time of symptom onset is unknown, this shall refer to the last time the patient was observed as asymptomatic.
• A computed tomography (CT) or magnetic resonance imaging (MRI) scan compatible with the clinical diagnosis of acute non-lacunar IS in the region of the middle cerebral artery (with cortical or subcortical involvement).
• A score on the National Institute of Health Stroke Scale (NIHSS) of 8-20, with at least two of these points in sections 5 and 6 (motor deficit) at the time of inclusion. NIHSS evaluation for screening of these patients will take place after finalization of reperfusion therapies (if they have been performed) providing that the clinical condition of the patient is stable with no prevision of immediate recovery. A measurable focal neurologic disabilty must persist to the time of treatment.
• A prestroke score on the Modified Rankin Scale (mRS) ≤1 (no significant disability).
• Female subjects non-child bearing potential. Female subjects who are of non-childbearing potential are defined as meeting at least 1 of the following criteria:

Have undergone a documented hysterectomy and/or bilateral oophorectomy; Have medically confirmed ovarian failure; or Achieved postmenopausal status, defined as follows: cessation of regular menses for at least 12 consecutive months with no alternative pathological or physiological cause.

• Female subjects of child-bearing potential need a negative pregnancy test and must agree to use adequate contraception for the duration of the study (from screening through the final of the study). The following types of contraception are considered adequate provided they are locally authorized for use: oral, transdermal, or injectable (depot) estrogen and/or progestogen, selective estrogen receptor modulator therapy, intrauterine contraceptive device, double barrier method (e.g., condom and diaphragm or spermicidal gel) or vasectomy.
• Signed informed consent

Exclusion Criteria:

• Comatose patients; patients with a score of 2 or more on item 1a of the NIHSS related to the degree of awareness.
• Evidence on neuroimaging of brain tumour, cerebral oedema with midline shift and a clinically significant compression of ventricles, cerebellar or brainstem infarction and intraventricular, intracerebral or subarachnoid haemorrhage. Small petechial haemorrhages are not exclusion criteria.
• Current drug or alcohol use or dependence
• Active infectious disease, including human immunodeficiency virus, hepatitis B, and hepatitis C. A controlled infection is not an exclusion criterion.
• Pre-existing dementia.
• A health status, any clinical condition (eg, short life expectancy, and coexisting disease or a surgical or endovascular planned procedure) or other characteristic that precludes appropriate diagnosis, treatment, or follow-up in the trial.
• Patients who are participating in another clinical trial.
• Inability or unwillingness of the individual or their legal guardian/representative to provide written informed consent.

Data will be available from the corresponding author on reasonable request, considered compliant General Data Protection Regulation and the data-sharing agreement is approved by the relevant Spanish authorities. Upon study finalization, anonymized individual patient data will be available on a public repertoire of the Community of Madrid.

Treatment and placebo solutions have identical appearance. Protocols will be designed to ensure that the physician evaluating patient safety and efficacy outcome as well as laboratory analysis, will not have access to the randomisation codes.