The primary purpose of this study is to evaluate the safety and the efficacy of (Human Umbilical Cord-Derived Mesenchymal Stem Cells) UCMSCs for patients with Alzheimer's disease (AD).

Study Type: Interventional Study Design: Treatment, Parallel Assignment, Double Blind (Subject, Outcomes Assessor), Randomized, Safety/ Efficacy Study Official Title: Multicenter, Randomized, Double-blind, Placebo Controlled Trial of UCMSCs in Subjects With Alzheimer's Disease

Inclusion Criteria:

• Ages 50 to 80, male and female.
• A diagnosis of probable AD and Mixed Dementia according to the criteria of the NINCDS-ADRDA
• Treatment with other cholinesterase inhibitors, such as a stable dose of donnepiazide tablets (5mg/ day or 10mg/ day) or the use of heavy tartaric acid karbalin capsules, is currently being used.
• MMSE score between 10 and 26.
• Voluntarily participating subject who sign the Inform Concent

Exclusion Criteria:

• Caused by other reasons of dementia (vascular dementia, infectious disease of the central nervous system (such as HIV, syphilitic dementia), g - she's disease, Parkinson's disease, Lou gehrig's disease, huntington's disease DLB, traumatic brain dementia, other physical and chemical factors (such as: drug poisoning, alcoholism, carbon monoxide poisoning and other dementia), important body disease (such as hepatic encephalopathy, pulmonary encephalopathy dementia), intracranial placeholder lesions, endocrine system disease, such as thyroid disease, parathyroid disease), and vitamins and other causes of dementia)
• The Hamilton depression scale (HAMD) score > 17, or patients with a history of depression or other psychiatric or psychiatric disorders.
• The Hachinski ischemic index scale (HIS) scored > 4.
• The brief intelligence status examination scale (MMSE) score of 10 patients.
• Liver function (ALT, AST) exceeded the normal range limit of 1.5 times, SCr exceeded normal range upper limit, white blood cell count < 4.0 x 109/L or platelet < 100 x 109/L, hemoglobin < 100g/L.
• Patients with type 1 diabetes, obstructive pulmonary disease (copd) or asthma, vitamin B12 or folate deficiency patients, not control good digestion, liver, kidney, endocrine and cardiovascular system diseases (especially sick sinus syndrome and conduction block), patients with HIV/AIDS, syphilis, active tuberculosis, etc.
• A person with cancer or a history of cancer.
• People with a clinically significant history of stroke, who have had a seizure or a head injury in the past two years, have caused the disorder.
• There is a history of congestive heart failure or a history of myocardial infarction, and a blood disease in two years.
• Drug clinical trials were performed within 3 months of screening.
• Anti-ad agents are being used in addition to the programme requirements.
• The use of stem cell therapy in half a year.
• People with history of alcoholism and substance abuse, allergies, or history of allergies.
• Patients who had been hospitalized for more than 3 months before screening. of allergies.
• The researchers think it is inappropriate to participate in this clinical trial.