Safety and Exploratory Efficacy Study of NEUROSTEM® Versus Placebo in Patients With Alzheimer's Disease

1 stage Inclusion Criteria: 1. Korean male or female at 50 -85 years of age 2. Diagnosis of Probable Alzheimer type according to NINCDS-ADRDA criteria at Visit 1 (Screening) 3. Korea Mini-Mental State Examination (KMMSE) score of 18 - 26 at Visit 1 (Screening) 4. Positive for Amyloid on PIB-PET or Florbetaben PET 5. A subject who is informed of the clinical trial and signs a consent form (if unable to sign, a consent from a legally acceptable representative is required) 2 stage Inclusion Criteria: 1. Korean male or female at 50 -85 years of age 2. Diagnosis of Probable Alzheimer type or mild cognitive impairment due to Alzheimer's disease (stage A) according to NIA-AA criteria at Visit 1(Screening) 3. Korea Mini-Mental State Examination (KMMSE) score of over 18 at Visit 1 (Screening) 4. Positive for Amyloid on Florbetaben PET 5. A subject with neurodegeneration (mild atrophy of the brain) as confirmed by MRI 6. A subject who is informed of the clinical trial and signs a consent form (if unable to sign, a consent from a legally acceptable representative is required) Exclusion Criteria: 1. Concurrent mental disorder (such as schizophrenia, depression, bi-polar diseases or others) aside from dementia 2. Concurrent dementia as a result of other neurodegenerative disorders (due to infectious disease of the central nervous system such as HIV, syphilis), head injury, Creutzfeld-Jacob disease, Pick's disease, Huntington's disease, or Parkinson's disease 3. Diagnosis of severe white matter hyperintensitivity (WMH) according to CREDOS (Clinical REsearch Center for Dementia of South Korea), which is defined as ≥ 25mm of the deep white matter and ≥ 10mm of the periventricular capping/banding in lengths 4. History of stroke within 3 months prior to study enrollment 5. Severe liver disorder (equivalent to double the normal values of ALT and AST) at Visit 1 6. Severe kidney disorder (serum creatinine ≥1.5mg/dL) at Visit 1 7. Pregnant or lactating females 8. Abnormal Laboratory findings at Visit 1 * Hemoglobin \< 9.5 g/dL for male and \<9.0 g/dL for female * Total WBC Count \< 3000/mm3 * Total Bilirubin \>= 3 mg/dL 9. Suspected active lung disease based on chest X-ray at Visit 1 10. Woman of childbearing age who refuses to practice medically acceptable contraceptive method (post menopausal patient with no menstruation for at least 12 months is considered as infertile) 11. History of screening failure for the clinical trial of NEUROSTEM® in the past 6 months 12. Participation in another clinical trial in the past 3 months prior to the beginning (Week 0) of this clinical trial 13. Bleeding disorder (abnormal blood coagulation test result (i.e. platelet count of \< 150,000/mm3, PT ≥ 1.5 INR, or aPTT ≥ 1.5 x control anti-coagulant or anti-platelet, without anticoagulant or anti-platelet therapy) 14. Diagnosis of cancer (of any body system, including brain tumor) 15. Substance/alcohol abuse 16. Contraindicated for any of the tests performed during the clinical trial period (for example, MRI, CT, PET) 17. A subject in whom Ommaya reservoir insertion is considered difficult 18. Whom the principal investigator considers inappropriate for participation in the study due to any reasons other than those listed above