Study to Assess Safety and Efficacy of PRI-002 in Patients With MCI to Mild Dementia Due to Alzheimer's Disease (AD)

Inclusion Criteria:

1. Signed and dated written informed consent obtained from the subject and studycompanion in accordance with applicable regulations.

2. Male or female, aged 55 to 80 years, inclusive.

3. For female subjects: not being of child-bearing potential. This is defined as eitherpermanently sterilised (via hysterectomy, bilateral salpingectomy, or bilateraloophorectomy) or postmenopausal (defined as no menses for 12 months without analternative medical cause). For male subjects who are sexually active with women of child-bearing potential:agreeing to use acceptable contraception (using a condom or having demonstratedsuccessful vasectomy) and not donate sperm from Screening until 12 weeks after thelast dose of study treatment.

4. Body mass index (BMI) between 18.5 and 30.0 kg/m2, inclusive.

5. Diagnosed with MCI due to AD or mild dementia due to AD, according to the NIA-AAcriteria.

6. MMSE score of 22 to 30, inclusive.

7. Repeatable battery for the assessment of neuropsychological status - delayed memoryindex (RBANS-DMI) score ≤85.

8. CDR global score of 0.5 or 1 with a memory score ≥0.5.

9. Confirmation of AD diagnosis, by

• CSF biomarker profile reflecting AD, according to NIA-AA, or

• existing positive amyloid positron emission tomography (PET) evidence.

10. Fluency in local language and evidence of adequate intellectual functioning in theopinion of the investigator.

11. Having a reliable informant or caregiver who is willing and able to act as the studycompanion throughout the duration of the subject's participation. The subject andthe study companion must have frequent interaction (defined as a minimum of 6hours/week on average) according to subject's report.

Exclusion Criteria:

1. Unable to give informed consent in accordance with applicable regulations.

2. Diagnosed with moderate or severe dementia due to AD according to NIA-AA.

3. History or evidence of any other central nervous system (CNS) disorder(s) that couldbe interpreted as a cause of cognitive impairment or dementia.

4. History of known or suspected seizures, loss of consciousness, or significant headtrauma within 2 years before Screening.

5. History of known or suspected stroke or transient ischaemic attack (TIA) within 2years before Screening.

6. Evidence of other clinically significant lesions on brain MRI (Fazekas score 3).

7. History or presence of clinically evident cerebrovascular disease (diagnosis ofpossible, probable, or definite vascular dementia).

8. Other significant pathological findings on brain MRI (for example more than 10microhaemorrhages or a single macrohaemorrhage >10 mm at the greatest diameter).

9. Unstable medical, neurological, or psychiatric condition, or presence of majordepressive episode at Screening.

10. Life-time history of schizophrenia or history of uncontrolled bipolar disorderwithin 5 years before Screening.

11. Having a bleeding disorder that is not under adequate control (defined as a plateletcount <50000 or international normalised ratio [INR] >1.5). Participants who are onanticoagulant therapy (for example, warfarin), should have their anticoagulantstatus optimised and be on a stable dose for 30 days before Screening. Anticoagulanttherapy (e.g., clopidogrel bisulfate, carbasalate calcium 100 mg/day, or aspirin 325mg/day or less) is permitted provided this therapy does not represent acontraindication for a lumbar puncture and CSF sampling (if CSF sampling is requiredin the absence of historical PET evidence).

12. Having significant kidney disease as indicated by either of the following:

• Creatinine clearance (eGFR) ≤30 mL/min/1.73m2) as estimated using themodification of diet in renal disease (MDRD) method, or

• Creatinine ≥2 mg/dL.

13. Having impaired hepatic function as indicated by aspartate amino transferase (AST)or alanine amino transferase (ALT) >3-fold the upper limit of normal (ULN), or totalbilirubin >2-fold ULN, at Screening.

14. Known to be human immunodeficiency virus (HIV) positive.

15. Known to be hepatitis C or chronic hepatitis B positive.

16. Having any other clinically significant abnormalities in physical examination, vitalsigns, laboratory tests, MRI, or ECG at Screening or Baseline which in the opinionof the investigator requires further investigation or treatment or which mayinterfere with study procedures or safety.

17. Use of licensed symptomatic AD medication for less than 90 days or at a non-stabledose over the past 90 days at Baseline (for example acetylcholinesterase inhibitors,memantine, ginkgo).

18. Use of anti-Aβ monoclonal antibody therapy at Baseline.

19. Treatment with one of the following substances:

20. Typical antipsychotic or neuroleptic medication within 90 days before Screening (except for ≤1 mg risperidon, and ≤300 mg quetiapin).

21. Chronic use of opiates or opioids (including long-acting opioid medication)within 90 days before Screening.

22. Stimulant medications (amphetamine, methylphenidate preparations, or modafinil)within 30 days before Screening.

23. Chronic use of benzodiazepines, barbiturates, or hypnotics within 90 daysbefore Screening.

24. Contraindication to MRI. Patients with MRI compatible pacemakers may be allowed toenter the study.

25. Prior or current participation in a clinical trial testing active immunisationagainst Aβ or tau.

26. Participation in a clinical trial and having taken at least 1 dose of theinvestigational medicinal product (IMP), within 5 times the IMP half-life timebefore Baseline, unless confirmed as having been on placebo.