The Purpose of This Study is to Evaluate the Safety and Tolerability of X/T+X-EC in Participants With Alzheimer's Disease Who Are Currently Treated With Lecanemab.

Exclusion Criteria

• •1\. Risk of suicidal behaviour during the study as determined by the investigator's clinical assessment and/or C-SSRS (baseline version) as confirmed by the following:
• •a. Answers "Yes" on items 4, or 5 (C-SSRS-ideation) with the most recent episode occurring within the 2 months before screening or, b. Answers "Yes" to any of the 5 items (C-SSRS-behavior) with an episode occurring within the 12 months before screening 2. Any current primary psychiatric diagnosis (e.g., major depression, schizoaffective disorder, bipolar disorder) or severe psychiatric symptoms (e.g., hallucination, agitation or delusions) if, in the judgment of the investigator, the psychiatric disorder or symptom is likely to confound interpretation of treatment effect, affect cognitive assessment, or may impact the participants ability to complete the study.
• •3\. Participants with history of schizophrenia or other chronic psychosis. 4. Any prior or on-going uncontrolled/unstable psychiatric disorder that could interfere with study assessments.
• •Medical Conditions 5. History or presence of clinically significant cardiovascular (e.g., untreated or unstable hypertension, clinically significant tachycardia), pulmonary, renal, hematologic, gastrointestinal (e.g., obstructive disorders \[including conditions that may decrease GI motility, such as ulcerative colitis, intestinal atony, and myasthenia gravis\]), endocrine, immunologic, dermatologic, neurologic, or oncologic disease or any other condition that, in the opinion of the investigator, would jeopardize the safety of the participant or the validity of the study results.
• •6\. History of ischemic stroke within 12 months prior to the screening visit, or any evidence of hemorrhagic stroke.
• •7\. History of cerebral amyloid angiopathy, epilepsy, CNS neoplasm, or unstable thyroid function.
• •8\. History or high risk of urinary retention (for male participants, includes PVR urine volume \> 150 mL at screening; re-test is permitted when PVR urine volume is 151 through 175 mL at screening), gastric retention, or narrow-angle glaucoma.
• •9\. Active biliary disease (e.g., symptomatic gallstones, cholangitis, biliary sphincter contraction, cholecystitis). A history of other biliary disease may be eligible and should be discussed with the medical monitor.
• •10\. Participants with any of the following:
• •a. history of bladder stones b. history of recurrent urinary tract infections c. For male participants, serum prostate-specific antigen \>10 ng/mL at screening d. For male participants, an IPSS score of 5 (i.e., "almost always") on items 1, 3, 5, or 6 e. For male participants, an IPSS score ≥ 9 for the sum of items 1, 3, 5, and 6 11. All grades of hepatic impairment (mild \[Child-Pugh Class A\], moderate \[Child-Pugh Class B\], and severe \[Child-Pugh Class C\]).
• •12\. Participants with HIV with detectible viral load, HCV, cirrhosis, biliary duct abnormalities, hepatobiliary carcinoma, and/or active hepatic viral infections based on either medical history or LFT results.
• •13\. History of irritable bowel syndrome (with or without constipation) or any serious constipation requiring treatment within the last 6 months.
• •14\. History of allergy/hypersensitivity to any component (including excipients) of the study intervention or related compounds.
• •15\. History of any of the following:
• •1. New York Heart Association Class II or greater congestive heart failure
• •2. Grade 2 or greater angina pectoris
• •3. Sustained ventricular tachycardia
• •4. Ventricular fibrillation
• •5. Torsades de pointes
• •6. Implantable cardiac defibrillator
• •7. Myocardial infarction within the 6 months prior to the screening visit.
• •8. Personal or family history of symptoms of long QT syndrome as evaluated by the investigator.
• •16\. Known acute infection or symptomatic illness within 2 weeks before screening; antigen or polymerase chain reaction local testing can be done at the discretion of the investigator. Rescreening can be permitted after the infection/illness is resolved and consultation with the medical monitor.
• •17\. Participation in another clinical study in which the participant received an experimental or investigational drug within 4 weeks before screening or has participated in more than 2 clinical studies in the 12 months prior to screening.
• •18\. Clinically significant abnormal finding on the physical or neurological examination, ECG, or clinical laboratory results at screening.
• •19\. Any significant pathological findings on historical brain MRI (prior to 14th infusion of Leqembi®) submitted at screening that could impact a participant's safety or interfere with study procedure, including, but not limited to: encephalomalacia, aneurysms, vascular malformations, infective lesions, evidence of any intracranial hemorrhage greater than 10 mm, more than 4 cerebral microbleeds, vasogenic edema, cerebral contusion or infection, more than 1 area of superficial siderosis, evidence of multiple lacunar infarcts (with an axial diameter of \< 1.5 cm on neuroimaging) or stroke involving a major vascular territory, severe small vessel disease, or severe white matter disease as defined by a score of 3 on the Fazekas scale; space-occupying lesions or brain tumors (with the exception for meningiomas and arachnoid cysts \< 1 cm in greatest diameter, which are permitted).
• •20\. Participants with any of the following:
• •a. history of unexplained syncope b. history of symptomatic orthostatic hypotension c. history of dysautonomia d. symptomatic orthostatic hypotension (symptomatic reduction of 20 mmHg or more in systolic blood pressure, and/or a symptomatic reduction of 10 mmHg or more in diastolic pressure) at screening. Asymptomatic orthostatic hypotension with a reduction of 20-30 mmHg in systolic blood pressure, and/or a reduction of 10 15 mmHg in diastolic pressure at screening may be eligible and should be discussed with the medical monitor.
• •21\. History of medically significant bradycardia or heart rate \< 50 bpm at screening.
• •Reproductive Status 22. Individuals who are pregnant, breastfeeding, or less than 3 months postpartum.
• •23\. Any investigational therapy within 4 weeks prior to screening. 24. Prior exposure to X/T. 25. Currently taking or exposure to within 6 months prior to screening, a disease modifying anti- amyloid treatment for AD except Leqembi®.
• •26\. Unable to taper and discontinue a concomitant medication that would preclude participation in this study (e.g., cannot stop potent anticholinergic or antihistamine medication).
• •27\. No benzodiazepines may be taken within 12 hours prior to cognitive assessments (ADAS- Cog14, MMSE etc) unless taken regularly. If taken regularly, benzodiazepines must be taken at the same time interval prior to all cognitive assessments.
• •28\. Recent history as defined as the past 3 months of receiving monoamine oxidase inhibitors, anticonvulsants (e.g., lamotrigine, divalproex), mood stabilizers (e.g., lithium), tricyclic antidepressants (e.g., imipramine, desipramine), or any other psychoactive medications except for as needed anxiolytics (e.g., lorazepam).
• •Selective serotonin reuptake inhibitors and serotonin norepinephrine reuptake inhibitors taken at a stable dose for at least 12 weeks prior to screening may be permitted.
• •MRTS (Mrazapine) or trazodone may be used as a hypnotic if started at least 8 weeks prior to screening.
• •29\. Inability to comply with restrictions and prohibited treatments as listed in Appendix 4.
• •Physical and Laboratory Test Findings 30. An eGFR of \< 50 mL/min. 31. PSA ˃ 10 ng/ML at screening. 32. Elevations in hepatic transaminases at screening ≥ 3 × ULN for ALT and AST and/or bilirubin \> 2 × ULN, unless in the context of Gilbert's syndrome.
• •33\. Unstable hypertension or tachycardia as evidenced by:
• •1. Blood pressure of ≥ 150/100 mmHg (average of triplicate seated measures) at screening.
• •2. Heart rate of ≥ 100 bpm (average of triplicate seated measures) at screening. 34. Urine toxicology screen positive for phencyclidine, amphetamines, opiates, cocaine, or alcohol (clinically significant alcohol use in the opinion of the Investigator).
• •35\. Clinically significant abnormal finding on the physical examination, medical history, ECG (QTcF of \> 450 msec in males and \> 470 msec in females (as assigned at birth) ), or clinical laboratory results at screening.
• •38\. Participants with contraindications to the performance of brain MRI including cardiac pacemaker/defibrillator, ferromagnetic metal implants (e.g., in the skull and cardiac devices other than those approved as safe for use in MRI scanners).
• •39\. History of moderate-to-severe alcohol or substance use disorder within the past 2 years.
• •40\. If, in the opinion of the investigator and/or Sponsor/Medical Monitor, participant is unsuitable for enrollment in the study or participant has any finding that, in the view of the investigator and/or Sponsor/Medical Monitor, may compromise the safety of the participant or affect his/her ability to adhere to the protocol visit schedule or fulfil visit requirements.
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