A Study of QLH2405 in Healthy Participants and Participants With Mild Cognitive Impairment Due to Alzheimer's Disease and Mild Alzheimer's Disease

Prior treatment

• History of blood donation, significant blood loss (total volume ≥400 mL), or blood transfusion within 3 months prior to screening.
• History of alcohol abuse within 1 year prior to screening; or positive alcohol breath test.
• Participation in any drug or medical device clinical trial within 3 months prior to screening.
• History of stroke within 6 months prior to screening, or imaging evidence of clinically significant central nervous system diseases.
• History of epileptic seizures or epileptiform abnormalities on EEG within 6 months prior to screening.
• Unstable or severe diseases within 6 months prior to screening that, in the investigator's judgment, make the participant unsuitable for study participation.
• Current use or anticipated need during the study period for any medication prohibited by the study protocol.

Other illness

• History of significant diseases, or any existing disease may affect the study or pose an unacceptable risk to the participant.
• Positive for HBsAg, HIV-Ab, Treponema pallidum antibody, or HCV-Ab.
• History of drug abuse and/or substance abuse; or positive drug screening.
• Any other condition that, in the investigator's judgment, makes the participant unsuitable for participation in this study.
• Cognitive impairment or dementia caused by any disease other than AD.
• Any other condition that, in the investigator's judgment, makes the participant unsuitable for participation in this study.

Lab values

• eGFR \<60 mL/min/1.73 m².
• AST or ALT \>3 × upper limit of normal (ULN), or total bilirubin \>2 × ULN.

Other

• Pregnant or lactating women, or women of childbearing potential with a positiveβ-hCG test.

• Voluntarily participate and sign the informed consent.
• Male or female, aged 18 to 65 years (inclusive).
• Healthy status as confirmed by medical evaluation.
• Body mass index (BMI) of 19-28 kg/m² (inclusive).
• Agree to use effective contraception and have no plans for sperm/egg donation or pregnancy from ICF signing until 9 months post-dose.
• Voluntarily participate and sign the informed consent, able to communicate well with the investigator and complete the trial per protocol.
• Male or female, aged 50 to 85 years (inclusive).
• A diagnosis of mild MCI due to AD or mild AD according to the National Institute on Aging and the Alzheimer's Association (NIA-AA) criteria.
• Has subjective cognitive and memory decline for ≥6 months.
• Confirmation of Alzheimer's disease pathological changes by amyloid PET (Aβ-PET) scan.
• Has one (or more) reliable study partner (s)/adult caregiver(s) can accompany the participant to all visits.
• Agree to use effective contraception and have no plans for sperm/egg donation or pregnancy from ICF signing until 9 months post-dose.