The Clinical Dementia Rating-Sum of Boxes (CDR-SB) rates impairment in 6 categories (memory, orientation, judgement and problem solving, community affairs, home and hobbies and personal care) on a 5-point scale in which no impairment = 0, questionable impairment = 0.5 and mild, moderate and severe impairment = 1, 2 and 3 respectively. The score range is from 0 to 18 with a high score indicating a high disease severity. The difference in mean change from Baseline to Week 73 between Semorinemab doses and Placebo treated participants was estimated. The difference in mean change from Baseline to Week 73 between Semorinemab doses and Placebo treated participants was estimated.

Modified intent-to-treat (mITT) population included all randomized participants who received at least one dose of study drug and had at least one postbaseline primary efficacy Clinical Dementia Rating-Sum of Boxes (CDR-SB) measurement.

Percentage of participants with at least one adverse event

The safety-evaluable population included all participants who were randomly allocated and received at least one dose of study drug (MTAU9937A or placebo) during the double-blind treatment period with treatment groups defined according to actual treatment received.

The RBANS is a validated neuropsychological assessment has been shown to be a useful tool in both clinical and research settings. The RBANS consists of ten subtests that are combined to provide five indices, one for each of the five domains tested (immediate memory, visuospatial/constructional, language, attention, and delayed memory). Scores range from 40 to 160 and a higher score indicates better cognitive functioning. A decrease in the outcome measure from baseline corresponds to disease worsening. The difference in mean change from Baseline to Week 73 between Semorinemab doses and Placebo treated participants was estimated.

Modified intent-to-treat (mITT) population included all randomized participants who received at least one dose of study drug and had at least one postbaseline primary efficacy Clinical Dementia Rating-Sum of Boxes (CDR-SB) measurement.

The ADAS-Cog-13 assesses multiple cognitive domains including memory, comprehension, praxis, orientation, and spontaneous speech. Most of these are assessed by tests although some are rated by the clinician on a 5-point scale. The ADAS-Cog-13 is the ADAS-Cog-11 with 2 further items: delayed word recall and total digit cancellation. The score range for ADAS-Cog-13 is from 0 to 85 with high scores representing severe dysfunction. The difference in mean change from Baseline to Week 73 between Semorinemab doses and Placebo treated participants was estimated.

Modified intent-to-treat (mITT) population included all randomized participants who received at least one dose of study drug and had at least one postbaseline primary efficacy Clinical Dementia Rating-Sum of Boxes (CDR-SB) measurement.

The Amsterdam iADL questionnaire is an informant-based instrument for measuring iADL problems in participants with dementia. This instrument consists of 70 items, scored on a 5-point scale, that uses item response theory for scoring. Items presented to the informant are tailored to responses to earlier items; thus each administration of the Amsterdam iADL may consist of less than the total of 70 items. The resulting score ranges from 20 to 80 with lower scores indicating poorer performance. A decrease in the outcome measure from baseline corresponds to disease worsening. The difference in mean change from Baseline to Week 73 between Semorinemab doses and Placebo treated participants was estimated.

Modified intent-to-treat (mITT) population included all randomized participants who received at least one dose of study drug and had at least one postbaseline primary efficacy Clinical Dementia Rating-Sum of Boxes (CDR-SB) measurement.

The ADCS-ADL (Alzheimer's Disease Cooperative Study-Activities of Daily Living) is the scale most widely used to assess functional outcomes in participants with AD. The ADCS-ADL covers both basic ADL (e.g., eating and toileting) and more complex 'instrumental' ADL or iADL (e.g., using the telephone, managing finances and preparing a meal). The ADCS-ADL consists of 23 questions with a score range of 0 to 78 where a higher score represents better function. The difference in mean change from Baseline to Week 73 between Semorinemab doses and Placebo treated participants was estimated.

Modified intent-to-treat (mITT) population included all randomized participants who received at least one dose of study drug and had at least one postbaseline primary efficacy Clinical Dementia Rating-Sum of Boxes (CDR-SB) measurement.

Serum concentrations of Semorinemab at specified timepoints.

The PK-evaluable population is defined as patients who received Semorinemab treatment and had at least one measureable PK concentration.

Presence of anti-drug antibodies during the study relative to their presence at baseline.

The immunogenicity analyses will include participants with at least one predose and one postdose ADA assessment, with participants grouped according to treatment arm.

Categories are as defined in the Classification Algorithm for Suicide Assessment (CASA) based on the Columbia Suicide Severity Rating Scale (C-SSRS) questionnaire. SI1: Passive category is "Wish to be dead", SI2: Active-Nonspecific (no method, intent or plan), SI3: Active-Method, but no intent or Plan, SI4: Active-Method and intent, but no plan in C-SSRS. The worst post-baseline suicidal ideation is the highest across post-baseline visits, with highest as SI5 and lowest as SI1. Percentages are based on the total number of subjects in a treatment group. Baseline is the last observation prior to initiation of study drug.

The safety-evaluable population included all participants who were randomly allocated and received at least one dose of study drug (MTAU9937A or placebo) during the double-blind treatment period with treatment groups defined according to actual treatment received.

Other abnormal MRI findings by visit. For the Double Blind Period, baseline is defined as last results prior to initiation of study drug. For the Open Label Extension Period, baseline is defined as last results prior to entering the open label period.

The safety-evaluable population included all participants who were randomly allocated and received at least one dose of study drug (MTAU9937A or placebo) during the double-blind treatment period with treatment groups defined according to actual treatment received.