The Montgomery Åsberg Depression Rating Scale (MADRS, SIGMA version), is a clinician rated scale designed to measure depression severity and detects changes due to antidepressant treatment. The test consists of 10 items, each of which is scored from 0 (item not present or normal) to 6 (severe or continuous presence of the symptoms), for a total possible score of 0 - 60. Higher scores represent a more severe condition. The MADRS evaluates apparent sadness, reported sadness, inner tension, sleep, appetite, concentration, lassitude, interest level, pessimistic thoughts and suicidal thoughts. The MADRS was collected electronically by qualified personnel.

Since the MADRS total score at 24 hours was evaluated post the single first infusion (prior to the second infusion), the bi-weekly and single dosing regimens of the same dose level are pooled as one arm for 0.048 mg/kg and 0.16 mg/kg.

Full Analysis Set (all randomized and treated participants)

Treatment-emergent adverse events (TEAEs) and adverse events of special interest (AESIs) in Core period

Safety Set

AUClast of MIJ821 in plasma after 1st infusion. AUClast is the Area Under the Curve (AUC) from time zero to the last measurable concentration sampling time (tlast). Since PK was evaluated post the single first infusion, the bi-weekly and single dosing regimens of the same dose level are pooled as one arm for 0.048 mg/kg and 0.16 mg/kg.

PK Analysis Set: included all participants who received MIJ821 and provided at least one evaluable measurement.

Cmax of MIJ821 in plasma after 1st infusion. AUClast is the maximum (peak) observed plasma, blood, serum, or other body fluid drug concentration after single dose administration. Since PK was evaluated post the single first infusion, the bi-weekly and single dosing regimens of the same dose level are pooled as one arm for 0.048 mg/kg and 0.16 mg/kg.

PK Analysis Set: included all participants who received MIJ821 and provided at least one evaluable measurement.

Response criteria of ≥50% reduction from baseline in MADRS total score over time in the Core Period.

The Montgomery Åsberg Depression Rating Scale (MADRS, SIGMA version), is a clinician rated scale designed to measure depression severity and detects changes due to antidepressant treatment. The test has a total possible score of 0 - 60. Higher scores represent a more severe condition.

Full Analysis Set

Sustained response (≥50% reduction from baseline) from baseline in MADRS total score for a period of at least four weeks in the Core Period.

The Montgomery Åsberg Depression Rating Scale (MADRS, SIGMA version), is a clinician rated scale designed to measure depression severity and detects changes due to antidepressant treatment. The test has a total possible score of 0 - 60. Higher scores represent a more severe condition.

Full Analysis Set

Remission criteria of MADRS total score of ≤12 over time in the Core Period. The Montgomery Åsberg Depression Rating Scale (MADRS, SIGMA version), is a clinician rated scale designed to measure depression severity and detects changes due to antidepressant treatment. The test has a total possible score of 0 - 60. Higher scores represent a more severe condition.

Full Analysis Set

Remission criteria of MADRS total score of ≤12 sustained for a period of at least four weeks in the Core Period.

The Montgomery Åsberg Depression Rating Scale (MADRS, SIGMA version), is a clinician rated scale designed to measure depression severity and detects changes due to antidepressant treatment. The test has a total possible score of 0 - 60. Higher scores represent a more severe condition.

Full Analysis Set

For participants classified as responders in the core period who entered the extension period. Response is defined as a ≥ 50% reduction from the baseline MADRS score at any visit during the study.

All participants meeting criteria for relapse over fixed period in the Extension Period. A relapse manifests as the appearance of new depressive symptoms or worsening of previously stable or improving MDD symptoms. During the Extension Period, participants experiencing deterioration must be assessed by the treating physician and the relapse must be confirmed by assessment with MADRS during scheduled or unscheduled visit.

Responders/remitters who entered the 52 weeks extension period

Relapsing participants meeting response criteria or remission criteria after the first infusion of MIJ821 retreatment in the Extension Period.

Response criteria (>=50% reduction from baseline in MADRS total score). Reinfusions are given at Day 1, 15 and 29 after relapse.

Retreatment Set - included participants who received at least one dose for the retreatment of relapse. Participants who received Placebo in the core period received one of active MIJ821 treatment for the treatment of the relapse and are counted under the respective arm.

Relapsing participants meeting response criteria or remission criteria after the first infusion of MIJ821 retreatment in the Extension Period.

Remission criteria (MADRS total score <=12). Reinfusions are given at Day 1, 15 and 29 after relapse.

Retreatment Set - included participants who received at least one dose for the retreatment of relapse. Participants who received Placebo in the core period received one of active MIJ821 treatment for the treatment of the relapse and are counted under the respective arm.