A Randomized, Double-blind, Placebo-controlled Trial of ALTO-207 in Adults With Treatment-resistant Depression

Inclusion Criteria: * Male and female participants, ages 18 to 75 years, inclusive, at the time of signing the ICF. * Prior diagnosis of MDD without psychotic symptoms (in the current episode) and have confirmatory diagnosis of current MDD (moderate to severe). * Failure to respond (\<50% improvement) to at least 2-5 antidepressant treatments (including the current treatment) * Currently taking a stable dose of at least 1 but no more than 2 oral antidepressants at baseline Exclusion Criteria: * Evidence of unstable medical condition * Concurrent use of any prohibited medications or substanc…