The goal of this clinical trial is to evaluate the effectiveness and safety of bilateral stimulation of the subcallosal cingulate white matter (SCCwm) using Deep Brain Stimulation (DBS) as an adjunctive treatment of non-psychotic unipolar Major Depressive Disorder (MDD) in adults.

The aim of this prospective, multi-centered, double-blind, randomized, delayed-stimulation/ Sham-stimulation controlled 12-month study is to evaluate the effectiveness and safety of bilateral stimulation of the subcallosal cingulate white matter (SCCwm) using the Infinity™ Deep Brain Stimulation (DBS) system as an adjunctive treatment of non-psychotic unipolar Major Depressive Disorder (MDD) for adults who are experiencing a Major Depressive Episode (MDE) with inadequate response to 4 or more antidepressant treatments.

In a double-blind fashion, half the subjects will receive active DBS therapy, while half will receive sham stimulation. After the 12-month endpoint, all subjects will be unblinded to their treatment group, and subjects in the control arm will receive active DBS therapy.

Inclusion Criteria:

1. The patient must be diagnosed with non-psychotic unipolar Major Depressive Disorder.
2. The patient must be in a major depressive episode for ≥12 months or have had at least 3 lifetime depressive episodes.
3. The patient has tried and failed a minimum of four different types of antidepressant treatments as measured by a tool designed for this purpose.
4. Depression medication and treatment regimen must be stable for a minimum of 4 weeks before the first baseline visit

Exclusion Criteria:

1. Pregnant or those who plan to become pregnant during study
2. Presence of other anatomic or comorbid conditions, or other medical, social, or psychological conditions that could limit participation in the study or interfere with adherence to the study protocol.
3. Current or lifetime history of psychotic features in any Major Depressive Episode.
4. Has an intracranial Central Nervous System disease that impairs motor, sensory or cognitive function or that requires intermittent or chronic medication.
5. Significant acute suicide risk.
6. Diagnosis of Substance Use Disorder or Alcohol Use Disorder without sustained remission (12 months or longer).
7. Current and ongoing use of neurostimulation treatment that may interfere with DBS therapy/system.
8. Treatment with another investigational device or investigational drugs.