A Randomised, Placebo-controlled, Double-blind Trial of the Antidepressant Efficacy of a Novel CNS-penetrant P2X7 Receptor Antagonist, JNJ-54175446, in People With Major Depressive Disorder, an Incomplete Response to Monoaminergic Antidepressant Drugs, and a Biomarker Profile Predictive of Active P2X7 Signalling - ICH GCP - Clinical Trials Registry