This is a randomised, double-blind, placebo-controlled, multi-centre, parallel group Phase 1b study, designed to evaluate the pharmacodynamic effects, clinical efficacy and safety of AZD0284 compared with placebo as measured by the relative change from baseline in Psoriasis Area Severity Index (PASI score), other disease assessments of involved body surface area (BSA), static physicians global assessment score (sPGA), pruritis and biomarkers associated with the mechanism of disease and AZD0284. Disease activity will be assessed throughout the study as will changes in skin biopsy biomarkers. The study population will be comprised of patients with moderate to severe plaque psoriasis as defined by PASI score, BSA and sPGA.