Inhaled RB042 in Healthy Adult Volunteers, Healthy Adult Smokers and Patients With Chronic Obstructive Pulmonary Disease

The purpose of this study is to measure the safety, tolerability, PK, and PD of inhaled RB042 compared with inhaled placebo in healthy adult volunteers, healthy adult smokers and patients with moderate to severe chronic obstructive pulmonary disease. Study details include: * Overall study duration of up to 19 months. * Participants in Part A (healthy adult volunteers) will be required to visit the study site for assessments on 11 occasions, including a 4-day in-house stay, over 4 months. * Participants in Parts B will be required to visit the study site for assessments on 13 occasions, including a 17-day (Day -1 to 16) and 3-day (Day 21 to 24) in-house stay, over 5 months. * Participants in Part C will be required to visit the study site for assessments on 10 occasions, including in-house stays between Day -1 to 2, Day 7 to 8, Day 14 to 15, Day 21 to 23 over 5 months. * Patients in Part D will be required to visit the study site for assessments on 10 occasions over 5 months. * Participants will be administered a single dose (Part A) or multiple doses (Parts B, C and D) of study intervention.