Inhaled RB042 in Healthy Adult Volunteers and Healthy Adult Smokers

Inclusion Criteria: * Participants must be overtly healthy as determined by medical evaluation * Part C only: have a ≥10 pack years smoking history, have smoked tobacco products (cigarettes, cigars, or equivalent) regularly for the past 12 months, and currently smoke daily. * Have forced expiratory volume (FEV1) ≥80% predicted and FEV1 to FVC ratio (FEV1/FVC) ≥0.7 at Screening and on Day -1 * Body weight at least 50 kg and have a body mass index (BMI) within the range 18.0 and 32.0 kg/m2 (inclusive) * Women of childbearing potential (WOCBP) must have a negative pregnancy test and must not be lactating. * Participants must agree to use an approved method(s) of highly effective contraception as defined in the protocol. Exclusion Criteria: * Clinically significant history or presence of gastrointestinal, hepatic, renal, cardiovascular, respiratory, endocrine, neurologic, hematologic, metabolic, autoimmune, or oncologic disorders that may affect safety or study outcomes. * Chronic or active respiratory disease (e.g., asthma, COPD) or history of angioedema within 3 years. * Active or chronic liver disease, or abnormal liver function tests (ALT, AST, or bilirubin outside reference range, except Gilbert's syndrome). * QTcF \>450 msec (males) or \>470 msec (females). * Renal impairment (creatinine clearance \<90 mL/min) or thrombocytopenia (\<150 × 10⁹/L). * Positive test for hepatitis B surface or core antigen, hepatitis C (unless HCV-RNA negative), or HIV. * Active respiratory infection within 5 days before study start. * Recent or concurrent use of medications, herbal supplements, vaccines, or blood products that could interfere with study safety or interpretation. * Participation in another investigational study within 30 days, or blood donation \>400 mL within 30 days. * Parts A and B only: Regular smoking (≥1 day per week) within 6 months prior to dosing, or a positive urine cotinine test at screening or Day -1. * Excessive alcohol consumption (\>21 drinks/week for males or \>14 for females). * History of severe drug reaction or anaphylaxis. * Contraindication to, or unwillingness to undergo, bronchoscopy. * Any psychiatric or medical condition that, in the investigator's opinion, could compromise safety or compliance.