This study is a first-in-human, Phase I, randomized, double-blind, placebo-controlled, single-center, dose-escalation study to evaluate the safety, tolerability, pharmacokinetics (PK) and pharmacodynamics of GLPG3667 after oral single ascending doses (SAD) of GLPG3667 (part 1) and after oral multiple ascending doses (MAD) for 13 days of GLPG3667 (part 2) in healthy male subjects. In addition, the effect of food (FE) on safety, tolerability, and PK of GLPG3667 oral suspension will be evaluated (part 3 - will not be completed), and the relative bioavailability (rBA) of the capsule versus the oral suspension with the effect of food on the bioavailability of the capsule (part 4), both part 3 and 4 using an open-label, randomized, crossover design.

Inclusion Criteria:

• Male between 18-55 years of age (extremes included), on the date of signing the informed consent form (ICF)
• A body mass index (BMI) between 18-30 kg/m2, inclusive
• Judged to be in good health by the investigator based upon the results of a medical history, physical examination, vital signs, 12-lead electrocardiogram (ECG), and fasting clinical laboratory safety tests, available at screening and prior to randomization. Hemoglobin, neutrophil, lymphocyte, and platelet counts must be above the lower limit of normal range. Bilirubin, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) must be within normal ranges. Other clinical laboratory safety test results must be within the reference ranges or test results that are outside the reference ranges need to be considered not clinically significant in the opinion of the investigator

Exclusion Criteria:

• Known hypersensitivity to Investigational Medicinal Product (IMP) ingredients or history of a significant allergic reaction to IMP ingredients as determined by the investigator
• Known contraindication or hypersensitivity to Interferon-alpha (IFN-α) or any component of Intron-A® (Note: this criterion is only applicable to subjects in the MAD part)
• Positive serology for hepatitis B virus surface antigen (HBsAg) or hepatitis C virus (HCV) or history of hepatitis from any cause with the exception of hepatitis A that was resolved at least 3 months prior to first dosing of the IMP.