This study is designed to evaluate the effect of VX-509 on the pharmacokinetics (PK) of corticosteroids (prednisone or methylprednisolone) and the effect of corticosteroids on the PK of VX-509 and its metabolite. The study will also evaluate the safety and tolerability of VX-509 when coadministered with each of these corticosteroids.

Inclusion Criteria:

• Male subjects between 18 and 55 years of age, inclusive
• Body mass index (BMI) of 18.0 to 31.0 kg/m2, inclusive, and a total body weight >50 kg

Exclusion Criteria:

• History of any illness that, in the opinion of the investigator or the subject's general practitioner, might confound the results of the study or pose an additional risk in administering study drug(s) to the subject. This may include, but is not limited to, history of cardiovascular or central nervous system disease, diabetes, history or presence of clinically significant pathology, or history of mental disease
• Treatment with an investigational drug within 30 days or 5 half-lives preceding the first dose of study drug
• Subject has a female partner who is pregnant, nursing, or planning to become pregnant during the study or within 90 days of the last dose of study drug
• Positive test result for any of the following infectious disease tests at the Screening Visit: T-SPOT tuberculosis (TB) test, hepatitis B surface antigen, hepatitis C virus antibody, and human immunodeficiency virus 1 and 2 antibodies