Open-Label Crossover Study Comparing CTP-543 to Jakafi®

The crossover design will assess the safety, tolerability, PK and metabolite profiles of a
single dose of CTP-543 compared to a single dose of Jakafi. Approximately 12 healthy
volunteers will be enrolled in this open label study.

Inclusion Criteria:

- Healthy adult males and females between 18 and 50 years of age, inclusive

- Body weight ≥ 50 kg and BMI within the range of 18 to 30 kg/m2, inclusive

Exclusion Criteria:

- History of clinically significant central nervous system (eg, seizures), cardiac,
pulmonary, metabolic, renal, hepatic, or gastrointestinal (GI) conditions

- PR interval > 220 msec or QRS duration > 120 msec or QTcF interval > 450 msec
obtained at screening visit or prior to the first dose of study drug

- History of herpes zoster

- Hemoglobin, white blood cell, or platelet levels below the lower reference limit at
screening or prior to the first dose of study drug

- Liver function tests greater than the upper limit of normal

- Positive blood screen for human immunodeficiency virus (HIV antibody), hepatitis B
virus surface antigen, or hepatitis C virus antibody

- Urinalysis positive for protein or glucose

- A positive screen for alcohol, drugs of abuse, or tobacco use

- Donation of blood, plasma or other blood products prior to screening

- A positive tuberculosis test