A Hepatic Impairment Study for PF-04965842.

Inclusion Criteria: * Body mass index (BMI) of 17.5 to 40 kg/m2; and a total body weight \>50 kg (110 pounds). * Subjects who are willing and able to comply with all scheduled visits, treatment plan, laboratory tests, and other study procedures. Additional Inclusion Criteria for subjects with hepatic impairment: * Satisfy the criteria for Class A or Class B of the Child Pugh classification (mild: Child Pugh Scores 5 to 6 points, and moderate: Child Pugh Scores 7 to 9 points), within 14 days of investigational product administration. * A diagnosis of hepatic dysfunction due to hepatocellular disease (and not secondary to any acute ongoing hepatocellular process) documented by medical history, physical examination, liver biopsy, hepatic ultrasound, computerized tomography scan, or magnetic resonance imaging (MRI). Exclusion Criteria: * Subjects with clinically significant infections within the past 3 months (for example, those requiring hospitalization, or as judged by the Investigator), evidence of any infection (including influenza) within the past 7 days, history of disseminated herpes simplex infection or recurrent (\>1 episode) or disseminated herpes zoster. * Subjects with a malignancy or with a history of malignancy, with the exception of adequately treated or excised non metastatic basal cell or squamous cell cancer of the skin or cervical carcinoma in situ. Additional exclusion criteria for subjects with hepatic impairment: * Hepatic carcinoma or hepatorenal syndrome or limited predicted life expectancy (defined as less than 1 year). * Subjects who have previously had a transplanted kidney, liver, or heart. * At Screening, persistent severe, uncontrolled hypertension.