The purpose of this study is to determine the safety, tolerability, and pharmacokinetics (PK) after intravenous (IV) administration of ASP2408 manufactured from a new production clone and also following single ascending doses of subcutaneous (SC) injections of the same clinical trial material.

The four doses will be studied in sequential cohorts of 8 subjects each, starting with the IV dose, followed by the subcutaneous doses in ascending order of dose. Within each cohort, subjects will be randomized to either active drug or matching placebo in a 3:1 ratio (6 active and 2 placebo).

All subjects in each arm will be confined for 8 days and followed for a minimum of 90 days up to 9 months if necessary. Subjects who have study drug terminated should remain in the study, if possible and have scheduled procedures and follow-up.

Subjects who have detectable blood levels of ASP2408 after Day 90 will be unblinded and followed monthly until ASP2408 levels are below the limit of quantification. In addition, subjects who have persistent anti-ASP2408 antibodies after Day 90 will be unblinded and followed every 30 (± 3) days for up to 9 months until the level of these antibodies are declining, no longer detectable, and/or have no clinical consequence.

Inclusion Criteria:

• The subject weighs at least 50 kg, a maximum of 92.5 kg and has a body mass index (BMI) of 18.0 to 32.0 kg/m2, inclusive
• The subject's 12-lead electrocardiogram (ECG) results are normal
• The female subject must be at least two years postmenopausal OR surgically sterile and not pregnant or lactating
• The male subject agrees to the use of male condoms until the end of study or 60 days post dose, whichever is longer

Exclusion Criteria:

• The subject has a history of any clinically significant cardiac, endocrinologic, hematologic, hepatic, immunologic, metabolic, urologic, pulmonary, neurologic, dermatologic, psychiatric, renal, and/or other major disease or malignancy excluding adequately-treated non-melanoma skin cancer
• The subject has a history of severe allergic or anaphylactic reactions
• The subject is a female of childbearing potential
• The subject has a history of consuming more than 14 units of alcoholic beverages per week or has a history of alcoholism or drug/chemical/substance abuse within the past 2 years (Note: one unit = 12 ounces of beer, 4 ounces of wine or 1 ounce of spirits)
• The subject has a positive test for alcohol or drugs of abuse
• The subject has/had a symptomatic, viral, bacterial (including upper respiratory infection), or fungal (non-cutaneous) infection within 1 week prior to clinic check-in
• The subject has a past history of opportunistic infection
• The subject has a supine mean systolic blood pressure < 90 or > 160 mmHg and a mean diastolic blood pressure < 50 or > 90 mmHg, or mean pulse rate higher than 100 beats per minute (bpm)
• The subject is known positive for human immunodeficiency virus (HIV) antibody
• The subject has a positive tuberculosis (TB) skin test, Quantiferon Gold test or T-SPOT® test
• The subject has a positive test for hepatitis C antibody, or positive test for hepatitis B surface antigen (HBsAg), or positive hepatitis B core antibody
• Subject's alanine aminotransferase (ALT) and/or aspartate aminotransferase (AST) values are greater than 1.5 times the upper limit of normal
• Subject's laboratory test results are outside the normal limits and considered to be clinically significant
• The subject received any vaccine within 60 days prior to study drug administration
• The subject received any systemic immunosuppressant agent within 2 months prior to study drug administration
• The subject has previously received any antibody or therapeutic biologic product prior to study drug administration
• The subject received any systemic steroid within 2 months or steroid inhaler within 1 month prior to study drug administration
• The subject has had treatment with prescription, non-prescription or complementary and alternative medicines (CAM) within 14 days prior to study drug administration with the exception of stable hormone replacement therapy (HRT) and/or intermittent acetaminophen (to a maximum of 2 g/day)
• The subject has received an experimental agent within 30 days or five half-lives, whichever is longer, prior to study drug administration
• The subject is participating in another clinical trial or has participated in another dose group of the current trial
• The subject has had any significant blood loss, donated one unit (450 mL) of blood or more, or received a transfusion of any blood or blood products within 60 days or donated plasma within 7 days prior to clinic admission
• The subject has any other condition which precludes the subject's participation in the trial
• The subject has a history of heavy smoking or has used tobacco-containing products and nicotine or nicotine-containing products in the past six months