This study is planned to investigate the safety, tolerability, and pharmacokinetics when a single intravenous dose of MT-3534 or a placebo is given to healthy adult male volunteers.

Inclusion Criteria:

• Healthy adult male volunteer
• Japanese (Part A) or White (Part B)
• Subjects with age of 18 to 55 years old at informed consent
• Subjects with a full understanding of the nature of this study and consented in writing to participate in the study

Exclusion Criteria:

Additional screening criteria check may apply for qualification:

• Subjects with a current or prior disease history of cardiac, hepatic, renal, gastrointestinal, respiratory, neuropsychiatric, hematopoietic, endocrine systems, etc. whom the investigator has judged to be unfit for study participation
• Subjects with a history of drug or food allergies
• Subjects with a history of hypersensitivity to any of the ingredients of MT-3534
• Subjects whose BMI is less than 18.5 kg/m^2 or exceeds 25.0 kg/m^2, or subjects weighing less than 50.0 kg or exceeds 80.0 kg at the time of screening or Day -1 tests (Part A). Subjects whose BMI is less than 18.5 kg/m^2 or exceeds 30.0 kg/m^2, or subjects weighing less than 50.0 kg or exceeds 100.0 kg at the time of screening or Day -1 tests (Part B). (For BMI, values rounded to the first decimal place will be used.)
• Subjects who have donated blood or from whom blood samples have been collected in a total amount of 400 mL or more in the 12 weeks, 200 mL or more in the 4 weeks, or 800 mL or more in the 52 weeks prior to informed consent
• Subjects who have donated blood platelets or from whom blood samples have been collected in the 2 weeks prior to informed consent
• Subjects with a current or prior history of dependence on drugs, alcohol, etc
• Subjects with a history of cancer
• Subjects who receive a live attenuated vaccine within 4 weeks before the start of investigational product administration
• Subjects with a positive result for serological test for syphilis, Hepatitis C virus (HCV) antibody, or HIV antigen/antibody at screening
• Subjects with a positive result for Hepatitis B virus surface (HBs) antigen, Hepatitis B virus core (HBc) antibody and HBs antibody at screening (Subjects with a negative for HBs antigen plus a positive for HBs antibody plus a negative for HBc antibody and who have obvious history of vaccination are eligible to enroll)
• Subjects with a history of recurrent infections such as Herpes simplex or Herpes zoster
• Subjects with a positive result for polymerase chain reaction (PCR) test for COVID-19 at Day -1 test
• Subjects who do not agree to contraception from the date of informed consent until 12 weeks after the end of the administration of the investigational product
• Subjects who have participated in other clinical studies and received other investigational products within 12 weeks before informed consent
• Subjects who have used any drug other than the investigational product in the period within the 7 days before the start of investigational product administration or 5 times the half-life of the drug, whichever is longer
• Subjects judged by the investigator (or subinvestigator) to be ineligible for the study for any other reason