The purpose of the study is to assess the efficacy and safety of PF-06462700 administered intravenously at 40 mg/kg/day for 4 days in Japanese participants with moderate and above aplastic anemia for making an approval application in Japan.

Inclusion Criteria:

• Male or female participants between the ages of 2 years and more, inclusive, at Visit

  1 (Screening).

• Participants who are willing and able to comply with all scheduled visits, treatment plan, laboratory tests, lifestyle considerations, and other study procedures.

• Have a clinical diagnosis of aplastic anemia by bone marrow aspiration/biopsy findings and/or magnetic resonance imaging (MRI) etc.

• Must meet the following criteria of moderate and above aplastic anemia

• Capable of giving signed informed consent/assent as described in Appendix 1, which includes compliance with the requirements and restrictions listed in the informed consent document (ICD)/assent document and in this protocol.

Exclusion Criteria:

• Eligible and willing to have a sibling allogeneic stem cell transplantation.

• Evidence of a myelodysplastic syndrome (except for refractory cytopenia in children), as well as other primitive marrow disease.

• History or clinical suspicion of congenital aplastic anemia (Fanconi anemia, Congenital keratosis, etc).

• History of malignant tumors with active disease within 5 years from study participation.

• Participants who are clearly infected with hepatitis B virus (HBV), hepatitis C virus (HCV), human immunodeficiency virus (HIV), and human T-cell leukemia virus type

  1 (HTLV-1).

• Pregnant or breast-feeding participants.

• Participants with severe hepatic, renal or cardiac failure, or any other life-threatening concurrent [aspartate aminotransferase (AST) or alanine aminotransferase (ALT) or total bilirubin values >5 × upper limit of normal (ULN), and/or creatinine value >2 × ULN].

• Participants with hypersensitivity such as shock after skin test of this study drug.

• Participants with uncontrolled severe infection (pneumonia, sepsis, etc).

• Participants who received live vaccine or live attenuated vaccine within 6 weeks prior to the first dose of study drug.

• Other acute or chronic medical or psychiatric condition including recent (within the past year) or active suicidal ideation or behavior or laboratory abnormality that may increase the risk associated with study participation or investigational product administration or may interfere with the interpretation of study results and, in the judgment of the investigator, would make the participant inappropriate for entry into this study.

• Prior immunosuppressive therapy with lymphocyte-depleting agents/therapies, including both non-B-cell selective and B-cell-depleting agents (e.g., alefacept, alemtuzumab, rituximab). However, participants previously treated with rATG may enroll.

• Previous history of stem cell transplantation.

• Previous administration with an investigational drug within 30 days (or as determined by the local requirement) or 5 half-lives preceding the first dose of investigational product used in this study (whichever is longer).

• Baseline 12-lead electrocardiogram (ECG) that demonstrates clinically relevant abnormalities that may affect participant safety or interpretation of study results (e.g., baseline corrected QT [QTc] interval >450 msec, complete left bundle branch block [LBBB], signs of an acute or indeterminate-age myocardial infarction, ST-T interval changes suggestive of myocardial ischemia, second- or third-degree atrioventricular [AV] block, or serious bradyarrhythmias or tachyarrhythmias). If the baseline uncorrected QT interval is >450 msec, this interval should be rate-corrected using the Fridericia method and the resulting QTcF should be used for decision making and reporting. If QTc exceeds 450 msec, or QRS exceeds 120 msec, the ECG should be repeated 2 more times and the average of the 3 QTc or QRS values should be used to determine the participant's eligibility. Computer-interpreted ECGs should be overread by a physician experienced in reading ECGs before excluding participants.

• Investigator site staff members directly involved in the conduct of the study and their family members, site staff members otherwise supervised by the investigator, or Pfizer employees, including their family members, directly involved in the conduct of the study.

Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.

Safety analysis population included all participants assigned to investigational product and who took at least 1 dose of investigational product.

Screening up to 24 weeks of follow-up (approximately up to 28 weeks)