MEDI-557 Adult Dosing

Inclusion Criteria: * 18-45 years * written informed consent obtained from subject prior to performing any protocol related procedures * healthy by medical history and physical exam * females of child-bearing potential must use 2 effective methods of birth control for 14 days prior to 1st dose and through 1 year after administration of study drug * nonsterilized, sexually active males with female partner of child-bearing potential must use 2 effective methods of birth control from Day 1 through Day 361 * weight \</= 110kg with a body mass index of \<32kg/m2 * ability to complete a follow-up period of approximately 360 days Exclusion Criteria: * inability to complete a follow-up period of 360 days * any condition in the opinion of investigator that would interfere with evaluation of IP or interpretation of subject safety or study results * concurrent enrollment in another clinical study * employees of the site or other individuals involved with the conduct of the study or immediate family members of such individuals * receipt of immunoglobulin or blood products within 60 days prior to randomziation * receipt of any investigational drug therapy within 6 months prior to IP dosing * clinically abnormal ECG at screening * blood donation in excess of 400mL, wihtin 6 months prior to randomization * previous receipt fo biologics * history of immunodeficiency * history of allergic disease or reactions likely to be exacerbated by any component of the IP * previous medical history or evidence of interurrent illness that may compromise the safety of the subject * positive lab test for Hep A, B, C or HIV * pregnancy or nursing mother * history of alcohol or drug abuse within past 2 years * positive urine Class A drug screen * acute illness within 7 days prior to randomization * fever \>/= 99.5F witin 7 days prior to randomization * any drug therapy within 7 days prior to randomization * systolic BP \>150mmHG and/or diastolic BP\>90mmHg * receipt of vaccine within 14 days prior to randomization * abnormal study labs (hem/wbc/platelet/BUN - see protocol for specific information)