Phase 1, Randomized, Double-Blind, Placebo-controlled Study to Evaluate the Safety and Tolerability of an Enterovirus D68-specific Monoclonal Antibody in Healthy Adults

Inclusion Criteria: 1. Provides written informed consent prior to initiation of any study procedures. 2. Is able to understand and agrees to adhere to planned study procedures and is available for all study visits. 3. Adult volunteers 18 to 49 years of age, inclusive. 4. Females who are of childbearing potential must agree not to become pregnant. Not of childbearing potential includes post-menopausal females (defined as no menses for at least 12 months without an alternative medical cause for amenorrhea) or surgically sterile females with documented history of hysterectomy, bilateral oophorectomy, tubal ligation/salpingectomy, or Essure(R) placement. 5. Females who have sexual intercourse with male partners must agree to use at least one acceptable form of contraception for the duration of the study. Acceptable methods of birth control include long-acting reversible contraception (LARC), combined pill, progestin-only pill, hormone-releasing transdermal patch or vaginal ring, and depot medroxyprogesterone acetate (DMPA) injection. Participants who choose to use a licensed hormonal product should use them for a minimum of 28 days prior to study infusion. True sexual abstinence or a monogamous relationship with a vasectomized partner who has been vasectomized for 180 days or more prior to the participant's first infusion are also acceptable contraceptive methods. Participants who report practicing true abstinence, defined as no heterosexual vaginal-penile intercourse, need to practice true abstinence at all times during the study. Periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods) and the withdrawal method are not acceptable methods of contraception. 6. Females of childbearing potential must agree to not donate ova or oocytes during the study. 7. Participant is in good health Good health is defined by the absence of a medical condition described in the exclusion criteria. If the participant has another current, ongoing medical condition, the condition cannot meet any of the following criteria: (1) was first diagnosed within 3 months of enrollment with a clinically significant condition, in the opinion of investigator that has worsened within 3 months of enrollment; (2) had non-elective surgery, clinically significant medical procedure, or hospitalization within 3 months of enrollment; (3) received new prescription for systemic medication within 30 days of enrollment, unless the new prescription is in the same class of agent or a transition from generic to/from brand name equivalent; or (4) takes medication that may pose a risk to participant's safety or impede assessment of adverse events or study endpoints if they participate in the study. 8. Must agree to refrain from donating blood or blood products during the study. This includes whole blood cells, red blood cells, platelets, plasma, and plasma derivatives collected and donated outside of the study blood draws. 9. Body mass index (BMI) 18 kg/m2 to 32 kg/m2, inclusive, and a weight of 125 kg or less at time of screening. 10. Must have adequate venous access for intravenous (IV) infusion and blood sampling. Exclusion Criteria: All participants meeting any of the exclusion criteria at baseline will be excluded from study participation. 1. Positive pregnancy test at screening or prior to infusion. 2. Female participant who is lactating. 3. Presence of significant psychiatric condition, that in the opinion of the site PI or appropriate sub-investigator, precludes study participation. 4. History of drug abuse or alcohol abuse within 6 months of enrollment that, in the opinion of the site PI or appropriate sub-investigator, precludes study participation. 5. Has a significant acute illness (with or without fever), as determined by the site PI or appropriate sub-investigator, within 72 hours prior to infusion. If the participant meets all other eligibility criteria, they may be enrolled and dosed once they meet this eligibility criterion. If the illness resolves within the 28-day screening window, they do not need to be rescreened, otherwise they will need to be rescreened. 6. Currently enrolled in or plans to participate in another clinical trial with an investigational agent that will be received during the study-reporting period. 7. Has a history of significant hypersensitivity, intolerance, or allergy to any drug compound, vaccine, food, or other substance, unless approved by the Investigator (or designee). Sensitivity to glycine, citric acid, trisodium citrate, sorbitol, or polysorbate 80 (components of the study product) is exclusionary. 8. Any history of an infusion reaction to any biologic product. 9. Receipt of a monoclonal antibody in the 180 days prior to infusion. 10. Receipt of a blood product within 120 days prior to infusion. 11. Received any live-attenuated vaccine in the 28 days prior or any other vaccine in the 14 days prior to infusion. 12. Has used any prohibited medication within 30 days prior to Day 1 or plans to use prohibited medication during the study. Prohibited medications include systemic immunosuppressive drugs, immune modulators (except acetaminophen or non-steroidal anti-inflammatory drugs), oral corticosteroids, and systemic anti-neoplastic agents. Topical, inhaled, and intranasal steroids, as well as topical anti-neoplastic agents are acceptable. 13. Has clinically significant findings on 12-lead electrocardiogram. Clinical significance will be determined by a cardiologist. Examples of findings that will lead to exclusion are significant left ventricular hypertrophy, right or left bundle branch block, advanced A-V heart block, non-sinus rhythm (excluding isolated premature atrial contractions), pathologic Q wave abnormalities, significant ST-T wave changes, and prolonged QTc interval. Long QT interval is defined in males as a median QTcB greater than 450 msec or in females as a median QTcB greater than 460 msec (Bazett's correction) at screening. 14. Abnormal vital signs (Grade 1 or higher) at screening or on Day 1. Grade 1 or higher is equivalent to: Systolic blood pressure (SBP) \> 140 mmHg or \< 85 mmHg Diastolic blood pressure (DBP) \> 90 mmHg Oral temperature \>/= 38.0 degrees Celsius (100.4 degrees Fahrenheit) 15. Abnormal laboratory results that are Grade 1 or worse at screening based on the Toxicity Tables in Appendix B7. Creatinine, alanine transaminase (ALT), hemoglobin (Hgb), platelets (PLT), white blood cell count (WBC), and total bilirubin (T bili). Laboratory studies can be repeated once if an alternative, transient etiology for abnormal laboratory values is identified. 16. Known, current human immunodeficiency virus (HIV), hepatitis B Virus (HBV), or hepatitis C virus (HCV) infection 17. Has any medical disease or condition that, in the opinion of the site PI or appropriate sub-investigator, precludes study participation. Medical conditions include, but are not limited to, kidney disease with creatinine clearance \< 90 mL/min/1.73 cm2 (CKD-EPI method); known active liver disease including steatosis; ischemic heart disease, clinically significant cardiac conduction disorder, arrhythmia requiring treatment, congenital long QT syndrome, uncompensated heart failure; diabetes requiring insulin; neuropathy or myopathy; and malignancy (not including squamous cell skin cancer, basal cell skin cancer, or cervical low-grade squamous intraepithelial lesions). Participation may be precluded due to safety concerns or inability to adequately evaluate clinical trial endpoints.