The purpose of this Phase I single ascending dose study is to evaluate the safety, pharmacokinetics (PK), and pharmacodynamics (PD) of BEAM-103 in healthy subjects between the ages of 18 and 55. The main questions the study aims to answer are:

• Safety and tolerability of BEAM-103
• The pharmacokinetic (PK) profile and pharmacodynamic (PD) characteristics of EAM-103
• The effect of BEAM-103 on hematologic parameters
• To assess the immunogenicity of BEAM-103

Researchers will determine and establish the therapeutic window of the antibody and select optimal doses for future trials in patients.

Subjects will:

• Be asked to participate in the study for a duration of 4-5 months total
• Be asked to sign informed consent
• Be assessed for eligibility
• Provide medical and medication history
• Receive a single intravenous infusion of BEAM-103 or placebo on study Day 1 according to their assigned cohort
• Be followed up to 4 months after infusion

Inclusion Criteria:

• Ages 18 to ≤55 years
• Body mass index (BMI) of 18.5 to 25 kg/m2
• Morning neutrophil count ≥2.6 × 109 cells/L for Black/African American subjects or ≥3.5 ×109 cells/L for Caucasian/Other subjects
• Baseline hemoglobin value of ≥14 g/dL for males and ≥12 g/dL for females
• Baseline platelet count of >150 × 109/L.
• Subjects must be in general good health without significant medical conditions (based on physical exam, electrocardiogram (ECG), and laboratory test results with no clinically significant deviations), per the investigator's assessment

Exclusion Criteria:

• Known hypersensitivity to any component of the investigational medicinal product (IMP).
• Participation in another clinical trial involving treatment with an investigational agent within 90 days of informed consent is prohibited.
• Positive serum pregnancy test or breastfeeding at screening (female participants).
• Live virus vaccination within 4 weeks prior to signing informed consent.
• Any severe or uncontrolled medical condition (eg. severe asthma or severe peanut allergy) that in the opinion of the investigator would put the subject at undue medical risk or impair the ability to interpret study results.