The main purpose of this study is to evaluate safety, tolerability, pharmacokinetics and pharmacodynamic parameters after single ascending intravenous doses of AON-D21 in healthy male subjects.

This study will potentially include 5 sequential cohorts with 8 subjects per cohort, then 40 enrolled subjects in total. Within each dose group 6 subjects will be randomized to receive AON-D21 and 2 subjects will be randomly assigned to placebo.

Inclusion Criteria:

• 18 to 55 years of age inclusive, at the time of signing the informed consent.
• Body mass index (BMI) within the range 18 - 30 kg/m2 with a body weight between 50 kg and 120 kg.
• Male subjects
• Subject is healthy as determined by medical evaluation
• Subject provided written informed consent
• Subject is willing to comply with all requirements and restrictions according to the study protocol.

Exclusion Criteria:

• Any concomitant disease, condition, or treatment that could interfere with the conduct of the study.
• Any acquired or congenital immune deficiency.
• Acute infection (including viral infections) in the preceding 6 weeks (8 weeks for respiratory infections).
• Any concomitant disease, condition, or treatment that could interfere with the conduct of the study.
• Any acquired or congenital immune deficiency.
• Acute infection (including viral infections) in the preceding 6 weeks (8 weeks for respiratory infections).
• Clinically relevant abnormality following the Investigator's review of the physical examination, vital signs, ECG and clinical study protocol-defined clinical laboratory tests that, in the opinion of the Investigator, would preclude inclusion in the trial at screening and admission.
• Evidence of COVID-19 signs or symptoms, exposure to infected person or confirmed COVID-19 infection within the last 2 weeks.
• Use of any concomitant medication or prescribed or non-prescribed drugs within 2 weeks or 5 times the half-life, whichever is longer, prior to the first study treatment administration.
• Administration of vaccine(s) within 2 weeks prior to screening or plans to receive such vaccines during the study.
• Use of any investigational drug or participation in any clinical study within 30 days or 5 half-life times, whichever is longer, prior to dosing.
• Positive drug or alcohol screen at screening and admission.
• Any significant blood loss, donated one unit (450 mL) of blood or more, or donated plasma, or received a transfusion of any blood or blood products within 30 days prior to dosing.
• Subjects who are unable to refrain from the consumption of Seville oranges, grapefruit or grapefruit juice and /or pomelos, exotic citrus fruits, grapefruit hybrids, starfruit or fruit juices from 72 hours prior to dosing on Day 1, until completion of the last pharmacokinetic (PK) blood sample time point.
• Legal incapacity or limited legal capacity, or incarceration.
• Inability to understand or communicate reliably with the Investigator.

Quadruple: Participant, Investigator, Outcomes Assessor and Care provider.