Inclusion Criteria:

• Male and female participants between 18 and 55 years of age inclusive.
• Participants who are overtly healthy as determined by medical evaluation including medical history, physical examination, laboratory tests, and ECG.
• Laboratory values within normal range unless the abnormality is considered not clinical relevant by the investigator. The following parameters, however, must be within normal range: platelet count, and CRP. ALT, AST, total bilirubin (unless the participant has documented or suspected Gilbert syndrome) should be <1.25 ULN and serum creatinine should be < ULN.
• Eosinophils <500 cells/µL
• Normal vital signs after 10 minutes resting in supine position
• Standard 12-lead ECG parameters after 10 minutes resting in supine position in the normal ranges and normal ECG tracing unless the Investigator considers an ECG tracing abnormality to be not clinically relevant.
• Body weight between 50 - 110 kg (inclusive) and body mass index (BMI) between 18 - 30 kg/m2 (inclusive) at screening.
• Only for part 2: Fitzpatrick skin type I - III

Exclusion Criteria:

• Any disease associated with immune system dysfunction.
• Known polyethylene glycol allergy
• Only for Part 2: Known seafood allergy
• Any current active viral, bacterial or fungal infection or any medically relevant infection having occurred within 3 weeks before inclusion.
• Any history or presence of clinically relevant cardiovascular, pulmonary, gastrointestinal, hepatic, renal, metabolic, hematological, neurological, osteomuscular, articular, psychiatric, autoimmune, systemic, ocular, or infectious disease, or signs of acute illness that would pose an unacceptable risk to the subject in the opinion of the investigator.
• Frequent headaches and/or migraine, recurrent nausea and/or vomiting (for vomiting only, more than twice a month).
• Blood donation >500 mL within 2 months before inclusion.
• Symptomatic postural hypotension, irrespective of the decrease in blood pressure, or asymptomatic postural hypotension defined as a decrease in systolic blood pressure ≥30 mmHg within 3 minutes when changing from supine to standing position.
• Presence or history of drug hypersensitivity, or allergic disease diagnosed and treated by a physician, except for history of mild allergic diseases which are not active at the time of inclusion and considered not clinically relevant in the opinion of the investigator.
• History or presence of drug or alcohol abuse.
• Smoking regularly more than 10 cigarettes or equivalent per week, unable to stop smoking during the study (occasional smoker can be enrolled).
• Excessive consumption of beverages containing xanthine bases.
• Presence or history of any atopic disease.
• for Part 1: Non-live booster COVID-19 vaccination within 14 days before randomization. First (and second, if applicable) COVID-19 vaccinations are not allowed within 4 weeks before randomization.
• for Part 2: Non-live vaccines including Covid-19: last administration of a vaccine within 4 weeks before randomization.
• Live vaccines: Last administration of a vaccine within 3 months before randomization; Immunomodulatory medication within 60 days before screening.
• Only for Part 2: Participants with known previous exposure to KLH.
• Any medication (including St John's Wort) within 14 days before inclusion or within 5 times the elimination half-life or pharmacodynamic half-life of the medication; any vaccination within the last 28 days (except COVID-19 booster vaccination) and any biologics (antibody or its derivatives) given within 4 months before inclusion.
• Positive result on any of the following tests: hepatitis B surface (HBs Ag) antigen, antihepatitis B core antibodies (anti-HBc Ab), anti-hepatitis C virus (anti-HCV) antibodies, anti-HIV1 and anti HIV2 Ab.
• Positive result on urine drug screen.
• Positive alcohol breath test.

The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.