ALX-0171 is a Nanobody directed against the human respiratory syncytial virus (RSV). The purpose of this first-in-man study is to determine the safety, tolerability and pharmacokinetics (PK) of ALX-0171 after single and multiple pulmonary administrations in healthy male volunteers.

Inclusion Criteria:

• Non-smoking healthy male volunteers, aged 18-55 years
• Good health condition, as determined by medical history, physical examination and clinical laboratory testing
• Forced expiratory volume in 1 second (FEV1) ≥ 90% of predicted value
• Diffusing capacity of the lung for CO (DLCO) ≥ 85% of predicted value
• Normal chest X-Ray (anteroposterior and lateral view)
• Minimum weight of 70.0 kg, minimum height of 1m70, body mass index between 18.0 and 30.0 kg/m²

Exclusion Criteria:

• Current smokers, or ex-smokers abstinent from tobacco for less than one year
• History or presence of atopy or pulmonary non-specific hyperreactivity
• Positive bronchial challenge test
• Symptomatic viral infection, or suspicion thereof (including rhinitis) in last 14 days prior to dosing
• Signs of active pulmonary infection or other inflammatory conditions, even in the absence of febrile episodes, in the last 14 days prior to dosing