This single center, single ascending dose (SAD) and repeat dose study in healthy adults comprises 2 parts. Part 1 will consist of 6 SAD cohorts, in which different dose levels of sargramostim will be given by intravenous (IV) infusion, subcutaneous (SC) injection, or inhalation (IH) administration. Part 2 will consist of 1 repeat dose cohort in which sargramostim will begiven by SC administration.

Blood samples for PK assessment will be collected before and over 24 hours after each study drug administration. Blood samples for PD assessment will be collected before and up to 14 days after drug administration in Part 1, as well as before the first and up to 14 days after the second drug administration in Part 2. Safety and tolerability will be assessed throughout the study. For Cohort 5 of Part 1 only, 3 subjects will provide a CSF sample for PK assessmen tonce after SC drug administration.

Inclusion Criteria:

• Healthy adult male and female participants
• Nonsmoker or ex-smoker
• Able to provide informed consent and comply with all study procedures
• Body Mass Index within 18.5-30.0 kilograms/meter squared, inclusive
• Females of childbearing potential willing to use highly-effective method of birth control.

Exclusion Criteria:

• Females who are pregnant or breastfeeding
• History of allergic to sargramostim or its excipients, other human GM-CSFs, or other yeast-derived products.
• History of severe allergic reactions to other drugs.
• History of or any current medical condition or laboratory finding that may jeopardize completion of the study, present an increased risk to the subject, or compromise interpretation of the study. .
• Immunization with COVID-19 vaccine within 14 days of the study.
• Scheduled immunization with COVID-19 vaccine during the study
• Use of prescription drugs within 28 days of the study or requirement for maintenance drugs during the study.
• Participation in another investigational drug study within 28 days