Phase 1 of this study will consist of 2 parts

• Part 1 will evaluate the safety, tolerability, pharmacokinetics and immunogenicity of PRA-216 in healthy volunteers through single ascending dose administered by either intravenous (IV) or subcutaneous (SC).
• Part 2 will evaluate the safety, tolerability, pharmacokinetics (PK) and immunogenicity of PRA-216 in healthy volunteers with repeat doses of multiple ascending dose administered subcutaneously.

Phase 2a of this study is a randomized, double-blind, placebo-controlled study to investigate the efficacy, safety and immunogenicity of PRA-216 in participants with mild to moderate asthma. The dose of PRA-216 for this phase was determined from Phase 1.

This study is a Phase 1/2a randomized, double-blind, placebo-controlled, single- and multiple-dose study with staggered dose escalations in healthy participants and participants with mild to moderate asthma. Single-ascending dose (SAD) cohorts will be evaluated for one single dose administered. Multiple ascending dose (MAD) cohorts will be evaluated for repeat doses .

Participants with mild to moderate asthma will be recruited for Phase 2a of this study, to evaluate safety of randomized, double blind, placebo controlled PRA-216. The dose of PRA-216 for this phase was determined from Phase 1 safety, tolerability, and PK data. Additional dose levels or schedules may be used for Phase 2a, depending on data from Phase 1.

This study consists of 2 phases, as follows:

Phase 1, Part 1:

SAD in healthy volunteers. Study visits in this section will entail a single dose administration of PRA-216 or placebo and collection of study data.

Phase 1, Part 2:

MAD in healthy volunteers. Study visits in this section will entail repeat doses of PRA-216 or placebo and collection of study data.

Phase 2a Participants with mild to moderate asthma will receive PRA-216 or placebo.

Phase 1

Inclusion Criteria:

• Age 18-65
• Must be in good health with no significant medical history
• Willing and able to attend all study visits, comply with study requirements
• Able and willing to provide written informed consent

Exclusion Criteria:

• Evidence of clinically significant condition or disease
• Any physical or psychological condition that prohibits study completion
• Known history of illicit drug use or drug abuse, harmful alcohol use (at the Investigator's discretion), alcoholism, and/or smoking or nicotine-containing product use within 3 months prior to the first dose of study agent
• History of severe allergic reactions or hypersensitivity
• Donation or loss of ≥ 1 unit of whole blood or plasma within 2 months prior to dosing

Phase 2a

Inclusion criteria:

• Age 18-65
• Must be in good health with no significant medical history
• Willing and able to attend all study visits, comply with study requirements.
• Able and willing to provide written informed consent
• Documented asthma diagnosis prior for at least 12 months prior to screening.
• Symptomatic asthma
• Currently receiving maintenance asthma medications

Exclusion Criteria:

• Evidence of clinically significant condition or disease
• Known history of illicit drug use or drug abuse, harmful alcohol use (at the Investigator's discretion), alcoholism, and/or smoking or nicotine-containing product use within 3 months prior to the first dose of study agent
• Donation or loss of ≥ 1 unit of whole blood or plasma within 2 months prior to dosing
• History of severe allergic reactions or hypersensitivity
• Current or former smoker with a smoking history of ≥10 pack-years
• Receipt of immunosuppressant therapies or biologic therapy for asthma within 6 months of screening
• Other investigational agent(s) within 30 days of dosing