A Study to Learn How Different Amounts of the Study Medicine Called PF-08103402 Are Tolerated and Act in the Body in Healthy Adults or Adults With Mild To-moderate Asthma

The purpose of this study is to learn about the safety of a new study medicine called PF-08103402 in healthy adults (do not have disease) and or in adults with mild-to-moderate asthma. This is the first time the study medicine is being given to people.

For Parts A, B, C, D and F, the study is seeking participants who:

• Are healthy (do not have disease) males or females who can no longer have children,
• Are 18 to 65 years old,
• Have a body mass index (BMI) of 16 to 32 kilograms per meter squared and a body weight of more than 50 kilograms (110 pounds). Body mass index is a way to measure body fat by using a person's height and weight

For Part A (optional group or cohort 3: Japanese participants only):

• A body weight of more than 45 kilograms (100 pounds).
• Have 4 biological Japanese grandparents who were born in Japan.

For Part E only:

• Adults with a documented history of asthma (confirmed by a doctor) for at least 12 months before entering the study.
• Have a body mass index (BMI) of 16 to 35 kilograms per meter squared and a total body weight of more than 50 kilograms (110 pounds).

The study has six parts: Part A, Part B, Part C, Part D, Part E and Part F. The study medicine will be taken as a suspension or tablet by mouth 1 time a day (except in Parts B and E where it will be taken 1 time a day for 14 days) at the study clinic. The study will help understand:

• how the body processes the study medicine in healthy participants (Parts A and B),
• how much of the study medicine gets into the bloodstream and if food affects the amount of study medicine in the blood in healthy participants (Part C),
• how the study medicine is broken down and leaves the body in healthy participants (Optional Part D),
• how the study medicine is processed in adults with mild-to-moderate asthma (Optional Part E),
• if taking the study medicine together with another medicine affects how each medicine is processed by the body in healthy participants (Optional Part F).

Participants will take part in the study for about 10 weeks (Parts A and F), 12 weeks (Part B), 9 weeks (Parts C and D), and 16 weeks (Part E).

During this time, they will have 2 study visits at the study clinic and up to 28 overnight stays (Part A), 18 overnight stays (Parts B and E), 10 overnight stays (Part C), 11 overnight stays (Part D), and 16 overnight stays (Part F). The study team will also call participants 1 time over the phone at the end of the study to assess how they are doing.

Study measurements will be taken by body examination, monitoring side effects, blood and urine tests, heart tests (ECG), vital signs (blood pressure and pulse), questionnaires (Parts C and E), stool samples (Part D only), and breathing tests (Part E only).