The purpose of this study is to learn about the safety and effects of the study medicine (called PF-07985631) for the possible treatment of a kidney disease called IgA nephropathy.

This study is seeking participants who

• are male or female between 18 and 45 years of age (55 for Japanese/Chinese/multiple dose participants)
• are deemed to be healthy

Participants in this study will receive PF-07985631 or placebo. A placebo does not have any medicine in it but looks just like the medicine being studied.

PF-07985631 or placebo will be given as a small needle injection (in the abdomen, thigh or back of the arm) or as an IV infusion in the arm (given directly into a vein) at the study clinic. Most participants will receive PF-07985631 or placebo one time. Some participants may receive PF-07985631 or placebo once a month for 3 months.

The study will compare the experiences of people receiving PF-07985631 to those of the people who do not. This will help decide if PF-07985631 is safe and effective.

Participants who take PF-07985631 or placebo only 1 time will take part in this study for about 4 months. During this time, they will stay at the study clinic for 11 to 14 days and will have 8 more study visits at the study clinic.

Participants who take PF-07985631 or placebo more than once will take part in this study for about 6 months. During this time, they will stay at the study clinic for about 4 days a month 3 times and will have 10 more study visits at the study clinic.

During study clinic stays and study visits, blood samples will be done and safety reviews completed.

Inclusion:

1. Between 18 and 45 years of age who are overtly healthy.
2. Japanese/Chinese and multiple dose cohorts only: Adult participants 18 to 55 years of age who are overtly healthy may be eligible at the discretion of PI.
3. Japanese/Chinese cohorts only: Participants must have 4 biological Japanese/Chinese grandparents who were born in Japan/China.

Exclusion:

1. Evidence or history of clinically significant hematological, renal, endocrine, pulmonary, gastrointestinal, cardiovascular, hepatic, psychiatric, neurological, or allergic disease (including drug allergies, but excluding untreated, asymptomatic, seasonal allergies at the time of dosing).

2. Participants with a history of allergic or anaphylactic reaction with any investigative biologic agents.

3. History of infections requiring treatment within 28 days prior to Day 1 or any active infection at Day 1.

4. Active or latent infection with tuberculosis.

5. History of recurrent urinary tract infections AND/OR sinopulmonary infections AND/OR gastrointestinal infections requiring antibiotic treatment.

6. Known fever within the 7 days prior to dosing.

7. Active gastrointestinal (GI) tract ulcerations or GI bleeding.

8. Vaccination within 6 weeks prior to Day 1 dosing or planned vaccination during the study.

9. Positive urine drug test.

10. Screening supine blood pressure (BP) ≥140 mm Hg (systolic) or ≥90 mm Hg (diastolic).

11. Estimated glomerular filtration rate (eGFR) <75 mL/min/1.73 m².

12. Chest X-ray showing any active disease in the chest, or pulmonary nodules >0.5 cm in diameter that have not been previously evaluated, cavitary lesions or evidence of bronchiectasis.

13. Standard 12 lead ECG that demonstrates clinically relevant abnormalities that may affect participant safety or interpretation of study results.

14. Positive stool hematest at screening or admission.

15. Participants with ANY of the following abnormalities in clinical laboratory tests at screening:

    • Alanine aminotransferase (ALT), aspartate aminotransferase (AST), bilirubin (direct and total) ≥1.05 × upper limit of normal
    • Immunoglobulin G, Immunoglobulin M, Immunoglobulin A below the lower limit of normal (LLN)
    • Total white blood cell (WBC) below the LLN
    • Lymphocyte count below the LLN
    • Platelet count below the LLN
    • Hemoglobin below the LLN

Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.