PF-07899895

The purposes of the study are as follows:
* To understand how safe and tolerable are different amounts of study medicine (PF-07899895).
* To measure the amount of PF-07899895 in blood after the medicine is taken by mouth.
The study is seeking participants who:
* Are male or female of 18 to 65 years of age.
* Are in good health condition.
* Have not had viral infections (HIV, HBV, or HCV). HIV, human immunodeficiency virus. - HBV, human hepatitis B virus. HCV, human hepatitis C virus.
* Have tested negative for tuberculosis.
Participants will receive either PF-07899895 or placebo (dummy pill) by chance. In the first part of the study (Part A):
* each participant will receive a total of up to 5 doses of the medicine or placebo with at least 5 days between each dose.
* after each dose, participants will stay in study clinic for 3 to5 days.
In the second part of the study (Part B):
- each participant will need to take 10 days of dosing and will stay in the study clinic for clinical checks for 13 days.
The planned duration of participation from screening to follow-up in:
* Part A of the study is up to 15 to 18 weeks.
* Part B of the study is up to 11 weeks. Participants will also have their blood collected by the study doctors for several times.