Idiopathic Inflammatory Myositis

The purpose of this study is to learn about the safety and effects of the study medication called PF-08154225 for the potential treatment of autoimmune diseases. An autoimmune disease is a condition that makes a person's immune system attack its healthy cells by mistake. This study is particularly looking at autoimmune diseases called as Systemic Lupus Erythematosus (SLE), Rheumatoid Arthritis (RA), Idiopathic Inflammatory Myositis (IIM) or Systemic Sclerosis (SSc). This study is divided into 3 parts: Part 1a, Part 1b and Part 2. Parts 1a and 1b are seeking participants with Systemic Lupus Erythematosus (SLE) or Rheumatoid Arthritis and Part 2 with also Idiopathic Inflammatory Myositis (IIM) or Systemic Sclerosis (SSc). Participants can take part only in one part of the study. All participants in this study will receive PF-08154225 at the study clinic. In Part 1a participants will receive single administration of PF-08154225 after which they will be observed at the study clinic during regular visits through week 16 or longer. In Part 1b the participants will receive multiple administration of PF-08154225 after which they will be monitored in similar a manner as in Part 1a through week 24 or longer. In Part 2 participants will receive multiple administrations of PF-08154225. After the last injection they will be monitored for safety through week 52 or longer.

Myositis are rare diseases for which the development of a cohort associated with a bank of biological samples (biobank) will allow for the conduct of researches to better delineate the underlying pathophysiology and find cures. This prospective cohort of patients with myositis will allow for identification of factors favouring the occurrence of myositis, whether they are constitutional (genetic) or acquired (environmental or drug). Different subgroups of myositis used for prognostication will be identified based on clinico-demographical variables, the nature of the organs involved beyond peripheral muscles (cardiac, diaphragm) and biomarkers abnormalities