A Study to Learn About a Medicine Called PF-08154225 in Participants With Autoimmune Diseases

This clinical trial consists of Part I and Part II. Phase I consists of dose escalation. The main goal of dose escalation is to evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of PF-08154225 in participants with Systemic Lupus Erythematosus (SLE) or Rheumatoid Arthritis (RA), and the main goal of Part II is to assess effects of PF-08154225 on the safety, tolerability, pharmacokinetics, pharmacodynamics and preliminary efficacy in participants with SLE or RA or IIM or SSc.

Select Inclusion Criteria

• At age between 18 and 70 years at Screening.
• Confirmed diagnosis of RA according to the 2010 American College of Rheumatology (ACR)/ European Alliance of Associations for Rheumatology (EULAR) criteria at Screening, with symptom at least 6 months prior to Screening
• Clinical diagnosis of SLE according to the 1997 ACR Criteria for the Classification of SLE Or confirmed diagnosis of SLE according to the Systemic Lupus International Collaborating Clinics (SLICC) Classification Criteria at Screening, with symptom at least 6 months prior to Screening.
• Clinical diagnosis of 1 of the 3 IIM subtypes based on phenotype, and/or prior muscle biopsy, and positive myositis-specific autoantibody (MSA) / myositis-associated antibody (MMA)
• Classification of SSc according to the 2013 ACR/EULAR criteria at Screening

Select Exclusion Criteria

• Any medical or psychiatric condition, including active suicidal ideation or any laboratory abnormality, that increases study risk or makes the participant unsuitable.
• Active central nervous system (CNS) co-morbidity
• Any complications of disease under study that in the judgement of the investigator may be life or organ threatening or require prohibited medication
• Known history of a primary immunodeficiency, splenectomy, or any underlying condition that predisposes the participant to infection
• Active or recent clinically significant infections
• Chronic or active Hepatitis B and C
• Past or current therapies with T-cell engager (TCEs), bone marrow cell transplant, stem cell transplant, chimeric antigen receptor T-cell (CAR-T) cell therapy.
• For SLE, no catastrophic or severe antiphospholipid syndrome (APS), severe unstable neuropsychiatric SLE.
• Felty's syndrome, juvenile arthritis or idiopathic arthritis before age of 16
• SSc renal crisis within 6 months prior to screening, UIP pattern if entering on interstitial lung disease interstitial lung disease (ILD) criteria
• Diagnosis of Inclusion body myositis (IBM) and Usual interstitial pneumonia (UIP) pattern if entering on ILD criteria