The purpose of this study is to investigate the safety and tolerability of LY4298445 in healthy participants and in participants with systemic lupus erythematosus (SLE) or rheumatoid arthritis (RA). Participation in the study will last up to approximately 52 weeks.
Have body weight of at least 50 kilograms (kg) and body mass index (BMI) between 18 and 32 kilogram per square meter (kg/m²), inclusive.
Are 18 to 75 years of age, inclusive.
Have body weight between 45 and 145 kg, inclusive, and BMI between 18 and 35 kg/m², inclusive.
Have a clinical diagnosis of SLE according to the 2019 European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) classification criteria at least 6 months prior to screening.
Have known allergies to LY4298445, related compounds, or any components of the formulation
Are individuals assigned female at birth (AFAB) who are lactating or have a positive pregnancy test at screening or Day -1.
Have severe active lupus-associated renal disease (lupus nephritis) defined clinically and/or by
urine protein/creatinine ratio greater than 200 milligrams per millimole (mg/mmol) (as an estimate of approximate proteinuria greater than 2 reams (g) per day) or
Parallel
LY4298445
DrugAdministered SC
LY4298445
DrugAdministered IV
6
Treatment groupsSee each treatment group below.
Number of Participants with One or More Serious Adverse Event(s) (SAEs) Considered by the Investigator to be Related to Study Drug Administration
A summary of SAEs regardless of causality, will be reported in the Reported Adverse Events module
Pharmacokinetics (PK): Area Under the Concentration Versus Time Curve (AUC) of LY4298445
PK: AUC of LY4298445
PK: Maximum Concentration (Cmax) of LY4298445
PK: Cmax of LY4298445
Pharmacodynamic (PD): Degree of Peripheral B Cell Depletion Following Biopsy in Participants
PD: Peripheral B cell depletion
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