The purpose of this study is to determine if the investigational (not FDA approved) drug VIB4920 can be an effective treatment for patients with active Lupus Nephritis (LN).

This study will compare treatment with MMF (mycophenolate mofetil), Prednisone, plus the study medication VIB4920 to treatment with MMF and Prednisone alone.

Participants will have 16 scheduled visits that will involve routine monitoring of disease activity, up to two kidney biopsies, and blood and urine specimen collections. Participation in this study will last approximately 1 year and 2 months. Compensation is available for participation.

The purpose of this study is determine the optimal dose, efficacy and safety of an investigational drug (a new drug not yet approved by the U.S. Food and Drug Administration) in adults with Advanced Systemic Mastocytosis. The investigational drug is known as CGT9486 and will be taken daily orally. Participation in the study is expected to be approximately 6 years.