ONT01 is a drug that is being studied for the treatment of Lupus Nephritis (LN) and Systemic Lupus Erythematosus (SLE) and is not approved by the FDA. The purpose of this study is to better determine whether ONT01 is safe and tolerated by people with lupus nephritis or SLE. The study also looks at how the administration of ONT01 in combination with widely used treatments given for lupus, including the medication mycophenolate mofetil and others, can improve symptoms of lupus. A total of 61 participants will be enrolled in this study.