Additional Study Information: The purpose of this study is to assess whether an investigational drug called XmAb819 has any effects on Clear Cell Renal Cell Carcinoma, to determine if it is safe and well tolerated, and to determine the dosing schedule. The investigational drug will be given by intravenous (IV into the vein) infusion over a 2-hour period. This study will also see how the body affects the study drug and how much study drug is in the blood (pharmacokinetics, or PK), how the drug affects the tumor and body (pharmacodynamics, or PD), and if the body develops antibodies against the study drug. An antibody is a protein made by the body's immune (defense) system to fight foreign substances by binding to them.