Additional Study Information: A sign of your kidney disease is the presence of too much protein in your urine. The purpose of this study is to evaluate if the investigational study drug abatacept can decrease the amount of protein in your urine and improve your kidney disease beyond the treatment you have received or are already receiving. Abatacept is being used in an investigational manner (not for the purpose that it is approved for) in this research study. This means that Abatacept has been approved by the Food and Drug Administration (FDA) for treating Rheumatoid Arthritis in adults and children, but it has not been approved for treatment resistant nephrotic syndrome (FSGS or MCD).