The incidence of progressive kidney disease associated with diabetes continues to rise worldwide. Current standard therapy with angiotensin–converting enzyme inhibitors and/or angiotensin receptor blockers achieves only partial renoprotection, increasing the need for novel therapeutic approaches. Previous studies described B7–1 induction in podocytes of patients with proteinuria, including those with FSGS and type 2 diabetic nephropathy (DN). These findings sparked great excitement in the renal community, implying that abatacept, a costimulatory inhibitor that targets B7–1, could be a novel therapy for diabetic renal disease. Given previous concerns over the value of B7–1 immunostaining and the efficacy of abatacept in patients with recurrent FSGS after renal transplantation, we investigated B7–1 expression in human and experimental DN before embarking on clinical studies of the use of B7–1 targeting strategies to treat proteinuria in DN. Immunohistochemical analysis of kidney specimens using different antibodies revealed that B7–1 is not induced in podocytes of patients with DN, independent of disease stage, or BTBR ob/ob mice, a model of type 2 diabetes. These results do not support the use of abatacept as a therapeutic strategy for targeting podocyte B7–1 for the prevention or treatment of DN.