Anti–CTLA-4 antibodies with distinct antitumor and autoimmune effects bound to an overlapping site on CTLA-4 and blocked B7-1/CTLA-4 interaction. (A-C) Cross-competition. Unlabeled anti–CTLA-4 antibody (100 μg/mL) was added to plates coated with CTLA-4 Ig. Given concentration of the biotinylated antibodies were added to the wells after 10 minutes. The amounts of biotinylated antibodies bound were determined by adsorption of horseradish peroxidase (HRP)–labeled streptavidin to the plates. Data shown are means and SEM of OD 490. (D) All anti–CTLA-4 antibodies used in the study block B7-1–CTLA-4 interaction. Chinese hamster ovary (CHO) cells transfected with human B7-1 were incubated with a mixture of CTLA-4 Ig and given anti–CTLA-4 antibodies. After washing away the unbound antibodies, the binding of CTLA-4 Ig was determined by flow cytometry using APC-labeled goat anti–human CTLA-4 antibody. Data shown are histograms depicting CTLA-4 Ig binding to human B7-1–transfected CHO cells. Frozen sections of kidney were analyzed after the mice were euthanized, when they reached early removal criteria (tumors reach 4000 mm³), with the exception of 2 mice in the L3D10-treated group in which tumors never reached the criteria for early removal. The incidences of IgG deposition in mice treated with K4G4 (P = .029) and L1B11 (P = .029), but not L3D10 (P = .47) are significantly higher than the control group.