ABSTRACT
BACKGROUND: The presence of antibodies to CTLA-4, a negative regulator of T-cell activation, was investigated in multiply transfused patients with malignant and non- malignant hematologic diseases. A previous study showed that, in multiply transfused patients, an immune response against nuclear matrix proteins can be induced by WBCs undergoing apoptosis during RBC unit storage. This study evaluated whether the same phenomenon could be involved in the induction of CTLA-4 antibodies in the patients analyzed. STUDY DESIGN AND METHODS: Patient sera were tested for binding to the recombinant full-length CTLA-4 beta-galactosidase fusion protein by an ELISA. Immuno-fluorescence stainings were performed to analyze the CTLA-4 epitopes recognized by the antibodies and to detect such epitopes in the apoptotic cells present in the RBC units. RESULTS: CTLA-4 antibodies were found in multiply transfused patients with beta-thalassemia (40%) and with other hemolytic diseases (33%) including leukemias (42%). A higher incidence of CTLA-4 antibodies was found in patients receiving non-WBC-reduced blood (88%) than in those receiving WBC-reduced blood (26%). Immunofluorescence staining showed that WBCs undergoing apoptosis in the RBC unit expressed CTLA-4 epitopes. CONCLUSIONS: The apoptotic WBCs present in the RBC units, after cold storage, express CTLA-4 epitopes. These epitopes can be released and induce formation of CTLA-4 antibodies with profound implications in the development of autoimmune disorders and in facilitating tumor dissemination and metastasis.