a target molecule for apoptosis induction of leukemic cells CTLA-4 is not restricted to the lymphoid cell lineage and can function as

ABSTRACTThe expression of CTLA-4 molecule in human normal and neoplastic hematopoietic cells both on the cell membrane and in the intracellular compartment was evaluated. Flow cytometric analysis carried out with a panel of anti-CTLA-4 human scFv antibodies revealed that CTLA-4 was not expressed on the surface, whereas it was highly expressed within the cytoplasm, in freshly isolated PBMCs, T cells, B cells, CD34 + stem cells and granulocytes. Various treatments with agents able to specifically activate each cell type induced CTLA-4 expression on surface of these cells. Similarly, increased CTLA-4 expression was observed in different hematopoietic cell lines although they expressed surface CTLA-4, at different degrees of intensity, also before activation. Surprisingly, CTLA-4 RNA transcripts were detectable in such cell lines only after nested PCR specific for CTLA-4 extracellular domain, suggesting a very fast CTLA-4 RNA processing accompanied by prolonged CTLA-4 protein accumulation. We further demonstrated surface expression of CTLA-4 in a variety of acute and chronic myeloid (AML and CML) leukemias and B- and T-lymphoid leukemias either adult or pediatric. CTLA-4 was expressed in 25% to 85% of AML and CML depending on the leukemia subtype and the epitope analyzed, whereas in acute B- and T-leukemias CTLA-4 expression was mainly cytoplasmic. Chronic B-leukemias appeared to express CTLA-4 both on surface and in cytoplasm, while few cases tested of chronic T-leukemias were negative. Two anti-CTLA-4 immunotoxins (scFvs-saporin) induced in vitro apoptosis of neoplastic cells from a representative AML suggesting a novel immunotherapeutic approach of AML based on CTLA-4 targeting.Author e-mail address: mariapia.pistillo@istge.itFrom bloodjournal.hematologylibrary.org by guest on June 2, 2013. For personal use only.