CTLA-4 is not restricted to the lymphoid cell lineage and can function as a target molecule for apoptosis induction of leukemic cells.
The expression of cytotoxic T-lymphocyte antigen-4 (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 single-chain fragment of variable domain (scFv) antibodies revealed that CTLA-4 was not expressed on the surface, whereas it was highly expressed within the cytoplasm, in freshly isolated peripheral blood mononuclear cells (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 the surface of these cells. Similarly, increased CTLA-4 expression was observed in different hematopoietic cell lines although they also expressed surface CTLA-4, at different degrees of intensity, before activation. Surprisingly, CTLA-4 RNA transcripts were detectable in such cell lines only after nested polymerase chain reaction (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 leukemias (AMLs and CMLs) and B- and T-lymphoid leukemias, either adult or pediatric. CTLA-4 was expressed in 25% to 85% of AMLs and CMLs 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 the surface and in cytoplasm, whereas 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 to AML based on CTLA-4 targeting.
Pistillo
Maria Pia
MP
Laboratory of Immunogenetics and Laboratory of Molecular Morphogenesis, National Cancer Research Institute, Advanced Biotechnology Center, Genoa, Italy. mariapia.pistillo@istge.it
Tazzari
Pier Luigi
PL
Palmisano
Giulio Lelio
GL
Pierri
Ivana
I
Bolognesi
Andrea
A
Ferlito
Francesca
F
Capanni
Paolo
P
Polito
Letizia
L
Ratta
Marina
M
Pileri
Stefano
S
Piccioli
Milena
M
Basso
Giuseppe
G
Rissotto
Laura
L
Conte
Roberto
R
Gobbi
Marco
M
Stirpe
Fiorenzo
F
Ferrara
Giovanni Battista
GB
D000069594:Abatacept; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D017209:Apoptosis / Q000187:drug effects*; D001773:Blood Cells; D060908:CTLA-4 Antigen; D002460:Cell Line; D019070:Cell Lineage; D003593:Cytoplasm / Q000737:chemistry; D005434:Flow Cytometry; D006412:Hematopoietic Stem Cells; D006801:Humans; D007118:Immunoassay; D018796:Immunoconjugates; D000922:Immunotoxins / Q000494:pharmacology; D007938:Leukemia / Q000473:pathology* / Q000628:therapy; D007962:Leukocytes / Q000166:cytology / Q000378:metabolism; D008213:Lymphocyte Activation; D012333:RNA, Messenger / Q000378:metabolism
D015703:Antigens, CD; D000943:Antigens, Differentiation; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; D018796:Immunoconjugates; D000922:Immunotoxins; D012333:RNA, Messenger; D000069594:Abatacept