Myeloid precursors and acute myeloid leukemia cells express multiple CD33-related Siglecs.
OBJECTIVE
CD33 is a cell surface marker of committed myelomonocytic precursors and circulating monocytes, and is also found on acute myeloid leukemia (AML) cells. CD33 belongs to a family of sialic acid-binding cell surface proteins named Siglecs, among which there are 7 other functional CD33-related Siglecs (CD33rSiglecs). We sought to characterize the spectrum of expression of the other CD33rSiglecs on bone marrow precursors and AML cells and asked if they can potentially serve as targets for therapy.


METHODS
Cell surface CD33rSiglecs were analyzed by flow cytometry. The ability of certain anti-Siglec antibodies to target toxin-mediated cell killing of Siglec-expressing cell lines was characterized and compared.


RESULTS
We demonstrate that Siglecs-3, -5, -6, -7, and -9 are expressed on subsets of normal bone marrow precursors, including promonocytes and myelocytes. Furthermore, most AML (but not ALL) cells express these Siglecs. There is substantial variability in Siglec type and expression level between cases, with each having a unique "CD33rSiglec fingerprint." Individual anti-Siglec antibodies along with a saporin toxin-conjugated secondary antibody can target myelomonocytic leukemia cells for death, and targeting of multiple Siglecs improves cell killing. Cytotoxicity was further enhanced by sialidase treatment of target cells, which improves antibody binding. We also confirmed that antibody binding induced rapid internalization of Siglecs from the cell surface, which is a requirement for cell killing via saporin.


CONCLUSIONS
Multiple CD33rSiglecs are expressed on normal and malignant myelomonoyctic cells. Targeting these Siglecs, possibly in combinations, could improve anti-CD33 antibody therapy or be used as an alternative to anti-CD33.
Nguyen
Dzung H
DH
Glycobiology Research and Training Center, University of California, San Diego, La Jolla, USA.
Ball
Edward D
ED
Varki
Ajit
A
D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology; D015703:Antigens, CD / Q000096:biosynthesis; D015214:Antigens, Differentiation, Myelomonocytic / Q000096:biosynthesis; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007152:Immunologic Capping / Q000187:drug effects / Q000276:immunology; D000922:Immunotoxins / Q000276:immunology / Q000494:pharmacology; D037102:Lectins / Q000096:biosynthesis*; D007951:Leukemia, Myeloid / Q000188:drug therapy / Q000276:immunology / Q000378:metabolism*; D023461:Myeloid Progenitor Cells / Q000276:immunology / Q000378:metabolism; D009699:N-Glycosyl Hydrolases / Q000494:pharmacology; D014411:Neoplastic Stem Cells / Q000276:immunology / Q000378:metabolism*; D010940:Plant Proteins / Q000494:pharmacology; D054789:Ribosome Inactivating Proteins, Type 1; D000076985:Saporins; D063268:Sialic Acid Binding Ig-like Lectin 3; D063265:Sialic Acid Binding Immunoglobulin-like Lectins; D020298:U937 Cells
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D000972:Antineoplastic Agents, Phytogenic; C571163:CD33 protein, human; D000922:Immunotoxins; D037102:Lectins; D010940:Plant Proteins; D054789:Ribosome Inactivating Proteins, Type 1; D063268:Sialic Acid Binding Ig-like Lectin 3; D063265:Sialic Acid Binding Immunoglobulin-like Lectins; D009699:N-Glycosyl Hydrolases; D000076985:Saporins