A study of CD33 (SIGLEC-3) antigen expression and function on activated human T and NK cells: two isoforms of CD33 are generated by alternative splicing

Abstract

The expression of CD33, a restricted leukocyte antigen considered specific for myeloid lineage, has been studied extensively on lymphoid cells. We demonstrated that wide subsets of mitogen- or alloantigen-activated human T and natural killer (NK) cells express CD33 at protein and nucleic acid levels. CD33+ and CD33- T and NK cell populations showed identical surface expression of activation markers such as CD25, CD28, CD38, CD45RO, or CD95. Myeloid and lymphoid CD33 cDNA were identical. However, lymphoid CD33 protein had lower molecular weight, suggesting cell type-specific, post-translational modifications. Additionally, reverse transcriptase-polymerase chain reaction and Northern blot analysis showed an unknown CD33 isoform (CD33m) expressed on all CD33+ cell lines or T cell clones tested. CD33m was identical to CD33 (CD33M) in the signal peptide, the immunoglobulin (Ig) domain C2, the transmembrane, and the cytoplasmic regions but lacked the extracellular ligand-binding variable Ig-like domain encoded by the second exon. CD33m mRNA was mostly detected on NKL and myeloid cell lines but poorly expressed on B cell lines and T lymphocytes. The CD33m extracellular portion was successfully expressed as a soluble fusion protein on transfected human cells, suggesting a functional role on cell membranes. Cross-linking of CD33 diminished the cytotoxic activity of NKL cells against K562 and P815 target cells, working as an inhibitory receptor on NK cells. These data demonstrate that CD33 expression is not restricted to the myeloid lineage and could exist as two different splicing variants, which could play an important role in the regulation of human lymphoid and myeloid cells.

T cells expressing CD123-specific chimeric antigen receptors exhibit specific cytolytic effector functions and antitumor effects against human acute myeloid leukemia

“…17,36,37 Similar to TIM-3, CD33 is expressed on a subset of T cells, making it a nonideal target for a CARbased therapy. 38 Additionally, the antileukemic activity of CD33-targeting therapies was often accompanied by slow recovery of hematopoiesis and cytopenias, likely the result of CD33 expression on long-term self-renewing normal HSCs. 39 Further, hepatotoxicities are a common side effect of CD33-targeted treatments and are possibly due to the unintended targeting of CD33…”

Preclinical Characterization of AMG 330, a CD3/CD33-Bispecific T-Cell–Engaging Antibody with Potential for Treatment of Acute Myelogenous Leukemia

“…One is shedding of CD33 (9, 10), which could create a sink for AMG 330 in plasma or bone marrow inhibiting its target binding. The other is neoexpression of CD33 on activated T cells (23), which would turn newly activated T cells into CD33 þ target cells for lysis. As previously reported for BiTE antibodies binding to CEA (30) and EpCAM (31), we could not observe a significant impact of soluble CD33 at physiologically relevant concentrations on redirected lysis or T-cell activation by AMG 330.…”

“…Activated human NK and T cells were shown to newly express CD33 (23). Using ten different healthy donor PBMCs, we have investigated what percentage of CD4 þ and CD8 þ T cells becomes CD33 þ after 48, 72, and 144 hours of T-cell stimulation with anti-CD19 BiTE antibody AMG 103 in the presence of CD19 þ NALM-6 target cells.…”

Advances in Anticancer Immunotoxin Therapy

“…CD33 was originally thought to be a myeloid-specific marker; however, some natural killer and T-cell subsets also express this leukocyte-differentiation antigen [45]. Importantly, many acute myelogenous leukemias (AMLs) have strong CD33 surface expression [46].…”