Chemoenzymatic Labeling of LacNAc as a Method for Identifying and Improving Effector & Memory CD8+ T Cell Functions
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The terminal glycans of CD8+T cells undergo remodeling during T cell maturation and activation. Glycan remodeling in turn affects the interaction between the T cell's glycans and their cognate lectins in the extracellular milieu. In this thesis, we study the consequences of ex-vivo glycan engineering on the binding and signaling of galectin-1, a lectin that induces apoptosis in activated, but not naive, CD8 +T cells. We focused on the galectin-1 ligand sialylated-LacNAc or "sLacNAc," which lacks the fucose monosaccharide that makes up sialylafed-Lex or "sLex." sLex binds to E-selectin, a lectin that is upregulated in response to inflammation to mediate homing of lymphocytes from the bloodstream to the inflamed tissue.;We hypothesized that ex-vivo fucosylation of sLacNAc on activated CD8+T cells would generate sLex that improves binding to E-selectin. interferes with binding to galectin-1. and improves overall T cell survival. In order to test this hypothesis, we optimized conditions for identifying activated CD8+ T cells on the basis of their expression of LacNAc and sLacNAc-containing glycans. Chemoenzymatic labeling of LacNAc with alpha1,3 FucT and GDP-FucAl showed that both in vitro and in vivo effector CD8+ T cells expressed higher levels of LacNAc than naive T cells. Among CD8+ T splenocytes, LacNAc expression differed on the basis of activation state, such that effector cells were LacNAc hi compared to central memory cells that were LacNAcint and naive T cells that were LacNAclo. In fact, effector T cells expressed nearly 8 times more LacNAc than naive T cells, as demonstrated on ovalbumin antigen-specific transgenic cells (OT-I) and endogenous, wild type ovalbumin-responsive CD8+ T cells. Chemoenzymatic labeling of cell-surface LacNAc and CD8 staining was sufficient for identifying activated CD8+ T cells in a heterogeneous population of splenocytes from Listeria-immunized mice.;Galectin-1 binding was undetectable by flow cytometry following ex vivo fucosylation with 500 muM GDP-fucose. In situ fucosylation also inhibited galectin-1 binding in a dose-dependent manner, improved E-selectin binding by 10-fold, and moderately protected T cells from galectin-1-mediated apoptosis in vitro. Finally, we showed that ex-vivo fucosylated effector T cells bearing ectopic sLex differentiated into memory cells that re-expanded considerably better than their unfucosylated counterparts during a secondary infection.
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