Targeting the glycan epitope type I N-acetyllactosamine enables immunodepletion of human pluripotent stem cells from early differentiated cells

Cell surface biomarkers are fundamental for specific characterization of human pluripotent stem cells (hPSCs). Importantly, they can be applied for hPSC enrichment and/or purification but also to remove potentially teratoma-forming hPSCs from differentiated populations before clinical application. Several specific markers for hPSCs are glycoconjugates comprising the glycosphingolipid (GSL)-based glycans SSEA-3 and SSEA-4. We applied an analytical approach based on multiplexed capillary gel electrophoresis coupled to laser-induced fluorescence detection to quantitatively assess the GSL glycome of human embryonic stem cells and human induced pluripotent stem cells as well as during early stages of differentiation into mesoderm, endoderm, and ectoderm. Thereby, we identified the GSL lacto-N-tetraosylceramide (Lc4-Cer, Galβ1-3GlcNAcβ1-3Galβ1-4Glc-Cer), which comprises a terminal type 1 LacNAc (T1LN) structure (Galβ1-3GlcNAc), to be rapidly decreased upon onset of differentiation. Using a specific antibody, we could confirm a decline of T1LN-terminating glycans during the first four days of differentiation by live-cell staining and subsequent flow cytometry. We could further separate T1LN-positive and T1LN-negative cells out of a mixed population of pluripotent and differentiated cells by magnetic activated cell sorting. Notably, not only the T1LN-positive but also the T1LN-negative population was positive for SSEA-3, SSEA-4, and SSEA-5 while expression of nuclear pluripotency markers OCT4 and NANOG was highly reduced in the T1LN-negative population, exclusively. Our findings suggest T1LN as a pluripotent stem cell-specific glycan epitope that is more rapidly down-regulated upon differentiation than SSEA-3, SSEA-4, and SSEA-5.

Enzymatic Synthesis of N-Acetyllactosamine (LacNAc) Type 1 Oligomers and Characterization as Multivalent Galectin Ligands

Repeats of the disaccharide unit N-acetyllactosamine (LacNAc) occur as type 1 (Galβ1, 3GlcNAc) and type 2 (Galβ1, 4GlcNAc) glycosylation motifs on glycoproteins and glycolipids. The LacNAc motif acts as binding ligand for lectins and is involved in many biological recognition events. To the best of our knowledge, we present, for the first time, the synthesis of LacNAc type 1 oligomers using recombinant β1,3-galactosyltransferase from Escherichia coli and β1,3-N-acetylglucosaminyltranferase from Helicobacter pylori. Tetrasaccharide glycans presenting LacNAc type 1 repeats or LacNAc type 1 at the reducing or non-reducing end, respectively, were conjugated to bovine serum albumin as a protein scaffold by squarate linker chemistry. The resulting multivalent LacNAc type 1 presenting neo-glycoproteins were further studied for specific binding of the tumor-associated human galectin 3 (Gal-3) and its truncated counterpart Gal-3∆ in an enzyme-linked lectin assay (ELLA). We observed a significantly increased affinity of Gal-3∆ towards the multivalent neo-glycoprotein presenting LacNAc type 1 repeating units. This is the first evidence for differences in glycan selectivity of Gal-3∆ and Gal-3 and may be further utilized for tracing Gal-3∆ during tumor progression and therapy.