The invention describes novel compositions of glycans, glycomes, from human embryonic stem cells, and especially novel subcompositions of the glycomes with specific monosaccharide compositions and glycan structures. The invention is further directed to methods for modifying the glycomes and analysis of the glycomes and the modified glycomes. Furthermore, the invention is directed to stem cells carrying the modified glycomes on their surfaces. The glycomes are preferably analysed by profiling methods able to detect reproducibly and quantitatively numerous individual glycan structures at the same time. The most preferred type of the profile is a mass spectrometric profile. The invention specifically revealed novel target structures and is especially directed to the development of reagents recognizing the structures.