Antigen expression in undifferentiated stem cells

The invention provides a method of producing differentiated cells, comprising causing a population of undifferentiated stems cells to differentiate, wherein the undifferentiated stems cells have a nucleic acid molecule of the structure P-X, wherein X is a sequence causing expression of a cell surface antigen, and P is a transcriptional control element operatively linked to X, such that the surface antigen is expressed in undifferentiated cells. Preferably, remaining undifferentiated cells are then depleted by combining the cells with a ligand specific for the antigen, for example and antibody or lectin. The invention also relates to a method of producing a cell population depleted of undifferentiated stem cells, comprising genetically altering undifferentiated stem cells with an nucleic acid molecule comprising the structure P-X as defined above, and depleting undifferentiated cells by combining the cells with a ligand specific for the antigen. In preferred embodiments, X encodes a glycosyltransferase, preferably an alpha(1,3)galactosyltransferase. P is preferably a promoter of telomerase reverse transcriptase (TERT) or an OCT-4 promoter. The invention also relates to a stem cell genetically modified to express a carbohydrate antigen not normally expressed by the cell. The stem cell may be modified by a construct containing the alpha(1,3)galactosyltransferase gene under the control of a TERT or OCT-4 promoter.