Stemgent® StainAlive™ DyLight™ 549 Mouse anti-Mouse/Human SSEA-1 Antibody was screened on live, unfixed mouse embryonic stem (ES) cells by immunocytochemistry (ICC). This antibody was selected as the best conjugated SSEA-1 antibody available for EC/ES/iPS cells, utilizing fluorescent staining and real-time imaging without fixation or killing the cells. This formulation is useful to directly visualize the reprogramming process to iPS colonies. For use on live cells, this antibody has been specifically formulated with low endotoxin and no sodium azide and is confirmed to be free of bacteria, fungi, mycoplasma and mouse virus as tested. The live ES cell morphology, proliferation and expression of pluripotency markers did not change after staining with this antibody. The MC-480 antibody reacts with mouse and human stage-specific embryonic antigen-1 (SSEA-1), an antigenic epitope defined as a Lewis X carbohydrate structure. It is expressed on murine embryonal carcinoma cells (EC), murine embryonic stem cells (ES), and murine and human germ cells. It is widely used as positive surface marker for mouse undifferentiated stem cells and negative surface marker for human undifferentiated stem cells. Expression is down-regulated following differentiation of murine EC and ES cells, while the differentiation of human EC and ES cells is accompanied by an increase in SSEA-1 expression. The SSEA-1 molecule is associated with cell adhesion, migration and differentiation.