A concern recently has been raised that human embryonic stem cell (HESC) lines 
cultured with currently available methods may have limited clinical usefulness 
due to the immunogenicity of the nonhuman sialic acid Neu5Gc incorporated into 
their membranes during culturing. We find this concern has little relevance to 
neural differentiation protocols with B27/N2/noggin because of the gradual 
decline of Neu5Gc to less than 1% in differentiating cells upon switching to 
B27/N2 medium.