The disclosure provides a method of reducing or eliminating Neu5Gc in a cell culture or in a human subject. The method includes flooding the system with the human sialic acid i 7-acetylneuraminic acid (Neu5Ac) in glycosidically-bound or free form, or its precursor N-acetylmannosamine (ManNAc) in an amount sufficient to metabolically compete out the Neu5Gc, either as it enters the cells for the first time or when it recycles from break-down of preexisting cellular molecules. Additionally, Neu5Ac feeding results in reduction of Neu5Gc expression even in some animal cells capable of Neu5Gc production.
