A report in the February issue of Nature Medicine indicates that a foreign molecule present in human embryonic stem cells (HESCs) may lead to their being killed by the immune system if they are used in a transplantation setting.
HESCs can potentially generate every body cell type, making them excellent candidates for tissue-replacement therapies. HESC are typically cultured with animal-derived 'serum replacements', which are sources of sialic acid Neu5Gc, a molecule against which many humans have circulating antibodies. In their report, Ajit Varki and his colleagues show that HESCs incorporate substantial amounts of Neu5Gc under standard culture conditions. Exposure of these cells to human sera resulted in binding of antibodies against Neu5Gc, which would lead to cell killing in vivo.
The authors conclude that complete elimination of Neu5Gc would be likely to require using human serum instead of “serum replacements”, starting with fresh HESC that have never been exposed to animal products. The current legal climate in the United States precludes this approach, when using federal grant dollars.
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