David Prentice has more details at the FRC blog:
Manning has had three surgeries on his neck in the last 19 months, Little detail was available, but the information indicates that the procedure may have used adipose (fat) derived adult stem cells from Manning's own body; this autologous procedure (using your own adult stem cells) bypasses any problems of transplant rejection and is relatively safe. Manning's adult stem cells may have then been injected around the site of his problem vertebra in the neck, to assist healing and help with spinal disc fusion.
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