This study scaled vitrification and nanowarming to pig kidneys of about 100 g, stored for up to one year. During normothermic perfusion, rewarmed kidneys reperfused and produced urine; function was below 24-h cold storage but similar to kidneys exposed to cryoprotectant alone (Fig. 3, 4), suggesting little added cryogenic injury.
Alternative hypothesis: The similarity to cryoprotectant-only controls reflects differences between the groups, not little cryogenic injury. Five of nine controls, but one of eight vitrified kidneys, came from the circulatory-death donors used early in protocol development (Extended Data Table 1). Donor types were pooled after an overall check, yet these controls account for the lowest flows and highest resistances in Fig. 3c,e. Separately, the perfusion circuit used leukocyte-depleted blood with dexamethasone; after transplantation, vitrified grafts showed glomerular necrosis and endothelial damage absent from cold-stored grafts (Supplementary Fig. 11), so cryogenic injury may surface mainly in vivo.
Ideally, the two kidneys of each donor would be split between cryoprotectant alone and vitrification, processed concurrently and transplanted: persisting parity would support the authors' reading, while a deficit in the vitrified kidney would show the cost of the cryogenic steps. Or, at minimum, the existing comparison could be repeated within brain-death donors.