Our attempt to reduce islet immunogenicity by slow cooling to −40°C, storage at −196°C, and rapid thawing is based on the differential susceptibility of various cell types to a freeze-thaw process. Five hundred rat islets (≥10 μm) were immediately implanted or cryopreserved and then implanted beneath the renal capsule of streptozocin-induced diabetic mice with or without an injection of anti-lymphocyte serum at the time of transplantation. Thirteen days after transplantation, all fresh xenografts had rejected, whereas 37.5% of cryopreserved grafts were still functioning. In immunosuppressed mice, 6.2% of fresh xenografts and 54.5% of cryopreserved grafts were functioning 19 days after transplantation. These results show that cryopreservation can extend xenograft survival.

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