Effect of Cryopreservation on the Survival and Function of Murine Islet Isografts and Allografts

We compared the efficacy of fresh and frozen/thawed islets by determining the minimum number required to consistently reverse diabetes in mice. Defined numbers of islets, isolated from Balb/c (H-2^d) and CBA/J (H-2^k) mice, were transplanted into streptozotocin-induced diabetic Balb/c mice. Frozen/thawed grafts were cooled slowly to −40°C, stored at −196°C, and thawed rapidly. At 100 days after transplantation, isografts were recovered for measurement of insulin content. Mean (±SD) recovery of cryopreserved islets after thawing was 80 ± 3% (range 67–89%). For both fresh and frozen/thawed isografts and allografts, 200 islets were required to establish normoglycemia. The degree of metabolic function provided by equivalent quantities of fresh and frozen/thawed grafts was similar; and all normoglycemic isograft recipients remained so until graft nephrectomy. The insulin content of fresh and frozen/thawed isografts containing 200 and 300 islets were 151 ± 25 and 126 ± 8 mU and 259 ±36 and 278 ± 20 mU, respectively. Among allograft recipients, median survival ranged from 15 to 20 days, and was not influenced by cryopreservation or graft size. The results of this study demonstrate a high rate of recovery of viable islets following cryopreservation. The function of equivalent quantities of fresh and cryopreserved islet isografts and allografts in nonimmunosuppressed recipients is similar.