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Fig. 8.1. Pancreatic intraductal cannulation and collagenase perfusion.

When it is time to perform the transplant, the islets are collected from the tissue culture flasks and washed. The final islet product is suspended in transplant medium at an approximate concentration of 25-50 ml of medium/ml of tissue.

Islet Product Testing. Islet product testing in the setting of clinical transplantation should follow the regulatory framework of the U.S. Food and Drug Administration (FDA) Center for Biologics Evaluation and Research for cellular and tissue-based products.

Four regulatory requirements have been established for the manufacture of cellular and tissue-based products: 1) product safety, 2) product characterization, 3) control of the manufacturing process, and 4) reproducibility and consistency of product lots. To ensure product safety, specific tests must be established to determine sterility (aerobic, anaerobic, and fungal cultures), pyrogenicity and endotoxin content, and absence of mycoplasma or adventitious agents. Product characterization requires the design and implementation of batch production records and standard operating procedures to test cell and tissue identity, purity, potency, stability, viability, and cell number or amount of tissue. Table 8.4 summarizes current assays for islet product safety and characterization. Table 8.5 lists islet product release and post-release criteria.

Fig. 8.2. Pancreatic islet isolation schemia.

Islet Transplantation. Intraportal infusion of islets has emerged as the most common technique. Any history of abdominal surgery or liver abnormalities (hemangioma) is considered when deciding how to best access the portal vein. Percutaneous transhepatic catheterization is the most common access route in clinical islet transplantation.53,54 Alternative approaches to access the portal vein include mini-laparotomy and cannulation of an omental or mesenteric vein, and transjugular intrahepatic portosystemic access.

Access to the portal vein via transhepatic catheterization is provided by the interventional radiologists. Either the left or right intrahepatic portal system is accessed percutaneously. The position of the tip of the infusion catheter is guided to the main portal vein. Position is confirmed with contrast dye, the opening portal pressure is obtained, and a formal portogram is performed. If the portal pressure is <20 mm Hg, and no abnormalities are noted, the islet infusion bag is connected with the portal vein catheter using a standard intravenous infusion set. The islet are infused intraportally, over a period of 15 to 60 minutes, using gravity. Portal vein pressure is recorded halfway through the infusion process, and more often if deemed appropriate. Islet infusion is halted if the portal pressure exceeds

22 mm Hg; it is restarted only if the pressure drops below 18 mm Hg. If the pressure remains elevated, infusion is stopped. After completion of the islet infusion, and after a final rinse, the closing portal pressure is obtained and recorded. No additional intraportal contrast agents are given after islet infusion. The sheath is withdrawn and coils or gelatin-sponge (Gelfoam) pledgets are deployed in the puncture tract to prevent bleeding and augment hemostasis.

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