Islet cell transplantation (into the recipient's liver) has theoretical advantages over pancreas transplantation; the most important is that the procedure is less invasive. A secondary advantage is that islet cell transplantation appears to help maintain normoglycemia in patients who require total pancreatectomy for pain due to chronic pancreatitis. Nevertheless, the procedure remains developmental, although steady improvements appear to be occurring.
Its disadvantages are that transplanted glucagon-secreting alpha cells are nonfunctional (possibly complicating hypoglycemia) and several pancreata are usually required for a single islet cell recipient (exacerbating disparities between graft supply and demand and limiting use of the procedure).
Indications are the same as those for pancreas transplantation: type 1 diabetes with renal failure who are thus also candidates for kidney transplantation, repeated failure to control glycemia with standard treatment, and episodes of hypoglycemic unawareness. Simultaneous islet cell–kidney transplantation may be desirable in the future after the outcomes have improved.
(See also Overview of Transplantation.)
Процедура
A pancreas is removed from a brain-dead donor; collagenase is infused into the pancreatic duct to separate islets from pancreatic tissue. A purified islet cell fraction is infused percutaneously into the portal vein by direct puncture of that vein or via a branch of the mesenteric vein. Islet cells travel into hepatic sinusoids, where they lodge and secrete insulin.
Results are best when 2 cadavers are used, with each supplying 2 or 3 infusions of islet cells, followed by a posttransplantation immunosuppression regimen consisting of an anti-IL-2 receptor antibody (basiliximab), tacrolimus, and sirolimus (Edmonton protocol); corticosteroids are used sparingly because they cause hyperglycemia. Immunosuppression must be continued lifelong or until islet cell function ceases.
Complications of Pancreatic Islet Cell Transplantation
(See also Posttransplantation Complications.)
Rejection is poorly defined but can be detected by deterioration in blood glucose control and an increase in glycosylated hemoglobin (HbA1c); treatment of rejection is not established.
Procedural complications include percutaneous hepatic puncture with bleeding, portal vein thrombosis, and portal hypertension.
Prognosis for Pancreatic Islet Cell Transplantation
Successful islet cell transplantation maintains short-term normoglycemia, but long-term outcomes are unknown; additional injections of islet preparations may be necessary to obtain longer-lasting insulin independence.