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. Simultaneous islet cell–kidney transplantation may be desirable after the technique is improved.
(See also Overview of Transplantation.)
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 an immunosuppressive 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.
(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.