Evolving approaches to organ allocation for the whole pancreas vs islet transplantation

Currently, two strategies exist for β-replacement therapy for type 1 diabetes mellitus: whole pancreas (PTx) and pancreas islet transplantation (ITx). PTx is by far the most common approach given the historic challenges of ITx at achieving insulin independence, the nuances of islet isolation techniques, and the attrition of functioning islets after transplant. One of the fundamental differences between PTx and ITx recipients lies in the indications for β-replacement. While end-stage renal disease from diabetic nephropathy is the primary indication for PTx, hypoglycemic unawareness remains the primary indication for ITx. Although the Edmonton protocol has made tremendous strides in the ITx field, enthusiasm has been tempered by long-term outcome data and its use of multiple deceased donors for a single recipient. Furthermore, of the donor risk characteristics that impact outcomes for PTx and ITx, donor age and obesity are the risk factors that have been most intensely studied and have shaped allocation policy. Currently, US allocation guidelines recommend that organs from older (> 50 years old) or obese (BMI > 30 kg/m²) donors should preferentially be allocated to ITx whereas younger and leaner donors are preferentially allocated to PTx. This has created discontent in the ITx community, viewing these allocation guidelines as unfair and unequal. To understand the evolution of deceased donor pancreas allocation, it is important to understand how specific donor risk factors, specifically age and obesity, have influenced the decision-making algorithm for choosing a specific modality over the other. Finally, it is critical to contextualize the historic allocation guidelines in the United States and the United Kingdom with considerations into how donor risk and payer reimbursement within each system have shaped this dynamic process.