**1. Introduction**

#### **1.1. Islet cell transplantation for type 1 diabetes**

The transplantation of pancreatic islets of Langerhans is a promising treatment for "brittle" type 1 diabetics, because it is a minimally invasive procedure that replenishes the beta cell mass lost due to autoimmunity. This procedure also provides an opportunity for a "cure" from diabetes based on the achievement of freedom from dependence on exogenous insulin and severe hypoglycemic events. Although islet transplants had been attempted for several decades, they achieved minimum success in terms of post-transplant graft function. The publication of the Edmonton Protocol [1] documenting consistent achievement of insulin in‐ dependence after islet transplantation, has led to a dramatic increase not only in the number of procedures performed worldwide but also in other related areas in the field of islet trans‐ plantation. Breakthroughs have been made in the area of pancreas procurement and preser‐ vation with study into ductal preservation, the two layer method, and the type of preservation solution used. Furthermore, there has been much progress in the islet isolation process by bringing standards up to cGMP qualifications, optimization of collagenase en‐ zymes, and using iodixanol for continuous density gradient purification [2]. Some of the hurdles facing further success in this treatment are:


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#### **1.2. Post-transplant outcome**

According to a recent report from the Collaborative Islet Transplant Registry, 677 patients have received either an islet transplant alone (ITA) or islets-after-kidney (IAK) transplants [3]. There has been a remarkable improvement in the post-transplant graft function in recent times. Prior to the publication of Edmonton protocol, the achievement of insulin-independ‐ ent status by islet transplant recipients was <10%. Patients treated initially under the Ed‐ monton protocol showed remarkable achievement of 82% insulin-independent status at one year post-transplant. However, this result proved to be unsustainable when the five year in‐ sulin-independence rates fell to 12.5% at the same center [4]. This data resulted in skepticism on the use of allogeneic islet transplantation as a reliable treatment for long-term success. With the introduction of thymoglobulin at induction phase and the combination of prograf, rapamycin and/or mycophenolate mofetil as maintenance immunosuppressive agents, the islet transplant survival rate has significantly improved to 50% at five year post-transplant [5]. Control of inflammatory reaction during peri-transplant period with the use of TNF-α blockers also played a key role in this improvement. These remarkable results necessitated comparison with whole pancreas transplantation which is considered as an established clini‐ cal procedure. Although whole organ treatment achieved high levels of graft survival in the years 1994-1997, the islet survival rate at five years has reached around fifty percent in 2010-2011, comparable to the level of whole pancreas graft success [5]. Moreover, islet cell transplantation seems to confer significantly better glycemic control than maximal medical therapy, and essentially eliminates hypoglycemic unawareness. These results have brought back the enthusiasm in this field.

**2.2. Alloimmunity**

develop HLA antibodies against islet graft.

cially following discontinuation of immunosuppression [10-13].

The exposure of body to allogeneic tissues via organ/cell transplantation, blood transfusions, pregnancy can cause development of anti-human leukocyte antigen (HLA) antibodies [7]. These *de novo* HLA antibodies have been shown to play a significant role in the early graft loss after solid organ transplantation [8]. Currently, HLA matching between the recipients and donors is not performed before islet cell transplantation. Moreover, to achieve and/or maintain insulin independence and good metabolic control in an islet recipient, multiple is‐ let infusions from multiple donors and high doses of immunosuppressants are generally re‐ quired. The requirement of multi-donor infusions and reduction or weaning of immunosuppressants due to significant adverse effects could cause patients eventually to

Beta Cell Function After Islet Transplantation http://dx.doi.org/10.5772/ 52952 169

The issue of sensitization of alloantigens after islet cell transplantation has been raised by the Edmonton group in 2007 [9]. 98 islet transplant recipients were screened for HLA antibodies by flow-based methods. Twenty-nine patients (31%) represented *de novo* donor specific anti‐ bodies following islet transplantation. Among 14 recipients who discontinued immunosup‐ pression, 10 recipients (71%) were largely sensitized with panel reactive antibody ≥50%. On the other hand, only 11 of 69 (16%) recipients who continued immunosuppression became broadly sensitized posttransplant. This study suggested that development of HLA antibod‐ ies after islet transplantation is concerning and withdrawal of immunosuppression complete‐ ly following failed islet transplantation raises the risk for broad sensitization. Along with the report of Edmonton group, there are several studies that have demonstrated that islet alone transplant recipients develop donor-specific and/or nondonor-specific HLA antibodies, espe‐

In contrast, in the report of Geneva group it was shown that multiple islet infusions did not act as a risk factor for appearance of anti-HLA antibodies [14]. The group claimed that trans‐ plantation of islets in liver might cause less immunogenicity. After combined kidney-islet transplantation and continued immunosuppression even with failed islet graft function, pa‐

It has been known that islets express mainly HLA class I antigens on their surfaces. Previous reports demonstrated that patients develop antibodies posttransplant not only against HLA class I antigens, but also against HLA class II antigens [9]. Jackson et al. showed that there would be an induction of HLA class II expression on human islets under inflammatory con‐ ditions, which in return may be a possible cause of allosensitization [15]. For this aim, the group conducted an experiment in which they had two groups of isolated human islets; group 1 was control group and cultured at 37˚C, whereas group 2 was cultured in the same condition and treated with tumor necrosis factor alpha (TNF-α) and interferon gamma (INFγ). Presence of HLA class II on islet surface was analyzed by real-time polymerase chain re‐ action (PCR), immunofluorescence and flow cytometry. Expression of class II transactivator, HLA-DR-α and HLA-DR-β1 increased maximum 9.38, 18.95 and 46.5 fold respectively in group 2 compared to control group after 24 hours of incubation with TNF-α and INF-γ which is shown by real-time PCR analysis. Fluorescent imaging and flow cytometric analy‐ sis confirmed the significant increase in the expression of HLA class II expression both on

tients had a low risk for sensitization as long as their kidney remained functional.
