A narrative review on the evolution of islet isolation techniques and improving yields during total pancreatectomy and islet autotransplantation

Abstract

Total pancreatectomy with islet autotransplantation (TPIAT) is a specialized treatment for chronic pancreatitis (CP) patients experiencing intractable pain, aiming to preserve endocrine function and enhance quality of life. This narrative review explores the evolution of islet isolation techniques and their impact on yields and clinical outcomes in TPIAT. PubMed and Google Scholar were searched utilizing the keywords: total pancreatectomy, islet autotransplantation, islet transplantation, TPIAT, islet yields, islet isolation. This review underscores significant advances in islet isolation, from initial collagenase-based methods to the automated Ricordi technique and the enzyme Liberase, which have significantly improved islet yield and viability. Factors such as pancreatic fibrosis, preoperative nutritional status, and ischemia times are critical determinants of outcomes. Higher islet yields (> 5,000 islets/kg) correlate with substantially better insulin independence (20%–40% at 1 year), while pain relief (80%–90%) and quality of life improvements (60%–70%) are consistently observed. Variability in yields due to disease severity and levels of technical expertise continues to pose challenges. TPIAT has evolved into a widely accepted treatment option for CP, with advanced islet isolation techniques contributing to enhanced clinical success. Despite these advancements, variability in islet yields and outcomes highlights the need for standardized protocols and optimized preservation techniques. Future research should aim to address challenges associated with fibrosis and improve long-term graft function, thereby maximizing TPIAT’s therapeutic potential.

INTRODUCTION

Chronic pancreatitis (CP) is a condition that can severely affect a patient’s quality of life and life expectancy. The most debilitating symptom of CP is intractable pain, which affects patients mentally and physically. It also significantly impacts their quality of life through repeated hospital admissions. The consequences of these often prolonged inpatient periods include missed life events, employment issues, separation from their support network, anxiety, and deteriorating mental health [1,2]. Non-surgical treatment options are limited; however, they encompass oral and parenteral analgesics, regional blocks, and invasive procedures, such as endoscopic guided therapies. Surgical interventions may additionally involve partial resection, drainage procedures, combined resection and drainage and total pancreatectomy (TP) [3,4]. While TP eliminates all diseased pancreatic tissue, the procedure is technically challenging and therefore carries a considerable risk of postoperative morbidity and mortality. Furthermore, it results in the removal of all pancreatic islet cells, leading to immediate endocrine dysfunction [5].

Total pancreatectomy and islet autotransplantation (TPIAT), performed in only a small number of units worldwide, is an approach involving the infusion of the patient’s own islets, harvested from the pancreas following resection. Islet autotransplantation (IAT) can abrogate or reduce the need for exogenous insulin therapy, resulting in significantly improved blood sugar control, especially concerning hypoglycemic unawareness and “brittle” diabetes [6]. A schematic diagram outlining the entire TPIAT workflow from preoperative evaluation to postoperative outcomes is illustrated in Fig. 1.

Fig. 1.

Schematic of the total pancreatectomy with islet autotransplantation workflow. MDT, multidisciplinary team.

Early intervention is favored to limit the development of pancreatic fibrosis, which negatively impacts islet isolation and post-transplant endocrine function [7,8]. The most suitable candidates typically present with a shorter duration of disease, usually less than five years from diagnosis, with minimal evidence of fibrosis and calcification on imaging or histology. Postponing TPIAT until advanced fibrosis or preoperative diabetes occurs markedly diminishes the chances of achieving insulin independence [9]. Patients experiencing prolonged malnutrition or frequent hospitalizations also tend to have decreased islet yields due to deteriorated pancreatic tissue quality [10,11]. Timely referral for TPIAT evaluation is recommended when pain and quality-of-life disruptions endure after 6 to 12 months of optimized medical and endoscopic therapy, and prior to the appearance of significant endocrine or exocrine insufficiency. A multidisciplinary evaluation, incorporating input from gastroenterologists, surgeons, endocrinologists, and pain management specialists, is crucial to determine timing and to facilitate thorough preoperative preparation [12].

A critical step during TPIAT is the isolation of islets following surgical resection of the pancreas. Successful islet isolation is crucial for favorable outcomes in terms of endocrine function following IAT. Over the past 4 decades, advances in enzymatic digestion, purification, and preservation techniques have significantly improved the quality and number of islets isolated and recovered. Despite these advancements, however, significant variation in islet yields persists, influenced by factors that include disease duration and severity prior to surgery, pancreatic parenchymal composition, and technical expertise in islet cell laboratories.

The objective of this paper is to evaluate the progression of outcome reporting for IAT as TPIAT has increasingly become a standard procedure. A narrative review was conducted utilizing the following key words: total pancreatectomy, islet autotransplantation, islet transplantation, total pancreatectomy with islet autotransplantation, islet yields, and islet isolation.

ISLET ALLO- AND AUTOTRANSPLANTATION

For over a century, clinicians have been fascinated by the potential of treating diseases with specifically functional cells extracted from healthy organs. Advances in immunology and transplantation techniques (dating back to ancient observations and texts such as the Ebers Papyrus from 1550 B.C.) have shaped modern cellular therapy and organ transplantation. It was envisioned that these cells could be employed to address diseases caused by the failure or malfunction of a patient's own diseased cells [13,14]. Pioneering efforts, including Reverdin’s skin grafts in 1869, the first successful kidney transplant in 1954, and experimental cell injections by Brown-Séquard and Niehans in the 19th and early 20th centuries, established the framework for routine organ transplants and the evolution of cellular therapy [15-19].

The history of islet allotransplantation is marked by significant advances in islet isolation techniques, which led to a breakthrough in treating type 1 diabetes (T1D). Initially, islet transplantation (IT) was deployed for treating T1D through the infusion of insulin-producing cells from a donor pancreas into a T1D patient. Early methods, developed by Hellerström et al. [20], involved meticulous but time-consuming microdissection under a microscope, limiting their effectiveness due to the limited amount of endocrine tissue available. A significant breakthrough was achieved in 1965 when Moskalewski [21] introduced the use of collagenase in islet isolation during experiments with minced guinea pig pancreas to release islet clusters from exocrine tissue. Although the results were a successful proof of principle, there was widespread islet destruction resulting from the use of collagenase.

In 1967, Lacy and Kostianovsky [22] proposed that IT might be a superior treatment option for patients compared with exogenous insulin, due to the destruction of insulin-secreting cells in severe diabetes caused by autoimmune activity. Kemp et al. [23] also pioneered the intraductal injection of cold saline buffer to distend the pancreas gland, thus enlarging the surface area available for collagenase activity and enhancing islet release. This technique was proven effective in 1972 when Lacy conducted the first experiment demonstrating an improvement (but not a total reversal) of diabetes in a rodent model with iatrogenic diabetes. These groundbreaking techniques by Moskalewski and Lacy [21-24] propelled research in this field, establishing their methods as a standard for isolating islets in rodents. Subsequently, in 1972, Ballinger and Lacy [24] demonstrated the first experimental reversal of diabetes in rats using transplanted islets. Soon after, in 1973, Kemp et al. [23] conducted a study showing an association between the transplantation site and outcome in a rodent model. They achieved a complete reversal of diabetes within 24 hours when islets were transplanted into the liver, but observed no success when the same quantity of islets (400–600) were transplanted into the peritoneal cavity or subcutaneously. As a result of this pivotal study, the liver was established as the optimal site for IT in both animal and clinical models.

Success in rodent models led to a dramatic increase in research volume, significantly advancing islet isolation techniques. Transferring these techniques to larger animals posed a significant challenge until Horaguchi and Merrell [25] introduced a method for isolating sufficient islets for canine transplantation. This breakthrough allowed Rajotte [26] and his colleagues at the University of Alberta to refine experimental models of immunosuppression and islet cryopreservation. By the late 1970s, the clinical applications of these techniques began to be reported, with the University of Minnesota pioneering early human IT interventions for patients with T1D (Fig. 2) [7]. Although initially limited by inadequate immunosuppression, these efforts constituted an important step towards developing a safe clinical protocol. During this period, the first autologous islet cell transplants were performed in patients undergoing TP for CP. IAT not only offered a strategy to counteract absolute pancreatic endocrine deficiency but also served as a valuable model for studying IT without the confounding factors of rejection and immunosuppression issues [7,8,27].

Fig. 2.

Islet Cell Isolation and Autotransplantation.

In 1979, a significant advance in IT occurred when the team at the University of Zurich successfully performed a simultaneous transplantation of allogeneic pancreatic fragments along with a kidney in a patient with T1D, achieving 10 months of insulin independence [28]. This was followed in 1985 by reports from the University of Miami of promising but short-lived results from allogeneic IT, where inadequate immunosuppression was pinpointed as the primary reason for graft failure. Alongside immunological factors affecting graft tolerance, a major barrier to IT success in the 1980s and 1990s was the challenge of extracting and purifying sufficient quantities of islets from the pancreas. In 1986, this problem was addressed by the introduction of an automated technique known as the Ricordi method for islet cell isolation. The Ricordi method significantly increased the number of isolatable islet cells, further facilitating the development of clinical programs [29,30].

The Ricordi method involves the progressive disassembly of the pancreas by injecting an enzyme blend through the pancreatic duct. This blend induces a controlled digestion of the pancreas, yielding smaller, viable fragments. As the islets are released, they are captured by a filtration system and collected in compartments where further enzymatic activity is inhibited by cooling and dilution. The process culminates with the purification of the islets using a differential density gradient, typically utilizing a COBE 2991 cell processor. This method, along with the significant increase in the recovery of viable islets for transplantation, marked the advent of clinical protocol and program development in several centers, particularly in the USA (Fig. 3) [29-31].

Fig. 3.

Flowchart of the Ricordi method for islet isolation.

In 1994, there was a significant advancement in islet isolation following the introduction of an enzyme formulation known as Liberase HI^TM (Roche). Liberase is a low-endotoxin enzyme specifically designed for islet isolation. Liberase MNP-S comprises highly purified collagenase class I and class II from Clostridium histolyticum. The two collagenase isoforms are combined in a precise ratio with each other and with a medium concentration of highly purified thermolysin, a neutral protease isolated from Bacillus thermoproteolyticus. Clinical results demonstrated improved enzymatic action compared with preparations involving only collagenase [32]. Unfortunately, Liberase^TM was withdrawn from the market in 2007 due to the potential risk of transmitting bovine spongiform encephalopathy to patients because it was derived from C. histolyticum. At that time, it was the preferred enzyme for IT, leading to a significant decline in the number of clinical islet transplants performed [33]. More recently, recombinant alternatives have addressed these concerns and are now routinely employed in IT.

In 2000, the Edmonton group introduced a novel IT method known as the Edmonton protocol (Fig. 4) [33]. This protocol involves isolating pancreatic islets from deceased donors and infusing them into the recipient’s liver via the portal vein. The procedure, conducted under local anesthesia, is minimally invasive and allows the islets to lodge in the liver’s vasculature where they begin to secrete insulin in response to blood glucose levels. The Edmonton protocol differs from prior methods by excluding glucocorticoids and instead employing a combination of the immunosuppressive agents sirolimus, tacrolimus, and daclizumab, significantly enhancing graft survival and insulin independence [33].

Fig. 4.

Flowchart of the edmonton protocol for islet allotransplantation.

Islet allotransplantation emerged as an innovative strategy for managing T1D and has seen advancements in islet isolation and engraftment techniques, initially aimed at enhancing the survival and functionality of donor islets in the challenging immune environment of the recipient [34,35]. Gleaned insights from islet allotransplantation laid the groundwork for IAT development, a method designed to prevent diabetes following TP. Autotransplantation eliminates immune rejection concerns, thereby circumventing the need for prolonged immunosuppression. It replicates islet cell allografting and incorporates several technical innovations first introduced in allotransplantation (Table 1). The timeline showing significant milestones in the history of islet isolation is depicted in (Table 2) [21,22,25,29,30,32,33,36-40]

Table 1.

Technical refinements of allotransplantation that were adapted autotransplantation

Technique	Allotransplantation refinement	Adapted for autotransplantation
Islet isolation and purification	Enzymatic digestion protocols (e.g., collagenase) Density gradient centrifugation	Enhanced yield and purity of autologous islets
Islet preservation and transportation	Cold ischemia prevention and short-term culture media Storage solutions (e.g., University of Wisconsin solution)	Reduced ischemic damage Flexibility in timing
Quality assessment of islets	Viability and function assays (e.g., glucose-stimulated insulin secretion)	Assurance of viable, functional islets for infusion
Engraftment and site of transplantation	Intraportal liver infusion Alternative sites (e.g., omentum, muscle)	Liver and alternative site options for islet engraftment
Immunomodulation and supportive therapy	Anti-inflammatory therapies for islet protection	Short-term inflammation control to aid engraftment

Table 2.

Key milestones in the history of islet isolation

Researcher	Country	Year	Milestone
Bensley [40]	USA	1911	Islet staining with neutral red and hand-picking
Björkman et al. [36]	Sweden	1964	Microscope microdissection of islets
Moskalewski [21]	Poland	1965	Use of collagenase in mouse islet isolation
Lacy and Kostianovsky [22]	USA	1967	Pancreas distention by intraductal injection of cold saline buffer
Lindall et al. [37]	USA	1969	Islet purification by Ficoll density gradient
Horaguchi and Merrell [25]	USA	1981	Design of a new system to perfuse the pancreas
Ohzato et al. [38]	Japan	1985	Pancreas distention by intraductal injection of collagenase
Ricordi et al. [29,30]	USA	1988	Design of the “Ricordi chamber”
Lake et al. [39]	UK	1989	Introduction of the COBE 2991 in human islet isolation
Barton et al. [32]	USA	1994	Marketing of Liberase HI for optimization of human islet enzymatic dissociation
Shapiro et al. [33]	Canada	1999	Introduction of a recirculating controlled perfusion system in human islet isolation

IMPROVING ISLET YIELDS IN AUTOTRANSPLANTATION

The success of IAT predominantly hinges on the yield of islets from the resected pancreas. Research indicates that achieving insulin independence in patients post-TP requires at least 200,000 islets (~3,000 islets/kilograms/body weight) [41,42]. Enhancing islet yield directly contributes to both the duration and extent of insulin independence following TPIAT. Several factors may affect the number and viability of islets isolated from the residual pancreas after TP, which this section will address.

CP leads to fibrosis and calcification of the pancreas, which negatively impacts both endocrine and exocrine function. Pancreatic fibrosis is a critical factor influencing islet yield during TPIAT. The development of fibrosis, characterized by excess connective tissue secondary to chronic inflammation or injury, limits the number of viable islets available for transplantation [7]. In a fibrotic pancreas, the presence of sclerosed and scarred tissue increases the difficulty of islet isolation and heightens the risk of mechanical injury to the islet cells. As a result, increased pancreatic fibrosis is typically associated with reduced islet yields, thereby affecting the likelihood of maintaining insulin independence, decreasing the need for exogenous insulin, and achieving durable graft function after TPIAT. Patients who have previously undergone surgical drainage for CP without pancreatic resection are more likely to require exogenous insulin at 5-year follow-up [43]. Within this subgroup, if impaired glucose tolerance or preoperative endocrine dysfunction (such as diabetes mellitus) is present, favorable outcomes after IAT are unlikely [44].

The patient’s preoperative nutritional condition is another determinant of islet yield. Evidence from cadaveric donors studies indicates that extended hospitalization and malnutrition can significantly decrease islet yields [10,11]. Individuals with CP commonly experience deteriorating nutritional status due to malabsorption, voluntary food restriction to mitigate pain, and the systemic effects of chronic inflammation [1]. Malnutrition may undermine pancreatic and islet cell health, making the islets more vulnerable to damage during isolation and transplantation [44]. Impaired immune function associated with malnutrition can further compromise the post-transplant survival of islets. Additionally, adequate levels of critical nutrients, including vitamins A, D, E, and K, and essential fatty acids, support cell membrane integrity, oxidative defense, and inflammation regulation [45].

Operative factors also affect islet cell viability, with warm ischemia time (WIT) being particularly critical during TPIAT. The duration of WIT is significantly associated with both immediate and long-term outcomes following solid organ transplantation [46,47]. Preserving the pancreas’ vascular supply is essential for minimizing WIT. In 1990, Ricordi et al. [47] demonstrated that extended WIT negatively affects the yield of islets harvested and isolated from the pancreas. In cadaveric donors, WIT reduction is facilitated by infusing a cold organ perfusion solution (Euro-Collins solution) into the femoral or portal vein, or the aorta [11]. The primary operative strategy to reduce WIT involves maintaining the blood supply (gastroduodenal, transverse duodenal and splenic arteries and the splenic vein) until the pancreas is ready to be harvested. Ligation of these vessels, performed as the final step before pancreas removal, increases the technical complexity of the procedure, particularly in the mobilization of a fibrotic and inflamed pancreas.

During islet isolation for autotransplantation, the human pancreas is subjected to a combination of enzymatic digestion and mechanical dissociation in order to separate the islets of Langerhans from the exocrine tissue. Employing the widely-used Ricordi method, this process includes a perfusion of collagenase enzyme followed by continuous gentle agitation in a Ricordi chamber, which facilitates islet release while minimizing their damage [31]. This step is crucial in preserving the islets’ viability and functional integrity before transplantation. The procedure’s success relies on meticulous control of digestion parameters such as temperature, enzyme concentration, and agitation, alongside skilled monitoring by the operator to optimize the yield and purity of the islets [31].

In addition to WIT, cold ischemia time and pancreas preservation have also been demonstrated to directly impact islet yield [48]. While cold ischemia is less damaging compared to warm ischemia, it still influences both islet yield and viability. Evidence indicates that cold ischemia longer than 16 hours markedly decreases islet yield, and optimal outcomes are achieved when pancreas processing is completed within 12 hours [38]. In selected cases, pre-storage ductal distension with collagenase has been shown to enhance islet yield during isolation [49].

The isolated pancreas is digested with collagenase to facilitate the release the islets. The success of this digestion is contingent on the extent of enzyme infiltration throughout the pancreatic tissue. The standard technique is intraductal administration of collagenase, followed by mechanical dissociation in a specialized chamber [31]. Achieving thorough enzyme penetration is essential, as inadequate digestion results in diminished islet mass. In cases of CP, the presence of significant fibrosis impedes enzyme access, leading to incomplete tissue digestion and lower islet yields [11]. This fibrosis-associated limitation underscores the value of utilizing highly effective and consistent enzyme formulations such as Liberase, which has demonstrated superior performance over crude collagenase in isolating functionally islets from fibrotic pancreases tissue [50].

Following digestion, islets are isolated from exocrine tissue using density gradient centrifugation, often employing Ficoll or similar media. The purity of the islet preparation is crucial for successful transplantation, as contaminating exocrine cells can trigger immune responses and elevate the risk of thrombosis, particularly in intraportal IT [51]. Achieving a balance between purity and yield is critical, as more aggressive purification protocols can lead to a significant loss of islets, particularly in fibrotic glands where the islet cell mass is already compromised [11]. Optimizing the purification step is therefore pivotal in islet isolation procedures, especially in autotransplantation settings where every islet is crucial for the patient's postoperative glycaemic control. The difficulty and complexity of achieving purification significantly influence the variability in islet yields across institutions that perform TPIAT.

Animal models have successfully demonstrated IAT utilizing various transplantation sites, including intraportal, intrasplenic, beneath the renal capsule, and free intraperitoneal dispersal [52,53], although replicating these results in clinical settings has proven challenging. Human IAT primarily focuses on intraportal and intrasplenic sites due to their consistent success in achieving islet engraftment and function.

The intraportal route is often preferred because it may necessitate a smaller islet mass for successful IT compared to the intrasplenic route [53-55]. However, intraportal IAT is associated with potentially significant complications, such as elevated intraportal pressure, hepatic venous thrombosis, hepatic infarction, and disseminated intravascular coagulopathy [53,56,57]. The increased portal pressure typically results from injecting substantial volumes of islet isolate into the portal vein, while thrombotic complications are believed to be caused by pancreatic thromboplastins released during the digestion of the pancreas’s exocrine component. To reduce these complications, the volume of fluid used to suspend the islets has been decreased, facilitated by the enhanced purity of the islet isolate achieved through Ricoll gradient centrifugation. Nevertheless, this purification process may result in a significant loss of islets, which is particularly problematic in IAT where the initial number of islets from a fibrosed pancreas might be near the threshold needed for insulin independence. An optimal balance between purity and volume of the isolate is pivotal.

While intraportal infusion remains the preferred site for IAT due to its favorable engraftment and reduced islet mass requirements, alternative sites have been explored to address complications such as portal vein thrombosis and to potentially improve islet survival. These studies have examined locations including the spleen, renal subcapsule, peritoneal cavity, subcutaneous tissue, and submucosally in the stomach. Cantarelli and Piemonte [51] in 2011 reviewed these alternative transplantation sites, noting that intrasplenic transplantation in animal models demonstrated engraftment comparable to intraportal infusion but necessitated higher numbers of islets to achieve similar glycemic control, with the associated risk of splenic infarction. The renal subcapsule, studied extensively in rodent models, supports robust islet survival due to its rich vascular supply, yet is limited in humans by surgical complexity and space constraints [52]. In 2008, rodent studies by Merani et al. [52] showed that the peritoneal cavity allowed for substantial islet dispersal but resulted in poor survival due to hypoxia and the absence of immediate vascularization, with only 10% to 20% of islets remaining functional after 1 month. Subcutaneous transplantation sites, including the use of bioartificial devices such as the β air macrochamber, have demonstrated encouraging results in preclinical research. In 2012, Ludwig et al. [57] reported stable euglycemia in diabetic rodents for up to 3 months, attributed to improved oxygenation of the islet graft, although translation to clinical applications has been limited. A comparative study by Verhoeff et al. [54] in 2022 demonstrated that extrahepatic sites, including the omentum, were associated with lower C-peptide concentrations and decreased rates of insulin independence (15% vs. 35% at 1 year) compared to intraportal IAT, indicating the superior superior engraftment and functional outcomes achieved with hepatic implantation. These studies indicate that while alternative sites provide potential solutions to liver-specific complications, the intraportal route currently offers the best balance of islet survival and function, though the investigation into optimized extrahepatic sites is still necessary.

Refining islet isolation by utilizing islet cell culture focuses on optimizing the conditions for maintaining and expanding pancreatic islets ex vivo [58,59]. The goal of this process is to improve both islet cell viability and functional capacity, both of which are essential for adequate insulin synthesis post-transplant. Human serum albumin is commonly used in clinical islet culture protocols in order to minimize the risk of xenogeneic contamination that is associated with the use of fetal bovine serum (FBS). However, FBS has been shown to better support islet viability and mitigate the effects of pancreatic enzymes from the isolation process, although its clinical use is constrained by immunogenic risks [60,61]. Culturing islets at room temperature (22°C–26°C), as opposed to 37°C, has been found to be advantageous because temperatures reduce apoptosis and central necrosis by decreasing the islets’ oxygen requirements [62,63]. Additionally, preservation at 4°C using solutions such as University of Wisconsin solution provides further benefits by limiting enzyme release from acinar cells and maintaining islet morphology and size, both of which are crucial for optimal survival and function after transplantation [59].

In 2012, Ludwig et al. [57] introduced a purpose-built macrochamber intended for IT. This subcutaneous implantable device, known as the bioartificial pancreas or “β Air,” was developed to supply a stable and adequate oxygen environment while also safeguarding donor islets from immune rejection. This minimally invasive device was able to achieve normalization of blood glucose in streptozotocin-induced diabetic rodent models for up to three months [58]. Encapsulated islets within the device are arranged within an alginate matrix near an oxygen-permeable membrane, ensuring optimal oxygen delivery and establishing a robust immune barrier. Pre-treatment of islets with growth hormone-releasing hormone analogs inside the device resulted in improved graft functionality, highlighting the key importance of oxygenation for islet survival and performance. This approach demonstrated significant potential for achieving prolonged euglycemia in experimental diabetes and is undergoing clinical evaluation in the United Kingdom (UK) and Europe.

Although the encapsulation of individual islets within microcapsules composed of alginate or polymeric hydrogels has shown promise, successful translation to large animal and human applications has been limited, with challenges remaining in long-term efficacy and engraftment [63]. The approach, however, continues to garner significant interest due to its potential to obviate the need for immunosuppression in transplant recipients, to expand the islet donor pool, and to ease the transplantation process. Recent progress has centered on enhancing the viability and function of microencapsulated islets. One innovative strategy involves co-encapsulating islets with extracellular matrix proteins and mesenchymal stromal cells [64]. This approach aims to reestablish the native islet microenvironment and intercellular communications, which are frequently disrupted during the isolation process, while also taking advantage of the immunomodulatory effects of mesenchymal stromal cells to promote islet survival and function. Another emerging technique involves co-encapsulation of islets with cells engineered to produce insulin-like growth factor II (IGF-II), demonstrated to support islet viability.

While these novel methods await clinical validation, they offer a promising platform for ongoing research and may accelerate future clinical applications. Continued development in microencapsulation technologies provides optimism that full clinical implementation could be realized in the foreseeable future. These technological advancements underscore the considerable strides being taken to overcome existing challenges in IT, thereby moving closer to realizing the complete therapeutic benefit of microencapsulated islet grafts.

FUNCTIONAL OUTCOMES OF TPIAT

Functional outcomes following TPIAT, particularly in terms of post-transplant endocrine function, pain alleviation, and improvements in quality of life, represent key measures of procedural effectiveness and are influenced by islet yield, patient-specific factors, and technical aspects of the intervention (Table 3).

Table 3.

Functional outcomes of TPIAT

Outcome	Metric	1-year post-TPIAT	5-year post-TPIAT
Insulin independence	% of patient’s insulin-free	20%–40%	10%–25%
C-peptide persistence	% of patients with detectable C-peptide (indicating graft function)	80%–90%	70%–80%
Pain reduction	% of patients with significant pain relief	80%–90%	70%–80%
Opioid independence	% of patients off opioids	50%–60%	40%–50%
Quality of life improvement	% of patients with improved SF-36 or similar scores	60%–70%	50%–60%

TPIAT, total pancreatectomy with islet autotransplantation; SF-36, Short Form-36.

Post-transplant endocrine function

A central objective of IAT in the context of TPIAT is to prevent or reduce the insulin-dependent diabetes that typically develop after TP. Endocrine success is strongly associated with the number of islets transplanted, with approximately 5,000 islets per kilogram of body weight (islets/kg/BW) representing a critical threshold for achieving higher likelihoods of insulin independence [40]. Published data indicate that 20% to 40% of recipients maintain insulin independence 1-year after TPIAT, with this outcome particularly evident in those whose islet yields exceed 5,000 islets/kg [65,66]. Although achieving insulin independence is a primary aim of TPIAT, patients with lower yields still benefit from partial islet function, which decreases the risk of hypoglycemic unawareness, brittle diabetes and long-term complications [6].

Long-term data reveal that 70% to 80% of patients maintain detectable C-peptide levels, an indicator of graft function, at 5 years post-TPIAT, although insulin requirements typically increase over time due to islet attrition [67]. Variables such as the extent of pancreatic fibrosis, the presence of preoperative diabetes, and longer disease duration are associated with inferior endocrine outcomes, primarily through decreased islet yield and viability [42]. For instance, individuals with existing endocrine dysfunction before surgery are significantly less likely to attain insulin independence, with only 10% to 15% remaining insulin-free at 3 years, compared to 30% to 50% among those without antecedent diabetes [9]. Innovative strategies, including the Ricordi method and the application of Liberase enzyme, are crucial for enhancing islet isolation and maximizing endocrine function [29].

Pain reduction

Intractable pain is a defining characteristic of CP and the leading reason for undertaking TPIAT. Following TPIAT, 80%–90% of patients report marked pain relief, and 50%–60% are able to discontinue opioid use within 1 year [4]. A multicenter study reported that 85% of patients showed reduced pain scores at 1 year, with sustained improvements in 70% of cases at 5 years [67].

However, 10% to 20% of patients experience persistent or recurrent pain, often linked to central sensitization or sources of pain not related to the pancreas. This underscores the importance of preoperative psychological evaluation and postoperative multidisciplinary pain management [1]. The extent of pain relief is closely linked to improved functional status, enabling individuals to return to employment and participate more actively in social activities [5].

Improvement in quality of life

TPIAT results in significant enhancements in quality of life by mitigating pain and decreasing the frequency and severity of complications associated with CP. Established assessment tools, such as the Short Form-36 (SF-36) and the pancreatitis quality of life instrument, have documented notable improvements in both physical and mental health domains following TPIAT [68]. Approximately 60% to 70% of patients report improved quality of life at 1 year post-procedure, with sustained benefits observed in 50% to 60% at 5 years [2]. Major contributing factors include fewer hospital admissions, reduced opioid dependence, and improved glycaemic control, all of which help attenuate the psychological and social burden of CP [3].

The greatest improvements in quality of life are seen in patients who experience substantial pain relief and retain at least partial endocrine function [12]. Nonetheless, ongoing diabetes or persistent exocrine insufficiency—managed with pancreatic enzyme replacement therapy—can moderate the extent of these improvements for some patients. Thorough preoperative counseling combined with comprehensive postoperative support, encompassing both nutritional and psychological care, is essential for maximizing long-term quality of life outcomes.

CHALLENGES AND UNRESOLVED ISSUES OF ISLET AUTOTRANSPLANTATION

TPIAT provides considerable benefits for individuals with CP, including marked pain relief and the prospect of preserving endocrine function. However, several persistent challenges affect the consistency and durability of successful outcomes. These challenges include considerable variability in islet yield and viability, absence of standardized procedures across clinical centers, complications associated with intraportal delivery, declining long-term graft performance, and ongoing nutritional and metabolic concerns, along with the imperative for continual technological innovation. Addressing these issues is critical to realizing optimal patient outcomes and broadening access to TPIAT.

A leading challenge is the inconsistency in islet yield and viability, which exerts a direct influence on clinical success. Achieving optimal procedural results depends heavily on isolating sufficient, high-quality islets from the explanted pancreas. The fibrotic changes characteristic of CP make enzymatic digestion more difficult, typically leading to reduced islet yields and compromised viability. A 2025 study by Mattke et al. [69] identified pancreatic atrophy and ductal alterations—frequently seen in advanced fibrosis—as significant predictors of poor islet isolation outcomes, highlighting the detrimental impact of disease severity on TPIAT efficacy. Additional patient-dependent factors, including preoperative nutritional status and a history of pancreatic surgical interventions, further contribute to this variability and can hinder reproducibility of favorable outcomes.

Furthermore, the lack of standardized protocols for islet isolation, islet handling, and transplantation among different clinical centers gives rise to significant heterogeneity in outcomes. Differences in surgical methodologies, enzyme formulations, and perioperative management strategies all influence islet yield, quality, and patient outcomes. The specific composition and ratio of enzyme blends, notably collagenase to neutral protease, may vary significantly between centers and directly affect the effectiveness of tissue digestion, especially in cases of extensive fibrosis. Radomski and Zureikat [70] highlighted the pressing need for standardized guidelines to support reproducible and reliable results in this context. Although automated isolation platforms that comply with current good manufacturing practice (cGMP) standards have been developed to address this variability, broad implementation and robust multi-center validation are still needed, reinforcing the need for harmonized protocols.

The intraportal approach, as the preferred method for islet engraftment due to its clinical accessibility and relatively low procedural morbidity, introduces a distinct set of complications. Risks include portal vein thrombosis, increased portal venous pressure, and liver ischemia/reperfusion injury, all of which can contribute to substantial early islet loss. It is estimated that 50% to 70% of islets may be lost immediately after transplantation, largely due to adverse effects of the hepatic microenvironment, such as low oxygen levels and instant blood-mediated inflammatory response [40,55,57]. Delaune et al. [71] stressed the importance of optimizing islet purity and total infusion volume to minimize these procedural complications. While exploration of alternative recipient sites such as the omentum or intramuscular tissue is underway to circumvent these limitations, the intraportal route remains the standard and most effective option to date.

Long-term islet graft function remains a significant unresolved issue. While TPIAT achieves initial insulin independence in 20% to 40% of patients at one year, graft function tends to decline over time, with insulin independence rates falling to around 10.9% by 10 years post-procedure [72]. Although partial islet function continues in many patients, as demonstrated by detectable C-peptide levels, the gradual increase in insulin requirements underscores the problem of graft attrition [73]. Factors such as the hepatic microenvironment, mechanical stress during transplantation, and potential inflammatory responses contribute to this decline. Developing strategies to enhance long-term islet survival and function is a major research priority.

Nutritional and metabolic challenges following TPIAT are considerable. The complete removal of the pancreas leads to exocrine insufficiency and altered gastrointestinal anatomy, necessitating lifelong pancreatic enzyme replacement therapy and meticulous dietary management to address both macro- and micronutrient deficiencies. Hasse et al. [74] noted that postoperative gastrointestinal symptoms, such as delayed gastric emptying and malabsorption, often necessitate enteral nutrition as a bridge to oral intake, complicating recovery. Many TPIAT patients have pre-existing CP, typically causing exocrine dysfunction prior to surgery, which complicates postoperative management. Long-term outcomes indicate that steatorrhea affects 62% to 75% of patients and diarrhea impacts 73% to 87% at 3 months to 3 years following TPIAT. Forty-four to sixty-nine percent of patients report significant disruptions to daily life, and weight loss affects 17% to 46% [75]. Effective management involves individualized pancreatic enzyme replacement therapy regimens, regular monitoring of nutritional status, and patient education to ensure adherence, complemented by strategies including acid-suppressing agent co-administration or treatment for small intestinal bacterial overgrowth to manage persistent symptoms [75]. Future research should aim at optimizing PERT dosing protocols, improving adherence, and exploring novel therapies to enhance digestive function post-TPIAT. Managing endocrine function also requires close monitoring, as many patients require exogenous insulin, especially as graft function declines over time. These challenges underscore the need for comprehensive postoperative care to support patient recovery and enhance quality of life.

FUTURE DEVELOPMENTS AND PROSPECTS

Advances in islet isolation techniques are pivotal to enhancing the efficacy of TPIAT for CP, especially in addressing the challenges posed by pancreatic fibrosis and variable islet yields. Recent advancements include the use of tailored enzyme blends with optimized collagenase and neutral protease ratios, which improve the digestion of fibrotic pancreatic tissue and have enhanced the IEQ/kg results following pancreatectomy and islet isolation [76]. Techniques such as tissue premincing before enzymatic perfusion increased the surface area for enzyme action and enhance islet release from sclerosed glands, while pancreatic ductal stone ablation can facilitate uniform enzyme distribution, potentially mitigating incomplete digestion [76].

Emerging technologies, such as automated isolation systems adhering to cGMP standards, have the potential to reduce variability across centers by standardizing digestion parameters [77]. Additionally, novel assessment tools like islet-on-chip technology, can enable real-time evaluation of islet viability and function, optimizing the selection of high-quality islets for transplantation [77]. Furthermore, research into alternative islet sources, such as stem cell-derived islets, may supplement low yields in patients with severe pancreatic damage, though these methodologies are still in developmental phases [78]. Research exploring alternative transplantation sites to reduce early islet loss and enhance engraftment is progressing, and hypothermic and normothermic organ perfusion techniques are being examined to preserve pancreatic tissue integrity, potentially increasing islet yields by minimizing ischemic damage [79].

Future research aims to refine these methods, develop enzyme formulations specifically designed for fibrotic pancreases, and integrate stem cell-derived islets as a supplementary source for patients with low yields, though this requires further validation [77]. These advancements could significantly enhance insulin independence rates, currently 20% to 40% at 1 year, and improve glycemic control, although challenges such as severe fibrosis and long-term graft attrition will undoubtedly persist [66]. Ongoing innovation and clinical validation are crucial to standardize protocols and maximize TPIAT’s therapeutic potential.

CONCLUSION

TPIAT is an effective treatment for CP, alleviating intractable pain in 80% to 90% of patients and preserving endocrine function through advanced islet isolation techniques like the Ricordi method and Liberase enzyme use, achieving insulin independence in 20% to 40% of cases at 1 year. However, challenges such as pancreatic fibrosis, variable islet yields, and long-term graft attrition highlight the need for standardized protocols and improved preservation methods. Future advancements, including tailored enzyme blends, alternative transplantation sites, and technologies like islet-on-chip and stem cell-derived islets, aim to enhance outcomes, whilst key performance indicators can ensure consistency and optimize patient outcomes and glycaemic control.

Funding Statement

FUNDING None.