Pancreatic is located behind the stomach and is an important organ for endocrine regulating blood sugar and exocrine aiding digestion.
Human understanding of Islets began nearly 150 years ago: in 1869, German pathologist Paul Langerhans first observed irregular cell clusters scattered in the pancreas under a microscope, like countless small islands in the vast ocean (Figure 1). The islets were also named Islets of Langerhans. At that time, he had not yet realized the role of these cell clusters.
Figure 1 "islands" scattered in the pancreas
After scientists gradually discovered that the islets can secrete hormones such as insulin and glucagon . According to the staining and morphology, human pancreatic islet cells are mainly divided into α cells, β cells, δ cells, ε cells and PP cells. Among them, α cells account for about 20% of pancreatic islet cells, which can secrete glucagon and increase blood sugar; β cells account for 60% to 70% of pancreatic islet cells, which can secrete insulin and lower blood sugar.
The above-mentioned cells form a group of islet cells of varying sizes, with a diameter of between 50 and 500 microns; the total number is about 1 to 2 million, accounting for only 1% to 2% of the total number of pancreatic cells. In various environments such as eating and exercising, the above-mentioned cells play a synergistic role to control the body's blood sugar within a normal range.
Isle transplantation and diabetes
0 The clinical data in 2017 showed that the number of adult diabetes patients in China has reached 112 million, while the prevalence of in the early stage of diabetes exceeded 35%. Long-term poor blood sugar control can cause serious complications such as cardiovascular and cerebrovascular lesions, blindness, end-stage renal disease, and even life-threatening.
Take end-stage renal disease caused by diabetes as an example. In 2011, it only accounted for 10% of Shanghai Changzheng Hospital end-stage renal disease, but in 2016 it has risen rapidly to 30%, which is increasingly close to the proportion of developed countries in Europe and the United States. Among the various complications caused by unfavorable blood sugar control, diabetic nephropathy has replaced chronic glomerulonephritis and has become the first cause of chronic kidney disease in my country. The "China Annual Scientific Report on Kidney Diseases" released in 2015 once issued a warning: If intervention is not provided within a specific population, China will usher in the peak of diabetic nephropathy leading to uremia in the next 10 to 20 years.
For patients with type 1 diabetes and patients with type 2 diabetes (brittle diabetes) who have severely damaged pancreatic islet function, although insulin intensive treatment plans or insulin pump treatment can regulate blood sugar to a certain extent, the efficacy of these treatment methods is extremely limited and cannot effectively prevent the occurrence and development of complications of diabetes. Therefore, exploring treatment methods that are more in line with the physiological functions of the human body has always been a cutting-edge hot topic in diabetes research.
islet transplantation refers to the surgery in which the donor donated pancreas is obtained through digestion, isolation, purification and other steps in a laboratory that meets the product production quality management specifications (GMP) and transplanted to the patient.
islet transplantation is completely different from solid organ transplants with severe trauma (such as liver transplantation, kidney transplantation ). It only requires puncture and injection into the patient under local anesthesia with the help of ultrasound and digital processing angiography (DSA) imaging guidance. Patients after islet transplantation can re-secret insulin and glucagon in the body with the help of new islet cells, thereby achieving the effect of long-term detachment of insulin and stabilizing blood sugar.
Islet transplantation can be used to treat diabetic patients with absolute insulin secretion (brittle type 1, type 2 advanced islet function significantly declining, 3C pancreatic diabetes, etc.).
Figure 2 Islet Isolation-Islet Transplantation Schematic
According to data reported by the International Islet Transplantation Registration (CITR) in 2012, from 1999 to 2010, a total of 677 patients were subjected to islet transplantation worldwide, and more than 2,000 islet cell isolation were performed.
early stage (1999 to 2002), the proportion of patients who had lost insulin three years after islet transplantation was 27.1% (58/214); the intermediate stage (2003 to 2006), increased to 36.8% (94/255); the recent stage (2007 to 2010), reached 44.2% (92/208), and the proportion of patients who needed to undergo secondary transplantation decreased, and the clinical indicators of diabetes such as glycogenated hemoglobin , C peptide , glucose tolerance test have been significantly improved, and the incidence of hypoglycemia and other adverse events has also been significantly reduced.
This shows that pancreatic islet transplantation has undergone decades of continuous improvement and has entered a new stage of development. It has been proved to be an effective method for treating diabetes through clinical practice.
International pancreatic islet transplantation development history
1966, Professor William Kelly and others carried out the world's first pancreatic overall organ transplantation, which can effectively control diabetes after surgery, but pancreatic transplantation has a great degree of damage to the body, many surgical complications and high cost, and low patient acceptance.
In 1969, Howell and other studies found that most patients with type 1 diabetes have normal pancreatic exocrine function and do not need pancreatic overall organ transplantation. They proposed a new concept of using pancreatic islet transplantation instead of pancreatic overall organ transplantation. This view was quickly recognized by the academic community.
In 1974, Sutherland and others carried out the world's first human pancreatic islet transplantation. After the operation, the dosage of insulin in patients was significantly reduced and achieved certain therapeutic effects. Since then, clinical and basic research related to islet transplantation has gradually increased.
In 1980, Kolb and others first reported that patients with type 1 diabetes were completely deprived of insulin after receiving islet transplantation.
Figure 3 International development history of pancreatic islet transplantation
The difficulty of pancreatic islet transplantation technology lies in the isolation and purification of islet cells. In the early stage of the research, it mainly relies on a single glucosan or polysucrose density gradient islet separation and purification technology.
The first milestone occurred in 1989. The semi-automatic islet isolation system invented by Ricordi et al. overcame key technical difficulties in islet cell isolation and purification, and promoted the islet transplantation from experimental research to large-scale clinical applications.
In the same year, the COBE2991 cell separator invented by Lake et al. achieved one-time large-capacity continuous density gradient centrifugation, which was simple to operate and became a good tool for purifying human and animal pancreatic islet cells.
In 1990, Scharp and others were the first to perform combined islet transplantation for patients with type 1 diabetes after renal transplantation to treat diabetic nephropathy. All of these six patients were completely detached from exogenous insulin during the 6-month follow-up period after surgery, and their renal function was well protected. This suggests that for patients with diabetic nephropathy, kidney transplantation combined with islet transplantation is better than islet cell transplantation alone. Reported data from
CITR shows that from 1990 to 1995, islet transplantation ushered in the first peak, during which more than 180 islet transplants were conducted around the world. However, literature shows that about 53% of these patients have islet function within one week after transplantation, but one year after transplantation, 26% of patients have partial efficacy, and only 7% of patients can not use exogenous insulin. The failure of pancreatic islet cells to survive for a long time after transplantation, resulting in poor clinical efficacy, which is the main reason why large-scale islet transplantation has not been carried out for a period of time.
Until 2000, Shapiro and others formulated a series of complete standards for islet transplantation, including donor selection, islet equivalent, postoperative immunosuppressant regimen, etc. The standard recommends that multiple pancreas separate large amounts of islet cells for transplantation, and after the operation, a new immunosuppressive regimen without glucocorticoids and lowering the dose of calcine-neurin inhibitors— Edmonton protocol—that is, sirolimus, low-dose tacrolimus and daclizumab, has significantly improved clinical effects and is of great significance in the history of the development of islet transplantation, which has attracted widespread attention around the world. At this point, islet transplantation has ushered in the second peak.
CITR, founded in 2004 by National Institutes of Health (NIH), is the largest multi-center joint research organization in the world. There are about 50 clinical islet transplant centers participating around the world, with the purpose of improving the safety and long-term efficacy of clinical islet transplantation.
The international multicenter islet transplant clinical study report released by the annual meeting of the American Diabetes Association (ADA) in 2005 showed that the proportion of patients with islet transplantation performed using the Edmonton regimen was as high as 53% of patients who had lost insulin within 3 years after surgery.
2014 World Transplant Conference data shows that the proportion of patients who are out of insulin in most international centers has reached more than 50% after islet transplantation, and some centers even exceed 60%, which is similar to the long-term efficacy of pancreatic transplantation.
Development history and current status of pancreatic islet transplant in my country
The clinical application development of pancreatic islet transplant in my country has always kept pace with international pace. However, in the early days, due to the difficulty of islet cell isolation and purification technology, the expensive construction of GMP laboratory , and the long team cultivation cycle, the development path was quite tortuous.
As early as 1982, Hu Yuanfeng and others in Shanghai First People's Hospital carried out the first human embryonic islet tissue transplant in China. Since then, many domestic hospitals have also tried to carry out the work. In 2000, Tan Jianming's team from the former Nanjing Military Region Fuzhou General Hospital and the University of Miami in the United States successfully completed the first adult pancreatic islet transplantation in the treatment of type 1 diabetes patients.
In 2005, Xie Pingren, the Wuxi People's Hospital Affiliated to Nanjing Medical University, first used collagenase to perfusate the digestive pancreas and polysucrose isolation solution to establish a continuous density gradient, and used stratified purification method to obtain an ideal number of pancreatic islet cells.
In 2009, Tan Jianming and others took the lead in using the American Ricordi human islet isolation technology to carry out islet transplantation and kidney transplantation to treat 22 patients with diabetic nephropathy. The evaluation of pancreatic islet function and safety during the 3-year follow-up showed good efficacy.
In 2011, First Affiliated Hospital of China Medical University, Liu Yongfeng and others underwent 4 islet transplants in 3 patients with 2 diabetes and renal failure, with good clinical efficacy. For patients with insulin-dependent type 2 diabetes, if renal impairment occurs, islet transplantation can obtain significant therapeutic value.
In 2016, Yin Hao's team at Shanghai Changzheng Hospital of Naval Medical University took the lead in carrying out the first total pancreatic resection and autologous islet transplantation in Asia. More than 200 islet transplants have been completed so far. Among the patients who have been followed for more than one year, 60% of them have completely lost insulin, and the glycated hemoglobin has dropped from (9±4) % to (6±1) %. The average C peptide increment is 0.96 nmol/L. The short-term clinical efficacy has reached the level of first-class transplant centers in Europe and the United States.
Figure 4 Development history of domestic pancreatic islet transplantation
Challenges and response strategies for pancreatic islet transplantation
Islet transplantation has good efficacy and high safety in the treatment of insulin-dependent diabetes, but there are still many influencing factors that restrict its development. Especially in China, islet transplantation is still in its infancy and faces many problems and challenges, which require clinicians and scientific researchers to collaborate and innovate to actively respond.
Figure 5 Bottleneck problems faced by islet transplantation
Pancreatic donor organ shortage
Organ shortage is a problem that plagues the world's transplant field, and it also seriously restricts the large-scale development of islet transplantation. With the promotion of Edmonton clinical program and the continuous improvement of islet cell isolation technology, many transplant centers in the world have initially required pancreas transplantation from 3 to 4 donors to 1 recipient, and now they are isolated and successfully transplanted using a single pancreatic donor.
Live islet transplantation puts higher requirements on islet cell isolation technology. The world's first live islet transplantation was reported by Kyoto University in Japan. A 27-year-old female patient with type 1 diabetes received a pancreatic islet transplantation from the distal pancreas of her mother. After one year of follow-up, both the donor and the recipient maintained good blood sugar levels.
Compared with organ transplants such as liver and kidneys, the shortage of pancreatic donors is more serious.Since there are a large number of exocrine gland cells in the pancreas, pancreatic donors have poor tolerance for cold ischemia. Usually, donors whose cold ischemia time is more than 10 hours cannot be used for isolation, and the pancreatic donors must reach normal levels of glycated hemoglobin and C peptides.
data show that there are about 8,000 organ donors in the United States every year, of which less than 30% of the pancreas can be used for transplantation. The utilization rate of pancreas in my country is even lower. According to the author's experience, due to factors such as age, islet function, cold ischemia time, and the pancreas of less than 30% of donors can meet the clinical transplant requirements, while there are still fewer islet transplant centers with conditions and technology.
In order to further improve the utilization rate of pancreatic organs, while steadily promoting organ donation after citizens' death and expanding the source of donors, it is particularly important to accelerate the establishment of islet separation laboratories in major domestic transplant centers, establish pancreatic and islet cell freezing technology and resource banks, and strengthen the training of professional islet transplant physicians and experimental technicians.
stem cell transplantation may be another effective way to solve organ shortage. Currently, stem cells used for diabetes treatment mainly include mesenchymal stem cells (MSCs) and induced pluripotent stem cells (iPSCs).
MSC is an adult stem cell with strong multidirectional differentiation and self-renewal ability. It can improve insulin resistance in peripheral tissues through potential immunomodulation and anti-inflammatory effects, as well as promote pancreatic β-cell regeneration and protect β-cells. There are also studies that since MSCs can promote vascular regeneration of islet cells and at the same time reduce the innate immune damage caused by islet cells in the early stage of transplantation, combined transplantation of islet cells with MSCs can improve the survival rate of islet cells.
iPSC is an all-powerful stem cell with infinite proliferation potential. It can be differentiated into pancreatic islet β cells or insulin synthetic cells under certain conditions. However, pancreatic islets need to have a complete structure and cell ratio when exerting physiological functions in the body. At present, there are still many technical and ethical obstacles to be overcome in the clinical application of iPSC-derived pancreatic islet cells.
At the same time, domestic and foreign scholars are also actively studying xenois islet transplantation. In 1994, Groth and others transplanted pig-derived islets to humans for the first time and conducted clinical trials of xenograft. Since then, many institutions have also carried out related research. , Central South University Xiangya Third Hospital, , Wang Wei and others were the first in China to implement xenois islet transplantation and achieved certain results. The research and development of the above-mentioned technologies will help improve the problem of organ scarcity.
Pancreatic acquisition, transport and islet digestion separation and purification There is no standard process yet.
Islet isolation and purification technology has greatly improved the quality and quantity of islet cells obtained. However, there is still no unified standard process suitable for my country's national conditions in China, especially in many key links such as recipient selection, pancreatic acquisition, preservation and transportation. The operation details of each islet transplant center vary, and the loss of islet cell count may occur in multiple links mentioned above. We can learn from the standards for the preparation, scoring and quality control procedures of clinical pancreatic islet grafts formulated by the US pancreatic donor scoring system and CITR to speed up the formulation of domestic unified relevant quality control and operation standards.
Early rejection loss and adverse drug reactions of pancreatic islet cells
Early rejection reactions and adverse drug reactions of immunosuppressants after islet transplantation are still the main reasons for poor long-term clinical efficacy. In the early stage of islet transplantation, inflammatory responses, hypoxia and immune rejection can lead to the loss of islet cells. Inflammation reactions and hypoxia may cause apoptosis and death of about 50% of islet cells.
After islet transplantation, immunosuppressants are often taken orally to control immune rejection. However, immunosuppressants themselves can also cause many adverse reactions, directly causing apoptosis of pancreatic islet cells. Therefore, further optimizing the immunosuppression regimen, reducing the attack on the islets by the immune system and reducing the damage of drugs to the islets, will help improve the efficacy of islet transplantation.
Surgery method for transhepatic portal venipuncture in pancreatic islet transplantation
Currently, 90% of islet transplantation methods in clinical practice are percutaneous portal venipuncture, injecting pancreatic islet cells into them.Its advantage is that the liver, as the largest immune preferential organ in the body, is the physiologically active organ of insulin, and has abundant blood supply. Therefore, islet cells can survive better in the liver sinusoids compared with other transplant sites.
However, injecting pancreatic islet cells from the portal vein will cause more complications, such as vascular embolism, postoperative bleeding, portal hypertension, portal vein peripheral fat degeneration, especially the blood-mediated acute inflammatory reaction caused by it, which will cause a large loss of grafts in the very early stage after transplantation.
There are currently a variety of solutions to alleviate the acute inflammatory response mediated by blood, such as using low molecular weight heparin sodium or heparin sodium to apply islets, thrombin inhibitors, nicotinamide , etc., but it cannot be completely avoided. After portal intravenous transplantation, islet cells may experience adverse vascularization and insufficient oxygen supply, while islet β cells are particularly sensitive to hypoxia, which will lead to a large amount of apoptosis of pancreatic islet cells and a significant reduction in the secretion of corresponding insulin.
In short, the liver is not the most ideal place for islet transplantation, and the best islet cell transplantation site still needs further exploration.
Conclusion
Isle transplantation has greatly promoted the rapid development of diabetes cell therapy technology, especially for fragile insulin-dependent diabetes, diabetes combined with end-stage renal disease, so that patients can no longer rely on exogenous insulin, avoid the development of related complications, and protect important organs such as the kidneys. With innovative research on pancreatic donor acquisition, islet isolation and purification, transplant site selection, immunosuppression protocols, and the formulation of a series of standardized processes, this technology will surely be promoted.
At the same time, with the continuous development of new technologies, universal regenerated pancreatic islets prepared through "stem cell + gene editing technology" are expected to completely solve the two major problems of shortage of donor sources and immune rejection, becoming the best treatment for insulin-dependent diabetes, benefiting more patients.
-The author of this article is Yin Hao, director of the Department of Organ Transplantation and Liver Surgery of Shanghai Changzheng Hospital-
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