The primary targets of islet transpla in DM are to: o Provide insulin independence, o Improve quality of life, & o Limit secondary sequelae.
Islet transplant
Abbreviations
o AB: antibodies
o Ac Rj: Acute rejection.
o ADA: American Diabetes Association.
o AE: adverse events.
o BMI: body mass index.
o CITR: Collaborative Islet Transplant Registry.
o CT: computed tomography.
o CyA: Cyclosporine.
o Dc Np diabetic nephropathy
o Dc Nr diabetic neuropathy
o DCCT: Diabetes Control and Complications Trial.
o EPITA: the European Pancreas and Islet Transplant Association
o ESKD: end-stage kidney disease.
o FBS: fasting blood glucose.
o GC: glucocorticoids
o HDL: serum high-density lipoprotein.
o HG: hypoglycaemia.
o HLA: human leukocyte antigen.
o im/m: immunosuppressive therapy
o IPITA: International Pancreas and Islet Transplant Association
o KTx: kidney transplantation.
o LDL: low-density lipoprotein.
o Mgcp: magnetoencapsulation/magnetocapsules.
o Mic: Microencapsulation.
o MMF mycophenolate mofetil.
o MR: mortality rates.
o MRI: Magnetic resonance imaging.
o NEPECs: nonendocrine pancreatic epithelial cells.
o PAK: Pancreas after kidney.
o PET: positron-emission tomography.
o PTA: pancreas transplant alone.
o PV: Portal vein.
o SPK: simultaneous pancreas-kidney.
o SRL Sirolimus.
o Tac: tacrolimus.
o Tac: Tacrolimus.
o TNFa: Tumour necrosis factor-alpha.
o TPIAT: total pancreatectomy and islet auto transplantation.
o TR: Transplant recipients.
o Tx: transplantation.
o UB: urinary bladder.
o UNOS: United Network for Organ Sharing.
The primary targets of Tx in DM are to:
o Provide insulin independence,
o Improve quality of life, &
o Limit secondary sequelae.
Pancreas Tx is usually performed with simultaneous KTx in selected ptns with DM + ESKD who’re already requiring im/m for the kidney allograft. PAK & PTA are proceeded less commonly. Islet cell Tx is still under development. We will go through the history, technique, and clinical outcomes of pancreas & pancreatic islet Tx in hyperglycaemic ptns with longstanding DM type 1, focusing on islet Tx or pancreatic tissue alone. Both pancreas & islet Tx needs lifelong im/m to impede allograft rejection. ESKD ptns receiving SPK or PAK Tx are already maintained on im/m therapy for the kidney allograft, so, the impact of im/m therapy on quality of life is minimal. However, ptns may receive PTA with no Dc Np, the benefit of impeding the progression of secondary complications must be weight for the untoward effects of the im/m medications after Tx (e.g., diarrhoea, cytopenia, anaemia, fatigue, HT, osteoporosis, variable infections & secondary malignancies).
ADA criteria for Tx:
· SPK or PAK: ptns with type 1 DM & ESRD having had or plan to get KTx are candidates also for pancreas Tx. Successfully performed pancreatic Tx will help better glycemic control with better kidney survival. Pancreatic Tx usually proceeded in DM + ESKD. TR mostly receive SPK rather than PAK.
· PTA: considered only in ptns with intolerable diabetic sequelae where the quality of life is awfully difficult with complications like:
o Persistent, frequent & severe metabolic sequelae (HG, severe hyperglycaemia, ketoacidosis)
o Incapacity with clinical/emotional feelings related to exogenous insulin injection.
o Persistent resistance to insulin-based regimen to hold acute complications
· Islet: Islet Tx considered an evolving technique that is usually confined only to the controlled research work-up. Pre- Tx screening for CVS disease in PTA is similar to that in combined kidney-pancreas Tx.
Pancreas vs islet Tx:
There’re no direct, RCT comparing outcome of SOT vs islet Tx. Few observational studies compared pancreas & islet Tx. Report: single centre performed 33 PTA & 33 islet Tx, ptns undergoing PTA showed a higher rate of insulin independence after one-y. follow-up. Long-term side effects (timing/frequency of hospitalization, re-intervention for acute surgical/immunologic sequelae, infection) was higher with pancreas Tx. Retrospective study: compared 15 PTA & 10 islet Tx, the rate of insulin independence at 3 ys was similar. Database from pancreas & islet Tx showed elevated rate of insulin independence with pancreas Tx, but also a higher morbidity related to general surgery. However, islet Tx is less invasive, so, it associated with lowered morbidity. However, the rate of long-term success (= insulin independence) is lesser.
PANCREATIC TX
It was the year 1966, when pancreas Tx was 1st used to treat DM in humans. The reported rates of graft & ptn survival were low; consequently, very few operations were implemented in the early/mid-1970s. With subsequent advent of better im/m plans (especially CyA & anti-T-cell AB), new surgical approaches, & selection of healthier TR resulted in a greatly better outcome. So, the number of pancreatic Tx were rising each year in the US, up to its peak at 1484 in 2004. In the US within 2016, 791 SPK, 73 PAK, and 73 PTA) Tx were implemented. The decline in frequency of pancreas Tx probably related to improved therapies of insulin-based protocols since the DCCT results and the subsequent lower rates of secondary sequelae of chronic hyperglycaemia.
Outcomes: MR/morbidity, and results of Tx vary with team experience & TR selection.
TR survival
● Considering 2004-2015 data, ptn survival for SPK, PAK, or PTA = 96-99 % at postoperative one y, 89-91 % at 5 ys, and 70-80 % at 10 ys. Most deaths in the 1st 3 mo post-Tx & subsequently were related to CVS or cerebrovascular disorder.
● Few data on survival benefits for TR as compared to waitlisted ptns. The following findings rely on the retrospective analysis of Tx registries from 1995-2003:
o Survival rates for SPK TR was much better than waitlisted ptns maintained on DX. The lowered MR is partly related to the documented survival benefit offered by KTx alone (KTA; even with no pancreatic Tx) as compared to DX.
o Among PTA or PAK TRs, survival at 4 ys was equivalent to that on waiting list.
o Retrospective study: 11,572 Dcs with preserved renal function on waiting list for pancreatic Tx, survival (4 ys): significant worsened with PTA as compared to waitlist ptns on conventional plans. However, there could be clear variables between the PTA g. and the waitlisted ptns. This repetition could induce bias on the outcome of this report favouring ptns on the waiting list.
Graft survival: Based on 2004-2015 data, early graft loss (on 90 d.s) seen in about 8-9.4 % of TR. 5-y pancreatic graft survival for SPK, PAK, & PTA was: 73, 65, & 53 %, resp. Pancreatic graft survival is inversely related to many donor factors, i.e., age, BMI, and CVS death. TR of pancreas Tx alone with organs coming from donors with poor donor indices showed declined rate of graft survival as compared to SPK TR.
Definition of pancreatic graft survival has variable definition in Tx centres (e.g., persistent entire insulin independence, persistent C-peptide production). Consensus in definition may strengthen future outcome trials. In the US, the UNOS has admitted a new definition of graft failure (2018) that includes using of insulin ≥0.5 units/kg/d for 90 consecutives d.s. In 2018, a classified graft function was admitted by the IPITA & EPITA. They are based primarily on glycated HB (A1C), severity of HG episodes, insulin requirement, & C-peptide. Graft function could be:
o Optimal function: Near-normal glycemic control (A1C ≤6.5 %) + No severe HG or insulin/other antihyperglycemic agents + raised C-peptide as compared to pre-Tx.
o Good function: A1C <7 % + no severe HG + significant decline in insulin needs (>50 % decline = <0.5 units/kg/d) + raised C-peptide compared with pre-Tx.
o Marginal function: A1C ≥7 %, + severe HG, or < 50 % decline in insulin needs, when there’s rise in C-peptide compared to pre-Tx.
o Failed graft: Lack of any evidence for clinically significant C-peptide availability.
Metabolic effects: pancreatic Tx can induce independence from exogenous insulin + improved glucose metabolism, A1C, acute insulin response to IV glucose, & counterregulatory s. glucagon & glucose to insulin-induced HG. These benefits can be attributed to resuming islet function that can be maintained for ys. (15 ys in some centres).
Ptn with functioning graft showed normal insulin response to oral & IV glucose triggering and to IV arginine & IV secretin. However, considering the systemic (rather than portal) venous drainage of the allograft basal and stimulated peripheral insulin concentrations are 2-3 times higher than normal. So, the hepatic 1st-pass uptake & degradation of insulin secretion into the PV are bypassed; normally, 50-90 % of insulin in PV blood undergoes 1st -pass hepatic metabolism. Post-Tx hyperinsulinemia has no impact on CVS risk. S. triglyceride & LDL tend to drop while s. HDL tend to rise.
Glucose counter-regulating hormones after HG can be corrected by pancreas Tx. This is beneficial as ptns with DM for years prior to Tx typically show abnormal glucose counter regulating system due to lowered s. glucagon & epinephrine response to HG. The improved glucose counter regulation in TR of pancreatic Tx is due normalizing the glucagon & improving the epinephrine counterregulatory responses. Awareness of HG Sms also improved. HG due to pancreas Tx has been reported, but it is usually mild. Many studies conducted ptns with combined kidney-pancreas Tx.
Following successful pancreas Tx:
o Recurrent & de novo Dc Np have been aborted. PTA can reverse the already established Dc lesions in TR with early Dc Np alterations.
o Stabilized and may be, improved peripheral & autonomic Dc Nr.
o The impact on Dc retinopathy is not evident. Some reports: no benefit regarding holding or reversing an advanced retinopathy, others: observed stabilized or may be regressed retinal lesions after successful pancreatic Tx.
o S. triglyceride & LDL cholesterol tend to decline & HDL tends to be elevated.
o Quality-of-life: clear benefits, e.g., back to work and successful pregnancy, with no clear side effects to the foetus or the TR mother.
These observations regarding the impact of pancreatic Tx on Dc microvascular lesions must be interpreted in view of the fact that most TR receiving pancreatic Tx have already had DM for > 2 decades with advanced sequalae. Data are currently scarce from prospective trials of ptns receiving pancreatic Tx, as compared to matched control cohorts.
Technique: The technique applied for pancreatic Tx is the same whether a KTx is placed into the pelvic region at the same timing. The most used procedure, a whole pancreas, still attached to a small partition of the duodenum that contained the ampulla of Vater, is taken from a deceased donor. Pancreas can be placed in the lateral pelvis, with arterial anastomosis connecting to an iliac artery branch & venous anastomosis to an iliac vein branch leading to insulin secretion firstly pushed to the systemic (rather than portal) circulation. A modified approach may include portal rather than systemic draining of the endocrine pancreas. Duodenal segment can be connected to the UB or more commonly applied to the bowel receiving the pancreatic exocrine function. Bladder drainage provides an advantage of monitoring urine amylase levels to identify early allograft Rj but may be also induce metabolic acidosis, haematuria, & recurrent UTI. The native pancreas is kept intact. Despite most ptns receiving pancreas from a deceased donor, some ptns may receive a segment of pancreas donated by a living-related donor willing to perform a hemi-pancreatectomy.
Immunosuppression: Both pancreas & islet Tx are currently requiring lifelong im/m to hold allograft Rj. Conventional maintenance protocols are consisting of a collection of im/m agents with variable mechanisms of action. These regimens limit morbidity & MR related to each agent while augmenting the overall efficacy. Despite variability of protocols, most TR of pancreatic Tx are currently receiving monoclonal or polyclonal anti-T-cell AB at the timing of surgery with chronic im/m regimen that include CNI (CyA or Tac) + antimetabolite (MMF or Azathioprine). Since 2007, most ptns have received Tac & MMF. With the availability of new im/m drugs, some centres are performing pancreas Tx with no AB therapy, and avoiding GC is increasingly prevalent.
Graft loss: Aetiology of pancreas Tx loss vary with timing after Tx. “Early” graft loss, = (seen within h.s/d.s after surgery) usually attributed to thrombosis, leak, bleeding, infection, & pancreatitis (= technical failure). Report: 211 ptns undergoing pancreas Tx, technical graft failure seen in 23 ptns (11%), mostly due to thrombosis. Risk factors of technical failure may include donor & TR obesity + higher preservation timing of the donated organ. “Late” graft loss seen after several weeks is more prevalent and is mostly attributed to immunologic Rj.
Rejection: Tx pancreas can be rejected within days or after y.s of successful Tx. Ac Rj of the pancreas is common, observed in 60-80 % of pancreatic grafts. Therapy include hospitalization + augmented im/m. Techniques used with Ac Rj of a pancreas Tx alone are as applied to Rj of kidney-pancreas Tx.
Detection: Identification of pancreatic Rj became easier with a KTx. A crucial clinical sign observed in kidney-pancreas TR is that pancreatic Rj is uncommonly seen in absence of concomitant kidney graft Rj (≤15 %), with a tendency to be delayed in intensity behind the kidney. So, estimation of SCr is currently utilized to monitor the possible Ac Rj of both grafts in ptns with a functioning kidney graft. A relatively small rise in SCr is typically the 1st clinically observed sign of kidney graft Rj, despite a possible role of non-immunologic factors must be excluded. The recognition of Rj is more difficult in TR with PTA. In ptn with bladder drainage, the indices of Rj include:
o Increased serum amylase levels.
o Increased blood glucose levels.
o Decline in urinary amylase output (coming from donor exocrine pancreas)
The above markers are less sensitive if compared with a rising SCr when there’s a concurrent kidney allograft. Particularly, rising FBS is a relatively delayed indicator of allograft failure, and rising enzymatic levels, e.g., amylase, are nonspecific indicator of Rj. If Rj is suspected, a cystoscopic-guided transduodenal pancreatic biopsy is our best choice.
ISLET TX: Islet Tx has been offered for ptns with type 1 DM and in ptns with chronic pancreatitis. In contrary to type 1 DM, ptns with chronic pancreatitis perform islet Tx associated with total pancreatectomy + infusing of their own islets (auto-islet Tx), that does not need the addition im/m agents.
Type 1 DM: A less invading procedure of islet Tx in ptns with DM is arranged to be safer and less costly as compared with pancreas Tx. Efforts have been implemented to settle the best technique maximizing the quality of islets that have been isolated from multiple sources that could be reflected on improving the techniques for organ procurement with standardized methods of islet isolation. Almost 500,000 islets could be extracted from the deceased pancreases then infused through a percutaneous central catheter to be introduced to the liver proceeding retrograde to the PV of TR.
Metabolic outcome: The 9th report of the CITR that involved the data about 1011 islet grafts Tx between 1999-2013, almost 50 % of adults with type 1 DM receiving islet Tx (isolated or after kidney) became insulin independent at one y. with decreased rates by time (30 % for islet alone, 20 % for islet after kidney at 5 ys). Since the year 2000, more potent with less toxicity im/m agents with better harvesting manoeuvres have been introduced associated with a significant rise in success rate of islet Tx. Analysis of 677 islet allograft TR by year of Tx, 55 % of Tx from still insulin independent at 2 y.s. Incidence of insulin independence at 3 ys post Tx was improving from 27 to 37 to 44 %, with the % of TR receiving sequential islet infusion dropped from 60-65 % to <50 % in the most recent reports. Along 3-5 ys following TR, near normal glycemic control (= A1C <6.5 %) was stabilized in almost 60 % of Tx. Whilst >90 % of ptns suffering from severe HG before Tx, >90 % still free of severe HG episodes over 5 ys.
Adverse events (AE): Minimally 50 % of islet Tx showed at least one AE. AE are related to im/m (neutropenia, raised liver function tests, high SCr) & procedural sequelae (e.g., intraperitoneal bleeding). Despite there were no post-Tx MR in a multinational study: 38 serious AE observed, & 18 hospitalized. AE related to im/m, SRL & Tac were reported in all 26 Dc with allogeneic islet Tx. 4 TR were withdrawn from im/m (sever toxicity); all TR experienced transient rise in liver enzyme, and most TR showed sustained rise in LDL. Added potential sequelae of islet Tx is sensitization (developing DSA). As islets are obtained from several donors, islet TR have been exposed to several HLA mismatching. Multiple mismatches induce AB production that may impede future Tx (islet, kidney, pancreas) due to a diminished likelihood to find a compatible allograft. One series: 31 % of islet TR developed new DSA. Withdrawal of im/m. resulted in an abrupt rise in HLA AB. So, the potential for AE impeding the chance receiving a future Tx must be discussed with all potential TR.
Experimental technique: The advent of islet Tx as de novo technique has achieving its potential to manage intense HG or labile type 1 DM. Technically wise efforts exerted for better islet harvest, engraftment, limit apoptosis, with less toxic im/m plans, achieve immune tolerance, & non-invasive monitoring of islet cell longevity after Tx.
Islet donors: One of the major limitations of islet Tx is the need for several donors. Studies suggest: insulin independence can be achieved via a single donor (opposing to 2-4 donors) using fewer total islets. Study 8 ptns, the improved success with fewer islets was related to an induction im/m plan of ATG + etanercept (TNFa inhibitor), + daclizumab. However, only obese donors (having more islets than thin ones) were chosen in this report, and 10-18 of the donated pancreases still to be excluded due to inadequate islet yield. So, the advent of single donor islet Tx still uncertain.
Alternate islet sources: To harvest enough healthy human islets from cadaveric sources is the major barrier precluding successful islet Tx. Islets constitute < 2 % of the total mass of the adult human pancreas. Research is currently ongoing to recognize an alternative source for beta cells. Several studies, in vitro/in vivo try to identify islet-producing stem cells and to provide differentiated islets:
o Islets Tx in vitro via culturing mouse pancreatic ductal cells into Dc mice has induced reversal of insulin-dependent DM.
o Human embryonic stem cells can be differentiated in vitro into endodermal cells. After implanted into mice, these cells transformed into glucose-responsive, insulin-producing cells. Theoretically, endodermal cells could be triggered to differentiate into insulin-secreting beta cells in vitro, then providing large quantities of B cells required for a successful islet Tx.
o Endocrine differentiation can be provided via NEPECs, Tx along with foetal pancreas cells, into immunodeficient mice. Insulin release was supposed to emerge from endocrine stem or progenitor cells within the epithelial part of the pancreas.
o Splenic cells Injection + immune adjuvant into Dc mice > reversed type 1 DM; the spleen was suggested to be a source of islet stem cells. Studies: using immune adjuvant protocol (complete Freund's adjuvant), have successful reproduced reversal of type 1 DM in 32 % of Dc mice. However, authors cannot provide an evidence of the graft spleen cell survival suggesting that the im/m allowed proliferation of small quantity of the remainder islets in the mouse pancreas.
Xenotransplantation: of islets has also been assessed. Intraportal Tx of islets after culturing in pigs into Dc non-human primates (macaques) after ttt with monoclonal AB to abolish T cell activation resulted in reversal of DM for over 100 d.s. Noticeable morbidity was complicating im/m agents, and clinically potential xenografting the islet Tx still uncertain.
Engraftment site: Most islet Tx are provided via infusing it into the PV to be engrafted in the liver. Variety of findings, added to the risk of bleeding during intraportal catheterization, denoting the liver may NOT be the optimal location for islet infusion:
o Intrahepatic islet Tx grafts (auto/allografts) cannot secrete glucagon responding to sustained HG, despite responding to an arginne stimulus. This can be explained by intrahepatic a cells do not sense HG, as they’re flooded by free glucose related to HG-induced rise in glycogenolysis. So, some advice using non-hepatic & hepatic sites for islet Tx, to preserve a cell function protecting the TR from severe HG.
o Intrahepatic islets are vulnerable to intercurrent toxins in addition to the higher im/m agents’ levels that can impede beta cell missions.
o Intrahepatic infused islets must be purified to prevent injecting large tissue amount into the liver (may obstruct portal flow + portal HT). Almost 50-70 % of islet amount can be fade out during purification procedure. To avoid these obstacles, omentum, peritoneum, or bone marrow have been suggested as alternate locations.
Microencapsulation (Mic): Technical tools providing immunoisolation for Tx islets remain under investigations. Mic is a process whereby individual islets are surrounded with thin membrane permeable to insulin but NOT to native AB. Mic can limit the need for im/m. However, many technical obstacles still unsolved with Mic applications, including the power of cytokines to pass easily via the membrane destructing the Tx islets. Some researchers have managed 2 type 1 Dc with a prepared Mic human islet injected into the peritoneal cavity. There were no given im/m agents. At 6-mo & one-y., C-peptide was detected; they continue requiring exogenous insulin, but overall metabolic management of their DM was better, with a decline in HG episodes.
Monitoring islet engraftment: Islet Tx can induce transient insulin independence. The fate of infused islets is not clear. Post Tx monitoring of islets may provide enough data about accuracy of infusion, success rate of engraftment, and Tx islet longevity. Scanning with PET + CT provide clearing islet survival and distribution after Tx. This manoeuvre may be useful to evaluate alternate locations of implantation or providing better plans for intrahepatic Tx.
MRI, if combined with Mgcp, may be beneficial for monitoring islet cell survival. Mgcp is a technique providing immunoisolation + MRI tracking of the grafted cells. Animal studies: islets incorporation into Mgcp with intraperitoneal infusion were shown to be functioning. Animal studies: Mgcp infused into PV via real-time MRI monitoring can be visualized as hypointense areas within the liver that can be traced to estimate graft longevity. Human studies: lab measuring of beta cell mass before islet implants correlated greatly to tools of insulin secretory reservoir after Tx via glucose triggering of arginine-induced insulin production.
Chronic pancreatitis: Common complications of chronic pancreatitis may include intense chronic abdominal pain, lost weight, diarrhoea, poor quality of life, and narcotic abuse. Inflammatory process of acinar cells may extend to involve the endocrine function, so, progressive damage of the islets of Langerhans may ensue leading to DM. The course of inflammation can be ameliorated by multiple pancreatic duct stenting and/or partial pancreatectomy. “Total pancreatectomy” may be suggested for pain relief that immediately resulted in total insulin-dependent DM. In the 1980s, surgeons (Univ. of Minnesota) suggested that the removed pancreas could be used for islet isolation/implantation into the liver (auto-islet Tx) that could prevent DM. Fortunately, auto-islet Tx does not require im/m administration.
Metabolic outcomes
[1] Insulin independence: In contrary to most early reports of Tx of islet grafts in Dcs, islet autograft Tx has been successful in non-diabetic adults & children with chronic painful pancreatitis. So many islet autograft TR achieved normoglycemia with normal serum insulin response to oral/IV glucose as well as IV arginine after Tx. This impact can persist for years after Tx. Series: 10-14 ptns received > 300,000 islets were insulin independent 2 y.s after Tx that was also supported by another series with much larger number of TR. Assessment of beta cell function after TPIAT has been observed to be like normal subjects when the secretory data are normalized to the number of Tx islets. Difference in outcome can be clarified as follows:
o Freshly isolated islets (within 3-4 h.s of pancreatic resection) opposing to the prolonged duration required to collect islets from human donors.
o Lack of autoimmune activity destructing beta cell, as in type 1 DM
o No im/m agents are currently required that is usually toxic to beta cells
[2] Hypoglycaemia (HG): Ptns undergoing TPIAT frequently experienced episodes of HG with exercise & meals. One study: lack of glucagon response with insulin clamp + HG, as was earlier observed in type 1 Dc TR of alloislet Tx. Lack of glucagon response was not seen in a subgroup of TR whose auto-islets were implanted into both intrahepatic & non-hepatic locations. The postulated mechanism of failed intra-hepatic islets to provide glucagon with HG may be attributed to the intrahepatic glycogenolysis with release of free glucose intra-hepatically inhibiting intrahepatic islet glucagon release. Subsequent reports: on intrahepatic auto-islet TR, no rise in endogenous glucose secretion with moderate exercise, and absence of the glucagon response during post-prandial HG.
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