Primate Islet Isolation and Purification in Iodixanol-UWS • @1MEMO_20260425

by Michel van der Burg , April 25th, 2026

Synopsis

In early 1999, a pilot study at the Biomedical Primate Research Centre in Holland successfully tested an innovative Iodixanol-UWS density gradient solution for isolating and purifying islets from four macaques, achieving 94% purity and 90% recovery. Viability of the purified islets was confirmed at 98% after one day in culture. The strict biosafety protocols required for this primate work provided valuable preparation for the subsequent launch of human islet isolations at Leiden University Medical Center. The protocol was further validated in a second series of eight rhesus islet isolations in 2000.

February 1999

In early February 1999, a few weeks before we received the green light for the official launch of the clinical islet transplantation project (1) in our Leiden University Medical Center (LUMC), I also started preparations to isolate non-human primate islets at the Biomedical Primate Research Centre in Holland.

At the time, we were already collaborating with researchers from the Biomedical Primate Research Centre for xenotransplantation of purified pig islets in macaque monkeys (2).

With our innovative purification solution — made from Iodixanol (the radio contrast agent Optiprep/Visipaque) , mixed with University of Wisconsin solution (UWS), the solution traditionally used for cold storage of human donor organs — we had successfully isolated and purified the islets of Langerhans from pig pancreases since 1996, and transplanted them into mice, rats, and cynomolgus macaque monkeys (2, 3, 4).

This Iodixanol-UWS purification solution had been successfully trialed on human donor islets during my 1998 visit to the Diabetes Research Institute (DRI) in Miami (5,6).

I had now been asked at our Surgery department (LUMC, Leiden, Holland) to examine whether this isolation method using Iodixanol-UWS can be used also in the non-human primate model , with a view to the application for a new research project on allo-transplantation of islets in Rhesus macaques, and in vitro research into the immunogenicity of these purified islets.

For these pilot experiments, the islets were isolated from donor pancreases procured by Michel van der Burg (me), and the transplant surgeons André Baranski, Jan Ringers, and Jan IJzermans, from one cynomolgus (Macaca fascicularis) and three rhesus macaques (Macaca mulatta), that were obtained during surgery upon euthanasia of these laboratory animals for the termination of unrelated experiments by other research groups at the Biomedical Primate Research Centre.

I had previously watched rhesus islet isolation at the DRI in Miami during that working visit in 1998. So , now before starting the isolations the first week of March 1999, I contacted the experienced DRI researcher Norma Kenyon for advise on the optimal donor age , and optimal amount of enzyme (Liberase-HI) for digestion of the pancreas in this species.

Following digestion of the pancreas with the Liberase-HI enzyme in Hanks’ balanced salt solution , the islets were isolated with our manual method in cold UWS (ViaSpan), and purified by centrifugation in the cold Iodixanol-UWS density gradient solution.

Excellent results were obtained in this pilot of 4 primate islet isolations .
Before the purification step , after digestion of the pancreas , the yield of isolated islets amounted to a mean 3697 islets / gram pancreas (IEQ; islet equivalents*).

After purification of these islets in our Iodixanol-UWS density gradient solution , virtually pure islets were obtained (a mean 94% purity) , with virtually no loss of islets (a mean 90 % recovery).

The purified islets were stored in suspension in culture medium up to 1 week after isolation. Both before culture and after 4 days culture, aliquots of the rhesus islets were prepared for analysis of the immunogenicity of the islets in a Mixed Lymphocyte Islet Culture (MLIC) by co-worker Krista Haanstra.

I photographed the isolated cynomolgus islets both before culture (stained red with dithizone), and after one day culture (not stained, in the petri dishes used for culture).

Survival of 98% of the islets after staying one day in suspension in a culture solution at 37°C demonstrated the excellent viability of these cynomolgus islets.

The viability was confirmed by staining these cultured islets with a mixture of two fluorescent dyes — acridine orange and propidium iodide (AO/PI). Fluorescence microscopy shows the live (green) cells , and few dead (red/yellow) cells in these islets.

The strict biosafety and biosecurity precautions required for this work, especially due to the risk of infection via aerosols during trituration, sieving, and pouring of the large volumes of tissue and cell suspensions from these non-human primates, proved valuable preparation for the subsequent launch, later that month—March 1999—of human islet isolations from donor organs, in our provisional human islet laboratory at the Department of Surgery—pending the completion of the LUMC GMP facility with a cleanroom for our clinical islet laboratory, that I was preparing together with Amon Wafelman the executive head of the future GMP Facility.

I continued this project of rhesus islet isolation, purification and banking, with in vitro research into the immunogenicity of these purified islets, a year later (July-Dec 2000), coaching medical student Gabe Bleeker who corroborated the efficacy of our protocol in that second series of eight rhesus islet isolations (7). He would also assist me at the time in our islet laboratory with the automated ‘Ricordi’ method for human islet isolation, islet banking and quality control by transplants of aliquots of the human islets in nude mice.

Notes

* IEQ : One islet equivalent (IEQ), is defined as the volume of one islet with a 0.15 mm diameter. Because there a more smaller than large islets in the pancreas , the volume of islets is used to indicate islet yield, and expressedin number of ‘islet equivalents’.

1. Ekkelboom J. Hulp voor suikerzieke klieren. In: Volkskrant April 10th 1999 https://www.volkskrant.nl/wetenschap/hulp-voor-suikerzieke-klieren~b7046616

2) Successful Islet Transplantation After Purification in Iodixanol-UWS • IPITA 1999 Sydney • @1MEMO 20260326 • Michel van der Burg • Miracles.Media • URL michelvanderburg.com/2026/03/26/

3) Innovative Islet Purification in Iodixanol-UWS • IPITA 97 • Michel van der Burg • Miracles.Media • @1MEMO 20250128 • URL michelvanderburg.com/2025/01/28/

4) Iodixanol-UWS Purification for Porcine Islet Transplantation • AIDSPIT 1998 • Michel van der Burg • Miracles.Media • @1MEMO 20250131 • TakeNode 1f185515-7aeb-44ac-b721-2cec76df67b7 • URL michelvanderburg.com/2025/01/31/

5) Human Islet Isolation • DRI Miami 1998 • Michel van der Burg • Miracles.Media • @1MEMO 20250204 • TakeNode 86e4a319-a769-44d5-8fa5-de2ca90ab63c • URL michelvanderburg.com/2025/02/04/

6) Efficacy of the novel iodixanol-UWS density gradient for human islet purification • Igls Aidspit 1999 • Michel van der Burg • Miracles.Media • 20241202 • URL michelvanderburg.com/2024/12/02/

7) Protocol for the isolation of islets of Langerhans from the pancreas of the rhesus monkey (dutch : Protocol voor isolatie van eilandjes van Langerhans uit het pancreas van de rhesus-aap) • Studies on the isolation and immunogenicity/immunology of monkey (rhesus) islets • Gabe B. Bleeker (MSc student Medicine) at the Department of Surgery of the Leiden University and the BPRC – TNO centre.

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Citation info : Primate Islet Isolation and Purification in Iodixanol-UWS • @1MEMO_20260425 • Michel van der Burg • Miracles.Media • URL michelvanderburg.com/2026/04/25/