Editors' ChoiceCell Transplantation

The Midas Touch

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Science Translational Medicine  07 Sep 2011:
Vol. 3, Issue 99, pp. 99ec147
DOI: 10.1126/scitranslmed.3003141

Pancreatic islet cell transplantation enables a more precise regulation of insulin levels in the body than does constant monitoring of blood sugar levels and insulin injections. However, transplanted cells suffer from immune rejection and therefore have yet to become a viable treatment for type 1 diabetes. Microencapsulation of islets could potentially prevent rejection and eliminate the need for toxic immunosuppressive drugs. Encapsulation provides a semipermeable membrane that allows passage of cell-derived factors, including insulin, but prevents passage of antibodies, thus preserving the biologic function of pancreatic islets for a longer period than the naked (unencapsulated) islets, which quickly break down into individual cells.

To evaluate the various encapsulation methods that are being developed, there is a need for better imaging tools—specifically, to visualize real-time delivery, cell engraftment, and capsule integrity. Arifin et al. struck gold when they co-encapsulated a gold nanoparticle:gadolinium chelate (GG) with pancreatic islet cells in alginate. The authors then transplanted these capsules into the peritoneum of diabetic mice. Within 1 week, the mice transplanted with encapsulated islet cells achieved normal blood glucose levels, which persisted for 6 weeks. Moreover, the mice did not need immunosuppressants. Importantly, the encapsulated GG nanoparticles had a strikingly bright appearance when viewed with magnetic resonance imaging, ultrasound, and microcomputed tomography. Because of this “trimodal” visibility in vitro and in vivo, these GG nanoparticles could be used for noninvasive tracking of transplanted islets.

Much is required before this can be translated into a clinical reality. For example, further studies are needed to determine GG biocompatibility, long-term immunoprotective efficacy of the alginate-based capsules, dosage of islets and capsules needed for effective treatment, and the sensitivity of the contrast agents in vivo in humans. Mining for more gold is not necessary, however; by their estimates, a 70-kg individual would only need about 100 μg of gold for imaging.

D. R. Arifin et al., Trimodal gadolinium-gold microcapsules containing pancreatic islet cells restore normoglycemia in diabetic mice and can be tracked by using US, CT, and positive-contrast MR imaging. Radiology, 260, 790–798 (2011). [Abstract]

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