Xenotransplantation of microencapsulated canine islets into diabetic rats

Improved Assessment of Isolated Islet Tissue Volume Using Digital Image Analysis

Accurate and consistent measurement of tissue volume is critical to performing many types of islet research; however, conventional visual determination of isolated islet yields through a microscope is heavily operator dependent. An improved method of islet volume determination using digital image analysis (DIA) was developed to remove operator bias and automate the islet counting process. A series of 140 porcine islet isolations were used to evaluate the DIA method in three separate stages. In Stage 1 ( n = 29 isolations), the conventional and DIA methods were correlated with two other independent islet quantitation methods: insulin extraction, and DNA extraction. It was found that volumes determined by DIA correlated more closely with insulin content and DNA content than did conventionally determined volumes. In Stages 2 and 3 ( n = 54 and 57 isolations, respectively), it was shown that an increase in the number of fields analyzed by DIA did not significantly improve the quality of the correlations. Inclusion of very small tissue (<50 fun in diameter), which is ignored in the conventional protocol affected yields by less than 10% and did not significantly improve the correlation with insulin or DNA content. Quantitation of isolated islet tissue volume using DIA has been shown to be rapid, consistent, and objective. In the laboratory, use of this method as the standard for islet volume measurement will allow more meaningful comparison of experimental results between centers. In the clinic, its use will allow more accurate dosing of transplanted tissue. © 1998 Elsevier Science Inc.

The isolation and function of porcine islets from market weight pigs

The efficacy of clinical islet transplantation has been demonstrated with autografts, and although islet allografts have established insulin independence in a small number of IDDM patients, the treatment is confounded by the necessity of immunosuppression. the lack of donor tissue, and recurring islet immunogenicity. These limitations underscore a need to develop therapies to serve the large population of diabetic patients. Porcine islet xenotransplantation, together with a successful immune intervention strategy, may provide the necessary clinical alternative. However, a major obstacle in evaluating this approach has been the difficulty of obtaining adequate volumes of functional islet tissue from pigs. Donors of market weight are preferable to retired breeders due to their abundance, lower animal and husbandry costs. and are more suitable to meet regulatory guidelines for donor tissue for xenotransplantation. We describe a simple isolation procedure that following purification yields a mean of 350,000 IE, corresponding to 179 units of insulin and 1.8 mg of DNA with an islet purity and viability in excess of 85% (n = 317 isolations). In both short- and long-term cell cultures, porcine islets demonstrated glucose-responsive insulin secretion. However, this secretion is density dependent, which may have significant consequences in the development of immunoisolation technologies to support porcine islet xenotransplantation. Following implantation into diabetic nude mice, porcine islets remained functional in excess of 1 year. Implantation of a bioartificial pancreas containing porcine islets into pancreatectomized dogs provided significant clinical benefit with an improved diabetic condition. Finally, secretagogue-induced insulin release was demonstrated in vitro from these devices after removal from immunocompetent recipients. Immunohistochemical staining identified well-granulated islets following long-term implantation in both the rodent and canine models. This study demonstrates the ability to isolate porcine islets in clinically relevant numbers from market animals, which survive and remain functional for prolonged periods of time in an immune-deficient or immunoprotected environment.

Immunocompatibility and biocompatibility of cell delivery systems

Immunoisolation therapy overcomes important disadvantages of implanting free cells. By mechanically blocking immune attacks, synthetic membranes around grafted cells should obviate the need for immunosuppression. The membrane used for encapsulation must be biocompatible and immunocompatible to the recipient and also to the encapsulated graft. The ability of the host to accept the implanted graft depends not only on the material used for encapsulation, but also on the defense reaction of the recipient, which is very individual. Such a reaction usually starts as absorption of cell-adhesive proteins, immunoglobulins, complement components, growth factors and some other proteins on the surface of the device. The absorption of proteins is difficult to avoid, but the amount and specificity of absorbed proteins can be controlled to some extent by selection and modification of the device material. If the adsorption of proteins to the surface of the implanted material is reduced, the overgrowth of the device with fibroblast-like and macrophage-like cells is also reduced. Cell adhesion at the surface of the implanted device is, in addition to the selected polymeric material, greatly influenced by the device content. Xenografts trigger a more vigorous inflammatory reaction than allografts, most probably due to the release of antigenic products from encapsulated deteriorated and dying cells which diffuse through the membrane and activate adhering immune cells. There is an evident effect of autoimmune status on the fate of the encapsulated graft. While encapsulated xenogeneic islets readily reverse streptozotocin-induced diabetes in mice, the same xenografts are short-functioning in NOD autoimmune diabetes-prone mice. Autoantibodies, to which most devices are impermeable, are not involved. Among the cytotoxic factors which are responsible for the limited survival of the encapsulated graft the most important are cytokines and perhaps some other low-molecular-weight factors released by activated macrophages at the surface of the encapsulating membrane.

Engineering challenges in the development of an encapsulated cell system for treatment of type 1 diabetes

Implantation of glucose-responsive, insulin-secreting cells is promising in providing a treatment for type I diabetes, which is more effective, less invasive, and potentially less costly than conventional insulin injections. However, in spite of promising results with animal studies, a clinical product or therapeutic procedure based on encapsulated cells does not yet exist. This is because a number of barriers remain to be addressed, which include a source of functional cells, a stable, biocompatible membrane offering immune protection to the implant, a construct architecture ensuring cell viability and construct function, and the engineering of immune acceptance of the construct post-implantation. This article reviews these barriers and the current state-of-the-art, with special emphasis on the engineering challenges involved, and discusses possible ways to tackle the complex problems currently preventing this approach from reaching clinical practice.

The rescue effect of 15-deoxyspergualin on intraperitoneal microencapsulated xenoislets

Because the development of surface neogrowth composed mainly of macrophages and fibroblasts precedes the recurrence of hyperglycemia in treated diabetic animals, the pericapsular macrophages may adversely affect the graft function of i.p. alginate-poly-L-lysine-alginate (A-P-A) microencapsulated islets. In order to clarify the role of pericapsular macrophages on late islet xenograft dysfunction, we investigated whether 15-deoxyspergualin (15-DSG), a macrophage inhibitor, has a rescue effect on the recurrent hyperglycemia in streptozotocin-induced diabetic mice that had been treated with i.p. transplantation of A-P-A microencapsulated rat islets. The mean duration of normoglycemia (whole blood glucose level below 8.3 mmol/l) in streptozotocin-induced diabetic mice treated with implantation of about 2200-2400 of A-P-A microencapsulated rat islets was 75 days. When the blood glucose levels were higher than 11.1 mmol/l for two consecutive determinations, 15-DSG at a dose of 0.625 mg/kg body weight or isotonic sodium chloride solution (control group) was given daily s.c.. The blood glucose levels decreased significantly from 13.9 +/- 0.5 mmol/l to 11.0 +/- 1.3 mmol/l (n = 18, p < 0.05) at the fourth day and to 7.6 +/- 1.0 mmol/l (n = 18) at the 14th day of 15-DSG administration. That was not significantly different from the mean glycemic level during the normoglycemic period (7.6 +/- 1.0 vs. 7.0 +/- 1.7 mmol/l, n = 18, p = NS). Isotonic sodium chloride solution injections did not reduce glycemic levels of mice in the control group. As another control, 10 streptozotocin-induced diabetic mice were given the same daily doses of 15-DSG for 14 days. 15-DSG did not decrease the blood glucose levels of diabetic mice in the control group. We further studied the effect of 15-DSG on the expression of interleukin-1beta (IL-1beta) in peritoneal exudate mononuclear cells (PEMCs) using reverse transcription-polymerase chain reaction. It was found that the mRNA of IL-1beta was undetectable in PEMCs of 15-DSG-treated diabetic mice even after those cells were stimulated by lipopolysaccharides in vitro. Administration of 15-DSG at a daily dose of 0.625 mg/kg body weight from the 22nd to the 28th day after transplantation and 7 consecutive days every 3 weeks thereafter did not prolong graft survival of i.p. microencapsulated rat islets. Our data suggest that 15-DSG has a rescue effect when A-P-A microencapsulated islets have induced cellular overgrowth that threatens the survival of the graft. It is possible that the surface overgrowth composed of macrophages is involved in the pathophysiology of late failure of A-P-A microencapsulated xenogeneic islets.

Studies on smaller (approximately 315 microM) microcapsules: IV. Feasibility and safety of intrahepatic implantations of small alginate poly-L-lysine microcapsules

The most successful transplantation site of nonencapsulated islets of Langerhans is the liver. Because usual alginate poly-L-lysine microcapsules were too large (700-1200 microm diameter) for intravascular implantations and were almost exclusively implanted intraperitoneally, the question of the preferred implantation site of microencapsulated islets has received little attention. The feasibility of implanting smaller (approximately 315 microm) alginate poly-L-lysine microcapsules into the liver and the effect of such implantations on portal pressure and liver histology was evaluated in Wistar rats. A bolus of 10,000 microcapsules of 315 microm diameter was injected intraportally (group 1; n = 22). The portal pressure increased from 6.4 +/- 1.8 mmHg to a maximum of 19 mmHg, returned to basal levels within 2 h, and remained normal after 2 months. In group 2 (n = 3), following the injection of 10,000 larger microcapsules (420 microm), the portal pressure increased to > 60 mmHg and two out of the three rats died within 3 h. When 5,000 microcapsules of 420-microm diameter were injected (group 3; n = 5), the portal pressure peaked to 30 +/- 8 mmHg and remained elevated after 4 h (12 +/- 3 mmHg), but returned to normal (8 +/- 1 mmHg) after 2 weeks. Histological studies showed normal hepatic architecture without collagen deposition into portal tracts occupied by microcapsules.

CONCLUSION

intrahepatic implantations of approximately 315-microm alginate poly-L-lysine microcapsules are feasible and safe. These results justify further investigation of this potential implantation site for microencapsulated islets.

The move from dead to living membranes: bioartificial organ support of failing systems

Several studies show that the diagnosis of acute renal failure still is predictive of high mortality. The reasons for this dismal prognosis despite improvements in dialytic methodologies and critical care are not entirely clear. Continuous renal replacement therapies have to date not shown improved outcome. Dialysis is conceptually not truly a "renal replacement therapy," because the many reabsorptive, metabolic, synthetic, and endocrine functions that occur in the kidney are not duplicated. This dilemma is applicable in varying degrees to other failing organs. Another therapeutic approach to a variety of organ failure conditions could be the transplantation of specific cell types to replace specific functions in the diseased host. The phenomenon of bioencapsulation with synthetic semipermeable membranes offers the possibility of allowing transplanted cells to function while sequestering them from the host's immune system. At this time, a bioartificial kidney is being developed that can be placed in series with a hemofilter and consists of proximal tubular cells layered on the surface of the hollow fibers of a dialyzer. Metabolic and transport functions appear to be intact. Further testing and refinement of this model will occur, which represents a potentially revolutionary form of therapy for renal disease.

Cytomedical therapy for IgG1 plasmacytosis in human interleukin-6 transgenic mice using hybridoma cells microencapsulated in alginate-poly(L)lysine-alginate membrane

Cytomedical therapy for human interleukin-6 transgenic mice (hIL-6 Tgm) was implemented by the intraperitoneal injection of alginate-poly(L)lysine-alginate (APA) membranes microencapsulating SK2 hybridoma cells (APA-SK2 cells) which secrete anti-hIL-6 monoclonal antibodies (SK2 mAb). IgG1 plasmacytosis in the hIL-6 Tgm was suppressed by a single injection of APA-SK2 cells, and the survival time of these mice was remarkably prolonged. The viable cell number and the SK2 mAb-secretion of APA-SK2 cells increased for at least one month both under culture conditions and in allogeneic recipients (in vivo). Moreover, SK2 mAb which were secreted from APA-SK2 cells injected into allogeneic recipients was detected in serum at high concentrations; 3-5 mg/ml from day 14 to day 50 post-injection. In contrast, the injection of free SK2 cells had no therapeutic effect on hIL-6 Tgm. These results strongly suggest that APA membranes microencapsulating cells which were modified to secrete molecules useful for the treatment of a disorder were effective as an in vivo long-term delivery system of bioactive molecules, as 'cytomedicine'.