Non-autologous transplantation with immuno-isolation in large animals--a review

Classic Studies on the Potential of Stem Cell Neuroregeneration

The 1990s and 2000s were the beginning of an exciting time period for developmental neuroscience and neural stem cell research. By better understanding brain plasticity and the birth of new neurons in the adult brain, contrary to established dogma, hope for therapy from devastating neurological diseases was generated. The potential for stem cells to provide functional recovery in humans remains to be further tested and to further move into the clinical trial realm. The future certainly has great promise on stem cells to assist in alleviation of difficult-to-treat neurologic disorders. This article reviews classic studies of the 1990s and 2000s that paved the way for the advances of today, which can in turn lead to tomorrow's therapies.

Review of the history and current status of cell-transplant approaches for the management of neuropathic pain

Treatment of sensory neuropathies, whether inherited or caused by trauma, the progress of diabetes, or other disease states, are among the most difficult problems in modern clinical practice. Cell therapy to release antinociceptive agents near the injured spinal cord would be the logical next step in the development of treatment modalities. But few clinical trials, especially for chronic pain, have tested the transplant of cells or a cell line to treat human disease. The history of the research and development of useful cell-transplant-based approaches offers an understanding of the advantages and problems associated with these technologies, but as an adjuvant or replacement for current pharmacological treatments, cell therapy is a likely near future clinical tool for improved health care.

Microencapsulation of pancreatic islets with canine ear cartilage for immunoisolation

Improving human islet transplantation is often limited by the shortage of donors and the side effects of immunosuppressive agents. If immunoisolation is properly used, it can overcome these obstacles. Because artificial materials are adopted in this technique, however, there are still multiple issues with biocompatibility and foreign body reactions. We developed a chondrocyte microencapsulated immunoisolated islet (CMI-islet) that allows living cells to act as the immunoisolating material. To manufacture CMI-islets for xenotransplantation, isolated rat pancreatic islets were placed on low cell-binding culture dishes. Subsequently, expanded canine auricular cartiage primary cells were seeded on these dishes at a high density and maintained in a suspended state via a shaking culture system. Morphological evaluations showed good islet viability and a clear progression of the islet- encapsulation events. When the cells were challenged with glucose, they were able to secrete sufficient insulin according to glucose concentrations. The CMI-islets responded better to the glucose challenge than did nude pancreatic islets and created better glucose-insulin feedback regulation. Moreover, insulin secretion into the culture medium was confirmed over a period of 100 days, showing the survival and secretory capacity of the CMI-islet cells. By microencapsulating pancreatic islets with recipient ear cartilage cells, long-term insulin secretion can be maintained and the response to glucose challenges improved. This new immunodelusion technology differs from other immunoisolation techniques in that the donor tissue is enclosed with the recipient's tissue, thus allowing the transplanted cells to be recognized as recipient cells. This microencapsulation method may lead to developing viable xenotransplantation techniques that do not use immunosuppressive drugs.

A Newly Developed Immunoisolated Bioartificial Pancreas with Cell Sheet Engineering

The term “immunoisolation” refers to the encapsulation of a graft in a selectively permeable membrane. Encapsulation of cellular grafts may provide a way to protect the graft from immune attack without the need for immunosuppressive agents. Although numerous types of artificial materials have been used for encapsulating membranes, their incomplete biocompatibility causes foreign body reaction against the membranes. A new technique has been developed, called cell sheet engineering using temperature-responsive culture dishes, that allows the use of living cells as an immunoisolating membrane in this study. Using this method, the cultured cells can be easily harvested in the shape of a sheet by a simple change of the temperature without the use of proteolytic enzymes. A cell sheet can be created with three-dimensional structure by making multiple cell sheet layers. In this study, a new technique of macroencapsulation (bioartificial organs) has been developed using chondrocyte sheets. Among the various candidate cells, pancreatic islet cells were selected for a bioartificial organ in this study. A chondrocyte sheeting immunodelusive immunoisolated bioartificial pancreas (CSI-BAP) was manufactured by means of cell sheet engineering. An auricular cartilage, which is a histologically elastic cartilage from dogs (beagle), was used as a source of immunoisolating membrane. CSI-BAP was made by multilayering the chondrocyte sheets, and the donor's islets were located between each sheet. Islets were isolated and prepared from the dog (ALLO-model) and Brown Norway (BN) rat (XENO-model). The CSI-BAP was cultured for 83 days and the cultured medium was collected every 24 h to measure the insulin concentrations. The CSI-BAP was examined histologically using hematoxyhin and eosin (H&E), and azan dye staining. In addition, immunohistochemical staining was performed to demonstrate the insulin production of CSI-BAP. Insulin secretion of CSI-BAP on day 16 was reduced to 21.4% of the insulin secretion level of day 10, which was the start point of measurement. Although a gradual reduction was observed, insulin secretion was maintained for 3 months. The CSI-BAP was capable of secreting insulin to the culture medium during the observation period. Histological evaluations demonstrated the good viability of the islets, and immunohistochemistry showed the positive staining of insulin. This novel technology may be used for other kinds of endocrine cells or hepatocytes, which may become the models for immunoisolated bioartificial organs in the near future.

Cell therapy for neuropathic pain in spinal cord injuries

Cell therapy to treat neuropathic pain after spinal cord injury (SCI) is in its infancy. However, the development of cellular strategies that would replace or be used as an adjunct to existing pharmacological treatments for neuropathic pain have progressed tremendously over the past 20 years. The earliest cell therapy studies for pain relief tested adrenal chromaffin cells from rat or bovine sources, placed in the subarachnoid space, near the spinal cord pain- processing pathways. These grafts functioned as cellular minipumps, secreting a cocktail of antinociceptive agents around the spinal cord for peripheral nerve injury, inflammatory or arthritic pain. These initial animal, and later clinical, studies suggested that the spinal intrathecal space was a safe and accessible location for the placement of cell grafts. However, one major problem was the lack of a homogeneous, expandable cell source to supply the antinociceptive agents. Cell lines that can be reversibly immortalised are the next phase for the development of a practical, homogenous cell source. These technologies have been modelled with a variety of murine cell lines, derived from embryonic adrenal medulla or CNS brainstem, in which cells are transplanted, which downregulate their proliferative, oncogenic phenotype either before or after transplant. An alternative approach for existing human cell lines is the use of neural or adrenal precursors, in which the antinociceptive properties are induced by in vitro treatment with molecules that move the cells to an irreversible neural or chromaffin, and non-oncogenic, phenotype. Although such human cell lines are at an early stage of investigation, their clinical antinociceptive potential is significant given the daunting problem of difficult-to-treat neuropathic SCI pain.

Biological properties of photocrosslinked alginate microcapsules

An alternative form of gene therapy using recombinant cell lines delivering therapeutic products encapsulated in alginate hydrogel has proven effective in treating many murine models. The lack of long-term capsule stability has led to a new strategy to reinforce the microcapsules with a photopolymerized interpenetrating covalent network of N-vinylpyrrolidone (NVP) and sodium acrylate. Here the properties for potential application in gene therapy are reported. In assessing potential toxicity of the unpolymerized residues, HPLC showed that even after 1 week of washing, no toxic monomers could be detected. Their ability to sustain cell growth was monitored with growth of the encapsulated cells in vitro and in vivo. Although the initial photopolymerization caused significant cell damage, the cells were able to recover normal growth rates thereafter. After implanting into mice, the NVP-modified capsules showed a high level of biocompatibility as measured by hematological and biochemical functional tests. There was also no difference in the amount and type of plasma proteins adsorbing to the NVP-modified and the classical alginate capsules, thus indicating their similar biological compatibility. Both in vitro and in vivo tests confirmed that the NVP-modified capsules were more resistant to osmotic stress than the alginate microcapsules. Furthermore, when applied to the treatment of a murine model of human cancer by delivering encapsulated cells secreting angiostatin, the NVP-modified microcapsules suppressed tumor growth as successfully as the regular alginate microcapsules. In conclusion, the covalently modified microcapsules have shown a high level of biocompatibility, safety, increase in stability, and clinical efficacy for use as immunoisolation devices in gene therapy.

Useful cell lines derived from the adrenal medulla

Five approaches for the preparation of adrenal chromaffin cell lines have been developed. Initially, continuous chromaffin lines were derived from spontaneous pheochromocytoma tumors of the medulla, either from murine or human sources, such as the rat PC12 cell line and the human KNA and KAT45 cell lines. Over the last few decades, more sophisticated molecular methods have allowed for induced tumorigenesis and targeted oncogenesis in vivo, where isolation of specific populations of mouse cell lines of endocrine origin have resulted in model cells to examine a variety of regulatory pathways in the chromaffin phenotype. As well, conditional immortalization with retroviral infection of chromaffin precursors has provided homogeneous and expandable chromaffin cells for transplant studies in animal models of pain. This same strategy of immortalization with conditionally expressed oncogenes has been expanded recently to create the first disimmortalizable chromaffin cells, with an excisable oncogenic cassette, as might be envisioned for the creation of human chromaffin cell lines. Eventually, as we increase our understanding of regulating the phenotypic fate of chromaffin cells in vitro, stem or progenitor adrenal medullary cell lines will be derived as an alternative source for expansion and clinical use.

Transient production of bone morphogenetic protein 2 by allogeneic transplanted transduced cells induces bone formation

The aim of this study was to evaluate the use of transplantation of genetically modified allogeneic cells as a method to induce bone formation. In this study, we infected a murine osteoprogenitor cell line with a retroviral vector containing the human bone morphogenic protein 2 (BMP2) gene. Transduced cells exhibited more alkaline phosphatase activity than cells treated with any of the tested doses of recombinant human BMP2 protein (rhBMP2). The transduced cells were suspended in a collagen solution and injected into the quadriceps muscle in immunocompetent outbred mice. Radiographic and histological examinations demonstrate abundant ectopic bone formation in 85% of the transplanted animals (n = 13). PCR and Southern blot analysis for the puromycin resistance gene revealed that the transplanted cells were detectable for up to 1 week, but not at later time points. None of the animals developed tumors. Our results suggest that allogeneic BMP2-expressing transduced cells may have therapeutic potential for enhancing new bone formation. This model also provides a simple, inexpensive, and sensitive assay for evaluating in vivo the osteoinductive potentials of secreted proteins without the requirement of protein purification or the use of immunodeficient animals.

Xenotransplantation of cells using biodegradable microcapsules

BACKGROUND

The use of immunoisolation to protect transplanted cells from the immune system of the host has broad application to the treatment of major diseases such as diabetes and a wide range of other disorders resulting from functional defects of native cell systems. In most cases, limitations in functional cell longevity will necessitate periodic replenishment of the cells. We describe a hydrogel-based microcapsule that breaks down at a rate that can be adjusted to correspond to the functional longevity of the encapsulated cells. These injectable capsules can be engineered to degrade over several weeks to months for short-term drug delivery, or to remain intact and immunoprotective for more extended periods. When the supply of cells needs to be replenished, no surgery will be required to localize and remove the old capsules.

METHODS

Porcine and bovine islets were immobilized in "composite" microcapsules fabricated from alginate and low-relative molecular mass (Mr) poly (L-lysine[PLL]) (Mr exclusion <120 Kd) and implanted into the peritoneum of normal and streptozotocin-induced diabetic rats. In addition to demonstrating long-term islet viability and function, a series of in vitro studies were carried out to determine the permeability and biodegradability of the microcapsules used in the present system.

RESULTS

Xenogeneic islets implanted in nonimmunosuppressed rats remained in excellent condition indefinitely (>40 weeks)(viability was comparable to that of preimplant control specimens). In contrast, no islets survived in uncoated alginate spheres after 2 weeks postimplantation. By changing the concentration of the alginate, it was possible to vary the rate of capsule breakdown in rats from mechanically unstable (outer matrix <0.5-0.75% alginate) to stable for >1 year (> or =1.5% alginate). In addition to in vivo breakdown studies, the biodegradability of the capsular components was verified in vitro using a mixture of tritosomes (enzymes isolated from animal cells).

CONCLUSIONS

We have designed a microcapsule system with controllable biodegradability which allows breakdown and absorption of implants when the cells die or become functionally inactive. These results may have application to other alginate-PLL encapsulation systems. The ability to cross species lines using these biodegradable microcapsules has the potential to expand dramatically the number of patients and the scope of diseases that can be successfully treated with cellular therapy.