Encapsulated cell transplantation

Cellular transplants as sources for therapeutic agents

Soluble factors normally produced by cells of the human body are of increasing importance as potential therapeutic agents. Although considerable progress has been made in understanding the etiology and pathogenesis of disease, in developing animal models and newer experimental therapeutics, few discoveries have been translated into clinically effective ways of delivering the multiple therapeutic agents obtained from living mammalian cells. This review examines the use of transplanted cells as alternatives to conventional delivery systems to deliver a variety of protein based therapeutic agents. The chapter begins with a set of questions to establish the complexity and challenges of this form of drug delivery. The following section focuses the discussion on our understanding of genetic engineering, tissue engineering, and some areas of developmental biology as they relate to the development of this nascent field. Much of the discussion has a neuro/endocrine emphasis. The chapter ends by listing the basic ingredients needed to push the use of transplanted cells toward medical practice and some general comments about future developments.

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

Transplantation has become a successful method for the management of functional failure of a variety of tissues or organs. However, the majority of clinical transplantations use non-autologous allogeneic donor tissue implanted from one human to another. In order to prevent rejection of the allogeneic tissue, methods to overcome the immune barrier are necessary. Although prevention of organ rejection is currently achieved with pharmacological immune suppression, the undesirable side effects of this method have incited interest in novel methods to overcome the immune barrier. One such novel method of preventing immune reaction is immuno-isolation, in which the non-autologous tissues are physically isolated from the host tissues by placement in devices with perm-selective membranes. The membranes of these devices allow release of the therapeutic product required from the transplanted tissues, as well as diffusion of nutrients and waste necessary for survival of the non-autologous tissues. The membranes also prevent host immune mediators from contacting the non-autologous cells, thus preventing immune rejection. This technology has been tested for efficacy in large animal models, and is currently in the process of clinical trials in humans. This review will discuss the progress made in using immuno-isolation of non-autologous tissues in large animals. Immuno-isolation can be subdivided into two major areas of interest based on whether the non-autologous tissue used in the immuno-isolation device is genetically altered (gene therapy) or not. Studies using non-genetically altered non-autologous cells for immune-isolation have been dominated by the use of pancreatic islet cells for the treatment of diabetes. This work has been tested in large animal models of diabetes, including canine and primate model animals, and human clinical trials are underway. As well, there has also been work on treatment of neurological disorders such as Parkinson's disease or chronic pain using non-autologous immuno-isolated adrenal chromaffin cells or dopaminergic PC12 cells in large animals such as sheep and primates. This work will be reviewed in detail as to the types of disorders, immuno-isolation devices used and the type of large animals involved. Immune-isolation for gene therapy is a more recently developed field of research. In this case, the non-autologous cells used are first genetically altered to secrete a recombinant therapeutic product before placement in the immune-isolation devices. Genetic engineering of the non-autologous cells is beneficial, as it allows the use of a cell type that tolerates well the environment of the immune-isolation device, while still delivering the therapeutic product of interest. This form of gene therapy has been tested in our laboratory for delivery of marker products such as human growth hormone to canines. As several large animal models of human genetic disorders are available, such as canines affected with hemophilia or the lysosomal storage disease mucopolysaccharidosis, testing the efficacy of immuno-isolation for gene therapy in large animal models is an important prelude to human clinical trials. This review will discuss the topics outlined above, as well as some further considerations of the usefulness of large animal models in studying immune-isolation for non-autologous transplantation. Large animals may be more appropriate model organisms than rodents in which to study immune-isolation, as issues such as biocompatibility and immune response in a larger animal can be addressed. As well, large animal studies of immune isolation may provide data that are more relevant than rodent studies to the eventual application to human clinical trials.

Encapsulated beta-islet cells as a bioartificial pancreas to treat insulin-dependent diabetes during pregnancy

OBJECTIVE

Our purpose was to determine the effectiveness of the bioartificial pancreas technique in correcting (1) maternal carbohydrate metabolism and (2) fetal malformation rates in a pregnant diabetic animal model.

STUDY DESIGN

Insulin secretion from encapsulated rat islets cultured in the presence of homologous rat prolactin was determined and compared with that of controls. Streptozotocin-induced diabetic Balb/c mice were then transplanted with rat islet cells encapsulated within alginate microbeads and were then bred. Blood glucose determinations were made after transplantation and throughout gestation. Pups were delivered by cesarean section on day 19 of gestation. Outcome parameters from the transplanted study animals were compared with those of nondiabetic controls and untreated diabetic animals.

RESULTS

Insulin secretion was increased twofold in encapsulated rat islets exposed to prolactin compared with control values. Throughout gestation maternal weights and blood, glucose levels of transplanted animals were similar to those of nondiabetic controls. A fetal malformation rate of only 1.4% was observed in the pups from transplanted animals.

CONCLUSIONS

Transplanted encapsulated islets are capable of normalizing maternal carbohydrate metabolism in a pregnant diabetic animal model. This therapy, if instituted before conception, also appears to eliminate the increase in fetal malformations seen in diabetic pregnancies.

Encapsulated cell technology

The potential therapeutic applications of encapsulated cells are enormous. In the US alone, it has been estimated that nearly half-a-trillion dollars are spent each year to care for patients who suffer tissue loss or dysfunction. Over 6 million patients suffer from neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease, over 14 million patients suffer from diabetes, and millions more from liver failure, hemophilia, and other diseases caused by the loss of specific vital cellular functions. It appears likely that by the end of the decade clinical trials of encapsulated cells to treat many of these diseases will become a reality. The Food and Drug Administration has already authorized studies to evaluate the safety and biological activity of several types of systems. A number of issues will have to be addressed, including the sourcing of raw materials, the design and building of manufacturing facilities, the scale-up and optimization process, storage and distribution of the product, and quality control.

Engineering challenges in cell-encapsulation technology

The use of implantable immunoisolation devices, in which the tissue is protected from immune rejection by enclosure within a semipermeable membrane or encapsulant, is one approach in the development of cell therapies. However, further research is required in the areas of: tissue supply from primary or cell-culture sources; maintenance of cell viability and function, its relationship to device design, and the role of, and factors affecting, oxygen-supply limitations; and, protection from immune rejection, especially in view of the mechanisms thought to operate in the presence of a semipermeable membrane, the properties of that membrane, and the implications for biology and device design.