Thomas Ming Swi Chang

Cell encapsulation: Promise and progress

In cell encapsulation, transplanted cells are protected from immune rejection by an artificial, semipermeable membrane, potentially allowing transplantation (allo- or xenotransplantation) without the need for immunosuppression. Yet, despite some promising results in animal studies, the field has not lived up to expectations, and clinical products based on encapsulated cell technology continue to elude the scientific community. This commentary discusses the reasons for this, summarizes recent progress in the field and outlines what is needed to bring this technology closer to clinical application.

Therapeutic applications of polymeric artificial cells

Polymeric artificial cells have the potential to be used for a wide variety of therapeutic applications, such as the encapsulation of transplanted islet cells to treat diabetic patients. Recent advances in biotechnology, molecular biology, nanotechnology and polymer chemistry are now opening up further exciting possibilities in this field. However, it is also recognized that there are several key obstacles to overcome in bringing such approaches into routine clinical use. This review describes the historical development and principles behind polymeric artificial cells, the present state of the art in their therapeutic application, and the promises and challenges for the future.

Stablisation of enzymes by microencapsulation with a concentrated protein solution or by microencapsulation followed by cross-linking with glutaraldehyde

Summary Enzymes like catalase, asparaginase and urease can be stabilised by microencapsulating them with a high concentration of protein solution. This way, their stability can be greatly increased. After microencapsulation, enzymes can be cross-linked by treatment with glutaraldehyde. This way, they are more stable at a body temperature of 37°C.

Procedures for microencapsulation of enzymes, cells and genetically engineered microorganisms.

Methods to microencapsulate enzyme, cells, and genetically engineered cells have been described in this article. More specific examples of enzyme encapsulation include the microencapsulation of xanthine oxidase for Lesch-Nyhan disease; phenylalanine ammonia lyase for pheny, ketonuria and microencapsulation of multienzyme systems with cofactor recycling for multistep enzyme conversions. Methods for cell encapsulation include the details for encapsulating hepatocytes for liver failure and for gene therapy. This also includes the details of a novel two-step method for encapsulation of high concentrations of smaller cells. Another new approach is the detailed method of the encapsulation of genetically engineered Escherichia coli DH5 cells for lowering urea, ammonia, and other metabolites in kidney or, liver failure and other diseases.

Bioartificial liver: implanted artificial cells microencapsulated living hepatocytes increases survival of liver failure rats.

Suspension of living hepatocytes were microencapsulated inside 300 micron mean diameter alginate artificial cells. The galactosamine fulminant hepatic failure rat model was used. 48 hours after the injection of galactosamine, grade II coma hepatic failure rats were divided into pairs. One of the pair was randomly chosen for the control group, and the other for the treated group. Each rat in the control group received one peritoneal injection of microcapsules containing no hepatocytes. Each rat in the treated group received one peritoneal injection of microcapsules containing hepatocytes. The survival of the treated group is significantly higher than the control group.

Therapeutic uses of microencapsulated genetically engineered cells

Microencapsulated genetically engineered cells have the potential to treat a wide range of diseases. For example, in experimental animals, implanted microencapsulated cells have been used to secrete growth hormone to treat dwarfism, neurotrophic factors for amyotrophic lateral sclerosis, beta-endorphin to decrease pain, factor XI for hemophilia B, and nerve growth factors to protect axotomized neurons. For some applications, microencapsulated cells can even be given orally. They can be engineered to remove unwanted molecules from the body as they travel through the intestine, and are finally excreted in the stool without being retained in the body. This application has enormous potential for the removal of urea in kidney failure, ammonia in liver failure and amino acids such as phenylalanine in phenylketonuria and other inborn errors of metabolism.

Hepatocytes immobilised by microencapsulation in artificial cells: effects on hyperbilirubinemia in Gunn rats

The possibility of using hepatocytes encapsulated in a calcium-alginate-polylysine matrix to lower bilirubin levels in hyperbilirubinemia was investigated. The animal model was the Gunn rat. The microencapsulated hepatocytes were injected intraperitoneally. 15 X 10(6) microencapsulated hepatocytes from Wistar rats, lowered the bilirubin from 14 mg/100 ml to 6 mg/100 ml after 20 days. The bilirubin is still depressed after 90 days. After encapsulation, Sprague-Dawley hepatocytes were as effective as free hepatocytes in lowering bilirubin levels in Gunn rats. After 68 days, the free Sprague-Dawley hepatocytes were not rejected.

Future generations of red blood cell substitutes

Chang TMS (Artificial Cells & Organs Research Center, McGill University, Montreal, Quebec, Canada). Future generations of red blood cell substitutes (Minisymposium). J Intern Med 2003; 253: 527–535.

Future prospects for artificial blood

Concern about potential infective agents in donated blood has stimulated the recent development of blood substitutes. Chemically cross-linked hemoglobins are already undergoing clinical trials and might soon be ready for routine use. New generations of modified hemoglobin are being prepared to modulate the effects of nitric oxide and oxygen radicals, and artificial red blood cells are also under development.

THE VIABILITY AND REGENERATION OF ARTIFICIAL CELL MICROENCAPSULATED RAT HEPATOCYTE XENOGRAFT TRANSPLANTS IN MICE

Viable hepatocytes were microencapsulated within artificial cells to form a bio-artificial liver. Trypan blue stain exclusion testing generally showed that 60% of the encapsulated hepatocytes remained viable immediately after encapsulation. To determine if xenogeneic hepatocytes can be successfully transplanted, encapsulated rat hepatocytes were implanted intra-peritoneally into mice and galactosamine induced liver failure mice. After 29 days of implantation in mice and 8 days of implantation in liver failure induced mice there was no significant change observed in the number of hepatocytes within the free floating microcapsules recovered from the peritoneal cavity. The percentage viability of the hepatocytes inside the recovered microcapsules increased from 62% to nearly 100% after 29 days of implantation in mice. The percentage viability of the encapsulated hepatocytes implanted in the liver failure induced mice was followed for 8 days. The percentage viability of the hepatocytes inside the microcapsule also increased from 42% to nearly 100%. In mice implanted with free rat hepatocytes, no viable hepatocytes were observed as early as 4 and 5 days after implantation. Instead a larger number of lymphoid cells and remnants of hepatocytes were recovered from the peritoneal cavity. In all cases the viability of the rat hepatocytes were determined with trypan blue stain.