Development of cellulose sulfate-based polyelectrolyte complex microcapsules for medical applications

Microencapsulation of natural products using spray drying; an overview

AIMS

This study examines microencapsulation as a method to enhance the stability of natural compounds, which typically suffer from inherent instability under environmental conditions, aiming to extend their application in the pharmaceutical industry.

METHODS

We explore and compare various microencapsulation techniques, including spray drying, freeze drying, and coacervation, with a focus on spray drying due to its noted advantages.

RESULTS

The analysis reveals that microencapsulation, especially via spray drying, significantly improves natural compounds' stability, offering varied morphologies, sizes, and efficiencies in encapsulation. These advancements facilitate controlled release, taste modification, protection from degradation, and extended shelf life of pharmaceutical products.

CONCLUSION

Microencapsulation, particularly through spray drying, presents a viable solution to the instability of natural compounds, broadening their application in pharmaceuticals by enhancing protection and shelf life.

Droplet-based microfluidics: an efficient high-throughput portable system for cell encapsulation

One of the goals of tissue engineering and regenerative medicine is restoring primary living tissue function by manufacturing a 3D microenvironment. One of the main challenges is protecting implanted non-autologous cells or tissues from the host immune system. Cell encapsulation has emerged as a promising technique for this purpose. It involves entrapping cells in biocompatible and semi-permeable microcarriers made from natural or synthetic polymers that regulate the release of cellular secretions. In recent years, droplet-based microfluidic systems have emerged as powerful tools for cell encapsulation in tissue engineering and regenerative medicine. These systems offer precise control over droplet size, composition, and functionality, allowing for creating of microenvironments that closely mimic native tissue. Droplet-based microfluidic systems have extensive applications in biotechnology, medical diagnosis, and drug discovery. This review summarises the recent developments in droplet-based microfluidic systems and cell encapsulation techniques, as well as their applications, advantages, and challenges in biology and medicine. The integration of these technologies has the potential to revolutionise tissue engineering and regenerative medicine by providing a precise and controlled microenvironment for cell growth and differentiation. By overcoming the immune system's challenges and enabling the release of cellular secretions, these technologies hold great promise for the future of regenerative medicine.

Cultivation of Encapsulated Primary Human B Lymphocytes: A First Step toward a Bioartificial Germinal Center

Polyelectrolyte microcapsules based on sodium cellulose sulfate (SCS) and poly-diallyl-dimethyl-ammonium chloride (PDADMAC) have previously been proposed as a suitable ex vivo microenvironment for the cultivation and differentiation of primary human T lymphocytes. Here, the same system is investigated for the cultivation of human primary B cells derived from adult tonsillar tissue. Proliferation and differentiation into subtypes are followed and compared to suspension cultures of B cells from the same pool performed in parallel. Total cell expansion is somewhat lower in the capsules than in the suspension cultures. More importantly, however, the differentiation of the initially mainly memory B cells into various subtypes, in particular into plasma cell (PC), shows significant differences. Clearly, the microenvironment provided by the microcapsules is beneficial for an accelerated induction of a germinal center-like B cell phenotype and afterward supports the long-term survival of the PC cells. Then, varying the encapsulation conditions (i.e., presence of human serum and dedicated cytokines in the capsule core) provides a tool for finetuning the B cell response. Hence, this methodology is suggested to pave the way toward ex vivo development of human immune organoids.

Cell microencapsulation technologies for sustained drug delivery: Clinical trials and companies

In recent years, cell microencapsulation technology has advanced, mainly driven by recent developments in the use of stem cells or the optimization of biomaterials. Old challenges have been addressed from new perspectives, and systems developed and improved for decades are now being transferred to the market by novel start-ups and consolidated companies. These products are mainly intended for the treatment of diabetes mellitus (DM), but also cancer, central nervous system (CNS) disorders or lysosomal diseases, among others. In this review, we analyze the results obtained in clinical trials to date and define the global key players that will lead the cell microencapsulation market to bring this technology to the clinic in the future.

Semipermeable Cellulose Beads Allow Selective and Continuous Release of Small Extracellular Vesicles (sEV) From Encapsulated Cells

The clinical benefit of therapies using Mesenchymal Stem Cells (MSCs) is attributable to their pleiotropic effect over cells and tissues, mainly through their secretome. This paracrine effect is mediated by secreted growth factors and extracellular vesicles (EV) including small EV (sEV). sEV are extra-cellular, membrane encompassed vesicles of 40 to 200 nm diameter that can trigger and signal many cellular responses depending on their cargo protein and nucleic acid repertoire. sEV are purified from cell culture conditioned media using several kits and protocols available that can be tedious and time-consuming, involving sequences of ultracentrifugations and density gradient separations, making their production a major challenge under Good Manufacturing Practices (GMP) conditions. We have developed a method to efficiently enrich cell culture media with high concentrations of sEV by encapsulating cells in semipermeable cellulose beads that allows selectively the release of small particles while offering a 3D culture condition. This method is based on the pore size of the capsules, allowing the release of particles of ≤ 200 nm including sEV. As a proof-of-principle, MSCs were encapsulated and their sEV release rate (sEV-Cap) was monitored throughout the culture and compared to sEV isolated from 2D seeded cells (sEV-2D) by repetitive ultracentrifugation cycles or a commercial kit. The isolated sEV expressed CD63, CD9, and CD81 as confirmed by flow cytometry analysis. Under transmission electron microscopy (TEM), they displayed the similar rounded morphology as sEV-2D. Their corresponding diameter size was validated by nanoparticle tracking analysis (NTA). Interestingly, sEV-Cap retained the expected biological activities of MSCs, including a pro-angiogenic effect over endothelial cells, neuritic outgrowth stimulation in hippocampal neurons and immunosuppression of T cells in vitro. Here, we successfully present a novel, cost, and time-saving method to generate sEV from encapsulated MSCs. Future applications include using encapsulated cells as a retrievable delivery device that can interact with the host niche by releasing active agents in vivo, including sEV, growth factors, hormones, and small molecules, while avoiding cell clearance, and the negative side-effect of releasing undesired components including apoptotic bodies. Finally, particles produced following the encapsulation protocol display beneficial features for their use as drug-loaded delivery vehicles.

Release characteristics of cellulose sulphate capsules and production of cytokines from encapsulated cells

The size and speed of release of proteins of different sizes from standard cellulose sulphate capsules (Cell-in-a-Box®) was investigated. Proteins with molecular weights of up to around 70kD can be released. The conformation, charge and concentration of the protein being released play a role in the release kinetics. Small proteins such as cytokines can be easily released. The ability to produce cytokines at a sustained and predefined level from encapsulated cells genetically engineered to overexpress such cytokines and implanted into patients may aid immunotherapies of cancer as well as infectious and other diseases. It will also allow allogeneic rather than autologous cells to be used. We show that cells encapsulated in polymers of cellulose sulphate are able to release cytokines such as interleukin-2 (IL-2) in a stimulated fashion e.g. using phorbol 12-myristate 13-acetate (PMA) plus ionomycin. Given the excellent documented safety record of cellulose sulphate in patients, these data suggest that clinical usage of the technology may be warranted for cancer treatment and other diseases.

Encapsulated cells expressing a chemotherapeutic activating enzyme allow the targeting of subtoxic chemotherapy and are safe and efficacious: data from two clinical trials in pancreatic cancer

Despite progress in the treatment of pancreatic cancer, there is still a need for improved therapies. In this manuscript, we report clinical experience with a new therapy for the treatment of pancreatic cancer involving the implantation of encapsulated cells over-expressing a cytochrome P450 enzyme followed by subsequent low-dose ifosfamide administrations as a means to target activated ifosfamide to the tumor. The safety and efficacy of the angiographic instillation of encapsulated allogeneic cells overexpressing cytochrome P450 in combination with low-dose systemic ifosfamide administration has now been evaluated in 27 patients in total. These patients were successfully treated in four centers by three different interventional radiologists, arguing strongly that the treatment can be successfully used in different centers. The safety of the intra-arterial delivery of the capsules and the lack of evidence that the patients developed an inflammatory or immune response to the encapsulated cells or encapsulation material was shown in all 27 patients. The ifosfamide dose of 1 g/m²/day used in the first trial was well tolerated by all patients. In contrast, the ifosfamide dose of 2 g/m²/day used in the second trial was poorly tolerated in most patients. Since the median survival in the first trial was 40 weeks and only 33 weeks in the second trial, this strongly suggests that there is no survival benefit to increasing the dose of ifosfamide, and indeed, a lower dose is beneficial for quality of life and the lack of side effects. This is supported by the one-year survival rate in the first trial being 38%, whilst that in the second trial was only 23%. However, taking the data from both trials together, a total of nine of the 27 patients were alive after one year, and two of these nine patients were alive for two years or more.

Simple preparation of polyelectrolyte complex beads for the long-term release of small molecules

We report a simple method for preparing solid polyelectrolyte complex (PEC) beads, which provide effective barriers to diffusion and can be used for the multiple-day release of small molecules. Single-phase poly(allylamine) (PAH) and poly(styrenesulfonate) (PSS) mixtures were prepared at pH 11.6 (significantly above the effective pKa of PAH), where the PAH amine groups were deprotonated and therefore neutral. These mixtures were added dropwise into acid baths, whereupon the rapid acid diffusion into the polyelectrolyte droplets led to instant ionization of PAH amine groups and, thus, the formation of PEC beads (i.e., via phase inversion). In stark contrast to the PEC particles prepared through phase inversion in previous studies, which had (solvent-filled) capsule-like morphologies, these beads had solid internal structures. The solute permeabilities of these PEC matrices could be extensively tuned by air drying the beads, which led to the apparently-irreversible closure of pores. Thus, by tuning the drying conditions and polymer compositions used during bead preparation, a model small molecule (Fast Green FCF dye) was released over times ranging between 2 and 18 days.

Phase I/II clinical trial of encapsulated, cytochrome P450 expressing cells as local activators of cyclophosphamide to treat spontaneous canine tumours

Based upon promising preclinical studies, a clinical trial was performed in which encapsulated cells overexpressing cytochrome P450 enzyme isoform 2B1 were implanted around malignant mammary tumours arising spontaneously in dogs. The dogs were then given cyclophosphamide, one of the standard chemotherapeutic agents used for the treatment of mammary tumours. The dogs were assessed for a number of clinical parameters as well as for reduction in tumour size. The treatment was well tolerated with no evidence of adverse reactions or side effects being associated with the administration of the encapsulated cells. Reductions in tumour size of more than 50% were observed for 6 out of the 11 tumours analysed while 5 tumours showing minor responses, i.e. stable disease. In contrast, the tumours that received cyclophosphamide alone showed only stable disease. Taken together, this data suggests that encapsulated cytochrome P450 expressing cells combined with chemotherapy may be useful in the local treatment of a number of dog mammary tumours and support the performance of further clinical studies to evaluate this new treatment.

Polymers in cell encapsulation from an enveloped cell perspective

In the past two decades, many polymers have been proposed for producing immunoprotective capsules. Examples include the natural polymers alginate, agarose, chitosan, cellulose, collagen, and xanthan and synthetic polymers poly(ethylene glycol), polyvinyl alcohol, polyurethane, poly(ether-sulfone), polypropylene, sodium polystyrene sulfate, and polyacrylate poly(acrylonitrile-sodium methallylsulfonate). The biocompatibility of these polymers is discussed in terms of tissue responses in both the host and matrix to accommodate the functional survival of the cells. Cells should grow and function in the polymer network as adequately as in their natural environment. This is critical when therapeutic cells from scarce cadaveric donors are considered, such as pancreatic islets. Additionally, the cell mass in capsules is discussed from the perspective of emerging new insights into the release of so-called danger-associated molecular pattern molecules by clumps of necrotic therapeutic cells. We conclude that despite two decades of intensive research, drawing conclusions about which polymer is most adequate for clinical application is still difficult. This is because of the lack of documentation on critical information, such as the composition of the polymer, the presence or absence of confounding factors that induce immune responses, toxicity to enveloped cells, and the permeability of the polymer network. Only alginate has been studied extensively and currently qualifies for application. This review also discusses critical issues that are not directly related to polymers and are not discussed in the other reviews in this issue, such as the functional performance of encapsulated cells in vivo. Physiological endocrine responses may indeed not be expected because of the many barriers that the metabolites encounter when traveling from the blood stream to the enveloped cells and back to circulation. However, despite these diffusion barriers, many studies have shown optimal regulation, allowing us to conclude that encapsulated grafts do not always follow nature's course but are still a possible solution for many endocrine disorders for which the minute-to-minute regulation of metabolites is mandatory.

Use of the mitochondria toxicity assay for quantifying the viable cell density of microencapsulated jurkat cells

The mitochondria toxicity assay (MTT assay) is an established method for monitoring cell viability based on mitochondrial activity. Here the MTT assay is proposed for the in situ quantification of the living cell density of microencapsulated Jurkat cells. Three systems were used to encapsulate the cells, namely a membrane consisting of an interpenetrating polyelectrolyte network of sodium cellulose sulphate/poly(diallyldimethylammonium chloride) (NaCS/PDADMAC), a calcium alginate hydrogel covered with poly(L-lysine) (Ca-alg-PLL), and a novel calcium alginate-poly(ethylene glycol) hybrid material (Ca-alg-PEG). MTT results were correlated to data obtained by the trypan blue exclusion assay after release of the cells from the NaCS/PDADMAC and Ca-alg-PLL capsules, while a resazurin-based assay was used for comparison in case of the Ca-alg-PEG material. Analysis by MTT assay allows quick and reliable determination of viable cell densities of encapsulated cells independent of the capsule material. The assay is highly reproducible with inter-assay relative standard deviations below 10%.

Magnetic field-controlled gene expression in encapsulated cells

Cell and gene therapies have an enormous range of potential applications, but as for most other therapies, dosing is a critical issue, which makes regulated gene expression a prerequisite for advanced strategies. Several inducible expression systems have been established, which mainly rely on small molecules as inducers, such as hormones or antibiotics. The application of these inducers is difficult to control and the effects on gene regulation are slow. Here we describe a novel system for induction of gene expression in encapsulated cells. This involves the modification of cells to express potential therapeutic genes under the control of a heat inducible promoter and the co-encapsulation of these cells with magnetic nanoparticles. These nanoparticles produce heat when subjected to an alternating magnetic field; the elevated temperatures in the capsules then induce gene expression. In the present study we define the parameters of such systems and provide proof-of-principle using reporter gene constructs. The fine-tuned heating of nanoparticles in the magnetic field allows regulation of gene expression from the outside over a broad range and within short time. Such a system has great potential for advancement of cell and gene therapy approaches.

Islets transplanted in immunoisolation devices: a review of the progress and the challenges that remain

The concept of using an immunoisolation device to facilitate the transplantation of islets without the need for immunosuppression has been around for more than 50 yr. Significant progress has been made in developing suitable materials that satisfy the need for biocompatibility, durability, and permselectivity. However, the search is ongoing for a device that allows sufficient oxygen transfer while maintaining a barrier to immune cells and preventing rejection of the transplanted tissue. Separating the islets from the rich blood supply in the native pancreas takes its toll. The immunoisolated islets commonly suffer from hypoxia and necrosis, which in turn triggers a host immune response. Efforts have been made to improve the supply of nutrients by using proangiogenic factors to augment the development of a vascular supply in the transplant site, by using small islet cell aggregates to reduce the barrier to diffusion of oxygen, or by creating scaffolds that are in close proximity to a vascular network such as the omental blood supply. Even if these efforts are successful, the shortage of donor islet tissue available for transplantation remains a major problem. To this end, a search for a renewable source of insulin-producing cells is ongoing; whether these will come from adult or embryonic stem cells or xenogeneic sources remains to be seen. Herein we will review the above issues and chart the progress made with various immunoisolation devices in small and large animal models and the small number of clinical trials carried out to date.

Immunoisolating semi-permeable membranes for cell encapsulation: focus on hydrogels

Cell-based medicine has recently emerged as a promising cure for patients suffering from various diseases and disorders that cannot be cured/treated using technologies currently available. Encapsulation within semi-permeable membranes offers transplanted cell protection from the surrounding host environment to achieve successful therapeutic function following in vivo implantation. Apart from the immunoisolation requirements, the encapsulating material must allow for cell survival and differentiation while maintaining its physico-mechanical properties throughout the required implantation period. Here we review the progress made in the development of cell encapsulation technologies from the mass transport side, highlighting the essential requirements of materials comprising immunoisolating membranes. The review will focus on hydrogels, the most common polymers used in cell encapsulation, and discuss the advantages of these materials and the challenges faced in the modification of their immunoisolating and permeability characteristics in order to optimize their function.

Creation of a prevascularized site for cell transplantation in rats

INTRODUCTION

Transplanted cells, especially islet cells, are likely to become apoptotic due to local hypoxia leading to graft dysfunction. Isolated pancreatic islet cells depend on the diffusion of oxygen from the surrounding tissue; therefore, access to sufficient oxygen supply is beneficial, particularly when microcapsules are used for immunoisolation in xenotransplantation. The aim of this study was to create a prevascularized site for cell transplantation in rats and test its effectiveness with microencapsulated HEK293 cells.

METHODS

The combination of implantation of a foam dressing, vacuum-assisted wound closure (foam+VAC) and hyperbaric oxygenation (HBO) was used in 40 Sprague-Dawley rats. Blood flow and vascular endothelial growth factor (VEGF) levels were determined. Sodium cellulose sulphate (SCS)-microencapsulated HEK293 cells were xenotransplanted into the foam dressing in rats pre-treated with HBO, and angiogenesis and apoptosis were assessed.

RESULTS

Vessel ingrowth and VEGF levels increased depending on the duration of HBO treatment. The area containing the foam was perfused significantly better in the experimental groups when compared to controls. Only a small amount of apoptosis occurs in SCS-microencapsulated HEK293 cells after xenotransplantation.

CONCLUSION

As ischemia-damaged cells are likely to undergo cell death or loose functionality due to hypoxia, therefore leading to graft dysfunction, the combination foam+VAC and HBO might be a promising method to create a prevascularized site to achieve better results in xenogeneic cell transplantation.

Progress technology in microencapsulation methods for cell therapy

Cell encapsulation in microcapsules allows the in situ delivery of secreted proteins to treat different pathological conditions. Spherical microcapsules offer optimal surface-to-volume ratio for protein and nutrient diffusion, and thus, cell viability. This technology permits cell survival along with protein secretion activity upon appropriate host stimuli without the deleterious effects of immunosuppressant drugs. Microcapsules can be classified in 3 categories: matrix-core/shell microcapsules, liquid-core/shell microcapsules, and cells-core/shell microcapsules (or conformal coating). Many preparation techniques using natural or synthetic polymers as well as inorganic compounds have been reported. Matrix-core/shell microcapsules in which cells are hydrogel-embedded, exemplified by alginates capsule, is by far the most studied method. Numerous refinement of the technique have been proposed over the years such as better material characterization and purification, improvements in microbead generation methods, and new microbeads coating techniques. Other approaches, based on liquid-core capsules showed improved protein production and increased cell survival. But aside those more traditional techniques, new techniques are emerging in response to shortcomings of existing methods. More recently, direct cell aggregate coating have been proposed to minimize membrane thickness and implants size. Microcapsule performances are largely dictated by the physicochemical properties of the materials and the preparation techniques employed. Despite numerous promising pre-clinical results, at the present time each methods proposed need further improvements before reaching the clinical phase.

Current status and future prospects for cell transplantation to prevent congestive heart failure

Although most cardiac cell therapy trials have focused on patients with acute myocardial infarction, attempts at "regenerating" chronically failing hearts have also been performed. These studies have entailed use of skeletal myoblasts and bone marrow-derived cells. In the case of skeletal myoblasts, the randomized placebo-controlled myoblast autologous grafting in ischemic cardiomyopathy (MAGIC) trial has failed to show that myoblast injections increased ejection fraction beyond that seen in controls but the finding that the highest dose of myoblasts resulted in a significant antiremodeling effect compared with the placebo group provides an encouraging signal. In the case of bone marrow cells, surgical injections of the mononuclear fraction combined with coronary artery bypass surgery have not shown a substantial benefit but positive results have been reported with intraoperative epicardial injections of CD133(+) progenitors. There are three possible reasons for these mixed results. The first is the marked heterogeneity of cell functionality (particularly in the case of bone marrow), which would expectedly translate into variable clinical outcomes. The second reason is the low rate of sustained engraftment. The third possible explanation is a mismatch between the choice of end points and the presumed mechanism of action of the cells. The initial assumption that adult stem cells could effect myocardial tissue regeneration has led to usual focus on ejection fraction as the major surrogate endpoint. It is now increasingly recognized that adult stem cells, in contrast to their embryonic counterparts, have little if any regenerative capacity and that their presumed beneficial effects more likely involve paracrine signaling, in which case infarct size, perfusion, or left ventricular volumes might be more appropriate markers. Altogether, these observations provide a framework for future research, the results of which will then have to be integrated in the protocol design of second-generation clinical trials.

Colon-targeted delivery of live bacterial cell biotherapeutics including microencapsulated live bacterial cells

There has been an ample interest in delivery of therapeutic molecules using live cells. Oral delivery has been stipulated as best way to deliver live cells to humans for therapy. Colon, in particular, is a part of gastrointestinal (GI) tract that has been proposed to be an oral targeted site. The main objective of these oral therapy procedures is to deliver live cells not only to treat diseases like colorectal cancer, inflammatory bowel disease, and other GI tract diseases like intestinal obstruction and gastritis, but also to deliver therapeutic molecules for overall therapy in various diseases such as renal failure, coronary heart disease, hypertension, and others. This review provides a comprehensive summary of recent advancement in colon targeted live bacterial cell biotherapeutics. Current status of bacterial cell therapy, principles of artificial cells and its potentials in oral delivery of live bacterial cell biotherapeutics for clinical applications as well as biotherapeutic future perspectives are also discussed in our review.

Cryopreservation of Insulin-Producing Cells Microencapsulated in Sodium Cellulose Sulfate

INTRODUCTION

Diabetes mellitus may be treated with pancreatic islet cell transplantation. The use of xenogenic islet cells may overcome the shortage of human donor organs. Microencapsulation seems to be a promising method for immunoprotection. Since isolation, purification, encapsulation, and transplantation of islet cells are labor-intensive, cryopreservation has emerged as an attractive system for islet banking. In this study sodium cellulose sulfate (NaCS), a novel method for microencapsulation of islet cells, was tested for its capability to protect cells during cryopreservation.

METHODS

HIT-T15 cells were microencapsulated in NaCS. Cells were frozen and thawed using three different media containing varying amounts of dimethylsulfoxide (DMSO) and glycerol. Cell viability and cell growth were monitored using 3-(-4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide before freezing and 1 week after thawing.

RESULTS

NaCS did not show any negative impact on the growth rates of encapsulated HIT-T15 cells compared with nonencapsulated controls. Nonencapsulated cells were adequately cryopreserved by both DMSO- and glycerol-containing freezing media. DMSO was not suitable for cryopreservation of encapsulated HIT-T15 cells, whereas glycerol seemed to produce no considerable cell loss during freezing and thawing.

DISCUSSION

Islet banking of cells encapsulated in NaCS was feasible. Microencapsulation did not harm islet cell recovery. As NaCS is less immunogenic and more biocompatible than other materials used for microencapsulation, it may be a promising method for immunoisolation of islet cells to replace the endocrine pancreas in a physiological way.

Morphological and functional characterization of a pancreatic beta-cell line microencapsulated in sodium cellulose sulfate/poly(diallyldimethylammonium chloride)

BACKGROUND

Late diabetic complications cannot be prevented totally by current antidiabetic strategies. Therefore, new therapeutic concepts of insulin replacement such as pancreas transplantation are evolving. Due to the shortage of human donor organs, transplantation of microencapsulated xenogeneic pancreatic islet cells has attracted considerable attention. Sodium cellulose sulfate/poly(diallyldimethylammonium chloride) (NaCS/PDADMAC) is a material with favorable biogenic properties that has been used for microencapsulation of various cell types. However, there are no data on the suitability of NaCS/PDADMAC for microencapsulation of pancreatic beta-cells.

MATERIAL AND METHODS

Cell growth and viability of NaCS/PDADMAC-microencapsulated HIT-T15 cells, an immortalized hamster pancreatic beta-cell line, were assessed using a dimethylthiazol-diphenyltetrazoliumbromide (MTT)-based cell growth determination kit and apoptosis was detected by antibodies against activated caspase 3. Glucose-dependent insulin secretion was assessed with ELISA and the uptake of glucose was measured using fluorescence-labeled glucose.

RESULTS

Statistical analysis revealed no differences in glucose-dependent cell proliferation, insulin secretion and glucose uptake between non-microencapsulated and microencapsulated HIT-T15 cells. Stimulation of HIT-T15 cells with glucose (100 mg/ml) resulted in a biphasic insulin secretion response.

CONCLUSION

Microencapsulation of HIT-T15 cells in NaCS/PDADMAC does not influence cell proliferation, insulin secretion and glucose uptake. Our results indicate that NaCS/PDADMAC is well suited for microencapsulation of pancreatic beta-cells.

Design of high-throughput-compatible protocols for microencapsulation, cryopreservation and release of bovine spermatozoa

With a rate exceeding 90% in cattle, artificial insemination (AI) is the prime reproduction technology in stock farming. AI success is expected to increase with extended persistence of sperms in utero. In order to enable controlled sperm release during artificial insemination we have designed two strategies for the automated microencapsulation of bovine spermatozoa in either alginate-Ca2+ or cellulose sulfate (CS)-poly-diallyldimethyl ammonium chloride (pDADMAC) capsules using standard encapsulation hardware. Animal protein- and citric acid-free sperm extenders and encapsulation protocols have been developed to ensure encapsulation compatible with sperm physiology. Bovine spermatozoa have showed high motility rates inside CS-pDADMAC-based capsules, were preserved by standard cryoconservation and rescued with high viability/motility following disintegration of the thawed capsules. CS-pDADMAC-based capsules break up within 72 h after addition of either purified cellulase or cellulase-filled alignate-Ca2+ capsules. The controlled release, associated with the microencapsulation of bovine spermatozoa, may be a promising approach to increase the success rate of artificial insemination.

Porcine islet cells microencapsulated in sodium cellulose sulfate

One hundred fifty million people suffer from diabetes mellitus worldwide. Modern exogenous insulin therapy cannot prevent late complications. Islet cell transplantation could be a sufficient therapeutic option but the shortage of human organs limits this option. The use of xenogeneic porcine islet cells may also be a viable alternative. One way to manage hyperacute rejection is by the protection of xenogeneic cells from the immune system by microencapsulation. In this study sodium cellulose sulfate (NaCS) was evaluated as a material for encapsulation. An insulin-producing cell line (HIT-T15) was established in our laboratory. Glucose-dependent insulin production and cell growth were monitored. Cells were encapsulated with NaCS by Austrianova, Vienna. The insulin production and mitosis rate were examined. Cell growth and insulin production by HIT-T15 cells affected the glucose levels in the nutrient solution. Cell viability and glucose-dependent insulin production were not influenced by NaCS. Encapsulation with NaCS is feasible and it could be shown that the material is permeable to nutrients and metabolic side products. The encapsulated cells are able to detect the glucose concentration in the nutrient solution and to react in a proper way by producing insulin. Encapsulation with NaCS, which is more biocompatible and less immunogenic than other materials, seems to be a promising method for immunoisolation of porcine beta cells for xenotransplantation to replace the endocrine pancreas in a physiologic way.

A multiprong approach to cancer gene therapy by coencapsulated cells

Immune-isolation of nonautologous cells with microencapsulation protects these cells from graft rejection, thus allowing the same recombinant therapeutic cell line to be implanted in different recipients. This approach was successful in treating HER2/neu-expressing tumors in mice by delivering an interleukin-2 fusion protein (sFvIL-2), or angiostatin. However, treatment with interleukin-2 led to profuse inflammation, while angiostatin delivery did not result in long-term tumor suppression, in part due to endothelial cell-independent neovascularization (vascular mimicry). We hypothesize that coencapsulating the two producer cells in the same microcapsules may enhance the efficacy and ameliorate the above side effects. Hence, B16-F0/neu tumor-bearing mice were implanted with sFvIL-2- and angiostatin-secreting cells coencapsulated in the same alginate-poly-L-lysine-alginate microcapsules. However, this protocol only produced an incremental but not synergistic improvement, as measured with greater tumor suppression and improved survival. Compared to the single sFvIL-2 treatment, the coencapsulation protocol showed improved efficacy associated with: mobilization of sFvIL-2 from the spleen; a higher level of cytokine delivery systemically and to the tumors; increased tumor and tumor-associated endothelial cell apoptosis; and a reduced host inflammatory response. However, compared to the single angiostatin treatment, the efficacy was reduced, primarily due to a "bystander" effect in which the angiostatin-secreting cells suffered similar transgene silencing as the coencapsulated cytokine-secreting cells. Nevertheless, the level of "vascular mimicry" of the single angiostatin treatment was significantly reduced. Hence, while there was no synergy in efficacy, an incremental improvement and some reduction in undesirable side effects of inflammation and vascular mimicry were achieved over the single treatments.

CellMAC: a novel technology for encapsulation of mammalian cells in cellulose sulfate/pDADMAC capsules assembled on a transient alginate/Ca2+ scaffold

Microencapsulation of desired mammalian cell phenotypes in biocompatible polymer matrices represents a powerful technology for cell-based therapies and biopharmaceutical manufacturing of protein therapeutics. We have pioneered a novel jet break-up-compatible process for encapsulation of mammalian cells in cellulose sulfate (CS)/poly-diallyl-dimethyl-ammoniumchloride (pDADMAC) (CellMAC) capsules. CS and pDADMAC polymerize on a transient ad hoc co-assembled Ca2+/alginate scaffold and form homogenous capsules following dissolution of the alginate core by Ca2+ chelating agents. CellMAC capsules exhibited excellent mechanical properties and showed a molecular weight cut-off between 43 and 77kDa. Chinese hamster ovary cells engineered for constitutive production of the glycohormone erythropoietin reached high viable cell densities when grown inside CellMAC capsules, while specific erythropoietin (EPO) productivities matched those of conventional non-encapsulated control cultures. CellMAC-encapsulated EPO-production cell lines induced increased EPO serum levels when implanted intraperitoneally into mice and provided robust glycoprotein production during standard stirred-tank bioreactor operation. We expect the CellMAC technology to foster advances in therapeutic encapsulation of engineered cell lines as well as manufacturing of protein pharmaceuticals.

Creating artificial perichondrium by polymer complex membrane macroencapsulation: immune protection and stabilization of subcutaneously transplanted tissue-engineered cartilage

Functional organ or tissue failure is one of the most frequent, devastating and costly problems in modern health care. The field of tissue engineering has tremendous potential for developing new functional tissue. In reconstructive surgery, cartilage engineering could be a serious alternative to the established method of autologous cartilage transplantation. Recent studies demonstrate cartilage engineering by subcutaneous implantation of chondrocyte-seeded PGA/PLA-fibrin glue scaffolds in the backs of nude mice. In both autologous cartilage transplantation and cartilage engineering, the host immune response affects transplant integrity and cartilage morphology to an unforeseeable extent. To investigate whether polyelectrolyte complex (PEC) membranes can prevent rejection of cartilage transplants without neglecting tissue metabolism, tissue-engineered cartilage encapsulated with a PEC membrane was subcutaneously implanted in the backs of nude mice. Non-encapsulated tissue-engineered cartilage was used for the control group. Histochemistry and scanning electron microscopy were performed 4 and 12 weeks after implantation. There was no interaction between the host and the implant with an intact PEC membrane. With protection by PEC encapsulation, implanted tissue-engineered cartilage showed no signs of degeneration and had a significantly weaker cellular immune response than without it. Thus, PEC membrane encapsulation appears to be a novel approach for protecting cartilage implants from host immune response after autologous transplantation.

Microencapsulation of parathyroid tissue with photosensitive poly(L-lysine) and short chain alginate-co-MPEG

Human parathyroid glands were encapsulated using the alginate-PLL system in this study. In order to improve the mechanical strength and the biocompatibility, the microcapsules were fabricated with a three-layer structure that consisted of alginate/photosensitive poly(L-lysine)/short chain alginate-co-MPEG. These modified microcapsules were used for encapsulating human parathyroid tissue. In vitro experiments revealed that microencapsulated parathyroid glands maintained differentiative properties in culture, and the capsular membrane was freely permeable to the human parathyroid hormone. For in vivo experiments, these capsules were transplanted into parathyroidectomized SD-rats. After parathyroidectomy, serum calcium decreased from 2.25 to 1.68 mmol/L and remained in a constantly low concentration until transplantation. Parathyroidectomized SD-rats were normocalcemic after transplant of encapsulated parathyroid tissue. The microcapsules were then explanted at 12 weeks for examination. Histological evaluations of excised transplants revealed that the microcapsules remained intact structurally and were free of cell adhesions. The results demonstrated that human parathyroid tissue microencapsulated by this system retains stability and is functional both in vitro and in vivo. This encapsulating system will have valuable application for endocrine surgery in the future.

Photo-crosslinkable microcapsules formed by polyelectrolyte copolymer and modified collagen for rat hepatocyte encapsulation

New anionic polyelectrolyte tetra-copolymers with photo-crosslinkable 4-(4-methoxycinnamoyl)phenyl methacrylate monomer in addition to a HEMA-MMA-MAA ter-copolymer system were synthesized. The tetra-copolymers were used to form photo-crosslinkable microcapsules with modified collagen by complex coacervation for rat hepatocytes encapsulation. The hepatocytes were encapsulated within a two-layered membrane comprising of modified collagen as the inner core and an outer photo-crosslinkable copolymer shell. Upon photo-crosslinking of the microcapsules with UV-Vis light irradiation, the mechanical strength and chemical stability of the microcapsules, and the cellular functions of the encapsulated hepatocytes were enhanced. Particularly, the mechanical stability of the microcapsules was dramatically strengthened. The new photo-crosslinkable tetra-copolymer formulation described in this article has opened a way to the development of hepatocyte microencapsulation technology for bioartifical liver assist device.

History, challenges and perspectives of cell microencapsulation

Cell microencapsulation continues to hold significant promise for biotechnology and medicine. The controlled, and continuous, delivery of therapeutic products to the host by immunoisolated cells is a potentially cost-effective method to treat a wide range of diseases. Although there are several issues that need to be addressed, including capsule manufacture, properties and performance, in the past few years, a stepwise analysis on the essential obstacles and limitations has brought the whole technology closer to a realistic proposal for clinical application. This paper summarizes the current situation in the cell encapsulation field and discusses the main events that have occurred along the way.

Intra-arterial instillation of microencapsulated, Ifosfamide-activating cells in the pig pancreas for chemotherapeutic targeting

BACKGROUND

The therapeutic efficacy of intratumoral instillation of genetically engineered, CYP2B1-expressing, microencapsulated cells in combination with ifosfamide had been previously demonstrated in xenografted human pancreatic ductal carcinomas [Gene Ther 1998;5:1070-1078]. Prior to a clinical study, the feasibility of an intra-arterial application of microencapsulated cells to the pancreas and its consequences to the organ had to be evaluated.

MATERIAL AND METHODS

Microencapsulated, CYP2B1-producing cells were instilled both in vivo (transfemoral angiographical access) and in vitro (perfusion model) in the splenic lobe of the pig pancreas. In vivo, animals were monitored clinically for 7 days, then treated with ifosfamide and sacrificed. In vitro, ifosfamide was administered intra-arterially.

RESULTS

In all animals, 100 microcapsules could be instilled safely via the femoral route without clinical, biochemical or histological signs of pancreatitis. Histological examination revealed partial obstruction of small arteries by the capsules, without causing any parenchymal damage. In vitro, instillation reduced blood flow by half. Ifosfamide, also in combination with the capsules, did not add any damage to the pancreas.

CONCLUSION

Intra-arterial instillation of microencapsulated cells to the pig pancreas is feasible and safe. Neither pancreatitis, foreign body reactions nor circulatory disturbances were observed. Clinical application of this genetically enhanced chemotherapeutic method seems possible.