Immunoisolation 1. Chang, T.M.S. Semipermeable microcapsules. Science 146, 524 525 (1964). 2. Lim, F. & Sun, A.M. Microencapsulated islets as bioartificial endocrine pancreas. Science 210, 908 909 (1980). In 1964, T.M.S. Chang 1 proposed the idea of using ultrathin polymer membrane microcapsules for the immunoprotection of transplanted cells and introduced the term artificial cells to define the concept of bioencapsulation. This was implemented 20 years later to immobilize xenograft islet cells. When implanted into rats, the microencapsulated islets corrected the diabetic state for several weeks 2.,
Cell/Tissue Transplantation Diabetes (insulin) Parkinson s disease (dopamine producing cells) is a degenerative disorder of the central nervous system that often impairs the sufferer's motor skills, speech, and other functions Chronic pain Alzheimer s, common form of dementia, degenerative, and terminal disease Huntington s disease is a progressive neurodegenerative genetic disorder, CNS malignancies Cell/tissue sources: Autogeneic: arising from self; pertaining to an autograft Allogeneic: denoting individuals (or tissues) that are of the same species but antigenically distinct Xenogenic: Originating outside the organism or from a foreign substance introduced into the organism Genetically engineered: they could potentially lead to generate tumor
Immunoisolation Cells and tissue are enclosed in a semipermeable membrane. The function of this semipermeable membrane; Must prevent immune attack by host Must allow diffusion of nutrients metabolic products and therapeutic agent Cell microencapsulation. a, Nutrients, oxygen and stimuli diffuse across the membrane, whereas antibodies and immune cells are excluded. b, Pre-vascularized solid support system to facilitate optimal nutrition of the enclosed cells.
Immune System Cellular Component T-cells Macrophages, etc. Humoral Component Antibodies (IgGs, IgMs) Complement (C3, C5a, etc.) Cytokines (interleukin 1, IL1, etc.) These will interact with the capsule if the membrane does not have proper characteristics.
Immunoisolation Membranes can be made microporous, pore size ~0.6 micronmeter Nanoporous ( molecular weight cut off ~ 30,000 Da ) IgG MW ~ 150 kda IgM MW ~ 900 kda C3 MW ~ 200 kda IL1- MW ~ 17 kda Bigger Challenge : Macrophages can generate small molecular weight species that can affect cell viability (free radicals, H 2 O 2, NO)
Microencapsulation of islets Glucose islet Insulin O 2 & nutrients Immune cells Antibodies
Allow diffusion of: Membrane Function Nutrients, O 2, waste products Metabolic products, therapeutic agent Signal that triggers production of therapeutic agent. Prevent diffusion of immune rejection by host fibrous formation (important one, because if you get fibrous capsule forming around the implant, it ll ellicit an inflammatory response, fibroblasts will compete for nutrients. viral transfer to host (in the case of xenotransplantation) invasion of the host by the transplanted cells
Challenges for Cell Transplantation 1.Cell/Tissue Source Tissue donors Xenogeneic cells Cell lines For the treatment of conditions affecting the CNS (alzheimer s), ~10 6 cells may be required. For the treatment of diabetes, ~10 9 cells may be required. Enough tissue may not be available because of lack of donors. 2.Semipermeable Membrane The precise molecular weight cut off of the membrane has not been established. C5 MW 10 kda IL-a MW 17 kda Some studies suggest that diffusion of molecules with MW ~75 kda are necessary to sustain long term survival of the transplanted cells
Challenges for Cell Transplantation 3.Oxygen supply to transplanted cells This will depend on the metabolic activity of the cells Site of implantation p O2 ~100 torrs in arterous blood p O2 ~ 40 torrs in microvasculature Approaches for cell encapsulation: Hallow fibers/capsules: cells are on the outside and blood is circulating in the hallow fiber. Cell encapsulation with hydrogel (high water content). This will allow fast diffusion of nutrients, most important property of the hydrogel will be the crosslink density and the thickness.
Types of Bioartificial Pancreas Diffusion chamber, Hollow fiber unit and Microcapsule The diffusion chamber and hollow fiber types of bioartificial pancreas can be classified as a macrocapsule type. In diffusion chamber type pancreases, Nuclepore membranes with a pore size of 0.05 1 μm have been used as an immunoisolation membrane. It was reported that normoglycemia was maintained for 30 weeks in streptozotocin (STZ)-induced diabetic rats by implanting a device that encapsulated mice pancreatic beta cell lines (MIN6) (xenotransplantation). Hallow fiber device consists of a chamber passing a semi-permeable tubular membrane that is connected to vascular grafts. Islets are placed between the housing chamber and the tubular membrane.
Types of Bioartificial Pancreas Bioartificial pancreas. (a) The concept of the immunoisolation membrane. (b) Islets enclosed in agarose microcapsules.
Types of Bioartificial Pancreas Islets can be encapsulated by forming a suspension in alginate, consists of polysaccharide followed by exposure to Ca +2 ions Microencapsulation of islets with alginate polylysine.
Techniques of Encapsulation Air-jet syringe pump droplet generator: The device consists of an air jacket surrounding an alginate nozzle through which alginate solution is injected. As alginate droplets are forced out of the end of the needle by the syringe pump, the droplets are pulled off by the shear forces set up by the flowing air stream. The size of the spherical droplets is controlled by adjusting the flow rate of the air jacket. Interfacial polymerization:the technique involves physical adsorption of the initiator eosin Y on the islet cell surface, which then allows polymerization to occur on the islet prepolymer interface. The interfacial photoinitiation process employed with this technique results in conformal coating of cross-linked PEGbased hydrogel on the islet cell surface. The process of selective withdrawal is another novel method reported recently for the purpose of coating cell clusters, such as islet cells.171 Briefly, the process involves the insertion of a tube into a container such that its tip is suspended at a specific height above an interface separating two immiscible fluids.
Techniques of Encapsulation Layer-by-layer Assembly of Conformal Nano-thin PEG Coating poly(l-lysine)-g-poly(ethylene glycol)biotin and streptavidin (SA), Wilson, Cui, Chaikof, Nanoletters, 2008; 8(7):1940-1948.
Fluorescent Staining Assay rinse NHS-PEG-biotin Streptavidin Biotin-PEG-FITC
Insulin Concentration ( g/l) Dynamic insulin response to glucose stimulation of coated and uncoated rat islets Insulin Released per Minute as a Fraction of Total Insulin Insulin secretion is enhanced after formation of biotin-peg- NHS/SA/biotin-PEG-GLP-1 coating on islet surface. Insulin secretion is higher after third step of surface coating, which binds GLP-1 to islet surface. Insulin is normalized as a fraction of total insulin. 7.0 6.0 5.0 biotin-peg SA-biotin-PEG GLP-1-PEG-biotin-SA-biotin-PEG Control 0.001 0.0008 Control Modified 4.0 0.0006 3.0 0.0004 2.0 1.0 0.0002 0.0 0 10 20 30 40 50 60 Time (min) 3.3 mm glucose 16.7 mm glucose 3.3 mm glucose 0 0 10 20 30 40 50 60 Time (min)
Microencapsulation of islets Interfacial polymerization Xenotransplantion of Porcine Islets into rats. Mice maintained normoglycemia for up to 110 days. (~100 micron) Selective withdrawal (~20 micron) Alginate encapsulation (~800 micron) Cruise GM et al., Cell Transplantation, Vol. 8 pp. 293-306, 1999. Wyman, Kizilel, Mrksich, Nagel, Garfinkel, Small, 2007 Apr;3(4):683-90. Kim S, Kim SW, Bae YH, Biomaterials 26, 3597-3606, 2005.
Stem Cells Stem cells offer the potential to replicate indefinetely in culture but also to generate many or most of the cells in the body (including those cells that normally do not regenerate such those found in the central nervous system and cardiac muscle). A stem cell can replicate and produce cells that take more specialized functions. Development potential or potency of a stem cell refers to the breadth of functions that more differentiated daughter cells and their progeny can adopt.
Stem Cells http://stemcells.nih.gov/info/basics/ To generate cultures of specific types of differentiated cells heart muscle cells, blood cells, or nerve cells scientists try to control the differentiation of embryonic stem cells. The chemical composition of the culture medium, the surface of the culture dish may be changed or the cells can be altered by inserting specific genes. Scientists have established some basic protocols or recipes for the directed differentiation of embryonic stem cells into some specific cell types.
Stem Cells Unipotent stem cells give rise to only one type of differentiated cells The terms oligopotent, pluripotent, and multipotent represent and increase in the number of differentiated cells that can be derived from a stem cell (from few to many to most) A totipotent cell can generate all of the different cell types that comprise an organism.
Normal differentiation pathways of adult Stem Cells In a living animal, adult stem cells are available to divide for a long period, when needed, and can give rise to mature cell types that have characteristic shapes and specialized structures and functions of a particular tissue. http://stemcells.nih.gov/info/basics/
Normal differentiation pathways of adult Stem Cells Hematopoietic stem cells give rise to all the types of blood cells: red blood cells, B lymphocytes, T lymphocytes, natural killer cells, neutrophils, basophils, eosinophils, monocytes, and macrophages. Mesenchymal stem cells have been reported to be present in many tissues. Those from bone marrow (bone marrow stromal stem cells, skeletal stem cells) give rise to a variety of cell types: bone cells (osteoblasts and osteocytes), cartilage cells (chondrocytes), fat cells (adipocytes), and stromal cells that support blood formation. However, it is not yet clear how similar or dissimilar mesenchymal cells derived from non-bone marrow sources are to those from bone marrow stroma. Neural stem cells in the brain give rise to its three major cell types: nerve cells (neurons) and two categories of non-neuronal cells astrocytes and oligodendrocytes. Epithelial stem cells in the lining of the digestive tract occur in deep crypts and give rise to several cell types: absorptive cells, goblet cells, Paneth cells, and enteroendocrine cells. Skin stem cells occur in the basal layer of the epidermis and at the base of hair follicles. The epidermal stem cells give rise to keratinocytes, which migrate to the surface of the skin and form a protective layer. The follicular stem cells can give rise to both the hair follicle and to the epidermis. http://stemcells.nih.gov/info/basics/
Specialized cells Stem Cells
Stem Cells Only a few stem cell types can be classified as pluripotent/totipotent: Embryonal carcinoma cells (EC); derived from a teratocarcinomas that arose from transfer of a postimplantation embryo to an ectopic site. Ebryonic stem cells (ES); derived from the inner cellular mass (ICM) of preimplantation embryos. Embryonic germ cells (EG); derived from primordial germ cells (PGC) that migrate to and colonize the gonad.
Stem Cells Multipotent stem cells can be obtained from fetal and adult sources. The best known are cells derived from bone marrow which contains hematopoietic stem cells. Pluripotent cells posses high levels of alkalyne phosphatase (AP) activity and present specific cell surface glycolipids and glycoproteins. However, these are not sufficient and/or necessary conditions for pluripotency.
Stem Cells The only direct measurement of developmental potential is the analysis of cell differentiation. Most EC and EG require leukemia inhibitory factor (LIF; ~1000 U/ml) in the culture media to remain pluripotent. Withdrawal of LIF enables cell differentiation if the cells are put in an environment conductive to aggregation rather than adhesion to a substrate.
Stem Cells ES/EG can generate cells of hemapoietic lineage and cardiomyocytes if the proper growth and differentiation factors are supplemented to the culture media. Mouse ES have been used to generate in vitro cultures of neurons, skeletal muscle, vascular endothelial cells, adipocytes, and visceral endoderm.
Stem Cells Exogenous factors can also be used to direct differentiation (retinoic acid, dimethyl sulfoxide, hexamethyl bisacetamide, dibutryl camp, forskolin, 3-isobutyl-1-methyl-xanthine. The modes of action by which these compounds act are not fully understood. Growth factors can also be used to induce differentiation of pluripotent stem cells.
Stem Cells The exact components that cause a desired differentiation effect are often unknown. The nature of the substrate that the cell attaches to also has a strong impact in its characteristics. Collagens I and IV have been used to promote adhesion and cell division in a number of cells (vascular and endothelial cells). Laminin has been shown to promote neurite outgrowth in many culture systems including ES cell-derived neuronal cells.
Stem Cells Cell derived extracellular matrices and human ECM have also been used to support differentiation of cells. Human mesenchymal stem cells comprise only 0.01-0.0001 % of total nucleated cells in bone marrow. Genetic selection, transcription factor expression, fluorescence activated cell sorting can be used identify and generate pure populations of specific cell lines.
Stem Cells When bone marrow derived from a variety of species is placed in a diffusion chamber that is implanted into the peritoneum of immunotolerant hosts, bone and cartilage are synthesized inside the diffusion chambers from the marrow derived MSCs and their descendents. (Hematopoietic cells expire within the chamber while mesenchymal cells divide and differentiate into cartilage and bone forming cells. Adv Drug Del Rev 1998, 33,3.
Stem Cells Bone develops along the inner surface closer to the overlying vasculature. Cartilage forms in the central region, away from vasculature in an envirenment that is not as rich in environmental stimuli. If the host is irradiated prior to implantation of cell loaded diffusion chamber, neither bone, nor cartilage develops, instead, hematopoietic cells multiply. Adv Drug Del Rev 1998, 33,3.
Adv Drug Del Rev 1998, 33,3.
Adv Drug Del Rev 1998, 33,3.
Stem Cells The in vivo environment of old rats supports the differentiation of MSCs into osteoblasts at levels similar to those observed in young rats. The osteogenic potential of MSCs from young and old rats is identical. The number of marrow-derived osteoprogenitors declines as a function of donor age. Adv Drug Del Rev 1998, 33,3.