Patent Application
20050084959
The present invention relates to a method for expanding cells, and in particular to a method for expanding stem cells that have been difficult to obtain in a sufficient quantity.
Further, the present invention also relates to a method for utilizing the thus expanded cells. The present invention also relates to regeneration medicine using the thus expanded cells.
Transplantation of hematopoietic stem cells that is performed for intractable blood diseases such as leukemia requires a large quantity of blood stem cells. Hematopoietic stem cells are undifferentiated cells that differentiate into blood components including leukocytes, erythrocytes and platelets. Hematopoietic stem cells can be collected from bone marrow, peripheral blood or cord blood by bone marrow biopsy, peripheral blood stem cell collection or the like.
To date, hematopoietic stem cells have been used to treat tumors and hematologic disorders. Cord blood is used as a supply source of blood stem cells, instead of stem cells from bone marrow. However, one problem is that it is difficult to obtain the blood stem cells of cord blood in a number sufficient for treatment.
Therefore, in vitro expansion of hematopoietic stem cells has been attempted. For example, Dick et al. succeeded in expanding hematopoietic stem cells by 2- to 4-fold within 4 days in the presence of stem cell factor (SCF), fit 3 ligand (FL), granulocyte colony-stimulating factor (G-CSF), interleukin-3 (IL-3) and interleukin-6 (IL-6) and even in the absence of stromal cells. However, in a longer culture, reduced stem cell activity was observed (J Exp Med 186: 619). Meanwhile, Eaves et al. reported that they could achieve a 3-fold expansion of murine stem cells using a stromal cell-free culture system supplemented with interleukin 11, FL and SCF, and a 2-fold expansion of human stem cells by stimulating the stem cells with SCF, FL, G-CSF, IL-3 and IL-6 (Proc. Natl. Acad. Sci. USA vol. 94, 13648).
Recently, it is increasingly understood that contact between stromal cells and the sub-cultured cells is important in maintaining the totipotency of stem cells. For example, expansion of hematopoietic stem cells was attempted by means of in vitro coculture with supporting cells (stroma cell or stromal cell) and various cytokines, so that expansion was achieved to some extent, but this was insufficient for clinical application (Experimental Hematology 29, 174-182).
Further, the involvement of telomerase in canceration of cells has been suggested. Accordingly, cell immortalization has been attempted by introducing a telomerase gene in combination with an oncogene such as ras. Although cell immortalization has been attempted by introducing telomerase into several types of cells, none of these attempts have succeeded in cell immortalization while keeping the normal cell functions without canceration (Nature Vol. 400 p. 465).
Objects to be Achieved by the Invention
A first object of the present invention is to develop a method for expanding cord blood-derived hematopoietic stem cells to a degree sufficiently safe for clinical applications such as hematopoietic stem cell transplantation into adult patients.
Currently, erythrocytes of the same type provided by blood donation are mainly used as a source of erythrocyte transfusion for patients with anemia. However, problems exist, such as a shortage of blood cell donors with rare blood types and possible inoculation of an unknown source of infection. A second object of the present invention is to establish a safe supply source of erythrocytes in large quantities by amplifying hematopoietic stem cells using immortalized stromal cells, and then preparing a system that induces production of erythroid precursor cells at a high rate.
A third object of the present invention is to develop an artificial culture product that can expand hematopoietic stem cells stably for the long term together with the supporting cells, that is, to develop artificial bone marrow.
Furthermore, an object of the present invention is, in regeneration of various tissues and organs, to artificially regenerate, from tissues other than fetal cells, tissues such as cardiovascular tissues or nerve tissues that are effective for treatment.
Means to Achieve the Objectives
First we introduced a virus vector having an oncogene or an immortalizing gene such as telomerase incorporated therein into a stromal cell in vitro. As a result, we have found that cell expansion is maintained after repeated cell division when telomerase alone has been introduced. Specifically, we have found that although the cell lifespan is drastically extended, the cell shape remains the same as that of a normal cell, and the cells can be used as expansion-supporting cells for blood precursor cells in a manner similar to that for normal cells.
By the use of the immortalized stromal cells having drastically extended lifespans as supporting cells for hematopoietic precursor cells that are obtained from cord blood or the like, expansion of hematopoietic precursor cells can be surprisingly enhanced. Further, production of erythroid precursor cells is induced by the use of the thus expanded hematopoietic precursor cell line, so that a system for supplying erythrocytes in large quantities for patients with anemia or the like can be developed without fear of unknown infection.
Moreover, we have also found that by the introduction of an immortalizing gene alone such as telomerase not only into a stromal cell but also into a mesenchymal stem cell, the mesenchymal stem cell can also be immortalized without losing its properties as a stem cell, such that the cell can induce cell differentiation when appropriate conditions are employed for inducing differentiation. We have then found that not only stem cells, but also the precursor cells of mesenchymal cells that can differentiate into mesenchymal cells and cells that are derived from mesenchymal cells can also be immortalized similarly, and thus we have completed the present invention.
Furthermore, we have found that when the thus immortalized mesenchymal stem cells, mesenchymal precursor cells, and mesenchymal cells are allowed to coexist with cells of various tissues, these tissues can be expanded and an artificial tissue construct can be established.
Lane 1. Molecular weight marker
Lane 2. Negative control
Lane 3. Heat sample of 5.
Lane 4. Primary stromal cells
Lane 5. hTERT-stromal cells
Lane 6. Hela cells
A dotted line shows the cutoff (0.1%) of successful transplantation of human hematopoietic cells.
p*<0.05 (by Mann-Whiteney U test) compared with pre-cocultured CD 34+ cells.
Lanes 1-3, mice (3) transplanted with only accessory cells.
Lanes 4-8, mice (5) transplanted with pre-cocultured CD34+ cells.
Lane 9, PC (positive control, and human peripheral blood monocytes).
Lane 10, NC (a non-transplanted, negative control mouse (1)).
The figure shows analytical results when pre-coculured CD34+ cells (upper right), hematopoietic cells expanded for 4 weeks on primary stromal cells (lower left), or hematopoietic cells expanded for 4 weeks on h-TERT stromal cells (lower right) were transplanted to NOD/SCID mice. Data obtained using an isotype match antibody against a monocyte of the peripheral blood of the transplanted mouse are also shown (upper left).
The Y-axis shows staining with PI (propidium iodide).
CD34+ cells were transplanted into NOD/SCID mice after (A) 4 weeks of expansion on primary stromal cells, (B) 4 weeks of expansion on hTERT-stromal cells or (C) without expansion (pre-coculture). To confirm human origination, hematopoietic cells were immuno-labeled with FITC-conjugated hCD45 antibodies, and further immuno-labeled with PE-conjugated antibodies specific to the indicated lineage markers.
Lane 1, primary stromal cells; lane 2, h-TERT stromal cells (PD=10); lane 3, h-TERT stromal cells (PD=60); Lane 4, h-TERT stromal cells (PD=100) 9
Lane 1, primary stromal cells; lane 2, h-TERT stromal cells (PD=10); lane 3, h-TERT stromal cells (PD=60); Lane 4, h-TERT stromal cells (PD=100)
The present invention encompasses: (1) a method for cell immortalization, which involves introducing immortalizing genes into mesenchymal stem cells, mesenchymal precursor cells, mesenchymal cells or cells derived from mesenchymal cells (hereinafter, referred to as mesenchymal cell-related cells) to immortalize the cells, and the thus immortalized cells; (2) cells that are differentiated from the immortalized mesenchymal stem cells and a method for differentiating the same; (3) a method for long-term cell expansion, which involves introducing immortalizing genes into stromal cells when hematopoietic stem cells (precursor cells) are cocultured with stromal cells; (4) a method for long-term cell expansion and a method for regulating cell differentiation, which involve introducing immortalizing genes into mesenchymal cells when cardiovascular cells are cocultured with mesenchymal cells; (5) a method for long-term cell expansion, and a method for regulating cell differentiation, which involve introducing immortalizing genes into mesenchymal cells, when bone, cartilage, tendon, skeletal muscle, adipose tissue or the like is cocultured with mesenchymal cells; (6) a method for long-term cell expansion, and a method for regulating cell differentiation, which involve introducing immortalizing genes into mesenchymal cells when neural cells are cocultured with mesenchymal cells; (7) a method for long-term cell expansion, and a method for regulating cell differentiation, which involve introducing immortalizing genes into mesenchymal cells when endocrine cells are cocultured with mesenchymal cells; and (8) an examination method and a therapy using immortalized cells or cells subjected to modification such as expansion or differentiation using immortalized cells.
The present invention further encompasses an in vitro assay using immortalized, mesenchymal system-related cells, preferably an in vitro assay which is an examination method for evaluating drug efficacy and a kit for this in vitro assay. The present invention further encompasses methods for analyzing the pathological conditions of diseases, diagnostic methods, therapies, blood transfusion therapies, therapies for the cardiovascular system, therapies for bone, cartilage, tendon, skeletal muscle, and adipose tissue, therapies for nervous diseases, therapies for endocrine diseases, therapies for ischemic heart diseases and arteriosclerosis obliterans, therapies for osteoarthritis, rheumatic arthropathy, injury, intractable bone/cartilage defects, and therapies for neurodegenerative diseases, dementia, cerebrovascular disorder and nerve injury.
Immortalized cells (cell immortalization) in the present invention refer to cells that can continuously expand even after cell division has been repeated a certain number of times. Normal cells cease their expansion after repeating cell division for a particular number of times.
An immortalizing gene in the present invention refers to a telomerase or a gene that regulates the expression or the activity of telomerase. Preferably, a human telomerase can be used. Further, for example, the myc gene is said to enhance telomerase activity.
Any known various methods can be used for introducing immortalizing genes into mesenchymal system-related cells such as stromal cells or mesenchymal stem cells. Examples of such methods that can be used herein include a transformation method, which incorporates an immortalizing gene into a plasmid vector, introducing the vector into mesenchymal cells such as stromal cells, mesenchymal stem cells or the like in the presence of calcium-phosphate; an introduction method, which introduces an immortalizing gene together with a liposome-like vesicle into mesenchymal cells or mesenchymal stem cells through contact with these cells; an introduction method, which involves eletroporation in the presence of immortalizing genes; and an introduction method, which incorporates immortalizing genes into various virus vectors, and allowing mesenchymal cells, mesenchymal stem cells or the like to be infected with these virus vectors.
Examples of introduction methods using a virus vector include methods using a retrovirus, an adenovirus, or an adeno-associated virus. One example of such a method uses the MoMLV virus as a retrovirus vector. Preferably, the pBabe vector can be used.
Furthermore, when immortalized cells are returned into a patient, it is considered safer to previously remove a foreign gene such as an immortalizing gene or the like insofar as is possible. Such an immortalizing gene that has been introduced into a cell can be removed by previously established techniques. For example, preferably, a technique that can be used herein involves specifically removing an immortalizing gene placed between loxP sequences or loxP-like sequences by treatment with recombinase such as Cre recombinase.
The mesenchymal system-related cell refers to mesenchymal stem cells, mesenchymal cells, precursor cells of mesenchymal cells or a cell that is derived from mesenchymal cells.
The mesenchymal stem cell refers to, for example, a stem cell that can be obtained from bone marrow, peripheral blood, skin, hair root, muscle tissue, endometrium, blood, or cord blood, and also from the product of primary culturing of various tissues. Further, it is also known that the mesenchymal stem cells can also be isolated from ES cells or teratoma cells. Examples of stem cells include totipotent stem cells that have totipotency and are capable of differentiating into all the types of cells, and stem cells having pluripotency that can differentiate into the tridermal lineage as fetal stem cells can do, but having limited capability of differentiating into extraembryonic trophoblasts. Examples of stem cells further include multipotent stem cells that can differentiate into many cells of a tissue. Mesenchymal stem cells are known to undergo the transplanted site-specific differentiation. When mesenchymal stem cells are transplanted in the abdominal cavity of a sheep embryo, it is known that the cells differentiate into cartilage in cartilage tissue, skeletal muscle in skeletal muscle tissue, cardiac muscle in the heart, adipocytes in adipose tissue, and interstitial cells in the thymus or the bone marrow. Thus, mesenchymal stem cells are thought to be pluripotent. Because of such a property, it is considered that if a sufficient number of mesenchymal stem cells can be cultured, damaged tissues or organs can be regenerated by transplanting such mesenchymal stem cells so as to cause local differentiation of the cells. A preferred example of the mesenchymal stem cell is a stem cell that is obtained from interstitial cells attached to the bottom surface of a culture dish after primary culturing of bone marrow.
The precursor cells of mesenchymal cells refer to cells in the process of differentiation from mesenchymal stem cells to mesenchymal cells.
Mesenchymal cells differentiate from mesenchymal stem cells. Mesenchymal cells cannot undergo multidirectional differentiation as stem cells can do, but are capable of differentiating in a given direction and are capable of expanding. Under normal conditions, mesenchymal cells stay at phase G0, but can shift to phase G1 (initiation of division) when stimulated. Examples of mesenchymal cells include stromal cells and cells having the properties of stromal cells. Mesenchymal cells are present in every organ including subcutaneous tissue, lungs, liver, and mesenchymal tissue such as bone, cartilage, fat, tendon, skeletal muscle and the stroma of bone marrow.
Examples of cells derived from mesenchymal cells include (1) cells of the cardiovascular system such as endothelial cells or cardiac muscle cells or the precursor cells of the cells of the cardiovascular system, and cells having the properties of these cells; (2) cells of any one of bone, cartilage, tendon and skeletal muscle, the precursor cells of the cells of any one of bone, cartilage, tendon, skeletal muscle and adipose tissue, and the cells having the properties of these cells; (3) neural cells or the precursor cells of neural cells, and the cells having the properties of these cells; (4) endocrine cells or the precursor cells of endocrine cells, and the cells having the properties of these cells; (5) hematopoietic cells or the precursor cells of hematopoietic cells, and the cells having the properties of these cells; and (6) hepatocytes or the precursor cells of hepatocytes, and the cells having the properties of these cells.
Substances derived from immortalized cells refer to, for example, soluble cytokines and the like contained in a conditioned medium, adhesion molecules that are supplied by contact with cells and insoluble cytokine ligands. The expansion and differentiation of cells can be regulated by coculturing with these substances.
Examples of soluble cytokines include soluble SCF (kit ligand), flt3 ligand, thrombopoietin (TPO) and erythropoietin (EPO) in addition to insulin-like growth factor (IGF), various interleukins (interleukin-1, interleukin-2, interleukin-3, interleukin-12, interleukin-15, interleukin-18 and the like), various interferons, various factors to regulate expansion and differentiation (FGF, fibroblast growth factor; BDNF, brain derived neurotrophic factor; CNTF, ciliary neurotrophic factor; EGF, epidermal growth factor; G-CSF, granulocyte colony stimulating factor; GM-CSF, granulocyte/macrophage colony stimulating factor; M-CSF, macrophage colony stimulating factor; NGF, nerve growth factor; NT-3, Neurotrophin-3; NT-4, Neurotrophin-4; OSM, Oncostatin M; PDGF, platelet derived growth factor; TGFalpha, transforming growth factor alpha; TGFbeta, transforming growth factor beta; a secretory TNF family molecule group including a secretory CD40 ligand and the like, VEGF, vascular endothelial growth factor; Angiopoietin-1; Angiopoietin-2; PGF, placental growth factor/placenta-derived growth factor; and the like), and various chemokines (interleukin-8; RANTES; MIF, migration inhibitory factor; and MIP-1alpha and macrophage inflammatory protein-1alpha).
Examples of so-called adhesion molecules and extracellular matrix acting on contact with cells include the integrin family, the cadherin family, the immunoglobulin superfamily, the selectin family, collagen (types I to XVI), fibronectin, elastin, the laminin group, osteocalcin, osteonectin, osteopontin, tenascin, thrombospondin, vitronectin and cartilage matrix protein.
Examples of insoluble cytokine ligands include a membrane-bound SCF (kit ligand), a membrane-bound CD40 ligand, and a membrane-bound TNF family molecule group containing TNF and the like.
Further, the present invention enables differentiation of mesenchymal stem cells into bone, cartilage and adipose tissue by immortalizing the cells and then employing appropriate conditions for inducing the differentiation of the cells. This is useful for intractable bone fracture and arthropathy. Stem cells are expanded by immortalizing the cells, so that it becomes possible to secure a number of the stem cells sufficient for treatment, and thus to use the cells practically.
The present invention further encompasses the construction of an artificial cell construct of cardiovascular system, artificial bone, artificial cartilage, artificial tendon, artificial skeletal muscle or artificial adipose tissue by coculturing the precursor cells of cardiovascular cells, bone, cartilage, skeletal muscle or adipose tissue with immortalized, mesenchymal system-related cells including mesenchymal stem cells, mesenchymal precursor cells, mesenchymal cells or cells derived from mesenchymal cells.
The present invention further encompasses the construction of a cell group that is part of the nervous system or a cell group coexisting in the nervous system, whose expansion or differentiation can be regulated, and the construction of a cell group that is part of the endocrine tissue or a cell group coexisting in the endocrine tissue, whose expansion or differentiation can be regulated by coculturing precursor cells of the nervous system or the same of the endocrine system with immortalized and mesenchymal system-related cells including mesenchymal stem cells, precursor cells of the mesenchymal cells and mesenchymal cells and cells derived from mesenchymal cells.
In addition, examples of the precursor cells of cardiovascular cells include the precursor cells of cardiac muscle derived from the heart tissue, myoblasts derived from skeletal muscle, vascular endothelial cell precursor cells in peripheral blood or bone marrow and angioblasts.
Examples of hematopoietic stem cells include a cell group containing hematopoietic stem cells in peripheral blood or bone marrow, and particularly CD34+ cells, a cell group containing hematopoietic stem cells of cord blood, and particularly CD 34+ cells, or hematopoietic stem cells derived from ES cells and CD 34+ cells.
Examples of “cells having the properties of the precursor cells of the cells of any one of bone, cartilage, tendon, skeletal muscle and adipose tissue” include osteoblasts, osteoclast-related cells, chondroblasts, myoblasts derived from skeletal muscle and adipose tissue-related cells.
Examples of “a cell group that is part of the nervous system or coexisting in the nervous system” include nerve stem cells, neurocytes, glial precursor cells, glia cells, and neurocytes forming retina and neural precursor cells.
Examples of “a cell group that is part of the endocrine tissue or a cell group coexisting in the endocrine tissue” include islets of Langerhans cells or the precursor cells thereof, and adrenal cells or the precursor cells thereof.
Further, the present invention also encompasses the fact that artificial bone marrow can be constructed by coculturing immortalized stromal cells with hematopoietic cells such as cord blood-derived CD34 positive cells.
1. Collection of the primary stromal cells Mononuclear cells were isolated from 10 ml of bone marrow fluid that had been obtained from the ilium of a healthy adult man. After the mononuclear cells were cultured overnight, cells attached to a flask were used as stromal cells.
2. A gene encoding the catalytically active subunit (hTERT) of human telomerase was used as a gene to be transduced into a stromal cell. The sequence of hTERT is described in, for example, Science 277, pp. 955-959. Further, an ras gene and an SV40T gene that are known as genes relating to cell canceration were also transduced into stromal cells.
3. Vector to be used for transduction into stromal cells (
4. Preparation of retrovirus-producing cells and infection by the virus using the same were performed according to “A Separate Volume of Experimental Medicine, The Protocol Series, Experimental Protocols for Gene Introduction & Expression Analysis (ed., Izumi SAITOH and Sumio KANNO, YODOSHA, pp. 58-62).”
Specifically, using BOSC23 packaging cells (Proc. Natl. Acad. Sci. USA, 90: 8392-8396, 1993), ? CRIP packaging cells (Proc. Natl. Acad. Sci. USA, 90: 3539-3543, 1993) were prepared as described below.
4-1. Preparation of Recombinant Retrovirus Vector-Producing Cells
(i) 5.5×10′ BOSC23 cells were inoculated on a 10 cm dish at 18 to 24 hours before transfection.
(ii) 800 μl of OPTI-MEM (Gibco/BRL) was added gently to 15 μg of DNA (retrovirus vector), and then agitated, thereby preparing solution A.
(iii) 750 μl of OPTI-MEM was collected in a sterilized tube. 50 μl of LIPOFECTAMINE (2 mg/ml Gibco/BRL) was added to the tube, and then slowly mixed, thereby preparing solution B.
(iv) Solution A was gently mixed with solution B to prepare solution C. Solution C was allowed to stand at room temperature for 30 to 45 minutes.
(v) BOSC23 cells were washed once with a medium at 37° C. from which an antibiotic agent and FBS had been removed.
(vi) Solution C (1.6 ml) was added gently to BOSC23 cells.
(vii) 2.4 ml of OPTI-MEM was further added.
(viii) Incubation was performed for 5 hours under 5% CO2.
(ix) 4 ml of DMEM containing 20% fetal calf serum was added, and then incubation was performed overnight.
(x) The medium was exchanged with a medium at 37° C. containing 10% fetal calf serum, and 1 to 2×106? CRIP packaging cells were inoculated on the 10 cm dish at the same time.
(xi) 24 hours later, the medium of BOSC23 cells was passed through a 0.45 or 0.20 μm syringe filter. The medium of ? CRIP was exchanged with a 5 ml of the filtered medium. At the same time, polybrene (Hexadimethrine Bromide, SIGMA H-9268) was added to 8 μg/ml.
(xii) After 4 to 24 hours of culture, 5 ml of a medium was added, followed by overnight culture.
(xiii) Drug selection was performed, so that the retrovirus-producing ? CRIP cells were prepared.
Next, the 3 above types of vectors were separately expanded by retrovirus-producing cells (? CRIP/P131), and then transduced (infection) into stromal cells as described below (
First, on the day before infection, stromal cells were re-inoculated to a 5×104 cell/10 cm dish, and then cultured after exchanging the medium of retrovirus-producing ? CRIP/P131, that is, 10% bovine serum-containing DMEM, with a 12.5% inactivated equine serum and 12.5% inactivated fetal calf serum/2-Mercaptoethanol/hydrocortisone-containing a-MEM medium. On that day, the culture supernatant was passed through a 0.20 μm filter, and then polybrene was added for a final concentration of 8 μg/ml. The recombinant retrovirus vector produced in the supernatant was then allowed to infect stromal cells. 4 hours later, the culture supernatant was exchanged with a new medium, followed by 2 days of culture. Subsequently, pBABE-hygro-hTERT was subjected to 5 days of drug selection using hygromycin (100 μg/ml), pBABE-puro-rasV12 was subjected to 5 days of drug selection using puromycin (1 μg/ml), and pMFG-tsT-IRES-neo was subjected to 5 days of drug selection using G418 (1 mg/ml).
Cells were infected using combinations of 3 types of retrovirus vectors; (1) control; (2) pBABE-hygro-hTERT vector only; (3) pMFG-tsT-IRES-neo vector only; (4) pBABE-puro-ras-V12 vector only; (5) 2 types of vectors, pMFG-tsT-IRES-neo and pBABE-hygro-hTERT; (6) 2 types of vectors, pBABE-puro-ras-V12 and pBABE-hygro-hTERT; (7) 2 types of vectors, pMFG-tsT-IRES-neo and pBABE-puro-ras-V12; and (8) 3 types of vectors, pBABE-puro-ras-V12 and pMFG-tsT-IRES-neo and pBABE-hygro-hTERT.
In addition, these viruses and cells are kept under conditions such that they are ready for subdivision at anytime after obtaining a patent.
When X-gal staining was performed for cells infected with pMFG-lacZ, staining was confirmed for approximately 3% of stromal cells.
Cell expansion after the drug selection was examined. Primary stromal cells (Primary) expanded for 43 days, and then ceased division with a generation number of 11 (PD (population doubling)=11).
SV40T-transduced cells and ras-transduced cells both showed a higher division rate than that of the primary cells (primary), but ceased division on day 102 with a generation number of 67 (PD=67), and on day 61 with a generation number of 41 (PD=41), respectively. In contrast, hTERT-transduced cells were maintaining their division rate and can be subcultured, even now, after a lapse of 550 days and beyond a generation number of 80 (PD=80) (
Next, mixed infection of SV40T and ras was studied. First, SV40T/ras ceased division on day 109 with a generation number of 68 (PD=68), which was almost the same behavior as that of the case of SV40T alone (
Further, SV40, ras and SV40T/ras, respectively having hTERT gene transduced therein, were studied (
Cases other than that wherein hTERT gene was transduced alone were all contact inhibition-free, and in particular, ras-transduced stromal cells showed expansion also in a vertical direction.
To morphologically observe these stromal cells, May-Giemsa staining was performed (
To confirm the expression of hTERT gene transduced into a target cell and the generation of hTERT activity, telomerase activity was examined using a Telo Chaser of TOYOBO.
Telomerase activity was measured according to the protocols of Telo Chaser (TOYOBO) using Hela samples attached to the kit as a positive control. Telomerase was extracted respectively from stromal cells, hTERT gene-transduced stromal cells, and Hela cells that had been isolated by a method similar to that of Example 1. Using telomerase extracted from each type of cells, and telomerase heat-treated at 70° C. for 10 minutes after extraction from hTERT gene-transduced stromal cells, a reaction to add telomeric repeats to a substrate primer was performed, PCR was performed using reverse primers, and then polyacrylamide gel electrophoresis was performed for visualization.
Further, telomere length was measured using a Telo TAGGG telomere length assay (Roche Molecular Biochemicals, Sandhofer, Germany). In sum, the genomic DNA was denatured using restriction enzymes, Rsa I and Hinf I, and then isolated by 0.8% agarose gel. DNA was transferred to a nylon membrane using a capillary. Hybridization was performed using a telomere-specific probe labeled with digoxigenin.
Telomerase activity was then measured, and then the telomere lengths of hTERT-stromal cells were measured for a long period (
(1) Study of Surface Antigen
Bone-marrow fluid was collected from the ilia of NK and KY of healthy individuals by bone marrow aspiration, and then mononuclear cells were separated by densimetric centrifugation. The obtained cells were cultured overnight, and then on the next day the cells attached to the flask were used as primary stromal cells.
Similar to Example 1, hTERT gene was transduced into a stromal cell using pBABE-hygro-hTERT.
Primary stromal cells and hTERT gene-transduced stromal cells were subjected to the expression analysis of cell surface antigens using FACS. The antibodies used herein were: CD45, CD9, CD105 (SH2), CD73 (SH3), CD166 (ALCAM) and CD157 (BST-1). Data collection and analysis were performed using Cell Quest. CD45 and CD9 were obtained from Immunotech, Marseille, France; CD166 (ALCAM) was obtained from Antigenix America, Huntington, USA; CD105 was obtained from Ancell, Bayport, USA; CD73 (SH-2) was obtained from Alexis biochemicals; and CD157 (BST-1) was obtained from MBL, Nagoya, Japan.
As shown in
(2) Chromosome Type
When karyotyping of hTERT gene-transduced stromal cells (used in (1) above) was performed, the chromosome number was 46 (normal), and neither deletion nor translocation of chromosomes was observed.
(3) Expression of Cytokine
The expression of cytokines produced from stromal cells was studied at the mRNA level. RNA was extracted from the cells, and then cDNA was prepared using reverse transcriptase. PCR was performed for the cytokines TPO, SCF, FL and M-SCF using the cDNA as a template and primers corresponding to the cytokines. Band amplification was confirmed by agarose gel electrphoresis. The expression of the 4 above types of cytokines was observed for both types of the cells (
The supporting capacity of the blood stem cells of stromal cells that had been subjected to gene introduction similar to Example 1 was first verified by colony assay. Gene introduction was performed using the same vector as used in Example 1 under the conditions of (2), (3), (5), (6), (7) and (8) for the infection with retrovirus vectors in Example 1. Specifically, the cells (primary stromal cells) stored at the time of bone marrow collection were used as control, and the cells were infected with retroviruses, followed by the drug selection. The thus obtained stromal cells having 1 to 3 types of genes transduced therein were cultured for 3 months.
The stromal cells infected with retroviruses were inoculated again in a 25 cm2 flask. When the cells reached subconfluence, they were irradiated with 21 to 22 Gy to arrest cell growth. Then the medium of the stromal cells was removed. Next, removal was repeated after the addition of X-VIVO10, so that serum contained in the stromal medium was removed. Then X-VIVO 10 supplemented with TPO (50 ng/ml), FL (50 ng/ml) and SCF (10 ng/ml) were added, and then 5×103 CD34+ cord blood cells that had been previously put in X-VIVO 10 (with TPO (50 ng/ml), FL (50 ng/ml) and SCF (10 ng/ml)) was added. Thus, in the presence of CD34+ cord blood cells, coculture was performed for 2 weeks with the stromal cells that had been subjected to transduction using the vector. The culture supernatant was collected, and then 2×103 cells were used for colony assay. 2 weeks later, colonies were counted. The results are shown in Table 1 below.
Among the cocultured stromal cells, colony assay could be performed only for the control (primary stromal cells) and stromal cells having only the hTERT gene transduced therein. Culturing of the remainder could not be continued because the stromal cells came off the culture plates during the coculture. The cell death may be caused by apoptosis due to radiation exposure or failure in suppression of growth. Cicuttini et al. reported that the expansion of SV40 T gene-transduced stromal cells could not be regulated by radiation exposure (Blood, 80: 1992, 102-112).
The amplification rates of the number of colonies in the cases of control and transduction of the hTERT gene alone were 22.3-fold and 14.8-fold, respectively. From the results, it was confirmed that hTERT possesses to some degree a capacity for supporting blood stem cells even after 3 months of culture, and even the established stromal cells can be cocultured.
Next, to confirm reproducibility, 5×103 CD34+ cord blood cells were added, and then cultured using a serum-free medium of X-VIVO 10 supplemented with 50 ng/ml TPO, 50 ng/ml FL and 10 ng/ml SCF. On day 7, the same medium was added again, and then coculture was performed again. From week 2, only the suspended cells were collected (cells that had gotten into the stromal cells were not collected). After that time, cells were collected every week, and a study was conducted as described above until week 8 concerning total cell number, number of CD34+ cells, number of colonies formed (CFU-C), number of immature colonies (CFU-Mix), granulocytic cell colonies and erythroblastic cell colonies. The results are shown in FIGS. 12 to 14.
Furthermore, comparison was made among a case involving the absence of stromal cells, and cases involving stromal cell hTERT 2 and hTERT3 that had been established by transducing hTERT gene into stromal cells collected from other healthy individuals. The results are shown in
Each stromal cell having hTERT-transduced therein showed slight differences depending on the samples, but showed, until day 35, in vitro expansion in total cell number, CD34+ cell and CFU-C.
Next, differentiation of mesenchymal stem cells having capability of both differentiation into bone, cartilage, muscle and the like, and autoreproduction was studied, as was the supporting capacity of blood stem cells.
Bone marrow aspiration was performed for the ilia of healthy individuals, and then mononuclear cells were collected by densimetric centrifugation. The obtained cells were cultured overnight in a 10% inactivated fetal calf serum-containing DMEM. From the next day, the adherent cells were cultured. 2 weeks later, the cells collected using T-E (trypsin-EDTA) were cryopreserved as primary mesenchymal stem cells. Subsequently, the hTERT gene was transduced into the cells similar to Example 1. Next, growth curve was compared between the primary mesenchymal stem cells and hTERT gene-transduced immortalized mesenchymal stem cells. The results are shown in
Next, it was studied whether the prepared mesenchymal stem cells possess pluripotency.
(1) First, differentiation into adipocytes (adipogenesis) was induced using 1 μM dexamethazone, 60 μM indomethacine, 0.5 μM 3-isobutyl-1-methylxanthine (isobutylmethylxanthine) and 5 μg/ml insulin. After approximately 1 week of culture, the cells were stained with Oil Red 0 stain (the fatty drop is red).
(2) Subsequently, cartilage differentiation (chondrogenesis) was induced using 1 μM dexamethazone, 50 μg/ml ascorbate-2-phosphate, 6.25 μg/ml insulin, 6.25 μg/ml transferrin, 5.35 μg/ml selenic acid, 1.25 mg/ml linoleic acid and 10 ng/ml TGF-β. After 2 to 3 weeks of culture, the cells were stained with Alcian blue. Chondroitin within the stained (frozen sections) cartilage matrix was stained blue.
(3) Furthermore, bone differentiation (osteogenesis) was induced using 1 μM dexamethazone, 50 μM ascorbate-2-phosphate and 10 mM β-glycerophosphate. After 2 to 3 weeks of culture, the cells were stained with von Kossa stain (mineral deposition).
The results are shown in
Supporting capacity for blood cells was studied by exchanging a medium of mesenchymal stem cells that had been collected and immortalized by a method similar to that of Example 5 with a medium for supporting cells.
After the medium of the mesenchymal stem cells (10% inactivated fetal calf serum-containing DMEM) was exchanged with the medium of supporting cells (stromal cells) (composition: 12.5% inactivated fetal calf serum, 12.5% inactivated equine serum, 1×10−6 M hydrocortisone and 10−4 M 2-ME-containing a-MEM medium), coculture with cord blood CD34 positive cells was performed. On day 7 after the coculture, macroscopic observation was performed. In
Stromal cells that had been immortalized by transducing hTERT gene in the manner similar to Example 1 were inoculated in a 25 cm2 flask. When the cells reached subconfluence, the cells were subjected to 21 to 22 Gy X-radiation so as to stop cell expansion.
5×103 CD34+ cord blood cells were cocultured with stromal cells in the presence of TPO (50 ng/ml), FL (50 ng/ml) and SCF (10 ng/ml) for 2 weeks or 4 weeks, so that hematopoietic precursor-stem cells were amplified (stem cell amplification phase). Hemocytes amplified on the stroma were collected, the number of the cells was counted and the proportion of Glycophorin A (GPA) positive cells was analyzed by flow cytometry.
The total number of cells collected on day 14 of the stem cell amplification phase was 2×106. The cells could be amplified to a number approximately 400-fold greater than the cell number of 5000 (before amplification). Among these cells, the proportion and the number of GPA positive cells, the markers for erythroblasts, were 22.9% and 2.9×104, respectively. On day 28 of the stem cell amplification phase, the yield was as high as the total cell number of 3.6×106, and the proportion and the number of GPA positive cells were 2.0% and 6.1×103, respectively.
The amplified 5×103 hematopoietic precursor-stem cells were cultured for 8 days in a medium for inducing differentiation: (1) Erythropoietin (EPO) induction medium (composition: X-VIVO 10, 500 μg/ml diferric transferrin, 1% deionized bovine serum albumin (BSA) and 2 U/ml EPO) or (2) Erythropoietin in combination with stem cell factor (SCF) medium (composition: X-VIVO 10, 500 μg/ml diferric transferrin, 1% deionized bovine serum albumin (BSA), 2 U/ml EPO and SCF 10 ng/ml) so as to induce erythroblast production (erythroblast induction phase).
The thus obtained erythroblasts were analyzed by flow cytometry involving photomicroscopic images of the inside of the culture dish, smears, total cell number and GPA positive cell proportion.
Findings of Erythroblast by May-Giemsa Staining
Further erythroblast induction using erythrpoietin alone or using both erythropoietin and SCF is described in the following references:
1. Shintani N, Niitsu Y. et al. Expression and extracellular release of transferrin receptors during peripheral erythroid progenitor cell differentiation in liquid culture. Blood, 83. 1994:1209-1215.
2. Kapur R., Zhang L. et al. A novel mechanism of cooperation between c-Kit and erythropoietin receptor. Stem cell factor induces the expression of Stat5 and erythropoietin receptor, resulting in efficient proliferation and survival by erythropoietin. J Biol Chem 276 2001: 1099-1106.
(1) Method:
CD34 positive cells were separated from cord blood using a MACS separation kit (Miltenyi Biotec). Differentiation and expansion into erythrocytes involved 3 steps. In the 1st phase (days 0 to 14), CD34 positive cells were suspended at a concentration of 5×103/3 ml together with immortalized stromal cells that had reached confluence in a medium of X-VIVO10 supplemented with Stem Cell Factor (SCF) 10 ng/ml, Thrombopoietin (TPO) 50 ng/ml and Flt-3/Flk-2 Ligand (FL) 50 ng/ml in a 25 cm2 flask. Then the cells were cultured for 14 days. On day 7, 3 ml of a medium with a composition the same as that described above was added. In the 2nd phase (days 14 to 28), the cells were suspended at a concentration of 1×105/3 ml in a medium of X-VIVO10 supplemented with 1% deionized bovine serum albumin, divalent iron-transferrin 500 μg/ml, 2% human AB type serum, SCF 100 ng/ml, IL-3 10 ng/ml and EPO 4 U/ml on a 6-well plate. Then liquid culture was performed for 14 days. On day 21, 3 ml of a medium with a composition the same as that described above was added. In the 3rd phase (days 28 to 31), the cells were suspended at a concentration of 1×106/3 ml in a medium of X-VIVO10 supplemented with 1% deionized bovine serum albumin, divalent iron-transferrin 500 μg/ml, 2% human type AB serum and EPO 4 U/ml on a 6-well plate. The cells were cocultured with macrophages for 3 days. Macrophages used herein were derived from healthy human peripheral blood monocytes. Specifically, on day 21, peripheral blood was collected from a healthy individual, and monocytes were separated using a Rosette SepTM Antibody Cocktail (StemCell Technologies). The monocytes were suspended at a concentration of 3×105/3 ml in IMDM supplemented with 2% human type AB serum and macrophage colony stimulating factor (M-CSF) 100 ng/ml, and then cultured for 7 days, so as to cause the monocytes to differentiate into macrophages. All of the cells were cultured under conditions of 37° C. and 5% CO2. The cells were collected at each phase, total cell number was counted, and then cell surface character was analyzed by flow cytometry. Further, cytospin samples were prepared, and May-Giemsa staining was performed, so that the cell morphology was observed.
(2) Results:
It was confirmed by the above results that efficient differentiation and expansion of cord blood-derived CD34 positive cells into erythroblastic cells are possible by allowing the cells to expand by 14 days of coculture with immortalized stromal cells (hTERT stromal cell) followed by a further 14 days of liquid culturing in the presence of cytokines containing erythropoietin (EPO), and that efficient production of mature erythrocytes is possible by 3 days of coculture of the obtained erythroblastic cells with macrophages to enucleate the erythroblasts.
(1) Transplantation into NOD/SCID (Nonobese Diabetic/Severe Combined Immunodeficiency) Mice
The mice used for transplantation were 6 to 10-week-old NOD/LtSz-scid (NOD/SCID) mice bred from breeding parents that had been obtained from LShultz (Jackson Laboratory, bay Harbor, Me., USA). All the mice were treated under sterilization, and kept in microisolators. In the presence of TPO, SCF and FL, a primary stromal cell layer or an hTERT-stromal cell layer was cocultured with CB CD34+ cells for 2 to 4 weeks. All the hematopoietic cells (HPCs) that had expanded above and beneath the stromal cell layer were collected. The contamination rate of stromal cells in hematopoietic cells was 0.01% or less under a microscope. Stromal cells can be easily distinguished from hematopoietic cells based on cell size and morphological features under a microscope. The obtained hematopoietic cells were injected via the lateral tail vein of mice irradiated with a dose of 400 cGy. Mononuclear cells were collected from the peripheral blood of a normal volunteer. 5×106 mononuclear cells were then irradiated with a dose of 1500 cGy, and then cocultured as accessory cells with hematopoietic cells.
(2) Study of Engraftment of Transplanted Cells
The mice were sacrificed by cervical dislocation 6 weeks after transplantation, and then the bone marrow and peripheral blood mononuclear cells (as was reported previously) were collected. The presence of human hematopoietic cells was quantitatively determined by (i) detecting using flow cytometry cells that were stained by FITC-anti-human CD45 conjugates, and (ii) detecting a human genome ALU repetitive sequence gene DNA as described below.
Detection of Gene of Human ALU Repetitive Sequence
Genomic DNA was isolated from the bone marrow and peripheral blood mononuclear cells of the transplanted NOD/SCID mice.
As primer sequences, 5′-CACCTGTAATCCCAGCAGTTT-3′ and 5′-CGCGATCTCGGCTCACTGCA-3′ were used. After being denatured at 94° C. for 4 minutes, DNA samples were amplified by repeating 35 times a cycle consisting of 94° C. for 1 minute (denaturation), 55° C. for 45 seconds (annealing) and 72° C. for 1 minute (extension).
The amplified products were visualized by ethidium bromide staining on 2.5% agarose gel electrophoresis as a 221 bp band.
(3) Results
Expansion of SRC (severe combined immunodeficiency (SCID) repopulating cells, SCID-repopulating cells).
As a substitute for the in vivo human stem cell assay used to evaluate the expansion of HSCs (Hematopoietic stem cells, human hematopoietic stem cells), the engraftment of SRC was examined. The pre-cocultured cord blood CD34+ cells or the total expanded HPCs that had been generated from 2 or 4 weeks of coculture with each stromal cell line were transplanted into irradiated NOD/SCID mice. Simultaneously, irradiated, 5×106 peripheral blood mononuclear cells were co-transplanted to roughly adjust the total number of the transplanted cells. Human cells in the bone marrow and peripheral blood of NOD/SCID mice were evaluated by flow cytometry and ALU PCR 6 weeks after transplantation (
Next, surface markers of hematopoietic cells differentiating from SRC that had expanded on hTERT-stromal cells were tested (
Figures are multiples of the initial number of cells.
*P < 0.05 vs. stroma free (n = 4) (Student's t test).
CFU-C indicates Colony-Forming Units in culture, and CFU-Mix indicates Colony-Forming Unit mixed cells.
The results are represented by mean value±standard deviation (n=4).
*P < 0.05, compared with a pre-cocultured group (Mann-Whitney U test).
n.d. shows that hCD45% was lower than the cut-off value (0.1%).
Differentiation from Mesenchymal Stem Cells into Hepatocytes
(1) Method
Mesenchymal stem cells (MSC) were prepared by the method described in Example 5. The mesenchymal stem cells obtained from the primary culture were prepared and subcultured by the method described in Example 5, and then were used in the following experiment at PD4 (at the time period after 4 instances of population doubling) from the primary culture.
Spragne-Dawley (SD) rats (approximately 150 g, 5-week-old male) purchased from CHARLES RIVER JAPAN, INC., were used.
Preparation of Hepatopathy Model and Transplantation of MSC into Liver
From the day before the hepatectomy (day-1), intraperitoneal administration of 10 mg/kg/day of cyclosporin A (CyA, Sandimmun: purchased from Novartis Pharm) to rats was begun. On day 0, partial (⅔) hepatectomy was performed according to a standard method (M. Brues et al J. Exp. Med. 65: 15, 1937), and then MSC (2×106/300 μl) was locally injected using a 23G syringe to the remaining caudate lobe of the liver.
(2) Study of Differentiation into Hepatocyte
On day 10 after hepatectomy, the rats were sacrificed. The liver was fixed by perfusion with 3% paraformaldehyde and embedded in an OTC compound to prepare frozen sections (6 μm). Then the sections were immuno-stained with an anti-human albumin antibody (Sigma, A6684), anti-human AFP antibody (Sigma, A8452), and anti-human CK19 antibody (Sigma, C6930).
(3) Results
On day 10 after locally injecting MSC at PD4 into the remaining liver after the partial (⅔) hepatectomy, the rats were sacrificed. The liver locally injected with MSC cells was excised, fixed, and then stained using an anti-human albumin antibody (Sigma, A6684). The presence of cells showing the expression of human albumin was confirmed in the liver tissue of the normal rat (
These examples demonstrated that under conditions and environment that are sufficiently appropriate for inducing differentiation into liver, such as within the liver tissue of an animal subjected to partial hepatectomy, human mesenchymal stem cells can be efficiently differentiated into mature hepatocytes.
According to the present invention, a number of mesenchymal stem cells or mesenchymal cells that have conventionally been obtained in extremely a small number can be prepared, and mesenchymal cells can be differentiated into various cells. Thus, it becomes possible to implement various tests or therapies that have previously been unable to be performed, because of conventional inavailability of sufficient amount of cells.
For example, the above examples demonstrated that erythroblasts can be collected in large quantities by amplifying stem cells using TERT stromal cells, and then inducing the differentiation using SCF and EPO. Normally, the number of CD34 positive cells obtained from one umbilical cord is as few as approximately 1×105. However, according to the present invention, 0.5 to 1×106 erythroblasts can be produced from 5000 CD34 positive cells. Hence, from 1×105 CD34 positive cells, a yield of around 1 to 2×107 erythroblastic precursor cells can be expected every 2 weeks. This yield is far higher than that obtained from conventional methods. If a sufficient amount of cord blood can be supplied by the method of the present invention, the product obtained by this method has hidden potential to be a new source for blood transfusions. Therefore the present invention is very useful.
This description and the drawings include by reference the contents as disclosed in the description and the drawings of Japanese Patent Application No. 2001-335375 filed with the Japanese Patent Office on Oct. 31, 2001, which is a priority document of the present application.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2001-335375 | Oct 2001 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP02/11389 | 10/31/2002 | WO |
