Allografts Combined with Tissue Derived Stem Cells For Bone Healing

[0001] This application is a continuation of U.S. application Ser. No. 12/612,583, filed Nov. 4, 2009, which claims the benefit under 35 U.S.C. § 119 (e) of U.S. Provisional Patent Application Number 61/116,484, filed Nov. 20, 2008, both of which are hereby incorporated herein by reference in their entireties.

[0002] Regenerative medicine requires an abundant source of human adult stem cells that can be readily available at the point of care.

[0003] Adipose-derived stem cells (ASCs), which can be obtained in large quantities, have been utilized as cellular therapy for the induction of bone formation in tissue engineering strategies.

[0004] Allografts may be combined with stem cells. This requires a significant amount of tissue processing and cellular processing prior to seeding the allograft substrate.

[0005] Allografts seeded with living cells generally provide better surgical results.

[0006] In an embodiment, there is provided a method of combining mesenchymal stem cells with a bone substrate, the method comprising obtaining adipose tissue having the mesenchymal stem cells together with unwanted cells; digesting the adipose tissue to form a cell suspension having the mesenchymal stem cells and the unwanted cells; adding the cell suspension with the mesenchymal stem cells to seed the bone substrate so as to form a seeded bone substrate; culturing the mesenchymal stem cells on the seeded bone substrate for a period of time to allow the mesenchymal stem cells to adhere to the bone substrate; and rinsing the bone substrate to remove the unwanted cells from the bone substrate.

[0007] In another embodiment, there is provided an allograft product including a combination of mesenchymal stem cells with a bone substrate, and the combination manufactured by obtaining adipose tissue having the mesenchymal stem cells together with unwanted cells; digesting the adipose tissue to form a cell suspension having the mesenchymal stem cells and the unwanted cells; adding the cell suspension with the mesenchymal stem cells to seed the bone substrate so as to form a seeded bone substrate; culturing the mesenchymal stem cells on the seeded bone substrate for a period of time to allow the mesenchymal stem cells to adhere to the bone substrate; and rinsing the bone substrate to remove the unwanted cells from the bone substrate.

[0008] In still another embodiment, there is provided a method of combining mesenchymal stem cells with a bone substrate, the method comprising obtaining adipose tissue having the mesenchymal stem cells together with unwanted cells; digesting the adipose tissue to form a cell suspension having the mesenchymal stem cells and the unwanted cells to acquire a stromal vascular fraction, and the digesting includes making a collagenase I solution, and filtering the solution through a 0.2 μm filter unit, mixing the adipose solution with the collagenase I solution, and adding the adipose solution mixed with the collagenase I solution to a shaker flask; placing the shaker with continuous agitation at about 75 RPM for about 45 to 60 minutes so as to provide the adipose tissue with a visually smooth appearance; aspirating a supernatant containing mature adipocytes so as to provide a pellet; adding the cell suspension with the mesenchymal stem cells to seed the bone substrate so as to form a seeded bone substrate; culturing the mesenchymal stem cells on the seeded bone substrate for a period of time to allow the mesenchymal stem cells to adhere to the bone substrate; and rinsing the bone substrate to remove the unwanted cells from the bone substrate.

[0009] In yet another embodiment, there is provided an allograft product including a combination of mesenchymal stem cells with a bone substrate, and the combination manufactured by obtaining adipose tissue having the mesenchymal stem cells together with unwanted cells; digesting the adipose tissue to form a cell suspension having the mesenchymal stem cells and the unwanted cells to acquire a stromal vascular fraction, and the digesting includes making a collagenase I solution, and filtering the solution through a 0.2 μm filter unit, mixing the adipose solution with the collagenase I solution, and adding the adipose solution mixed with the collagenase I solution to a shaker flask; placing the shaker with continuous agitation at about 75 RPM for about 45 to 60 minutes so as to provide the adipose tissue with a visually smooth appearance; aspirating a supernatant containing mature adipocytes so as to provide a pellet; adding the cell suspension with the mesenchymal stem cells to seed the bone substrate by adding the pellet onto the bone substrate so as to form a seeded bone substrate; culturing the mesenchymal stem cells on the seeded bone substrate for a period of time to allow the mesenchymal stem cells to adhere to the bone substrate; and rinsing the bone substrate to remove the unwanted cells from the bone substrate.

[0010] In an embodiment, there is provided a method of combining mesenchymal stem cells with a bone substrate, the method comprising obtaining tissue having the mesenchymal stem cells together with unwanted cells; digesting the tissue to form a cell suspension having the mesenchymal stem cells and the unwanted cells; adding the cell suspension with the mesenchymal stem cells to seed the bone substrate so as to form a seeded bone substrate; culturing the mesenchymal stem cells on the seeded bone substrate for a period of time to allow the mesenchymal stem cells to adhere to the bone substrate; and rinsing the bone substrate to remove the unwanted cells from the bone substrate.

[0011] In another embodiment, there is provided an allograft product including a combination of mesenchymal stem cells with a bone substrate, and the combination manufactured by obtaining tissue having the mesenchymal stem cells together with unwanted cells; digesting the tissue to form a cell suspension having the mesenchymal stem cells and the unwanted cells; adding the cell suspension with the mesenchymal stem cells to seed the bone substrate so as to form a seeded bone substrate; culturing the mesenchymal stem cells on the seeded bone substrate for a period of time to allow the mesenchymal stem cells to adhere to the bone substrate; and rinsing the bone substrate to remove the unwanted cells from the bone substrate.

[0012] In still another embodiment, there is provided a method of combining mesenchymal stem cells with a bone substrate, the method comprising obtaining bone marrow tissue having the mesenchymal stem cells together with unwanted cells; digesting the bone marrow tissue to form a cell suspension having the mesenchymal stem cells and the unwanted cells; adding the cell suspension with the mesenchymal stem cells to seed the bone substrate so as to form a seeded bone substrate; culturing the mesenchymal stem cells on the seeded bone substrate for a period of time to allow the mesenchymal stem cells to adhere to the bone substrate; and rinsing the bone substrate to remove the unwanted cells from the bone substrate.

[0013] In yet another embodiment, there is provided an allograft product including a combination of mesenchymal stem cells with a bone substrate, and the combination manufactured by obtaining bone marrow tissue having the mesenchymal stem cells together with unwanted cells; digesting the bone marrow tissue to form a cell suspension having the mesenchymal stem cells and the unwanted cells; adding the cell suspension with the mesenchymal stem cells to seed the bone substrate so as to form a seeded bone substrate; culturing the mesenchymal stem cells and the bone substrate for a period of time to allow the mesenchymal stem cells to adhere to the bone substrate; and rinsing the bone substrate to remove the unwanted cells from the bone substrate.

[0014] In an embodiment, there is provided a method of combining mesenchymal stem cells with a bone substrate, the method comprising obtaining muscle tissue having the mesenchymal stem cells together with unwanted cells; digesting the muscle tissue to form a cell suspension having the mesenchymal stem cells the unwanted cells; adding the cell suspension with the mesenchymal stem cells to seed the bone substrate so as to form a seeded bone substrate; culturing the mesenchymal stem cells on the seeded bone substrate for a period of time to allow the mesenchymal stem cells to adhere to the bone substrate; and rinsing the bone substrate to remove the unwanted cells from the bone substrate.

[0015] In another embodiment, there is provided an allograft product including a combination of mesenchymal stem cells with a bone substrate, and the combination manufactured by obtaining muscle tissue having the mesenchymal stem cells together with unwanted cells; digesting the muscle tissue to form a cell suspension having the mesenchymal stem cells and the unwanted cells; adding the cell suspension with the mesenchymal stem cells to seed the bone substrate so as to form a seeded bone substrate; culturing the mesenchymal stem cells on the seeded bone substrate for a period of time to allow the mesenchymal stem cells to adhere to the bone substrate; and rinsing the bone substrate to remove the unwanted cells from the bone substrate.

[0016] Other embodiments are also disclosed.

[0024] Unless otherwise described, human adult stem cells are generally referred to as mesenchymal stem cells or MSCs. MSCs are pluripotent cells that have the capacity to differentiate in accordance with at least two discrete development pathways. Adipose-derived stem cells or ASCs are stem cells that are derived from adipose tissue. Stromal Vascular Fraction or SVF generally refers to the centrifuged cell pellet obtained after digestion of tissue containing MScs. In one embodiment, the pellet may include multiple types of stem cells. These stem cells may include, for example, one or more of hematopoietic stem cells, epithelial progenitor cells, and mesenchymal stem cells. In an embodiment, mesenchymal stem cells are filtered from other stem cells by their adherence to a bone substrate, while the other stem cells (i.e., unwanted cells) do not adhere to the bone substrate. Other cells that do not adhere to the bone substrate may also be included in these unwanted cells.

[0025] Adipose derived stem cells may be isolated from cadavers and characterized using flow cytometry and tri-lineage differentiation (osteogenesis, chondrogenesis and adipogenesis) may be performed in vitro. The final product may be characterized using histology for microstructure and biochemical assays for cell count. This consistent cell-based product may be useful for bone regeneration.

[0026] Tissue engineering and regenerative medicine approaches offer great promise to regenerate bodily tissues. The most widely studied tissue engineering approaches, which are based on seeding and in vitro culturing of cells within the scaffold before implantation, is the cell source and the ability to control cell proliferation and differentiation. Many researchers have demonstrated that adipose tissue-derived stem cells (ASCs) possess multiple differentiation capacities. See, for example, the following, which are incorporated by reference:

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[0056] Additionally, adipose tissue is probably the most abundant and accessible source of adult stem cells. Adipose tissue derived stem cells have great potential for tissue regeneration. Nevertheless, ASCs and bone marrow-derived stem cells (BMSCs) are remarkably similar with respect to growth and morphology, displaying fibroblastic characteristics, with abundant endoplasmic reticulum and large nucleus relative to the cytoplasmic volume. See, for example, the following, which are incorporated by reference:

• • [0057] Gimble, J. and F. Guilak, Adipose-derived adult stem cells: isolation, characterization, and differentiation potential. Cytotherapy, 2003. 5(5): p. 362-9.
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  • [0062] Kim, Y., et al., Direct comparison of human mesenchymal stem cells derived from adipose tissues and bone marrow in mediating neovascularization in response to vascular ischemia. Cell Physiol Biochem, 2007. 20(6): p. 867-76.
  • [0063] Lin, L., et al., Comparison of osteogenic potentials of BMP4 transduced stem cells from autologous bone marrow and fat tissue in a rabbit model of calvarial defects. Calcif Tissue Int, 2009. 85(1): p. 55-65.
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[0068] Other common characteristics of ASCs and BMSCs can be found in the transcriptional and cell surface profile. Several studies have already been done in the field of bone tissue engineering using ASCs. See, for example, the following, which are incorporated by reference:

[0069] Rada, T., R. L. Reis, and M. E. Gomes, Adipose Tissue-Derived Stem Cells and Their Application in Bone and Cartilage Tissue Engineering. Tissue Eng Part B Rev, 2009.

[0070] Tapp, H., et al., Adipose-Derived Stem Cells: Characterization and Current Application in Orthopaedic Tissue Repair. Exp Bioi Med (Maywood), 2008.

[0071] Tapp, H., et al., Adipose-derived stem cells: characterization and current application in orthopaedic tissue repair. Exp Bioi Med (Maywood), 2009. 234(1): p. 1-9.

[0072] De Girolamo, L., et al., Human adipose-derived stem cells as future tools in tissue regeneration: osteogenic differentiation and cell-scaffold interaction. Int J Artif Organs, 2008. 31(6): p. 467-79.

[0073] Di Bella, C., P. Farlie, and A. J. Penington, Bone regeneration in a rabbit critical-sized skull defect using autologous adipose-derived cells. Tissue Eng Part A, 2008. 14(4): p. 483-90.

[0074] Grewal, N. S., et al., BMP-2 does not influence the osteogenic fate of human adipose-derived stem cells. Plast Reconstr Surg, 2009. 123(2 Suppl): p. 158S-65S.

[0075] Li, H., et al., Bone regeneration by implantation of adipose-derived stromal cells expressing BMP-2. Biochem Biophys Res Commun, 2007. 356(4): p. 836-42.

• • [0076] Yoon, E., et al., In vivo osteogenic potential of human adipose-derived stem cells/poly lactide-co-glycolic acid constructs for bone regeneration in a rat critical-sized calvarial defect model. Tissue Eng, 2007. 13(3): p. 619-27.

[0077] These studies have demonstrated that stem cells obtained from the adipose tissue exhibit good attachment properties to most of the material surfaces and the capacity to differentiate into osteoblastic-like cells in vitro and in vivo. Recently it has been shown that ASCs may stimulate the vascularization process. See, for example, the following, which are incorporated by reference:

• • [0078] Butt, O. I., et al., Stimulation of peri-implant vascularization with bone marrow-derived progenitor cells: monitoring by in vivo EPRoximetry. TissueEng, 2007. 13(8): p. 2053-61.
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[0080] Demineralized bone substrate, as an allogeneic material, is a promising bone tissue-engineering scaffold due to its close relation to autologous bone in terms of structure and function. Combined with MSCs, these scaffolds have been demonstrated to accelerate and enhance bone formation within osseous defects when compared with the matrix alone. See, for example, the following, which are incorporated by reference:

• • [0081] Chen, L. Q., et al., [Study of MSCs in vitro cultured on demineralized bone matrix of mongrel]. Shanghai Kou Qiang Yi Xue, 2007. 16(3): p. 255-8.
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  • [0090] Xie, H., et al., The performance of a bone-derived scaffold material in the repair of critical bone defects in a rhesus monkey model. Biomaterials, 2007.28(22): p. 3314-24.
  • [0091] Liu, G., et al., Tissue-engineered bone formation with cryopreserved human bone marrow mesenchymal stem cells. Cryobiology, 2008. 56(3): p. 209-15.
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[0094] As discussed herein, human ASCs seeded bone substrates may be characterized in terms of microstructure, cell number and cell identity using histology, biochemical assay and flow cytometry. In an embodiment, these substrates may include bone material which has been previously subjected to a demineralization process.

[0095] FIG. 1 is a flow chart of a process for making an allograft with stem cells product. In an embodiment, a stromal vascular fraction may be used to seed the allograft. It should be apparent from the present disclosure that the term “seed” relates to addition and placement of the stem cells within, or at least in attachment to, the allograft, but is not limited to a specific process. FIG. 2 illustrates a pellet of the stromal vascular fraction containing the desired stem cells.

[0096] In an exemplary embodiment, a method of combining mesenchymal stem cells with a bone substrate is provided. The method may include obtaining adipose tissue having the mesenchymal stem cells together with unwanted cells. Unwanted cells may include hematopoietic stem cells and other stromal cells. The method may further include digesting the adipose tissue to form a cell suspension having the mesenchymal stem cells and at least some or all of the unwanted cells. In another embodiment, this may be followed by negatively depleting some of the unwanted cells and other constituents to concentrate mesenchymal stem cells.

[0097] Next, the method includes adding the cell suspension with the mesenchymal stem cells to the bone substrate. This may be followed by culturing the mesenchymal stem cells and the bone substrate for a period of time to allow the mesenchymal stem cells to adhere to the bone substrate. In order to provide a desired product, the method includes rinsing the bone substrate to remove the unwanted cells from the bone substrate.

[0098] In one embodiment, an allograft product may include a combination of mesenchymal stem cells with a bone substrate such that the combination is manufactured by the above exemplary embodiment.

[0099] In an embodiment, the adipose tissue may be obtained from a cadaveric donor. A typical donor yields 2 liters of adipose containing 18 million MSCs. In one embodiment, a bone substrate may be from the same cadaveric donor as the adipose tissue. In another embodiment, the adipose tissue may be obtained from a patient. In addition, both the bone substrate and the adipose tissue may be obtained from the same patient. This may include, but is not limited to, removal of a portion of the ilium (e.g., the iliac crest) may be removed from the patient by a surgical procedure and adipose cells may be removed using liposuction. Other sources, and combination of sources, of adipose tissue, other tissues, and bone substrates may be utilized.

[0100] Optionally, the adipose tissue may be washed prior to or during digestion. Washing may include using a thermal shaker at 75 RPM at 37° C. for at least 10 minutes. Washing the adipose tissue may include washing with a volume of PBS substantially equal to the adipose tissue. In an embodiment, washing the adipose tissue includes washing with the PBS with 1% penicillin and streptomycin at about 37° C.

[0101] For example, washing the adipose tissue may include agitating the tissue and allowing phase separation for about 3 to 5 minutes. This may be followed by aspirating off an infranatant solution. The washing may include repeating washing the adipose tissue multiple times until a clear infranatant solution is obtained. In one embodiment, washing the adipose tissue may include washing with a volume of growth media substantially equal to the adipose tissue.

[0102] In another exemplary embodiment, a method of combining mesenchymal stem cells with a bone substrate is provided. The method may include obtaining bone marrow tissue having the mesenchymal stem cells together with unwanted cells. Unwanted cells may include hematopoietic stem cells and other stromal cells. The method may further include digesting the bone marrow tissue to form a cell suspension having the mesenchymal stem cells and the unwanted cells. In another embodiment, this may be followed by naturally selecting MSCs and depleting some of the unwanted cells and other constituents to concentrate mesenchymal stem cells.

[0103] Next, the method includes adding the cell suspension with the mesenchymal stem cells to the bone substrate. This may be followed by culturing the mesenchymal stem cells and the bone substrate for a period of time to allow the mesenchymal stem cells to adhere to the bone substrate. In order to provide a desired product, the method includes rinsing the bone substrate to remove the unwanted cells from the bone substrate.

[0104] In one embodiment, an allograft product may include a combination of mesenchymal stem cells with a bone substrate such that the combination is manufactured by the above exemplary embodiment.

[0105] In another exemplary embodiment, a method of combining mesenchymal stem cells with a bone substrate is provided. The method may include obtaining muscle tissue having the mesenchymal stem cells together with unwanted cells. Unwanted cells may include hematopoietic stem cells and other stromal cells. The method may further include digesting the muscle tissue to form a cell suspension having the mesenchymal stem cells and the unwanted cells. In another embodiment, this may be followed by naturally selecting MSCs to concentrate mesenchymal stem cells.

[0106] Next, the method includes adding the cell suspension with the mesenchymal stem cells to the bone substrate. This may be followed by culturing the mesenchymal stem cells and the bone substrate for a period of time to allow the mesenchymal stem cells to adhere to the bone substrate. In order to provide a desired product, the method includes rinsing the bone substrate to remove the unwanted cells from the bone substrate.

[0107] In one embodiment, an allograft product may include combination of mesenchymal stem cells with a bone substrate such that the combination is manufactured by the above exemplary embodiment.

[0108] In another exemplary embodiment, a method of combining mesenchymal stem cells with a bone substrate is provided. The method may include obtaining tissue having the mesenchymal stem cells together with unwanted cells. Unwanted cells may include hematopoietic stem cells and other stromal cells.

[0109] The method may further include digesting the tissue to form a cell suspension having the mesenchymal stem cells and at least some of the unwanted cells. In another embodiment, this may be followed by negatively depleting some of the unwanted cells and other constituents to concentrate mesenchymal stem cells.

[0110] Next, the method includes adding the cell suspension with the mesenchymal stem cells to the bone substrate. In an embodiment, this substrate may include a bone material which has been subjected to a demineralization process. In another embodiment, this substrate may be a non-bone material, which may include (but is not limited to) a collagen based material. This may be followed by culturing the mesenchymal stem cells and the bone substrate for a period of time to allow the mesenchymal stem cells to adhere to the bone substrate. In order to provide a desired product, the method includes rinsing the bone substrate to remove the unwanted cells from the bone substrate.

[0111] In one embodiment, an allograft product may include a combination of mesenchymal stem cells with a bone substrate such that the combination is manufactured by the above exemplary embodiment.

[0112] Digesting the cell suspension may include making a collagenase I solution, and filtering the solution through a 0.2 μm filter unit, mixing the adipose tissue with the collagenase I solution, and adding the cell suspension mixed with the collagenase I solution to a shaker flask. Digesting the cell suspension may further include placing the shaker with continuous agitation at about 75 RPM for about 45 to 60 minutes so as to provide the adipose tissue with a visually smooth appearance.

[0113] Digesting the cell suspension may further include aspirating supernatant containing mature adipocytes so as to provide a pellet, which may be referred to as a stromal vascular fraction. (See, for example, FIG. 2.) Prior to seeding, a lab sponge or other mechanism may be used to pat dry bone substrate.

[0114] In one embodiment, adding the cell suspension with the mesenchymal stem cells to the bone substrate may include using a cell pellet for seeding onto the bone substrate. In an embodiment, adding the cell suspension with the mesenchymal stem cells to the bone substrate may include using a cell pellet for seeding onto the bone substrate. In another embodiment, adding the cell suspension with the mesenchymal stem cells to the bone substrate may include using a cell pellet for seeding onto the bone substrate of cortical bone. In another embodiment, adding the cell suspension with the mesenchymal stem cells to the bone substrate may include adding the cell pellet onto the bone substrate of cancellous bone. In another embodiment, adding the cell suspension with the mesenchymal stem cells to the bone substrate may include adding the cell pellet onto the bone substrate of ground bone. In another embodiment, adding the cell suspension with the mesenchymal stem cells to the bone substrate may include adding the cell pellet onto the bone substrate of cortical/cancellous bone. In another embodiment, adding the cell suspension with the mesenchymal stem cells to the bone substrate may include adding the cell pellet onto the bone substrate of demineralized cancellous bone.

[0115] In an embodiment, the method may include placing the bone substrate into a cryopreservation media after rinsing the bone substrate. This cryopreservation media may be provided to store the final products. For example, the method may include maintaining the bone substrate into a frozen state after rinsing the bone substrate to store the final products. The frozen state may be at about negative 80° C.

[0116] In another embodiment, Ficoll density solution may be utilized. For example, negatively depleting the concentration of the mesenchymal stem cells may include adding a volume of PBS and a volume of Ficoll density solution to the adipose solution. The volume of PBS may be 5 ml and the volume of Ficoll density solution may be 25 ml with a density of 1.073 g/ml. Negatively depleting the concentration of the mesenchymal stem cells may also include centrifuging the adipose solution at about 1160 g for about 30 minutes at about room temperature. In one embodiment, the method may include stopping the centrifuging the adipose solution without using a brake.

[0117] Negatively depleting the concentration of the mesenchymal stem cells is optional and may next include collecting an upper layer and an interface containing nucleated cells, and discarding a lower layer of red cells and cell debris. Negatively depleting the concentration of the mesenchymal stem cells may also include adding a volume of D-PBS of about twice an amount of the upper layer of nucleated cells, and inverting a container containing the cells to wash the collected cells. Negatively depleting the concentration of the mesenchymal stem cells may include centrifuging the collected cells to pellet the collected cells using the break during deceleration.

[0118] In an embodiment, negatively depleting the concentration of the mesenchymal stem cells may further include centrifuging the collected cells at about 900 g for about 5 minutes at about room temperature. Negatively depleting some of the unwanted cells may include discarding a supernatant after centrifuging the collected cells, and resuspending the collected cells in a growth medium.

[0119] In one embodiment, adding the cell suspension with the mesenchymal stem cells to the bone substrate may include adding the cell pellet onto the bone substrate. Adding the solution with the mesenchymal stem cells to the bone substrate may include adding cell pellet onto the bone substrate which was subjected to a demineralization process. In another embodiment, adding the cell suspension with the mesenchymal stem cells to the bone substrate may include adding the cell pellet onto the bone substrate of cortical bone. In an embodiment, adding the cell suspension with the mesenchymal stem cells to the bone substrate includes adding the cell pellet onto the bone substrate of cancellous bone. In another embodiment, adding the cell suspension with the mesenchymal stem cells to the bone substrate may include adding the cell pellet onto the bone substrate of ground bone. In another embodiment, adding the cell suspension with the mesenchymal stem cells to the bone substrate may include adding the cell pellet onto the bone substrate of corticallcancellous bone. In another embodiment, adding the cell suspension with the mesenchymal stem cells to the bone substrate may include adding the cell pellet onto the bone substrate of demineralized cancellous bone.

[0120] In an embodiment, the method may further include placing the bone substrate into a cryopreservation media after rinsing the bone substrate. This cryopreservation media may be provided to store the final products. The method may include maintaining the bone substrate into a frozen state after rinsing the bone substrate to store the final products. The frozen state may be at about negative 80° C.

[0121] The seeded allografts are cultured for a period of time to allow the mesenchymal stem cells to adhere to the bone substrate. The unwanted cells were rinsed and removed from the bone substrate. After culturing, a lab sponge or other mechanism may be used to pat dry the bone substrate.

[0122] The mesenchymal stem cells are anchorage dependent. The mesenchymal stem cells naturally adhere to the bone substrate. The mesenchymal stem cells are non-immunogenic and regenerate bone. The unwanted cells are generally anchorage independent. This means that the unwanted cells generally do not adhere to the bone substrate. The unwanted cells may be immunogenic and may create blood and immune system cells. For cell purification during a rinse, mesenchymal stem cells adhere to the bone while unwanted cells, such as hematopoietic stem cells, are rinsed away leaving a substantially uniform population of mesenchymal stem cells on the bone substrate.

[0123] The ability to mineralize the extracellular matrix and to generate bone is not unique to MSCs. In fact, ASCs possess a similar ability to differentiate into osteoblasts under similar conditions. Human ASCs offer a unique advantage in contrast to other cell sources. The multipotent characteristics of ASCs, as wells as their abundance in the human body, make these cells a desirable source in tissue engineering applications.

[0124] In various embodiments, bone substrates (e.g., cortical cancellous dowels, strips, cubes, blocks, discs, and granules, as well as other substrates formed in dowels, strips, cubes, blocks, discs, and granules)may be subjected to a demineralization process to remove blood, lipids and other cells so as to leave a matrix. FIGS. 3A-3D illustrate various examples of strips (FIGS. 3A and 3B) and dowels (FIGS. 3C and 3D). Generally, these substrates may have a 3-D cancellous matrix structure, which MSCs may adhere to.

[0125] In addition, this method and combination product involve processing that does not alter the relevant biological characteristics of the tissue. Processing of the adipose/stem cells may involve the use of antibiotics, cell media, collagenase. None of these affects the relevant biological characteristics of the stem cells. The relevant biological characteristics of these mesenchymal stem cells are centered on renewal and repair. The processing of the stem cells does not alter the cell's ability to continue to differentiate and repair.

[0126] In the absence of stimulation or environmental cues, mesenchymal stem cells (MSCs) remain undifferentiated and maintain their potential to form tissue such as bone, cartilage, fat, and muscle. Upon attachment to an osteoconductive matrix, MSCs have been shown to differentiate along the osteoblastic lineage in vivo. See, for example, the following, which are incorporated by reference:

• • [0127] Arinzeh T L, Peter S J, Archambault M P, van den Bas C, Gordon S, Kraus K, Smith A, Kadiyala S. Allogeneic mesenchymal stem cells regenerate bone in a critical sized canine segmental defect. J Bone Joint Surg Am. 2003; 85-A:1927-35.
  • [0128] Bruder S P, Kurth A A, Shea M, Hayes W C, Jaiswal N, Kadiyala S. Bone regeneration by implantation of purified, culture-expanded human mesenchymal stem cells, J Orthop Res. 1998; 16:155-62.

[0129] Adipose was recovered from cadaveric donors. Adipose aspirate may be collected using liposuction machine and shipped on wet ice.

[0130] Adipose tissue was warmed up in a thermal shaker at RPM=75, 37° C. for 10 min. Adipose was washed with equal volume of pre-warmed phosphate buffered saline (PBS) at 37° C., 1% penicillin/streptomycin. Next, the adipose was agitated to wash the tissue. Phase separation was allowed for about 3 to 5 minutes. The infranatant solution was aspirated. The wash was repeated 3 to 4 times until a clear infranatant solution was obtained.

[0131] The solution was suspended in an equal volume of growth media (DMEM/F12, 10% FBS, 1% penicillin/streptomycin) and stored in a refrigerator at about 4° C.

Digestion and Combining of Cell Suspension with Allografts

[0132] Digestion of the adipose was undertaken to acquire a stromal vascular fraction (SVF) followed by combining the solution onto an allograft.

[0133] Digestion involved making collagenase I solution, including 1% fetal bovine serum (FBS) and 0.1% collagenase I. The solution was filtered through a 0.2 urn filter unit. This solution should be used within 1 hour of preparation.

[0134] Next, take out the washed adipose and mix with collagenase I solution at 1:1 ratio. Mixture was added to a shaker flask.

[0135] The flask was placed in an incubating shaker at 37° C. with continuous agitation (at about RPM=75) for about 45 to 60 minutes until the tissue appeared smooth on visual inspection.

[0136] The digestate was transferred to centrifuge tubes and centrifuged for 5 minutes at about 300-500 g at room temperature. The supernatant, containing mature adipocytes, was then aspirated. The pellet was identified as the stromal vascular fraction (SVF).

[0137] Growth media was added into every tube (i.e., 40 ml total was added into the 4 tubes) followed by gentle shaking

[0138] All of the cell mixtures were transferred into a 50 ml centrifuge tube. A 200 μl sample was taken, 50 μl is for initial cell count, and the remainder of the 150 μl was used for flow cytometry.

[0139] Aliquot cell mixtures were measured into 2 centrifuge tubes (of 10 ml each) and centrifuged at about 300 g for 5 minutes. The supernatant was aspirated.

[0140] A cell pellet obtained from one tube was used for seeding onto allografts. The allografts may include cortical/cancellous or both which was subjected to a demineralization process.

[0141] Certain volume of growth medium was added into the cell pellets and shaken to break the pellets. A very small volume of cell suspension was added onto allografts. After culturing in CO₂ incubator at 37° C. for a few hours, more growth medium (DMEM/F12, 10% FBS with antibiotics) was added. This was astatic “seeding” process. A dynamic “seeding” process can be used for particular bone substrate. 10 ml of a cell suspension and bone substrate were placed in a 50 ml centrifuge tube on an orbital shaker and agitated at 100 to 300 rpm for 6 hours.

[0142] After a few days (about 1 to 3 days), the allograft was taken out and rinsed thoroughly in PBS and sonicated to remove unwanted cells. The allograft was put into cryopreservation media (10% DMSO, 90% serum) and kept frozen at −80° C. The frozen allograft combined with the mesenchymal stem cells is a final product.

[0143] Adipose was recovered from cadaveric donors. Adipose aspirate may be collected using liposuction machine and shipped on wet ice.

[0144] Adipose tissue was processed in a thermal shaker at RPM=75, 37° C. for 10 min. Adipose was washed with equal volume of pre-warmed phosphate buffered saline (PBS) at 37 ° C., 1% penicillin/streptomycin. Next, the adipose was agitated to wash the tissue. Phase separation was allowed for about 3 to 5 minutes. The supernatant solution was sucked off. The wash was repeated 3 to 4 times until a clear infranatant solution was obtained.

[0145] Ficoll concentrated stem cells were acquired and seeded onto an allograft. 5 ml PBS was placed into the 50 ml tube with cells and 25 ml of 1.073 g/ml Ficoll density solution was added to the bottom of the tube with a pipet.

[0146] The tubes were subjected to centrifugation at 1160 g for 30 min at room temperature and stopped with the brake off. The upper layer and interface, approximately 15 to 17 ml containing the nucleated cells were collected with a pipet and transferred to a new 50 ml disposable centrifuge tube. The lower layer contained red cells and cell debris and was discarded.

[0147] Next, 2 volumes of 0-PBS were added. The tubes were capped and mix gently by inversion to wash the cells.

[0148] The tubes with the diluted cells were then subjected to centrifugation at 900 g for 5 minutes at room temperature to pellet the cells with the brake on during deceleration.

[0149] The supernatant was discarded and the washed cells were resuspended in 10 ml of growth medium. 10 ml of growth media was added into the tube and it was shaken gently. A 1 ml sample was taken with 100 μl is for cell count, and the remainder of 900 μl was used for flow cytometry.

[0150] The remainder of the cell mixtures were centrifuged at about 300 g for about 5 minutes. The supernatant was aspirated.

[0151] A cell pellet was used for “seeding” onto allografts. Allografts may include demineralized bone, cortical/cancellous bone, or both. A very small volume of medium was added into the cell pellet and shaken. 100 μl of cell mixtures were added onto a 15 mm disc within a 24-well culture plate.

[0152] After culturing the allograft in a CO2 incubator at about 37° C., 1 ml growth medium (DMEM/F12, 10% FBS with antibiotics) was added. This was a static “seeding” process. A dynamic “seeding” process can be used for a particular bone substrate.

[0153] After a few days (about 1 to 3 days), the allograft was taken out and rinsed thoroughly in PBS to remove unwanted cells. The allograft was put into cryopreservation media (10% DMSO, 90% serum) and kept frozen at −80° C. The frozen allograft combined with the stem cells is a final product.

[0154] Adipose was recovered from cadaveric donors. Adipose aspirate may be collected using liposuction machine and shipped on wet ice.

[0155] The bone marrow sample is washed by adding 6 to 8 volumes of Dulbecco's phosphate buffered saline (D-PBS) in a 50 ml disposable centrifuge, inverting gently and subjecting to centrifugation (800 g for 10 min) to pellet cells to the bottom of the tube.

[0156] The supernatant is discarded and the cell pellets from all tubes are resuspended in 1-2 ml of growth medium (DMEM, low glucose, with 10% FBS and 1% pen/strap). The cell mixtures are seeded onto allografts. With a few hours of culture in CO2 incubator at 37° C., more growth medium is added. A few days later, the allograft is taken out and rinsed thoroughly in PBS and put into cryopreservation media (10% DMSO, 90% serum) and kept frozen.

[0157] Skeletal muscle may be recovered from cadaveric donors.

[0158] Minced skeletal muscle (1-3 mm cube) is digested in a 3 mg/ml collagenase D solution in a −MEM at 37° C. for 3 hours. The solution is filtered with 100 um nylon mesh. The solution is centrifuged at 500 g for 5 min.

[0159] The supernatant is discarded and the cell pellets from all tubes are resuspended in 1-2 ml of growth medium (DMEM, low glucose, with 10% FBS and 1% pen/strap). The cell mixtures are seeded onto allografts. With a few hours of culture in CO2 incubator at 37° C., more growth medium will be added. A few days later, the allograft is taken out and rinsed thoroughly in PBS and put into cryopreservation media (10% DMSO, 90% serum) and kept frozen.

[0160] Adipose was recovered from a cadaveric donor within 24 hours of death and shipped in equal volume of DMEM in wet ice.

[0161] Adipose were washed 3 times with PBS and suspended in an equal volume of PBS supplemented with Collagenase Type I prewarmed to 37° C. The tissue was placed in a shaking water bath at 37° C. with continuous agitation for 45 to 60 minutes and centrifuged for 5 minutes at room temperature. The supernatant, containing mature adipocytes, was aspirated. The pellet was identified as the SVF (stromal vascular fraction).

[0162] Human cortical cancellous bone was recovered from ilium crest from the same donor. The samples were sectioned into strips (20×50×5 mm), and then they were subjected to a demineralization process with HCl for 3 hours, rinsed with PBS until the pH is neutral.

Digestion and Combining of Cell Suspension with Allograft

[0163] The adipose-derived stem cells (ASCs) were added onto the grafts and cultured in CO2 incubator at 37° C. Then the allografts were rinsed thoroughly in PBS to remove antibiotics and other debris. At the end, the allografts were put into cryopreservation media and kept frozen at −80° C.

[0164] The following antibodies were used for flow cytometry. PE anti-CD73 (clone AD2) Becton Dickinson, PE anti-CD90 (clone F15-42-1) AbD SeroTec, PE anti-CD105 (clone SN6) AbD SeroTec, PE anti-Fibroblasts/Epithelial Cells (clone 07-FIB) AbD SeroTec, FITC anti-CD34 (clone 8G12) Becton Dickinson, FITC Anti-CD45 (clone 2D1) Becton Dickinson, and PE anti-CD271 (clone ME20.4-1.H4) Miltenyi BioTec. The Isotype controls were FITC Mouse IgG1 Kappa (clone MOPC-21) Becton Dickinson, PE Mouse IgG1 Kappa (clone MOPC-21) Becton Dickinson, and PE Mouse IgG2a Kappa (clone G155-178) Becton Dickinson.

[0165] A small aliquot of the cells were stained with a propidium iodide/detergent solution and fluorescent nuclei were counted using a hemocytometer on a fluorescent microscope. This total cell count was used to adjust the number of cells per staining tube to no more than 5.0×105 cells. The cells were washed with flow cytometric wash buffer (PBS supplemented with 2% FBS and 0.1% NaN3), stained with the indicated antibodies and washed again before acquisition. Staining was for 15 minutes at room temperature (15-30DC).

[0166] At least 20,000 cells were acquired for each sample on a FACScan flow cytometer equipped with a 15-mW, 488-nm, argon-ion laser (BD Immunocytometry Systems, San Jose, Calif.). The cytometer QC and setup included running SpheroTech rainbow (3 μm, 6 peaks) calibration beads (SpheroTech Inc.) to confirm instrument functionality and linearity. Flow cytometric data were collected and analyzed using Cell Quest software (BD Immunocytometry Systems). The small and large cells were identified by forward (FSC) and side-angle light scatter (SSC) characteristics. Autofluorescence was assessed by acquiring cells on the flow cytometer without incubating with fluorochrome labeled antibodies. Surface antigen expression was determined with a variety of directly labeled antibodies according to the supplier's recommendations. Antibodies staining fewer than 20% of the cells relative to the Isotype-matched negative control were considered negative (this is standard-of-practice for immunophenotyping leukocytes for leukemia lymphoma testing). The viability of the small and large cells was determined using the Becton Dickinson Via-Probe (7-AAD).

[0167] Osteogenesis—Confluent cultures of primary ASCs were induced to undergo osteogenesis by replacing the stromal medium with osteogenic induction medium (Stempro® osteogenesis differentiation kit, Invitrogen). Cultures were fed with fresh osteogenic induction medium every 3 to 4 days for a period of up to 3 weeks. Cells were then fixed in 10% neutral buffered formalin and rinsed with Dl water. Osteogenic differentiation was determined by staining for calcium phosphate with Alizarin red (Sigma).

[0168] Adipogenesis—Confluent cultures of primary ASCs were induced to undergo adipogenesis by replacing the stromal medium with adipogenic induction medium (Stempro® adipogenesis differentiation kit, Invitrogen). Cultures were fed with fresh adipogenic induction medium every 3 to 4 days for a period of up to 2 weeks. Cells were then fixed in 10% neutral buffered formalin and rinsed with PBS. Adipogenic differentiation was determined by staining for fat globules with oil red O (Sigma).

[0169] Chondrogenesis—Confluent cultures of primary ASCs were induced to undergo chondrogenesis by replacing the stromal medium with chondrogenic induction medium (Stempro® chondrogenesis differentiation kit, Invitrogen). Cultures were fed with fresh chondrogenic induction medium every 3 to 4 days for a period of up to 3 weeks. Cells were then fixed in 10% neutral buffered formalin and rinsed with PBS. Chondrogenic differentiation was determined by staining for proteoglycans with Alcian blue (Sigma).

[0170] Cell count may be preformed [sic] with a CCK-8 Assay. Cell Counting Kit 8 (CCK-8, Dojindo Molecular Technologies, Maryland) allows sensitive colorimetric assays for the determination of the number of viable cells in cell proliferation assays. With reference to FIG. 4, there is illustrated a standard curve of total live ASCs using the CCK-8 assay. WST-8 [2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyi)-2H-tetrazolium, monosodium salt] is reduced by dehydrogenases in cells to give a yellow colored product (formazan), which is soluble in the tissue culture medium. The amount of the formazan dye generated by the activity of dehydrogenases in cells is directly proportional to the number of living cells. The allografts were thawed and rinsed with PBS and then patted dry. Growth medium and CCK-8 solution were added into the allografts at a ratio of 10:1 cultured at 37° C. for 2 hours and evaluated in a plate reader with excitation set to 460 nm and emission set to 650 nm. The results were interpolated from a standard curve (FIG. 4) based on ASCs only (passage=3).

[0171] When the cultures were terminated, the constructs were fixed in 10% neutral buffered formal in (Sigma, St. Louis, Mo.) for 48 h, put in a processor (Citadel 2000; Thermo Shandon, Pittsburgh, Pa.) overnight, and embedded in paraffin. Sections were cut to 8 μm and mounted onto glass slides and stained with hematoxylin and eosin (H&E). Conventional light microscopy was used to analyze sections for matrix and cell morphology.

[0172] All quantitative data were expressed as the mean±standard deviation. Statistical analysis was performed with one-way analysis of variance. A value of p<0.05 was considered statistically significant.

[0173] FIGS. 3A-3D illustrate an appearance of strips, dowels and disks. In these embodiments, all have a cortical bottom and cancellous top. Other embodiments may be used.

[0174] The SVF were stained with CD105, CD90 and CD73 to determine if there were significant numbers of MSC present. The immunophenotype of the stromal vascular fraction was consistent from donor to donor. The large cells (mean 3%) have the following immunophenotype and mean percentage: D7-FIB+ (36%), CD105+ (43%), CD90+ (63%), CD73+ (28%) and CD34+ (62%). The small cells (mean 97%) contain only a small percentage of the markers tested and therefore could not be immunophenotyped with this method: D7-FIB (5%), CD105 (6%), CD90 (15%), CD73 (6%) and CD34 (10%). The SVF contained a significant population of CD34+cells (Large CDC34+62% and small CD34+10%). The paucity of CD45+cells (Large 15% and small 3%) would suggest that the SVF does not contain significant numbers of WBC (CD45+, low FSC, low SSC) or hematopoietic stem cells (CD34+, low CD45+, medium FSC, low SSC). The anti-Fibroblasts/Epithelial Cells (clone D7-FIB) antibody has been reported to be a good marker for MSC. The large cells were D7-FIB+ 36% and the small cells were D7-FIB+ 5%. CD271 should be negative on SVF cells and the large cells were CD271+ 10% and the small cells were CD271+ 0%. Following adherence of the SVF (ASCs, P1), the immunophenotype became more homogenous for both the large and small cells. The large cells (53%) have the following immunophenotype and percentage: D7-FIB+ (93%), CD105+ (98%), CD90+ (96%) and CD73+ (99%). The small cells (47%) have the following immunophenotype and percentage: D7-FIB+ (77%), CD105+ (75%), CD90+ (58%) and CD73+ (83%). The ASCs has lost CD34 marker expression (P3: large 4% and small 1%) (P1: large 8% and small 6%) and the CD45+ cells remained low (P3: large 2% and small 2%) (P1: large 3% and small 1%). This would suggest that there are few WBC (CD45+, low FSC, low SSC) or hematopoietic stem cells (CD34+, low CD45+, medium FSC, low SSC) present. The anti-Fibroblasts/Epithelial Cell (clone D7-FIB)antibody for the adherent and cultured cells showed an increased expression. The large cells were D7-FIB+93% and the small cells were D7-FIB+77%. CD271 should become positive following adherence and culture of the SVF. For P3 the large cells were CD271+4% and the small cells were CD271+1%. For P1 the large cells were CD271+27% and the small cells were CD271+3%. CD271 does not seem to be a useful marker for cultured MSC but more data is required.

[0175] CD105 was chosen to estimate the mean total percentage of MSC; although there is no single surface marker that can discern MSC in a mixed population. For the SVF with a mean of 3% large cells, a mean of 43% CD105+ cells, the mean total percentage would be 1.3%. For the SVF with a mean of 98% small cells, a mean of 6% CD105+ cells, the mean total percentage would be 5.9%. Combining the large and small totals gives a mean total of 7.2% MSC for the SVF.

In vitro Tri-Lineage Differentiation

[0176] FIG. 5 illustrates mineral deposition by ASCs cultured in osteogenic medium (A) indicating early stages of bone formation. The samples were stained with alizarin red S. Negative control (D) showed no sign of bone formation. Fat globules seen in ASCs cultured in adipogenic medium (B) indicating differentiation into adipocytes. The samples were stained with Oil red O. The picture (E) is negative control. Proteoglycans produced by ASCs cultured in chondrogenic medium (C) indicating early stages of chondrogenesis. The samples were stained with alcian blue. The negative control (F) showed no sign of chondrogenesis.

[0177] For the osteogenic differentiation, morphological changes appeared during the second week of the culture. At the end of the 21-day induction period, some calcium crystals were clearly visible. Cell differentiation was confirmed by alizarin red staining (FIG. 5 image (A)).

[0178] The adipogenic potential was assessed by induction of confluent ASCs. At the end of the induction cycles (7 to 14 days), a consistent cell vacuolation was evident in the induced cells. Vacuoles brightly stained for fatty acid with oil red O staining (FIG. 5 image (B)). Chondrogenic potential was assessed by induction of confluent ASCs. At the end of the induction cycles (14 to 21 days), the induced cells were clearly different from non-induced control cells. Cell differentiation was confirmed with Alcian blue staining (FIG. 5 image (C)).

[0179] Cell count: CCK-8 Assay

[0180] 28 grafts were tested from 8 donors and had an average of 50,000 live cells/graft.

[0181] H&E was performed to demonstrate cell morphology in relation to the underlying substrate (cancellous bone matrix). The stem cells are elongated and adhere to the surface of cancellous bone. FIG. 6 is an illustration of H&E staining that showed that stem cells adhered to the bone surface.

[0182] The ability of DBM to enhance osteogenesis of ASCs in vitro and in vivo is believed to be due to the interaction of osteoprogenitors with these matrix incorporated osteoinductive factors, which can induce MSCs into osteoblasts. In turn, the incorporation of an osteogenic cell source into DBM can potentially limit the need for the migration and expansion of indigenous osteoprogenitors within defect sites, allowing for an increased rate of bone formation and osseointegration. See, for example, the following, which are incorporated by reference:

• • [0183] Liu, G., et al., Evaluation of partially demineralized osteoporotic cancellous bone matrix combined with human bone marrow stromal cells for tissue engineering: an in vitro and in vivo study. Calcif Tissue Int, 2008. 83(3): p. 176-85.
  • [0184] Wang, J. and M. J. Glimcher, Characterization of matrix-induced osteogenesis in rat calvarial bone defects: II. Origins of bone forming cells. Calcif Tissue Int, 1999. 65(6): p. 486-93.
  • [0185] Wang, J. and M. J. Glimcher, Characterization of matrix-induced osteogenesis in rat calvarial bone defects: I. Differences in the cellular response to demineralized bone matrix implanted in calvarial defects and insubcutaneous sites. Calcif Tissue Int, 1999. 65(2): p. 156-65.

[0186] Wang, J., et al., Characterization of demineralized bone matrix-induced osteogenesis in rat calvarial bone defects: III. Gene and protein expression. Calcif Tissue Int, 2000. 67(4): p. 314-20.

[0187] Bruder, S. P. and B. S. Fox, Tissue engineering of bone. Cell based strategies. Clin Orthop Relat Res, 1999(367 Suppl): p. S68-83.

[0188] Many studies have demonstrated that purified, culture-expanded human MSCs can be directed into the osteogenic lineage in vitro, culminating in a mineralized matrix production. See, for example, the following, which are incorporated by reference:

• • [0189] Chen, L. Q., et al., [Study of MSCs in vitro cultured on demineralized bone matrix of mongrel]. Shanghai Kou Qiang Yi Xue, 2007. 16(3): p. 255-8.
  • [0190] Honsawek, S., D. Dhitiseith, and V. Phupong, Effects of demineralized bone matrix on proliferation and osteogenic differentiation of mesenchymal stem cells from human umbilical cord. J Med Assoc Thai, 2006. 89 Suppl 3: p. 8189-95.
  • [0191] Kasten, P., et al., Ectopic bone formation associated with mesenchymal stem cells in a resorbable calcium deficient hydroxyapatite carrier. Biomaterials, 2005. 26(29): p. 5879-89.
  • [0192] Qian, Y., Z. Shen, and Z. Zhang, [Reconstruction of bone using tissue engineering and nanoscale technology]. Zhongguo Xiu Fu Chong Jian Wai Ke Za Zhi, 2006. 20(5): p. 560-4.
  • [0193] Liu, G., et al., Tissue-engineered bone formation with cryopreserved human bone marrow mesenchymal stem cells. Cryobiology, 2008. 56(3): p. 209-15.
  • [0194] Ko, E. K., et al., In vitro osteogenic differentiation of human mesenchymal stem cells and in vivo bone formation in composite nanofiber meshes. Tissue Eng Part A, 2008. 14(12): p. 2105-19.

[0195] The ability to mineralize the extracellular matrix and to generate bone is not unique to MSCs. In fact, ASCs possess a similar ability to differentiate into osteoblasts under similar conditions. Human ASCs offer a unique advantage in contrast to other cell sources. The multipotent characteristics of ASCs, as wells as their abundance in the human body, make these cells a popular source in tissue engineering applications. This consistent cell-based new product has the potential to be effective for bone regeneration.