Methods of screening biological agents Number:7,101,709 from the United States Patent and Trademark Office (PTO) owispatent The invention discloses methods of proliferation and differentiation of multipotent neural stem cells. Also provided are methods of making cDNA libraries and methods of screening biological agents which affect proliferation differentiation survival phenotype or function of CNS cells.<H biological, screening, Methods, of, scre, 7101709.html, Patent, pto, 7101709

Title: Methods of screening biological agents

Abstract: The invention discloses methods of proliferation and differentiation of multipotent neural stem cells. Also provided are methods of making cDNA libraries and methods of screening biological agents which affect proliferation differentiation survival phenotype or function of CNS cells.

Patent Number: 7,101,709 Issued on 09/05/2006 to Weiss, et al.

Inventors: Weiss; Samuel (Alberta, CA), Reynolds; Brent (Alberta, CA), Hammang; Joseph P. (Barrington, RI), Baetge; E. Edward (Barrington, RI)
Assignee: Neurospheres Holdings Ltd. (Calgary, CA)

Appl. No.: 10/199,189

Filed: July 19, 2002

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
08486313	Jun., 1995	6497872
08270412	Jul., 1994
07726812	Jul., 1991
10199189
08385404	Feb., 1995
07961813	Oct., 1992
07726812
10199189
08359945	Dec., 1994
08221655	Apr., 1994
07967622	Oct., 1992
07726812
10199189
08376062	Jan., 1995
08010829	Jan., 1993
07726812
10199189
08149508	Nov., 2003
07726812
10199189
08311099	Sep., 1994
07726812
10199189
08338730	Nov., 1994
07726812

Current U.S. Class: 435/377 ; 435/375; 435/395

Current International Class: C12N 5/00 (20060101); C12N 5/02 (20060101)

Field of Search: 435/375,377,395

References Cited [Referenced By]

U.S. Patent Documents


4753635	June 1988	Sagen et al.
4980174	December 1990	Sagen et al.
5082670	January 1992	Gage
5175103	December 1992	Lee et al.
5411883	May 1995	Boss et al.
5612211	March 1997	Wilson et al.
5753506	May 1998	Johe
6294346	September 2001	Weiss et al.
6497872	December 2002	Weiss et al.

Foreign Patent Documents


0 233 838	Aug., 1987	EP
WO 89/03872	May., 1989	WO
WO 90/06757	Jun., 1990	WO
WO 91/02003	Feb., 1991	WO
WO 91/09936	Jul., 1991	WO
WO 91/17242	Nov., 1991	WO
WO 93/01275	Jan., 1993	WO
WO 93/09802	May., 1993	WO
WO 94/03199	Feb., 1994	WO

Other References

Almazan et al., Developmental Brain Research, 21:257-264 (1985). cited by other .
Anchan et al., J. Cell Biol., 109:58a, Abstract No. 308 (1989). cited by other .
Anchan et al., Neuron 6(6):923-936 (1991). cited by other .
Bayer et al., Annals NY Acad. Sci. 457:163-172 (1985). cited by other .
Bjorklund et al., Annals NY Acad. Sci., 457:53-81 (1985). cited by other .
Bouvier et al., Society for Neuroscience Abstracts, vol. 18, Abstract No. 403.7 (1992). cited by other .
Boyles et al. , J. Biol. Chem., 265(29):17805-17815 (1990). cited by other .
Calof et al., Neuron, 3:115-127 (1989). cited by other .
Cattaneo et al., TINS, 14(8):338-340 (1991). cited by other .
Cattaneo et al., Nature, 347:762-765 (1990). cited by other .
Cepko, Ann. Rev. Neurosci., 12:47-65 (1989). cited by other .
Deloulme et al., Journal of Neuroscience Research, 29:499-509 (1991). cite- d by other .
Dunnett et al., TINS, 266-270 (1983). cited by other .
Emerich et al., Cell Transplantation, 1:1-27 (1992). cited by other .
Faaland et al., Mol. Cell. Biol. 11(5):2697-2703 (1991). cited by other .
Ferrari et al., Developmental Biology, 133:140-147 (1989). cited by other .
Frederickson et al., Society for Neuroscience Abstracts, 13:182 Abstract No. 55.6 (1987). cited by other .
Frederiksen et al., The Journal of Neuroscience 8(4):1144-1151 (1988). cit- ed by other .
Frederiksen et al., Neuron, 1:439-448 (1988). cited by other .
Freed et al., Arch. Neurol., 47:505-512 (1990). cited by other .
Freshney, "Culture of Animal Cells--A Manual of Basic Techniques", Alan R. Liss, Inc., N.Y. pp. 190-195 (1987). cited by other .
Freshney, "Culture of Animal Cells--A Manual of Basic Techniques", Alan R. Liss, Inc., N.Y. Chapter 11, pp. 137-153 (1987). cited by other .
Geller et al., Science, 241:1667-1669 (1988). cited by other .
Gensburger et al., FEBS Letts, 217(1):1-5 (1987). cited by other .
Godfraind et al., Journal of Cell Biology 109(5):2405-2416. cited by other .
Groves et al., Nature, 362:453 (1993). cited by other .
Hall et al., Development, 106:619-633 (1989). cited by other .
Hoffman et al., Exp. Neurol. 122:100-106 (1993). cited by other .
Hunter et al., Developmental Brain Research, 54(2):235-248 (1990). cited by other .
Hunter et al., Biol. Abstr. 90.7 , Abstract No. 78581 (1990). cited by oth- er .
Hurtig et al., Annals of Neurology, 25(6):607-614 (1989). cited by other .
Jiao et al., Brain Research, 575:143 (1992). cited by other .
Kaplan, J. Comp. Neurol., 195:323 (1981). cited by other .
Kawaja et al., J. Neurosci., 12(7):2849 (1992). cited by other .
Korr et al., J. Comp. Neurol., 150(2):169-176 (1973). cited by other .
Lendahl et al., Cell, 60:585-595 (1990). cited by other .
Lin et al., Science, 260:1130 (1993). cited by other .
Lindvall et al., Science, 247:574-577 (1990). cited by other .
Lois et al., Society for Neuroscience Abstracts, vol. 19, Abstract No. 361.6 (1993). cited by other .
Luskin et al., Society for Neuroscience Abstracts, vol. 19, Abstract No. 361.9 (1993). cited by other .
Masters et al., Regulatory Peptides, 33(2):117-131 (1991). cited by other .
Masters et al., Biol. Abstr. 93:3, Abstract No. 31828 (1992). cited by oth- er .
McKinnon et al., Neuron, 5:603-614 (1990). cited by other .
Metcalf, Bioassays 14(12):799-805 (1992). cited by other .
Morrison et al., Science, 238:72-75 (1987). cited by other .
Morshead et al., Society for Neuroscience Abstracts, vol. 19, Abstract No. 360.7 (1993). cited by other .
Morshead et al., The Journal of Neuroscience, 12(1):249-256 (1992). cited by other .
Murphy et al., Jour. Of Neuroscience Research, 25(4):463-475 (1990). cited by other .
Mytilineou et al., Neuroscience Letters, 135:62-66 (1992). cited by other .
Nakafuku et al., FEBS Letts, 315(3):227-232 (1993). cited by other .
Notter et al., Cell Tissue Res., 244:69-76 (1986). cited by other .
Pallage et al., Brain Research, 386:197-208 (1986). cited by other .
Palmer et al., Proc. Nat'l. Acad. Sci. USA, 88:1330-1334 (1991). cited by other .
Perlow et al., Science, 204:643-646 (1979). cited by other .
Piszczkiewicz et al., Society for Neuroscience Abstracts, 19:1709 Abstract No. 704.7 (1993). cited by other .
Potten et al., Development, 110:1001-1020 (1990). cited by other .
Raff et al., Nature, 303:390-396 (1983). cited by other .
Rakic, Science, 227:1054 (1985). cited by other .
Ramatowski et al., Society for Neuroscience Abstracts, vol. 19, Abstract No. 360.10 (1993). cited by other .
Reh et al., The Journal of Neuroscience, 9(12):4179-4189 (1989). cited by other .
Renfranz et al., Cell, 66:713-729 (1991). cited by other .
Reynolds et al., "EGF responsive stem cells in the mammalian central nervous system", Neuronal Cell Death and Repair, Ch. 19, pp. 247 ed. Cuello (1993). cited by other .
Reynolds et al., Restorative Neurology and Neuroscience, 4(3) Abstract No. 34.P3 (1992). cited by other .
Reynolds et al., J. Neurosci., 12(11):4565-4574 (1992). cited by other .
Reynolds et al., Soc. Neurosc. Abstracts, 16 Abstract No. 474.2 (Oct./Nov. 1990). cited by other .
Reynolds et al., Science, 255:1707-1710 (1992). cited by other .
Rohrer et al., Biol. Chem. Hoppe Seyles, 368(10):1290-1296 (1987). cited by other .
Ronnett et al., Science, 248:603-605 (1990). cited by other .
Rosenberg et al., Science, 242:1575-1578 (1988). cited by other .
Sensenbrenner et al., Reviews in the Neurosciences, 5:43-53 (1994). cited by other .
Smart et al., J. Comp. Neurol., 116:325 (1961). cited by other .
Snyder et al., Cell, 68:33-51 (1992). cited by other .
Soreto et al., in Neurochemistry: A Practical Approach, Chapter 2, pp. 27-63 (1987). cited by other .
Steinbusch et al., Progress in Brain Research, 82:81-86 (1990). cited by other .
Temple, Nature, 340:471-473 (1989). cited by other .
Travis, Science, 259:1829 (1993). cited by other .
Van Der Maazen et al., Biosis Abstract No. 91:324328, Radiother. Oncol 20 (1991). cited by other .
Vescovi et al., Society for Neuroscience Abstracts, vol. 19, Abstract No. 360.12 (1993). cited by other .
Walsh et al., Science, 241:1342 (1988). cited by other .
Watts et al., Neurology 39 (Suppl. 1) Abstract No. PP72 (1989). cited by other .
Weiss et al., Proc. Natl. Acad. Sci. USA, 83:2238-2242 (1986). cited by other .
Williams, Cell, 67:1097 (1991). cited by other .
Williams et al., P.N.A.S. 83:9231 (1986). cited by other .
Widner et al., New Eng. J. Med., 327(22):1556 (1992). cited by other .
Wolff et al., PNAS, 86:9014 (1989). cited by other .
Wolswijk et al., Development, 105:387-400 (1989). cited by other .
Yamada et al.,Cold Spring Harbor Conferences on Cell Proliferation, vol. 9, 131-143 (1982). cited by other .
Nurcombe et al., Growth of cells in hormonally defined media--Book A, Science, 260:103-106 (1993). cited by other .
Brickman et al., Journal of Biological Chemistry, 270(42)24941-24948 (1995). cited by other .
Blakemore et al., Developmental Neuroscience, 10:1-11 (1988). cited by oth- er .
Pezzoli et al., Movement Disorders, 6(4):281-287 (1991). cited by other .
Stenevi et al., Brain Research, 69(2):217-234 (1974). cited by other .
Palella et al., Gene, 80:137-144 (1989). cited by other .
Olson, Stereotact Funct. Neurosurg., 54-55:250-167 (1990). cited by other .
Jackowski, British Journal of Neurosurgery, 9:303-317 (995). cited by othe- r .
Lubetzki et al., Ann. New York Acad. Sci., 605:66-70 (1990). cited by othe- r .
Friedmann, TIG, 10(6):210-214 (1994). cited by other .
Orkin et al., "Report & Recommendations of the Panel to Assess the NIH Investment in Reserarch on Gene", NIH, pp. 1-40 (Dec. 7, 1995). cited by other .
Kumar et al., Biochemical and Biophysical Research Comm., 185(3):1151-1161 (1992). cited by other .
Stratagene, Product Catalog, pp. 115-116 (1991). cited by other .
Sambrook et al., 2.sup.nd. Ed., Cold Spring Harbor Press 12.2-12.10 (1989). cited by other .
Lo et al., Developmental Biology, 145:139-153 (1991). cited by other .
Drago et al., Proc. Natl. Acad. Sci. USA, 88(6):2199-203 (1991). cited by other .
Isacson et al., Exp. Brain Res. 75(1):213-20 (1989). cited by other .
Lindvall et al, Archives of Neurology, 46(6):615-31 (1989). cited by other .
Wendt et al., Exp. Neurology, 79(2);452-61 (1983). cited by other .
Kesslak et al., Exp. Neurology, 94(3):615-26 (1986). cited by other .
Andres, J. Neural Transplantation, 1(1):11-22 (1989). cited by other .
Price et al., Development, 104(3): 473-82 (1988). cited by other .
Federoff et al., Proc. Natl. Acad. Sci. USA, 89(5):1636-1640 (1992). cited by other .
Akerud et al., Journal of Neuroscience, 21(20):8108-8118 (2001). cited by other .
Baetge. Annals of the New York Academy of Sciences, 695:285-291 (1993). cited by other .
Bray, Current Opinion in Neurology and Neurosurgery, 3:926-933 (1990). cit- ed by other .
Brustle et al., Nature Biotechnology, 16:1040-1044 (1998). cited by other .
Flax et al., Nature Biotechnology, 16:1033-1039 (1998). cited by other .
Cattaneo et al., Molecular Brain Research, 42:161-166 (1996). cited by oth- er .
Fricker et al., The Journal of Neuroscience, 19(14):5990-6005 (1999). cite- d by other .
Goetz et al., Neurology, 41:1719-1722 (1991). cited by other .
Hammang et al., Methods in Neurosciences, 21:281-293 (1994). cited by othe- r .
Hammang et al., Experimental Neurology, 147:84-95 (1997). cited by other .
Lindvall et al., Science, 247:574-577 1990). cited by other .
McKay, Science, 276:66-71 (1997). cited by other .
Micci et al., Gastroentrology, 121:757-766 (2001). cited by other .
Milward et al., Journal of Neuroscience Research, 50:862-871 (1997). cited by other .
Price and Williams, Current Opinion in Neurobiology, 11:564-567 (2001). cited by other .
Rezvani et al., Radiation Research, 156:408-412 (2001). cited by other .
Toda et al., Neuroscience Letters, 316:9-12 (2001). cited by other .
Weiss et al., The Journal of Neuroscience, 16(23):7599-7609 (1996). cited by other .
Winkler et al., Molecular and Cellular Neuroscience, 11:99-116 (1998). cit- ed by other .
Yandava et al., Proc. Natl. Acad. Sci. USA, 96:7029-7034 (1999). cited by other .
Zhang et al., Proc. Natl. Acad. Sci. USA, 96:4089- 4094 (1999). cited by other .
Zigova and Sanberg, Nature Biotechnology, 15:1007-1008 (1995). cited by other .
Saneto, et al. J Neuro Sci Res 21: 210-219 (1988). cited by other .
Fults, et al. J Neuropathol Exp Neuropathol Exp Neurol 51: 272-280 (1992). cited by other .
Tohyama, et al. Lab Investig 66: 303-313 (1992). cited by other .
European Search Report for EP 03 00 7791, mailed Jul. 17, 2003. cited by other .
Zecchinelli, et al., Soc. for Neurosci. Abstr., Abstract No. 413.17 (1990). cited by other .
Kamholz, et al., Proc. Natl. Acad. Sci. USA, "Identification of Three Forms of Human Myelin Basic Protein by cDNA Cloning", 83(13): 4962-4966 (1986). cited by other .
Bernard, et al., J. of Neurosci. Res., "Role of the c-myc and the N-myc Proto-Oncogenes in the Immortalization of Neural Precursors", 24:9-20 (1989). cited by other .
Emerich, et al., Cell Transplantation, "Behavioral Effects of Neural Transplantation", 1:401-427 (1992). cited by other .
Cotter, et al., "The Induction of Apoptosis by Chemotherapeutic Agents Occurs in All Phases of the Cell Cycle", Anticancer Res., 12(3):773-780 (1992). cited by other .
Villa, et al., "Synthesis of Specific Proteins in Trophic Factor-Deprived Neurons Undergoing Apoptosis", J. Neurochem., 62(4):1468-1475 (1994). cit- ed by other.

Primary Examiner: Falk; Anne-Marie
Attorney, Agent or Firm: Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C. Elrifi; Ivor R. Stock; Christina K.

Parent Case Text

RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 08/486,313, filed Jun. 7, 1995, now U.S. Pat. No. 6,497,872 which is a continuation-in-part of U.S. Ser. No. 08/270,412, filed Jul. 5, 1994, now abandoned, which is a continuation of U.S. Ser. No. 07/726,812, filed Jul. 8, 1991 now abandoned; a continuation-in-part of U.S. Ser. No. 08/385,404, filed Feb. 7, 1995, now abandoned, which is a continuation of U.S. Ser. No. 07/961,813, filed Oct. 16, 1992, now abandoned, which is a continuation-in-part of U.S. Ser. No. 07/726,812, filed Jul. 8, 1991 now abandoned; a continuation-in-part of U.S. Ser. No. 08/359,945, filed Dec. 20, 1994, now abandoned, which is a continuation of U.S. Ser. No. 08/221,655, filed Apr. 1, 1994, now abandoned, which is a continuation of U.S. Ser. No. 07/967,622, filed Oct. 28, 1992, now abandoned, which is a continuation-in-part of U.S. Ser. No. 07/726,812, filed Jul. 8, 1991, now abandoned; a continuation-in-part of U.S. Ser. No. 08/376,062, filed Jan. 20, 1995, now abandoned, which is a continuation of U.S. Ser. No. 08/010,829, filed Jan. 29, 1993, now abandoned, which is a continuation-in-part of U.S. Ser. No. 07/726,812, filed Jul. 8, 1991, now abandoned; a continuation-in-part of U.S. Ser. No. 08/149,508, filed Nov. 9, 1993, now abandoned, which is a continuation-in-part of U.S. Ser. No. 07/726,812, filed Jul. 8, 1991, now abandoned; a continuation-in-part of U.S. Ser. No. 08/311,099, filed Sep. 23, 1994, now abandoned, which is a continuation-in-part of U.S. Ser. No. 07/726,812, filed Jul. 8, 1991, now abandoned, and a continuation-in-part of U.S. Ser. No. 08/338,730, filed Nov. 14, 1994, now abandoned, which is a continuation-in-part of U.S. Ser. No. 07/726,812, filed Jul. 8, 1991, now abandoned.

Claims

We claim:

1. A method for screening biological agents which affect proliferation, differentiation, survival, phenotype, or function of CNS cells, comprising: a) preparing an adherent cell culture of an undifferentiated neural cell population comprising multipotent neural stem cells, wherein a single multipotent neural stem cell is capable of producing progeny that are capable of differentiating into neurons and glia, including astrocytes; b) contacting said neural cell population with at least one biological agent, and c) determining if said biological agent has an effect on proliferation, differentiation, survival, phenotype, or function of said neural cell population.

2. The method of claim 1, wherein step c) comprises determining the effects of said biological agent on differentiation of said neural cell population.

3. The method of claim 1 further comprising the step of inducing differentiation of said neural cell population prior to performing step b).

4. The method of claim 1, wherein the source of said multipotent neural stem cells is a human.

5. The method of claim 1, wherein said biological agent is a growth factor selected from the group consisting of fibroblast growth factor-1 (FGF-1), FGF-2, epidermal growth factor (EGF), EGF-like ligands, transforming growth factor-.alpha. (TGF.alpha.), insulin-like growth factor (IGF-1), nerve growth factor (NGF), platelet-derived growth factor (PDGF), and TGF.beta.s.

6. The method of claim 1, wherein said biological agent is a trophic factor selected from the group consisting of brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), and glial-derived neurotrophic factor (GDNF).

7. The method of claim 1, wherein said biological agent is a regulatory factor selected from the group consisting of phorbol 12-myristate 13-acetate, stauroporine, CGF-41251, tyrphostin, compounds which interfere with activation of the c-fos pathway, compounds which suppress tyrosine kinase activation, and heparan sulfate.

8. The method of claim 1, wherein said biological agent is a hormone selected from the group consisting of activin and thyrotropin releasing hormone (TRH).

9. The method of claim 1, wherein said biological agent is a macrophage inflammatory protein (MIP) selected from the group consisting of MIP-1.alpha., MIP-1.beta., and MIP-2.

10. The method of claim 1, wherein the effect of the biological agent on proliferation of the neural cell population is determined by observing changes in size or number of the multipotent neural stem cells.

11. The method of claim 1, wherein the source of said multipotent neural stem cells is a fetal mammal.

Description

FIELD OF THE INVENTION

This invention relates to a method for the in vitro culture and proliferation of multipotent neural stem cells, and to the use of these cells and their progeny as tissue grafts. In one aspect, this invention relates to a method for the isolation and in vitro perpetuation of large numbers of non-tumorigenic neural stem cell progeny which can be induced to differentiate and which can be used for neurotransplantation in the undifferentiated or differentiated state, into an animal to alleviate the symptoms of neurologic disease, neurodegeneration and central nervous system (CNS) trauma. In another aspect, this invention relates to a method of generating neural cells for the purposes of drug screening of putative therapeutic agents targeted at the nervous system. In another aspect, this invention also relates to a method of generating cells for autologous transplantation. In another aspect, the invention relates to a method for the in vivo proliferation and differentiation of the neural stem cell progeny in the host.

BACKGROUND OF THE INVENTION

The development of the mammalian central nervous system (CNS) begins in the early stage of fetal development and continues until the post-natal period. The mature mammalian CNS is composed of neuronal cells (neurons), and glial cells (astrocytes and oligodendrocytes).

The first step in neural development is cell birth, which is the precise temporal and spatial sequence in which stem cells and stem cell progeny (i.e daughter stem cells and progenitor cells) proliferate. Proliferating cells will give rise to neuroblasts, glioblasts and new stem cells.

The second step is a period of cell type differentiation and migration when undifferentiated progenitor cells differentiate into neuroblasts and gliolblasts which give rise to neurons and glial cells which migrate to their final positions. Cells which are derived from the neural tube give rise to neurons and glia of the CNS, while cells derived from the neural crest give rise to the cells of the peripheral nervous system (PNS). Certain factors present during development, such as nerve growth factor (NGF), promote the growth of neural cells. NGF is secreted by cells of the neural crest and stimulates the sprouting and growth of the neuronal axons.

The third step in development occurs when cells acquire specific phenotypic qualities, such as the expression of particular neurotransmitters. At this time, neurons also extend processes which synapse on their targets. Neurons are generated primarily during the fetal period, while oligodendrocytes and astrocytes are generated during the early post-natal period. By the late post-natal period, the CNS has its full complement of nerve cells.

The final step of CNS development is selective cell death, wherein the degeneration and death of specific cells, fibers and synaptic connections "fine-tune" the complex circuitry of the nervous system. This "fine-tuning" continues throughout the life of the host. Later in life, selective degeneration due to aging, infection and other unknown etiologies can lead to neurodegenerative diseases.

Unlike many other cells found in different tissues, the differentiated cells of the adult mammalian CNS have little or no ability to enter the mitotic cycle and generate new nerve cells. While it is believed that there is a limited and slow turnover of astrocytes (Korr et al., J. Comp. Neurol., 150:169, 1971) and that progenitors for oligodendrocytes (Wolsqijk and Noble, Development, 105:386, 1989) are present, the generation of new neurons does not normally occur.

The second step is a period of cell type differentiation and migration when undifferentiated progenitor cells differentiate into neuroblasts and gliolbiasts which give rise to neurons and glial cells which migrate to their final positions. Cells which are derived from the neural tube give rise to neurons and glia of the CNS, while cells derived from the neural crest give rise to the cells of the peripheral nervous system (PNS). Certain factors present during development, such as nerve growth factor (NGF), promote the growth of neural cells. NGF is secreted by cells of the neural crest and stimulates the sprouting and growth of the neuronal axons.

The third step in development occurs when cells acquire specific phenotypic qualities, such as the expression of particular neurotransmitters. At this time, neurons also extend processes which synapse on their targets. Neurons are generated primarily during the fetal period, while oligodendrocytes and astrocytes are generated during the early post-natal period. By the late post-natal period, the CNS has its full complement of nerve cells.

The final step of CNS development is selective cell death, wherein the degeneration and death of specific cells, fibers and synaptic connections "finetune" the complex circuitry of the nervous system. This "finetuning" continues throughout the life of the host. Later in life, selective degeneration due to aging, infection and other unknown etiologies can lead to neurodegenerative diseases.

Unlike many other cells found in different tissues, the differentiated cells of the adult mammalian CNS have little or no ability to enter the mitotic cycle and generate new nerve cells. While it is believed that there is a limited and slow turnover of astrocytes (Korr et al., J. Comp. Neurol., 150:169, 1971) and that progenitors for oligodendrocytes (Wolsqijk and Noble, Development, 105:386, 1989) are present, the generation of new neurons does not normally occur.

Neurogenesis, the generation of new neurons, is complete early in the postnatal period. However, the synaptic connections involved in neural circuits are continuously altered throughout the life of the individual, due to synaptic plasticity and cell death. A few mammalian species (e.g. rats) exhibit the limited ability to generate new neurons in restricted adult brain regions such as the dentate gyrus and olfactory bulb (Kaplan, J. Comp. Neurol., 195:323, 1981; Bayer, N.Y. Acad. Sci., 457:163, 1985). However, this does not apply to all mammals; and the generation of new CNS cells in adult primates does not occur (Rakic, Science, 227:1054, 1985). This inability to produce new nerve cells in most mammals (and especially primates) may be advantageous for long-term memory retention; however, it is a distinct disadvantage when the need to replace lost neuronal cells arises due to injury or disease.

The low turnover of cells in the mammalian CNS together with the inability of the adult mammalian CNS to generate new neuronal cells in response to the loss of cells following injury or disease has lead to the assumption that the adult mammalian CNS does not contain multipotent neural stem cells.

The critical identifying feature of a stem cell is its ability to exhibit self-renewal or to generate more of itself. The simplest definition of a stem cell would be a cell with the capacity for self-maintenance. A more stringent (but still simplistic) definition of a stem cell is provided by Potten and Loeffler (Development, 110:1001, 1990) who have defined stem cells as "undifferentiated cells capable of a) proliferation, b) self-maintenance, c) the production of a large number of differentiated functional progeny, d) regenerating the tissue after injury, and e) a flexibility in the use of these options."

The role of stem cells is to replace cells that are lost by natural cell death, injury or disease. The presence of stem cells in a particular type of tissue usually correlates with tissues that have a high turnover of cells. However, this correlation may not always hold as stem cells are thought to be present in tissues functions including memory.

Many motor deficits are a result of degeneration in the basal ganglia. Huntington's Chorea is associated with the degeneration of neurons in the striatum, which leads to involuntary jerking movements in the host. Degeneration of a small region called the subthalamic nucleus is associated with violent flinging movements of the extremities in a condition called ballismus, while degeneration in the putamen and globus pallidus is associated with a condition of slow writhing movements or athetosis. In the case of Parkinson's Disease, degeneration is seen in another area of the basal ganglia, the substantia nigra par compacta. This area normally sends dopaminergic connections to the dorsal striatum which are important in regulating movement. Therapy for Parkinson's Disease has centered upon restoring dopaminergic activity to this circuit.

Other forms of neurological impairment can occur as a result of neural degeneration, such as amyotrophic lateral sclerosis and cerebral palsy, or as a result of CNS trauma, such as stroke and epilepsy.

Demyelination of central and peripheral neurons occurs in a number of pathologies and leads to improper signal conduction within the nervous systems. Myeiin is a cellular sheath, formed by glial cells, that surrounds axons and axonal processes that enhances various electrochemical properties and provides trophic support to the neuron. Myelin is formed by Schwann cells in the PNS and by oligodendrocytes in the CNS. Among the various demyelinating diseases MS is the most notable.

To date, treatment for CNS disorder has been primarily via the administration of pharmaceutical compounds. Unfortunately, this type of treatment has been fraught with many complications including the limited ability to transport drugs across the blood-brain barrier and the drug-tolerance which is acquired by patients to whom these drugs are administered long-term. For instance, partial restoration of dopaminergic activity in Parkinson's patients has been achieved with levodopa, which is a dopamine precursor able to cross the blood-brain barrier. However, patients become tolerant to the effects of levodopa, and therefore, steadily increasing dosages are needed to maintain its effects. In addition, there are a number of side effects associated with levodopa such as increased and uncontrollable movement.

Recently, the concept of neurological tissue grafting has been applied to the treatment of neurological diseases such as Parkinson's Disease. Neural grafts may avert the need not only for constant drug administration, but also for complicated drug delivery systems which arise due to the blood-brain barrier. However, there are limitations to this technique as well. First, cells used for transplantation which carry cell surface molecules of a differentiated cell from another host can induce an immune reaction in the host. In addition, the cells must be at a stage of development where they are able to form normal neural connections with neighboring cells. For these reasons, initial studies on neurotransplantation centered on the use of fetal cells. Perlow, et al. describe the transplantation of fetal dopaminergic neurons into adult rats with chemically induced nigrostriatal lesions in "Brain grafts reduce motor abnormalities produced by destruction of nigrostriatal dopamine system," Science 204:643 647 (1979). These grafts showed good survival, axonal outgrowth and significantly reduced the motor abnormalities in the host animals.

In both human demyelinating diseases and rodent models there is substantial evidence that demyelinated neurons are capable of remyelination in vivo. In MS, for example, it appears that there are often cycles of de- and remyelination. Similar observations in rodent demyelinating paradigms lead to the prediction that exogenously applied cells would be capable of remyelinating demyelinated axons. This approach has proven successful in a number of experimental conditions [Freidman et al., Brain Research, 378:142 146 (1986); Raine, et al., Laboratory Investigation 59:467 476 (1988); Duncan et al., J. of Neurocytology, 17:351 360 (1988)]. The sources of cells for some of these experiments included dissociated glial cell suspensions prepared from spinal cords (Duncan et al., supra), Schwann cell cultures prepared from sciatic nerve [Bunge et al., 1992, WO 92/03536; Blakemore and Crang, J. Neurol. Sci., 70:207 223 (1985)]; cultures from dissociated brain tissue [Blakemore and Crang, Dev. Neurosci. 10:1 11 (1988)], oligodendrocyte precursor cells [Gumpel et al., Dev. Neurosci. 11:132 139 (1989)], O-2A cells [Wolswijk et al., Development 109:691 608 (1990); Raff et al., Nature 3030:390 396 (1983); Hardy et al., Development 111:1061 1080 (1991)], and immortalized O-2A cell lines, [Almazan and McKay Brain Res. 579:234 245 (1992)].

O-2A cells are glial progenitor cells which give rise in vitro only to oligodendrocytes and type II astrocytes. Cells which appear by immunostaining in vivo to have the O-2A phenotype have been shown to successfully remyelinate demyelinated neurons in vivo, [Godfraind et al., J. Cell Biol. 109:2405 2416 (1989)]. Injection of a large number of O-2A cells is required to adequately remyelinate all targeted neurons in vivo, since it appears that O-2A cells (like other glial cell preparations) do not continue to divide in vivo. Although O-2A progenitor cells can be grown in culture, currently the only available isolation technique employs optic nerve as starting material. This is a low yield source, which requires a number of purification steps. There is an additional drawback that O-2A cells isolated by the available procedures are capable of only a limited number of divisions [Raff Science 243:1450 1455 (1989)].

Although adult CNS neurons are not good candidates for neurotransplantation, neurons from the adult PNS have been shown to survive transplantation, and to exert neurotrophic and gliotrophic effects on developing host neural tissue. One source of non-CNS neural tissue for transplantation is the adrenal medulla. Adrenal chromaffin cells originate from the neural crest like PNS neurons, and receive synapses and produce carrier and enzyme proteins similar to PNS neurons. Although these cells function in an endocrine manner in the intact adrenal medulla, in culture these cells lose their glandular phenotype and develop certain neural features in culture in the presence of certain growth factors and hormones [Notter, et al., "Neuronal properties of monkey adrenal medulla in vitro, Cell Tissue Research 244:69 76 (1986)]. When grafted into mammalian CNS, these cells survive and synthesize significant quantities of dopamine which can interact with dopamine receptors in neighboring areas of the CNS.

In U.S. Pat. No. 4,980,174, transplantation of monoamine-containing cells isolated from adult rat pineal gland and adrenal medulla into rat frontal cortex led to the alleviation of learned helplessness, a form of depression in the host. In U.S. Pat. No. 4,753,635, chromaffin cells and adrenal medullary tissue derived from steers were implanted into the brain stem or spinal cord of rats and produced analgesia when the implanted tissue or cell was induced to release nociceptor interacting substances (i.e. catecholamines such as dopamine). Adrenal medullary cells have been autologously grafted into humans, and have survived, leading to mild to moderate improvement in symptoms (Watts, et al., "Adrenal-caudate transplantation in patients with Parkinson's Disease (PD):1-year follow-up," Neurology 39 Suppl 1: 127 [1989], Hurtig, et al., "Postmortem analysis of adrenal-medulla-to-caudate autograft in a patient with Parkinson's Disease," Annals of Neurology 25: 607 614 [1989]). However, adrenal cells do not obtain a normal neural phenotype, and are therefore probably of limited use for transplants where synaptic connections must be formed.

Another source of tissue for neurotransplantation is from cell lines. Cell lines are immortalized cells which are derived either by transformation of normal cells with an oncogene (Cepko, "Immortalization of neural cells via retrovirus-mediated oncogene transduction," Ann. Rev. Neurosci. 12:47 65 [1989]) or by the culturing of cells with altered growth characteristics in vitro (Ronnett, et al., "Human cortical neuronal cell line: Establishment from a patient with unilateral megalencephaly," Science 248:603 605 [1990]). Such cells can be grown in culture in large quantities to be used for multiple transplantations. Some cell lines have been shown to differentiate upon chemical treatment to express a variety of neuronal properties such as neurite formation, excitable membranes and synthesis of neurotransmitters and their receptors. Furthermore, upon differentiation, these cells appear to be amitotic, and therefore noncancerous. However, the potential for these cells to induce adverse immune responses, the use of retroviruses to immortalize cells, the potential for the reversion of these cells to an amitotic state, and the lack of response of these cells to normal growth-inhibiting signals make cell lines less than optimal for widespread use.

Another approach to neurotransplantation involves the use of genetically engineered cell types or gene therapy. Using this method, a foreign gene or transgene can be introduced into a cell which is deficient in a particular enzymatic activity, thereby allowing the cell to express the gene. Cells which now contain the transferred gene can be transplanted to the site of neurodegeneration, and provide products such as neurotransmitters and growth factors (Rosenberg, et al., "Grafting genetically modified cells to the damaged brain: Restorative effects of NGF Expression," Science 242:1575 1578, [1988]) which may function to alleviate some of the symptoms of degeneration. However, there still exists a risk of inducing an immune reaction using currently available cell lines. In addition, these cells may also not achieve normal neuronal connections with the host tissue.

Genetically modified cells have been used in neurological tissue grafting in order to replace lost cells which normally produce a neurotransmitter. For example, fibroblasts have been genetically modified with a retroviral vector containing a cDNA for tyrosine hydroxylase, which allows them to produce dopamine, and implanted into animal models of Parkinson's Disease (Gage et al., U.S. Pat. No. 5,082,670).

While the use of genetically modified fibroblasts to treat CNS disorders has shown promise in improving some behavioral deficits in animal models of Parkinson's Disease, and represents a novel approach to supplying a needed transmitter to the CNS, it suffers from several significant drawbacks as a treatment for Parkinson's Disease and in general as a therapeutic approach for treating neurodegenerative diseases and brain injury. First, the CNS is primarily composed of three cell types--neurons, astrocytes and oligodendrocytes. The implantation of a foreign cell such as a fibroblast into the CNS and its direct and indirect effects on the functioning of the host cells has yet to be studied. However, it is likely that the expression of membrane bound factors and the release of soluble molecules such as growth factors and proteases will alter the normal behavior of the surrounding tissue. This may result in the disruption of neuronal firing patterns either by a direct action on neurons or by an alteration in the normal functioning of glial cells.

Another concern that arises when fibroblasts are implanted into the CNS is the possibility that the implanted cells may lead to tumor formation because the intrinsic inhibition of fibroblast division is poorly controlled. Instead, extrinsic signals play a major role in controlling the number of divisions the cell will undergo. The effect of the CNS environment on the division of implanted fibroblasts and the high probability of a fibroblastic tumor formation has not been studied in the long-term.

A third concern in transplanting fibroblasts into the CNS is that fibroblasts are unable to integrate with the CNS cells as astrocytes, oligodendrocytes, or neurons do. Fibroblasts are intrinsically limited in their ability to extend neuronal-like processes and form synapses with host tissue. Hence, although the genetic modification and implantation of fibroblasts into the CNS represents an improvement over the current technology for the delivery of certain molecules to the CNS, the inability of fibroblasts to integrate and function as CNS tissue, their potential negative effects on CNS cells, and their limited intrinsic control of proliferation limits their practical usage for implantation for the treatment of acute or chronic CNS injury or disease.

A preferred tissue for genetic modification and implantation would be CNS cells--neurons, astrocytes, or oligodendrocytes. One source of CNS cells is from human fetal tissue. Several studies have shown improvements in patients with Parkinson's Disease after receiving implants of fetal CNS tissue. Implants of embryonic mesencephalic tissue containing dopamine cells into the caudate and putamen of human patients was shown by Freed et al. (N Engl J Med 327:1549 1555 (1992)) to offer long-term clinical benefit to some patients with advanced Parkinson's Disease. Similar success was shown by Spencer et al. (N Engl J Med 327:1541 1548 (1992)). Widner et al. (N Engl J Med 327:1556 1563 (1992)) have shown long-term functional improvements in patients with MPTP-induced Parkinsonism that received bilateral implantation of fetal mesencephalic tissue.

While the studies noted above are encouraging, the use of large quantities of aborted fetal tissue for the treatment of disease raises ethical considerations and political obstacles. There are other considerations as well. Fetal CNS tissue is composed of more than one cell type, and thus is not a well-defined source of tissue. In addition, there are serious doubts as to whether an adequate and constant supply of fetal tissue would be available for transplantation. For example, in the treatment of MPTP-induced Parkinsonism (Widner supra) tissue from 6 to 8 fetuses were used for implantation into the brain of a single patient. There is also the added problem of the potential for contamination during fetal tissue preparation. Moreover, the tissue may already be infected with a bacteria or virus, thus requiring expensive diagnostic testing for each fetus used. However, even diagnostic testing might not uncover all infected tissue. For example, the diagnosis of HIV-free tissue is not guaranteed because antibodies to the virus are generally not present until several weeks after infection.

While currently available transplantation approaches represent a significant improvement over other available treatments for neurological disorders, they suffer from significant drawbacks. The inability in the prior art of the transplant to fully integrate into the host tissue, and the lack of availability of cells in unlimited amounts from a reliable source for grafting are, perhaps, the greatest limitations of neurotransplantation.

It would be more preferable to have a well-defined, reproducible source of neural tissue for transplantation that is available in unlimited amounts. Since adult neural tissue undergoes minimal division, it does not readily meet these criteria. While astrocytes retain the ability to divide and are probably amenable to infection with foreign genes, their ability to form synapses with neuronal cells is limited and consequently so is their extrinsic regulation of the expression and release of the foreign gene product.

Oligodendrocytes suffer from some of the same problems. In addition, mature oligodendrocytes do not divide, limiting the infection of oligodendrocytes to their progenitor cells (e.g. O2A cells). However, due to the limited proliferative ability of oligodendrocyte progenitors, the infection and harvesting of these cells does not represent a practical source.

The infection of neurons with foreign genes and implantation into the CNS would be ideal due to their ability to extend processes, make synapses and be regulated by the environment However, differentiated neurons do not divide and transfection with foreign genes by chemical and physical means is not efficient, nor are they stable for long periods of time. The infection of primary neuronal precursors with retroviral vectors in vitro is not practical either because neuroblasts are intrinsically controlled to undergo a limited number of divisions making the selection of a large number of neurons, that incorporate and express the foreign gene, nearly impossible. The possibility of immortalizing the neuronal precursors by retroviral transfer of oncogenes and their subsequent infection of a desired gene is not preferred due to the potential for tumor formation by the implanted cells.

In addition to the need for a well-defined, reproducible source of neural cells available in unlimited amounts for transplantation purposes, a similar need exists for drug screening purposes and for the study of CNS function, dysfunction, and development. The mature human nervous system is composed of billions of cells that are generated during development from a small number of precursors located in the neural tube. Due to the complexity of the mammalian CNS, the study of CNS developmental pathways, as well as alterations that occur in adult mammalian CNS due to dysfunction, has been difficult. Such areas would be better studied using relatively simple models of the CNS under defined conditions

Generally, two approaches have been taken for studying cultured CNS cells: the use of primary neural cultures; and the use of neural cell lines. Primary mammalian neural cultures can be generated from nearly all brain regions providing that the starting material is obtained from fetal or early post-natal animals. In general, three types of cultures can be produced, enriched either in neurons, astrocytes, or oligodendrocytes. Primary CNS cultures have proven valuable for discovering many mechanisms of neural function and are used for studying the effects of exogenous agents on developing and mature cells. While primary CNS cultures have many advantages, they suffer from two primary drawbacks. First, due to the limited proliferative ability of primary neural cells, new cultures must be generated from several different animals. While great care is usually taken to obtain tissue at identical states of development and from identical brain regions, it is virtually impossible to generate primary cultures that are identical. Hence, there exists a significant degree of variability from culture to culture.

A second disadvantage of primary cultures is that the tissue must be obtained from fetuses or early post-natal animals. If primary cultures are to be performed on a regular basis, this requires the availability of a large source of starting material. While this is generally not a problem for generating primary cultures from some species (e.g. rodents), it is for others (e.g. primates). Due to the limited supply and ethical concerns, the culturing of primary cells from primates (both human and non-human) is not practical.

Due to the limited proliferative ability of primary neural cells, the generation of a large number of homogenous cells for studies of neural function, dysfunction, and drug design/screening has previously not been achieved. Therefore, homogenous populations of cells that can generate a large number of progeny for the in vitro investigation of CNS function has been studied by the use of cell lines. The generation of neural cell lines can be divided into two categories: 1) spontaneously occurring tumors, and 2) custom-designed cell lines.

Of the spontaneously occurring tumors, probably the most studied cell line for neurobiology is the rat pheochromocytoma (PC12) cells that can differentiate into sympathetic-like neurons in response to NGF. These cells have proven to be a useful model for studying mechanisms of neural development and alterations (molecular and cellular) in response to growth factors. Neuroblastoma and glioma cell lines have been used to study neuronal and glial functioning [Liles, et al., J. Neurosci. 7, 2556 2563 (1987); Nister et al. Cancer Res. 48(14) 3910 (1988)]. Embryonal carcinoma cells are derived from teratoma tumors of fetal germ cells and have the ability to differentiate into a large number of non-neural cell types with some lines (e.g. P19 cells) [Jones-Villeneuve et al. J. Cell Biol. 94, 253 262 (1982)] having the ability to differentiate into neural cells [(McBurney et al. J. Neurosci. 8(3) 1063 73 (1993)]. A human teratocarcinoma-derived cell line, NTera 2/cl.D1, with a phenotype resembling CNS neuronal precursor cells, can be induced to differentiate in the presence of retinoic acid. However, the differentiated cells are restricted to a neuronal phenotype [Pleasure and Lee J. Neurosci. Res. 35: 585 602 (1993)]. While these types of cell lines are able to generate a large number of cells for screening the effects of exogenous agents on cell survival or function, the limited number of these types of lines, the limited number of phenotypes that they are able to generate and the unknown nature of their immortalization (which may effect the function of the cells in an undefined manner) makes these types of cell lines less than ideal for in vitro models of neural function and discovery of novel therapeutics.

An alternative approach to spontaneously occurring cell lines is the intentional immortalization of a primary cell by introducing an oncogene that alters the genetic make-up of the cell thereby inducing the cell to proliferate indefinitely. This approach has been used by many groups to generate a number of interesting neural cell lines [(Bartlett et al. Proc. Nat. Acad. Sci. 85(9) 3255 3259 (1988); Frederiksen et al. Neuron 1, 439 448 (1988); Trotter et al. Oncogene 4: 457 464 (1989); Ryder et al. J. Neurobiol. 21: 356 375 (1980); Murphy et al. J. Neurobiol 22: 522 535 (1991); Almazan and McKay et al. Brain Res. 579: 234 245 (1992)]. While these lines may prove useful for studying the decisions that occur during cell determination and differentiation, and for testing the effects of exogenous agents, they suffer from several drawbacks. First, the addition of an oncogene that alters the proliferative status of a cell may affect other properties of the cell (oncogenes may play other roles in cells besides regulating the cell cycle). This is well illustrated in a study by Almazan and McKay, supra, and their immortalization of an oligodendrocyte precursor from the optic nerve which is unable to differentiate into type II astrocytes (something that normal optic nerve oligodendrocyte precursors can do). The authors suggest the presence of the immortalizing antigen may alter the cells ability to differentiate into astrocytes.

Another drawback to using intentionally immortalized cells results from the fact that the nervous system is composed of billions of cells and possibly thousands of different cell types, each with unique patterns of gene expression and responsiveness to their environment. A custom-designed cell line is the result of the immortalization of a single progenitor cell and its clonal expansion. While a large supply of one neural cell type can be generated, this approach does not take into account cellular interactions between different cell types. In addition, while it is possible to immortalize cells from a given brain region, immortalization of a desired cell is not possible due to the lack of control over which cells will be altered by the oncogene. Hence, while custom designed cell lines offer a few advantages over spontaneously occurring tumors, they suffer from several drawbacks and are less than ideal for understanding CNS function and dysfunction.

Therefore, in view of the aforementioned deficiencies attendant with prior art methods of neural cell culturing, transplantation, and CNS models, a need exists in the art for a reliable source of unlimited numbers of undifferentiated neural cells for neurotransplantation and drug screening which are capable of differentiating into neurons, astrocytes, and oligodendrocytes. Preferably cellular division in such cells from such a source would be epigenetically regulated and a suitable number of cells could be efficiently prepared in sufficient numbers for transplantation. The cells should be suitable in autografts, xenografts, and allografts without a concern for tumor formation. There exists a need for the isolation, perpetuation and transplantation of autologous neural cells from the juvenile or adult brain that are capable of differentiating into neurons and glia.

A need also exists for neural cells, capable of differentiating into neurons, astrocytes and oligodendrocytes that are capable of proliferation in vitro and thus amenable to genetic modification techniques.

Additionally, there exists a need for the repair of damaged neural tissue in a relatively non-invasive fashion, that is by inducing neural cells to proliferate and differentiate into neurons, astrocytes, and oligodendrocytes in vivo, thereby averting the need for transplantation.

Accordingly, a major object of the present invention is to provide a reliable source of an unlimited number of neural cells for neurotransplantation that are capable of differentiating into neurons, astrocytes, and oligodendrocytes.

It is another object of the present invention to provide a method for the in vitro proliferation of neural stem cells from embryonic, juvenile and adult brain tissue, to produce unlimited numbers of precursor cells available for transplantation that are capable of differentiating into neurons, astrocytes, and oligodendrocytes.

A further object of the invention is to provide methods for inducing neural cells to proliferate and differentiate in vivo, thereby averting the need for neurotransplantation.

A still further object of the invention is to provide a method of generating large numbers of normal neural cells for the purpose of screening putative therapeutic agents targeted at the nervous system and for models of CNS development, function, and dysfunction.

SUMMARY OF THE INVENTION

This invention provides in one aspect a composition for inducing the proliferation of a multipotent neural stem cell comprising a culture medium supplemented with at least one growth factor, preferably epidermal growth factor or transforming growth factor alpha.

The invention also provides a method for the in vitro proliferation and differentiation of neural stem cells and stem cell progeny comprising the steps of (a) isolating the cell from a mammal, (b) exposing the cell to a culture medium containing a growth factor, (c) inducing the cell to proliferate, and (d) inducing the cell to differentiate. Proliferation and perpetuation of the neural stem cell progeny can be carried out either in suspension cultures, or by allowing cells to adhere to a fixed substrate. Proliferation and differentiation can be done before or after transplantation, and in various combinations of in vitro or in vivo conditions, including (1) proliferation and differentiation in vitro, then transplantation, (2) proliferation in vitro. transplantation, then further proliferation and differentiation in vivo, and (3) proliferation in vitro, transplantation and differentiation in vivo.

The invention also provides for the proliferation and differentiation of the progenitor cells in vivo, which can be done directly in the host without the need for transplantation.

The invention also provides a method for the in vivo transplantation of neural stem cell progeny, treated as in any of (1) through (3) above, which comprises implanting, into a mammal, these cells which have been treated with at least one growth factor.

Furthermore, the invention provides a method for treating neurodegenerative diseases comprising administering to a mammal neural stem cell progeny which have been treated as in any of (1) through (3), and induced to differentiate into neurons and/or glia.

The invention also provides a method for treating neurodegenerative disease comprising stimulating in vivo mammalian CNS neural stem cells to proliferate and the neural stem cell progeny to differentiate into neurons and/or glia.

The invention also provides a method for the transfection of neural stem cells and stem cell progeny with vectors which can express the gene products for growth factors, growth factor receptors, and peptide neurotransmitters, or express enzymes which are involved in the synthesis of neurotransmitters, including those for amino acids, biogenic amines and neuropeptides, and for the transplantation of these transfected cells into regions of neurodegeneration.

In a still further aspect, the invention provides a method for th