WO1995000554A2 - Recepteurs de cellules souches hematopoietiques totipotentes et leurs ligands - Google Patents

Recepteurs de cellules souches hematopoietiques totipotentes et leurs ligands Download PDF

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WO1995000554A2
WO1995000554A2 PCT/US1994/006944 US9406944W WO9500554A2 WO 1995000554 A2 WO1995000554 A2 WO 1995000554A2 US 9406944 W US9406944 W US 9406944W WO 9500554 A2 WO9500554 A2 WO 9500554A2
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Ihor R. Lemischka
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The Trustees Of Princeton University
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K14/00—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
    • C07K14/435—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from animals; from humans
    • C07K14/475—Growth factors; Growth regulators
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K14/00—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
    • C07K14/435—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from animals; from humans
    • C07K14/705—Receptors; Cell surface antigens; Cell surface determinants
    • C07K14/71—Receptors; Cell surface antigens; Cell surface determinants for growth factors; for growth regulators
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K2319/00—Fusion polypeptide

Definitions

  • the present invention relates to hematopoietic stem cell receptors, ligands for such receptors, and nucleic acid molecules encoding such receptors and ligands.
  • the mammalian hematopoietic system comprises red and white blood cells. These cells are the mature cells that result from more primitive lineage-restricted cells. The cells of the hematopoietic system have been reviewed by Dexter and Spooncer in the Annual Review of Cell Biology _3, 423-441 (1987).
  • BFU-E erythroid burst- forming units
  • CFU-E erythroid colony-forming units
  • the white blood cells contain the mature cells of the lymphoid and myeloid systems.
  • the lymphoid cells include B lymphocytes and T lymphocytes.
  • the B and T lymphocytes result from earlier progenitor cells referred to by Dexter and Spooncer as preT and preB cells.
  • the myeloid system comprises a number of cells including granulocytes, platelets, monocytes, macrophages, and mega aryocytes.
  • the granulocytes are further divided into neutrophils, eosinophils, basophils and mast cells.
  • erythrocytes are responsible for oxygen and carbon dioxide transport.
  • T and B lymphocytes are responsible for cell-and antibody-mediated immune responses, respectively.
  • Platelets are involved in blood clotting.
  • Granulocytes and macrophages act generally as scavengers and accessory cells in the immune response against invading organisms and their by-products.
  • hematopoietic stem cells At the center of the hematopoietic system lie one or more totipotent hematopoietic stem cells, which undergo a series of differentiation steps leading to increasingly lineage-restricted progenitor cells. The more mature progenitor cells are restricted to producing one or two lineages.
  • G - CFC granulocyte/macrophage colony-forming cells
  • Meg-CFC megakaryocyte colony-forming cells
  • Eos-CFC eosinophil colony-forming cells
  • Bas-CFC basophil colony-forming cells
  • the hematopoietic system functions by means of a precisely controlled production of the various mature lineages.
  • the totipotent stem cell possesses the ability both to self renew and to differentiate into committed progenitors for all hematopoietic lineages. These most primitive of hematopoietic cells are both necessary and sufficient for the complete and permanent hematopoietic reconstitution of a radiation-ablated hematopoietic system in mammals.
  • the ability of stem cells to reconstitute the entire hematopoietic system is the basis of bone marrow transplant therapy.
  • hematopoiesis in vitro hematopoiesis can be established in the absence of added growth factors, provided that marrow stromal cells are added to the medium.
  • the relationship between stromal cells and hematopoietic growth factors in vivo is not understood. Nevertheless, hematopoietic growth factors have been shown to be highly active in vivo.
  • hematopoietic growth factors appear to exhibit a spectrum of activities. At one end of the spectrum are growth factors such as erythropoietin, which is believed to promote proliferation only of mature erythroid progenitor cells. In the middle of the spectrum are growth factors such as IL-3, which is believed to facilitate the growth and development of early stem cells as well as of numerous progenitor cells.
  • growth factors induced by IL-3 include those restricted to the granulocyte/macrophage, eosinophil, megakaryocyte, erythroid and mast cell lineages.
  • the receptor is the product of the W locus, c-kit, which is a member of the class of receptor protein tyrosine kinases.
  • the ligand for c-kit which is referred to by various names such as stem cell factor (SCF) and mast cell growth factor (MGF), is believed to be essential for the development of early hematopoietic stem cells and cells restricted to the erythroid and mast cell lineages in mice; see, for example, Copeland et al.. Cell (63, 175-183 (1990).
  • the c-kit ligand which stimulates a small number of mature cells, is believed to be more important in the renewal and development of stem cells then is IL-3, which is reported to stimulate proliferation of many mature cells (see above).
  • c-kit is a protein tyrosine kinase (pTK). It is becoming increasingly apparent that the protein tyrosine kinases play an important role as cellular receptors for hematopoietic growth factors.
  • Other receptor pTKs include the receptors of colony stimulating factor 1 (CSF-1) and PDGF.
  • the pTK family can be recognized by the presence of several conserved amino acid regions in the catalytic domain. These conserved regions are summarized by Hanks et al. in Science 241, 42-52 (1988), see Figure 1 starting on page 46 and by ilks in Proc. Natl. Acad. Sci. USA 8j5, 1603-1607 (1989), see Figure 2 on page 1605.
  • Additional protein tyrosine kinases that represent hematopoietic growth factor receptors are needed in order more effectively to stimulate the self-renewal of the totipotent hematopoietic stem cell and to stimulate the development of all cells of the hematopoietic system both in vitro and in vivo.
  • Novel hematopoietic growth factor receptors that are present only on primitive stem cells, but are not present on mature progenitor cells, are particularly desired.
  • Ligands for the novel receptors are also desirable to act as hematopoietic growth factors. Nucleic acid sequences encoding the receptors and ligands are needed to produce recombinant receptors and ligands.
  • the receptor protein tyrosine kinases having the amino acid sequences shown in Figure la. Figure lb and Figure 2 (See SEQ. ID. NOS. 2 , 4 and 6, respectively); ligands for the receptors; nucleic acid sequences that encode the ligands; and methods of stimulating the proliferation of primitive mammalian hematopoietic stem cells comprising contacting the stem cells with a ligand that binds to a receptor protein tyrosine kinase expressed in primitive mammalian hematopoietic cells and not expressed in mature hematopoietic cells.
  • Figure la.l through la.6 shows the cDNA and amino acid sequences of murine Flk2. All subsequent references to Figure la are intended to refer to Figure la.l through la.6.
  • the amino acid residues occur directly below the nucleotides in the open reading frame.
  • Amino acids -27 to -1 constitute the hydrophobic leader sequence.
  • Amino acids 1 to 517 constitute the extracellular receptor domain.
  • Amino acids 518 to 537 constitute the transmembrane region.
  • Amino acids 538 to 966 constitute the intracellular catalytic domain.
  • the sequence at residues 709-785 is a signature sequence characteristic of Flk2.
  • the protein tyrosine kinases generally have a signature sequence in this region. (See SEQ. ID. NOS. 1-2)
  • Figure lb.l through lb.6 shows the complete cDNA and amino acid sequences of human Flk2 receptor. All subsequent references to Figure lb are intended to refer to Figure lb.l through lb.6.
  • Amino acids -27 to -1 constitute the hydrophobic leader sequence.
  • Amino acids 1 to 516 constitute the extracellular receptor domain.
  • Amino acids 517 to 536 constitute the transmembrane region.
  • Amino acids 537 to 966 constitute the intracellular catalytic domain. (See SEQ. ID. NOS. 3-4)
  • Figure 2.1 through 2.9 shows the cDNA and amino acid sequences of murine Flkl. All subsequent references to Figure 2 are intended to refer to Figure 2.1 through 2.9.
  • Amino acids -19 to -1 constitute the hydrophobic leader sequence.
  • Amino acids 1 to 743 constitute the extracellular receptor domain.
  • Amino acids 744 to 765 constitute the transmembrane region.
  • Amino acids 766 to 1348 constitute the intracellular catalytic domain. (See SEQ. ID. NOS. 5-6)
  • Figure 3 shows the time response of binding between a murine stromal cell line (2016) and APtag-Flk2 as well as APtag-Flkl.
  • APtag without receptor SEAP
  • Figure 4 shows the dose response of binding between stromal cells (2016) and APtag-Flk2 as well as APtag-Flkl.
  • APtag without receptor SEAP
  • the invention relates to an isolated mammalian nucleic acid molecule encoding a receptor protein tyrosine kinase expressed in primitive mammalian hematopoietic cells and not expressed in mature hematopoietic cells.
  • the nucleic acid molecule may be a DNA, cDNA, or RNA molecule.
  • the mammal in which the nucleic acid molecule exists may be any mammal, such as a mouse, rat, rabbit, or human.
  • the nucleic acid molecule encodes a protein tyrosine kinase (pTK).
  • pTK protein tyrosine kinase
  • Members of the pTK family can be recognized by the conserved amino acid regions in the catalytic domains. Examples of pTK consensus sequences have been provided by Hanks et al. in Science 241, 42-52 (1988); see especially Figure 1 starting on page 46 and by Wilks in Proc. Natl. Acad. Sci. USA J3j5, 1603-1607 (1989); see especially Figure 2 on page 1605.
  • a methionine residue at position 205 in the conserved sequence WMAPES is characteristic of pTK's that are receptors.
  • the Hanks et al article identifies eleven catalytic sub- domains containing pTK consensus residues and sequences.
  • the pTKs of the present invention will have most or all of these consensus residues and sequences.
  • a pTK of the invention may contain all thirteen of these highly conserved residues and sequences. As a result of natural or synthetic mutations, the pTKs of the invention may contain fewer than all thirteen strongly conserved residues and sequences, such as 11, 9, or 7 such sequences.
  • the receptors of the invention generally belong to the same class of pTK sequences that c-kit belongs to. It has surprisingly been discovered, however, that a new functional class of receptor pTKs exists.
  • the new functional class of receptor pTKs is expressed in primitive hematopoietic cells, but not expressed in mature hematopoietic cells.
  • a primitive hematopoietic cell is totipotent, i.e. capable of reconstituting all hematopoietic blood cells in vivo.
  • a mature hematopoietic cell is non-self-renewing, and has limited proliferative capacity - i.e., a limited ability to give rise to multiple lineages.
  • Mature hematopoietic cells for the purposes of this specification, are generally capable of giving rise to only one or two lineages in vitro or in vivo. It should be understood that the hematopoietic system is complex, and contains many intermediate cells between the primitive totipotent hematopoietic stem cell and the totally committed mature hematopoietic cells defined above. As the stem cell develops into increasingly mature, lineage-restricted cells, it gradually loses its capacity for self-renewal.
  • the receptors of the present invention may and may not be expressed in these intermediate cells.
  • the necessary and sufficient condition that defines members of the new class of receptors is that they are present in the primitive, totipotent stem cell or cells, and not in mature cells restricted only to one or, at most, two lineages.
  • fetal liver kinase 2 An example of a member of the new class of receptor pTKs is called fetal liver kinase 2 (Flk2) after the organ in which it was found. There is approximately 1 totipotent stem cell per IO 4 cells in mid-gestation (day 14) fetal liver in mice. In addition to fetal liver, Flk2 is also expressed in fetal spleen, fetal thymus, adult brain, and adult marrow.
  • Flk2 is expressed in individual multipotential CFU-Blast colonies capable of generating numerous multilineage colonies upon replating. It is likely, therefore, that Flk2 is expressed in the entire primitive (i.e. self-renewing) portion of the hematopoietic hierarchy. This discovery is consistent with Flk2 being important in transducing putative self-renewal signals from the environment.
  • Flk2 is the first receptor tyrosine kinase known to be expressed in the T-lymphoid lineage.
  • the fetal liver mRNA migrates relative to 28S and 18S ribosomal bands on formaldehyde agarose gels at approximately 3.5 kb, while the brain message is considerably larger.
  • Flk2 m-RNA from both brain and bone marrow migrated at approximately 3.5 kb.
  • a second pTK receptor is also included in the present invention.
  • This second receptor which is called fetal liver kinase 1 (Flkl)
  • Flkl fetal liver kinase 1
  • the amino acid sequence of murine Flkl is given in Figure 2. (See SEQ. ID. NOS. 5-6)
  • the present invention includes the Flkl receptor as well as DNA, cDNA and RNA encoding Flkl.
  • the DNA sequence of murine Flkl is also given in Figure 2. (See SEQ. ID. NO. 5) Flkl may be found in the same organs as Flk2, as well as in fetal brain, stomach, kidney, lung, heart and intestine; and in adult kidney, heart, spleen, lung, muscle, and lymph nodes.
  • the receptor protein tyrosine kinases of the invention are known to be divided into easily found domains.
  • the DNA sequence corresponding to the pTKs encode, starting at their 5'-ends, a hydrophobic leader sequence followed by a hydrophilic extracellular domain, which binds to, and is activated by, a specific ligand.
  • a hydrophobic transmembrane region Immediately downstream from the extracellular receptor domain, is a hydrophobic transmembrane region. The transmembrane region is immediately followed by a basic catalytic domain, which may easily be identified by reference to the Hanks et al. and Wilks articles discussed above.
  • the following table shows the nucleic acid and amino acid numbers that correspond to the signal peptide, the extracellular domain, the transmembrane region and the intracellular domain for murine Flkl ( Flkl), murine Flk2 (mFlk2) and human Flk2 (hFlk2).
  • the present invention includes the extracellular receptor domain lacking the transmembrane region and catalytic domain.
  • the hydrophobic leader sequence is also removed from the extracellular domain.
  • the hydrophobic leader sequence includes amino acids -27 to -1. (See SEQ. ID. NOS. 2 and 4)
  • the transmembrane region of Flk2 which separates the extracellular receptor domain from the catalytic domain, is encoded by nucleotides 1663 (T) to 1722 (C). These nucleotides correspond to amino acid residues 545 (Phe) to 564 (Cys). (See SEQ. ID. NOS. 1-2)
  • the amino acid sequence between the transmembrane region and the catalytic sub-domain (amino acids 618-623) identified by Hanks et al. as sub-domain I (i.e., GXGXXG) is characteristic of receptor protein tyrosine kinases.
  • the extracellular domain may also be identified through commonly recognized criteria of extracellular amino acid sequences. The determination of appropriate criteria is known to those skilled in the art, and has been described, for example, by Hopp et al, Proc. Nat'l Acad. Sci. USA 7_8, 3824-3828 (1981); Kyte et al, J. Mol. Biol. 157, 105-132 (1982); Emini, J. Virol. j55_, 836-839 (1985); Jameson et al, CA BIOS 4., 181-186 (1988); and Karplus et al, Naturwissenschaften 72, 212-213 (1985). Amino acid domains predicted by these criteria to be surface exposed characteristic of extracellular domains.
  • nucleic acid molecules that encode the receptors of the invention may be inserted into known vectors for use in standard recombinant DNA techniques.
  • Standard recombinant DNA techniques are those such as are described in Sambrook et al., "Molecular Cloning,” Second Edition, Cold Spring Harbor Laboratory Press (1987) and by
  • the vectors may be circular (i.e. plasmids) or non- circular. Standard vectors are available for cloning and expression in a host.
  • the host may be prokaryotic or eucaryotic. Prokaryotic hosts are preferably E. coli.
  • Preferred eucaryotic hosts include yeast, insect and mammalian cells. Preferred mammalian cells include, for example, CHO, COS and human cells.
  • the invention also includes ligands that bind to the receptor pTKs of the invention.
  • the ligands stimulate the proliferation of additional primitive stem cells, differentiation into more mature progenitor cells, or both.
  • the ligand may be a growth factor that occurs naturally in a mammal, preferably the same mammal that produces the corresponding receptor.
  • the growth factor may be isolated and purified, or be present on the surface of an isolated population of cells, such as stromal cells.
  • a partial amino acid sequence of a Flk2 ligand is AQSLSFXFTKFDLD, wherein X is any amino acid. (See SEQ. ID. NO. 11)
  • the ligand may also be a molecule that does not occur naturally in a mammal.
  • antibodies, preferably monoclonal, raised against the receptors of the invention or against anti-ligand antibodies mimic the shape of, and act as, ligands if they constitute the negative image of the receptor or anti-ligand antibody binding site.
  • the ligand may also be a non- protein molecule that acts as a ligand when it binds to, or otherwise comes into contact with, the receptor.
  • nucleic acid molecules encoding the ligands of the invention are provided.
  • the nucleic acid molecule may be RNA, DNA or cDNA.
  • the invention also includes a method of stimulating the proliferation and/or differentiation of primitive mammalian hematopoietic stem cells as defined above.
  • the method comprises contacting the stem cells with a ligand in accordance with the present invention.
  • the stimulation of proliferation and/or differentiation may occur in vitro or in vivo.
  • a ligand according to the invention to stimulate proliferation of stem cells in vitro and in vivo has important therapeutic applications.
  • Such applications include treating mammals, including humans, whose primitive stem cells do not sufficiently undergo self-renewal.
  • Example of such medical problems include those that occur when defects in hematopoietic stem cells or their related growth factors depress the number of white blood cells.
  • Examples of such medical problems include anemia, such as macrocytic and aplastic anemia. Bone marrow damage resulting from cancer chemotherapy and radiation is another example of a medical problem that would be helped by the stem cell factors of the invention.
  • the invention includes functional equivalents of the pTK receptors, receptor domains, and ligands described above as well as of the nucleic acid sequences encoding them.
  • a protein is considered a functional equivalent of another protein for a specific function if the equivalent protein is immunologically cross-reactive with, and has the same function as, the receptors and ligands of the invention.
  • the equivalent may, for example, be a fragment of the protein, or a substitution, addition or deletion mutant of the protein.
  • amino acids for example, it is possible to substitute amino acids in a sequence with equivalent amino acids.
  • Groups of amino acids known normally to be equivalent are:
  • Substitutions, additions and/or deletions in the receptors and ligands may be made as long as the resulting equivalent receptors and ligands are immunologically cross reactive with, and have the same function as, the native receptors and ligands.
  • the equivalent receptors and ligands will normally have substantially the same amino acid sequence as the native receptors and ligands.
  • An amino acid sequence that is substantially the same as another sequence, but that differs from the other sequence by means of one or more substitutions, additions and/or deletions is considered to be an equivalent sequence.
  • Equivalent nucleic acid molecules include nucleic acid sequences that encode equivalent receptors and ligands as defined above. Equivalent nucleic acid molecules also include nucleic acid sequences that differ from native nucleic acid sequences in ways that do not affect the corresponding amino acid sequences.
  • a source of stem cells is provided. Suitable sources include fetal liver, spleen, or thymus cells or adult marrow or brain cells.
  • suitable mouse fetal liver cells may be obtained at day 14 of gestation.
  • Mouse fetal thymus cells may be obtained at day 14-18, preferably day 15, of gestation.
  • Suitable fetal cells of other mammals are obtained at gestation times corresponding to those of mouse.
  • Total RNA is prepared by standard procedures from stem cell receptor-containing tissue. The total RNA is used to direct cDNA synthesis. Standard methods for isolating RNA and synthesizing cDNA are provided in standard manuals of molecular biology such as, for example, in Sambrook et al., "Molecular Cloning," Second Edition, Cold Spring Harbor Laboratory Press (1987) and in Ausubel et al., (Eds), "Current Protocols in Molecular Biology,” Greene Associates/Wiley Interscience, New York (1990).
  • the cDNA of the receptors is amplified by known methods.
  • the cDNA may be used as a template for amplification by polymerase chain reaction (PCR); see Saiki et al.. Science, 239. 487 (1988) or Mullis et al., U.S. patent 4,683,195.
  • the sequences of the oligonucleotide primers for the PCR amplification are derived from the sequences of known receptors, such as from the sequences given in Figures la and lb for Flk2 and in Figure 2 for Flkl, preferably from Flk2. (See SEQ. ID. NOS. 1, 3 and 5, respectively)
  • the oligonucleotides are synthesized by methods known in the art. Suitable methods include those described by Caruthers in Science 230, 281-285 (1985).
  • the upstream oligonucleotide is complementary to the sequence at the 5' end, preferably encompassing the ATG start codon and at least 5-10 nucleotides upstream of the start codon.
  • the downstream oligonucleotide is complementary to the sequence at the 3' end, optionally encompassing the stop codon.
  • a mixture of upstream and downstream oligonucleotides are used in the PCR amplification. The conditions are optimized for each particular primer pair according to standard procedures. The PCR product is analyzed by electrophoresis for the correct size cDNA corresponding to the sequence between the primers.
  • the coding region may be amplified in two or more overlapping fragments.
  • the overlapping fragments are designed to include a restriction site permitting the assembly of the intact cDNA from the fragments.
  • the amplified DNA encoding the receptors of the invention may be replicated in a wide variety of cloning vectors in a wide variety of host cells.
  • the host cell may be prokaryotic or eukaryotic.
  • the DNA may be obtained from natural sources and, optionally, modified, or may be synthesized in whole or in part.
  • the vector into which the DNA is spliced may comprise segments of chromosomal, non-chromosomal and synthetic DNA sequences.
  • suitable prokaryotic cloning vectors include plasmids from E. coli, such as colEl, pCRl, pBR322, pMB9, pUC, pKSM, and RP4.
  • Prokaryotic vectors also include derivatives of phage DNA such as M13 and other filamentous single-stranded DNA phages.
  • DNA encoding the receptors of the invention are inserted into a suitable vector and expressed in a suitable prokaryotic or eucaryotic host.
  • Vectors for expressing proteins in bacteria, especially E.coli are known. Such vectors include the PATH vectors described by Dieckmann and Tzagoloff in J. Biol. Chem. 260, 1513-1520 (1985). These vectors contain DNA sequences that encode anthranilate synthetase (TrpE) followed by a polylinker at the carboxy terminus.
  • TrpE anthranilate synthetase
  • Vectors useful in yeast are available.
  • a suitable example is the 2 ⁇ plasmid.
  • Suitable vectors for use in mammalian cells are also known.
  • Such vectors include well-known derivatives of SV-40, adenovirus, retrovirus-derived DNA sequences and shuttle vectors derived from combination of functional mammalian vectors, such as those described above, and functional plasmids and phage DNA.
  • the expression vectors useful in the present invention contain at least one expression control sequence that is operatively linked to the DNA sequence or fragment to be expressed.
  • the control sequence is inserted in the vector in order to control and to regulate the expression of the cloned DNA sequence.
  • useful expression control sequences are the lac system, the trp system, the tac system, the trc system, major operator and promoter regions of phage lambda, the control region of fd coat protein, the glycolytic promoters of yeast, e.g., the promoter for 3-phosphoglycerate kinase, the promoters of yeast acid phosphatase, e.g., Pho5, the promoters of the yeast alpha-mating factors, and promoters derived from polyoma, adenovirus, retrovirus, and simian virus, e.g., the early and late promoters or SV40, and other sequences known to control the expression of genes of prokaryotic or eukaryotic cells and their
  • Vectors containing the receptor-encoding DNA and control signals are inserted into a host cell for expression of the receptor.
  • Some useful expression host cells include well-known prokaryotic and eukaryotic cells.
  • Some suitable prokaryotic hosts include, for example, E. coli, such as E. coli SG-936, E. coli HB 101, E. coli W3110, E. coli X1776, E. coli X2282, E. coli DHI, and E. coli MRC1, Pseudomonas, Bacillus, such as Bacillus subtilis, and Streptomyces.
  • suitable eukaryotic cells include yeast and other fungi, insect, animal cells, such as COS cells and CHO cells, human cells and plant cells in tissue culture.
  • RNA encoding the receptors are obtained from a source of human cells enriched for primitive stem cells. Suitable human cells include fetal spleen, thymus and liver cells, and umbilical cord blood as well as adult brain and bone marrow cells. The human fetal cells are preferably obtained on the day of gestation corresponding to mid-gestation in mice.
  • the amino acid sequences of the human flk receptors as well as of the nucleic acid sequences encoding them are homologous to the amino acid and nucleotide sequences of the mouse receptors.
  • sequence of a first protein such as a receptor or a ligand, or of a nucleic acid molecule that encodes the protein, is considered homologous to a second protein or nucleic acid molecule if the amino acid or nucleotide sequence of the first protein or nucleic acid molecule is at least about 30% homologous, preferably at least about 50% homologous, and more preferably at least about 65% homologous to the respective sequences of the second protein or nucleic acid molecule.
  • the amino acid or nucleotide sequence of the first protein or nucleic acid molecule is at least about 75% homologous, preferably at least about 85% homologous, and more preferably at least about 95% homologous to the amino acid or nucleotide sequence of the second protein or nucleic acid molecule.
  • Combinations of mouse oligonucleotide pairs are used as PCR primers to amplify the human homologs from the cells to account for sequence divergence.
  • the remainder of the procedure for obtaining the human flk homologs are similar to those described above for obtaining mouse flk receptors.
  • the less than perfect homology between the human flk homologs and the mouse oligonucleotides is taken into account in determining the stringency of the hybridization conditions.
  • the receptor may be the entire protein as it exists in nature, or an antigenic fragment of the whole protein.
  • the fragment comprises the predicted extra-cellular portion of the molecule.
  • Antigenic fragments may be identified by methods known in the art. Fragments containing antigenic sequences may be selected on the basis of generally accepted criteria of potential antigenicity and/or exposure. Such criteria include the hydrophilicity and relative antigenic index, as determined by surface exposure analysis of proteins. The determination of appropriate criteria is known to those skilled in the art, and has been described, for example, by Hopp et al, Proc. Nat'l Acad. Sci. USA 78, 3824-3828 (1981); Kyte et al, J. Mol. Biol. 157, 105-132 (1982); Emini, J. Virol.
  • Amino acid domains predicted by these criteria to be surface exposed are selected preferentially over domains predicted to be more hydrophobic or hidden.
  • the proteins and fragments of the receptors to be used as antigens may be prepared by methods known in the art. Such methods include isolating or synthesizing DNA encoding the proteins and fragments, and using the DNA to produce recombinant proteins, as described above.
  • Fragments of proteins and DNA encoding the fragments may be chemically synthesized by methods known in the art from individual amino acids and nucleotides. Suitable methods for synthesizing protein fragments are described by Stuart and Young in “Solid Phase Peptide Synthesis," Second Edition, Pierce
  • the receptor fragment may be conjugated to a carrier molecule in order to produce antibodies.
  • suitable carrier molecules include keyhole limpet hemocyanin, Ig sequences, TrpE, and human or bovine serum albumen. Conjugation may be carried out by methods known in the art. One such method is to combine a cysteine residue of the fragment with a cysteine residue on the carrier molecule.
  • the antibodies are preferably monoclonal.
  • Monoclonal antibodies may be produced by methods known in the art. These methods include the immunological method described by Kohler and Milstein in Nature 256, 495-497 (1975) and Campbell in “Monoclonal Antibody Technology, The Production and Characterization of Rodent and Human Hybridomas” in Burdon et al., Eds, Laboratory Techniques in Biochemistry and Molecular Biology, Volume 13, Elsevier Science Publishers, Amsterdam (1985); as well as by the recombinant DNA method described by Huse et al in Science 246, 1275-1281 (1989).
  • Polyclonal or monoclonal antisera shown to be reactive with receptor-encoded native proteins, such as with Flkl and Flk2 encoded proteins, expressed on the surface of viable cells are used to isolate antibody-positive cells.
  • One method for isolating such cells is flow cytometry; see, for example, Loken et al., European patent application 317,156.
  • the cells obtained are assayed for stem cells by engraftment into radiation-ablated hosts by methods known in the art; see, for example, Jordan et al.. Cell 61, 953-963 (1990).
  • Additional novel receptor tyrosine kinase cDNAs are obtained by amplifying cDNAs from stem cell populations using oligonucleotides as PCR primers; see above.
  • suitable oligonucleotides are PTKl and PTK2, which were described by Wilks et al. in Proc. Natl. Acad. Sci. USA 86, 1603-1607 (1989).
  • Novel cDNA is selected on the basis of differential hybridization screening with probes representing known kinases.
  • the cDNA clones hybridizing only at low stringency are selected and sequenced. The presence of the amino acid triplet DFG confirms that the sequence represents a kinase.
  • the diagnostic methionine residue in the WMAPES motif is indicative of a receptor-like kinase, as described above.
  • Potentially novel sequences obtained are compared to available sequences using databases such as Genbank in order to confirm uniqueness.
  • Gene-specific oligonucleotides are prepared as described above based on the sequence obtained. The oligonucleotides are used to analyze stem cell enriched and depleted populations for expression.
  • Such cell populations in mice are described, for example, by Jordan et al. in Cell .61, 953-956 (1990); Ikuta et al. in Cell 62, 863-864 (1990); Spangrude et al. in Science 241, 58-62 (1988); and Szilvassy et al. in Blood _4, 930-939 (1989). Examples of such human cell populations are described as CD33 ⁇ CD34 * by Andrews et al. in the Journal of Experimental Medicine 169, 1721-1731
  • Cells that may be used for obtaining ligands include stromal cells, for example stromal cells from fetal liver, fetal spleen, fetal thymus and fetal or adult bone marrow. Cell lines expressing ligands are established and screened.
  • cells such as stromal (non-hematopoietic) cells from fetal liver are immortalized by known methods.
  • known methods of immortalizing cells include transduction with a temperature sensitive SV40 T-antigen expressed in a retroviral vector. Infection of fetal liver cells with this virus permits the rapid and efficient establishment of multiple independent cell lines. These lines are screened for ligand activity by methods known in the art, such as those outlined below.
  • Ligands for the receptors of the invention may be obtained from the cells in several ways.
  • a bioassay system for ligand activity employs chimeric tagged receptors; see, for example, Flanagan et al.. Cell 63, 185-194 (1990).
  • One strategy measures ligand binding directly via a histochemical assay.
  • Fusion proteins comprising the extracellular receptor domains and secretable alkaline phosphatase (SEAP) are constructed and transfected into suitable cells such as NIH/3T3 or COS cells.
  • SEAP secretable alkaline phosphatase
  • Flanagan et al. refer to such DNA or amino acid constructs as APtag followed by the name of the receptor - i.e. APtag-c-kit.
  • the fusion proteins bind with high affinity to cells expressing surface-bound ligand. Binding is detectable by the enzymatic activity of the alkaline phosphatase secreted into the medium.
  • the bound cells which are often stromal cells, are isolated from the APtag-receptor complex.
  • some stromal cells that bind APtag-Flkl and APtag-Flk2 fusion proteins include mouse fetal liver cells (see example 1); human fetal spleen cells (see example 3); and human fetal liver (example 3).
  • Some stromal fetal thymus cells contain Flkl ligand (example 3).
  • a cDNA library is constructed from the isolated stromal cells in a suitable expression vector, preferably a phage such as CDM8, pSV Sport (BRL Gibco) or piH3, (Seed et al., Proc. Natl. Acad. Sci. USA 84, 3365-3369 (1987)).
  • a suitable expression vector preferably a phage such as CDM8, pSV Sport (BRL Gibco) or piH3, (Seed et al., Proc. Natl. Acad. Sci. USA 84, 3365-3369 (1987)
  • the library is transfected into suitable host cells, such as COS cells. Cells containing ligands on their surface are detected by known methods, see above.
  • transfected COS cells are distributed into single cell suspensions and incubated with the secreted alkaline phosphatase-flk receptor fusion protein, which is present in the medium from NIH/3T3 or COS cells prepared by the method described by Flanagan et al., see above.
  • Alkaline phosphatase-receptor fusion proteins that are not bound to the cells are removed by centrifugation, and the cells are panned on plates coated with antibodies to alkaline phosphatase.
  • Bound cells are isolated following several washes with a suitable wash reagent, such as 5% fetal bovine serum in PBS, and the DNA is extracted from the cells. Additional details of the panning method described above may be found in an article by Seed et al., Proc. Natl. Acad. Sci. USA 84 / 3365-3369 (1987).
  • the putative extracellular ligand binding domains of the receptors are fused to the transmembrane and kinase domains of the human c-fms tyrosine kinase and introduced into 3T3 fibroblasts.
  • the human c-fms kinase is necessary and sufficient to transduce proliferative signals in these cells after appropriate activation i.e. with the Flkl or Flk2 ligand.
  • the 3T3 cells expressing the chimeras are used to screen putative sources of ligand in a cell proliferation assay.
  • a retrovirus is introduced into random chromosomal positions in a large population of these cells. In a small fraction, the retrovirus is inserted in the vicinity of the ligand-encoding gene, thereby activating it. These cells proliferate due to autocrine stimulation of the receptor. The ligand gene is "tagged" by the retrovirus, thus facilitating its isolation.
  • Example 1 Cells containing mouse Flkl and Flk2 ligands. Murine stromal cell line 2018.
  • fetal liver cells are disaggregated with collagen and grown in a mixture of Dulbecco's Modified Eagle's Medium (DMEM) and 10% heat- inactivated fetal calf serum at 37°C.
  • DMEM Dulbecco's Modified Eagle's Medium
  • the cells are immortalized by standard methods.
  • a suitable method involves introducing DNA encoding a growth regulating- or oncogene-encoding sequence into the target host cell.
  • the DNA may be introduced by means of transduction in a recombinant viral particle or transfection in a plasmid. See, for example, Hammerschmidt et al.. Nature 340, 393-397 (1989) and Abcouwer et al. Biotechnology _]_, 939-946 (1989).
  • Retroviruses are the preferred viral vectors, although SV40 and Epstein-Barr virus can also serve as donors of the growth-enhancing sequences.
  • a suitable retrovirus is the ecotropic retrovirus containing a temperature sensitive SV40 T- antigen (tsA58) and a G418 resistance gene described by McKay in Cell .66., 713-729 (1991). After several days at 37°C, the temperature of the medium is lowered to 32°C. Cells are selected with G418 (0.5 mg/ml). The selected cells are expanded and maintained.
  • a mouse stromal cell line produced by this procedure is called 2018 and was deposited on October 30, 1991 in the American Type Culture Collection, Rockville, Maryland, USA (ATCC); accession number CRL 10907.
  • Example 2 Cells containing human Flkl and Flk2 ligands.
  • HBSS Hanks Balanced Salt Solution
  • the disrupted tissue is centrifuged at 200 xg for 15 minutes at room temperature.
  • the resulting pellet is resuspended in 10- 20 ml of a tissue culture grade trypsin-EDTA solution (Flow Laboratories).
  • the resuspended tissue is transferred to a sterile flask and stirred with a stirring bar at room temperature for 10 minutes.
  • One ml of heat-inactivated fetal bovine calf serum (Hyclone) is added to a final concentration of 10% in order to inhibit trypsin activity.
  • Collagenase type IV (Sigma) is added from a stock solution (10 mg/ml in HBSS) to a final concentration of 100 ug/ml in order to disrupt the stromal cells.
  • the tissue is stirred at room temperature for an additional 2.5 hours; collected by centrifugation (400xg, 15 minutes); and resuspended in "stromal medium," which contains Iscove's modification of DMEM supplemented with 10% heat-inactivated fetal calf serum, 5% heat-inactivated human serum (Sigma), 4 mM L- glutamine, lx sodium pyruvate, (stock of lOOx Sigma), lx non- essential amino acids (stock of lOOx, Flow), and a mixture of antibiotics kanomycin, neomycin, penicillin, streptomycin. Prior to resuspending the pellet in the stromal medium, the pellet is washed one time with HBSS. It is convenient to suspend the cells in 60 ml of medium. The number of cultures depends on the amount of tissue.
  • Resuspended Cells (example 2) that are incubated at 37°C with 5% carbon dioxide begin to adhere to the plastic plate within 10-48 hours. Confluent monolayers may be observed within 7-10 days, depending upon the number of cells plated in the initial innoculum. Non-adherent and highly refractile cells adhering to the stromal cell layer as colonies are separately removed by pipetting and frozen. Non-adherent cells are likely sources of populations of self-renewing stem cells containing Flk2. The adherent stromal cell layers are frozen in aliquots for future studies or expanded for growth in culture.
  • Non-adherent fetal stem cells attach to the stromal cells and form colonies (colony forming unit - CFU).
  • Stromal cells and CFU are isolated by means of sterile glass cylinders and expanded in culture.
  • a clone, called Fsp 62891 contains the Flk2 ligand.
  • Fsp 62891 was deposited in the American Type Culture Collection, Rockville, Maryland, U.S.A on November 21, 1991, accession number CRL 10935.
  • Fetal liver and fetal thymus cells are prepared in a similar way. Both of these cell types produce ligands of Flkl and, in the case of liver, some Flk2.
  • F.thy 62891 fetal thymus cell line
  • FL 62891 fetal liver cell line
  • Stable human cell lines are prepared from fetal cells with the same temperature sensitive immortalizing virus used to prepare the murine cell line described in example 1.
  • Plasmids that express secretable alkaline phosphatase are described by Flanagan and Leder in Cell .63., 185-194 (1990).
  • the plasmids contain a promoter, such as the LTR promoter; a polylinker, including Hindlll and Bglll; DNA encoding SEAP; a poly-A signal; and ampicillin resistance gene; and replication site.
  • Plasmids that express fusion proteins of SEAP and the extracellular portion of either Flkl or Flk2 are prepared in accordance with the protocols of Flanagan and Leader in Cell 63, 185-194 (1990) and Berger et al., Gene _ ⁇ _ ⁇ _, 1-10 (1988). Briefly, a Hindlll-Bam HI fragment containing the extracellular portion of Flkl or Flk2 is prepared and inserted into the Hindlll-Bglll site of the plasmid described in example 5.
  • the plasmids from Example 6 are transfected into Cos-7 cells by DEAE-dextran (as described in Current Protocols in Molecular Biology, Unit 16.13, "Transient Expression of Proteins Using Cos Cells," 1991); and cotransfected with a selectable marker, such as pSV7neo, into NIH/3T3 cells by calcium precipitation.
  • DEAE-dextran as described in Current Protocols in Molecular Biology, Unit 16.13, "Transient Expression of Proteins Using Cos Cells," 1991
  • a selectable marker such as pSV7neo
  • NIH/3T3 cells are selected with 600 ⁇ g/ml G418 in 100 mm plates. Over 300 clones are screened for secretion of placental alkaline phosphatase activity. The assay is performed by heating a portion of the supernatant at 65°C for 10 minutes to inactivate background phosphatase activity, and measuring the OD 405 after incubating with 1M diethanolamine (pH 9.8), 0.5 mM MgCl 2 , 10 mM L-homoarginine (a phosphatase inhibitor), 0.5 mg/ml BSA, and 12 mM p-nitrophenyl phosphate. Human placental alkaline phosphatase is used to perform a standard curve.
  • the APtaq-Flkl clones (F- 1AP21-4) produce up to 10 ⁇ g alkaline phosphatase activity/ml and the APtaq-Flk2 clones (F-2AP26-0) produce up to 0.5 ⁇ g alkaline phosphatase activity/ml.
  • APtaq-Flkl or APtag-Flk2 The binding of APtaq-Flkl or APtag-Flk2 to cells containing the appropriate ligand is assayed by standard methods. See, for example, Flanagan and Leder, Cell .63.:185-194, 1990).
  • Cells i.e., mouse stromal cells, human fetal liver, spleen or thymus, or various control cells
  • HBHA Hormonos balanced salt solution with 0.5 mg/ml BSA, 0.02% NaN 3 , 20 mM HEPES, pH 7.0).
  • Supernatants from transfected COS or NIH/3T3 cells containing either APtaq- Flkl fusion protein, APtag-Flk2 fusion protein, or APtag without a receptor are added to the cell monolayers and incubated for two hours at room temperature on a rotating platform.
  • the concentration of the APtaq-Flkl fusion protein, APtag-Flk2 fusion protein, or APtag without a receptor is 60 ng/ml of alkaline phosphatase as determined by the standard alkaline phosphatase curve (see above).
  • the cells are then rinsed seven times with HBHA and lysed in 350 ⁇ l of 1% Triton X- 100, 10 mM Tris-HCl (pH 8.0).
  • the lysates are transferred to a microfuge tube, along with a further 150 ⁇ l rinse with the same solution. After vortexing vigorously, the samples are centrifuged for five minutes in a microfuge, heated at 65°C for 12 minutes to inactivate cellular phosphatases, and assayed for phosphatase activity as described previously.
  • Plasmids that express fusion proteins of the extracellular portion of either Flkl or Flk2 and the intracellular portion of c-fms are prepared in a manner similar to that described under Example 6 (Plasmid for expressing APtag-Flk2 and APtag-Flkl fusion proteins). Briefly, a Hind III - Bam HI fragment containing the extracellular portion of Flkl or Flk2 is prepared and inserted into the Hind III - Bgl II site of a pLH expression vector containing the intracellular portion of c-fms.
  • the plasmids from Example 8A are transfected into NIH/3T3 cells by calcium.
  • the intracellular portion of c-fms is detected by Western blotting.
  • cDNA expressing mouse ligand for Flkl and Flk2 is prepared by known methods. See, for example. Seed, B., and Aruffo, A. PNAS .84.:3365-3369, 1987; Simmons, D. and Seed, B. J. Immunol. 141:2797-2800: and D'Andrea, A.D., Lodish, H.F. and Wong, G.G. Cell 7.:277-285, 1989).
  • RNA isolation (a) RNA isolation; (b) poly A RNA preparation; (c) cDNA synthesis; (d) cDNA size fractionation; (e) propagation of plasmids (vector);
  • guanidine thiocyanate (GuSCN) is dissolved in 0.55 ml of 25% LiCl (stock filtered through 0.45 micron filter). 20 ⁇ l of mercaptoethanol is added. (The resulting solution is not good for more than about a week at room temperature.)
  • the 2018 stromal cells are centrifuged, and 1 ml of the solution described above is added to up to 5 x IO 7 cells.
  • the cells are sheared by means of a polytron until the mixture is non-viscous.
  • the sheared mixture is layered on 1.5 ml of 5.7M CsCl (RNase free; 1.26 g CsCl added to every ml 10 mM EDTA pH8), and overlaid with RNase-free water if needed.
  • the mixture is spun in an SW55 rotor at 50 krpm for 2 hours.
  • RNA molecules e.g., 5S
  • the volumes are scaled down, and the mixture is overlaid with GuSCN in RNase-free water on a gradient (precipitation is inefficient when RNA is dilute ) .
  • a disposable polypropylene column is prepared by washing with 5M NaOH and then rinsing with RNase-free water. For each milligram of total RNA, approximately 0.3 ml (final packed bed) of oligo dT cellulose is added.
  • the oligo dT cellulose is prepared by resuspending approximately 0.5 ml of dry powder in 1 ml of 0.1M NaOH and transferring it into the column, or by percolating 0.1M NaOH through a previously used column.
  • the column is washed with several column volumes of RNase-free water until the pH is neutral, and rinsed with 2-3 ml of loading buffer.
  • the column bed is transferred to a sterile 15 ml tube using 4-6 ml of loading buffer.
  • Total RNA from the 2018 cell line is heated to 70°C for 2-3 minutes. LiCl from RNase-free stock is added to the mixture to a final concentration of 0.5M. The mixture is combined with oligo dT cellulose in the 15 ml tube, which is vortexed or agitated for 10 minutes. The mixture is poured into the column, and washed with 3 ml loading buffer, and then with 3 ml of middle wash buffer. The mRNA is eluted directly into an SW55 tube with 1.5 ml of 2 mM EDTA and 0.1% SDS, discarding the first two or three drops.
  • the eluted mRNA is precipitated by adding 1/10 volume of 3M sodium acetate and filling the tube with ethanol. The contents of the tube are mixed, chilled for 30 minutes at -20°C, and spun at 50 krpm at 5°C for 30 minutes. After the ethanol is decanted, and the tube air dried, the mRNA pellet is resuspended in 50-100 ⁇ l of RNase-free water. 5 ⁇ l of the resuspended mRNA is heated to 70°C in MOPS/EDTA/formaldehyde, and examined on an RNase-free 1% agarose gel. 9c. cDNA Synthesis
  • the protocol used is a variation of the method described by Gubler and Hoffman in Gene 25_, 263-270 (1983).
  • First Strand 4 ⁇ g of mRNA is added to a microfuge tube, heated to approximately 100°C for 30 seconds, quenched on ice. The volume is adjusted to 70 ⁇ l with RNAse-free water. 20 ⁇ l of RTl buffer, 2 ⁇ l of RNAse inhibitor (Boehringer 36 u/ ⁇ l), 1 ⁇ l of 5 ⁇ g/ ⁇ l of oligo dT (Collaborative Research), 2.5 ⁇ l of 20 mM dXTP's (ultrapure - US Bioche icals) , 1 ⁇ l of 1M DTT and 4 ⁇ l of RT-XL (Life Sciences, 24 u/ ⁇ l) are added. The mixture is incubated at 42°C for 40 minutes, and inactivated by heating at " 0°C for 10 minutes.
  • Second Strand 320 ⁇ l of RNAse-free water, 80 ⁇ l of RT2 buffer, 5 ⁇ l of DNA Polymerase I (Boehringer, 5 U/ ⁇ l), 2 ⁇ l RNAse H (BRL 2 u/ ⁇ l) are added to the solution containing the first strand. The solution is incubated at 15°C for one hour and at 22°C for an additional hour. After adding 20 ⁇ l of 0.5M EDTA, pH 8.0, the solution is extracted with phenol and precipitated by adding NaCl to 0.5M linear polyacrylamide (carrier) to 20 ⁇ g/ml, and filling the tube with EtOH. The tube is spun for 2-3 minutes in a microfuge, vortexed to dislodge precipitated material from the wall of the tube, and respun for one minute.
  • Adaptors provide specific restriction sites to facilitate cloning, and are available from BRL Gibco, New England Biolabs, etc. Crude adaptors are resuspended at a concentration of 1 ⁇ g/ ⁇ l. MgS0 4 is added to a final concentration of 10 mM, followed by five volumes of EtOH. The resulting precipitate is rinsed with 70% EtOH and resuspended in TE at a concentration of 1 ⁇ g/ ⁇ l. To kinase, 25 ⁇ l of resuspended adaptors is added to 3 ⁇ l of 10X kinasing buffer and 20 units of kinase. The mixture is incubated at 37°C overnight.
  • the precipitated cDNA is resuspended in 240 ⁇ l of TE (10/1). After adding 30 ⁇ l of 10X low salt buffer, 30 ⁇ l of 10X ligation buffer with 0.ImM ATP, 3 ⁇ l (2.4 ⁇ g) of kinased 12-mer adaptor sequence, 2 ⁇ l (1.6 ⁇ g) of kinased 8-mer adaptor sequence, and 1 ⁇ l of T4 DNA ligase (BioLabs, 400 u/ ⁇ l, or Boehringer, 1 Weiss unit ml), the mixture is incubated at 15°C overnight. The cDNA is extracted with phenol and precipitated as above, except that the extra carrier is omitted, and resuspended in 100 ⁇ l of TE.
  • a 20% KOAc, 2 mM EDTA, 1 ⁇ g/ml ethidium bromide solution and a 5% KOAc, 2 mM EDTA, 1 ⁇ g/ml ethidium bromide solution are prepared.
  • 2.6 ml of the 20% KOAc solution is added to the back chamber of a small gradient maker. Air bubbles are removed from the tube connecting the two chambers by allowing the 20% solution to flow into the front chamber and forcing the solution to return to the back chamber by tilting the gradient maker.
  • the passage between the chambers is closed, and 2.5 ml of 5% solution is added to the front chamber.
  • any liquid in the tubing from a previous run is removed by allowing the 5% solution to flow to the end of the tubing, and then to return to its chamber.
  • the apparatus is placed on a stirplate, and, with rapid stirring, the topcock connecting the two chambers and the front stopcock are opened.
  • a polyallomer 5W55 tube is filled from the bottom with the KOAc solution.
  • the gradient is overlaid with 100 ⁇ l of cDNA solution, and spun for three hours at 50k rpm at 22°C. To collect fractions from the gradient, the SW55 tube is pierced close to the bottom of the tube with a butterfly infusion set (with the luer hub clipped off).
  • SupF plasmids are selected in nonsuppressing bacterial hosts containing a second plasmid, p3, which contains, amber mutated ampicillin and tetracycline drug resistance elements. See Seed, Nucleic Acids Res., U, 2427-2445 (1983).
  • the p3 plasmid is derived from RPl, is 57 kb in length, and is a stably maintained, single copy episome. The ampicillin resistance of this plasmid reverts at a high rate so that amp r plasmids usually cannot be used in p3-containing strains. Selection for tetracycline resistance alone is almost as good as selection for ampicillin- tetracycline resistance.
  • Suppressor plasmids are selected in Luria broth (LB) medium containing ampicillin at 12.5 ⁇ g/ml and tetracycline at 7.5 ⁇ g/ml.
  • LB Luria broth
  • M9 Casamino acids medium containing glycerol 0.8% is employed as a carbon source. The bacteria are grown to saturation.
  • pSV Sport (BRL, Gaithersberg, Maryland) may be employed to provide SV40 derived sequences for replication, transcription initiation and termination in COS 7 cells, as well as those sequences necessary for replication and ampicillin resistance in E. coli. 9f. Isolation of Vector DNA/Plasmid
  • One liter of saturated bacterial cells are spun down in J6 bottles at 4.2k rpm for 25 minutes.
  • the cells are resuspended in 40 ml 10 mM EDTA, pH 8. 80 ml 0.2M NaOH and 1% SDS are added, and the mixture is swirled until it is clear and viscous.
  • 40 ml 5M KOAc, pH 4.7 (2.5M KOAc, 2.5M HOAc) is added, and the mixture is shaken semi-vigorously until the lumps are approximately 2-3 mm in size.
  • the bottle is spun at 4.2k rpm for 5 minutes.
  • the supernatant is poured through cheesecloth into a 250 ml bottle, which is then filled with isopropyl alcohol and centrifuged at 4.2k rpm for 5 minutes.
  • the bottle is gently drained and rinsed with 70% ethanol, taking care not to fragment the pellet.
  • the mixture is resuspended in 3.5 ml Tris base/EDTA (20 mM/10 mM) .
  • 3.75 ml of resuspended pellet and 0.75 ml 10 mg/ml ethidium bromide are added to 4.5 g CsCl.
  • VTi ⁇ O tubes are filled with solution, and centrifuged for at least 2.5 hours at 80k rpm.
  • Bands are extracted by visible light with 1 ml syringe and 20 gauge or lower needle.
  • the top of the tube is cut off with scissors, and the needle is inserted upwards into the tube at an angle of about 30 degrees with respect to the tube at a position about 3 mm beneath the band, with the bevel of the needle up.
  • the contents of the tube are poured into bleach.
  • the extracted band is deposited in a 13 ml Sarstedt tube, which is then filled to the top with n-butanol saturated with 1M NaCl extract. If the amount of DNA is large, the extraction procedure may be repeated.
  • the plasmid After adding linear polyacrylamide and precipitating the plasmid by adding three volumes of ethanol, the plasmid is resuspended in 50 ⁇ l of TE.
  • Trial ligations are carried out with a constant amount of vector and increasing amounts of cDNA. Large scale ligation are carried out on the basis of these trial ligations. Usually the entire cDNA prep requires 1-2 ⁇ g of cut vector.
  • Loading Buffer :.5M LiCl, 10 mM Tris pH 7.5, 1 mM EDTA .1% SDS.
  • Middle Wash Buffer :.15M LiCl, 10 mM Tris pH 7.5, 1 mM EDTA .1%
  • RT2 Buffer .1M Tris pH 7.5, 25 mM MgCl2, .5M KC1, .25 mg/ml BSA,
  • Cos 7 cells are split 1:5 into 100 mm plates in Dulbecco's modified Eagles medium (DME)/10% fetal calf serum (FCS), and allowed to grow overnight. 3 ml Tris/DME (0.039M
  • Tris, pH 7.4 in DME) containing 400 ⁇ g/ml DEAE-dextran (Sigma, D- 9885) is prepared for each 100 mm plate of Cos 7 cells to be transfected. 10 ⁇ g of plasmid DNA preparation per plate is added. The medium is removed from the Cos-7 cells and the DNA/DEAE-dextran mixture is added. The cells are incubated for 4.5 hours. The medium is removed from the cells, and replaced with 3 ml of DME containing 2% fetal calf serum (FCS) and 0.1 mM chloroquine. The cells are incubated for one hour.
  • FCS fetal calf serum
  • the cells After removing the chloroquine and replacing with 1.5 ml 20% glycerol in PBS, the cells are allowed to stand at room temperature for one minute. 3 ml Tris/DME is added, and the mixture is aspirated and washed two times with Tris/DME. 10 ml DME/10% FCS is added and the mixture is incubated overnight. The transfected Cos 7 cells are split 1:2 into fresh 100 mm plates with (DME)/10% FCS and allowed to grow.
  • the medium from transfected Cos 7 cells is aspirated, and 3 ml PBS/0.5 mM EDTA/0.02% sodium azide is added.
  • the plates are incubated at 37°C for thirty minutes in order to detach the cells.
  • the cells are triturated vigorously with a pasteur pipet and collected in a 15 ml centrifuge tube.
  • the plate is washed with a further 2 ml PBS/EDTA/azide solution, which is then added to the centrifuge tube. After centrifuging at 200 xg for five minutes, the cells are resuspended in 3 ml of APtaq-Flkl (F-
  • the cells are added to the antibody-coated plates containing 4 ml PBS/EDTA/azide/5% FBS, and allowed to stand at room temperature one to three hours. Non-adhering cells are removed by washing gently two or three times with 3 ml PBS/5% FBS.
  • 0.4 ml 0.6% SDS and 10 mM EDTA are added to the panned plates, which are allowed to stand 20 minutes.
  • the viscuous mixture is added by means of a pipet into a microfuge tube.
  • 0.1 ml 5M NaCl is added to the tube, mixed, and chilled on ice for at least five hours.
  • the tube is spun for four minutes, and the supernatant is removed carefully.
  • the contents of the tube are extracted with phenol once, or, if the first interface is not clean, twice.
  • Ten micrograms of linear polyacrylamide (or other carrier) is added, and the tube is filled to the top with ethanol. The resulting precipitate is resuspended in 0.1 ml water or TE.
  • the cDNA obtained is transfected into any suitable E. coli host by electroporation. Suitable hosts are described in various catalogs, and include MC1061/p3 or Electromax DH10B Cells of BRL Gibco.
  • the cDNA is extracted by conventional methods.
  • Cells expressing Flkl/fms or Flk2/fms are transfected with 20-30 ⁇ g of a cDNA library from either Flkl ligand or Flk2 ligand expressing stromal cells, respectively.
  • the cDNA library is prepared as described above (a-h).
  • the cells are co-transfected with 1 ⁇ g pLTR neo cDNA. Following transfection the cells are passaged 1:2 and cultured in 800 ⁇ g/ml of G418 in Dulbecco's medium (DME) supplemented with 10% CS.
  • DME Dulbecco's medium
  • the culture medium is defined serum-free medium which is a mixture (3:1) of DME and Ham's F12 medium.
  • the medium supplements are 8 mM NaHC0 3 , 15 mM HEPES pH 7.4, 3 mM histidine, 4 ⁇ M MnCl 2 , 10 uM ethanolamine, 0.1 ⁇ M selenous acid, 2 ⁇ M hydrocortisone, 5 ⁇ g/ml transferrin, 500 ⁇ g/ml bovine serum albumin/linoleic acid complex, and 20 ⁇ g/ml insulin (Ref. Zhan, X, et al. Oncogene 1: 369-376,1987).
  • the cultures are refed the next day and every 3 days until the only cells capable of growing under the defined medium condition remain.
  • the remaining colonies of cells are expanded and tested for the presence of the ligand by assaying for binding of APtag - Flkl or APtag - Flk2 to the cells (as described in Example 8).
  • the DNA would be rescued from cells demonstrating the presence of the Flkl or Flk2 ligand and the sequence.
  • the cDNA is sequenced, and expressed in a suitable host cell, such as a mammalian cell, preferably COS, CHO or NIH/3T3 cells.
  • a mammalian cell preferably COS, CHO or NIH/3T3 cells.
  • the presence of the ligand is confirmed by demonstrating binding of the ligand to APtag-Flk2 fusion protein (see above).
  • Cross linking experiments are performed on intact cells using a modification of the procedure described by Blume-Jensen et al et al., EMBO J. , 1 , 4121-4128 (1991). Cells are cultured in 100mm tissue culture plates to subconfluence and washed once with PBS-0.1% BSA.
  • stromal cells from the 2018 stromal cell line are incubated with conditioned media (CM) from transfected 3T3 cells expressing the soluble receptor Flk2-APtag.
  • CM conditioned media
  • Cross linking studies of soluble ligand to membrane bound receptor are performed by incubating conditioned media from 2018 cells with transfected 3T3 cells expressing a Flk2-fms fusion construct.
  • Binding is carried out for 2 hours either at room temperature with CM containing 0.02% sodium azide to prevent receptor internalization or at 4°C with CM (and buffers) supplemented with sodium vanadate to prevent receptor dephosphorylation. Cells are washed twice with PBS-0.1% BSA and four times with PBS.
  • Cells are solubilized in solubilization buffer: 0.5% Trito - X100, 0.5% deoxycholic acid, 20 mM Tris pH 7.4, 150 mM NaCl, lOmM EDTA, ImM PMFS, 50 mg/ml aprotinin, 2 mg/ml bestatin, 2 mg/ml pepstatin and lOmg/ml leupeptin. Lysed cells are immediately transferred to 1.5 ml Nalgene tubes and solubilized by rolling end to end for 45 minutes at 4°C. Lysates are then centrifuged in a microfuge at 14,000g for 10 minutes.
  • Solubilized cross linked receptor complexes are then retrieved from lysates by incubating supernatants with 10% (v/v) wheat ger lectin-Sepharose 6MB beads (Pharmacia) at 4°C for 2 hours or overnight.
  • Cross linked Flk2-APtag and Flk2-fms receptors are detected using rabbit polyclonal antibodies raised against human alkaline phosphatase and fms protein, respectively.
  • the remainder of the procedure is carried out according to the instructions provided in the ABC Kit (Pierce).
  • the kit is based on the use of a biotinylated secondary antibody and avidin-biotinylated horseradish peroxidase complex for detection.
  • Example 12 Expression and purification of Flaq-Flk2.
  • a synthetic DNA fragment (Fragment 1) is synthesized using complementary oligonucleotides BP1 and BP2 (see below and SEQ. ID. NOS. 7 and 8).
  • the fragment encoded the following features in the 5' to 3' order: Sal I restriction site, 22 base pair (bp) 5' untranslated region containing an eukaryotic ribosome binding site, an ATG initiation codon, preprotrypsinogen signal sequence, coding region for the FLAG peptide (DYKDDDDKI) and Bgl II restriction site.
  • a cDNA fragment (Fragment 2) encoding Asn 27 to Ser 544 of murine Flk2 is obtained by polymerase chain reaction (PCR) using primers designed to introduce an in frame Bgl II site at the 5' end (oligonucleotide BP5, see below and SEQ. ID. NO. 9) and a termination codon followed by a Not I site at the 3' end (oligonucleotide BP10, see below and SEQ. ID. NO. 10).
  • the template for the PCR reaction is full length Flk2 cDNA (Matthews et al.. Cell .65:1143 (1991)). Fragment 2 is extensively digested with Bgl II and Not I restriction enzymes prior to ligation.
  • Fragments 1 and 2 are ligated in a tripartate ligation into Sal I and Not I digested plasmid pSPORT (Gibco/BRL, Grand Island, NY) to give the plasmid pFlag-Flk2.
  • the Flag-Flk2 protein is attached at either end to the Fc portion of an immunoglobulin (Ig).
  • the Ig is preferably attached to the Flk2 portion of the Flag-Flk2 protein.
  • the sequences coding for the CH 1 domain of human immunoglobulin G (IgG 1 ) are placed downstream of the Flk2 coding region in the plasmid pFlag-Flk2 as per the method described by Zettlemeissl et al., DNA and Cell Biology .9: 347-352 (1990).
  • Oligonucleotide BP1 Oligonucleotide BP1:
  • Oligonucleotide BP2 Oligonucleotide BP2:
  • Oligonucleotide BP5 5'-TGAGAAGATCTCAAACCAAGACCTGCCTGT-3'
  • Oligonucleotide BP10 Oligonucleotide BP10:
  • the Sail to Not I fragment from pFlag-Flk2 is subcloned into the plasmid pSVSPORT (Gibco/BRL) to give the plasmid pSVFlag-Flk2.
  • pSVFlag-Flk2 is transfected into COS monkey cells using the DEAE-dextran method.
  • the Sal I-Not I fragment of pFlag-Flk2 is cloned into the EcoRV and Not I sites of the plasmid pcDNA I/Neo (Invitrogen Co., San Diego, CA) .
  • the Sal I 3' recessed terminus of pFlag-Flk2 is filled with the Klenow fragment of DNA polymerase I and a mixture of deoxyribonucleotides to make the site compatible with the EcoRV site of the vector.
  • the resulting construct is introduced into cultured mammalian cells using either the Lipofectin (Gibco/BRL) or the calcium phosphate methods.
  • the Sail to Hind III (from pSPORT polylinker) fragment of pFlag-Flk2 is subcloned into the BamHl-Hind III sites of the baculovirus transfer vector pBlueBac III (Invitrogen).
  • the vector Bam HI site and the insert Sal I site are blunted with Klenow (see above).
  • Production of the recombinant virus and infection of the Sf9 insect cells is performed as per manufacturers directions (Invitrogen).
  • Flag-Flk2 protein is detected by Western blotting of SDS-PAGE separated conditioned media (mammalian cells) or cell lysates (insect cells) with the anti-Flag monoclonal antibody (mAb) Ml (International Biotechnology, Inc. [IBI], New Haven, CT).
  • mAb monoclonal antibody
  • Affinity purification of the Flag-Flk2 protein from conditioned media or insect cell lysates is performed using immobilized mAb Ml (IBI) as per manufacturers specifications.
  • Murine stromal lines eg. 2018 cells ATCC CRL 10907 (see below), see example 1, supra ) considered to be candidates for expression of the Flk2 ligand were deposited at the American Type Culture Collection, ATCC CRL 10907 (see below) and cultured in Dulbecco's modified Eagles medium (DMEM; Gibco/BRL) supplemented with 10% fetal calf serum. The cells are grown to confluency in 10 cm plates and washed once with PBS. Conditioned media containing Flag-Flk2 is incubated with the cells at 4°C for 2 hrs.
  • DMEM Dulbecco's modified Eagles medium
  • the cell monolayers are rinsed extensively to remove the non-bound protein, solubilized and centrifuged to remove insoluble cellular material.
  • Glycoproteins in the lysates are partially purified with wheat germ agglutinin-Sepharose (Pharmacia LKB, Piscataway, NJ), boiled in an SDS sample buffer, separated on SDS-PAGE gels and transferred to nitrocellulose membranes. The membranes are probed with the Ml antibody to detect the presence of cell-associated Flag-Flk2 protein.
  • Flag-Flk2 protein labelled with Nal25I via the Chloramine T method is used to asses the ability of the soluble extracellular domain of the Flk2 receptor to bind transmembrane form of the Flk2 ligand in cultured stromal lines.
  • the labelled protein is added to monolayers of stromal cells on ice for 2 hr in the presence or absence of excess unlabelled protein. Specific binding is calculated by subtracting counts bound in the presence of excess unlabelled protein from the total counts bound.
  • the Flag-Flk2 protein is used in attempts to identify the Flk2 ligand in conditioned media from stromal cell cultures via modification of the direct N-terminal sequencing method of Pan et al., Bioch. Biophys. Res. Comm. 166:201 (1990). Briefly, the Flag-Flk2 protein N-terminally sequenced by automatic Edman degradation chemistry an an ABI 477A sequncer with on line PTH amino acid analysis. Approximatelly 15 amino acids are determined. The protein is then immobilized on Nugel PAF silica beads via free NH4+ groups.
  • the immobilized Flag-Flk2 is incubated with conditioned media from putative ligand-producing cells for 30 in at 4°C and washed free off non-bound proteins with phosphate buffered saline adjusted to 2M NaCl. The resulting protein complex is resequenced. For each sequencing cycle, any amino acid not expected at this position in the FLAG-Flk2 protein is considered as possibly originating from a protein complexed to the Flk2 receptor.
  • Flag-Flk2 protein is immobilized on a stable support such as Sepharose. 35S-methionine labelled-conditioned media from stromal cell lines are passed over the affinity matrix and bound material is analyzed by SDS-PAGE gel electrophoresis and autoradiography.
  • a method of expression cloning of integral membrane proteins in COS cells has been described (Aruffo and Seed, Proc. Natl. Acad. Sci. j84:8573 (1987)).
  • a cDNA library is prepared from an appropriate stromal cell line such as 2018 and is transfected into COS cells. Cells transiently expressing the Flk2 ligand are affinity adsorbed onto plastic plates coated with the Flag-Flk2 protein. The cells are lysed, the plasmid DNA is recovered and amplified in a bacterial host. The cycle of transfection into COS cells is repeated until a single cDNA clone encoding the ligand molecule is isolated.
  • pools of transfected COS cells are screened for binding of 125I-Flag-Flk2. Positive cells pools are selected and plasmid DNA is recovered and amplified in E. coli. The resulting DNA preparation is used in subsequent rounds of transfection and transient expression until all cells are positive for binding of 125I-Flag-Flk2. The cDNA in the final plasmid preparation is then sequenced to determine the sequnce of the putative Flk-2 ligand.
  • the Flk2 ligand is isolated from tissue culture medium conditioned by phytohemagglutinin-stimulated human peripheral blood leukocytes (PHA-LCM) .
  • the medium is prepared by isolating normal human peripheral blood mononuclear cells (leukocytes) from whole blood by density centrifugation (Ficoll-Hypaque, Pharmacia Biotech, Inc, Piscataway, NJ) and incubating these cells at a concentration of 2 X 10 6 cells/ml with the lectin phytohemagglutinin (PHA, Gibco Laboratories, Grand Island, NY) in a commercially-prepared, serum-free defined culture medium (AIMV; Gibco Laboratories, Grand Island, NY) for one week.
  • PHA-LCM is harvested by removal of cells and debris by centrifugation.
  • the Flk2 ligand is one of a large number of proteins that are specifically secreted by PHA-activated cells into the medium. Several purification steps using conventional chromatographic techniques are required to isolate the Flk2 ligand.
  • the chromatographic columns used include: Blue Sepharose Fast Flow (Pharmacia Biotech, Inc, Piscataway, NJ) to remove the medium component albumin, anion exchange (Q-Sepharose Fast Flow, Pharmacia Biotech, Inc, Piscataway, NJ) , cation exchange (S-Sepharose Fast Flow, Pharmacia Biotech, inc, Piscataway, NJ), gel filtration (Superdex 75, Pharmacia Biotech, Inc, Piscataway, NJ) , heparin sepharose (Pharmacia Biotech, Inc, Piscataway, NJ), ConA (Pharmacia Biotech, Inc, Piscataway, NJ) , wheat germ agglutinin (Pharmacia Biotech, Inc, Piscataway, Piscat
  • Biological assays are used throughout the .purification to identify which column fractions contain the Flk2 ligand.
  • the Flk2 ligand specifically stimulates proliferation in vitro of cell lines transfected with constructs expressing the full length Flk2 receptor or a chimeric receptor comprising of the the extracellular domain of the Flk2 receptor and the intracellular domain of a different protein tyrosine kinase receptor such as fms, the receptor for CSF-1.
  • the Flk2 ligand specifically stimulates proliferation of murine NIH 3T3 fibroblast cell line transfected with constructs expressing the murine or human Flk2 receptor in either full length or chimeric form (see example 8B).
  • the parent untransfected 3T3 cells do not respond to the Flk2 ligand.
  • the format of the Flk2 receptor 3T3 cell assay uses 96 well tissue culture plates (Becton Dickenson, Lincoln Park, NJ), where column fractions or other test samples are serially diluted across the plates in wells containing a mixture of AIMV and Dulbecco's modification of Eagle's medium (DMEM, Gibco Laboratories, Grand Island, NY). Samples are tested for their ability to stimulate proliferation of Flk2 receptor 3T3 cells initially cultured at 3 X 10" cells/well. Survival of Flk2 receptor 3T3 cells is dependent on the presence of the Flk2 ligand.
  • Viable Flk2 receptor 3T3 cells are quantitated after three to five days in culture either visually or spectrophotometrically (Molecular Devices Corporation, Menlo Park, CA) using a tetraformazan salt (XTT, Diagnostic Chemicals Ltd, Oxford, CT) that when cleaved by actively respiring cells forms diformazan salt which absorbs light at a wavelength (450 nm) that is different from the starting compound (560 nm) .
  • Relative (units/ml) and specific (units/mg) activities are defined as the reciprocal dilution at which half-maximal stimulation is detected.
  • the human Flk2 ligand isolated from PHA-LCM is a glycosylated protein and has an apparent molecular weight of 18 kDa, as determined by SDS-PAGE analysis run under reducing ( ⁇ - mercaptoethanol) and non-reducing conditions. Its N-terminal fourteen amino acid sequence is A Q S L S F X F T K F D L D, wherein X is any amino acid. (See SEQ. ID. NO. 11) Its biological activity is inactivated at 100° C but not 60° C in five minutes and the activity is retained after the Flk2 ligand is subjected to a pH of 2.8 at room temperature for two hours.
  • the 18 kDa Flk2 ligand may act alone, in combination with other cytokines (e.g., interleukin 1, interleukin 3, interleukin 6, interleukin 11 or the kit ligand), or as a component of a complex of proteins that stimulate the Flk2 receptor in transfected 3T3 cell or in primitive hematopoietic progenitors.
  • the complex of proteins may include a soluble or membrane-bound form of the Flk2 receptor.
  • a radiolabeled form of the Flk2 ligand may be used to detect and to measure the levels of Flk2 receptor, such as the soluble form of the Flk2 receptor, for example, in serum or urine of patients with bone marrow disorders.
  • the Flk2 ligand In addition to acting on Flk2 receptor-expressing 3T3 cells, the Flk2 ligand specifically stimulates proliferation of cells that naturally express the Flk2 receptor. In assays using either a human myeloid cell line or a subset of primitive hematopoietic progenitors expressing the surface phenotype CD34, the Flk2 ligand promotes proliferation but not differentiation into mature progeny.
  • the Flk2 ligand alone or in combination with other cytokines e.g. Interleukin 1, Interleukin 3, Interleukin 6, Interleukin 11, or the kit ligand
  • MOLECULE TYPE cDNA
  • HYPOTHETICAL NO
  • ANTI-SENSE NO
  • FRAGMENT TYPE N-terminal
  • AGT AAA AGA GAA AAA TTT CAC AGG ACT TGG ACA GAG ATT TTC AAG GAA 2217 Ser Lys Arg Glu Lys Phe His Arg Thr Trp Thr Glu He Phe Lys Glu 680 685 690
  • CTGTGTCCCG CAGCCGGATA ACCTGGCTGA CCCGATTCCG CGGACACCCG TGCAGCCGCG 60
  • GAG AAA CAG AGC CAC ATG GTC TCT CTG GTT GTG AAT GTC CCA CCC CAG 1479
  • Trp Glu Phe Pro Arg Asp Arg Leu Lys Leu Gly Lys Pro Leu Gly Arg 810 815 820

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Abstract

L'invention concerne des molécules d'acides nucléiques de mammifère isolés codant les tyrosines kinases protéiques réceptrices exprimées dans les cellules hématopoïétiques primitives et non exprimées dans les cellules hématopoïétiques matures. L'invention porte également sur les récepteurs codés par lesdites molécules d'acides nucléiques; les molécules d'acides nucléiques codant les tyrosines kinases protéiques réceptrices comprenant les séquences représentées dans la Figure 1a (Flk2 murine), la Figure 1b (Flk2 humaine) et la Figure 2 (Flk1 murine), sur les tyrosines kinases protéiques réceptrices comprenant les séquences d'acides aminés représentées dans les Figures 1a, 1b, et 2; sur des ligands des récepteurs; sur des séquences d'acides nucléiques codant les ligands; et sur les procédés de stimulation de la prolifération et/ou la différenciation de cellules souches hématopoïétiques de mammifère primitives consistant à mettre lesdites cellules souches en contact avec un ligand se fixant sur une tyrosine kinase protéique réceptrice exprimée dans les cellules hématopoïétiques de mammifère primitives et non exprimée dans les cellules hématopoïétiques matures.
PCT/US1994/006944 1993-06-18 1994-06-17 Recepteurs de cellules souches hematopoietiques totipotentes et leurs ligands WO1995000554A2 (fr)

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Cited By (9)

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WO1998017808A1 (fr) * 1996-10-18 1998-04-30 Takara Shuzo Co., Ltd. Acide nucleique codant une proteine kinase du type recepteur
US6084060A (en) * 1996-12-09 2000-07-04 Imclone Systems Incorporated Composition and method for preserving progenitor cells
US6310195B1 (en) 1997-06-24 2001-10-30 Imclone Systems Incorporated Nucleic acid encoding a lectin-derived progenitor cell preservation factor
US6630143B1 (en) * 1993-05-24 2003-10-07 Immunex Corporation Antibodies against flt3 ligand
US6846630B2 (en) 1996-10-18 2005-01-25 Takara Shuzo Co., Ltd. Nucleic acid encoding receptor type protein kinase
US6991794B1 (en) 1997-06-24 2006-01-31 Imclone Systems Incorporated Progenitor cell preservation factors and methods for and products of their use
US7112653B2 (en) 1996-12-09 2006-09-26 Inclone Systems, Incorporated Composition and method for preserving progenitor cells
US7150992B1 (en) 1995-10-04 2006-12-19 Innunex Corporation Methods of preparing dendritic cells with flt3-ligand and antigen
US7361330B2 (en) 1995-10-04 2008-04-22 Immunex Corporation Methods of using flt3-ligand in the treatment of fibrosarcoma

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US5185438A (en) * 1991-04-02 1993-02-09 The Trustees Of Princeton University Nucleic acids encoding hencatoporetic stem cell receptor flk-2

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US5185438A (en) * 1991-04-02 1993-02-09 The Trustees Of Princeton University Nucleic acids encoding hencatoporetic stem cell receptor flk-2

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Title
ONCOGENE, Volume 6, issued September 1991, O. ROSNET et al., "Murine Flt3, a Gene Encoding a Novel Tyrosine Kinase Receptor of the PDGFR/CSF1R Family", pages 1641-1650. *
ONCOGENE, Volume 8, Number 4, issued April 1993, S.D. LYMAN et al., "Characterization of the Protein Encoded by the Flt3 (Flk2) Receptor-Like Tyrosine Kinase Gene", pages 815-822. *

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6630143B1 (en) * 1993-05-24 2003-10-07 Immunex Corporation Antibodies against flt3 ligand
US7150992B1 (en) 1995-10-04 2006-12-19 Innunex Corporation Methods of preparing dendritic cells with flt3-ligand and antigen
US7361330B2 (en) 1995-10-04 2008-04-22 Immunex Corporation Methods of using flt3-ligand in the treatment of fibrosarcoma
WO1998017808A1 (fr) * 1996-10-18 1998-04-30 Takara Shuzo Co., Ltd. Acide nucleique codant une proteine kinase du type recepteur
US6846630B2 (en) 1996-10-18 2005-01-25 Takara Shuzo Co., Ltd. Nucleic acid encoding receptor type protein kinase
US8178292B2 (en) 1996-10-18 2012-05-15 Takara Bio Inc. Methods of diagnosing acute myeloid leukemia using nucleic acids encoding FLT3 kinase
US6084060A (en) * 1996-12-09 2000-07-04 Imclone Systems Incorporated Composition and method for preserving progenitor cells
US7112653B2 (en) 1996-12-09 2006-09-26 Inclone Systems, Incorporated Composition and method for preserving progenitor cells
US6310195B1 (en) 1997-06-24 2001-10-30 Imclone Systems Incorporated Nucleic acid encoding a lectin-derived progenitor cell preservation factor
US6852321B2 (en) 1997-06-24 2005-02-08 Imclone Systems Incorporated Lectin-derived progenitor cell preservation factor and methods of use
US6991794B1 (en) 1997-06-24 2006-01-31 Imclone Systems Incorporated Progenitor cell preservation factors and methods for and products of their use

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WO1995000554A3 (fr) 1996-10-10

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