PROTEIN TYROSINE PHOSPHATASES OF HEMATOPOIETIC CELLS

Abstract: This invention concerns new non-receptor protein tyrosine phosphatases of the hematopoietic stem cells (PTP HSC). The invention specifically concerns native murine and human PTP HSCs, their analogs in other mammals, and their functional derivatives. The invention further relates to nucleic acid encoding these proteins, vectors containing and capable of expressing such nucleic acid, and recombinant host cells transformed with such nucleic acid. Assays for identifying agonists and antagonists of the native PTP HSCs, methods for expansion of undifferentiated stem cells, and methods for the induction of stem cell differentiation are also within the scope of the invention.

Description: PROTEIN TYROSINE PHOSPHATASES OF HEMATOPOIETIC CELLS Field of the Invention The present invention concerns novel protein tyrosine phosphatases More particularly the invention concerns non-receptor protein tyrosine phosphatases of hematopoietic stem cells (PTP HSCs ) Background of the Invention The ability ofthe hematopoietic stem cell to function as a source of committed progenitors throughout the lifetime ofthe organism is, at present, a poorly understood phenomenon The major characteπstic of the hematopoietic stem cell is its ability to self renew in the absence of differentiation (Morrison et al , Ann Rev Oil Dev Biol . ϋ, 35-71 [1995]) This self renewal phenomenon is especially remarkable in light ofthe fact that the hematopoietic stroma, which is in close physical contact with the stem cell, is known to be a source that is rich in factors which mediate the growth and differentiation of hematopoietic progenitors (Deryugma and Muller-Sieberg, Crit Rev in Immunol 13.(2), 1 15-150 [1993]) For example, a recent PCR analysis of hematopoietically active endothelial cell stromal lines derived from the murine yolk sac revealed that these cells produced a plethora of growth and differentiation factors including stem cell factor, FLT 3 ligand, M-CSF LIF and IL-6 (Fennie er a/ . Blood 86(12). 4454-4467 [19951) Such growth factors, in addition to many others, are known to induce the expansion and differentiation of stem cells, and these endothelial cell lines induced a rapid expansion and differentiation of embryonic hematopoietic stem cells along the myeloid pathway, although very early progenitor cells are also amplified by these stromal cells (C Fennie and L Lasky-unpub shed data) It has also been shown that incubation of highly purified stem cell populations m the presence of various purified hematopoietic growth factors induces differentiation with subsequent loss ofthe cells' ability to competitively repopulate the hematopoietic compartment of lethally irradiated animals, consistent with the induction of terminal differentiation (Peters et al . Blood 87( 1 ) 30-37 [1996]) Thus, the stem cell, whether in an embryonic or adult stromal environment, must maintain an undifferentiated state in spite of the fact that it is being exposed to a variety such maturation factors (Deryugma and Muller-Sieberg, supra) Although the hematopoietic growth factors are very diverse both structurally and functionally, they are all believed to play a role in mediating protein phosphorylation (Paulson and Bernstein, Semin Immunol 7(4), 267-77 [ 1995]) This protein modification can occur via direct means, such as in the cases ofthe stem cell factor and FLT-3 receptors, both of which have intrinsic tyrosine kinase activity, or via indirect means, as is the case of the hematopoietic/cytokine growth factor receptors for, for example, IL-3, EPO and TPO In the case of the hematopoietic/cytokine growth factor receptors, tyrosine phosphorylation is indirectly accomplished by the activation ofthe JAK kinases, which occurs after growth factor mediated receptor dimerization (Ihle et al , Annu Rev Immunol 13. 369-398 [1995]) In both cases, diverse complex pathways of protein phosphorylation are stimulated upon receptor bmdmg The intrinsic tyrosine kinase receptors mediate their signals via an elaborate series of tyrosine phosphorylation events which ultimately activate the RAS signaling pathway (Fantl et al , Ann Rev Biochem 62. 453-481 [1993]) This pathway eventually leads to the activation of the seπne/threonine specific MAP kinase pathway which results in transcriptional activation In contrast to this intricate pathway hematopoietic growth factor-induced receptor dimerization mediates more direct activation events Thus the stimulation of the JAK kinases by receptor binding leads to the tyrosine phosphorylation and subsequent dimerization of various STAT proteins These activated STAT proteins than migrate to the nucleus bind to STAT responsive sites in the nuclear DNA and induce transcription of differentiation and growth specific genes Thus, a major effect ofthe growth factors produced by the hematopoietic stroma is to mediate the activation of various cellular pathways by protein phosphorylation The regulation of protein tyrosine phosphorylation is accomplished by a balance between protein tyrosine kinases and protein tyrosine phosphatases (PTPs) (Walton and Dixon, Ann Rev Biochem 62 , 101 - 120 [1993]. Sun and Tonks. Trends Biochem Sci . 19(1 1).480-485 [1994]) All PTPs contain a phosphatase domain including a subset of highly conserved ammo acids, and a recent crystal structure analysis of PTP 1 B complexed with a tyrosine phosphorylated peptide revealed that many of these conserved residues are involved with substrate recognition and tyrosine dephosphorylation (Jia et al , Science 268(5218), 1754- 1758 [ 1995]) PTPs fall into two general categories receptor type and non-receptor type The receptor type PTPs have variously sized extracellular domains and, generally, two intracellular phosphatase domains Walton and Doxm supra. Sun and Tonks, supra The extracellular domams often contam a number of motifs that are generally utilized in cell adhesion including immunoglobulin domains and fϊbronectin-like regions Many of these PTPs appear to function as homotypic and heterotypic sensors ofthe extracellular space, and they have been hypothesized to play roles in contact inhibition, cell guidance and other intercellular functions (Brady-Kalnay and Tonks, Curr Opin Cell Biol. 7(5), 65-657 [ 1995]) The non-receptor PTPs are generally intracellular enzymes They have various cellular localizations, depending upon the types of domains they contain, and some ofthe enzymes contain SH2 motifs which allow them to interact intimately with phosphotyrosine residues While many ofthe non-receptor PTPs are in various cytoplasmic locations, a small number of these enzymes are found in the nucleus (Flores et al . Mol Cell. Biol. 14(7). 4938-46 [1994]) Many non-receptor PTPs appear to function as both activators as well as inhibitors of diverse tyrosine phosphorylated proteins A subset appear to play important roles in hematopoiesis For example, the motheaten mouse, which has a phenotype of lethal myeloid amplification and flammation, has been found to have a mutation in the PTP 1 C gene (Schulz et al . Cell 73(7). 1445-54 [1993]), (McCulloch and Siminovitch, Adv. Exp Med Biol 365. 145-54 [1994]) ln addition, the level of tyrosine phosphorylation ofthe EPO receptor, as well as the level of receptor activation, appears to be in part controlled by the PTP IC enzyme as well (Khngmuller e/ α/ , Ceϋ 8 (5), 729-38 [1995]) However, while these examples, as well as others, highlight the potential importance ofthe PTPs, very little is known regarding the physiological importance of these enzymes Summary of the Invention We have hypothesized that one mechanism by which the undifferentiated state ofthe stem cell might be maintained is by the dephosphorylation of tyrosine phosphorylated proteins by PTPs In order to examine this possibility, we have analyzed a large number of PTPs from a very primitive embryonic hematopoietic cell population using consensus PCR From this population we have cloned a novel intracellular PTP which has many of the characteristics, including down-regulation of the transcript as the hematopoietic stem cells differentiate, which might be expected from a PTP involved with the control of differentiation signals such as those mduced by hematopoetic growth factors We have designated this novel PTP as the "PTP of hematopoietic stem cells", which will be referred to hereafter as "PTP HSC " Accordmgiy, the present invention concerns an isolated non-receptor protein tyrosine phosphatase of hematopoietic stem cells (PTP HSC), which (1) is expressed predominantly in early hematopoietic stem/progenitor cells (2) predominantly lacks expression in adult tissues; (3) comprises an N-terminal tyrosine phosphatase domain, followed by a region rich in serine, threonine, and proline, and a carboxy terminal region of about 15 to 25 amino acids rich in basic amino acid residues; and (4) is capable of tyrosine dephosphorylation in hematopoietic stem cells or progenitor cells. This novel PTP preferably downregulates STAT activation. A preferred group ofthe PTP HSC proteins ofthe present invention includes a protein comprising the amino acid sequence shown in Figure 1 (SEQ. ID. NO:2); a protein comprising the amino acid sequence shown in Figure 8 (SEQ. ID. NO: 17), a further mammalian homologue of either protein; and derivatives of the foregoing proteins retaining the ability of tyrosine dephosphorylation in hematopoietic stem cells or progenitor cells. The PTP HSCs, including derivatives (e.g. amino acid sequence variants) of the native proteins, preferably have an active N-terminal tyrosine phosphatase domain, retaining a serine residue at a position corresponding to amino acid position 37 in Figure 1 , and retaining an active site cysteine residue at a position corresponding to amino acid position 229 in Figure 1 , a region rich in serine, threonine, and proline, and a carboxy-terminal region showing at least about 80% sequence homology with the amino acid sequence between positions 430 and 451 in Figure 1. Most preferably, such derivatives have at least about 65% overall sequence homology with the amino acid sequence shown in Figure 1 or Figure 8 and retain the ability of tyrosine dephosphorylation in hematopoietic stem cells or progenitor cells. In another aspect, the present invention concerns agonists and antagonists of PTP HSCs. In yet another aspect, the invention concerns isolated nucleic acid molecules encoding the PTP HSCs herein. In a further aspect, the invention concerns vectors comprising nucleic acid encoding the PTP HSCs herein, operably linked to control sequences recognized by a host cell transformed with the vector, and to cells transformed with such vectors. ln a still further aspect of the present invention, there are provided antibodies capable of specific binding to the PTP HSCs of this invention, and hybridoma cell lines producing such antibodies. The antibodies may be agonist antibodies, which stimulate the ability of the native PTP HSCs of the present invention to dephosphorylate tyrosines, or antagonist antibodies, which block this activity. The present invention further concerns an assay for identifying an antagonist or an agonist of a PTP HSC ofthe present invention, which comprises contacting the phosphatase domain of the PTP HSC with a candidate antagonist or agonist, and monitoring the ability of the phosphatase domain to dephosphorylate tyrosine residues. In another embodiment, the invention concerns an assay for identifying an antagonist or agonist of a PTP HSC of the present invention by cultivating a PTP HSC-expressing hematopoietic stem cell line or progenitor cell line in the presence of a candidate antagonist or agonist, and monitoring the differentiation of the progenitor cells. The invention further concerns a method for the differentiation of undifferentiated malignant hemopoietic (e.g. leukemia) cells, comprising contacting said cells with an antagonist of a PTP HSC of the present invention. In an additional aspect, the invention concerns a method for the induction of hematopoietic stem cell differentiation, comprising contacting said stem cells with an antagonist of a PTP HSC ofthe present invention. In another aspect, the invention concerns a method for expansion undifferentiated hematopoietic stems cells in ceil culture, comprising cultivating stem cells in the presence of a PTP HSC ofthe present invention or an agonist antibody specifically binding a native PTP HSC. In yet another aspect, the invention concerns a method for the expansion of undifferentiated stem cells in vivo comprising administering to a patient an agonist of PTP HSC of the present invention or an agonist antibody specifically binding a native PTP HSC, and a stem cell growth factor. Brief Description of the Drawings Figure 1. DNA and deduced protein sequence of the murine PTP HSC cDNA. Illustrated is the DNA sequence (SEQ. ID. NO: 1) and deduced protein sequence (SEQ. ID. NO: 2) of the murine PTP HSC cDNA. The overlined region is the phosphatase homologous domain. The asterisk denotes the active site cysteine residue. The P,S,T-rich region is illustrated by boxes around these residues. The shaded carboxy terminal region is homologous to a nuclear localization signal found on murine PTP PEP (Flores et a!., Mol. Cell. Biol. 14(7). 4938-46 119941). Figure 2. Sequence homologies of murine PTP HSC, murine PTP PEP, and human PTP PEST. A. The phosphatase domain homologies show that these three proteins are highly related to each other. A star over the residue (amino acid 37 of PTP HSC) illustrates a conserved serine that is phosphorylated by protein kinases A and C and which appears to negatively regulate PTPase activity (Garton and Tonks, EMBO J. 13( 16), 3763-71 [1994]). The amino acid sequence of positions 24 - 301 of PTP PEP is shown in SEQ. ID. NO: 18; the amino acid sequence of positions 24 - 299 of PTP PEST is shown in SEQ. ID. NO: 19. B. A second highly homologous region is found at the carboxy terminus of these three proteins (SEQ. ID. NO: 22 showing amino acids 783 - 803 of PTP PEP; SEQ. ID. NO: 23 showing amino acids 761 - 781 of PTP PEST). This region has been shown to confer nuclear localization on PTP PEP. Interestingly PTP PEST is localized to the cytoplasm, and it has been hypothesized that this is due to the two negatively charged residues shown by the arrows. As can be seen, PTP HSC also contains these negatively charged residues, suggesting that it is also localized to the cytoplasm. Figure 3. The PTP PST family. Illustrated are the three so far identified members of this family including the currently described novel PTP (PTP HSC). Shown are the amino terminal PTP domains (black), the P,S,T rich domains, and the carboxy terminal nuclear localization homology (shaded). Figure 4. Intron sites superimposed on the PTP HSC domain structure. Analysis of the gene encoding PTP HSC revealed the location of 14 introns that are shown as triangles in this figure. Figure 5. In vitro tyrosine phosphatase activity of the PTP HSC. Shown is the enzymatic activity obtained using isolated, bacterially produced GST-phosphatase domain of PTP HSC. Black squares, serial dilutions of GST-PTP HSC in the absence of orthovanadate; white squares, enzymatic activity of GST-PTP HSC in the presence of vanadate; closed circle, enzymatic activity of GST alone; open circles enzymatic activity with an inactive GST-PTP (J. Cheng and L. Lasky-unpublished data). The initial undiluted reaction contained 2 μg of each protein. Figure 6. PCR analysis of PTP HSC expression. A. lin lo CD34 hl sca hl or lin'°CD34 h 'sca io hematopoietic progenitor cells were isolated from murine embryos at day 1 1 of development. RNA was isolated and analyzed by quantitative PCR. The upper band corresponds to the PTP HSC transcript while the lower band corresponds to the triose phosphate isomerase (TPI) internal standard. B. lin'°CD34 nι sca nι hematopoietic progenitor/stem cells were purified from murine fetal liver and incubated for up to 14 days in IL-s, IL-s, EPO and GM-CSF. RNA was isolated at various times and analyzed by quantitative PCR as described in A. Figure 7. PTP HSC Transcript analysis in embryonic and adult tissues and hematopoietic cell lines. A. Illustrated is a tissue northern blot probed with a cDNA encoding PTP HSC. The left panel illustrates RNA isolated from variously aged embryos, while the right panel illustrates RNA isolated from: a. heart, b., brain, c. spleen, d. lung, e. liver, f. skeletal muscle, g. kidney, h. testis. B. Illustrated is a northern blot of RNA isolated from BAF 3 (a), 32D (b) and FDCP (c) hematopoietic progenitor cells. Also shown is the ethidium bromide stain ofthe same gel prior to transfer. C. PCR analysis of RNA isolated from BAF 3 (a), 32 D (b), T cell clone (c), FDCP (d), 1 1 day embryos (e) and a control with no reverse transcriptase (f) Figure 8. Partial DNA and deduced protein sequence of the human PTP HSC cDNA. Illustrated is the partial DNA sequence (SEQ. ID. NO: 17 ) and deduced protein sequence (SEQ. ID. NO: 18) of the human PTP HSC cDNA. Detailed Description of the Invention A. Definitions The phrases "non-receptor protein tyrosine phosphatase of hematopoietic stem cells", "tyrosine phosphatase of hematopoietic stem cells" and "PTP HSC" are used interchangeably and refer to a native intracellular protein tyrosine phosphatase which (1) is expressed predominantly in early hematopoietic stem and progenitor cells; (2) predominantly lacks expression in adult tissues; (3) comprises an N-terminal tyrosine phosphatase domain, followed by a region rich in serine, threonine, and proline, and a carboxy terminal region of about 15 to 25 amino acids rich in basic amino acid residues; and (4) is capable of tyrosine dephosphorylation in hematopoietic progenitor cells, and functional derivatives of such native tyrosine phosphatase. The term "native tyrosine phosphatase" in this context refers to a naturally occurring tyrosine phosphatase, having the described properties, of any human or non-human animal species, with or without the initiating methionine, whether purified from native source, synthesized, produced by recombinant DNA technology or by any combination of these and/or other methods. Native PTP HSCs specifically include the native murine and native human HSC proteins (SEQ. ID. NOs: 2 and , respectively). A "functional derivative" of a polypeptide is a compound having a qualitative biological activity in common with the native polypeptide. Thus, a functional derivative of a native PTP HSC polypeptide is a compound that has a qualitative biological activity in common with a native PTP HSC. "Functional derivatives" include, but are not limited to, fragments of native polypeptides from any animal species (including humans), derivatives of native (human and non-human) polypeptides and their fragments, and peptide and non-peptide analogs of native polypeptides, provided mat they have a biological activity in common with a respective native polypeptide. "Fragments" comprise regions within the sequence of a mature native polypeptide. The term "derivative" is used to define amino acid sequence variants, and covalent modifications of a native polypeptide. "Non-peptide analogs" are organic compounds which display substantially the same surface as peptide analogs ofthe native polypeptides Thus, the non-peptide analogs ofthe native PTP HSCs ofthe present invention are organic compounds which display substantially the same surface as peptide analogs of the native PTP HSCs Such compounds interact with other molecules in a similar fashion as the peptide analogs, and mimic a biological activity of a native PTP HSC ofthe present mvention The polypeptide functional derivatives ofthe native PTP HSCs ofthe present invention preferably have an active N-terminal tyrosine phosphatase domain, retaining a serine residue at a position corresponding to ammo acid position 37 in Figure I , and retaining an active site cysteine residue at a position corresponding to amino acid position 229 in Figure 1 , a region rich in serine, threonine, and proline, and a carboxy-terminal region showmg at least about 80% sequence homology with the ammo acid sequence between positions 430 and 451 in Figure 1 Preferably, such derivatives have at least about 65% more preferably at least about 75 %, even more preferably at least about 85%, most preferably at least about 95% overall sequence homology with the ammo acid sequence shown in Figure 1 (SEQ ID NO 2) or Figure 8 (SEQ ID NO 18) and retain the ability of tyrosine dephosphorylation in hematopoietic progenitor cells The term "biological activity" in the context ofthe definition of functional derivatives is defined as the possession of at least one adhesive, regulatory or effector function qualitatively in common with a native polypeptide (e g PTP HSC) The functional derivatives ofthe native PTP HSCs ofthe present invention are unified by their qualitative ability of tyrosine dephosphorylation in hematopoietic progenitor cells ln addition the functional derivatives of the native PTP HSCs herein preferably are capable of downregulating STAT activation The term "agonist" is used to refer to peptide and non-peptide analogs of the native PTP HSCs of the present invention and to antibodies specifically binding such native PTP HSCs provided that they retain the qualitative ability of tyrosine dephosphorylation in hematopoietic progenitor cells The term "antagonist" is used to refer to a molecule inhibiting the ability of a PTP HSC ofthe present invention to dephosphorylate tyrosines Preferred antagonists essentially completely block tyrosine dephosphorylation caused by a PTP HSC "Identity" or "homology" with respect to a native polypeptide and its functional derivative is defined herem as the percentage of ammo acid residues in the candidate sequence that are identical with the residues of a corresponding native polypeptide, after aligning the sequences and introducing gaps, if necessary, to achieve the maximum percent homology, and not considering any conservative substitutions as part of the sequence identity Neither N- or C-terminal extensions nor insertions shall be construed as reducing identity or homology Methods and computer programs for the alignment are well known in the art The term "stem cell" is used in the broadest sense to describe cells which are not terminally differentiated and have the ability to divide throughout the lifetime ofthe organism, yielding some progeny that differentiate and others that remain stem cells, including stem cells of any tissue type, such as the lining of the gut, the epidermal layer ofthe skin and the blood-forming tissues The term "hematopoietic stem cell" is used in the broadest sense to refer to stem cells from which blood cells derive, including pluripotent stem cells, lymphoid and myeloid stem cells The term "hematopoietic progenitor cell" refers to the progeny of a pluripotent hematopoietic stem cell which are committed for a particular line of differentiation These committed progenitor cells are irreversibly determined as ancestors of only one or a few blood cell types, e g erythrocytes or granulocytes "Hematopoietic growth factors" are growth factors that influence blood cell formation or differentiation in vivo, such as EPO, TPO, IL-3, IL-6, stem cell growth factor, M-CSF, G-CSF, GM-CSF. FTL 3 ligand, LIF, etc , unified by their role in mediating protein phosphorylation The receptors of these growth factors are either transmembrane tyrosine kinases or are members of the cytokine receptor family Ordinarily, the terms "ammo acid" and "ammo acids" refer to all naturally occurring L-α-amino acids ln some embodiments, however, D-ammo acids may be present in the polypeptides or peptides ofthe present invention order to facilitate conformational restriction For example, in order to facilitate disulfide bond formation and stability, a D amino acid cysteme may be provided at one or both termini of a peptide functional deπvative or peptide antagonist ofthe native PTP HSCs ofthe present invention The ammo acids are identified by either the single-letter or three-letter designations Asp D aspartic acid He I isoleucine Thr T threonine Leu L leucine Ser S serine Tyr Y tyrosine Glu E glutamic acid Phe F phenylalanine Pro P proline His H histidme Gly G glycine Lys K lysme Ala A alanine Arg R arginine Cys C cysteine Trp W tryptophan Val V valine Gin Q glutamine Met M methion e Asn N asparagme These ammo acids may be classified accordmg to the chemical composition and properties of their side cha s They are broadly classified into two groups, charged and uncharged Each of these groups is divided into subgroups to classify the amino acids more accurately I Charged Ammo Acids Acidic Residues aspartic acid, glutamic acid Basic Residues lysine, argmme, histid e II Uncharged Amino Acids H y drophilic Residues serine, threonine, asparagme, glutamine Aliphatic Residues glycine, alanine, valine, leucine, isoleucine Non-polar Residues cysteine, methionine, proline Aromatic Residues phenylalanine, tyrosine, tryptophan The term "amino acid sequence variant" refers to molecules with some differences in their ammo acid sequences as compared to a native ammo acid sequence Substitutional variants are those that have at least one ammo acid residue in a native sequence removed and a different ammo acid inserted in its place at the same position The substitutions may be smgle, where only one ammo acid in the molecule has been substituted, or they may be multiple, where two or more ammo acids have been substituted in the same molecule Insertional variants are those with one or more ammo acids inserted immediately adjacent to an amino acid at a particular position in a native sequence Immediately adjacent to an ammo acid means connected to either the α -carboxy or α-ammo functional group of the amino acid Deletional variants are those with one or more amino acids in the native ammo acid sequence removed Ordinarily, deletional variants will have one or two amino acids deleted in a particular region ofthe molecule "Antibodies (Abs)" and "immunoglobulins (Igs)" are glycoproteins having the same structural characteristics While antibodies exhibit binding specificity to a specific antigen, immunoglobulins include both antibodies and other antibody-like molecules which lack antigen specificity Polypeptides ofthe latter kind are, for example, produced at low levels by the lymph system and at increased levels by myelomas Native antibodies and immunoglobulins are usually heterotetrameπc glycoproteins of about 150 000 daltons, composed of two identical light (L) chams and two identical heavy (H) chains Each light chain is linked to a heavy chain by one covalent disulfide bond, while the number of disulfide linkages vanes between the heavy chams of different immunoglobulin isotypes Each heavy and light chain also has regularly spaced lntrachain disulfide bridges Each heavy chain has at one end a variable domain (Vι_ j ) followed by a number of constant domains Each light chain has a variable domain at one and (V^) and a constant domain at its other end, the constant domam ofthe light chain is aligned with the first constant domain ofthe heavy chain, and the light chain variable domain is aligned with the variable domam of the heavy chain Particular amino acid residues are believed to form an interface between the light and heavy chain variable domains (Cloth ia et al , J Mol Biol 186. 651 -663 [1985], Novotny and Haber, Proc Natl Acad Sci USA 82, 4592-4596 [ 1985]) The term "variable" refers to the fact that certain portions ofthe variable domains differ extensively in sequence among antibodies and are used in the binding and specificity of each particular antibody for its particular antigen However, the variability is not evenly distributed through the variable domains of antibodies It is concentrated m three segments called complementarity determining regions (CDRs) or hypervaπable regions both in the light chain and the heavy chain variable domains The more highly conserved portions of variable domains are called the framework (FR) The variable domains of native heavy and light chains each comprise four FR regions, largely adopting a β-sheet configuration, connected by three CDRs, which form loops connecting, and m some cases formmg part of, the β-sheet structure The CDRs in each chain are held together in close proximity by the FR regions and, with the CDRs from the other chain, contribute to the formation ofthe antigen binding site of antibodies (see Kabat, E A et al , Sequences of Proteins of Immunological Interest. National Institute of Health, Bethesda, MD [ 1991]) The constant domains are not involved directly in binding an antibody to an antigen, but exhibit various effector functions, such as participation ofthe antibody in antibodv- dependent cellular toxicity Papain digestion of antibodies produces two identical antigen binding fragments, called Fab fragments each with a single antigen binding site, and a residual "Fc" fragment, whose name reflects its ability to crystallize readily. Pepsin treatment yields an F(ab')2 fragment that has two antigen combining sites and is still capable of cross-linking antigen. "Fv" is the minimum antibody fragment which contains a complete antigen recognition and binding site. This region consists of a dimer of one heavy and one light chain variable domain in tight, non-covalent association. It is in this configuration that the three CDRs of each variable domain interact to define an antigen binding site on the surface ofthe ^-V^ dimer. Collectively, the six CDRs confer antigen binding specificity to the antibody. However, even a single variable domain (or half of an Fv comprising only three CDRs specific for an antigen) has the ability to recognize and bind antigen, although at a lower affinity than the entire binding site. The Fab fragment also contains the constant domain of the light chain and the first constant domain (CH I ) of the heavy chain. Fab' fragments differ from Fab fragments by the addition of a few residues at the carboxy terminus of the heavy chain CH I domain including one or more cysteines from the antibody hinge region. Fab'-SH is the designation herein for Fab' in which the cysteine residue(s) ofthe constant domains bear a free thiol group. F(ab') 7 antibody fragments originally were produced as pairs of Fab' fragments which have hinge cysteines between them. Other, chemical couplings of antibody fragments are also known. The light chains of antibodies (immunoglobulins) from any vertebrate species can be assigned to one of two clearly distinct types, called kappa and lambda (λ), based on the amino acid sequences of their constant domains. Depending on the amino acid sequence of tiie constant domain of their heavy chains, immunoglobulins can be assigned to different classes. There are five major classes of immunoglobulins: IgA, IgD, IgE, IgG and IgM, and several of these may be further divided into subclasses (isotypes), e.g. IgG- 1 , IgG-2, IgG-3, and lgG-4; IgA-1 and IgA-2. The heavy chain constant domains that correspond to the different classes of immunoglobulins are called α, delta, epsilon, γ, and μ, respectively. The subunit structures and three-dimensional configurations of different classes of immunoglobulins are well known. The term "antibody" is used in the broadest sense and specifically covers single monoclonal antibodies (including agonist and antagonist antibodies), antibody compositions with polyepitopic specificity, as well as antibody fragments (e.g., Fab, Ff^b'^, and Fv), so long as they exhibit the desired biological activity. The term "monoclonal antibody" as used herein refers to an antibody obtained from a population of substantially homogeneous antibodies, i.e., the individual antibodies comprising the population are identical except for possible naturally occurring mutations that may be present in minor amounts. Monoclonal antibodies are highly specific, being directed against a single antigenic site. Furthermore, in contrast to conventional (polyclonal) antibody preparations which typically include different antibodies directed against different determinants (epitopes), each monoclonal antibody is directed against a single determinant on the antigen. In addition to their specificity, the monoclonal antibodies are advantageous in that they are synthesized by the hybridoma culture, uncontaminated by other immunoglobulins. The modifier "monoclonal" indicates the character ofthe antibody as being obtained from a substantially homogeneous population of antibodies, and is not to be construed as requiring production of the antibody by any particular method. For example, the monoclonal antibodies to be used in accordance with the present invention may be made by the hybridoma method first described by Kohler & Milstein, Nature 256 495 (1975), or may be made by recombinant DNA methods [see, e g U S Patent No 4,816,567 (Cabilly et al )] The monoclonal antibodies herein specifically include "chimeric" antibodies (immunoglobulins) in which a portion ofthe heavy and/or light chain is identical with or homologous to corresponding sequences in antibodies derived from a particular species or belonging to a particular antibody class or subclass, while the remainder ofthe chaιn(s) is identical with or homologous to correspondmg sequences m antibodies derived from another species or belonging to another antibody class or subclass, as well as fragments of such antibodies, so long as they exhibit the desired biological activity (U S Patent No 4,816,567 (Cabilly et al , Morrison et al Proc Natl. Acad Sci USA 81. 6851 -6855 [1984]) "Humanized" forms of non-human (e g murine) antibodies are chimeric immunoglobulins immunoglobulin chams or fragments thereof (such as Fv, Fab, Fab', F(ab') 2 or other antigen-binding subsequences of antibodies) which contain minimal sequence derived from non-human immunoglobulin For the most part, humanized antibodies are human immunoglobulins (recipient antibody) which residues from a complementary determining region (CDR) of the recipient are replaced by residues from a CDR of a non- human species (donor antibody) such as mouse, rat or rabbit having the desired specificity, affinity and capacity In some instances, Fv framework residues ofthe human immunoglobulin are replaced by corresponding non- human residues Furthermore, humanized antibody may comprise residues which are found neither in the recipient antibody nor in the imported CDR or framework sequences These modifications are made to further refine and optimize antibody performance In general, the humanized antibody will comprise substantially all of at least one, and typically two, variable domains, in which all or substantially all of the CDR regions correspond to those of a non-human immunoglobulin and all or substantially all ofthe FR regions are those of a human immunoglobulin consensus sequence The humanized antibody optimally also will comprise at least a portion of an immunoglobulin constant region (Fc), typically that of a human immunoglobulin For further details see Jones et al . Nature 321. 522-525 [1986], Reichmann et al . Nature 332. 323-329 [ 1988], EP-B-239 400 published 30 September 1987, Presta, Curr Op Struct Biol 2 593-596 [1992], and EP-B-451 216 published 24 January 1996) In the context of the present invention the expressions "cell", "cell line", and "cell culture" are used interchangeably, and all such designations include progeny It is also understood that all progeny may not be precisely identical in DNA content, due to deliberate or inadvertent mutations Mutant progeny that have the same function or biological property, as screened for in the originally transformed cell, are included The terms "rep cable expression vector" and "expression vector" refer to a piece of DNA, usuall double-stranded, which may have inserted into it a piece of foreign DNA Foreign DNA is defined as heterologous DNA, which is DNA not naturally found in the host cell The vector is used to transport the foreign or heterologous DNA into a suitable host cell Once in the host cell, the vector can replicate independently of the host chromosomal DNA, and several copies ofthe vector and its inserted (foreign) DNA may be generated ln addition, the vector contains the necessary elements that permit translating the foreign DNA into a polypeptide Many molecules ofthe polypeptide encoded by the foreign DNA can thus be rapidly synthesized "Oligonucleotides" are short-length, single- or double-stranded polydeoxynucleotides that are chemically synthesized by known methods [such as phosphotπester, phosphite, or phosphoramidite chemistn, using solid phase techniques such as those described in EP 266,032, published 4 May 1988, or via deoxynucleoside H-phosphanate intermediates as described by Froehler et ai. Nucl. Acids Res. 14, 5399 ( 1986). They are then purified on polyacrylamide gels. B. Production of PTP HSCs by recombinant DNA technology 1. Identification and isolation of nucleic acid encoding PTP HSCs The native PTP HSC proteins ofthe present invention may be isolated from relatively undifferentiated, early hematopoietic stem or progenitor cells. The isolation of murine PTP HSC from the CD34 fraction of murine 10.5 day yolk sac or embryo cells is illustrated in the examples. Similarly, murine PTP HSC can be isolated from CD34 population originated from bone marrow or fetal liver. The purity of these murine cells was found to be a critical step in isolating the mRNA encoding the new murine PTP HSC of the present invention. A high degree of purity was achieved by purification with a rabbit anti-murine CD34 antibody followed by a lineage depletion step and a positive selection step with the Sea antibody. Alternatively, murine PTP HSC can be detected and obtained from other relatively undifferentiated precursors of mature murine hematopoietic cells, such as, BAF 3, 32D and FDCP hematopoietic progenitor cells, available from the American Type Culture Collection (ATCC). Native human PTP HSC can, for example, be identified in and obtained from human CMK progenitor cells. As the PTP HSCs enzymes have an extremely low abundance in embryonic tissues, their purification by traditional methods would be very cumbersome and inefficient. Instead, cDNA or genomic clones encoding the PTP HSC proteins of the present invention can be prepared using standard techniques of recombinant DNA technology. For example, cDNA library can be constructed by obtaining polyadenylated mRNA from a cell line known to express the desired PTP HSC, and using the mRNA as a template to synthesize double stranded cDNA. Exemplary human and non-human cell lines suitable for this purpose have been listed hereinabove. A PTP HSC polypeptide gene can also be obtained from a genomic library, such as a human genomic cosmid library. Libraries, either cDNA or genomic, are then screened with probes designed to identify the gene of interest or the protein encoded by it. For cDNA expression libraries, suitable probes include monoclonal and polyclonal antibodies that recognize and specifically bind to a PTP HSC polypeptide. For cDNA libraries, suitable probes include carefully selected oligonucleotide probes (usually of about 20-80 bases in length) that encode known or suspected portions of a PTP HSC polypeptide from the same or different species, and/or complementary or homologous cDNAs or fragments thereof that encode the same or a similar gene. Appropriate probes for screening genomic DNA libraries include, without limitation, oligonucleotides, cDNAs, or fragments thereof that encode the same or a similar gene, and/or homologous genomic DNAs or fragments thereof. Screening the cDNA or genomic library with the selected probe may be conducted using standard procedures as described in Chapters 10-12 of Sambrook et ai. Molecular Cloning: A Laboratory Manual. New York, Cold Spring Harbor Laboratory Press, 1989. If DNA encoding an enzyme of the present invention is isolated by using carefully selected oligonucleotide sequences to screen cDNA libraries from various tissues, the oligonucleotide sequences selected as probes should be sufficient in length and sufficiently unambiguous that false positives are minimized. The actual nucleotide sequence(s) is/are usually designed based on regions which have the least codon redundance. The oligonucleotides may be degenerate at one or more positions. The use of degenerate oligonucleotides is of particular importance where a library is screened from a species in which preferential codon usage is not known. The oligonucleotide must be labeled such that it can be detected upon hybridization to DNA in the library being screened. The preferred method of labeling is to use ATP (e.g., γ P) and polynucleotide kinase to radiolabel the 5' end ofthe oligonucleotide. However, other methods may be used to label the oligonucleotide, including, but not limited to, biotinylation or enzyme labeling. cDNAs encoding PTP HSCs can also be identified and isolated by other known techniques of recombinant DNA technology, such as by direct expression cloning, or by using the polymerase chain reaction (PCR) as described in U.S. Patent No. 4,683,195, issued 28 July 1987, in section 14 of Sambrook et al., supra, or in Chapter 15 of Current Protocols in Molecular Biology. Ausubel et ai eds., Greene Publishing Associates and Wiley-Interscience 1991. The use ofthe PCR technique for obtaining cDNA encoding murine PTP HSC or the PTP domain of this native protein is also illustrated in the examples. Once cDNA encoding a PTP HSC enzyme from one species has been isolated, cDNAs from other species can also be obtained by cross-species hybridization. According to this approach, human or other mammalian cDNA or genomic libraries are probed by labeled oligonucleotide sequences selected from known PTP HSC sequences (such as murine PTP HSC) in accord with known criteria, among which is that the sequence should be sufficient in length and sufficiently unambiguous that false positives are minimized. Typically, a P- labeled oligonucleotide having about 30 to 50 bases is sufficient, particularly if the oligonucleotide contains one or more codons for methionine or tryptophan. Isolated nucleic acid will be DNA that is identified and separated from contaminant nucleic acid encoding other polypeptides from the source of nucleic acid. Hybridization is preferably performed under "stringent conditions" which means (1 ) employing low ionic strength and hgh temperature for washing, for example, 0.015 sodium chloride/0.0015 M sodium citrate/0.1% sodium dodecyl sulfate at 50 ° C, or (2) employing during hybridization a denaturing agent, such as formamide, for example, 50% (vol/vol) formamide with 0.1% bovine serum albumin/0.1% polyvinylpyrrolidone/50 nM sodium phosphate buffer at pH 6.5 with 650 mM sodium chloride, 75 mM sodium citrate at 42 °C. Another example is the use of 5)% formamide, 5 x SSC (0.75 M sodium chloride, 0.075 M sodium citrate), 50 mM sodium phosphate (pH 6.8), 0.1% sodium pyrophosphate, 5 x Denhardt's solution, sonicated salmon sperm DNA (50 μg/ml), 0.1% SDS, and 10% dextran sulfate at 42 ° C, with washes at 42 ° C in 0.2 x SSC and 0.1 % SDS. Once the sequence is known, the gene encoding a particular PTP HSC polypeptide can also be obtained by chemical synthesis, following one ofthe methods described in Engels and Uhlmann, Agnew. Chem. Int. Ed. Engl. 28. 716 (1989). These methods include triester, phosphite, phosphoramidite and H-phosphonate methods, PCR and other autoprimer methods, and oligonucleotide syntheses on solid supports. 2. Cloning and expression of nucleic acid encoding PTP HSCs Once the nucleic acid encoding PTP HSC is available, it is generally ligated into a replicable expression vector for further cloning (amplification ofthe DNA), or for expression. Expression and cloning vectors are well known in the art and contain a nucleic acid sequence that enables the vector to replicate in one or more selected host cells. The selection ofthe appropriate vector will depend on 1 ) whether it is to be used for DNA amplification or for DNA expression, 2) the size ofthe DNA to be inserted into the vector, and 3) the host cell to be transformed with the vector. Each vector contains various components depending on its function (amplification of DNA of expression of DNA) and the host cell for which it is compatible The vector components generally include, but are not limited to, one or more ofthe following a signal sequence, an origin of replication, one or more marker genes, an enhancer element, a promoter and a transcription termination sequence Construction of suitable vectors contammg one or more of the above listed components, the desired codmg and control sequences, employs standard ligation techniques Isolated plasmids or DNA fragments are cleaved, tailored, and rehgated in the form desired to generate the plasmids required For analysis to confirm correct sequences in plasmids constructed, the ligation mixtures are commonly used to transform E coli cells, e g E. coli K12 strain 294 (ATCC 31 ,446) and successful transformants selected by ampicillin or tetracycline resistance where appropriate Plasmids from the transformants are prepared, analyzed by restriction endonuclease digestion, and or sequenced by the method of Messing et al , Nucleic Acids Res 9 309 (1981 ) or by the method of Maxam et al , Methods m Enzymology 65, 499 ( 1980) The polypeptides ofthe present invention may be expressed in a variety of prokaryotic and eukaryotic host cells Suitable prokaryotes mclude gram negative or gram positive organisms, for example £ coh or bacilli A preferred cloning host is E coli 294 (ATCC 31 ,446) although other gram negative or gram positive prokaryotes such as £ ≤oii B, E ≤ojj XI 776 (ATCC 31 ,537), E coli W31 10 (ATCC 27.325), Pseudomonas species, or Serratia Marcesans are suitable In addition to prokaryotes, eukaryotic microbes such as filamentous fungi or yeast are suitable hosts for vectors herem Saccharomyces cerevisiae. or common baker's yeast, is the most commonly used among lower eukaryotic host microorganisms However, a number of other genera, species and strains are commonly available and useful herein, such as S pombe [Beach and Nurse, Nature 290. 140 (1981)], Kluvveromvces lactis [Lou vencourt et al , J Bacteriol 737 ( 1983 )] , varrowia (EP 402,226), Pichia pastoris (EP 183.070), Trichoderma reesia (EP 244,234), Neurospora crassa [Case et al . Proc Natl Acad Sci USA 76. 5259-5263 ( 1979)], and Aspergillus hosts such as A. nidulans [Ballance et al , Biochem Biophvs Res Commun 1 12. 284-289 ( 1983) Tilburn e/ α/ , Ωene 6, 205-221 (1983). Yelton et al . Proc Natl Acad Sci. USA 81. 1470-1474 ( 1984)] and A niger [Kelly and Hynes, EMBO J 4, 475-479 ( 1985)] Suitable host cells may also derive from multicellular organisms Such host cells are capable of complex processing and glycosylation activities In principle, any higher eukaryotic cell culture is workable whether from vertebrate or invertebrate culture, although cells from mammals such as humans are preferred Examples of invertebrate cells include plants and insect cells Numerous baculoviral strains and variants and correspondmg permissive sect host cells from hosts such as Spodoptera frugiperda (caterpillar), Aedes aegvpti (mosquito), Aedes albopictus (mosquito), Drosophila melangaster (fruitfly), and Bombvx oπ host cells have been identified See, e g Luckow et al , Bio/Technologv 6,, 47-55 ( 1988), Miller et al , in Genetic Engineering Setlow, J K et al , eds , Vo! 8 (Plenum Publishmg, 1986), pp 277-279, and Maeda et al , Nature 315. 592-594 (1985) A variety of such viral strains are publicly available, e g the L-l variant of Autographa californica NPV and such viruses may be used as the virus herem accordmg to the present invention, particularly for transfection of Spodoptera frugiperda cells Plant cell cultures of cotton, corn, potato, soybean, petunia, tomato, and tobacco can be utilized as hosts Typically, plant cells are transfected by incubation with certain strains of the bacterium Agrobacterium tumefaciens. which has been previously manipulated to contain the PTP HSC DNA During incubation of the plant cell culture with A tumefaciens. the DNA encoding a PTP HSC is transferred to the plant cell host such that it is transfected, and will, under appropriate conditions, express the PTP HSC DNA In addition, regulatory and signal sequences compatible with plant cells are available, such as the nopalme synthase promoter and polyadenylation signal sequences Depicker et al , J Mol Appl Gen 1, 561 ( 1982) In addition, D A segments isolated from the upstream region ofthe T-DNA 780 gene are capable of activating or increasing transcription levels of plant-expressible genes in recombinant DNA-contaming plant tissue See EP 321 , 196 published 21 June 1989 However, interest has been greatest in vertebrate cells, and propagation of vertebrate cells in culture (tissue culture) is rjei ge well known See Tissue Culture. Academic Press, Kruse and Patterson, editors ( 1973) Examples of useful mammalian host cell lines are monkey kidney CV 1 line transformed by SV40 (COS-7. ATCC CRL 1651), human embryonic kidney cell line [293 or 293 cells subcloned for growth in suspension culture Graham et al , J Gen Virol 26, 59 ( 1977)], baby hamster kidney cells 9BHK, ATCC CCL 10), Chinese hamster ovary cells/-DHFR [CHO, Urlaub and Chasm, Proc Natl. Acad Sci USA 77, 4216 (1980)], mouse sertolii cells [TM4, Mather. Biol Reprod 23. 243-251 (1980)], monkey kidney cells (CV 1 ATCC CCL 70), African green monkey kidney cells (VERO-76, ATCC CRL- 1587), human cervical carcinoma cells (HELA, ATCC CCL 2) canine kidney cells (MDCK, ATCC CCL 34), buffalo rat liver cells (BRL 3 A, ATCC CRL 1442), human lung cells (W138, ATCC CCL75), human liver cells (Hep G2, HB 8065), mouse mammary tumor (MMT 060562 ATCC CCL51), TRI cells [Mather et al . Annals N Y Acad Sci. 383. 44068 (1982)], MRC 5 cells, FS4 cells, and a human hepatoma cell line (Hep G2) Preferred host cells are human embryonic kidney 293 and Chinese hamster ovary cells Particularly useful in the practice of this mvention are expression vectors that provide for the transient expression mammalian cells of DNA encoding a PTP HSC In general, transient expression involves the use of an expression vector that is able to replicate efficiently in a host cell, such that the host cell accumulates many copies of the expression vector and, in turn, synthesizes high levels of a desired polypeptide encoded by the expression vector Transient systems, comprising a suitable expression vector and a host cell, allow for the convenient positive identification of polypeptides encoded by clones DNAs, as well as for the rapid screening of such polypeptides for desired biological or physiological properties Thus, transient expression systems are particularly useful in the invention for purposes of identifying analogs and variants of a PTP HSC Other methods, vectors, and host cells suitable for adaptation to the synthesis ofthe PTP HSC polypeptides in recombmant vertebrate cell culture are described in Getting et al , Nature 293. 620-625 (1981 ), Mantel et al , Nature 281. 40-46 (1979), Levinson et al , EP 1 17,060 and EP 1 17,058 Particularly useful plasmids for mammalian cell culture expression of the PTP HSC polypeptides are pRK5 (EP 307,247), or pSV16B (PCT Publication No WO 91/08291) Other clonmg and expression vectors suitable for the expression of the PTP HSCs of the present invention in a variety of host cells are, for example, descπbed in EP 457,758 published 27 November 1991 A large variety of expression vectors is now commercially available An exemplary commercial yeast expression vector is pPIC 9 (Invitrogen), while an commercially available expression vector suitable for transformation of E. coli cells is PET 15b (Novagen) C. Culturing the Host Cells Prokaryotes cells used to produced the PTP HSCs of this invention are cultured in suitable media as describe generally in Sambrook et al , supra Mammalian cells can be cultured in a variety of media Commercially available media such as Ham's F10 (Sigma), Minimal Essential Medium (MEM, Sigma), RPMI- 1640 (Sigma), and Dulbecco's Modified Eagle's Medium (DMEM, Sigma) are suitable for culturing the host cells In addition, any of the media described in Ham and Wallace, Meth Enzymol 5.8, 44 (1979), Barnes and Sato, Anal Biochem 102. 255 ( 1980), US 4,767,704, 4,657,866, 4,927,762, or 4,560,655, WO 90/03430, WO 87/00195 or US Pat Re 30 985 may be used as culture media for the host cells Any of these media may be supplemented as necessary with hormones and/or other growth factors (such as insulin, transferπn, or epidermal growth factor), salts (such as sodium chloride, calcium, magnesium, and phosphate), buffers (such as HEPES), nucleosides (such as adenos e and thymidine), antibiotics (such as Gentamyc drug) trace elements (defined as inorganic compounds usuallj present at final concentrations in the micromolar range), and glucose or an equivalent energy source Any other necessary supplements may also be mcluded at appropriate concentrations that would be known to those skilled m the art The culture conditions, such as temperature, pH and the like, suitably are those previously used with the host cell selected for clonmg or expression, as the case may be, and will be apparent to the ordinary artisan The host cells referred to this disclosure encompass cells in in vitro cell culture as well as cells that are within a host animal or plant It is further envisioned that the PTP HSCs of this invention may be produced by homologous recombmation, or with recombmant production methods utilizmg control elements mtroduced into cells already containing DNA encoding the particular PTP HSC D. Detecting Gene Amplification/Expression Gene amplification and or expression may be measured in a sample directly, for example, by conventional Southern blotting, Northern blotting to quantitate the transcription of mRNA [Thomas, Proc Natl Acad Sci. USA 22, 5201-5205 (1980)], dot blotting (DNA analysis), or in situ hybridization, using an appropriately labeled probe, based on the sequences provided herein Various labels may be employed, most commonly radioisotopes, particularly P However, other techniques may also be employed, such as using biotm-modified nucleotides for introduction into a polynucleotide The biotin then serves as a site for binding to avidin or antibodies, which may be labeled with a wide variety of labels, such as radionuchdes, fluorescers, enzymes, or the like Alternatively, antibodies may be employed mat can recognize specific duplexes, including DNA duplexes, RNA duplexes, and DNA-RNA hybrid duplexes or DNA-protein duplexes The antibodies in turn may be labeled and the assay may be carried out where the duplex is bound to the surface, so that upon the formation of duplex on the surface, the presence of antibody bound to the duplex can be detected Gene expression, alternatively, may be measured by immunological methods such as immunohistochemical staining of tissue sections and assay of cell culture or body fluids, to quantitate directly the expression of gene product With immunohistochemical staining techniques, a cell sample is prepared typically by dehydration and fixation, followed by reaction with labeled antibodies specific for the gene product coupled, where the labels are usually visually detectable, such as enzymatic labels, fluorescent labels luminescent labels, and the like. A particularly sensitive staining technique suitable for use in the present invention is described by Hse et ai. Am. J. Clin. Pharrη. 75. 734-738 (1980). Antibodies useful for immunohistochemical staining and/or assay of sample fluids may be either monoclonal or polyclonal, and may be prepared in any animal. Conveniently, the antibodies may be prepared against a native PTP HSC polypeptide, or against a synthetic peptide based on the DNA sequence provided herein as described further hereinbelow. E. Amino Acid Sequence Variants of a native PTP HSCs Amino acid sequence variants of native PTP HSCs are prepared by methods known in the art by introducing appropriate nucleotide changes into a PTP HSC DNA, or by in vitro synthesis of the desired polypeptide. There are two principal variables in the construction of amino acid sequence variants: the location ofthe mutation site and the nature ofthe mutation. With the exception of naturally-occurring alleles, which do not require the manipulation ofthe DNA sequence encoding the PTP HSC, the amino acid sequence variants of PTP HSCs are preferably constructed by mutating the DNA, either to arrive at an allele or an amino acid sequence variant that does not occur in nature. One group ofthe mutations will be created within the phosphatase (PTP) domain of the enzymes of the present invention. Non-conservative substitutions within this domain may result in PTP HSC variants which loose their ability to dephosphatase tyrosines and will, therefore, be useful as antagonists of native PTP HSCs. PTP HSC variants mutated to enhance their enzymatic activity will be useful, for example, as more effective inhibitors of progenitor/stem cell differentiation. Alternatively or in addition, amino acid alterations can be made at sites that differ in PTP HSC proteins from various species, or in highly conserved regions, depending on the goal to be achieved. Sites at such locations will typically be modified in series, e.g. by ( 1 ) substituting first with conservative choices and then with more radical selections depending upon the results achieved, (2) deleting the target residue or residues, or (3) inserting residues of the same or different class adjacent to the located site, or combinations of options 1 -3. One helpful technique is called "alanine scanning" (Cunningham and Wells. Science 244. 1081-1085 [1989]). After identifying the desired mutation(s), the gene encoding a PTP HSC variant can, for example, be obtained by chemical synthesis as hereinabove described. More preferably, DNA encoding a PTP HSC amino acid sequence variant is prepared by site-directed mutagenesis of DNA that encodes an earlier prepared variant or a nonvariant version ofthe PTP HSC. Site-directed (site-specific) mutagenesis allows the production of PTP HSC variants through the use of specific oligonucleotide sequences that encode the DNA sequence ofthe desired mutation, as well as a sufficient number of adjacent nucleotides, to provide a primer sequence of sufficient size and sequence complexity to form a stable duplex on both sides of the deletion junction being traversed. Typically, a primer of about 20 to 25 nucleotides in length is preferred, with about 5 to 10 residues on both sides of the junction ofthe sequence being altered. In general, the techniques of site-specific mutagenesis are well known in the art, as exemplified by publications such as, Edelman et ai, DNA 2, 183 (1983). As will be appreciated, the site-specific mutagenesis technique typically employs a phage vector that exists in both a single- stranded and double-stranded form. Typical vectors useful in site-directed mutagenesis include vectors such as the M13 phage, for example, as disclosed by Messing et ai, Third Cleveland Symposium on Macromolecules and Recombinant DNA. A. Walton, ed., Elsevier, Amsterdam (1981 ). This and other phage vectors are commercially available and their use is well known to those skilled in the art. A versatile and efficient procedure for the construction of oligodeoxyribonucleotide directed site-specific mutations in DNA fragments using l 3- derived vectors was published by Zoller, M.J. and Smith, M.. Nucleic Acids Res. 10. 6487-6500 [1982]). Also. plasmid vectors that contain a single-stranded phage origin of replication (Veira et ai. Meth. Enzymol. 153. 3 [1987]) may be employed to obtain single-stranded DNA. Alternatively, nucleotide substitutions are introduced by synthesizing the appropriate DNA fragment in vitro, and amplifying it by PCR procedures known in the art. The PCR technique may also be used in creating amino acid sequence variants of a PTP HSC. In a specific example of PCR mutagenesis, template plasmid DNA (1 μg) is linearized by digestion with a restriction endonuclease that has a unique recognition site in the plasmid DNA outside ofthe region to be amplified. Of this material, 100 ng is added to a PCR mixture containing PCR buffer, which contains the four deoxynucleotide triphosphates and is included in the GeneAm kits (obtained from Perkin-Elmer Cetus, Norwalk, CT and Emeryville, CA), and 25 pmole of each oligonucleotide primer, to a final volume of 50 μl. The reaction mixture is overlayered with 35 μl mineral oil. The reaction is denatured for 5 minutes at lOOoC, placed briefly on ice, and then 1 μl Thermus aquaticus (Taq) DNA polymerase (5 units/ I), purchased from Perkin-Elmer Cetus, Norwalk, CT and Emeryville, CA) is added below the mineral oil layer. The reaction mixture is then inserted into a DNA Thermal Cycler (purchased from Perkin-Elmer Cetus) programmed as follows: 2 min. 55°C, 30 sec. 72°C, then 19 cycles of the following: 30 sec. 94oC, 30 sec. 55oC, and 30 sec. 72oC. At the end ofthe program, the reaction vial is removed from the thermal cycler and the aqueous phase transferred to a new vial, extracted with phenol/chloroform (50:50 vol), and ethanol precipitated, and the DNA is recovered by standard procedures. This material is subsequently subjected to appropriate treatments for insertion into a vector. Another method for preparing variants, cassette mutagenesis, is based on the technique described by Wells et al. fGene 34. 315 (1985)1. Additionally, the so-called phagemid display method may be useful in making amino acid sequence variants of native or variant PTP HSCs or their fragments. This method involves (a) constructing a replicable expression vector comprising a first gene encoding an receptor to be mutated, a second gene encoding at least a portion of a natural or wild-type phage coat protein wherein the first and second genes are heterologous, and a transcription regulatory element operably linked to the first and second genes, thereby forming a gene fusion encoding a fusion protein; (b) mutating the vector at one or more selected positions within the first gene thereby forming a family of related plasmids; (c) transforming suitable host cells with the plasmids; (d) infecting the transformed host cells with a helper phage having a gene encoding the phage coat protein; (e) culturing the transformed infected host cells under conditions suitable for forming recombinant phagemid particles containing at least a portion ofthe plasmid and capable of transforming the host, the conditions adjusted so that no more than a minor amount of phagemid particles display more than one copy ofthe fusion protein on the surface of the particle; (f) contacting the phagemid particles with a suitable antigen so that at least a portion ofthe phagemid particles bmd to me antigen, and (g) separating the phagemid particles that bmd from those that do not Steps (d) through (g) can be repeated one or more tunes Preferably in this method the plasmid is under tight control ofthe transcription regulatory element, and the culturing conditions are adjusted so that the amount or number of phagemid particles displaymg more than one copy ofthe fusion protein on the surface of the particle is less than about 1% Also, preferably, the amount of phagemid particles displaying more than one copy ofthe fusion protein is less man 10% ofthe amount of phagemid particles displaymg a smgle copy ofthe fusion protein Most preferably, the amount is less than 20% Typically in this method, the expression vector will further contain a secretory signal sequence fused to the DNA encoding each subunit of the polypeptide and the transcription regulatory element will be a promoter system Preferred promoter systems are selected from lac Z, p L , tac, T7 polymerase, tryptophan, and alkaline phosphatase promoters and combinations thereof Also, normally the method will employ a helper phage selected from M 13K07, M 13R408, M 13-VCS, and Phi X 174 The preferred helper phage is M13K07, and the preferred coat protein is the M13 Phage gene III coat protein The preferred host is E coli, and protease-deficient strains of E coli Further details ofthe foregomg and similar mutagenesis techniques are found in general textbooks such as, for example, Sambrook et al , supra, and Current Protocols in Molecular Biology. Ausubel et al eds , supra Naturally-occurring ammo acids are divided into groups based on common side chain properties ( 1 ) hydrophobic norleucine, met, ala, val. leu, lie, (2) neutral hydrophobic cys, ser, thr, (3) acidic asp, glu, (4) basic asn, gin, his, lys, arg, (5) residues that influence chain orientation gly, pro, and (6) aromatic trp, tyr, phe Conservative substitutions involve exchanging a member within one group for another member within the same group, whereas non-conservative substitutions will entail exchanging a member of one of these classes for another Ammo acid sequence deletions generally range from about 1 to 30 residues, more preferably about 1 to 10 residues, and typically are contiguous Ammo acid insertions include amino- and/or carboxyl-terminal fusions ranging in length from one residue to polypeptides contammg a hundred or more residues, as well as intrasequence insertions of single or multiple amino acid residues Intrasequence insertions (l e insertions within the PTP HSC protein ammo acid sequence) may range generally from about 1 to 10 residues, more preferably 1 to 5 residues, more preferably 1 to 3 residues Examples of terminal insertions mclude the PTP HSC polypeptides with an N-terminal methionyl residue, an artifact of its direct expression in bacteπal recombmant cell culture, and fusion of a heterologous N- termmal signal sequence to the N-termmus ofthe PTP HSC molecule to facilitate the secretion ofthe mature PTP HSC from recombinant host cells Such signal sequences will generally be obtained from, and thus homologous to, the intended host cell species Suitable sequences include STII or Ipp for E coli. alpha factor for veast and viral signals such as heφes gD for mammalian cells Other insertional variants ofthe native PTP HSC molecules include the fusion ofthe N- or C-terminus ofthe TRAF molecule to immunogenic polypeptides, e g bacterial polypeptides such as beta-lactamase or an enzyme encoded by the E coli trp locus, or yeast protein, and C-termmal fusions with proteins having a long half-life such as immunoglobulin regions (preferably immunoglobulin constant regions) albumin or ferritin, as described in WO 89/02922 published on 6 April 1989 Since it is often difficult to predict in advance the characteristics of a variant PTP HSC it will be appreciated that some screening will be needed to select the optimum variant F. Covalent Modifications of PTP HSC Polypeptides Covalent modifications of PTP HSCs are included within the scope herein Such modifications are traditionally mtroduced by reacting targeted ammo acid residues of the PTP HSC polypeptides with an organic deπvatizing agent that is capable of reacting with selected sides or terminal residues, or by harnessing mechanisms of post-translational modifications that function in selected recombinant host cells The resultant covalent derivatives are useful in programs directed at identifying residues important for biological activity for immunoassays of the PTP HSC, or for the preparation of anti-PTP HSC antibodies for immunoaffinity purification ofthe recombmant For example, complete inactivation ofthe biological activity ofthe protein after reaction with ninhydrin would suggest that at least one argmyl or lysyl residue is critical for its activity, whereafter the mdividual residues which were modified under the conditions selected are identified by isolation of a peptide fragment contammg the modified ammo acid residue Such modifications are within the ordinary skill in the art and are performed without undue experimentation Cysteiπyl residues most commonly are reacted with α-haloacetates (and corresponding amines), such as chloroacetic acid or chloroacetamide, to give carboxymethyl or carboxyamidomethyl derivatives Cysteinyl residues also are derivatized by reaction with bromotrifluoroacetone, α-bromo- β-(5-ιmιdozoyl)propιoπιc acid, chloroacetyl phosphate, N-alkylmaleimides, 3-nιtro-2-pyπdyl disulfide, methyl 2-pyπdyl disulfide, p- chloromercuπbenzoate, 2-chloromercuπ-4-nιtrophenol, or chloro-7-nιtrobenzo-2-oxa-l ,3-dιazole Histidyl residues are derivatized by reaction with diethylpyrocarbonate at pH 5 5-7 0 because this agent is relatively specific for the histidyl side chain Para-bromophenacyl bromide also is useful, the reaction is preferably performed in 0 1 M sodium cacodylate at pH 6 0 Lysmyl and ammo terminal residues are reacted with succinic or other carboxylic acid anhydrides Derivatization with these agents has the effect of reversing the charge of the lysinyl residues Other suitable reagents for deπvatizing α-amino-contammg residues mclude lmidoesters such as methyl picolinimidate pyridoxal phosphate, pyridoxal, chloroborohydπde, tπnitrobenzenesulfonic acid, O-methyiisourea, 2,4- pentanedione, and transaminase-catalyzed reaction with glyoxylate Arginyl residues are modified by reaction with one or several conventional reagents, among them phenylglyoxal, 2,3-butanedιone, 1,2-cyclohexanedιone and ninhydrin Derivatization of argmme residues requires that the reaction be performed in alkaline conditions because ofthe high pK a ofthe guanidine functional group Furthermore, these reagents may react with the groups of lysine as well as the arginine epsilon-amino group The specific modification of tyrosyl residues may be made, with particular interest in introducing spectral labels into tyrosyl residues by reaction with aromatic diazonium compounds or tetranitromethane Most commonly, N-acetyhmidizole and tetranitromethane are used to form O-acetyl tyrosyl species and 3-nιtro deπvatives, respectively Tyrosyl residues are lodinated using I or 3 ' I to prepare labeled proteins for use in radioimmunoassay Carboxyl side groups (aspartyl or glutamyl) are selectively modified by reaction with carbodnmides (R 1 - N=C=N-R') such as l-cyclohexyl-3-(2-morpholιnyl-4-ethyl) carbodiimide or l -ethyl-3-(4-azonιa-4 4- dimethylpentyl) carbodiimide Furthermore, aspartyl and glutamyl residues are converted to asparaginyl and glutaminyi residues by reaction with ammonium ions Glutammyl and asparaginyl residues are frequently deamidated to the correspondmg glutamyl and aspartyl residues Alternatively, these residues are deamidated under mildly acidic conditions Either form of these residues falls within the scope of this invention Other modifications mclude hydroxylation of proline and lysine, phosphorylation of hydroxyl groups of seryl, threonyl or tyrosyl residues, methylation ofthe α-amino groups of lysine, arginine, and histidine side chams (T E Creighton, Proteins Structure and Molecular Properties. W H Freeman & Co , San Francisco, pp 79-86 [1983]), acetylation of the N-termmal amine, and amidation of any C-terminal carboxyl group The molecules may further be covalently linked to nonproteinaceous polymers, e g polyethylene glycol polypropylene glycol or polyoxyalkylenes, in the manner set forth in U S S N 07/275,296 or U S patents 4,640,835, 4,496,689, 4,301 ,144, 4,670,417, 4,791 ,192 or 4,179,337 Derivatization with bifunctional agents is useful for preparing intramolecular aggregates of the PTP HSCs with polypeptides as well as for cross-lmkmg the PTP HSC polypeptide to a water insoluble support matrix or surface for use in assays or affinity purification In addition, a study of interchain cross-links will provide direct information on conformational structure Commonly used cross-lmkmg agents include 1 , 1 - bιs(dιazoacetyI)-2-phenylethane, glutaraldehyde, N-hydroxysuccinimide esters, homobifunctional imidoesters, and bifunctional maleunides Deπvatizing agents such as methyl-3-[(p-azιdophenyl)dιthιo]propιoιmιdate yield photoactivatable intermediates which are capable of formmg cross-links m the presence of light Alternatively reactive water insoluble matrices such as cyanogen bromide activated carbohydrates and the systems reactive substrates descπbed in U S Patent Nos 3,959,642, 3,969,287, 3,691,016, 4, 195,128, 4,247,642, 4,229,537, 4,055,635, and 4,330,440 are employed for protein immobilization and cross-linking Certain post-translational modifications are the result of the action of recombmant host cells on the expressed polypeptide Glutaminyi and aspaπginyl residues are frequently post-translationally deamidated to the corresponding glutamyl and aspartyl residues Alternatively, these residues are deamidated under mildly acidic conditions Either form of these residues falls within the scope of this invention Other post-translational modifications mclude hydroxylation of prolme and lysine, phosphorylation of hydroxyl groups of seryl, threonyl or tyrosyl residues, methylation ofthe α-amino groups of lysine, argmme, and histidme side chams [T E Creighton, Proteins Structure and Molecular Properties. W H Freeman & Co , San Francisco, pp 79-86 (1983)] Other derivatives comprise the novel peptides of this invention covalently bonded to a nonproteinaceous polymer The nonproteinaceous polymer ordinarily is a hydrophilic synthetic polymer, i e a polymer not otherwise found in nature However, polymers which exist in nature and are produced by recombinant or in vitro methods are useful, as are polymers which are isolated from nature Hydrophilic polyvinyl polymers fall within the scope of this invention, e.g. polyvinylalcohol and polyvinylpyrrolidone. Particularly useful are polyvinylalkylene ethers such a polyethylene glycol, polypropylene glycol. The PTP HSC polypeptides may be linked to various nonproteinaceous polymers, such as polyethylene glycol, polypropylene glycol or polyoxyalkylenes, in the manner set forth in U.S. Patent Nos. 4,640,835; 4,496,689; 4,301 , 144; 4,670,417; 4,791 , 192 or 4, 179,337. The PTP HSCs may be entrapped in microcapsules prepared, for example, by coacervation techniques or by interfacial polymerization, in colloidal drug delivery systems (e.g. liposomes. albumin microspheres. microemulsions, nano-particles and nanocapsules), or in macroemulsions. Such techniques are disclosed in Remington's Pharmaceutical Sciences. 16th Edition, Osol, A., Ed. (1980). G. Anti-PTP HSC antibody preparation (i) Polyclonal antibodies Polyclonal antibodies to a PTP HSC molecule generally are raised in animals by multiple subcutaneous (sc) or intraperitoneal (ip) injections ofthe PTP HSC and an adjuvant. It may be useful to conjugate the PTP HSC or a fragment containing the target amino acid sequence to a protein that is immunogenic in the species to be immunized, e.g. keyhole limpet hemocyanin, serum albumin, bovine thyroglobulin. or soybean trypsin inhibitor using a bifunctional or derivatizing agent, for example maleimidobenzoyi sulfosuccinimide ester (conjugation through cysteine residues), N-hydroxysuccinimide (through lysine residues), glytaraldehyde, succinic anhydride, SOC^, or R N=C=NR, where R and R are different alkyl groups. Animals are immunized against the immunogenic conjugates or derivatives by combining 1 mg or 1 μg of conjugate (for rabbits or mice, respectively) with 3 volumes of Freud's complete adjuvant and injecting the solution intradermally at multiple sites. One month later the animals are boosted with 1/5 to 1/10 the original amount of conjugate in Freud's complete adjuvant by subcutaneous injection at multiple sites. 7 to 14 days later the animals are bled and the serum is assayed for anti-PTP HSC antibody titer. Animals are boosted until the titer plateaus. Preferably, the animal boosted with the conjugate of the same PTP HSC. but conjugated to a different protein and or through a different cross-linking reagent. Conjugates also can be made in recombinant cell culture as protein fusions. Also, aggregating agents such as alum are used to enhance the immune response. (ii) Monoclonal antibodies Monoclonal antibodies are obtained from a population of substantially homogeneous antibodies, i.e., the individual antibodies comprising the population are identical except for possible naturally-occurring mutations that may be present in minor amounts. Thus, the modifier "monoclonal" indicates the character ofthe antibody as not being a mixture of discrete antibodies. For example, the anti-PTP HSC monoclonal antibodies of the invention may be made using the hybridoma method first described by Kohler & Milstein, Nature 256:495 ( 1975), or may be made by recombinant DNA methods [Cabilly, et al., U.S. Pat. No. 4,816,567]. In the hybridoma method, a mouse or other appropriate host animal, such as hamster is immunized as hereinabove described to elicit lymphocytes that produce or are capable of producing antibodies that will specifically bind to the protein used for immunization. Alternatively, lymphocytes may be immunized in vitro. Lymphocytes then are fused with myeloma cells using a suitable fusing agent, such as polyethylene glycol, to form a hybridoma cell [Godmg, Monoclonal Antibodies Principles and Practice, pp 59-103 (Academic Press 1986)] The hybridoma cells thus prepared are seeded and grown in a suitable culture medium that preferably contains one or more substances that inhibit the growth or survival ofthe unfused, parental myeloma cells For example, if the parental myeloma cells lack the enzyme hypoxanthme guanine phosphoπbosyl transferase (HGPRT or HPRT), the culture medium for the hybridomas typically will mclude hypoxanthme, aminopterin and thymidine (HAT medium), which substances prevent the growth of HGPRT-deficient cells Preferred myeloma cells are those that fuse efficiently, support stable high level expression of antibod} by the selected antibody-producing cells, and are sensitive to a medium such as HAT medium Among these preferred myeloma cell lines are murine myeloma lines, such as those derived from MOPC-21 and MPC-1 1 mouse tumors available from the Salk Institute Cell Distribution Center, San Diego, California USA, and SP-2 cells available from the American Type Culture Collection, Rockville, Maryland USA Human myeloma and mouse-human heteromyeloma cell lines also have been described for the production of human monoclonal antibodies [Kozbor, J Immunol 12 3001 (1984), Brodeur, et al , Monoclonal Antibodv Production Techniques and Applications, pp 51 -63 (Marcel Dekker, lnc , New York, 1987)] Culture medium in which hybπdoma cells are growing is assayed for production of monoclonal antibodies directed against PTP HSC Preferably, the binding specificity of monoclonal antibodies produced by hybridoma cells is determined by immunoprecipitation or by an m vitro binding assay such as radioimmunoassay (RIA) or enzyme-linked immunoabsorbent assay (ELISA) The binding affinity of the monoclonal antibody can, for example, be determined by the Scatchard analysis of Munson & Pollard, Anal Biochem I0J 220 (1980) After hybridoma cells are identified that produce antibodies ofthe desired specificity, affinity, and/or activity, the clones may be subcloned by limiting dilution procedures and grown by standard methods Goding, Monoclonal Antibodies. Principles and Practice, pp 59-104 (Academic Press, 1986) Suitable culture media for this puφose mclude, for example, Dulbecco's Modified Eagle's Medium or RPMI- 1640 medium ln addition the hybridoma cells may be grown in vivo as ascites tumors in an animal The monoclonal antibodies secreted by the subclones are suitably separated from the culture medium ascites fluid, or serum by conventional immunoglobulin purification procedures such as, for example protein A-Sepharose, hydroxylapatite chromatography, gel electrophoresis, dialysis, or affinity chromatography DNA encoding the monoclonal antibodies of the invention is readily isolated and sequenced using conventional procedures (e g , by using oligonucleotide probes that are capable of binding specifically to genes encoding the heavy and light chains of murine antibodies) The hybridoma cells of the invention serve as a preferred source of such DNA Once isolated, the DNA may be placed into expression vectors, which are then transfected into host cells such as simian COS cells Chinese hamster ovary (CHO) cells, or myeloma cells that do not otherwise produce immunoglobulin protein, to obtain the synthesis of monoclonal antibodies in the recombinant host cells The DNA also may be modified, for example, by substituting the coding sequence for human heavy and light chain constant domams in place ofthe homologous murine sequences Morrison et al Proc Nat Acad Sci 81. 6851 (1984), or by covalently joining to the immunoglobulin coding sequence all or part of the coding sequence for a non-immunoglobulin polypeptide In that manner, "chimeric" or "hybrid" antibodies are prepared that have the binding specificity of an anti-TRAF monoclonal antibody herein Typically such non-immunoglobulin polypeptides are substituted for the constant domains of an antibody ofthe mvention, or they are substituted for the variable domains of one antigen-combining site of an antibody ofthe invention to create a chimeric bivalent antibody comprising one antigen-combmmg site having specificity for a PTP HSC and another antigen-combining site having specificity for a different antigen Chimeric or hybrid antibodies also may be prepared in vitro using known methods in synthetic protein chemistry, mcludmg those involving crosslinking agents For example, immunotoxins may be constructed using a disulfide exchange reaction or by forming a thioether bond Examples of suitable reagents for this puφose mclude immothiolate and methyl-4-mercaptobutyπmιdate For diagnostic applications, the antibodies of the invention typically will be labeled with a detectable moiety The detectable moiety can be any one which is capable of producing, either directly or indirectly, a detectable signal For example, the detectable moiety may be a radioisotope, such as 3 H, C, P, S, or 12 I, a fluorescent or chemiluminescent compound, such as fluorescein isothiocyanate, rhodamine, or lucifeπn, biotin, radioactive isotopic labels, such as, e g , I, P, C, or H, or an enzyme, such as alkalme phosphatase, beta-galactosidase or horseradish peroxidase Any method known in the art for separately conjugating the antibody to the detectable moiety may be employed, including those methods described by Hunter, et al , Nature 144 945 ( 1962), David, et al , Biochemistry 13 1014 (1974). Pain, et al . I Immunol Meth. 40 219 (1981 ). and Nygren. J. Histoche and Cvtochem. 30 407 (1982) The antibodies of the present invention may be employed in any known assay method, such as competitive binding assays, direct and indirect sandwich assays, and immunoprecipitation assays Zola, Monoclonal Antibodies A Manual of Techniques, pp 147-158 (CRC Press, lnc , 1987) Competitive binding assays rely on the ability of a labeled standard (which may be a PTP HSC polypeptide or an immunologically reactive portion thereof) to compete with the test sample analyte (PTP HSC) for binding with a limited amount of antibody The amount of PTP HSC in the test sample is mversel} proportional to the amount of standard that becomes bound to the antibodies To facilitate determining the amount of standard that becomes bound, the antibodies generally are msolubilized before or after the competition, so that the standard and analyte that are bound to the antibodies may conveniently be separated from the standard and analyte which remain unbound Sandwich assays involve the use of two antibodies, each capable of binding to a different immunogenic portion, or epitope, ofthe prote to be detected In a sandwich assay, the test sample analyte is bound by a first antibody which is immobilized on a solid support, and thereafter a second antibody binds to the analyte thus forming an insoluble three part complex David & Greene, U S Pat No 4,376, 1 10 The second antibody ma> itself be labeled with a detectable moiety (direct sandwich assays) or may be measured using an anti- immunoglobultn antibody that is labeled with a detectable moiety (indirect sandwich assay) For example one type of sandwich assay is an ELISA assay, in which case the detectable moiety is an enzyme (in) Humanized antibodies Methods for humanizing non-human antibodies are well known in the art Generally, a humanized antibody has one or more amino acid residues mtroduced into it from a source which is non-human These non- human ammo acid residues are often referred to as "import" residues, which are typically taken from an "import" variable domain Humanization can be essentially performed following the method of Winter and co-workers [Jones et al , Nature 321. 522-525 (1986), Riechmann et al , Nature 332, 323-327 (1988), Verhoeyen et al , Science 239. 1534-1536 (1988)], by substituting rodent CDRs or CDR sequences for the corresponding sequences of a human antibody Accordingly, such "humanized" antibodies are chimeric antibodies (Cabilly, supra), wherem substantially less than an intact human variable domain has been substituted by the corresponding sequence from a non-human species In practice, humanized antibodies are typically human antibodies in which some CDR residues and possibly some FR residues are substituted by residues from analogous sites in rodent antibodies It is important that antibodies be humanized with retention of high affinity for the antigen and other favorable biological properties To achieve this goal, according to a preferred method, humanized antibodies are prepared by a process of analysis ofthe parental sequences and various conceptual humanized products using three dimensional models ofthe parental and humanized sequences Three dimensional immunoglobulin models are commonly available and are familiar to those skilled in the art Computer programs are available which illustrate and display probable three-dimensional conformational structures of selected candidate immunoglobulin sequences Inspection of these displays permits analysis ofthe likely role ofthe residues in the functioning of the candidate immunoglobulin sequence, l e the analysis of residues that influence the ability ofthe candidate immunoglobulin to bmd its antigen In this way, FR residues can be selected and combined from the consensus and import sequence so that the desired antibody characteristic, such as increased affinity for the target antιgen(s), is achieved ln general, the CDR residues are directly and most substantially involved in influencing antigen bmdmg For further details see U S application Serial No 07/934,373 filed 21 August 1992, which is a continuation-m-part of application Serial No 07/715,272 filed 14 June 1991 Alternatively, it is now possible to produce transgenic animals (e g mice) that are capable, upon immunization, of producmg a full repertoire of human antibodies m the absence of endogenous immunoglobulin production For example, it has been descπbed that the homozygous deletion ofthe antibody heavy chain joining region (J^) gene in chimeric and germ-line mutant mice results in complete inhibition of endogenous antibody production Transfer ofthe human germ-lme immunoglobulin gene array in such germ-line mutant mice will result in the production of human antibodies upon antigen challenge See, e g Jakobovits et al , Proc Natl Acad. Sci. USA 90. 2551-255 (1993), Jakobovits et al . Nature 362. 255-258 (1993) (iv) Bispecific antibodies Bispecific antibodies are monoclonal, preferably human or humanized, antibodies that have binding specificities for at least two different antigens In the present case, one of the binding specificities is for a PTP HSC, the other one is for any other antigen, for example an antigen expressed on the surface of a leukemia cell if the antibody is an antagonist of a native PTP HSC and is used to induce differentiation of undifferentiated lekemia cells If an agonist antibody specifically binding to a native PTP HSC is used to expand stem cells with growth factors, as hereinafter described, the second specificity could be provided by a stem cell growth factor Such constructs can also be referred to as bispecific immunoadhesins Methods for making bispecific antibodies (and bispecific immunoadhesins) are known in the art Traditionally, the recombmant production of bispecific antibodies is based on the coexpression of two immunoglobulin heavy chain-light chain pairs, where the two heavy chams have different specificities (Millstein and Cuello, Nature 305, 537-539 (1983)) Because ofthe random assortment of immunoglobulin heavy and light chams, ese hybridomas (quadromas) produce a potential mixture of 10 different antibody molecules of which only one has the correct bispecific structure The purification ofthe correct molecule, which is usually done by affinity chromatography steps, is rather cumbersome, and the product yields are low Similar procedures are disclosed in PCT application publication No WO 93/08829 (published 13 May 1993), and in Traunecker et al EMBO 10. 3655-3659 (1991) According to a different and more preferred approach, antibody variable domains with the desired bindmg specificities (antibody-antigen combining sites) are fused to immunoglobulin constant domain sequences The fusion preferably is with an immunoglobulin heavy chain constant domain, comprising at least part of the hinge, and second and third constant regions of an immunoglobulin heavy chain (CH2 and CH3) It is preferred to have the first heavy chain constant region (CH 1 ) contammg the site necessary for light chain binding, present in at least one of the fusions DNAs encoding the immunoglobulin heavy chain fusions and, if desired, the immunoglobulin light cham, are inserted into separate expression vectors, and are cotransfected into a suitable host organism This provides for great flexibility in adjusting the mutual proportions ofthe three polypeptide fragments in embodiments when unequal ratios ofthe three polypeptide chains used in the construction provide the optimum yields It is, however, possible to insert the codmg sequences for two or al! three polypeptide chains in one expression vector when the expression of at least two polypeptide chains in equal ratios results in high yields or when the ratios are of no particular significance In a preferred embodiment of this approach, the bispecific antibodies are composed of a hybrid immunoglobulin heavy chain with a first binding specificity in one arm, and a hybrid immunoglobulin heavy chain-light chain pair (providing a second binding specificity) in the other arm It was found that this asymmetric structure facilitates the separation of the desired bispecific compound from unwanted immunoglobulin chain combinations, as the presence of an immunoglobulin light chain in only one half of the bispecific molecule provides for a facile way of separation This approach is disclosed in copending application Serial No 07/931 ,81 1 filed 17 August 1992 For further details of generating bispecific antibodies see, for example, Suresh et al , Methods in Enzvmologv 121. 210 (1986) (v) Heteroconjugate antibodies Heteroconjugate antibodies are also within the scope of the present invention Heteroconjugate antibodies are composed of two covalently jomed antibodies Such antibodies have, for example, been proposed to target immune system cells to unwanted cells (U S Patent No 4,676,980), and for treatment of HIV infection (PCT application publication Nos WO 91/00360 and WO 92/200373, EP 03089) Heteroconjugate antibodies may be made using any convenient cross-linking methods Suitable cross-linking agents are well known in the art, and are disclosed m U S Patent No 4,676,980, along with a number of cross-linking techniques H. Peptide and non-peptide analogs of polypeptide PTP HSCs Peptide analogs ofthe PTP HSC polypeptides of the present invention are modelled based upon the three-dimensional structure ofthe native polypeptides. Peptides may be synthesized by well known techniques such as the solid-phase synthetic techniques initially described in Merrifield, J. Am. Chem. Soc. J_5. 2149-2154 ( 1963). Other peptide synthesis techniques are, for examples, described in Bodanszky et ai , Peptide Synthesis, John Wiley & Sons, 2nd Ed., 1976. as well as in other reference books readily available for those skilled in the art. A summary of peptide synthesis techniques may be found in Stuart and Young, Solid Phase Peptide Synthelia, Pierce Chemical Company, Rockford, IL ( 1984). Peptides may also be prepared by recombinant DNA technology, using a DNA sequence encoding the desired peptide. In addition to peptide analogs, the present invention also contemplates non-peptide (e.g. organic) compounds which display substantially the same surface as the peptide analogs ofthe present invention, and therefore interact with other molecules in a similar fashion. I. Use of the PTP HSCs The PTP HSCs ofthe present invention are useful for a variety of puφoses. For example, native PTP HSCs are useful for the identification and isolation of a PTP HSC analog in another mammalian species. Native PTP HSCs and their functional equivalents are also useful in screening assays designed to identify agonist of antagonist of native PTP HSCs. Such assays may take the form of any conventional cell-type or biochemical binding assay, and can be performed in a variety of assay formats well known for those skilled in the art. As example is the so called "two-hybrid" assay format using the Matchmaker Two-Hybrid System (Clontech) according to the manufacturer's instructions. The PTP HSCs of the present invention as well as their agonists can additionally be used for the maintenance of stem/progenitor cells in cell culture. Agonists which inhibit differentiation but allow for hematopoietic stem cell growth are particularly useful for this puφose, since their use results in an amplification ofthe stem cells without differentiation (self-renewal). This process might be useful, as an example, for the expansion of hematopoietic stem cells prior to autologous or heterologous bone marrow transplantation. The same approach can be used in vivo for the expansion of stem cells with growth factors, in the absence of diferentiation. It is believed mat the native PTP HSCs of the present invention may be expressed in leukemic cells. Accordingly, antagonist of the PTP HSCs of the present invention may be used for the induction of differentiation of undifferentiated leukemia cells. This might allow for aggressive undifferentiated leukemia cells to become differentiated, which, in turn, facilitates their treatment. PTP HSC antagonists may also be used to induce differentiation of hematopoietic stem cells. As inhibition ofthe native PTP HSC enzyme might induce progenitor cells to differentiate, an antagonist of PTP HSC might act as a pan-inducer of myeloid, erythroid and lymphoid production. This use of PTP HSC antagonists may obviate or decrease the need for the use of stem cell growth factors. Further details ofthe invention are illsutrated in the following non-limiting examples. Example 1 Identification and cloning of murine PTP HSC A. Materials and Methods Isolation of embryonic lin CD34 nι Sca hematopoietic stem cells. Yolk sacs or embryos were dissected from timed pregnant females at day 10.5. Fetal livers were isolated from day 13.5-14 embryos. Yolk sac and embryonic tissues were dissociated with 1 % collagenase in RPMI medium at 37 C for 15 minutes. Cells were further dissociated by two passages through a 16 gauge needle. Fetal liver was only dissociated by passage through a 16 guage needle. Adherent cells were attached to plastic by overnight incubation, after which the non adherent hematopoietic cells were incubated with a lineage cocktail of antibodies ( 1 μg each of TER 1 19, Gr- 1 , Ly-1 , transferrin receptor and B220) for 1 hr on ice. Cells were washed, and the lineage positive cells were depleted using magnetic beads and a Miltenyi column. Lineage negative cells were pelleted, resuspended in 2% FCS, PBS and incubated with rabbit anti-murine CD34 antibody (Baumhueter et ai, Science 262. 436-38 [1993]) on ice for 1 hr. Cells were washed three times in 2% FCS, PBS, resuspended in the same buffer and incubated with donkey, anti-rabbit FITC conjugated antibody and, in some cases, PE conjugated anti Sea antibody for 1 hr on ice. The cells were washed five times with 2% FCS, PBS. and than isolated by cell sorting on an ELITE cell sorter. PCR analysis of mRNA isolated from lin'°CD34 n, Sca hematopoietic stem cells. Messenger RNA was isolated from the Lin CD34 Sea fraction of fetal yolk-sac hematopoietic cells (Micro-FastTrack. InVitrogene). Poly A+ RNA was reverse transcribed with random hexamers (Promega) and Moloney murine Leukemia virus revere transcriptase (Superscript II, GIBCO BRL). 1/4 of this cDNA was amplified by PCR using degenerate mixed oligonucleotides primers. Sense and antisense primers corresponding to the concensus PTP amino acid sequences H/pFWRJVl yW (5'-A C / τ TT C / τ TGG A / c GIATG A / G TITGG-3') (SEQ. ID. NO: 14, where the degenerate positions are designated by "N") and WPDVι_,GVP (5'- GGIAC G / A T / A G / A G / A TCIGGCCA-3') (SEQ. ID. NO: 15, wherein the degenerate positions are designated by "N") respectively were used. PCR were carry out in 1 X Taq DNA polymerase buffer (GIBCO BRL) plus 0.2 M of each dNTP, 10% DMSO and 5 units Taq polymerase (GIBCO BRL) for 25 cycles of 94° C for 1 minute, 55 C for 1 min and 72 C for 1 minute. The PCR products were treated with Klenow enzyme (New England Biolabs) at 30° C for 30 minutes, cloned into Smal site of pRK-5 (EP 307,247, published March 15, 1989) plasmid, and subsequently sequenced (Sequenase, USB). cDNA and genomic cloning. Adapter-linked double strain cDNA was prepared from A+ RNA of day- 10 murine embryos (Marathon-ready cDNA synthesize kit, Clontech) using either random hexamer or oligo dT primer. Full-length cDNA was isolated by 5' or 3' rapid amplification of cDNA ends (RACE) of the marathon- ready cDNAs. Genomic clones encoding the PTP HSC gene were isolated using standard techniques. The plaque purified lambda phage DNA was digested with Not 1 , and the insert fragment was directly cloned without purification into Not 1 digested Bluescript. Exons were mapped using a combination of restriction digestion and southern blotting as well as DNA sequencing using custom primers. Bacterial expression of the PTP. cDNA sequences encode amino acid 8 to 323 containing the phosphatase domain were obtained by PCR using sense oligomer 5 - CACGGTCGACGGTGAGGAGCTTCTTTGAGCAGCTGGAGG-3' (SEQ. ID. NO: 3), and antisense oligomer 5'-GTTGCGGCCGCGATTGGAGCGCAGTTCTCCTTGAGGTTCTGG-3' (SEQ ID NO 4) The PCR fragment was treated with Sail and NotI restriction enzyme and cloned mto Sail and NotI digested pGEX-4T-l plasmid (Pharmacia) Fusion protein was affinity purified using a glutathione sepharose column (Pharmacia) Tyrosine phosphatase assays on the GST-fusion protein were carried out following the manufacture's procedure using two different tyrosine phosphorylated peptides from a tyrosine phosphatase assay kit (Boehπnger Mannheim) Quantitative PCR analysis of RNA isolated from hematopoietic cells. cDNA was made from + RNA by reverse transcription (RT) with random hexamer PCR was then used to amplified quantitatively PTP HSC cDNA and, as an internal standard, triosephosphate isomerase (TPI) cDNA For each PCR, 6 ul ofthe 20 ul RT reaction was brought to 50 ul so as to contain 0 3 mM of dNTPs, 4μCι of 32 P dATP (3,000Cι/mmol, Amersham), 100 pmol of each of the four primers, and 5 units of Taq DNA polymerase (GIBCO BRL) Seventeen PCR cycles of 94 C for 50 seconds, 55° C for 50 seconds, and 70° C for 70 seconds One-tenth of each PCR samples was electrophoresed a 6% polyacrylamide gel, and the PCR products were quantitate by phosphoπmaging (Fuji) Conditions for accurate quantitation of either PTP HSC or TPI were assessed in experiments that used serial dilutions of a standard preparation of A + RNA from 32D cells to determine for each primer pair the times of primer annealing and primer extension and the cycles that provided for a linear correlation between the amount of template RNA and the PCR product Under the PCR conditions ultimately chosen, certain amount of sample RNA was analyzed simultaneously with serial dilutions ofthe standard RNA and a reverse transcriptase minus control Northern blot analysis of tissues and cell lines. A Sall-NotI 1 3 kb PTP HSC cDNA fragment was used to probe murine multi-tissue northern blot (Clontech) The same northern blot was used with various other probes, all of which demonstrated detectable undegraded transcripts PCR primer pairs 5' RACE primers antisense primer 5'-CCTGGAGGGTCCTGAGAGTGATGTCTGCATTCAGTG-3' (SEQ ID NO 5), 5'-CCTCTTGGAGCAGGGAAAGGATGACTCTTGTCTC-3' (SEQ ID NO 6), 5'- CAGCTGCTCCAAGAAGCTCCTCACCAAGTC-3' (SEQ ID NO 7) Sense primer API and AP2 (Clontech) 3'RACE primers sense primer 5'-GGTAGAGGTGGGCAGGGTGAAGTGTTCTCGC-3' (SEQ ID NO 8), 5'- CACTGAATGCAGACATCACTCTCAGGACCCTCCAGG-3' (SEQ ID NO 9), 5'- GAGACAAGAGTCATCCTTTCCCTGCTCCAAGAGG-3' (SEQ ID NO 10) Antisense primer API and AP2 (Clontech) Quantitative RT-PCR primers PTP HSC sense primer 5 - CACTGAATGCAGACATCACTCTCAGGACCCTCCAGG-3 * (SEQ ID NO 9), antisense primer 5 - GAATGGTAACCTGGAGGGTCCTGAG-3' (SEQ ID NO 1 1 ) TPI sense primer 5'- GAGAAGGTCGTGTTCGAG (SEQ ID NO 12), antisense primer 5'-GTGTACTTCCTGTGCCTG-3' (SEQ ID NO 13) B. cDN A cloning of PTPs from Hematopoietic Stem Cells In order to analyze PTPs potentially involved with the maintenance ofthe hematopoietic stem cell, we isolated a highly purified population of these cells from either the muπnelO 5 day yolk sac or embryo Previously, we showed that both progenitor activity as well as stromal cell repopulating activity were found in the CD34 m fraction of these embryonic cells [3] (C Fennie and L Lasky-unpub shed observations) In addition others have shown that the murine CD34 nι population isolated from bone marrow (Krause et al , Blood 84(3), 691 -701 [ 1994]), or fetal liver (Ziegler et al , Blood 84, 2422-2450 [1994]) contains stem cells capable of reconstituting lethally irradiated animals In order to isolate a more highly purified fraction of these progenitor cells, we included a lineage depletion step as well as a positive selection step with the Sea antibody (Uchida et al , Blood 8_3(12), 3758-3779 [ 1994]), m addition to the CD34 antibody These moφhologically primitive hematopoietic cells show a higher degree of stromal cell repopulating ability as well as cobblestone formation as compared to the previously described CD34 progenitor cells, and we are currently investigating their in vivo repopulating activity (C Fennie and L Lasky-unpubhshed observations) Previous investigators have shown that the lm Sea fraction of bone marrow hematopoietic cells has a high level of repopulating activity (Sprangrude et al , Science 241. 58-62 [1988]) Thus, it is likely that the lιn lo CD34 Sca hl cells isolated from the early embryo contam self renewing hematopoietic stem cells (Uchida et al , supra, Krause et al supra, Ziegler et al supra Consensus PCR using primers derived from two highly conserved regions of the PTP phosphatase domain resulted in the clonmg and sequencing of- 70 PCR fragments As shown in Table 1 , a diversity of known receptor and non-receptor PTPs were detected in this fraction of these progenitor cells, and many of these PTPs have not previously been described in the hematopoietic stem cell compartment Two novel PTPs (referred to in the table as PTP 38 and PTP 49) were also isolated One is a receptor PTP which is related to the homotypically interacting μ, K and LAR family and is the subject of a patent application filed concurrently herewith The second PTP was found to be most homologous to two previously described non-receptor PTPs murine PTP PEP (Matthews et al , Mol Cell Biol 12(5), 2396-2405 [1992]) and muπne/human PTP PEST (Takekawa et al , Biochem Biophvs Res Commun 189(2). 1223-1230 [ 1992], Yang et al , J Biol Chem 268(23) 17650 [1993], and Charest et al . Biochem J. 308(2).425-432 [1995]), both of which contain a region that is very high in proline, glutamate, serine and threonine (the "PEST' domain) One of these PTPs, PEP, has been demonstrated to be localized to the nucleus (Flores et al , supra) (see below), so it appeared that the novel PTP fragment may have been a new member of this potentially nuclear-localized PTP family Initial PCR and northern analyses with the PTP fragment revealed that the transcript encoding this enzyme is extremely rare m embryonic and adult tissues Thus, the full Iength cDNA was cloned using the RACE procedure and RNA isolated from day 10 embryos Because the RACE cloning of the 5 prime region was particularly difficult, the final 5 prime sequence was confirmed using the genomic clone encoding this PTP As can be seen in figure 1, this transcript encodes an open reading frame of 453 ammo acids specifying a protein of molecular weight 50,253 daltons Homology searches revealed that the region encoding amino acids 25-290 were highly homologous to a variety of PTPs, with the highest degree of homology with murine PTP PEP (Matthews et al supra) and muπne/human PTP PEST (Takekawa et al supra Yang et al supra, and Charest et al supra) (figure 2) Interestingly, PTP PEP has also been found to be expressed in mature hematopoietic cells (Matthews et al supra, Flores et al , supra) although human and murine PTP PEST appear to have a more generalized expression pattern (Yang et al , supra, Charest et al supra) As has been shown in these two previously descπbed PTPs, the novel PTP reported here contains a region 3 prime of the PTP domain which is very rich in proline, serine, and threonine (-29%) (boxed residues in figure 1). This region lacks other significant homology with PTPs PEP and PEST, and it is also much shorter in the novel PTP described here. Finally, a short region of 20 amino acids at the very carboxy terminus of the protein is highly homologous to similar carboxy-terminal regions in PTPs PEP and PEST (figure 2). This region is rich in basic residues and the homologous area in PTP PEP has been shown to be involved with the localization of this enzyme to the nucleus (Flores et ai, supra). However, this region also contains two negatively charged residues (arrowheads in figure 2), so it is likely that this novel PTP is a cytopiasmically localized enzyme, as has been demonstrated for PTP PEST (Charest et ai, supra). Finally, the novel PTP described here contains a serine residue at position 37 (shown starred in figure 2) which is conserved in all three members of this family and which has been shown to be phosphorylated in PTP PEST by protein kinases C and A (Garton and Tonks, EMBO J. J_3_( 16), 3763-7 ! [1994]). Interestingly, increased phosphorylation at this site is inhibitory to the PTPase activity of this PTP (Banville et ai . Genomics 27( 1 ). 165-173 [1995]). In summary, the novel PTP described here appears to be a new member of a family of non-receptor PTPs which contain P, S and T rich regions (figure 3). In addition, all three of these PTPs contain a homologous carboxy-terminal region which has been shown to function as a nuclear localization signal for one ofthe family members (PTP PEP), although the murine PEST enzyme has been found to localize to the cytoplasm. Previous analyses of the genomic structures of other PTPs suggested that these enzymes were constructed from genes containing a large number of introns. This appears to be the case for the novel PTP described here as well. As can be seen from figure 4, the hematopoietic progenitor cell PTP gene is subdivided by 14 introns. Analysis ofthe intronic structure of this novel PTP as compared with that found for other PTPs suggests that the novel progenitor cell enzyme is divided into a comparable number of coding exons (for example, Banville et ai, supra). In addition, as described below, there appears to be at least one other smaller transcript, as well as a heterogeneous collection of large transcripts, suggesting that altemate splicing may occur in this gene. Finally, chromosomal localization studies have demonstrated that the gene encoding the human form of this PTP is found on chromosome 14 (D. Dowbenko and L. Lasky, unpublished data). While the sequence ofthe N-terminal PTP domain contained many ofthe conserved amino acids found to be critical for substrate recognition and tyrosine dephosphorylation (Jia et ai, supra), it was important to demonstrate that this sequence indeed encoded an active PTP domain . To this end we produced a construct using the glutathione-S-transferase (GST) fusion system which contained the entire PTP-homologous region derived from the novel cDNA clone. The protein was isolated from induced cultures of bacteria, and it was tested for the dephosphorylation of tyrosine using two different phosphorylated peptides (see materials and methods). As can be seen from figure 5, the isolated GST-PTP domain fusion protein had a very high level of PTP activity, with significant dephosphorylation at only 20 picograms of enzyme per reaction, which was partially sensitive to inhibition by orthovanadate. The only partial inhibition of enzyme activity by orthovanadate was likely due to the high level of activity as well as insufficient levels of the inhibitor. These data indicate that this hematopoietic progenitor cell PTP is an active tyrosine phosphatase. C. Expression of the progenitor cell PTP transcript The isolation of the novel PTP from the lin CD34 nι sca population of hematopoietic stem cells suggested that this PTP might be specific for very early progenitor cells. As figure 6A illustrates, quantitative PCR comparing the levels ofthe transcript encoding this PTP in the lin lo CD34 hl sca nι , a largely undifferentiated population containing hematopoietic stem cells (Spangrude et al , supra, Krause et al , supra. Zeigler et al . Blood 84(8), 2422-2430 [1994]), versus the hn lo CD34 nι sca l0 population, a more differentiated cell population (Spangrude et al , supra), containing committed progenitors, demonstrated that there was an approximately 10 fold lower level of the transcript in the more differentiated sca'° cells In order to examine if this downregulation continued as differentiation progressed, quantitative PCR was performed using RNA isolated from suspension cultures of lin lo CD34 ni sca nι cells that were exposed to IL-1 , 1L-3, EPO and GM-CSF for various periods of time in the absence of stromal cells. Analysis of cell numbers, together with Wπght-Giemsa staining of the cultures, revealed that the undifferentiated lm CD34 sea cell population dramatically expanded in the presence of these growth and differentiation factors and also metamoφhosed along the myeloid pathway to ultimately give rise to cultures that contained predominately macrophages after 14 days (data not shown) As figure 6B illustrates, the transcript encoding the novel PTP disappears as the cells replicate and develop, and it is completely absent after approximately 7 days m culture These data are consistent with a role for this PTP in early stem or progenitor cells, but not in the mature, committed cell populations The potential importance of this PTP specifically to the hematopoietic system is illustrated in figure 7A where northern blot analyses of various tissues and cell lines are shown As can be seen from this figure, the transcript appears to be undetectable in the embryonic samples, and it is expressed at exceedingly low levels in adult lung and kidney. Thus, while there are clearly hematopoietic stem cells m the embryo, they must be so rare as to not allow for the direct detection of the transcript encoding the novel PTP. Particularly interesting is the lack of a signal in the RNA isolated from the adult spleen, a hematopoietic compartment that contains predominately mature, differentiated hematopoietic cells and which was previously shown to express PTP PEP (Matthews et al , supra). The very faint transcπpts detected in the lung have been confirmed by non-quantitative PCR analysis (J. Cheng and L. Lasky-unpubhshed data). However, the transcripts in the lung are very rare and may be aberrant, since screening of an adult lung library (1x10 clones) resulted in only two positive isolates, both of which contained introns (J. Cheng and L. Lasky-unpublished observations) The lack of detectable signal in most tissues ofthe adult and embryo, coupled with the identification of the transcript in the highly purified stem cell population, but not m the differentiated hematopoietic cells, suggested that this PTP might be expressed in hematopoietic progenitor cell lines. As figure 7B illustrates, the transcripts encoding this novel PTP are easily detectable in the three different murine hematopoietic progenitor cell lines tested by both northern and PCR analyses. In all three cases, these lines represent relatively undifferentiated precursors of mature hematopoietic cells, although they are certainly not self-renewing stem cells. The cells appear to encode two major transcripts, in addition to a diversity of minor transcripts One major transcript is an -1.8 kB RNA that corresponds to the cDNA clone described above, while the other encodes a -0.7 kB RNA that remains to be characterized. However, it is likely that this smaller transcript is due to alternative splicing, since, as described above, the gene encoding this PTP is divided into a large number of exons (Figure 4). Figure 7C illustrates that the PTP HSC transcript is undetectable by PCR in a differentiated T cell clone, a result which is again consistent with the downregulation of this PTP m differentiated cells Finally, PCR analysis of various human cell lines using the murine primer pair revealed expression of a similarly sized fragment in human CMK progenitor cells, and the sequence of this PCR fragment revealed that the human homologue is highly conserved with the murine PTP (J Cheng, Kai Wu and L Lasky-unpubhshed results) In summary, the novel PTP described here appears to be expressed predominately in very early hematopoietic progenitor cells, consistent with a potential role in the regulation ofthe differentiation state of these cells D. Discussion The ability ofthe hematopoietic stem cell to self renew the absence of differentiation is an important factor which allows for this cell to provide a large number of progeny throughout the lifetime ofthe organism The ma tenance of the undifferentiated state must occur at the same time as the stem cell replicates, since this cell type must be continually replenished Thus, there must be specific mechanisms that decrease some aspects of cellular activation, such as differentiation, while not affecting others, such as division Because tyrosine phosphorylation is a critical aspect of cellular activation, based upon the results disclosed herein, it is likely that distinctive mechanisms which regulate tyrosine phosphorylation are involved with the maintenance of the self renewmg stem cell Such specificity can be accomplished in part by the expression of the appropriate growth factors by the hematopoietic cell stroma However, another means by which such regulation can occur is by the dephosphorylation of a subset of tyrosine phosphorylated proteins One mechanism that would allow for specific dephosphorylation is via PTPs which recognize only a fraction ofthe tyrosine phosphorylated proteins in the cell Thus, the analysis of PTPs expressed by hematopoietic stem cells might further our understanding of the mechanisms by which stem cell self renewal is attained The non-receptor PTP described in the present application has some of the features that might be expected for a regulator of stem cell differentiation Several aspects of this novel PTP which is referred to throughout the specification and claims as the PTP of hematopoietic stem cells or PTP HSC, are consistent with a role in the regulation of aspects of early hematopoietic progenitor cell biology First, the specific expression ofthe transcript in very early hematopoietic progenitor cells, together with the down-regulation ofthe message as the cells differentiate, is compatible with a role for this enzyme in physiological aspects of the less differentiated stem cell While little is understood regarding the regulation of genes in very early hematopoietic progenitor cells, the apparently unique expression of this gene predominately in these comparatively undifferentiated cells suggests that novel mechanisms of transcriptional regulation might be utilized the control of this locus (Orkin, Curr Opin Cell Biol 7(6), 870- 877 [ 1995]) ln addition, the predominate lack of expression of this PTP in most adult tissues, with the exception of extremely low levels in the lung and the kidney, is also consistent with a role for this enzyme specifically within the hematopoietic progenitor cell compartment This is in stark contrast to the expression of PTP PEP, which is found m the lymphoid compartment (Takekawa et al , supra), and PTP PEST, which is apparently ubiquitously expressed in a number of cell lines and tissues (Yang et al supra) Second, the PTP domain can be thought of as a moderator of cell activation by virtue of its ability to dephosphorylate tyrosine residues Tyrosine phosphorylation can either up- or down-regulate the activities of various proteins (Fantl et al supra), so that the PTP HSC might activate or inhibit a specific subset of tyrosine phosphorylated proteins In a cell that requires a down-regulation of differentiation, this type of specific modulation would allow for the control of the phosphotyrosine levels of protems activated by various growth factors produced by the hematopoietic stroma Together, these data are compatible with a function for this enzyme in the modulation of development ofthe stem cell that is induced by the various growth factors produced by the hematopoietic microenvironment The hypothesis that PTPs such as PTP HSC are involved with the maintenance of an undifferentiated state in the hematopoietic stem cell suggests possibilities regarding the substrates recognized by this type of PTP Several of the substrates for the PTPs have been previously characterized For example the alpha PTP a receptor PTP, has been found to regulate the levels of src tyrosine phosphorylation which results in differentiation of neuronal progenitor cells Lar, as well as CD45, are apparently involved with the regulation of the tyrosine phosphorylation levels of the insulin receptor (Kulas et al , J Biol Chem 271(2). 748-754 (1996), Kulas et al . J Biol Chem 271(2). 755-760 [1996]) From the standpoint of hematopoiesis, the SH 2 domam contammg PTP IC phosphatase has been shown to be critically involved with the regulation of mveloid development in the motheaten mouse as well as with the activation state of the EPO receptor (Schulz et al supra, McCulloch (Klingmuller et al , supra) Finally, another SH2-contaιnmg PTP, PTP 1 D has been found to positively regulate the activity ofthe prolactin receptor (Ah et al EMBO J 15( 1). 135-142 [1996]) These examples, among others, are consistent with a role for cytoplasmically-locahzed PTP domains in the regulation of a variety of cellular processes However, the nature of the substrates recognized by the rarer nuclear PI P family is unknown The dual specificity (i e tyrosine and seπne/threonine dephosphorylation) phosphatase encoded by the cdc25 locus is a nuclear enzyme that is critical for the regulation of mitosis (Gautier et al Cell £2(1), 197-21 1 [ 1991]) In addition, PAC-1, another nuclear localized PTP, appears to be involved with the regulation ofthe mitogen activated protein kinases A recently described dual specificity phosphatase, TYP 1 related to the vaccmia virus VH 1 phosphatase, appears to be involved with the regulation of both the ERK and JNK family of mitogen activated protein kinases (King et al , Oncogene JJ . , 2553-2563 [ 1995]) These data suggest that several currently described phosphatases appear to play roles in the regulation of tyrosine phosphorylated nuclear proteins Another possible substrate for both the nuclear and cytoplasmic PTP enzymes are the STAT proteins These transcriptional activators encompass a family of at least 6 different members, all of which are activated by the JAK tyrosine kinases (Darnell et al . Science 264(5164). 141501421 [1994], Ihle et al Annu Rev Immunol Ll, 369-398 [1995]) JAK phosphorylation is stimulated by the formation of receptor complexes that are stimulated by the binding of various hematopoietic and other growth factor-like molecules (Darnell et al supra) The phosphorylated STAT proteins than dimerize, migrate to the nucleus and bmd specifically to various DNA elements that regulate the transcription of growth and differentiation genes (Shuai et al Science 261(5129) 1744-1746 [1993], Heim et al , Science 2≤7(5202), 1347-49 [1995]) Thus, because these transcription factors are linked with the activation of hematopoietic differentiation factors, they provide appealing targets for negative regulation in hematopoietic stem cells The absolute requirement for tyrosine phosphorylation of these transcriptional activators thus suggests that the novel PTP reported here could regulate STAT activation via dephosphorylation of tyrosine residues In this manner, the upregulation of genes specific to the differentiated state could be inhibited by the dephosphorylation of one or more activated STAT molecules This hypothesis is especially appealing in the case ofthe hematopoietic stem cells In this case, the activation ofthe STAT protems by the bindmg of various hematopoietic growth and differentiation factors, a state which would mduce terminal differentiation, could be downregulated by a stem cell specific PTP such as PTP HSC If this hypothesis is correct, the manner by which specific STAT dephosphorylation occurs must be investigated However, it is possible that the proline, serine, threonine rich domam of PTP HSC might function to bind to only a subset of STATs Finally, recent data have shown that PTP PEST can associate with the p52 snc and p66 snc SH2- containing adaptoφroteins m a prote kmase C dependent fashion (Habib et al , J Biol Chem 269(41 ), 25243- 25246 [1994]) This association was through an interaction between the N-terminal region of SHC and the carboxy-terminal P,S,T rich region of the PTP PEST The fact that this association was enhanced by protein k ase C suggested that serine or threonine phosphorylation might be involved, and a serine in the P,S,T rich region of PTP PEST is known to be phosphorylated by protein kinase C (Garton and Tonka supra) Interestingly, carbachol, an activator of G protem coupled signaling, was also able to stimulate this association, suggesting that PTP PEST may be involved with the cross talk between G coupled and tyrosine kmase pathways Because of the similarity of PTP HSC to PTP PEST, we suggest that the novel hematopoietic cell PTP of the present mvention may also mteract with SHC, and we are currently examining this possibility using the yeast two hybrid system In summary, the data disclosed in this example suggest that hematopoietic stem/progenitor cells specifically express a PTP which appears to be downregulated as the cells differentiate The PTP seems to be predominately specific to hematopoietic progenitor cells, suggesting an important role in the development of this cell compartment However, while these data are potentially important, a number of studies remain to be accomplished Thus, the possibility that the STATs are substrates for this enzyme, the possible interaction of the enzyme with SHC, the constitutive expression ofthe enzyme in transfected cells and in transgenic animals, and the effects of null mutations at this locus in vivo may provide for further insights into the mechanisms by which stem cell self renewal is regulated Example 2 Cloning of a human PTP HSC Two oligonucleotides (sense 5ΑCTTGGTGAGGAGCTTCTTGGAGCAGCTGGAGG3' (SEQ ID NO 20), and antisense- 5'GGAATGTAACCTGGAGGGTCCTGA3' (SEQ ID NO 21)) were used as PCR primers with reverse transcribed RNA isolated from human CMK hematopoietic progenitor cells The conditions for PCR were identical to those described in Example 1 for the isolation ofthe PCR fragment encoding murine PTP HSC The PCR fragment was subcloned into pBS (Bluescript) plasmid, and the DNA sequence was determined as described for the murine sequence in Example 1 The partial nucleotide sequence and deduced amino acid sequence ofthe human PTP HSC are shown in Figure 8 Example 3 Expression of the murine and human PTP HSC The native murine PTP HSC polypeptides are expressed in mammalian cells using standard techniques Briefly, a DNA fragment encoding the entire PTP HSC is ligated into an expression vector (e g PRK5) The expression vector is then transfected into mammalian cells (e g embryonic kidney 292 cells), and the protein expression is determined usmg a monoclonal or polyclonal antibody directed against the native PTP HSC to be expressed All documents cited throughout this application as well as the documents cited therein are hereb expressly incoφorated by reference Table 1 PTPs expressed in lin CD34 nι hematopoietic progenitor cells Name (GenBank) Frequency (%) Type MMPRTYPHA -27 receptor, single catalytic domain MUSC57B16A - 17 cytoplasmic, band 4 1 homology MUSHCPA - 14 cytoplasmic SH2 domains, hematopoietic cells MMPTPNU3 - 1 1 receptor MMMPTPPES -4 cytoplasmic, pst DOMAIN MUSCPTP -4 cytoplasmic MUSPTPA -4 receptor, kappa, homophihc interacting MMTPBLR -3 receptor, epithelial cells, membrane binding RNU28356 ~3 cytoplasmic RATOSTP - 1 receptor, FN1II domains MUSPTPRL 10 ~ 1 cytoplasmic, band 4 1 homology M60103 -1 receptor, CD45 PTP-38 (novel) - 1 cytoplasmic, PST family related PTP-49 (novel) - 1 receptor related mu/kappa family SEQUENCE LISTING (1) GENERAL INFORMATION: (1) APPLICANT: Genentech, Inc. (11) TITLE OF INVENTION: Protein Tyrosine Phosphatases (in) NUMBER OF SEQUENCES: 23 (iv) CORRESPONDENCE ADDRESS: (A) ADDRESSEE: Genentech, Inc. (B) STREET: 460 Point San Bruno Blvd (C) CITY: South San Francisco (D) STATE: California (E) COUNTRY: USA (F) ZIP: 94080 (v) COMPUTER READABLE FORM: (A) MEDIUM TYPE: 3.5 inch, 1.44 Mb floppy disk (B) COMPUTER: IBM PC compatible (C) OPERATING SYSTEM: PC-DOS/MS-DOS (D) SOFTWARE: mPatin (Genentech) (vi ) CURRENT APPLICATION DATA: (A) APPLICATION NUMBER: (B) FILING DATE: (C) CLASSIFICATION: (vill) ATTORNEY/AGENT INFORMATION: (A) NAME: Dreger, Ginger R. (B) REGISTRATION NUMBER: 33,055 (C) REFERENCE/DOCKET NUMBER: P1010PCT (ix) TELECOMMUNICATION INFORMATION: (A) TELEPHONE: 415/225-3216 (B) TELEFAX: 415/952-9881 (C) TELEX: 910/371-7168 (2) INFORMATION FOR SEQ ID NO:l: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 1529 base pairs (B) TYPE: Nucleic Ac d (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 1 : CTCAGAGCGG GTCGCAGCAT GAGTCGCCAT ACGGACTTGG TGAGGAGCTT 50 CTTGGAGCAG CTGGAGGCCC GGGACTACCG GGAGGGGGCA ATCTTCGTTC 100 GTGAGTTCAG CGACATTAAG GCCCGCTCAG TGGCCTGGAA GTCTGAAGGT 150 GTGTGTTCCA CTAAAGCCGG CAGTCGGCTT GGGAACACGA ACAAGAACCG 200 CTACAAAGAT GTGGTAGCAT ATGATGAGAC AAGAGTCATC CTTTCCCTGC 250 TCCAAGAGGA GGGACATGGA AATTACATCA ATGCCAACTT CATCCGGGGC 300 ATAGATGGAA GCCAGGCCTA CATTGCGACG CAAGGACCCC TGCCTCACAC 350 ACTGTTGGAC TTCTGGCGCC TGGTTTGGGA GTTTGGGGTC AAGGTAATCC 400 TGATGGCCTG TCAAGAGACA GAAAATGGAC GGAGGAAGTG TGAACGCTAT 450 TGGGCCCGGG AGCAGGAGCC TCTAAAGGCT GGGCCTTTCT GCATCACCCT 500 GACAAAGGAG ACAACACTGA ATGCAGACAT CACTCTCAGG ACCCTCCAGG 550 TTACATTCCA GAAGGAATTC CGCTCTGTGC ACCAACTACA GTATATGTCC 600 TGGCCAGACC ACGGGGTTCC CAGCAGTTCT GATCACATTC TCACCATGGT 650 GGAGGAGGCC CGCTGCCTCC AAGGGCTTGG ACCTGGACCC CTCTGTGTCC 700 ACTGCAGTGC TGGCTGCGGA CGAACAGGTG TCCTGTGCGC TGTTGACTAT 750 GTGAGGCAGT TGCTGCTGAC CCAGACAATC CCTCCCAACT TCAGTCTCTT 800 CCAAGTGGTC CTGGAGATGC GGAAACAGCG GCCTGCAGCA GTGCAGACAG 850 AGGAGCAGTA CAGGTTCCTG TACCACACAG TGGCTCAGCT ATTCTCCCGC 900 ACTCTCCAGG ACACCAGCCC CCAATACCAG AACCTCAAGG AGAACTGCGC 950 TCCAATCTGC AAGGAAGCTT TCTCCCTCAG GACCTCCTCA GCCCTGCCTG 1000 CCACATCCCG GCCACCAGGA GGGGTTCTCA GGAGCATCTC GGTGCCTGCG 1050 CCCCCGACCC TCCCCATGGC TGACACTTAC GCTGTGGTGC AGAAGCGTGG 1100 CGCTTCGGCG GGCACAGGGC CGGGGCCGCG GGCGCCCACC AGCACGGACA 1150 CCCCGATTTA CAGCCAGGTG GCTCCACGTG CCCAGCGACC GGTGGCACAC 1200 ACGGAGGACG CACAGGGGAC AACGGCACTG CGCCGAGTTC CTGCGGACCA 1250 AAACTCTTCC GGGCCTGATG CCTACGAAGA AGTAACAGAT GGAGCACAGA 1300 CTGGAGGGCT AGGCTTCAAC TTGCGCATCG GAAGGCCCAA AGGGCCCCGG 1350 GATCCTCCAG CAGAGTGGAC ACGGGTGTAA CGAGTGCTGT GCCAGTTATA 1400 GCCTGCCACT CGGTGGTGGC TGGACTCCTG GAACCACCAT ACTGCTGTGC 1450 AGTGTGTTAT GTATGAGTGG GACTTGTGGG CCTGATTCAA AATAAAAGTT 1500 TCTCAGGGCG GAAAAAAAAA AAAAAAAAA 1529 (2) INFORMATION FOR SEQ ID NO:2 : (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 453 amino acids (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2: Met Ser Arg His Thr Asp Leu Val Arg Ser Phe Leu Glu Gin Leu 1 5 10 15 Glu Ala Arg Asp Tyr Arg Glu Gly Ala He Phe Val Arg Glu Phe 20 25 30 Ser Asp He Lys Ala Arg Ser Val Ala Trp Lys Ser Glu Gly Val 35 40 45 Cys Ser Thr Lys Ala Gly Ser Arg Leu Gly Asn Thr Asn Lys Asn 50 55 60 Arg Tyr Lys Asp Val Val Ala Tyr Asp Glu Thr Arg Val He Leu 65 70 75 Ser Leu Leu Gin Glu Glu Gly His Gly Asn Tyr He Asn Ala Asn 80 85 90 Phe He Arg Gly He Asp Gly Ser Gin Ala Tyr He Ala Thr Gin 95 100 105 Gly Pro Leu Pro His Thr Leu Leu Asp Phe Trp Arg Leu Val Trp 110 115 120 Glu Phe Gly Val Lys Val He Leu Met Ala Cys Gin Glu Thr Glu 125 130 135 Asn Gly Arg Arg Lys Cys Glu Arg Tyr Trp Ala Arg Glu Gin Glu 140 145 150 Pro Leu Lys Ala Gly Pro Phe Cys He Thr Leu Thr Lys Glu Thr 155 160 165 Thr Leu Asn Ala Asp He Thr Leu Arg Thr Leu Gin Val Thr Phe 170 175 180 Gin Lys Glu Phe Arg Ser Val His Gin Leu Gin Tyr Met Ser Trp 185 190 195 Pro Asp His Gly Val Pro Ser Ser Ser Asp His He Leu Thr Met 200 205 210 Val Glu Glu Ala Arg Cys Leu Gin Gly Leu Gly Pro Gly Pro Leu 215 220 225 Cys Val His Cys Ser Ala Gly Cys Gly Arg Thr Gly Val Leu Cys 230 235 240 Ala Val Asp Tyr Val Arg Gin Leu Leu Leu Thr Gin Thr He Pro 245 250 255 Pro Asn Phe Ser Leu Phe Gin Val Val Leu Glu Met Arg Lys Gin 260 265 270 Arg Pro Ala Ala Val Gin Thr Glu Glu Gin Tyr Arg Phe Leu Tyr 275 280 285 His Thr Val Ala Gin Leu Phe Ser Arg Thr Leu Gin Asp Thr Ser 290 295 " 300 Pro Gin Tyr Gin Asn Leu Lys Glu Asn Cys Ala Pro He Cys Lys 305 310 315 Glu Ala Phe Ser Leu Arg Thr Ser Ser Ala Leu Pro Ala Thr Ser 320 325 330 Arg Pro Pro Gly Gly Val Leu Arg Ser He Ser Val Pro Ala Pro 335 340 345 Pro Thr Leu Pro Met Ala Asp Thr Tyr Ala Val Val Gin Lys Arg 350 355 360 Gly Ala Ser Ala Gly Thr Gly Pro Gly Pro Arg Ala Pro Thr Ser 365 370 375 Thr Asp Thr Pro He Tyr Ser Gin Val Ala Pro Arg Ala Gin Arg 380 385 390 Pro Val Ala His Thr Glu Asp Ala Gin Gly Thr Thr Ala Leu Arg 395 400 405 Arg Val Pro Ala Asp Gin Asn Ser Ser Gly Pro Asp Ala Tyr Glu 410 415 420 Glu Val Thr Asp Gly Ala Gin Thr Gly Gly Leu Gly Phe Asn Leu 425 430 435 Arg He Gly Arg Pro Lys Gly Pro Arg Asp Pro Pro Ala Glu Trp 440 445 450 Thr Arg Val 453 (2) INFORMATION FOR SEQ ID NO: 3: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 39 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 3: CACGGTCGAC GGTGAGGAGC TTCTTTGAGC AGCTGGAGG 39 (2) INFORMATION FOR SEQ ID NO: 4 : (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 42 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 4: GTTGCGGCCG CGATTGGAGC GCAGTTCTCC TTGAGGTTCT GG 42 (2) INFORMATION FOR SEQ ID NO: 5 : (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 36 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 5: CCTGGAGGGT CCTGAGAGTG ATGTCTGCAT TCAGTG 36 (2) INFORMATION FOR SEQ ID NO: 6: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 34 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 6: CCTCTTGGAG CAGGGAAAGG ATGACTCTTG TCTC 34 (2) INFORMATION FOR SEQ ID NO: 7: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO:7 : CAGCTGCTCC AAGAAGCTCC TCACCAAGTC 30 (2) INFORMATION FOR SEQ ID NO: 8: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 31 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 8: GGTAGAGGTG GGCAGGGTGA AGTGTTCTCG C 31 (2) INFORMATION FOR SEQ ID NO: 9: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 36 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 9: CACTGAATGC AGACATCACT CTCAGGACCC TCCAGG 36 (2) INFORMATION FOR SEQ ID NO: 10: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 34 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 10: GAGACAAGAG TCATCCTTTC CCTGCTCCAA GAGG 34 (2) INFORMATION FOR SEQ ID NO: 11: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 25 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 11: GAATGGTAAC CTGGAGGGTC CTGAG 25 (2) INFORMATION FOR SEQ ID NO: 12: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 18 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 12: GAGAAGGTCG TGTTCGAG 18 ( 2 ) INFORMAT ION FOR SEQ I D NO : 13 : ( l ) SEQUENCE CHARACTERI STICS : ( A) LENGTH : 18 base pai rs ( B ) TYPE : Nucl e i c Ac i d (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 13: GTGTACTTCC TGTGCCTG 18 (2) INFORMATION FOR SEQ ID NO: 14: (ι) SEQUENCE CHARACTERISTICS: (A) LENGTH: 18 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 14: ANTTNTGGNG ATGNTTGG 18 (2) INFORMATION FOR SEQ ID NO: 15: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 15 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 15: GGACNNNNTC GGCCA 15 (2) INFORMATION FOR SEQ ID NO: 16: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 466 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 16: GCGCGGGGCG GCCGGGAGGG GGCAGTCCTC GCCGGCGAGT TCAGCGACAT 50 CCAGGCCTGC TCGGCCGCCT GGAAGGCTGA CGGCGTGTGC TCCACCGTGG 100 CCGGCAGTCG GCCAGAGAAC GTGAGGAAGA ACCGCTACAA AGACGTGCTG 150 CCTTATGATC AGACGCGAGT AATCCTCTCC CTGCTCCAGG AAGAGGGACA 200 CAGCGACTAC ATTAATGGCA ACTTCATCCG GGGCGTGGAT GGAAGCCTGG 250 CCTACATTGC CACGCAAGGA CCCTTGCCTC ACACCCTGC" AGACTTCTGG 300 AGACTGGTCT GGGAGTTTGG GGTCAAGGTG ATCCTGATGG CCTGTCGAGA 350 GATAGAGAAT GGGCGGAAAA GGTGTGAGCG GTACTGGGCC CAGGAGCAGG 400 AGCCACTGCA GACTGGGCTT TTCTGCATCA CTCTGATAAA GGAGAAGTGG 450 CTGAATGAGG ACATCA 466 (2) INFORMATION FOR SEQ ID NO: 17: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 155 amino acids (B) TYPE: Amino Acid (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 17: Ala Arg Gly Gly Arg Glu Gly Ala Val Leu Ala Gly Glu Phe Ser 1 5 10 15 Asp He Gin Ala Cys Ser Ala Ala Trp Lys Ala Asp Gly Val Cys 20 25 30 Ser Thr Val Ala Gly Ser Arg Pro Glu Asn Val Arg Lys Asn Arg 35 40 45 Tyr Lys Asp Val Leu Pro Tyr Asp Gin Thr Arg Val He Leu Ser 50 55 60 Leu Leu Gin Glu Glu Gly His Ser Asp Tyr He Asn Gly Asn Phe 65 70 75 He Arg Gly Val Asp Gly Ser Leu Ala Tyr He Ala Thr Gin Gly 80 85 90 Pro Leu Pro His Thr Leu Leu Asp Phe Trp Arg Leu Val Trp Glu 95 100 105 Phe Gly Val Lys Val He Leu Met Ala Cys Arg Glu He Glu Asn 110 . 115 120 Gly Arg Lys Arg Cys Glu Arg Tyr Trp Ala Gin Glu Gin Glu Pro 125 130 135 Leu Gin Thr Gly Leu Phe Cys He Thr Leu He Lys Glu Lys Trp 140 145 150 Leu Asn Glu Asp He 155 (2) INFORMATION FOR SEQ ID NO: 18: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 278 amino acids (B) TYPE: Amino Acid (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID N0:18: Phe Ala Ser Glu Phe Leu Lys Leu Lys Arg Gin Ser Thr Lys Tyr 1 5 10 15 Lys Ala Asp Lys He Tyr Pro Thr Thr Val Ala Gin Arg Pro Lys 20 25 30 Asn He Lys Lys Asn Arg Tyr Lys Asp He Leu Pro Tyr Asp His 35 ' 40 45 Ser Leu Val Glu Leu Ser Leu Leu Thr Ser Asp Glu Asp Ser Ser 50 55 60 Tyr He Asn Ala Ser Phe He Lys Gly Val Tyr Gly Pro Lys Ala 65 70 7b Tyr He Ala Thr Gin Gly Pro Leu Ser Thr Thr Leu Leu Asp Phe 80 85 90 Trp Arg Met He Trp Glu Tyr Arg He Leu Val He Val Met Ala 95 100 105 Cys Met Glu Phe Glu Met Gly Lys Lys Lys Cys Glu Arg Tyr Trp 110 115 120 Ala Glu Pro Gly Glu Thr Gin Leu Gin Phe Gly Pro Phe Ser He 125 130 135 Ser Cys Glu Ala Glu Lys Lys Lys Ser Asp Tyr Lys He Arg Thr 140 145 150 Leu Lys Ala Lys Phe Asn Asn Glu Thr Arg He He Tyr Gin Phe 155 160 165 His Tyr Lys Asn Trp Pro Asp His Asp Val Pro Ser Ser He Asp 170 175 180 Pro He Leu Gin Leu He Trp Asp Met Arg Cys Tyr Gin Glu Asp 185 190 195 Asp Cys Val Pro He Cys He His Cys Ser Ala Gly Cys Gly Arg 200 205 210 Thr Gly Val He Cys Ala Val Asp Tyr Thr Trp Met Leu Leu Lys 215 220 225 Asp Gly He He Pro Lys Asn Phe Ser Val Phe Asn Leu He Gin 230 235 240 Glu Met Arg Thr Gin Arg Pro Ser Leu Val Gin Thr Gin Glu Gin 245 250 255 Tyr Glu Leu Val Tyr Ser Ala Val Leu Glu Leu Phe Lys Arg His 260 265 270 Met Asp Val He Ser Asp Asn His 275 278 (2) INFORMATION FOR SEQ ID NO: 19: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 272 amino acids (B) TYPE: Ammo Acid (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 19: Phe Ala Arg Asp Phe Met Arg Leu Arg Arg Leu Ser Thr Lys Tyr 1 5 10 15 Arg Thr Glu Lys He Tyr Pro Thr Ala Thr Gly Glu Lys Glu Glu 20 25 30 Asn Val Lys Lys Asn Arg Tyr Lys Asp He Leu Pro Phe Asp His 35 40 45 Ser Arg Val Lys Leu Thr Leu Lys Thr Pro Ser Gin Asp Ser Asp 50 55 60 Tyr He Asn Ala Asn Phe He Lys Gly Val Tyr Gly Pro Lys Ala 65 70 7b Tyr Val Ala Thr Gin Gly Pro Leu Ala Asn Thr Val He Asp Phe 80 85 90 Trp Arg Met Val Trp Glu Tyr Asn Val Val He He Val Met Ala 95 100 105 Cys Arg Glu Phe Glu Met Gly Arg Lys Lys Cys Glu Arg Tyr Trp 110 115 120 Pro Leu Tyr Gly Glu Asp Pro He Thr Phe Ala Pro Phe Lys l e 125 130 135 Ser Cys Glu Asp Glu Gin Ala Arg Thr Asp Tyr Phe He Arg Thr 140 145 150 Leu Leu Leu Glu Phe Gin Asn Glu Ser Arg Arg Leu Tyr Gin Phe 155 160 165 His Tyr Val Asn Trp Pro Asp His Asp Val Pro Ser Ser Phe Asp 170 175 180 Ser He Leu Asp Met He Ser Leu Met Arg Lys Tyr Gin Glu His 185 190 195 Glu Asp Val Pro He Cys He His Cys Ser Ala Gly Cys Gly Arg 200 205 210 Thr Gly Ala He Cys Ala He Asp Tyr Thr Trp Asn Leu Leu Lys 215 220 225 Ala Gly Lys He Pro Glu Glu Phe Asn Val Phe Asn Leu He Gin 230 235 240 Glu Met Arg Thr Gin Arg His Ser Ala Val Gin Thr Lys Glu Gin 245 250 255 Tyr Glu Leu Val His Arg Ala He Ala Gin Leu Phe Glu Lys Gin 260 265 270 Leu Gin 272 (2) INFORMATION FOR SEQ ID NO:20: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 33 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 20: ACTTGGTGAG GAGCTTCTTG GAGCAGCTGG AGG 33 (2) INFORMATION FOR SEQ ID NO: 21: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 24 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Smgle (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 21: GGAATGTAAC CTGGAGGGTC CTGA 24 (2) INFORMATION FOR SEQ ID NO:22: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 19 ammo acids (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 22: Gly Phe Gly Asn Arg Phe Ser Lys Pro Lys Gly Pro Arg Asn Pro 1 5 10 15 Pro Ser Ala Trp 19 (2) INFORMATION FOR SEQ ID NO:23: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 21 ammo acids (B) TYPE: Ammo Acid (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 23: He Gly Phe Gly Asn Arg Cys Gly Lys Pro Lys Gly Pro Arg Asp 1 5 10 15 Pro Pro Ser Glu Trp Thr 20 21

Claims: Claims 1 An isolated non-receptor protein tyrosine phosphatase of hematopoietic stem cells (PTP HSC) which ( 1 ) is expressed predominantly in early hematopoietic stem cells or progenitor cells (2) predominantly lacks expression in adult tissues, (3) comprises an N-terminal tyrosine phosphatase domain, followed by a region rich in ser e, threonine, and proline, and a carboxy termmal region of about 15 to 25 amino acids rich in basic amino acid residues, and (4) is capable of tyrosine dephosphorylation in hematopoietic stem cells or progenitor cells 2 The PTP HSC of claim 1 which is murine 3 The PTP HSC of claim 1 which is human 4 The PTP HSC of claim 1 or a deπvative thereof, which downregulates STAT activation 5 An antagonist of the PTP HSC of claim 1 6 An antagonist ofthe PTP HSC of claim 4 7 An isolated non-receptor protein tyrosine phosphatase of hematopoietic stem cells (PTP HSC) selected from the group consisting of (1 ) a protem comprising the amino acid sequence shown in Figure 1 (SEQ ID NO 2), (2) a protem compπsmg the amino acid sequence shown in Figure 8 (SEQ ID NO 17) (3) a mammalian homologue of protein ( 1 ) or protein (2), and (4) a derivative of proteins ( 1) - (2) retaining the ability of tyrosine dephosphorylation in hematopoietic stem cells or progenitor cells 8 The PTP HSC of claim 7 comprising an active N-termmal tyrosine phosphatase domain, retaining a serine residue at a position corresponding to am o acid position 37 in Figure 1 , a region rich in serine, threonine, and proline, retammg an active site cysteme residue at a position corresponding to amino acid position 229 in Figure 1 , and a carboxy-terminal region showing at least about 80% sequence homology with the ammo acid sequence between positions 430 and 451 in Figure 1 , said derivative having an at least about 65% overall sequence homology with the ammo acid sequence shown in Figure 1 and retaining the ability of tyrosine dephosphorylation in hematopoietic progenitor cells 9 The PTP HSC of claun 7, comprising the amino acid sequence shown in Figure 1 (SEQ ID O 2), or in Figure 8 (SEQ. ID NO 17) 10 An antagonist of the PTP HSC of claim 7 1 1 An isolated nucleic acid molecule encoding the PTP HSC of claim 1 12 An isolated nucleic acid molecule encoding the PTP HSC of claim 7 13 An isolated nucleic acid molecule encoding the PTP HSC of claim 1 1 14 A vector comprising the nucleic acid molecule of claim 1 1 operably linked to control sequences recognized by a host cell transformed with the vector 15 A host cell transformed with the vector of claim 13 16 An antibody capable of specific binding to the PTP HSC of claim 7 17 A hybridoma cell line producing an antibody of claim 15 18 An assay for identifying an antagonist or agonist of a PTP HSC of claim 1 , which comprises contacting the phosphatase domain of said PTP HSC with a candidate antagonist or agonist, and monitoring the ability of said phosphatase domain to dephosphorylate tyrosine residues 19 An assay for identifying an antagonist or agonist of a PTP HSC of claim 1 , which comprises cultivating a PTP HSC-expressmg hematopoietic stem or progenitor cell line in the presence of a candidate antagonist or agonist, and monitoring the differentiation ofthe stem or progenitor cells 20 A method for the differentiation of undifferentiated malignant hematopoietic cells, comprising contacting said cells with an antagonist of a PTP HSC according to claim 7 21 The method of claim 19 wherein said cells are leukemia cells 22 A method for the induction of differentiation of stem cells, comprising contacting said cells with an antagonist of a PTP HSC according to claim 7 23 A method for the expansion undifferentiated stems cells in cell culture, comprising cultivating stem cells in the presence of a PTP HSC accordmg to claim 7 or an agonist antibody specifically binding a native PTP HSC 24 A method for the expansion of undifferentiated stem cells in vivo comprising administering to a patient an agonist of a PTP HSC according to claim 7 or an agonist antibody specifically binding a native PTP HSC, and a hematopoietic growth factor

Inventors: CHENG JILL, LASKY LAURENCE A, CHENG, JILL, LASKY, LAURENCE, A.
Applicants: GENENTECH INC, GENENTECH, INC.
Application year: 1997
Main classification: C12N15
IPC codes: A61K31, A61K38, A61K39, A61K45, A61P35, A61P43, C07K16, C12N5, C12N9, C12N15, C12P21, C12Q1, C12R1, G01N33