METHODS AND KITS USING MACROPHAGE STIMULATING PROTEIN

Abstract: The invention provides methods for stimulating megakaryocyte maturation and thrombocyte production using macrophage stimulating protein ("MSP"). In the methods, an effective amount of MSP can be administered in vivo, or alternatively, be used to stimulate maturation of megakaryocytes and produce thrombocytes in vitro. Methods for treating thrombocytopenia in a mammal with MSP are also provided. Kits and articles of manufacture which include MSP are further provided.

Description: METHODS AND KITS USING MACROPHAGE STIMULATING PROTEIN Field of Invention The invention relates generally to methods of stimulating egakaryocytopoiesis and thrombocytopoiesis. More particularly, the invention relates to methods of stimulating megakaryocyte maturation and thrombocyte production using macrophage stimulating protein. The invention also relates to methods of treating certain hematopoietic disorders, such as thrombocytopenia, and to kits containing macrophage stimulating protein. Background of the Invention 1. Hepatocvte Growth Factor Hepatocyte growth factor ("HGF") functions as a growth factor for particular tissues and cell types HGF was identified initially as a mitogen for hepatocytes [Michalopoulos et al . , Cancer Res .. 44 :4414-4419 (1984); Russel et al. , J. Cell. Phvsiol.. 119:183-192 (1984); Nakamura et al., Biochem. Biophvs. Res. Comm.. 122 :1450-1459 (1984)] . Nakamura et al . , supra, reported the purification of HGF from the serum of partially hepatectomized rats. Subsequently, HGF was purified from rat platelets, and its subunit structure was determined [Nakamura et al. , Proc. Natl. Acad. Sci. USA, £3:6489-6493 (1986) ; Nakamura et al. , FEBS Letters, 224:311-316 (1987)] The purification of human HGF ("huHGF") from human plasma was first described by Gohda et al . , J. Clin. Invest. , 81:414-419 (1988) . Both rat HGF and huHGF have been molecularly cloned, including the cloning and sequencing of a naturally occurring variant lacking 5 ammo acids designated "deltas HGF" [Miyazawa et al. , Biochem. Biophvs. Res. Com . , 163:967-973 (1989); Nakamura et al. , Nature, 34.2:440-443 (1989) , Seki et al, Biochem. Biophvs. Res. Commun. , 172 :321-327 (1990) ; Tashiro et al., Proc. Natl. Acad. Sci . USA, £37:3200-3204 (1990) ; Okaiima et al . , Eur. J. Biochem . 193-375-381 (1990)] . The mature form of huHGF, corresponding to the ma]or form purified from human serum, is a disulfide linked heterodimer derived by proteolytic cleavage of the human pro-hormone between amino acids R494 and V495. This cleavage process generates a molecule composed of an α-subunit of 440 am o acids (M r 69 kDa) and a /-.-subunit of 234 ammo acids (M,. 34 kDa) . The nucleotide sequence of the huHGF cDNA reveals that both the a- and the 3-chams are contained m a single open reading frame coding for a pre-pro precursor protein. In the predicted primary structure of mature huHGF, an interchain S-S bridge is formed between Cys 487 of the of-chain and Cys 604 in the 3-chaιn [see Nakamura et al. , Nature. supra] . The N- terminus of the α-cham is preceded by 54 ammo acids, starting with a methionine group. This segment includes a characteristic hydrophobic leader (signal) sequence of 31 residues and the prosequence. The -chain starts at ammo acid (aa) 55, and contains four kringle domains. The kringle l domain extends from about aa 128 to about aa 206, the kringle 2 domain s between about aa 211 and about aa 288, the kringle 3 domain is defined as extending from about aa 303 to about aa 383, and the kringle 4 domain extends from about aa 391 to about aa 464 of the c--cham. The definition of the various kringle domains is based on their homology with knngle-like domains of other proteins (prothrombm, plasminogen) , therefore, the above limits are only approximate. As yet, the function of these kringles nas not been determined. The 0-chain of huHGF shows high homology to the catalytic domain of ser e proteases (38% homology to the plasminogen serme protease domain) However, two of the three residues which form the catalytic triad of serme proteases are not conserved n huHGF. Therefore, despite its serme protease-like domain, huHGF appears to have no proteolytic activity, and the precise role of the β-chain remains unknown. HGF contains four putative glycosylation sites, which are located at positions 294 and 402 of the α-cham and at positions 566 and 653 of the 0-chain. In a portion of cDNA isolated from human leukocytes, m-frame deletion of 15 base pairs was observed. Transient expression of the cDNA sequence in COS-1 cells revealed that the encoded HGF molecule (delta5 HGF) lacking 5 amino acids the krmgle 1 domain was fully functional [Seki et al. , supra] . A naturally occurring huHGF variant has been identified which corresponds to an alternative spliced form of the huHGF transcript containing the coding sequences for the N-termmal finger and first two kringle domains of mature huHGF [Chan et al . . Science, .54:1382-1385 (1991) ; Miyazawa et al. , Eur. J Biochem., 197:15-22 (1991)] . This variant, designated HGF/NK2, has been proposed to be a competitive antagonist of mature huHGF. Comparisons of the ammo acid sequence of rat HGF with that of huHGF have revealed that the two sequences are highly conserved and have the same characteristic structural features. The length of the four krmgle domains in rat HGF is exactly the same as m huHGF Furthermore, the cysteine residues are located in exactly the same positions, an indication of similar three-dimensional structures [Oka 3 ιma et al. , supra; Tashiro et al . , supra] . The HGF receptor has been identified as the product of the c- Met proto-oncogene [Bottaro et al . , Science, 251:802-804 (1991) ; Naldini et al., Oncoσene. 6:501-504 (1991)] . The receptor is referred to as pigo"" and comprises a 190-kDa heterodimeric (a disulfide-linked 50-kDa α-cham and a 145-kDa 3-chaιn) membrane-spanning tyrosine k ase protein [Park et al., Proc. Natl Acad. Sci. USA, 84=6379-6383 (1987)] The binding activity of HGF to its receptor is conveyed by a functional domain located in the N-terminal portion of the molecule, including the first two kringles [Matsumoto et al . , Biochem Biophvs. Res. Commun , 181 :691-699 (1991); Hartmann et al. , Proc. Natl Acad Sci.. £9:11574-11578 (1992) ; Lokker et al., EMBO J , 11:2503-2510 (1992); Lokker and Godowski, J. Biol . Chem. , 268 :17145-117150 (1991)] . The c-Met protein becomes phosphorylated on tyrosine residues of the 145-kDa 3-subunιt upon HGF binding. Both the HGF and HGF receptor genes have been mapped to the long arm of chromosome 7 , within the region qll.2-q21.l [Dean et al . , Nature, 318 :385-388 (1985) ; Weidner et al. , Proc. Natl. Acad. Sc . USA, 8:7001-7005 (1991) ; Saccone et al., Genomics, 13:912-914 (1992)] . It has been observed that levels of HGF increase in the plasma of patients with hepatic failure [Gohda et al . , supra] and in the plasma [L droos et al., Hepatol . ■ 13:734-750 (1991)] or serum [Asa i et al . , J Biochem. , 109:8-13 (1991)] of animals with experimentally induced liver damage. The kinetics of this response are rapid, and precedes the first round of DNA synthesis during liver regeneration. HGF has also been shown to be a mitogen for certain cell types, including melanocytes, renal tubular cells, keratmocytes, certain endothelial cells and cells of epithelial origin [Matsumoto et al. , Biochem. Biophvs. Res. Commun. , 176 :45-51 (1991) ; Igawa et al . , Biochem. Biophvs. Res. Commun , 174:831-838 (1991) ; Han et al . , Biochem. , 2:9768-9780 (1991) ; Rubin et al. , Proc. Natl. Acad. Sc USA. £8:415-419 (1991)] . HGF can also act as a "scatter factor", an activity that promotes the dissociation of epithelial and vascular endothelial cells in vitro [Stoker et al . , Nature, 327 : 239-242 (1987) ; Weidner et al . , J. Cell Biol .. 111:2097-2108 (1990) ; Naldini et al. , EMBO . , 10:2867-2878 (1991) ; Giordano et al . , Proc. Natl. Acad. Sc . USA. .90:649-653 (1993)] . Moreover, HGF has recently been described as an epithelial morphogen [Montesano et al. , Cell. £7:901-908 (1991)] . Therefore, HGF has been postulated to be important m tumor invasion and m embryonic development. Chronic c-Met/HGF receptor activation has been observed certain malignancies [Cooper et al . , EMBO J . 5_:2623 (1986) ; Giordano et al . , Nature, ££9:155 (1989)] . HGF and HGF variants are described further m U.S. Patent Nos. 5,227,158, 5,316,921, and 5,328,837. 2. Macrophaσe Stimulating Protein A protein related to HGF has recently been identified. The protein referred to as HGF-like [Han et al. , supr ; Degen et al . , Biochemistry, £0:9781 (1991) ; Shimamoto et al . , FEBS, £33:61-66 (1993)] or macrophage stimulating protein ("MSP") [Leonard et al . , U.S. Patent No. 5,219,991; Skeel et al . , J. Ex . Med. , 173:1227-1234 (1991) ; Leonard et al. , Exp. Cell Res. , 114:117-126 (1978) ; Yoshimura et al . , J. Biol . Chem. , 268 : 15461-15468 (1993)] shares with HGF the overall four kringle structure. The cDNA coding for MSP has been identified. The protein appears to contain a similar domain structure as HGF with four kringle domains followed by a serine protease domain. MSP is a heterodimer that includes an α-chain of 53 kDa and a /3-chaιn of 25 kDa. MSP, however, s secreted as a single chain precursor [Yoshimura et al . , supra] . Like the HGF precursor [Naldmi et al . , EMBO J. , 11:4825-4833 (1992)] , it is presently believed that maturation of MSP into a biologically active a- β heterodimer is obtained by serum-dependent proteolytic cleavage [Wang et al., J Biol Chem , 2 9 : 3436-3440 (1994) ; Wang et al . , J Biol . Chem. , 269:14027-14031 (1994)] . Wang et al. , J Biol Chem., 269:13806-13810 (1994) report that certain proteases such as serum kallikrein. Factor XIla, nerve growth factor-gamma and epidermal growth factor-binding protein cleave and activate pro-MSP to the -β heterodimer. MSP has been found to bind and activate a receptor comprising a heterodimeric transmembrane glycoprotein referred to as "pi85 RON " or "RON" [Gaudmo et al. , EMBO J . 1£.3524-3532 (1994) ; Wang et al. , Science, ££6:117 (Oct. 7, 1994)] This glycoprotein has two chains linked by disulphide bonds: β (150 kDa) and a (35 kDa) . P185 ROH is synthesized as a single chain precursor (prl70 RON ) , which is subsequently converted into a mature, heterodimeric form by proteolytic cleavage. Unlike the unprocessed, single-chain precursor protein, the heterodimeric form of the protein is delivered to the cell surface. The protein sequence encoding RON was derived from a cDNA cloned from a human keratinocyte cDNA library described by Ronsin et al. , Oncogene, £:1195-1202 (1993) The RON cDNA encodes a protein of 1,400 amino acids which shares an overall similarity to the HGF receptor structurally and has about 63% sequence identity in the catalytic domain Both the MSP and the RON receptor genes have been mapped to chromosome 3p2.1 [Han et al. , supra. Ronsin et al . , supra] . The RON receptor is expressed mainly on cells of epithelial origin and in monocytes. P185 RON also possesses intrinsic tyrosine kinase activity that is stimulated by MSP and a MSP fusion protein, MSP-NK2 [Gaudmo et al. , supra] . Such tyrosine kinase activity is not stimulated, however, by HGF rid. ] . This lack of cross-reactivity has been further demonstrated by the inability of MSP to bind and activate the HGF receptor, pl 90 MET [ I d The majority of mRNA coding for MSP is expressed in the liver. It is also expressed, at lower levels, in the lung, adrenals and placenta. To date, the physiological roles of MSP in the body have not been fully understood. Serum MSP does not increase over a 24 hour period in response to intravenous lipopolysacchaπde, indicating that MSP is not likely to be an acute phase protein [Wang et al. , J. Leuk. Biol. , £4:289-295 (1993)] . Yoshimura et al , supra, have reported that MSP stimulates a chemotactic response to C5a in macrophages. Leonard et al. , U.S. Patent No 5,219,991, have disclosed the use of highly purified MSP for the treatment of pathogenic infections 3. Megakaryocyte and Thrombocyte Production Pluripotent stem cells found primarily in the bone marrow of mammals have the potential to give rise to different types of blood cells which circulate in the peripheral blood [Dexter et al . , Ann. Rev. Cell Biol., £:423-441 (1987)] . The pluripotent stem cells differentiate into various cell lineages through maturational stages, thereby giving rise to committed blood cell types. One cell lineage differentiated m the bone marrow is the megakaryocytic lineage. Regulation of megakaryocytopoiesis and thrombocyte production has been reviewed by Mazur. Exp Hemat. , 15:248 (1987) and Hoffman, Blood, 24 , :1196-1212 (1989) . At least three classes of megakaryocytic progenitor cells have been identified, (l) burst forming unit megakaryocytes (BFU-MK) , (2) colony-forming unit megakaryocytes (CFU-MK) ; and light density megakaryocyte progenitor cells (LD-CFU-MK) . Maturation of megakaryocytes has also been separated nto stages based on standard morphologic criteria. The earliest recognizable member of the cells is the megakaryoblast. The intermediate form of the cells is referred to as the promegakaryocyte or basophilic megakaryocyte. The later form of the cells is referred to as the mature (acidophilic, granular or platelet-producing) megakaryocyte. The mature megakaryocyte extends filaments of cytoplasm into sinusoidal spaces where they detach and fragment into individual thrombocytes or "platelets" [Williams et al. , Hematology, 1st Ed., McGraw-Hill, Inc., New York, New York (1972)] Megakaryocytopoiesis is believed to involve several regulatory factors [Williams et al . , Br. J Haematol.. £2:173 (1982) ; Williams et al . , J Cell Phys , 110 :101 (1982)] The early stage of megakaryocytopoiesis is believed to be mitotic, involving primarily cell proliferation and colony initiation from CFU-MK but not affected by platelet count [Burstein et al., J. Cell Phys., 109:333 (1981) ; Kimura et al. , EXP. Hematol.. 1£:1048 (1985)] . The later stage of maturation is primarily non-mitotic, involving nuclear polyploidization and cytoplasmic maturation [Odell et al., Blood, 48:765 (1976) ; Ebbe et al., Blood, £2:787 (1968)] . Thrombocytes generally circulate in the blood and play an important role in blood clotting and the body's response to in ury. Decreases in the circulating levels of thrombocytes in the blood can result from various pathological conditions and therapies. Thrombocytopenia, for instance, can result from impaired production of thrombocytes by the bone marrow, thrombocyte sequestration in the spleen, and increased destruction of thrombocytes by radiation or chemical therapy. Patients receiving large volumes of rapidly administered blood products can also develop thrombocytopenia due to dilution of the blood. Thrombopoietic disorders are further described in Schafner, "Thrombocytopenia and Disorders of Platelet Function," Internal Medicine, 3rd Ed., Hutton et al . , Eds. (1990) Certain cytokmes and growth factors have been identified as inducing thrombocyte production and megakaryocyte growth Cytokmes reported to have megakaryocyte stimulating activity (MK-CSA) include ιnterleukιn-3 (IL-3) [Williams et al. , Leukemia Res.. 9:1487-1491 (1985)], ιnterleukιn-6 (IL-6) [Bruno et al . , EXP. Hemat . 17:1038-1043 (1989)] , granulocyte-macrophage colony stimulating factor (GM-CSF) [Ishibashi et al., Blood, T5:1433-1438 (1990)] , ιnterleukιn-11 (IL-11) [Xu et al. , Blood, ££:2023-2030 (1994)] , erythropoiet (Epo) [Sakaguchi et al . , EXP. Hemat. , 15:1023-1034 (1987)] , and mterleukιn-12 (IL-12) [Waldburger et al. , Exp Hemat. , 2£:479a (1994) (suppl.)] Other cytokmes have been reported to modulate platelet development when combined with growth factors possessing established MK-CSA. These cytokmes include IL-1_ [Gordon et al. , Blood. £0:302-307 (1992)] and Leukemia Inhibitory Factor (LIF) [Metcalf et al. , "Actions of leukemia inhibitory factor on megakaryocyte and platelet formation, " Ciba Foundation Symposium] . The cMpl ligand has also been reported to be a stimulator of megakaryocytopoiesisand thrombopoiesis [de Sauvage et al. , Nature, £69:533-538 (1994); Lok et al. , Nature, 369:565-568 (1994); Kaushansky et al. , Nature, 369:568-571 (1994)]. Further, a synthetic protein reported to stimulate thrombopoiesis is PIXY 321 [van de Ven et al. , Exp. Hematol. , 20:743-751 (1992); Williams et al. , Blood, £2:366a (1993) (suppl.); Collins et al . , Blood, £2:366a (1993) (suppl.)] PIXY 321 is a fusion protein composed of GM-CSF and IL-3 linked by a synthetic peptide chain [Williams, et al. , Cancer, £7:2705-2707 (1991)]. IL-3 is believed to principally affect the differentiation (earliest) phase of the thrombocytopoiesis process [Moore et al. , Blood, 2i_:l (1991); Sonoda et al. , Proc. Natl. Acad. Sci. USA, 85:4360 (1988)] . IL-6 has been shown to induce megakaryocyte progenitor cell proliferation as well as maturation in murine and primate models, although some investigators have observed IL-6 effects only on cell maturation. The interaction between IL-3 and IL-6 is currently unclear, with some reports indicating that the MK-CSA of IL-3 is mediated by IL-6 since antibodies against murine IL-6 were found to abrogate the MK-CSA of murine IL-3 [Lotem et al. , Blood, JΛ : 1545-1551 (1989)] . Other investigators have reported that neutralizing antibodies to IL-6 alone do not diminish the MK-CSA of serum prepared from aplastic patients, and hypothesize a less crucial role for IL-6 in megakaryocytopoiesis. Nevertheless, a number of studies have demonstrated a stimulatory effect of IL-6 when administered to lethally irradiated animals [Burstein et al. , Blood. £0:420-428 (1992); Herodin et al., Blood, £0:68-74 (1992)]. In patients receiving high dose chemotherapy for metastatic sarcoma and lung cancer, IL-6 has reduced the decline m platelet count and hastened the recover to baseline levels [Demetri et al. , Blood, £2 :367a (1993) (suppl.), Crawford et al. , Blood, £2:367a (1993) (suppl.)] . Autologous bone marrow transplant recipients treated with IL-6 have been reported to experience a relatively rapid return of circulating platelets and a shorter period of platelet transfusion dependence than matched controls [Fay et al., Blood, £2:431a (1993) (suppl.)]. It is an object of the present invention to identify a molecule capable of stimulatingproduction of thrombocytes in vivo and in vitro. It is another object of the invention to identify a molecule capable of stimulating maturation of megakaryocytes in vivo and in vitro. It is another object of the invention to provide the molecule in a pharmaceutically-acceptable carrier for use in the treatment of physiological conditions characterized by existing or anticipated low levels of circulating thrombocytes. It is a further object of the invention to provide the molecule in an article of manufacture or kit that can be employed for purposes of stimulating production of thrombocytes and maturation of megakaryocytes . These and other objects of the invention will be apparent to those of ordinary skill in the art upon consideration of the application as a whole. Summary of the Invention Accordingly, in one embodiment of the invention, there is provided a method for stimulating thrombocyte production using macrophage stimulating protein. In another embodiment of the invention, there is provided a method for stimulating megakaryocyte maturation. In a further embodiment of the invention, there is provided an article of manuf cture and kit that include macrophage stimulating protein. The macrophage stimulating protein is provided in a container having a label which identifies the macrophage stimulating protein as an active agent for stimulating megakaryocyte maturation and thrombocyte production. Reduced levels of thrombocytes in the blood can jeopardize the health of individuals. As discussed in the Background of the Invention, dangerously low levels of thrombocytes in the blood can be the result of a variety of pathological conditions, as well as chemotherapies and irradiation. Applicants have surprisingly found that macrophage stimulating protein is useful for stimulating maturation of megakaryocytes and production of thrombocytes. The macrophage stimulating protein of the present invention can be employed in vitro and in vivo. For in vivo use, the macrophage stimulating protein can be administered as a curative therapy for those individuals suffering from hematopoietic disorders like thrombocytopenia. The macrophage stimulating protein can also be administered as a prophylactic therapy for individuals undergoing, or about to undergo, radiation and/or chemical therapies. Detailed Description of the Preferred Embodiments 1. Definitions As used herein, the terms "macrophage stimulating protein" and "MSP" refer to a growth factor, which growth factor typically has a structure comprising four kringle domains. The terms "macrophage stimulating protein" and "MSP" refer to the mature, pre, pre-pro, and pro forms of the protein, either purified from a natural source, chemically synthesized or recombinantly produced. The macrophage stimulating protein may be in a single chain form or heterodimeric form. The present definition specifically includes macrophage stimulating protein encoded by the sequence published by Yoshimura et al. , J. Biol . Chem.. ££8:15461-15468 (1993) (available from EMBL/GenBank/DDB under accession number L11924; the nucleotide and amino acid sequence also being provided herein in the SEQUENCE LISTING as SEQ ID NO:1 and SEQ ID NO:2, respectively) . The fusion protein referred to herein as "MSP-NK2" comprising the N-terminal region (the first two kringle domains) of macrophage stimulating protein fused with a C-terminal region of the human IgG-gammal heavy chain is also specifically included in the present definition. Fragments of macrophage stimulating protein may have the same activities described herein for macrophage stimulating protein, and the use of fragments with such activity is considered to come within the scope of the present invention. The terms "amino acid" and "ammo acids" refer to all naturally occurring L-α-ammo acids This definition is meant to include norleucme, ornithme, and homocyste e. The ammo acids are identified by either the smgle-letter or three-letter designations: Asp D aspartic acid He I lsoleuc e Thr T threonine Leu L leucme Ser S serine Tyr Y tyrosine GGlluu EE glutamic acid Phe F pheny1alanine Pro P proline His H histidine Gly G glycine Lys K lysine Ala A alanine Arg R arginine Cys C cysteine Trp W tryptophan VVaall VV valine Gin Q glutamine Met M methionine Asn N asparagine The term "megakaryocyte maturation" refers to a process involving differentiation of megakaryoblasts and promegakaryocytes or basophilic megakaryocytes into mature, platelet-producing cells. Megakaryocyte maturation is typically accompanied by cellular changes, such as increased ploidy and demarcation of membranes, and can be observed and quantitated, for instance, by ploidy analysis and microscopic analysis. The term "thrombocytopenia" refers to a physiological condition typically characterizedby a thrombocyte level below about 150 x 10' /liter blood. The terms "treating, " "treatment, " and "therapy" refer to curative therapy, prophylactic therapy, and preventative therapy. The term "mammal" refers to any mammal classified as a mammal, including humans, cows, horses, dogs and cats. In a preferred embodiment of the invention, the mammal is a human. 2. Methods and Compositions of the Invention The present invention provides methods for stimulating megakaryocyte maturation and thrombocyte production using macrophage stimulating protein, referred to hereinafter as "MSP". The MSP useful m the practice of the present invention can be prepared m a number of ways. For instance, the MSP can be prepared using an isolated or purified form of MSP. Methods of isolating and purifying MSP from natural sources are known in the art and are described, for example, by Skeel et al. , J. Exp. Med. , 173:1227-1234 (1991) and Leonard et al . , U.S. Patent No. 5,219,991. Such isolation and purification methods can be employed for obtaining MSP from serum or plasma. Alternatively, MSP can be chemically synthesized and prepared using recombinant DNA tecnniques known the art and described in further detail in Examples 1, 2 and 3 below. The MSP may be from human or any non-human species. For instance, a mammal may have administered MSP from a different mammalian species (e.g.. mice can be treated with human MSP) . There is substantial homology (about 81% ammo acid identity) between mouse MSP and human MSP, and thus, it is expected that MSP from different mammalian species can be employed. Preferably, however, the mammal is treated with homologous MSP (e.g. , humans are treated with human MSP) to avoid potential immune reactions to the MSP. The present invention includes methods for stimulating megakaryocyte maturation and thrombocyte production in vivo and in vitro In accordance with the method of the invention for stimulating megakaryocyte maturation in vitro, bone marrow cells or cell samples suspected of containing megakaryoblasts, promegakaryocytes and/or basophilic megakaryocytes are provided and placed in a cell culture medium. The cells are then cultured in the presence of an effective amount of MSP. Suitable tissue culture media are well known to persons skilled in the art and include, but are not limited to, Minimal Essential Medium ("MEM") , RPMI-1640, and Dulbecco's Modified Eagle's Medium ("DMEM") . These tissue culture medias are commercially available from Sigma Chemical Company (St. Louis, MO) and GIBCO (Grand Island, NY) . The cells are then cultured m the cell culture medium under conditions sufficient for the cells to remain viable and grow. The cells can be cultured in a variety of ways, including culturing n a clot, agar, or liquid culture. The cells are cultured in the presence of an effective amount of MSP. The amount of MSP may vary, but preferably is in the range of about 10 ng/ml to about 100 ng/ml. The MSP can of course be added to the culture at a dose determined empirically by those m the art without undue experimentation. The concentration of MSP m the culture will depend on various factors, such as the conditions under which the cells and MSP are cultured. The specific temperature and duration of incubation, as well as other culture conditions, can be varied depending on such factors as, e.g. , the concentration of the MSP, and the type of cells and medium. Those skilled in the art will be able to determine operative and optimal culture conditions without undue experimentation. Maturation of megakaryocytes in the cultures can be determined by various assays known in the art, such as those described in Williams et al., Leukemia Res. , £:1487-1491 (1985) ; Bruno et al . , Exp. Hematol. , 17:1038-1043 (1989) ; Ishibashi et al . , Blood, 21:1433-1438 (1990); Xu et al. , Blood, £3:2023-2030 (1994); Sakaguchi et al. , Exp. Hematol . , 15:1023-1034 (1987) ] . It is contemplated that using MSP to stimulate megakaryocyte maturation in vitro will be useful in a variety of ways. For instance, megakaryocytes cultured in vitro in the presence of MSP can be infused into a mammal suffering from reduceα levels of platelet-formingcells. In accordance with the method of the invention for stimulating megakaryocyte maturation and thrombocyte production in a mammal, an effective amount of MSP is administered to the mammal. It is contemplated that the MSP may be administered at the time of, or after, administering to the mammal therapy, such as high-dose irradiation or chemotherapy, which can adversely affect blood thromoocyte levels. The MSP may also be administered prophylactically so as to avoid a decrease in blood thrombocyte levels. The MSP is preferably administered to the mammal in a pharmaceutically-acceptable carrier. Suitable carriers and their formulations are described in Remington's Pharmaceutical Sciences, 16th ed. , 1980, Mack Publishing Co , edited by Oslo et al. Compositions particularly well suited for the clinical administration of the MSP used to practice this invention include sterile aqueous solutions or sterile hydratable powders such as lyophilized protein. Typically, an appropriate amount of a pharmaceutically-acceptable salt is also used in the formulation to render the formulation lsotonic. Examples of the pharmaceutically-acceptable carrier include saline, Ringer's solution and dextrose solution. It will be apparent to those persons skilled in the art that certain carriers may be more preferable depending upon, for instance, the route of administration and concentration of MSP being administered. The MSP is preferably administered to the mammal by injection (e.g. , intravenous, mtraperitoneal, subcutaneous, intramuscular) or by other methods such as infusion that ensure its delivery to the bloodstream in an effective form. Effective dosages and schedules for administering MSP may be determined empirically, and making such determinations is within the skill of the art. Interspecies scaling of dosages can be performed in a manner known in the art, e.g. as disclosed in Mordenti et al. , Pharmaceut. Res £:1351 (1991) It is understood by those skilled m the art that the dose of MSP that must be administered will vary depending on, for example, the mammal which will receive the MSP, the nature of the medical condition or therapy believed to be responsible for decreased thrombocyte levels, the extent of damage to the blood cell producing tissues, the route of administration, and the identity of any other drugs being administered to the mammal. It is also understood that it may be necessary to give more than one dose of MSP. Generally, multiple doses of MSP will be required for administration. Administration of MSP should be continued until acceptable thrombocyte levels in the mammal are attained. The invention also provides a method of treating thrombocytopenia in a mammal. In the method, the mammal is first diagnosed as suffering from thrombocytopenia. Making the diagnosis is within the skill in the art. Those skilled in the art will also appreciate that different thrombocyte levels may warrant a thrombocytopenia diagnosis for different mammalian species. The diagnosis is usually made in humans when thrombocyte levels fall below about 150 x 10 9 thrombocytes/liter of blood. Thrombocytopenia can be the result of a disorder of production, distribution or destruction of thrombocytes or thrombocyte-producingcells. To treat the thrombocytopenia, the MSP is administered to the mammal according to the modes and schedules of administrationdescribed above. In the aforementioned methods, the MSP can alternatively be administered in combination with one or more biologically or chemically active agents. Preferably, such agents have megakaryocytopoietic or thrombocytopoietic activity. It is presently believed, for example, that MSP can be administered in combination with cMpl ligand or thrombopoietin [de Sauvage et al. , supra; Lok et al., supra; Kaushansky et al .. supra] , IL-3, GM-CSF, or LIF to stimulate thrombocyte production. The skilled medical practitioner can determine the appropriate doses of each ager' useful herein, generally reducing the normal dose when MSP is combined wit any of these agents. The MSP can be administered in the same formulatic as the other agent (s) or separate administration of MSP and the other agent (s) can occur. The other agents are administered n modes, routes, and schedules appropriate for the particular agent. The megakaryocyte maturation and thrombocyte production can be measured or monitored in various ways. For instance, the maturation and thrombocyte production can be measured using in vitro assays Megakaryocyte progenitor assays are known in the art and can be performed, for example, by culturing the cells in methylcellulose as described by Tanaka et al. , Br. J Haematol. , 22: 8 (1989) . Single cell growth assays can also be performed as described by Williams et al . , Cell Tissue Kinetics, 15:483 (1982) ; Banu et al. , Br. J. Haematol.. 2-5:313 (1990) ; Oon et al . , Leukemia Res. , 10:403 (1986) ; Sparrow et al . , Leukemia Res. , 11 :31 (1987) . The maturation and thrombocyte production can also be monitored by peripheral blood or bone marrow analysis. Thrombocyte levels the circulating blood can be determined by cell count analysis . The cell count analysis may be performed by counting viable cells by trypan blue exclusion. The cells can also be examined morphologically. For example, bone marrow samples can be obtained from the mammal and prepared for microscopy using standard histological techniques known m the art . By staining the cells, one can observe the size, cellular characteristics, and number of megakaryocytes in the marrow sample. The invention further provides an article of manufacture and kit containing materials useful for stimulating megakaryocyte maturation and thrombocyte production. The article of manufacture comprises a container with a label. Suitable containers include, for example, bottles, vials, and test tubes. The containers may be formed from a variety of materials such as glass or plastic. The container holds a composition which is effective for stimulating megakaryocyte maturation and thrombocyte production. The active agent in the composition is MSP. The label on the container indicates that the composition is used for stimulating megakaryocyte maturation and thrombocyte production, and may also indicate directions for either in vivo or in vitro use, such as those described above. The kit of the invention comprises the container described above and a second container comprising a buffer. It may further include other materials desirable from a commercial and user standpoint, including other buffers, diluents, filters, needles, syringes, and package inserts with instructions for use. The invention will be more fully understood by reference to the following examples They should not, however, be construed as limiting the scope of the invention. All literature citations herein are incorporated by reference. Examples Example 1 : Recombinant Production of MSP A cDNA encoding the full-length MSP can be constructed by joining together cDNAs encoding MSP ammo acids 1-340 (clone 5' MSP) and 341-711 (clone 3' MSP) (using the numbering system reported by Yoshimura et al. , supra] . These cDNAs can be isolated by PCR amplication (as described in U.S. Patent No. 4,683,195, issued 28 July 1987 and m Current Protocols n Molecular Biology, Ausubel et al. eds. , Greene Publishing Associates and Wiley-Interscience 1991, Volume 2, Chapter 15) of cDNA from human liver. Total human liver RNA (10 ug) is used as a template for reversed transcription (RT) using a mixture of random hexamer and oligodT, using M-MLV-RT (commercially available from BRL, United Kingdom) To obtain clone 5' MSP, a PCR reaction is performed in a volume of 100 ul containing 10 ul of the RT reaction mixture, using 1 U of Vent DNA polymerase (commercially available from New England Biolabs) , and 50 pmol each of the forward primer CAGTGCAGCCTCCAGCCAGAA (SEQ ID NO:3) and of the reverse primer CTGTACAACGCCGGATCTGGTAG iSEQ ID NO:4) . After 30 cycles of denaturation, (95 * C, 1 mm.) , annealing (55' C, 45 seconds) , and extension (72 * C, 2 mm.) , 2 ul of the PCR reaction is re-amplified with the nested forward primer AGGACGAATCCACCATGGGGTGGCTCCCACTCCTGCTGCTTCTGACT (SEQ ID NO:5) and the nested reverse primer CCGGAATTCGAACTTCTGCCGGAACCCCGAC (SEQ ID NO:6) . To obtain clone 3' MSP, forward primer CCGGAATTCGAACTTCTGCCGGAACCCCGAC (SEQ ID NO 7) and reverse primer ACGGAATTCCCAAGGCATATGGCATCAAGGCT (SEQ ID NO:8) are used. The PCR products are digested with EcoRI restriction enzyme (commercially available from New England Biolabs) , purified and cloned m the vector pRK7 (EP 278,776, published 8/17/88) . The sequence of inserts amplified from separate PCR reactions can then be determined by dideoxynucleotide sequencing. The cDNA can be expressed and purified using techniques described by Yoshimura et al , supra Example 2 Recombinant Production of MSP/NK2 Fusion Protein A partial cDNA containing the N-terminal 268 amino acids of MSP [using the numbering system reported by Yoshimura et al , supra] is fused to a sequence of the human IgG-gammal heavy chain [Bennett et al , J Biol Chem. , £66:23060-23067 (1991)] This can be accomplished using synthesized complementary oligonucleotide GATCCGCAGATCGAGCGAGAATTCTGTACCTGCCGCGGTGCGAGACG (SEQ ID NO- 9) and GTGACCGTCTCGCACCGCGGCAGGTCACAGAATTCTCGCTCGATCTGCG (SEQ ID NO 10) to link the MSP sequences through the unique BamHI site in MSP to the BstEII site in human IgG-gamma heavy chain cDNA fid.1 The resulting construct contains the coding sequences of amino acids 1-268 of MSP, linker sequences encoding ammo acids Glu, Thr, Val, and Thr, followed by the coding sequences of amino acids 216-443 of human IgG-gammal heavy chain The cDNA encoding MSP/NK2 can be inserted into the EBV-based expression plasmid pCIS.EBON [U S Patent No 5,328,837] , and inserted into 293 cells [human embryonic kidney cell line, Graham et al. , J Gen Virol . ££:59 (1977)] using the procedure described by Cachianes et al. , Biotechniσues, 15:255-259 (1993) For MSP/NK2 purification, serum-free conditioned media from 293 cells expressing MSP/NK2 is sterile-filtered, and citrate buffer (pH 6) is added to give a final concentration of 100 mM citrate. All purificationprocedures are performed at 4' C The filtered media is then loaded onto a HiTrap™ Protein A column (Pharmacia LKB, Piscataway, NJ) equilibrated with 100 mM citrate, pH 6 Bound protein is eluted in 100 mM citrate, pH 6, 3 5 M MgCl 2 , 2% (v/v) glycerol Each fraction is immediately buffer-exchanged by passage through a PD-10 column (Sephadex G-25) preequilibrated with phosphate- buffered saline The fraction is then pooled and concentrated Protein concentration can be determined by an anti-human Fc ELISA (see, for example, U.S Patent Nos. 5,316,921 and 5,328,837) and by total ammo acid hydrolysis The NH2- erminal sequence of the purified MSP/NK2 can be confirmed by protein sequencing. Protein purity and integrity can be assessed by silver staining of SDS-PAGE gels as well as by western blotting using an antibody directed against the human Fc region of IgGl. Example 3 Effect of MSP on Maturation of Human Megakarvocytic Cell lines Human megakaryocytic cell lines were analyzed in vitro for their response to various concentrations of conditioned medium containing MSP and recombinant huHGF, prepared as described in sections A and B, respectively, below A. Preparation of Conditioned Medium Containing MSP cDNAs encoding MSP were prepared as described in Example 1 The sequence of the MSP was identical to the sequence of human MSP as reported by Yoshimura et al . , supra. The cDNAs were inserted into the expression plasmid pCIS.EBON (identified Example 2) , and stable populations of 293 cells (identified in Example 2) containing these plasmids were established as described by Cachianes et al. , Biotechniσues, supra. Media from 293 control cells and MSP transfectants were treated prior to use with 5% FCS for 1 hour at 37' C in order to allow pro-MSP processing to the mature two-chain form [Wang et al . , J. Biol Chem , 269:3436-3440 (1994)] Conditioned medium from cells transfected either with the vector alone or with the vector containing the MSP were collected over 48 hours and were utilized at a 1:10 dilution in the assays described below. B. Preparation of Recombinant huHGF Recombinant huHGF was prepared essentially as described in U.S. Patent No. 5,227,158. A huHGF cDNA clone (HLC3) isolated from a human leukocyte library as described by Seki et al . , supra, was cloned into the expression vector, pSVI6B5 (ATCC Deposit No. 68,151) . The complete ammo acid sequence of human leukocyte HGF is shown in U.S. Patent No 5,227,158, SEQ ID NO:2. CHO-dhfr cells [Urlaub et al. , Proc Natl. Acad. Sci . USA, 22 : 4216-4220 (1980)] were cotransfected with the above-described pSVI6B5-based hHGF expression vector and with a dhfr selection vector, pFDll [Simonsen et al. , Proc. Natl. Acad. Sci. USA, £0:2495-2499 (1983)], using the general procedure of Graham et al . , Virology, £2:456-467 (1973) . The latter plasmid encodes DHFR, thereby conferring methotrexate resistance on the transfected cells and allowing for selection of huHGF expressing transformants The transformed dhfr cells were selected by growth m glyc e-, hypoxanthme- and thymidine-deficient medium. Colonies that arose on this selection medium were isolated using cotton swabs and propagated in the same medium to several generations. After cell growth, the cells were amplified and selected with increasing amounts of methotrexate using standard techniques . Clones that could grow in selective media, and therefore incorporated the transfected DHFR containing plasmid, were screened for the presence of secreted HGF. HGF activity in the media of these clones was assayed with a mitogenic assay described in Nakamura et al. , Proc. Natl. Acad. Sci. USA, £0:7229-7233 (1983) . HGF activity in culture media may also be measured by incorporation of l25 I- labelled deoxyuπdine into rat hepatocytes in primary culture as described by Nakamura et al. , Nature, £42:440-443 (1989) . The huHGF was then purified essentially as described by Nakamura et al. , Proc. Natl. Acad Sci .. supra. C. Cell Culture Assays The human megakaryocytic cell lines "DAMI" (obtained from S Greenberg, Brigham and Women's Hospital, Boston, MA) and "CMK" (obtained from T. Sato, Chiba University, Japan) were employed in the assays. Both cell lines were maintained in culture as described by Greenberg et al , Blood. 22:1968-174 (1988) and Komatsu et al . , Blood, 2i ; 42 (1989) Cells were plated m 24 well culture plates (Corning, Corning, NY) at 2 x 10 s cells/ml in RPMI-1640 medium containing 5% platelet poor plasma ("PPP") (prepared as described in Avraham et al . , Blood, 79 : 365-371 (1992)) for 5 days at 5% CO-, humidified atmosphere. The cells were cultured with the MSP conditioned medium (described in Section A above) , recombinant huHGF (described m Section B above) at three different concentrations or 293 cell control conditioned medium and with or without phorbol-12- myristate-13-acetate ("PMA") . The PMA was used as a positive control. The PMA was prepared by dissolving PMA (Sigma, St. Louis, MO) m dimethylsulfoxide (DMSO) and stored at -80 * C. Just before use, the PMA was diluted in RPMI-1640 culture medium. The diluted PMA was then incubated with the cells at a concentration of 10 ng/ml. After incubation, the cells were washed twice with Hank's Balanced Salt Solution ("HBSS") and resuspended in Nuclei Isolation Medium ("NIM"; 0.2% BSA, 0.4% Nonidet p40, and 10 mM HEPES pH 7.4 m HBSS) plus 54 Worthmgton units/ml RNase A (Biolab, New England, MA) at 2 x 10 s cells/ml. DNA content, or ploidy, of the cultured cells was examined by staining the cells with an equal volume of NIM (described above) containing 25 ug/ml propidium iodide (Sigma, St. Louis, MO) . The samples were then kept in the dark at 4 " C and analyzed the same day using a fluorescein activated cell sorting scan (Becton Dickinson, Mountain View, CA) and CellFit™ software. The results are shown below in Table 1 The results are expressed as the mean + SEM of data obtained from three experiments performed in duplicate. TABLE 1 Effect of HGF and MSP on ploidy of CMK cells Treatment 2N S-phase 4N > 8N Control 52.2 28.8 12.9 3.8 PMA (5ng/ml) 52.2 18.4 17.3 3.8 HGF: 60.0 18.4 13.5 4.3 (lOng/ml) 57.6 18.4 12.3 2.7 59.3 24.7 11.0 3.38 (50ng/ml) (lOOng/ml) MSP 1:10 55.0 20.2 15.6 6.9 Control 58.3 16.5 13.0 2.86 Conditioned Medium 1:10 The results of the experiments revealed that MSP treatment over a range of concentrations enhanced the maturation of CMK cells as assayed by ploidy. In contrast, the huHGF over a range of concentrations had no effect on CMK ploidy. D. Northern Blot Analysis of DAMI and CMK Cells Total cellular RNA was extracted from the CMK and DAMI cells by a guanidine-isothiocyanatemethod, and 20 ug RNA was electrophoresed in 1% agarose gel with 2.2 mol/L formaldehyde. After transfer to nylon filters (Hybond-N) , the filters were hybridized with labeled radioactive complementary DNA inserts. This hybridization was done at 37' C in the presence of 50% formamide, 3 x sodium chloride and sodium citrate (SSC) , 0.5% sodium dodecyl sulfate (SDS), 10% dextran sulfate, and 100 ug/ml denatured salmon sperm DNA. Filters were washed at 60 * C for 2 hours in 0.2 x SSC and 0.5% SDS. Membranes were then exposed to Kodak Xomat films (Eastman Kodak, Rochester, NY) for 48 hours. The specific messenger RNA (mRNA) transcripts were detected with the partial human cDNA probe for RON, consisting of the kinase domain. The results of the blot analysis showed tnat specific transcripts of 5.0 kb and 0 kb of the RON gene were constitutively expressed in the CMK and DAMI cells (data not shown) . Example 4 • Effect of MSP on Cyto me Secretion By Human Marrow Megakaryocytes A. In vitro Assays Using specific cytokme assays, supernatants from cultured human megakaryocytes and DAMI cells, treated with MSP conditioned medium or recombinant huHGF, were assayed to examine synthesis and secretion of IL-6, IL-1/3 and GM-CSF Bone marrow was aspirated from healthy donors under sterile conditions m preservative-freehepaπn using standard techniques Primary bone marrow megakaryocytes were isolated by immunomagnetic beads coated with a cocktail of monoclonal antibodies to surface GpIIb/IIIa (M753, Dako, Carpenteπa, CA) , as described in Tanaka et al , Brit J Haematol , 73.18- 24 (1989) Purity of the isolated marrow megakaryocytes was then measured by flow cytometry (using the method of Tanaka et al. , supra) and determined to be 95-98% Isolated primary marrow megakaryocytes (10 s cells/ml) and DAMI cells (10 6 cells/ml) (obtained from S. Greenberg, Brigham _ Women's Hospital, Boston, MA) were cultured in RPMI-1640 medium containing 1% PPP (identified in Example 3, Section C) in the presence or absence of MSP conditioned medium (prepared as described in Example 3, Section A) , recombinant huHGF (prepared as described in Example 3, Section B) , or 293 cell control conditioned medium for 24 hours under conditions described by Avraham et al , supra Duplicate cultures were maintained for each test culture Platelet poor plasma was employed in the assays to avoid the presence of TGF-/3 and other platelet-derived mediators that may be present in relatively high quantities in serum. Supernatants from the cell cultures were obtained and assayed for immunoreactive cytokmes Immunoassays for human nterleukin-lβ, human GM-CSF, and human mterleukm-6 were purchased from R & D Systems, Minneapolis, MN and used according to manufacturer's instructions A standard curve with a cytokme-positive control was run in each assay The lower limit of detection was determined to be 0 35 pg/ml for IL-6, 1 5 pg/ml for GM-CSF, and 0 3 pg/ml for IL-13. The assay results, reported in Table 2 below, are expressed as the mean + SEM of data obtained from three assays performed in duplicate Statistical significance was determined using the Student's T-test TABLE 2 EFFECT OF MSP AND HGF ON CYTOKINE SECRETION BY PRIMARY BONE MARROW MEGAKARYOCYTESAND DAMI CELLS TREATMENT IL-6 GM-CSF IL-l / β Pπmarv Marrow 453 ± 46 130± 13 3624 ±215 Meeakarvocvte Medium + 2% PPP MSP 1389 ± 130* 210±20 4120±310 Control 373±37 lOO± 10 3611 ±305 Conditioned Medium DAMI 342 ± 31 08±01 35±05 Control Conditioned Medium MSP 902 ± 90* 17±03 44± 10 * Statistically significant compared to control conditioned medium. As shown in Table 2, the addition of MSP elicited an increase in IL-6 secretion in all cultures examined over all other treatments. A similar increase was observed with DAMI cells; about 34 pg/ml IL-6 was detected in cultures of untreated cultures as compared to 90 pg/ml of IL-6 detected in MSP treated cultures. To a lesser extent, MSP treatment enhanced secretion of GM-CSF and IL-lβ over all other treatments for primary bone marrow megakaryocytes and over the control for DAMI cells. Secretion of IL-lβ by the human megakaryocytes was also evaluated using a specific IL-lβ ELISA. IL-lβ protein was detected in the supernatants of unstimulated megakaryocytes. MSP modestly stimulated secretion of IL-lβ but did not appear to be significant No effect on secretion of GM-CSF by MSP or huHGF was observed. B. RNA Analysis of Megakaryocytes Total cellular RNA was extracted from the isolated primary bone marrow megakaryocytes. The RNA was extracted by the guanidme- isothiocyanate procedure, followed by ultra-centπfugation through a CsCl cushion. Total RNA was then run on a 1.2% formaldehyde agarose gel, and the intact RNA was visualized by ethidium bromide staining Reversed transcription (RT) of RNA was performed using 2 ug of total RNA from each sample. PCR assays, using RON primers, were performed with forward and reverse primers. The PCR products were analyzed on a 2% agarose gel (BRL, Bethesda, MD) . The amplified DNA bands were visualized with a UV transillum ator. Amplified DNA could be detected at the expected size by ethidium bromide staining of the gel. Internal reaction standards for PCR controls were performed. These standards included RNA with and without primers, primers without RNA, and RNA with actm primers All the primer stocks and total preparation RNAs were analyzed to exclude contamination by cellular DNA. The results of the RNA analysis showed that the isolated bone marrow megakaryocytes expressed specific mRNAs for RON (data not shown; . Example 5: Effect of MSP on Murine Megakaryocytopoiesis To examine the effect of MSP on murine megakaryocyte differentiation, single cell megakaryocyte growth assays were performed in accordance with the methods described in Oon et al. , Leukemia Research, 1£:403-412 (1986) and Sparrow et al. , Leukemia Research. .11:31-36 (1987) Single cell populations from bone marrow were prepared from femurs of normal C57B1/6 mice (purchased from Jackson Laboratories) by flushing the bones with DMEM containing 10% FCS. The immature megakaryocyte populations were obtained in 1.07- 1.085 g/cm 3 fractions from a suspension of single bone marrow cells separated by Percoll (Pharmacia) gradient. The fractionated cells were cultured at 10 5 cells/ml in DMEM- 10%FCS for 5 days at 37' C in a humidified incubator of 10% CO-, in the presence of titrated doses of MSP conditioned medium (prepared as described in Example 3, Section A) and IL-6 (purchased from R & D Systems, Minneapolis, MN) . The cultures were dried and stained for acetylcholmesterase as described by Williams et al. , Cell Tissue Kinetics. .15:483-494 (1982), Banu et al. , British J Haemat . 25 313-318 (1990); Oon et al. , supra,- Sparrow et al. , supra. Single murine megakaryocytes were scored as the number of acetylcholmesterasepositive cells per fractionated 5 x 10* bone marrow cell cultures Immature megakaryocyte growth was quantitated by the number of single large megakaryocytes that were detected by light microscopy. The results are shown Table 3. The results reported are the mean + SEM from triplicate cultures from three experiments. TABLE 3 Effect of MSP on immature murine megakaryocytes Treatment of Culture Single Megakaryocytes per 5 x 10 4 cells Control (FCS) 5.6 ± 0.8 IL-6 (25 ng/ml) 13.0 ± 2.0 IL-6 (25 ng/ml) + Anti-IL-6 Ab (1:10) 5.8 ± 2.5 IL-6 (25 ng/ml) + Non immune serum 13.5 ± 1.0 MSP 14.0 ± 2.8 MSP + Anti-IL-6Ab (1:10) 5.5 ± 0.8 MSP + Non immune serum 13.5 ± 1.5 Control Conditioned Medium 5.5 ± 1.0 Control conditioned Medium + Anti-IL- 6.2 ± 1.0 6 (1:10) Control Conditioned Medium + Non 4.8 ± 1.0 immune serum Addition of MSP to cultures of murine immature megakaryocyte populations showed an enhanced growth response with an increase in detectable numbers of acetylcholinesterase-pσsitivemegakaryocytes. Neutralization assays were also conducted using an indirect immune complex depletion method [Sparrow et al. , supra] . Neutralizing monoclonal antibodies for IL-6 were obtained from Genetics Institute, Boston, MA. Suboptimal levels of growth factors (MSP and huHGF) and optimal levels of antibodies (1:10 dilution) were selected to provide an antibody excess. The various growth factors and antibodies were mixed and incubated at 4" C for 2 hours. For controls, normal rabbit serum (purchased from Sigma, St. Louis, MO) was used. Immune complexes were precipitated by adding 50 ul Protein A-sepharose CL-4B™ (Pharmacia LKB, Piscataway, NJ) . Culture supernatants were collected and assayed for residual megakaryocyte stimulatory activity in the immature murine megakaryocyte growth assay described above. Results of the neutralization assays showed that the increased growth of immature murine megakaryocytes in response to MSP (as well as IL- 6) was neutralized by a monoclonal antibody directed against IL-6 See Table 3 Table 3 also shows that non immune serum added to IL-6 or MSP had no significant effect over IL-6 or MSP alone. Although not fully understood and without being limited to any one theory, the results suggest that MSP may function in regulating megakaryocyte maturation by inducing cytokme secretion from the megakaryocyte or induction of IL-6 by accessory cells. SEQUENCE LISTING (1) GENERAL INFORMATION: (l) APPLICANT: Genentech, Inc. New England Deaconess Hospital Corp. (li) TITLE OF INVENTION: Methoαs and Kits Using Macrophage Stimulating Protein (111) NUMBER OF SEQUENCES: 10 ( V) 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: WinPat (Genentech) (vi) CURRENT APPLICATION DATA: (A) APPLICATION NUMBER: (B) FILING DATE: (C) CLASSIFICATION: (vm) ATTORNEY/AGENT INFORMATION: (A) NAME: Marschang, Diane L. (B) REGISTRATION NUMBER: 35,600 (C) REFERENCE/DOCKET NUMBER: P0912PCT (IX) TELECOMMUNICATION INFORMATION: (A) TELEPHONE: 415/225-5416 (B) TELEFAX: 415/952-9881 (C) TELEX: 910/371-7168 (2) INFORMATION FOR SEQ ID NO:l: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 2232 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO:l: GAATTCCACC ATGGGGTGGC TCCCACTCCT GCTGCTTCTG ACTCAATGCT 50 TAGGGGTCCC TGGGCAGCGC TCGCCATTGA ATGACTTCCA AGTGCTCCGG 100 GGCACAGAGC TACAGCACCT GCTACATGCG GTGGTGCCCG GGCCTTGGCA 150 GGAGGATGTG GCAGATGCTG AAGAGTGTGC TGGTCGCTGT GGGCCCTTAA 200 TGGACTGCCG GGCCTTCCAC TACAACGTGA GCAGCCATGG TTGCCAACTG 250 CTGCCATGGA CTCAACACTC GCCCCACACG AGGCTGCGGC GTTCTGGGCG 300 CTGTGACCTC TTCCAGAAGA AAGACTACGT ACGGACCTGC ATCATGAACA 350 ATGGGGTTGG GTACCGGGGC ACCATGGCCA CGACCGTGGG TGGCCTGCCC 400 TGCCAGGCTT GGAGCCACAA GTTCCCGAAT GATCACAAGT ACACGCCCAC 450 TCTCCGGAAT GGCCTGGAAG AGAACTTCTG CCGTAACCCT GATGGCGACC 500 CCGGAGGTCC TTGGTGCTAC ACAACAGACC CTGCTGTGCG CTTCCAGAGC 550 TGCGGCATCA AATCCTGCCG GGAGGCCGCG TGTGTCTGGT GCAATGGCGA 600 GGAATACCGC GGCGCGGTAG ACCGCACGGA GTCAGGGCGC GAGTGCCAGC 650 GCTGGGATCT TCAGCACCCG CACCAGCACC CCTTCGAGCC GGGCAAGTTC 700 CTCGACCAAG GTCTGGACGA CAACTATTGC CGGAATCCTG ACGGCTCCGA 750 GCGGCCATGG TGCTACACTA CGGATCCGCA GATCGAGCGA GAGTTCTGTG 800 ACCTCCCCCG CTGCGGGTCC GAGGCACAGC CCCGCCAAGA GGCCACAACT 850 GTCAGCTGCT TCCGCGGGAA GGGTGAGGGC TACCGGGGCA CAGCCAATAC 900 CACCACTGCG GGCGTACCTT GCCAGCGTTG GGACGCGCAA ATCCCTCATC 950 AGCACCGATT TACGCCAGAA AAATACGCGT GCAAAGACCT TCGGGAGAAC 1000 TTCTGCCGGA ACCCCGACGG CTCAGAGGCG CCCTGGTGCT TCACACTGCG 1050 GCCCGGCATG CGCGCGGCCT TTTGCTACCA GATCCGGCGT TGTACAGACG 1100 ACGTGCGGCC CCAGGACTGC TACCACGGCG CAGGGGAGCA GTACCGCGGC 1150 ACGGTCAGCA AGACCCGCAA GGGTGTCCAG TGCCAGCGCT GGTCCGCTGA 1200 GACGCCGCAC AAGCCGCAGT TCACGTTTAC CTCCGAACCG CATGCACAAC 1250 TGGAGGAGAA CTTCTGCCGG AACCCAGATG GGGATAGCCA TGGGCCCTGG 1300 TGCTACACGA TGGACCCAAG GACCCCATTC GACTACTGTG CCCTGCGACG 1350 CTGCGCTGAT GACCAGCCGC CATCAATCCT GGACCCCCCA GACCAGGTGC 1400 AGTTTGAGAA GTGTGGCAAG AGGGTGGATC GGCTGGATCA GCGGCGTTCC 1450 AAGCTGCGCG TGGTTGGGGG CCATCCGGGC AACTCACCCT GGACAGTCAG 1500 CTTGCGGAAT CGGCAGGGCC AGCATTTCTG CGGGGGGTCT CTAGTGAAGG 1550 AGCAGTGGAT ACTGACTGCC CGGCAGTGCT TCTCCTCCTG CCATATGCCT 1600 CTCACGGGCT ATGAGGTATG GTTGGGCACC CTGTTCCAGA ACCCACAGCA 1650 TGGAGAGCCA AGCCTACAGC GGGTCCCAGT AGCCAAGATG GTGTGTGGGC 1700 CCTCAGGCTC CCAGCTTGTC CTGCTCAAGC TGGAGAGATC TGTGACCCTG 1750 AACCAGCGCG TGGCCCTGAT CTGCCTGCCC CCTGAATGGT ATGTGGTGCC 1800 TCCAGGGACC AAGTGTGAGA TTGCAGGCTG GGGTGAGACC AAAGGTACGG 1850 GTAATGACAC AGTCCTAAAT GTGGCCTTGC TGAATGTCAT CTCCAACCAG 1900 082 PCMJS95/13 GAGTGTAACA TCAAGCACCG AGGACGTGTG CGTGAGAGTG AGATGTGCAC 1950 TGAGGGACTG TTGGCCCCTG TGGGGGCCTG TGAGGGTGAC TACGGGGGCC 2000 CACTTGCCTG CTTTACCCAC AACTGCTGGG TCCTGGAAGG AATTATAATC 2050 CCCAACCGAG TATGCGCAAG GTCCCGCTGG CCAGCTGTCT TCACGCGTGT 2100 CTCTGTGTTT GTGGACTGGA TTCACAAGGT CATGAGACTG GGTTAGGCCC 2150 AGCCTTGATG CCATATGCCT TGGGGAGGAC AAAACTTCTT GTCAGACATA 2200 AAGCCATGTT TCCTCTTTAT GCCTGTCTCG AG 2232 (2) INFORMATION FOR SEQ ID NO:2: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 711 amino acids (B) TYPE: Amino Acid (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2: Met Gly Trp Leu Pro Leu Leu Leu Leu Leu Thr Gin Cys Leu Gly 1 5 10 15 Val Pro Gly Gin Arg Ser Pro Leu Asn Asp Phe Gin Val Leu Arg 20 25 30 Gly Thr Glu Leu Gin His Leu Leu His Ala Val Val Pro Gly Pro 35 40 45 Trp Gin Glu Asp Val Ala Asp Ala Glu Glu Cys Ala Gly Arg Cys 50 55 60 Gly Pro Leu Met Asp Cys Arg Ala Phe His Tyr Asn Val Ser Ser 65 70 75 His Gly Cys Gin Leu Leu Pro Trp Thr Gin His Ser Pro His Thr 80 85 90 Arg Leu Arg Arg Ser Gly Arg Cys Asp Leu Phe Gin Lys Lys Asp 95 100 105 Tyr Val Arg Thr Cys lie Met Asn Asn Gly Val Gly Tyr Arg Gly 110 115 120 Thr Met Ala Thr Thr Val Gly Gly Leu Pro Cys Gin Ala Trp Ser 125 130 135 His Lys Phe Pro Asn Asp His Lys Tyr Thr Pro Thr Leu Arg Asn 140 145 150 Gly Leu Glu Glu Asn Phe Cys Arg Asn Pro Asp Gly Asp Pro Gly 155 160 165 Gly Pro Trp Cys Tyr Thr Thr Asp Pro Ala Val Arg Phe Gin Ser 170 175 180 Cys Gly lie Lys Ser Cys Arg Glu Ala Ala Cys Val Trp Cys Asn 185 190 195 Gly Glu Glu Tyr Arg Gly Ala Val Asp Arg Thr Glu Ser Gly Arg 200 205 210 Glu Cys Gin Arg Trp Asp Leu Gin His Pro His Gin His Pro Phe 215 220 225 Glu Pro Gly Lys Phe Leu Asp Gin Gly Leu Asp Asp Asn Tyr Cys 230 " 235 240 Arg Asn Pro Asp Gly Ser Glu Arg Pro Trp Cys Tyr Thr Thr Asp 245 " 250 255 Pro Gin lie Glu Arg Glu Phe Cys Asp Leu Pro Arg Cys Gly Ser 260 ' 265 270 Glu Ala Gin Pro Arg Gin Glu Ala Thr Thr Val Ser Cys -r-he Arg 275 280 285 Gly Lys Gly Glu Gly Tyr Arg Gly Thr Ala Asn Thr Thr Thr Ala 290 295 300 Gly Val Pro Cys Gin Arg Trp Asp Ala Gin lie Pro His Gin His 305 310 315 Arg Phe Thr Pro Glu Lys Tyr Ala Cys Lys Asp Leu Arg Glu Asn 320 ' 325 330 Phe Cys Arg Asn Pro Asp Gly Ser Glu Ala Pro Trp Cys Phe Thr 335 340 345 Leu Arg Pro Gly Met Arg Ala Ala Phe Cys Tyr Gin lie Arg Arg 350 355 360 Cys Thr Asp Asp Val Arg Pro Gin Asp Cys Tyr His Gly Ala Gly 365 370 375 Glu Gin Tyr Arg Gly Thr Val Ser Lys Thr Arg Lys Gly Val Gin 380 385 390 Cys Gin Arg Trp Ser Ala Glu Thr Pro His Lys Pro Gin Phe Thr 395 400 405 Phe Thr Ser Glu Pro His Ala Gin Leu Glu Glu Asn Phe Cys Arg 410 415 420 Asn Pro Asp Gly Asp Ser His Gly Pro Trp Cys Tyr Thr Met Asp 425 430 435 Pro Arg Thr Pro Phe Asp Tyr Cys Ala Leu Arg Arg Cys Ala Asp 440 445 450 Asp Gin Pro Pro Ser lie Leu Asp Pro Pro Asp Gin Val Gin Phe 455 460 465 Glu Lys Cys Gly Lys Arg Val Asp Arg Leu Asp Gin Arg Arg Ser 470 475 480 Lys Leu Arg Val Val Gly Gly His Pro Gly Asn Ser Pro Trp Thr 485 490 495 Val Ser Leu Arg Asn Arg Gin Gly Gin His Phe Cys Gly Gly Ser 500 505 510 Leu Val Lys Glu Gin Trp lie Leu Thr Ala Arg Gin Cys Phe Ser 515 520 525 Ser Cys His Met Pro Leu Thr Gly Tyr Glu Val Trp Leu Gly Thr 530 535 540 Leu Phe Gin Asn Pro Gin His Gly Glu Pro Ser Leu Gin Arg Val 545 550 555 Pro Val Ala Lys Met Val Cys Gly Pro Ser Gly Ser Gin Leu Val 560 565 570 Leu Leu Lys Leu Glu Arg Ser Val Thr Leu Asn Gin Arg Val Ala 575 580 585 Leu lie Cys Leu Pro Pro Glu Trp Tyr Val Val Pro Pro Gly Thr 590 595 600 Lys Cys Glu lie Ala Gly Trp Gly Glu Thr Lys Gly Thr Gly Asn 605 610 615 Asp Thr Val Leu Asn Val Ala Leu Leu Asn Val lie Ser Asn Gin 620 625 630 Glu Cys Asn lie Lys His Arg Gly Arg Val Arg Glu Ser Glu Met 635 640 645 Cys Thr Glu Gly Leu Leu Ala Pro Val Gly Ala Cys Glu Gly Asp 650 655 660 Tyr Gly Gly Pro Leu Ala Cys Phe Thr His Asn Cys Trp Val Leu 665 670 675 Glu Gly lie lie lie Pro Asn Arg Val Cys Ala Arg Ser Arg Trp 680 685 690 Pro Ala Val Phe Thr Arg Val Ser Val Phe Val Asp Trp lie His 695 700 705 Lys Val Met Arg Leu Gly 710 711 (2) INFORMATION FOR SEQ ID NO:3: (1) SEQUENCE CHARACTERISTICS: (A) LENGTH: 21 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 3: CAGTGCAGCC TCCAGCCAGA A 21 (2) INFORMATION FOR SEQ ID NO: : (1) SEQUENCE CHARACTERISTICS: (A) LENGTH: 23 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear ( l) SEQUENCE DESCRIPTION: SEQ ID NO: : CTGTACAACG CCGGATCTGG TAG 23 (2) INFORMATION FOR SEQ ID NO: 5: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 47 base pairs (B) TYPE: Nucleic Ac d (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5: AGGACGAATC CACCATGGGG TGGCTCCCAC TCCTGCTGCT TCTGACT 47 (2) INFORMATION FOR SEQ ID NO: 6: (1) SEQUENCE CHARACTERISTICS: (A) LENGTH: 31 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 6: CCGGAATTCG AACTTCTGCC GGAACCCCGA C 31 (2) INFORMATION FOR SEQ ID NO: 7: (1) SEQUENCE CHARACTERISTICS: (A) LENGTH: 31 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 7: CCGGAATTCG AACTTCTGCC GGAACCCCGA C 31 (2) INFORMATION FOR SEQ ID NO: 8: (1) SEQUENCE CHARACTERISTICS: (A) LENGTH: 32 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 8 : ACGGAATTCC CAAGGCATAT GGCATCAAGG CT 32 (2) INFORMATION FOR SEQ ID NO: 9: (1) SEQUENCE CHARACTERISTICS: (A) LENGTH: 47 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 9: GATCCGCAGA TCGAGCGAGA ATTCTGTACC TGCCGCGGTG CGAGACG 47 (2) INFORMATION FOR SEQ ID NO: 10: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 49 base pairs (B) TYPE: Nucleic Acid (C) STRANDEDNESS: Single (D) TOPOLOGY: Linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 10: GTGACCGTCT CGCACCGCGG CAGGTCACAG AATTCTCGCT CGATCTGCG 49

Claims: WHAT IS CLAIMED IS : 1 A method of stimulating thrombocyte production in a mammal comprising administering to the mammal an effective amount of macrophage stimulating protein in a pharmaceutically-acceptablecarrier 2. The method of claim 1 wherein the macrophage stimulating protein is human macrophage stimulating protein. 3. The method of claim 1 wherein the macrophage stimulating protein is administered after cnemotherapy is administered to the mammal 4. The method of claim 1 wherein the macrophage stimulating protein is administered before chemotherapy is administered to the mammal 5. The method of claim l wherein the pharmaceutically-acceptable carrier is sterile saline. 6. A method of treating thrombocytopenia in a mammal, comprising administering to a mammal diagnosed as having thrombocytopeniaan effective amount of macrophage stimulating protein m a pharmaceutically-acceptable carrier. 7. A method for stimulating megakaryocyte maturation in vitro, comprising culturing a cell sample suspected of containing megakaryoblasts, promegakaryocytes and/or basophilic megakaryocytes in the presence of an effective amount of macrophage stimulating protein. 8. The method of claim 7 wherein the amount of macrophage stimulating protein is about 10 ng/ml to about 100 ng/ml. 9. An article of manufacture, comprising: a container; a label on said container; and a composition contained within said container; wherein the composition is effective for stimulating megakaryocyte maturation and thrombocyte production, the label on said container indicates that the composition can be used for stimulating megakaryocyte maturation and thrombocyte production, and the active agent in said composition comprises macrophage stimulating protein. 10. The article of manufacture of claim 9 further comprising instructions for administering the macrophage stimulating protein to a mammal. 11 The article of manufacture of claim 9 further comrismg instructions for using the macrophage stimulating protein in an m vitro cell culture. 12. A kit, comprising: a first container, a label on said container, and a composition contained within said container; wherein the composition is effective for stimulating megakaryocyte maturation and thrombocyte production, the label on said container indicates that the composition can be used for stimulating megakaryocyte maturation and thrombocyte production, and the active agent in said composition comprises macrophage stimulating protein; and a second container comprising a buffer.

Inventors: AVRAHAM HAVA KARSENTY, GODOWSKI PAUL J, AVRAHAM, HAVA, KARSENTY, GODOWSKI, PAUL, J.
Applicants: GENENTECH INC, NEW ENGLAND DEACONESS HOSPITAL, GENENTECH, INC., NEW ENGLAND DEACONESS HOSPITAL CORP.
Application year: 1995
Main classification: A61K38
IPC codes: A61K9, A61K38, A61P5, A61P7, C12N5, C12N15, C12P21, C12R1