| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | October 6, 1998 |
| PATENT TITLE |
Underivatized, aqueous soluable .beta.(1-3) glucan, composition and method of making same |
| PATENT ABSTRACT |
The present invention relates to neutral, aqueous soluble .beta.-glucans which exert potent and specific immunological effects without stimulating the production of certain cytokines, to preparations containing the novel .beta.-glucans, and to a novel manufacturing process therefor. The neutral, aqueous soluble .beta.-glucan preparation has a high affinity for the .beta.-glucan receptor of human monocytes and retains two primary biological (or immunological) activities, (1) the enhancement of microbicidal activity of phagocytic cells, and (2) monocyte, neutrophil and platelet hemopoietic activity. Unlike soluble glucans described in the prior art, the neutral, aqueous soluble .beta.-glucan of this invention neither induces nor primes IL-1.beta. and TNF.alpha. production in vitro and in vivo. Safe and efficacious preparations of neutral, aqueous soluble .beta.-glucan of the present invention can be used in therapeutic and/or prophylactic treatment regimens of humans and animals to enhance their immune response, without stimulating the production of certain biochemical mediators (e.g., IL-1.beta., TNF.alpha.) that can cause detrimental side effects, such as fever and inflammation. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | June 6, 1995 |
| PATENT REFERENCES CITED |
Janusz, M.J. et al., "Isolation of Soluble Yeast .beta.-Glucas That Inhibit Human Monocyte Phagocytosis Mediated by .beta.-Glucan Receptors," J. Immunol. 137: 3270-3276 (Nov. 15, 1986). Manners, D.J. et al., "The Structure of a .beta.-(1.fwdarw.3)-D-Glucan from Yeast Cell Walls," Biochem. J. 135: 19-30 (1973). Fleet, G.H., et al., "Isolation and Composition of an Alkali-Soluable Glucan from the Cell Walls of Saccharomyces cerevisiae," Journal of General Microbiology, 94: 180-192 (1976). Miyazaki, T., et al., "Structural Examination of Antitumour, Water-Soluable Glucans from Grifora umbellata by Use of Four Types of Glucanase," Carbohydrate Research, 65: 235-243 (1978). Reiskind, J.B. and Mullins, J.T., "Molecular Archiecture of the Hyphal Wall of Achlya ambisexualis Raper. II. Ultrastructural Analyses and a Proposed Model," Can. J. Microbiol., 27: 1100-1105 (1981). Latge , J.P. et al., "Composition Chimique et Ultrastructure des Parois des Corps Hyphaux et des Azygospores de Conidiobolus obscurus," Can. J. Microbiol., 30: 1507-1521 (1984). Sherwood, E.R. et al., "Soluable Glucan and Lymphokine-Activated Killer (LAK) Cells in the Therapy of Experimental Hepatic Metastases," Chemical Abstracts 108: 179752v (1988). Hara, C. et al., "A Branched (1.fwdarw.3)-.beta.-D-Glucan from a Water Extract of Dictyophora indusiata FISCH," Carb. Res. 145: 237-346 (1986). Goldman, R., "Induction of a .beta.-1, 3-D-Glucan Receptor in P388D1 Cells Treated with Retinoic Acid of 1,25-diphydroxyvitamin D.sub.3, " Immunology63:: 319-324 (1988). Konopski, A. et al., "Phagocytosis of .beta.-1, 3-D-Glucan-Derivatized Microbeads by Mouse Peritoneal Macrophages Involves Three Different Receptors," Scand. J. Immunol. 33: 297-306 (1991). Williams, D.L. et al., "Development of a Water-Soluble, Sulfated (1.fwdarw.3)-.beta.-D-Glucan Biological Response Modifier Derived from Saccharomyces cerevisiae," Carbohydrate Research 235: 247-257 (1992). Williams, D.L. et al., "A Sequential Multi-Assay Protocol for the Preclinical Assessment of Natural Product Complex Carbohydrate Immunomodulators," Develop. Biol. Standard, 77: 129-136 (1992). Williams, D.L. et al., "Development, Physicochemical Characterization and Preclinical Efficacy Evaluation of a Water Soluble Glucan Sulfate Derived from Saccharomyces cerevisiae," Immunopharmacology 22: 139-156 (1991). Pretus, H.A. et al., "Isolation, Physicochemical Characterization and Preclinical Efficacy Evaluation of Soluble Scleroglucan," The J. of Pharmacol and Exp. Therap. 257:500-510 (1991). Bacon, J. et al., "The Glucan Components of the Cell Wall of Baker's Yeast (Saccharomyces cerevisiae) Considered in Relation to its Ultrastructure," Biochem. J. 114: 557-567 (1969). Vestnik Federalniho Uradu Pro Vynalezy 10: 111 (1989). Vestnik Federalniho Uradu Pro Vynalezy 11: 122-123 (1989). Onderdonk, A.B. et al., "Anti-Infective Effect of Poly-.beta.1-6-Glucotrisyl-.beta.1-3-Glucopyranose Glucan In Vivo," Infect. Immun. 60: 1642-1647 (1992). Abel, G. and J.K. Czop, "Activation of Human Monocyte GM-CSF and TNF-.alpha. Production by Particulate Yeast Glucan," International Congress for Infectious Diseases, Montreal Canada (Abstract), Jul. 15-19, 1990. Chihara, G. et al., "Lentinan as a Host Defense Potentiator (HPD), " Int. J. Immunotherapy V(4): 145-154 (1989). Sherwood, E.R. et al., "Enhancement of Interleukin-1 and Interleukin-2 Production by Soluble Glucan," Int. J. Immunopharm. 9(3): 261-267 (1987). Williams, D.L. et al., "Pre-Clinical Safety Evaluation of Soluble Glucan, " Int. J. Immunopharmac. 10(4): 405-414 (1988). Browder, W. et al., "Beneficial Effect of Enhanced Macrophage Function in the Trauma Patient, " Ann. Surg. pp. 605-613 (1990). Jamas et al, "A Novel Class of Macrophage-Activating Immunomodulators" ACS Symposium Series, Polymeric Drugs and Delivery Systems, Chapter 5 pp. 44-45 (1991). Shiota, M. et al., "Comparison of .beta.-Glucan Structures in a Cell Wall Mutant of Saccharomyces cerevisiae and the Wild Type", J. Biochem. 98:1301-1307 (1985). Jamas et al., "PGG-A Novel Class of Macrophage Activating Immunomodulators", International Congress for Infectious Diseases, Montreal Canada (Abstract), Jul. 15-19, 1990. Katzen et al., "PGG, A Glucose Polymer, Primes Interleukin-1 and Tumor Necrosis Factor Production . . . ", International Congess for Infectious Diseases, Montreal Canada (Abstract), Jul. 15-19, 1990. Shah et al., "Influence of PGG on the Phagocytosis of Staphylococcus aureus or Escherichia coli . . . " International Congrss for Infectious Diseases, Montreal Canada (Abstract), Jul. 15-19, 1990. Onderdonk, A.B., "Effect of a New Carbohydrates Polymer on Survival in a Mouse Model for Experimental E. coli sepsis", International Congress for Infectious Diseases, Montreal Canada (Abstract), Jul. 15-19, 1990. A. Arbo and J.I. Santos, "Effect of PGG on Neutrophil (PMN) Function in Experimental Malnutrition", International Congress for Infectious Diseases, Montreal Canada (Abstract), Jul. 15-19, 1990. Onderdonk et al., "Protective Effect of a New Carbohydrate Polymer in a Rat Model for Experimental Intraabdominal Sepsis", First International Congress on Biological Response Modifiers, (Abstract) Quebec Canada, Mar. 22-14, 1991. P.H. Lagrange and M. Fourgeaud, "Enhanced Natural Resistance Against Severe Disseminated Candida albicans . . . ", Int'l J. of Experimental and Clin. Chemotherapy 4(1):48-55 (1991). Sakurai et al., "Intravenously Administered (1.fwdarw.3)-.beta.-D-Glucan, SSG, Obtained from Sclerotinia s sclerotiorum IFO 9395 . . . ", Chem. Pharm. Bull. 40(8):2120-2124 (1992). Jamas et al., "PGG-A Novel Class of Macrophage Activating Immunomodulators", Polymer Preprints 31:194-195, Aug. 8, 1990. |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. An underivatized, aqueous soluble .beta. (1-3)-glucan in a triple helix conformation, said glucan capable of enhancing immune response without stimulating production of biochemical mediators that cause inflammatory side effects, in vitro. 2. The underivatized, aqueous soluble .beta.(1-3)-glucan of claim 1 which, when incubated for greater than 3 hours at a concentration of about 1 .mu.g/ml with a human peripheral blood mononuclear cell culture of about 5.times.10.sup.6 cells/ml, results in a less than 2-fold increase in interleukin-1 .beta. and tumor necrosis factor-.alpha. synthesis over levels obtained following an otherwise identical incubation with a buffered solution lacking the .beta.-glucan component. 3. The underivatized, aqueous soluble .beta.(1-3)-glucan of claim 1 which, when incubated for greater than 3 hours at a concentration of about 1 .mu.g/ml with an endotoxin-stimulated human peripheral blood mononuclear cell culture of about 5.times.10.sup.6 cells/ml, results in a less than 2-fold increase in interleukin-1.beta. and tumor necrosis factor-.alpha. synthesis over levels obtained with endotoxin stimulation alone. 4. The .beta.(1-3)-glucan preparation of claim 3 in which the human peripheral blood mononuclear cells are stimulated with Escherichia coli lipopolysaccharide endotoxin at a concentration of about 1 ng/ml. 5. The .beta.(1-3)-glucan of claim 1 wherein the .beta.(1-3) glucan is derived from yeast. 6. The .beta.-glucan of claim 5 wherein the yeast is a strain of Saccharomyces cerevisiae. 7. The .beta.(1-3)-glucan of claim 6 wherein Saccharomyces cerevisiae is strain R4 (NRRL Y-15903) or strain R4 Ad (ATCC 74181). 8. An underivatized, aqueous soluble .beta.(1-3)-glucan consisting essentially of a molecular species which migrates as a single peak when analyzed by gel permeation chromatography, the molecular species being characterized by a triple helix conformation. 9. A method for producing underivatized, aqueous soluble .beta.(1-3)-glucan having a triple helix conformation, comprising: a) treating a suspension of insoluble .beta.(1-3)-glucan with an organic acid to dissolve the organic acid-soluble portion of the .beta.(1-3)-glucan; b) treating the organic acid-soluble .beta.(1-3)-glucan with alkali to denature the native conformation of the soluble .beta.(1-3)-glucan; c) neutralizing the solution containing the denatured soluble .beta.(1-3)-glucan to re-anneal the soluble .beta.(1-3)-glucan; and d) purifying the re-annealed soluble .beta.(1-3)-glucan to obtain an underivatized, aqueous soluble .beta.(1-3)-glucan having a triple helix conformation. 10. The method of claim 9 wherein the insoluble .beta.(1-3)-glucan is a whole glucan particle. 11. The method of claim 9 wherein step a) is performed at a pH of from about 1 to about 5 and a temperature of from about 20.degree. to about 100.degree. C. 12. The method of claim 9 wherein the organic acid is acetic acid or formic acid. 13. The method of claim 9 wherein step (b) is performed at a pH of from about 7 to about 14 and a temperature of from about 40.degree. to about 121.degree. C. 14. The method of claim 9 further comprising the step of purifying the denatured .beta.(1-3)-glucan prior to step (c) to remove insoluble .beta.(1-3)-glucans and aggregated soluble .beta.(1-3)-glucans therefrom. 15. The method of claim 14 wherein the purification prior to step (c) is performed using 1,000 to 100,000 dalton nominal molecular weight cut-off ultrafilters. 16. The method of claim 9 wherein step (c) is performed at a pH of about 3.5 to 11.0 and at a temperature of from about 50.degree. to 700.degree. C. 17. The method of claim 9 wherein step (d) is performed using a 30,000 to 70,000 nominal molecular weight cut-off ultrafilter and a 100,000 to 500,000 nominal molecular weight cut-off ultrafilter. 18. The method of claim 9 wherein the .beta.(1-3) glucan is derived from yeast. 19. The method of claim 18 wherein the yeast is a strain of Saccharomyces cerevisiae. 20. The method of claim 19 wherein Saccharomyces cerevisiae is strain R4 (NRRL Y-15903) or strain R4 Ad (ATCC 74181). 21. A composition comprising an underivatized, aqueous soluble .beta.(1-3)-glucan which is in a triple helix conformation, said glucan capable of enhancing immune response without stimulating production of biochemical mediators that cause inflammatory side effects, in vitro, the underivatized, aqueous soluble .beta.(1-3)-glucan being solubilized in a physiologically acceptable vehicle. 22. A composition of claim 21 which, when incubated for greater than 3 hours at a concentration of about 1 .mu.g/ml with a human peripheral blood mononuclear cell culture of about 5.times.10.sup.6 cells/ml, results in a less than 2-fold increase in interleukin-1.beta. and tumor necrosis factor-.alpha. synthesis over levels obtained following an otherwise identical incubation with a physiologically acceptable vehicle lacking the .beta.-glucan component. 23. The composition of claim 21 wherein the .beta.(1-3) glucan is derived from yeast. 24. The composition of claim 21 which enhances microbicidal activity of phagocytic cells. 25. The composition of claim 21 which enhances hemopoietic production of monocytes and neutrophils. 26. The composition of claim 21 wherein the physiologically acceptable vehicle is selected from the group consisting of water, sterile saline, phosphate buffered saline, isotonic saline and dextrose. 27. The composition of claim 21 wherein the concentration of glucan in the physiologically acceptable vehicle is from about 0.5 to 100 mg/ml. 28. The composition of claim 21 wherein the composition is in the form of a liquid, tablet, gel, ointment, lotion, capsule, powder, solution, emulsion or cream. 29. The composition of claim 21 wherein the yeast is a strain of Saccharomyces cerevisiae. 30. The composition of claim 29 wherein Saccharomyces cerevisiae is strain R4 (NRRL Y-15903) or strain R4 Ad (ATCC 74181). -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
BACKGROUND OF THE INVENTION In the early 1960's, zymosan, a crude insoluble yeast extract prepared by boiling yeast before and after trypsin treatment, was noted to produce marked hyperplasia and functional stimulation of the reticuloendothelial system in rodents. In animal studies, zymosan preparations were shown to inactivate complement component C3, to enhance antibody formation, to promote survival following irradiation, to increase resistance to bacterial infections, to inhibit tumor development, to promote graft rejection, and to inhibit dietary-induced hypercholesterolemia and cholesterosis. Zymosan was shown to consist of polysaccharides, proteins, fats, and inorganic elements; however, subsequent studies identified the active components of the yeast cell wall as a pure polysaccharide, specifically .beta.-glucan. In conventional nomenclature, the polysaccharide .beta.-glucan is known as poly-(1-6)-.beta.-D-glucopyranosyl-(1-3)-.beta.-D-glucopyranose (PGG). Repetition of biological assays with .beta.-glucan indicated that most of the above functional activities identified with zymosan were retained by the purified .beta.-glucan preparation. The properties of .beta.-glucan are quite similar to those of endotoxin in increasing nonspecific immunity and resistance to infection. The activities of .beta.-glucan as an immune adjuvant and hemopoietic stimulator compare to those of more complex biological response modifiers (BRMs), such as bacillus Calmette-Guerin (BCG) and Corynebacterium Rarvum. The functional activities of yeast .beta.-glucan are also comparable to those structurally similar carbohydrate polymers isolated from fungi and plants. These higher molecular weight (1-3)-.beta.-D-glucans such as schizophyllan, lentinan, krestin, grifolan, and pachyman exhibit similar immunomodulatory activities. A common mechanism shared by all these .beta.-glucan preparations is their stimulation of cytokines such as interleukin-1(IL-1) and tumor necrosis factor (TNF). Lentinan has been extensively investigated for its antitumor properties, both in animal models at 1 mg/kg for 10 days and in clinical trials since the late 1970's in Japan for advanced or recurrent malignant lymphoma and colorectal, mammary, lung and gastric cancers. In cancer chemotherapy, lentinan has been administered at 0.5-5 mg/day, intramuscularly (I.M.) or intravenously (I.V.), two or three times per week alone, or in combination with antineoplastic drugs. In addition to the activities ascribed to yeast glucans, studies suggest lentinan acts as a T-cell immunopotentiator, inducing cytotoxic activities, including production of interleukins 1 and 3 and colony-stimulating factors (CSF). (Chihara et al., 1989, Int. J. Immunotherapy, 4:145-154; Hamuro and Chihara, In Lentinan , An Immunorotentiator) Various preparations of both particulate and soluble .beta.-glucans have been tested in animal models to evaluate biological activities. The use of soluble and insoluble .beta.-glucans alone or as vaccine adjuvants for viral and bacterial antigens has been shown in animal models to markedly increase resistance to a variety of bacterial, fungal, protozoan and viral infections. The hemopoietic effects of .beta.-glucan have been correlated with increased peripheral blood leukocyte counts and bone marrow and splenic cellularity, reflecting increased numbers of granulocyte-macrophage progenitor cells, splenic pluripotent stem cells, and erythroid progenitor cells, as well as, increased serum levels of granulocyte-monocyte colony-stimulating factor (GM-CSF). Furthermore, the hemopoietic and anti-infective effects of .beta.-glucan were active in cyclophosphamide-treated immunosuppressed animals. .beta.-glucan was shown to be beneficial in animal models of trauma, wound healing and tumorigenesis. However, various insoluble and soluble preparations of .beta.-glucan differed significantly in biological specificity and potency, with effective dosages varying from 25to 500 mg/kg intravenously or intraperitoneally (I.P.) in models for protection against infection and for hemopoiesis. Insoluble preparations demonstrated undesirable toxicological properties manifested by hepatosplenomegaly and granuloma formation. Clinical interest was focused on a soluble glucan preparation which would retain biological activity yet yield negligible toxicity when administered systemically. Chronic systemic administration of a soluble phosphorylated glucan over a wide range of doses (40-1000 mg/kg) yielded negligible toxicity in animals (DiLuzio et al., 1979, Int. J. of Cancer, 24:773-779; DiLuzio, U.S. Pat. No. 4,739,046). The molecular mechanism of action of .beta.-glucan has been elucidated by the demonstration of specific .beta.-glucan receptor binding sites on the cell membranes of human neutrophils and macrophages. Mannans, galactans, .alpha.(1-4)-linked glucose polymers and .beta.(1-4)-linked glucose polymers have no avidity for this receptor. These .beta.-glucan binding sites are opsonin-independent phagocytic receptors for particulate activators of the alternate complement pathway, similar to Escherichia coli lipopolysaccharide (LPS) and some animal red blood cells. Ligand binding to the .beta.-glucan receptor, in the absence of antibody, results in complement activation, phagocytosis, lysosomal enzyme release, and prostaglandin, thromboxane and leukotriene generation; thereby increasing nonspecific resistance to infection. However, soluble .beta.-glucan preparations described in the prior art demonstrated stimulation of cytokines. Increases in plasma and splenic levels of interleukins 1 and 2 (IL-1, IL-2) in addition to TNF were observed in vivo and corresponded to induction of the synthesis of these cytokines in vitro. (See Sherwood et a l., 1987, Int. J. Immunopharmac., 9:261-267 (enhancement of IL-1 and IL-2 levels in rats injected with soluble glucan); Williams et al., 1988, Int. J. Immuno pharmac., 10:405-414 (systemic administration of soluble glucan to AIDS patients increased IL-1and IL-2levels which were accompanied by chills and fever); Browder et al., 1990, Ann. Sura., 211:605-613 (glucan administration to trauma patients increased serum IL-1 levels, but not TNF levels); Adachi et al., 1990, Chem. Pharm. Bull., 38:988-992 (chemically cross-linked .beta.(1-3) glucans induced IL-1 production in mice).) Interleukin-1 is a primary immunologic mediator involved in cellular defense mechanisms. Numerous studies have been carried out on the application of IL-1 to enhance non-specific resistance to infection in a variety of clinical states. Pomposelli et al., J. Parent. Ent. Nutr. 12(2):212-218, (1988). The major problem associated with the excessive stimulation or exogenous administration of IL-1 and other cellular mediators in humans is toxicity and side effects resulting from the disruption of the gentle balance of the immunoregulatory network. Fauci et al., Ann. Int. Med., 106:421-433 (1987). IL-1 is an inflammatory cytokine that has been shown to adversely affect a variety of tissues and organs. For instance, recombinant IL-1 has been shown to cause death, hypotensive shock, leukopenia, thrombocytopenia, anemia and lactic acidosis. In addition, IL-1 induces sodium excretion, anorexia, slow wave sleep, bone resorption, decreased pain threshold and expression of many inflammatory-associated cytokines. It is also toxic to the insulin secreting beta cells of the pancreas. Patients suffering from a number of inflammatory diseases have elevated levels of IL-1 in their systems. Administration of agents that enhance further IL-1production only exacerbate these inflammatory conditions. Tumor necrosis factor is also involved in infection, inflammation and cancer. Small amounts of TNF release growth factors while in larger amounts, TNF can cause septic shock, aches, pains, fever, clotting of blood, degradation of bone and stimulation of white blood cells and other immune defenses. SUMMARY OF THE INVENTION The present invention relates to neutral soluble .beta.-glucans which enhance a host's immune defense mechanisms to infection but do not induce an inflammatory response, to preparations containing the neutral soluble .beta.-glucans, and to a novel manufacturing process therefor. In the present method, soluble glucan which induces cytokine production is processed through a unique series of acid, alkaline and neutral treatment steps to yield a conformationally pure neutral soluble glucan preparation with unique biological properties. The neutral soluble glucan preparation retains a specific subset of immunological properties common to .beta.-glucans but uniquely does not induce the production of IL-1 and TNF in vitro or in vivo. Throughout this specification, unless otherwise indicated, the expressions "neutral soluble glucan" and "neutral soluble glucan" refer to the composition prepared as described in Example 1. The neutral soluble glucan preparation is produced by treating insoluble glucan with acid to produce a water soluble glucan, dissociating the native conformations of the soluble glucan at alkaline pH, purifying the desired molecular weight fraction at alkaline pH, re-annealing the dissociated glucan fraction under controlled conditions of time, temperature and pH to form a unique triple helical conformation, and further purifying under neutral pH to remove single helix and aggregated materials to yield a conformationally pure, neutral, water soluble, underivatized glucan which has a unique biological profile. The neutral soluble glucan preparation has a high affinity for the .beta.-glucan receptor of human monocytes and retains two primary biological activities, (1) the enhancement of microbicidal activity of phagocytic cells, and (2) monocyte, neutrophil and platelet hemopoietic activity. Unlike soluble glucans described in the prior art, the neutral soluble glucan of this invention neither induces nor primes mononuclear cells to increase IL-1 and TNF production in vitro and in vivo. The neutral soluble glucan preparation is appropriate for parenteral (e.g., intravenous, intraperitoneal, subcutaneous, intramuscular), topical, oral or intranasal administration to humans and animals as an anti-infective to combat infection associated with burns, surgery, chemotherapy, bone marrow disorders and other conditions in which the immune system may be compromised. Neutral soluble glucan produced by the present method can be maintained in a clear solution and equilibrated in a pharmaceutically acceptable carrier. Safe and efficacious preparations of the neutral soluble glucan of the present invention can be used in therapeutic and/or prophylactic treatment regimens of humans and animals to enhance their immune response, without stimulating the production of certain biochemical mediators (e.g., IL-1 and TNF) that can cause detrimental side effects, such as fever and inflammation. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the general structure of neutral soluble glucan as being a linear .beta.(1-3)-linked glucose polymer having periodic branching via a single .beta.(1-6)-linked glucose moiety. FIG. 2 shows a gel permeation chromatogram (pH 7) of soluble glucan which has not been purified by alkali dissociation and re-annealing. The chromatogram shows three species, referred to herein as high molecular weight aggregate (Ag), Peak A and Peak B (single helix glucan). FIG. 3 is a chromatogram obtained for the neutral soluble glucan by gel permeation chromatography. The solid line represents the neutral soluble glucan at pH 7 and the broken line represents the neutral soluble glucan at pH 13. FIG. 4 is a chromatogram obtained for the single helix .beta.-glucan (Peak B) by gel permeation chromatography. The solid line represents Peak B at pH 7 and the broken line represents Peak B at pH 13. FIG. 5 shows the change in serum TNF levels, over time, taken from patients intravenously infused with placebo (broken line) or neutral soluble glucan (solid line). FIG. 6 shows the change in serum IL-1 levels, over time, taken from patients intravenously infused with placebo (broken line) or neutral soluble glucan (solid line). FIG. 7 is a diagram representing peripheral blood counts from irradiated mice following administration of neutral soluble glucan. FIG. 8 is a diagram representing platelet cell counts from cisplatin-treated mice following administration of neutral soluble glucan. DETAILED DESCRIPTION OF INVENTION The invention relates to a neutral soluble .beta.-glucan polymer that can bind to the .beta.-glucan receptor and activate only a desired subset of immune responses. The terms "neutral soluble .beta.-glucan" and "neutral soluble glucan", unless otherwise specified, refer to the composition prepared as described in Example 1. This neutral soluble .beta.-glucan has been shown to increase the number of neutrophils and monocytes as well as their direct infection fighting activity (phagocytosis and microbial killing). However, the neutral soluble .beta.-glucan does not stimulate the production of biochemical mediators, such as IL-1 and TNF, that can cause detrimental side effects such as high fever, inflammation, wasting disease and organ failure. These advantageous properties make neutral soluble glucan preparations of this invention useful in the prevention and treatment of infection because they selectively activate only those components of the immune system responsible for the initial response to infection, without stimulating the release of certain biochemical mediators that can cause adverse side effects. The solution containing the neutral soluble .beta.-glucan also lacks the toxicity common to many immunomodulators. The neutral soluble .beta.-glucans of this invention are composed of glucose monomers organized as a .beta.(1-3) linked glucopyranose backbone with periodic branching via .beta.(1-6) glycosidic linkages. The neutral soluble glucan preparations contain glucans, which have not been substantially modified by substitution with functional (e.g., charged) groups or other covalent attachments. The general structure of the neutral soluble glucan is shown in FIG. 1. The biologically active preparation of this invention is a conformationally purified form of .beta.-glucan produced by dissociating the native glucan conformations and re-annealing and purifying the resulting unique triple helical conformation. The unique conformation of the neutral soluble glucan contributes to the glucan's ability to selectively activate the immune system without stimulating the production of detrimental biochemical mediators. The neutral soluble glucan preparations of this invention are prepared from insoluble glucan particles, preferably derived from yeast organisms. See Manners et al., Biochem. J., 135:19-30, (1973) for a general procedure to make insoluble yeast glucans. Glucan particles which are particularly useful as starting materials in the present invention are whole glucan particles (WGP) described by Jamas et al., in U.S. Pat. Nos. 4,810,646, 4,992,540, 5,082,936 and 5,028,703, the teachings of all of which are hereby incorporated herein by reference. The source of the whole glucan particles can be the broad spectrum of glucan-containing yeast organisms which contain .beta.-glucans in their cell walls. Whole glucan particles obtained from the strains Saccharomyces cerevisiae R4 (NRRL Y-15903; deposit made in connection with U.S. Pat. No. 4,810,646) and R4 Ad (ATCC No. 74181) are particularly useful. Other strains of yeast that can be used include Saccharomyces delbrueckii, Saccharomyces rosei, Saccharomyces microellipsodes, Saccharomyces carlsberaensis, Schizosaccharomyces pombe, Kluyveromyces lactis, Kluyveromyces fragilis, Kluyveromyces polys porus, Candida albicans, Candida cloacae, Candida tropicalis, Candida utilis, Hansenula wingei, Hansenula arni, Hansenula henricii, Hansenula americana. A procedure for extraction of whole glucan particles is described by Jamas et al., in U.S. Pat. Nos. 4,810,646, 4,992,540, 5,082,936 and 5,028,703. For the purpose of this present invention, it is not necessary to conduct the final organic extraction and wash steps described by Jamas et al. In the present process, whole glucan particles are suspended in an acid solution under conditions sufficient to dissolve the acid-soluble glucan portion. For most glucans, an acid solution having a pH of from about 1 to about 5 and at a temperature of from about 20.degree. to about 100.degree. C. is sufficient. Preferably, the acid used is an organic acid capable of dissolving the acid-soluble glucan portion. Acetic acid, at concentrations of from about 0.1 to about 5M or formic acid at concentrations of from about 50% to 98% (w/v) are useful for this purpose. The treatment time may vary from about 10 minutes to about 20 hours depending on the acid concentration, temperature and source of whole glucan particles. For example, modified glucans having more .beta.(1-6) branching than naturally-occurring, or wild-type glucans, require more stringent conditions, i.e., longer exposure times and higher temperatures. This acid-treatment step can be repeated under similar or variable conditions. One preferred processing method is described in the exemplification using glucan derived from S. cerevisiae strain R4 Ad. In another embodiment of the present method, whole glucan particles from the strain, S. cerevisiae R4, which have a higher level of .beta.(1-6) branching than naturally-occurring glucans, are used, and treatment is carried out with 90% (w/v) formic acid at 20.degree. C. for about 20 minutes and then at 85.degree. C. for about 30 minutes. The insoluble glucan particles are then separated from the solution by an appropriate separation technique, for example, by centrifugation or filtration. The pH of the resulting slurry is adjusted with an alkaline compound such as sodium hydroxide, to a pH of about 7 to about 14. The precipitate is collected by centrifugation and is boiled in purified water (e.g., USP) for three hours. The slurry is then resuspended in hot alkali having a concentration sufficient to solubilize the glucan polymers. Alkaline compounds which can be used in this step include alkali-metal or alkali-earth metal hydroxides, such as sodium hydroxide or potassium hydroxide, having a concentration of from about 0.01 to about 10N. This step can be conducted at a temperature of from about 4.degree. C. to about 121.degree. C., preferably from about 20.degree. C. to about 100.degree. C. In one embodiment of the process, the conditions utilized are a 1M solution of sodium hydroxide at a temperature of about 80.degree.-100.degree. C. and a contact time of approximately 1-2 hours. The resulting mixture contains solubilized glucan molecules and particulate glucan residue and generally has a dark brown color due to oxidation of contaminating proteins and sugars. The particulate residue is removed from the mixture by an appropriate separation technique, e.g., centrifugation and/or filtration. In another embodiment of the process the acid-soluble glucans are precipitated after the preceding acid hydrolysis reaction by the addition of about 1.5 volumes of ethanol. The mixture is chilled to about 4.degree. C. for two (2) hours and the resulting precipitate is collected by centrifugation or filtration and washed with water. The pellet is then resuspended in water, and stirred for three (3) to twelve (12) hours at a temperature between about 20.degree. C. and 100.degree. C. At this point the pH is adjusted to approximately 10 to 13 with a base such as sodium hydroxide. The resulting solution contains dissociated soluble glucan molecules. This solution is now purified to remove traces of insoluble glucan and high molecular weight soluble glucans which can cause aggregation. This step can be carried out by an appropriate purification technique, for example, by ultrafiltration, utilizing membranes with nominal molecular weight (NMW) levels or cut-offs in the range of about 1,000 to 100,000 daltons. It was discovered that in order to prevent gradual aggregation or precipitation of the glucan polymers the preferred membrane for this step has a nominal molecular weight cut-off of about 100,000 daltons. The soluble glucan is then further purified at alkaline pH to remove low molecular weight materials. This step can be carried out by an appropriate purification technique, for example, by ultrafiltration, utilizing membranes with nominal molecular weight levels or cut-offs in the range of 1,000 to 30,000 daltons. The resulting dissociated soluble glucan is re-annealed under controlled conditions of time (e.g., from about 10 to about 120 minutes), temperature (e.g., from about 50.degree. to about 70.degree. C.) and pH. The pH of the solution is adjusted to the range of about 3.5-11 (preferably 6-8) with an acid, such as hydrochloric acid. The purpose of this re-annealing step is to cause the soluble glucan to rearrange from a single helix conformation to a new ordered triple helical conformation. The re-annealed glucan solution is then size fractionated, for example by using 30,000-70,000 NMW and 100,000-500,000 NMW cut-off membrane ultrafilters to selectively remove high and low molecular weight soluble glucans. Prior to sizing, the soluble glucans exist as a mixture of conformations including random coils, gel matrices or aggregates, triple helices and single helices. The objective of the sizing step is to obtain an enriched fraction for the re-annealed conformation of specific molecular weight. The order in which the ultrafilters are used is a matter of preference. The concentrated fraction obtained is enriched in the soluble, biologically active neutral soluble glucan. The glucan concentrate is further purified, for example, by diafiltration using a 10,000 dalton membrane. The preferred concentration of the soluble glucan after this step is from about 2 to about 10 mg/ml. The neutralized solution can then be further purified, for example, by diafiltration, using a pharmaceutically acceptable medium (e.g., sterile water for injection, phosphate-buffered saline (PBS), isotonic saline, dextrose) suitable for parenteral administration. The preferred membrane for this diafiltration step has a nominal molecular weight cut-off of about 10,000 daltons. The final concentration of the glucan solution is adjusted in the range of about 0.5 to 10 mg/ml. In accordance with pharmaceutical manufacturing standards for parenteral products, the solution can be terminally sterilized by filtration through a 0.22 .mu.m filter. The neutral soluble glucan preparation obtained by this process is sterile, non-antigenic, essentially pyr bgen-free, and can be stored at room temperature (e.g., 15.degree.-30.degree. C.) for extended periods of time without degradation. This process is unique in that it results in a neutral aqueous solution of (pH 4.5 to 7.0) immunologically active glucans which is suitable for parenteral administration. For purposes of the present invention, the term "soluble" as used herein to describe glucans obtained by the present process, means a visually clear solution can be formed in an aqueous medium such as water, PBS, isotonic saline, or a dextrose solution having a neutral pH (e.g., from about pH 5 to about 7.5), at room temperature (about 20.degree.-25.degree. C.) and at a concentration of up to about 10 mg/ml. The term "aqueous medium" refers to water and water-rich phases, particularly to pharmaceutically acceptable aqueous liquids, including PBS, saline and dextrose solutions. The expression "visually clear" means that at a concentration of 1 mg/ml, the absorption of the solution at 530 nm is less than OD 0.01 greater than the OD of an otherwise identical solution lacking the B-glucan component. The resulting solution is substantially free of protein contamination, is non-antigenic, non-pyrogenic and is pharmaceutically acceptable for parenteral administration to animals and humans. However, if desired, the soluble glucan can be dried by an appropriate drying method, such as lyophilization, and stored in dry form. The neutral soluble glucans of this invention can be used as safe, effective, therapeutic and/or prophylactic agents, either alone or as adjuvants, to enhance the immune response in humans and animals. Soluble glucans produced by the present method selectively activate only those components that are responsible for the initial response to infection, without stimulating or priming the immune system to release certain biochemical mediators (e.g., IL-1, TNF, IL-6, IL-8 and GM-CSF) that can cause adverse side effects. As such, the present soluble glucan composition can be used to prevent or treat infectious diseases in malnourished patients, patients undergoing surgery and bone marrow transplants, patients undergoing chemotherapy or radiotherapy, neutropenic patients, HIV-infected patients, trauma patients, burn patients, patients with chronic or resistant infections such as those resulting from myelodysplastic syndrome, and the elderly, all of who may have weakened immune systems. An immunocompromised individual is generally defined as a person who exhibits an attenuated or reduced ability to mount a normal cellular and/or humoral defense to challenge by infectious agents, e.g., viruses, bacteria, fungi and protozoa. A protein malnourished individual is generally defined as a person who has a serum albumin level of less than about 3.2 grams per deciliter (g/dl) and/or unintentional weight loss of greater than 10% of usual body weight. More particularly, the method of the invention can be used to therapeutically or prophylactically treat animals or humans who are at a heightened risk of infection due to imminent surgery, injury, illness, radiation or chemotherapy, or other condition which deleteriously affects the immune system. The method is useful to treat patients who have a disease or disorder which causes the normal metabolic immune response to be reduced or depressed, such as HIV infection (AIDS). For example, the method can be used to pre-initiate the metabolic immune response in patients who are undergoing chemotherapy or radiation therapy, or who are at a heightened risk for developing secondary infections or post-operative complications because of a disease, disorder or treatment resulting in a reduced ability to mobilize the body's normal metabolic responses to infection. Treatment with the neutral soluble glucans has been shown to be particularly effective in mobilizing the host's normal immune defenses, thereby engendering a measure of protection from infection in the treated host. The present composition is generally administered to an animal or a human in an amount sufficient to produce immune system enhancement. The mode of administration of the neutral soluble glucan can be oral, enteral, parenteral, intravenous, subcutaneous, intraperitoneal, intramuscular, topical or intranasal. The form in which the composition will be administered (e.g., powder, tablet, capsule, solution, emulsion) will depend upon the route by which it is administered. The quantity of the composition to be administered will be determined on an individual basis, and will be based at least in part on consideration of the severity of infection or injury in the patient, the patient's condition or overall health, the patient's weight and the time available before surgery, chemotherapy or other high-risk treatment. In general, a single dose will preferably contain approximately 0.01 to approximately 10 mg of modified glucan per kilogram of body weight, and preferably from about 0.1 to 2.5 mg/kg. The dosage for topical application will depend upon the particular wound to be treated, the degree of infection and severity of the wound. A typical dosage for wounds will be from about 0.001 mg/ml to about 2 mg/ml, and preferably from about 0.01 to about 0.5 mg/ml. In general, the compositions of the present invention can be administered to an individual periodically as necessary to stimulate the individual's immune response. An individual skilled in the medical arts will be able to determine the length of time during which the composition is administered and the dosage, depending upon the physical condition of the patient and the disease or disorder being treated. As stated above, the composition may also be used as a preventative treatment to preinitiate the normal metabolic defenses which the body mobilizes against infections. Neutral soluble .beta.-glucan can be used for the prevention and treatment of infections caused by a broad spectrum of bacterial, fungal, viral and protozoan pathogens. The prophylactic administration of neutral soluble .beta.-glucan to a person undergoing surgery, either preoperatively, intraoperatively and/or post-operatively, will reduce the incidence and severity of post-operative infections in both normal and high-risk patients. For example, in patients undergoing surgical procedures that are classified as contaminated or potentially contaminated (e.g., gastrointestinal surgery, hysterectomy, cesarean section, transurethral prostatectomy) and in patients in whom infection at the operative site would present a serious risk (e.g., prosthetic arthroplasty, cardiovascular surgery), concurrent initial therapy with an appropriate antibacterial agent and the present neutral soluble glucan preparation will reduce the incidence and severity of infectious complications. In patients who are immunosuppressed, not only by disease (e.g., cancer, AIDS) but by courses of chemotherapy and/or radiotherapy, the prophylactic administration of the soluble glucan will reduce the incidence of infections caused by a broad spectrum of opportunistic pathogens including many unusual bacteria, fungi and viruses. Therapy using neutral soluble .beta.-glucan has demonstrated a significant radio-protective effect with its ability to enhance and prolong macrophage function and regeneration and, as a result enhance resistance to microbial invasion and infection. In high risk patients (e.g., over age 65, diabetics, patients having cancer, malnutrition, renal disease, emphysema, dehydration, restricted mobility, etc.) hospitalization frequently is associated with a high incidence of serious nosocomial infection. Treatment with neutral soluble .beta.-glucan may be started empirically before catheterization, use of respirators, drainage tubes, intensive care units, prolonged hospitalizations, etc. to help prevent the infections that are commonly associated with these procedures. Concurrent therapy with antimicrobial agents and the neutral soluble .beta.-glucan is indicated for the treatment of chronic, severe, refractory, complex and difficult to treat infections. The compositions administered in the method of the present invention can optionally include other components, in addition to the neutral soluble .beta.-glucan. The other components that can be included in a particular composition are determined primarily by the manner in which the composition is to be administered. For example, a composition to be administered orally in tablet form can include, in addition to neutral soluble .beta.-glucan, a filler (e.g., lactose), a binder (e.g., carboxymethyl cellulose, gum arabic, gelatin), an adjuvant, a flavoring agent, a coloring agent and a coating material (e.g., wax or plasticizer). A composition to be administered in liquid form can include neutral soluble .beta.-glucan and, optionally, an emulsifying agent, a flavoring agent and/or a coloring agent. A composition for parenteral administration can be mixed, dissolved or emulsified in water, sterile saline, PBS, dextrose or other biologically acceptable carrier. A composition for topical administration can be formulated into a gel, ointment, lotion, cream or other form in which the composition is capable of coating the site to be treated, e.g., wound site. Compositions comprising neutral soluble glucan can also be administered topically to a wound site to stimulate and enhance wound healing and repair. Wounds due to ulcers, acne, viral infections, fungal infections or periodontal disease, among others, can be treated according to the methods of this invention to accelerate the healing process. Alternatively, the neutral soluble .beta.-glucan can be injected into the wound or afflicted area. In addition to wound repair, the composition can be used to treat infection associated therewith or the causative agents that result in the wound. A composition for topical administration can be formulated into a gel, ointment, lotion, cream or other form in which the composition is capable of coating the site to be treated, e.g., wound site. The dosage for topical application will depend upon the particular wound to be treated, the degree of infection and severity of the wound. A typical dosage for wounds will be from about 0.01 mg/ml to about 2 mg/ml, and preferably from about 0.01 to about 0.5 mg/ml. Another particular use of the compositions of this invention is for the treatment of myelodysplastic syndrome (MDS). MDS, frequently referred to as preleukemia syndrome, is a group of clonal hematopoietic stem cell disorders characterized by abnormal bone marrow differentiation and maturation leading to peripheral cytopenia with high probability of eventual leukemic conversion. Recurrent infection, hemorrhaging and terminal infection resulting in death typically accompany MDS. Thus, in order to reduce the severity of the disease and the frequency of infection, compositions comprising modified glucan can be chronically administered to a patient diagnosed as having MDS according to the methods of this invention, in order to specifically increase the infection fighting activity of the patient's white blood cells. Other bone marrow disorders, such as aplastic anemia (a condition of quantitatively reduced and defective hematopoiesis) can be treated to reduce infection and hemorrhage that are associated with this disease state. Neutral soluble glucan produced by the present method enhances the non-specific defenses of mammalian mononuclear cells and significantly increases their ability to respond to an infectious challenge. The unique property of neutral soluble glucan macrophage activation is that it does not result in increased body temperatures (i.e., fever) as has been reported with many non-specific stimulants of those defenses. This critical advantage of neutral soluble glucan may lie in the natural profile of responses it mediates in white blood cells. It has been shown that the neutral soluble .beta.-glucan of the present invention selectively activates immune responses but does not directly stimulate or prime cytokine (e.g., IL-1 and TNF) release from mononuclear cells, thus distinguishing the present neutral soluble glucan from other glucan preparations (e.g., lentinan, krestin) and immunostimulants. In addition, it has been demonstrated herein that the neutral soluble glucan preparation of the present invention possesses an unexpected platelet stimulating property. Although it was known that glucans have the ability to stimulate white blood cell hematopoiesis, the disclosed platelet stimulating property had not been reported or anticipated. This property can be exploited in a therapeutic regimen for use as an adjuvant in parallel with radiation or chemotherapy treatment. Radiation and chemotherapy are known to result in neutropenia (reduced polymorphonuclear (PMN) leukocyte cell count) and thrombocytopenia (reduced platelet count). At present, these conditions are treated by the administration of colony-stimulating factors such as GM-CSF and granulocyte colony-stimulating factor (G-CSF). Such factors are effective in overcoming neutropenia, but fail to impact upon thrombocytopenia. Thus, the platelet stimulating property of the neutral soluble glucan preparation of this invention can be used, for example, as a therapeutic agent to prevent or minimize the development of thrombocytopenia which limits the dose of the radiation or chemotherapeutic agent which is used to treat cancer. |
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