Antitumor polysaccharide lentinan. A T cell adjuvant

Polysaccharides derived from Chinese medicinal herbs: A promising choice of vaccine adjuvants

Adjuvants have been used in vaccines for a long time to promote the body's immune response, reducing vaccine dosage and production costs. Although many vaccine adjuvants are developed, the use in human vaccines is limited because of either limited action or side effects. Therefore, the development of new vaccine adjuvants is required. Many studies have found that natural polysaccharides derived from Traditional Chinese medicine (TCM) possess good immune promoting effects and simultaneously improve humoral, cellular and mucosal immunity. Recently polysaccharide adjuvants have attracted much attention in vaccine preparation because of their intrinsic characteristics: immunomodulation, biocompatibility, biodegradability, low toxicity and safety. This review article systematically analysed the literature on polysaccharides possessing vaccine adjuvant activity from TCM plants, such as Astragalus polysaccharide (APS), Rehmannia glutinosa polysaccharide (RGP), Isatis indigotica root polysaccharides (IRPS), etc. and their derivatives. We believe that polysaccharide adjuvants can be used to prepare the vaccines for clinical use provided their mechanisms of action are studied in detail.

Lentinan improved the efficacy of vaccine against Trichinella spiralis in an NLRP3 dependent manner

There is an urgent need for the development of new, improved vaccine adjuvants against T. spiralis infection. Polysaccharides are effective, safe, and biodegradable as adjuvant. In our study, we first observed the protective efficacy of lentinan as adjuvant against helminth T. spiralis infection. Recombinant T. spiralis Serpin (rTs-Serpin) immunoscreened from a cDNA library of T. spiralis, as a vaccine, protect host against Trichinella infection. The reduction rate of helminth burden of rTs-Serpin+lentinan–immunized mice was significantly increased compared with rTs-Serpin+FCA -immunized mice. rTs-Serpin+lentinan induced IgG1-dominant immune response and higher levels of IFN-γ and IL-4. rTs-Serpin+lentinan displayed a lower reduction rate of parasite burden in NLRP3^-/- mice than that in WT mice and lower level of IgG1 than that in WT mice. The level of IL-4, but not IFN-γ, from NLRP3^-/- mice immunized by rTs-Serpin+lentinan was significantly lower than that from WT mice, suggesting that NLRP3 is associated with rTs-Serpin+lentinan -triggering Th2 protective immunity against T. spiralis infection. In summary, we revealed that lentinan was a novel adjuvant against T. spiralis infection via NLRP3. NLRP3 therefore represents an important target for adjuvant discovery and the control of T. spiralis infection.

Trichinella spp., pathogenic agents of trichinellosis, is foodborne zoonotic nematodes cause huge economic burden to the livestock industry. The potential of new adjuvants for improving veterinary vaccines remains largely unexploited to trigger safe and long-lasting immunity in large animals, including livestock. Polysaccharides are effective, safe, and biodegradable as adjuvant. We first observed the protective efficacy of lentinan as a novel adjuvant against helminth T. spiralis infection. NLRP3 is associated with lentinan -triggering Th2 protective immunity against T. spiralis infection. NLRP3 therefore represents an important target for adjuvant discovery and the control of T. spiralis infection.

Structural elucidation of a biologically active heteroglycan isolated from a hybrid mushroom of Pleurotus florida and Lentinula edodes

A water soluble heteroglycan isolated from hot aqueous extract of fruit bodies of an edible hybrid mushroom Pfle1r of Pleurotus florida and Lentinula edodes consists of d-glucose, d-mannose, and d-galactose residues in a molar ratio of nearly 1:1:1. This polysaccharide showed macrophage, splenocyte, and thymocyte activation. On the basis of sugar hydrolysis, methylation, periodate oxidation study, and NMR studies (1H, 13C, DEPT-135, TOCSY, DQF-COSY, NOESY, ROESY, HSQC, and HMBC), the structure of the repeating unit of the polysaccharide was established as: -->6)-α-D-Galp-(1-->6)-α-D-Glcp-(1-->2<--1β-D-Manp.

Effects of intraperitoneal and intranasal application of Lentinan on cellular response in rats

Lentinan (Ajinomoto, Japan) was administrated intraperitoneally (i.p.) and intranasally (i.n.) at different doses (1, 5 and 10 mg/kg) to rats. Effectiveness of Lentinan treatment was evaluated by comparative testing of cell activation (establishing the number, glycolytic and acid phosphatase activity, H2O2 production and killing ability against Salmonella enteritidis and Staphylococcus aureus) at two different compartments--peritoneal and broncho-alveolar cavities. The results indicated that Lentinan induced high-grade activation of peritoneal cells (PCs) and especially of broncho-alveolar cells (BACs) with markedly enhanced effector function (killing ability against S. aureus). Generally, Lentinan, known usually with its parenteral routes of application, can be successful to stimulate the host cell response in the respiratory tract by intranasal route of administration.

Therapeutic intervention with complement and beta-glucan in cancer

Complement (C) has two major effector systems available for host defense. The membrane attack complex (MAC) generated from components C5-C9 can form membrane-penetrating lesions that lead to cell death by causing a rapid loss of cytoplasmic components. The MAC is only effective against pathogens with outer phospholipid membranes, and cannot kill gram-positive bacteria or yeast whose membranes are protected by cell walls. The most important effector mechanism of C is the opsonization of microbial pathogens with the serum protein C3 that leads to their high avidity attachment to the C3-receptors of phagocytic cells. Pathogens that activate complement are first coated with the C3b fragment of C3, which is rapidly proteolyzed into the iC3b fragment by serum factor I. These iC3b fragments serve to promote the high avidity attachment of the 'iC3b-opsonized' pathogens to the iC3b-receptors (CR3, CD11b/CD18) of phagocytic cells and natural killer (NK) cells, stimulating phagocytosis and/or cytotoxic degranulation. Host cells, including neoplastic tumor cells, have been endowed with natural mechanisms for self-protection against both the MAC and the cytotoxic activation of CR3. This review discusses a novel type of immunotherapy for cancer that uses soluble yeast beta-glucan to override the normal resistance of iC3b-opsonized tumor cells to the cytotoxic activation of phagocyte and NK cell CR3, allowing this important effector mechanism of the C system to function against tumor cells in the same way that it normally functions against bacteria and yeast. Moreover, the cytotoxic activation of beta-glucan-primed NK cell CR3 by iC3b-opsonized tumors is shown to be accompanied by a tumor-localized secretion of the cytokines TNFalpha, IFNalpha, IFNgamma, and IL-6.

The β-Glucan-Binding Lectin Site of Mouse CR3 (CD11b/CD18) and Its Function in Generating a Primed State of the Receptor That Mediates Cytotoxic Activation in Response to iC3b-Opsonized Target Cells

Mouse leukocyte CR3 (Mac-1, αMβ2 integrin) was shown to function as a receptor for β-glucans in the same way as human CR3. Soluble zymosan polysaccharide (SZP) or pure β-glucans labeled with FITC or 125I bound in a saturable and reversible manner to neutrophils, macrophages, and NK cells. This lectin activity was blocked by anti-CD11b mAb M1/70 or 5C6 and did not occur with leukocytes from CR3−/− (CD11b-deficient) mice. SZP preparations containing primarily mannose or glucose bound to CR3, and the binding of 125I-labeled β-glucan to CR3 was competitively inhibited by β-glucans from barley or seaweed, but not by yeast α-mannan. Also, as with human CR3, the lectin site of mouse CR3 was inhibited by α- or β-methylglucoside (but not d-glucose), α- or β-methylmannoside, and N-acetyl-d-glucosamine. Phagocytosis of zymosan and serum-opsonized zymosan was partially inhibited by anti-CR3 and was reduced to &lt;40% of normal with leukocytes from CR3−/− mice. As with neutrophils from patients with CD18 deficiency, neutrophils from CR3−/− mice exhibited no phagocytosis of particulate β-glucan. SZP or β-glucans primed CR3 of neutrophils, macrophages, and NK cells for cytotoxicity of iC3b-opsonized tumor cells that otherwise did not trigger killing. β-Glucan priming for cytotoxicity was inhibited by anti-CR3 and did not occur with leukocytes from CR3−/− mice. The primed state of macrophage and NK cell CR3 remained detectable for 18 to 24 h after pulsing with β-glucans. The similarity of mouse and human CR3 in response to β-glucans highlights the utility of mouse tumor models for development of therapeutic β-glucans.

Application of chemical immunomodulators to the treatment of cancer and AIDS

A number of potential advantages, development of promising new agents, and the discovery of synergy with cytokines or cell products continue to spur research into the application of chemical immunomodulators for the treatment of cancer and AIDS. In preclinical in vitro and in vivo systems, chemical immunomodulators definitely modulate the immune system and have therapeutic efficacy. Although clinical trials have shown the ability of these agents to modulate the human immune system, thus far chemical immunomodulators have generally not fulfilled the therapeutic promise generated in animal models for the treatment of human diseases. While the discrepancy in results between animal models and human trials is obvious, the basis is not apparent. Species differences in elimination kinetics, presentation of active drug at the site of action, and the development of tachyphylaxis have been postulated as reasons for the minimal activity of these agents in humans. In addition, the use of investigational techniques established for cytotoxic agents may not be appropriate for immunomodulators. As with any immunomodulator, determining an optimal immunostimulatory dose and schedule and applying the therapy to patients with minimal tumor burden would perhaps be more appropriate than use of a maximally tolerated dose in patients with advanced disease. A dose-immunological effect relationship has recently been demonstrated for levamisole at doses higher than those used for many years in levamisole trials (99). While research and clinical investigation have identified several potentially useful chemical immunomodulators, the elementary understanding of the biochemical mechanisms involved in immunoregulation remains basic. Future research must elucidate these mechanisms, particularly in humans, to maximize the benefits of chemical immunomodulators as single agents or combined with cytotoxic chemotherapeutic agents, surgery, radiation therapy, other immunomodulators, and antiviral agents.

Intrapleural adaptive immunotherapy for breast cancer patients with cytologically-confirmed malignant pleural effusions: an analysis of 67 patients in Kyoto and Shiga Prefecture, Japan

Sixty-seven breast cancer patients with cytologically-confirmed malignant pleural effusion, who required intrapleural treatment, were analyzed retrospectively. The patients received their first thoracentesis between 1980 and 1990. Among them, 29 patients received intrapleural administration of OK-432, a streptococcal preparation, followed by the transfer of autologous pleural effusion lymphocytes cultured with interleukin-2. Other intrapleural treatments consisted of OK-432 alone (12 patients), chemotherapeutic agents alone (n = 9), a combination of OK-432 and chemotherapy (n = 16), or others (n = 1). Twenty-six of the 29 patients given OK-432 plus cultured effusion lymphocytes responded, while only 15 of the 38 patients who received other treatments did (p < 0.01). Median survival time and 5-year survival rate of patients who received OK-432 and cultured lymphocytes was 12 months and 36%, while those of the patients who received other treatments was 3 months and 0%, a significant (p < 0.001) difference in survival. Multivariate analysis using Cox's proportional hazard model revealed that the treatment (adoptive immunotherapy) was the most significant (p < 0.005) factor to prolong the survival of the patients among several prognostic factors. Thus, OK-432 and adoptive immunotherapy is a promising therapy that should be further evaluated in a prospective study.

Genetic control of the expression of two biological activities of an antitumor polysaccharide, lentinan

In order to make clear whether the expression of biological activities and antitumor polysaccharides are under genetic control, the responses of mice to lentinan, a beta-1,6;1,3-glucan, in the induction of several acute phase proteins (APPs) and T-cell-mediated vascular dilation and hemorrhage (VDH) were investigated. Twenty inbred strains of mice were divided into two groups according to their phenotypes in the induction of APPs when they were administered lentinan i.p. at a dose of 10 mg/kg; sensitive strains showed a marked increase in levels of APPs and resistant strains showed as low a level of APPs as non-treated control mice. No sex-related differences and no relation with H-2 halotypes were found in the responses. Only low-level responses were observed in F1 hybrid mice obtained by crosses between a sensitive and a resistant strain, indicating that the low APP response to lentinan is dominant. The N2 progeny between the F1 and a high responder segregated into high and low responders at a ratio of almost 1:1. These results suggest that a single major gene on an autosome is responsible for the induction of APPs. The induction of VDH also depended on the strains of mice. However, the strain distribution pattern of the VDH phenotype was distinct from that of the APP phenotype, indicating that the VDH-controlling gene was different from the APP-controlling gene. Further analyses with F1 hybrid and backcross progeny mice suggested that the high VDH response was dominant, and that the phenotype was determined by a single major gene.

The effect of lentinan on the resistance of mice to Mesocestoides corti

CBA/H mice were given the immunomodulator lentinan in multiple, ascending doses before (prophylactic) or after (therapeutic) inoculation with tetrathyridia of Mesocestoides corti or as a single prophylactic dose. The latter was without effect, but increasing multiple prophylactic and therapeutic doses of lentinan resulted in a marked reduction in the numbers of parasites in the peritoneal cavity, particularly in those mice that received lentinan therapeutically. In mice that received multiple doses of lentinan, liver granulomas were larger than in controls and there was more collagen deposition and fibrosis. Encapsulated parasites were dead or dying, and such damage appeared to be mediated by increased numbers of macrophages and giant cells.

Complement and cancer: activation of the alternative pathway as a theoretical base for immunotherapy

Activation of the APC is pointed out as the common factor in all sufficiently studied cancer treatments employing nonspecific, active immunotherapy. This chapter outlines the molecular biology of both APC and classical pathway of complement, summarizes the alternative pathway's biologic activities especially in relation to the C3/C5 convertase C3b,Bb, and its implications in the mechanism of host defense against malignancies, particularly relating to the activated macrophage. The many involvements of the APC in the various agents used for nonspecific active immunotherapy are reviewed, and possible clinical implications outlined. It is concluded that activation of the APC can be proposed as the specific theoretical basis so far lacking for this treatment modality and that it is accordingly feasible to attempt to monitor clinical application of this principle by fine-tuning of APC activation in cases of human cancer.

T-cell mediated vascular dilatation and hemorrhage induced by antitumour polysaccharides

Antitumour polysaccharide lentinan, capable of potentiating T-cell dependent reactions and some other antitumour polysaccharides such as pachymaran, carboxymethyl-pachymaran and zymosan were found to induce vascular dilatation and hemorrhage(VDH) in CD-1 normal mice starting the following day after a single injection. Polysaccharides which do not have the tumour-regressing activity, several immunopotentiators such as BCG, lipopolysaccharide, dextran sulfate and concanavalin A, and chemical mediators of inflammation such as histamine, serotonin and prostaglandin E1 did not induce VDH in mice. This response seems to be mediated by T-cells and macrophages, because VDH was not observed in CD-1 nu/nu mice treated with lentinan, and carrageenan, an antimacrophage drug, inhibited the appearance of VDH by lentinan. Furthermore, carrageenan inhibited the production of the VDH-inducing serum which was caused by lentinan, capable of passively transferring VDH to another mouse.

Mitogenic effect of the mannans from Saccharomyces cerevisiae on mouse spleen lymphocytes

The DNA synthetic activities of mannans isolated from two Saccharomyces cerevisiae strains were examined in vitro using spleen cells obtained from normal or nude BALB/c strain mice. A highly branched mannan isolated from the S. cerevisiae wild type strain induced a greater increase in mitogenic activity than those displayed by the mannan of the S. cerevisiae X2180-1A-5 mutant strain which possessed fewer branching moieties. Acid-hydrolyzed wild type strain mannan with two-thirds of the molecular weight of the parent intact mannan showed weak mitogenicity. Increases in the DNA synthetic activities of nude and normal spleen cells were almost the same as that of wild type strain mannan, while nylon wool column-passed spleen cells obtained from both normal and nude mice did not show mitogenicity with this mannan. The results indicated that the mitogenic activity was responsible for the highly branched structure of the wild type strain mannan, and that this mannan is a B-cell mitogen.

The cytotoxic effect of mouse macrophages stimulated in vitro by a beta-1,3-D-glucan from yeast cell walls

Macrophages stimulated by an insoluble beta-1,3-D-glucan from yeast cell walls were able to destroy tumour cells as measured by the release of radioactive label from prelabelled 14C-thymidine cells. Target cells were B-16 melanoma, P-815 mastocytoma, and the L-929 cell line. A significant target cell killing by macrophages stimulated by glucan was observed after 72-96 h. The cytolysis of L-929 cells was investigated in some detail. No stable soluble cytolytic factor appeared to be released into the medium during the stimulation of macrophages by glucan, since cell-free spent medium had no cytotoxic effect on L-929 cells. The densities of the macrophage monolayers were critical for an effective target cell killing; dense cultures showed more cytotoxicity than less dense cultures. The kinetics of the development of macrophage-mediated cytotoxicity suggests a minimum stimulation period of 4 days for maximal cytolysis.

The cellular reaction in normal and tumour-bearing mice following intraperitoneal glucan injection

The effect of a single intraperitoneal injection of yeast glucain in C3D2 mice was studied. The optimal dose for the induction of a cellular exudate was 0.4 mg/kg, producing 17.6 x 10(6) cells on day 7 after injection. The number of T-cells, B-cells and macrophages in this exudate was analysed by the use of morphology, immunofluorescence and the non-specific esterase staining. An increase in both T-cells, B-cells and macrophages was found after glucain injection. There was an 8-fold increase in macrophages, but the increase lasted only 14 days. The increase in T-cells was smaller, but lasted at least 35 days. The effect of pretreatment with glucan on the development of an inoculated syngeneic methyl cholanthrene induced sarcoma was studied. No effect on tumour take could be demonstrated, but differences in T-cell, B-cell and macrophage content of the developing tumour were found. A strinking feature was a prolonged increase in tumour T-cell content.

Effect of lentinan on tumor growth in murine allogeneic and syngeneic hosts

The effect of lentinan on retardation and regression of transplanted tumors was analysed in allogeneic and syngeneic tumor-host systems. The effect of lentinan treatment was most variable in random-bred Swiss albino mice bearing sarcoma 180. With inbred host strains, it was most effective in A/PH and less, or not at all, in others (A.BY, A.CA, A.SW, DBA/2, BALB/c, C3H/Di, AKR, BIO, BIO.1, BIO.BR, BIO.D2). In order to eliminate the allogeneic differences, a syngeneic transplantable 3-methylcholanthrene-induced sarcoma (A/PhMC.SI) has been developed in the A/Ph strain, previously found to be the most responsive to lentinan. The growth of this sarcoma was dramatically inhibited and regression was detected in all lentinan-treated syngeneic recipients. Both the lentinan-treated and untreated regressor animals exhibited a high degree of resistance to a secondary challenge. However, the growth of a spontaneous, transplantable syngeneic adenocarcinoma in A/Ph mice was not influenced by lentinan treatment. The results presented substantiate further the conclusion that the effect of lentinan is mediated through host mechanisms, and show that these mechanisms are able to act against a syngeneic tumor.

A B lymphocyte mitogen extracted from a fungus Peziza vesiculosa

A water-soluble mitogen was extracted with hot-water from the fruiting bodies of a fungus, Peziza vesiculosa, collected in the wild. The active substance, named vesiculogen, was able to stimulate selectively murine B cells because mitogenic activity was observed in the spleen cell cultures of congenitally athymic nude mice, but not in the thymus cell cultures. The possibility that the mitogenicity of vesiculogen was due to lipopolysaccharide was denied completely by the following evidence: 1) lipopolysaccharide in vesiculogen was undetectable(less than 0.001% in the Limulus test), 2) vesiculogen was able to stimulate strongly DNA synthesis of spleen cells from C3H/HeJ mice, and 3) the mitogenic activity of vesiculogen was not inhibited by polymyxin B. Vesiculogen increased antigen-nonspecifically the number of direct plaque forming cells to sheep erythrocytes, horse erythrocytes, and trinitrophenylated-horse erythrocytes. This result shows that vesiculogen acts as a polyclonal B cell activator on murine spleen cells.

Mechanism of the anti-tumour effect of glucans and fructosans: a comparison with C. parvum

The anti-tumour activity induced by glucans (lentinan, yeast cell walls, pseudonigeran, dextran, DEAE-dextran and dextran sulphate) and fructosans (levan and carboxymethyl-levan) was compared with the activity of C. parvum. The following effects on tumour systems in CBA mice were assayed: (a) adjuvant activity on the immune response against tumour-specific transplantation antigens (TSTA) with a methylcholanthrene-induced fibrosarcoma; (b) cytostatic activity of peritoneal macrophages against radiation-induced leukaemia cells; and (c) inhibition of tumour nodule formation in the lungs following i.v. injection of fibrosarcoma cells. All the polysaccharides induced cytostatic macrophages, but the dextrans and levans did so only after i.p. and not i.v. injection. Only lentinan, yeast cell walls and pseudonigeran were active in the lung-nodule inhibition test; and only lentinan and dextran sulphate showed slight adjuvant activity for TSTA. It is concluded that the anti-tumour activity induced by these polysaccharides is predominantly non-specific macrophage-mediated and much weaker than that found with C. parvum.

Selective suppression of T-cell activity in tumor-bearing mice and its improvement by lentinan, a potent anti-tumor polysaccharide

The cellular site of immunosuppression in Ehrlich tumor-bearing mice was analysed with particular reference to the T- and B-cell activities. The B-cell activity as measured by the anti-dinitrophenyl (DNP) antibody responses to DNP-thymus-independent carriers (TID) was not impaired in tumor-bearing mice as compared with normal mice, whereas the anti-DNP antibody response to DNP-thymus-dependent carriers (TD) and the development of helper T-cell activity to TD were markedly suppressed in tumor-bearing animals or mice pretreated with cell-free cancerous ascitic fluid. The selective suppression of T-cell response was not mediated by the generation of suppressor cell activity toward TD, which may depress the manifestation of developed helper T-cell activity. A marked suppression of T-cell response was observed when the animals were inoculated with tumor cells or injected with cancerous ascitic fluid prior to antigenic stimulation, but not when the animals were rendered tumor-bearing by such treatments after the immunization. The suppression of T-cell activity in both sarcoma 180 tumor-bearing mice and cell-free Ehrlich cancerous ascitic fluid-treated mice was prevented by treatment with lentinan, a potent anti-tumor polysaccharide. The applicability of this experimental system to the search for immunopotentiators relevant to tumor immunotherapy is discussed in the light of the preventive effect of lentinan on the suppression of T-cell response in tumor-bearing animals.