Effect of N alpha-acetylmuramyl-L-alanyl-D-isoglutaminyl-N epsilon-stearoyl- L-lysine on resistance to herpes simplex virus type-1 infection in cyclophosphamide-treated mice

Translation of peptidoglycan metabolites into immunotherapeutics

The discovery of defined peptidoglycan metabolites that activate host immunity and their specific receptors has revealed fundamental insights into host-microbe recognition and afforded new opportunities for therapeutic development against infection and cancer. In this review, we summarise the discovery of two key peptidoglycan metabolites, γ-d-glutamyl-meso-diaminopimelic acid (iE-DAP) and muramyl dipeptide and their respective receptors, Nod1 and Nod2, and review progress towards translating these findings into therapeutic agents. Notably, synthetic derivatives of peptidoglycan metabolites have already yielded approved drugs for chemotherapy-induced leukopenia and paediatric osteosarcoma; however, the broad effects of peptidoglycan metabolites on host immunity suggest additional translational opportunities for new therapeutics towards other cancers, microbial infections and inflammatory diseases.

Unleashing the therapeutic potential of NOD-like receptors

Nucleotide-binding and oligomerization domain (NOD)-like receptors (NLRs) are a family of intracellular sensors that have key roles in innate immunity and inflammation. Whereas some NLRs - including NOD1, NOD2, NAIP (NLR family, apoptosis inhibitory protein) and NLRC4 - detect conserved bacterial molecular signatures within the host cytosol, other members of this family sense 'danger signals', that is, xenocompounds or molecules that when recognized alert the immune system of hazardous environments, perhaps independently of a microbial trigger. In the past few years, remarkable progress has been made towards deciphering the role and the biology of NLRs, which has shown that these innate immune sensors have pivotal roles in providing immunity to infection, adjuvanticity and inflammation. Furthermore, several inflammatory disorders have been associated with mutations in human NLRgenes. Here, we discuss the effect that research on NLRs will have on vaccination, treatment of chronic inflammatory disorders and acute bacterial infections.

A novel immunostimulator, N-[alpha-O-benzyl-N-(acetylmuramyl)-L-alanyl-D-isoglutaminyl]-N6-trans-(m-nitrocinnamoyl)-L-lysine, and its adjuvancy on the hepatitis B surface antigen

N(2)-[alpha-O-benzyl-N-(acetylmuramyl)-L-alanyl-D-isoglutaminyl]-N(6)-trans-(m-nitrocinnamoyl)-L-lysine (muramyl dipeptide C, or MDP-C) has been synthesized as a novel, nonspecific immunomodulator. The present study shows that MDP-C induces strong cytolytic activity by macrophages on P388 leukemia cells and cytotoxic activity by cytotoxic T lymphocytes (CTLs) on P815 mastocytoma cells. Our results also indicate that MDP-C is an effective stimulator for production of interleukin-2 and interleukin-12 by murine bone marrow derived dendritic cells (BMDCs) and production of interferon-gamma by CTLs. Additionally, MDP-C increases the expression levels of several surface molecules, including CD11c, MHC class I, and intercellular adhesion molecule-1 in BMDCs. Moreover, MDP-C remarkably enhances the immune system's responsiveness to hepatitis B surface antigen (HBsAg) in hepatitis B virus transgenic mice for both antibody production and specific HBsAg T-cell responses ex vivo. Our results indicate that MDP-C is an apyrogenic, nonallergenic, and low-toxicity immunostimulator with great potential for diagnostic, immunotherapeutic, and prophylactic applications in diseases such as hepatitis B and cancers.

Adjuvant activity of muramyl dipeptide derivatives to enhance immunogenicity of a hantavirus-inactivated vaccine

The adjuvant effect of two lipophilic derivatives of muramyl dipeptide (MDP), B30-MDP and MDP-Lys(L18), on the ability of an inactivated vaccine of B-1 virus (B-1 vaccine) to induce immune response against Hantavirus causing hemorrhagic fever with renal syndrome (HFRS) was examined. When mice were immunized subcutaneously (s.c.) twice at 2-week intervals with B-1 vaccine admixed with or without 100 micrograms mouse-1 of B30-MDP (B-1/B30-MDP) or MDP-Lys(L18) [B-1/MDP-Lys(L18)], mice immunized with B-1/B30-MDP as well as B-1/MDP-Lys(L18) showed significantly higher indirect fluorescent antibody (IFA) titers against HFRS virus than mice immunized with B-1 vaccine alone. Both mice treated with B-1/B30-MDP and B-1/MDP-Lys(L18) also exhibited significantly higher neutralizing antibody titers against HFRS virus than mice immunized with B-1 vaccine alone during 3-9 weeks after the primary immunization. The evaluation of antibody-producing cells by enzyme-linked immunospot (ELISPOT) assay on week 4 revealed that both MDP derivatives enhanced the number of HFRS virus-specific IgG1 and IgM antibody-producing cells. Furthermore, mice treated with B-1/B30-MDP as well as B-1/MDP-Lys(L18) showed a higher level of Th-2 type cytokines, IL-4 and IL-6, in sera than mice treated with B-1 alone. In an in-vitro analysis of T lymphocyte proliferation to baculovirus-expressed recombinant nucleocapsid protein (rNP) of Hantaan 76-118 strain, the splenocytes of mice treated with B-1/B30-MDP and B-1/MDP-Lys(L18) on week 4 showed a significantly higher proliferating activity than those treated with B-1 vaccine alone. In addition, when mice were immunized once with B-1 vaccine admixed with or without B30-MDP and MDP-Lys(L18) and followed by intrafootpad (i.f.) injection of B-1 vaccine on day 7, mice immunized with B-1/B30-MDP and B-1/MDP-Lys(L18) induced a higher delayed-type hypersensitivity (DTH) reaction than mice immunized with B-1 vaccine alone. These results suggest that B30-MDP and MDP-Lys(L18) are useful immunoadjuvants to enhance the ability of inactivated B-1 vaccine to induce a humoral and cellular response to HFRS virus.

Study of the adjuvant activity of new MDP derivatives and purified saponins and their influence on HIV-1 replication in vitro

Muramyl dipeptide (MDP), eight new lipophilic MDP derivatives (MDPs) and three purified saponins were evaluated for their ability to induce immune responses in mice immunized with HIV-1 envelope protein rgp160 and for their ability to influence the HIV-1 replication in vitro. Three of nine new synthetic MDP derivatives (beta-butyl-MDP, MTPO-26 and beta-cholesteryl-MDP) and one saponin (Taurosid I) have been shown to induce strong humoral immune responses to HIV-1 envelope glycoproteins rgp160 and rgp120. Three substances (beta-butyl-MDP, MDP-cholyl and beta-G27-MDP) induced high levels of T-cell stimulation to HIV-1 rgp160. beta-butyl-MDP induced the strongest B- and T-cell responses to HIV-1 glycoproteins. Two substances (beta-butyl-MDP and Taurosid I) did not induce an enhancement of HIV-1 replication in vitro and can be considered as promising adjuvants.

Effect of MDP-Lys(L18), a derivative of MDP, on enhancing host resistance against Hantaan virus infection in newborn mice

We examined the effect of MDP-Lys(L18), a lipophilic derivative of muramyl dipeptide, on the enhancement of host resistance against virus infection in newborn mice. Newborn mice were inoculated with 4 LD50/mouse of Hantaan virus strain 76-118 (HTN) one day after birth. Mice given 100 micrograms/mouse of MDP-Lys(L18) before infection exhibited significantly higher survival rates than those of non-treated mice. The effect of MDP-Lys(L18) was also restorative when given to the mice 4 or 7 days after infection. The titers of virus isolated from the lungs and spleens 12 days after infection, were about 30-times lower in MDP-Lys(L18)-treated (lung: 1.0 x 10(3) FFU; spleen: 6.8 x 10(1) FFU/mouse), than those of non-treated mice (lung: 3.4 x 10(4) FFU; spleen: 1.9 x 10(3) FFU/mouse). Furthermore, the virus was undetectable in the brains of MDP-Lys(L18)-treated mice, whereas viruses were isolated from 3 of 6 non-treated mice. MDP-Lys(L18) augmented the number of peripheral leukocytes and splenocytes, as well as mitogenic responses of the cells from bone marrow and spleen of newborn mice. These results suggest that MDP-Lys(L18) enhanced the resistance of newborn mice against HTN virus in a systemic infection model, and that this mechanism is involved in the enhancement of hematopoiesis and responsiveness of immune-related cells to mitogens.

Effects of muramyl dipeptide derivatives as adjuvants on the induction of antibody response to recombinant hepatitis B surface antigen

The ability of two muramyl dipeptide (MDP) derivatives, B30-MDP and MDP-Lys(L18), to enhance the immunogenicity of recombinant hepatitis B surface antigen (rHBsAg) was examined. When mice were immunized intraperitoneally with rHBsAg together with each MDP derivative, the antibody titres were higher than those in mice immunized with alum-adsorbed rHBsAg, which is a commercially available hepatitis B vaccine. When mice were given a subcutaneous or intramuscular injection of rHBsAg and either MDP derivative, the antibody titres were the same as those in mice given alum-adsorbed rHBsAg. These results indicate the usefulness of MDP derivatives as immunoadjuvants for a new-generation vaccine.

Effect of the synthetic lipid A-related compound, DT-5461, on resistance to Sendai virus infection in mice

DT-5461 enhanced host resistance to Sendai virus infection in mice. Intranasal (i.n.) administration of 200 micrograms of DT-5461 per mouse 3 days before infection was the most effective administration route, dose and timing. DT-5461 enhanced the cytotoxicity of murine natural killer (NK) cells. In addition, DT-5461 activated murine peritoneal macrophages, resulted in augmented of cytotoxicity and the induction of tumor necrosis factor-alpha (TNF-alpha). Therefore, these immunomodulating activities presented by DT-5461 caused protection against Sendai virus infection.

Differences in interleukin 1 (IL-1), IL-6, tumor necrosis factor and IL-1 receptor antagonist production by human monocytes stimulated with muramyl dipeptide (MDP) and its stearoyl derivative, romurtide

The immunostimulatory reagents muramyl dipeptide (MDP) and its stearoyl derivative romurtide [MDP-Lys(L18)] were assessed for cytokine inducing activity in human monocytes. Both MDP and romurtide stimulated the production of interleukin-1 (IL-1), IL-6, tumor necrosis factor (TNF) and IL-1 receptor antagonist (IL-1Ra). Kinetics study indicated that IL-1, TNF and IL-1Ra were induced after 4 h stimulation but IL-6 was produced at a later phase. Romurtide induced these cytokines for longer period that MDP. Dose-response study indicated that romurtide was far more potent than MDP in induction of IL-1, IL-6 and TNF. Although the magnitude of the IL-1 and IL-6 induction was almost the same, that of TNF induction was greater in romurtide-stimulated monocytes than in MDP-stimulated cells. Among IL-1, IL-1 beta appeared to be a major product. In contrast to other cytokines, IL-1Ra was induced by MDP and romurtide in a similar dose and time dependent manner with similar magnitude of response. These studies indicate that MDP and romurtide, especially romurtide, are very potent inducers of both immunostimulatory and immunosuppressive cytokines by human monocytes but with different efficacy and kinetics.

MDP-Lys(L18), a lipophilic derivative of muramyl dipeptide, inhibits the metastasis of haematogenous and non-haematogenous tumours in mice

The antimetastatic effects of MDP-Lys(L18), a lipophilic derivative of muramyl dipeptide (MDP), against three different types of highly metastatic murine tumour cells, B16-BL6 melanoma, colon 26-M3.1 carcinoma and L5178Y-ML25 T lymphoma, were examined in C57BL/6, Balb/c and CDF1 mice, respectively. The administration of 100 micrograms of MDP-Lys(L18) 2 or 4 days before tumour inoculation led to a significant decrease in lung metastasis of B16-BL6 melanoma or colon 26-M3.1 carcinoma cells. MDP-Lys(L18) was also effective in the inhibition of liver metastasis of L5178Y-ML25 lymphoma cells by administration 2 or 4 days before tumour inoculation. The prophylactic effect of 100 micrograms of MDP-Lys(L18) on tumour metastasis was evident for the different administration routes, i.e. subcutaneous, intravenous or intranasal injection, or oral administration. It is of prime interest that oral administration of 1 mg of MDP-Lys(L18) induced a significant decrease in lung metastasis of B16-BL6 melanoma cells. Administration of MDP-Lys(L18) 4 days before assay led to induction of tumoricidal activity by peritoneal macrophages and growth inhibition by the sera against B16-BL6 or L929 cells. When MDP-Lys(L18) was subcutaneously administered five times after tumour inoculation to test therapeutic effect in an experimental and spontaneous metastasis model using B16-BL6 melanoma, the consecutive administrations of MDP-Lys(L18) significantly inhibited lung metastasis in tumour-bearing mice. These results suggest that MDP-Lys(L18) is able to enhance host resistance to reduce tumour metastasis and is a potent immunomodulating agent which may be applied prophylactically or therapeutically for the treatment of cancer metastasis.

Anti-viral activity of sulfated chitin derivatives against Friend murine leukaemia and herpes simplex type-1 viruses

Sulfated chitin derivatives, selected for their low toxicity and high inhibitory activity of melanoma metastasis, were examined for anti-viral activity against Friend murine leukaemia, herpes simplex type-1 (HSV) and Sendai viruses. Carboxymethyl chitin with a 7.66% degree of sulfation (SCM-chitin III) showed a significant inhibition of Friend murine leukaemia helper virus (F-MuLV) and HSV, but not of Sendai virus growth in vitro. Sulfated N-deacetylated chitin had a significant but weak activity against F-MuLV and HSV infections. Carboxymethyl chitin showed no effect on these infections in vitro. SCM-chitin III also exhibited anti-viral activity in vivo by suppressing the splenomegaly which was caused by prior infection of mice with FV, a complex of F-MuLV and spleen focus-forming virus.

Review: inducer of cytokines in vivo: overview of field and romurtide experience

We have reported that the bacterial cell-wall skeletons, such as mycobacteria, nocardia, corynebacteria, propionibacteria and listeria, had potent adjuvant activity on immune responses. It was reported that N-acetylmuramyl-L-alanyl-D-isoglutamine (MDP) was the minimum structural requirement of adjuvant activity of the bacterial cell-wall skeleton and a variety of MDP derivatives and related compounds were synthesized. Among the synthetic MDP derivatives, we have selected MDP-Lys(L18)(romurtide) as the immunostimulant, by using experimental models for non-specific host resistance against Escherichia coli in mice. Romurtide was shown to have host-stimulating activity against bacterial, fungal and viral infections, cytokine producing activity and the capacity to increase the number of leukocytes and platelets in experimental models. It was also shown that the clinical effectiveness of romurtide on the restoration of the number of leukocytes and platelets of cancer patients treated with chemotherapy or radiation therapy. The mechanism of action of romurtide is discussed.

Biologic response modifiers as antivirals in immunosuppressed hosts

A wide variety of immunomodulators/biologic response modifiers (BRM) have been demonstrated to provide broad spectrum antiviral activity against both RNA and DNA viruses in several animal species. Dramatic decreases in mortality, reduced virus titers in tissues, and reduced histopathology can be produced. The antivirally effective agents include microbially derived materials, polyanions, cytokines, and chemically diverse small molecular weight chemicals. Antiviral efficacy with BRM treatment has been shown in numerous kinds of immunosuppression, emphasizing the potential for BRM treatment in immunocompromised patients. The greatest protective effects are observed with prophylactic or early therapeutic treatment. BRMs act indirectly, most likely by activating cells and/or inducing antiviral mediators early in the course of viral pathogenesis. In general, viral specific immune responses in BRM-treated and infected mice are absent or similar to those in untreated mice. Because BRMs are pleiotropic in their immunomodulatory effects, it has been difficult to establish whether one cell type or mediator is critical for the broad spectrum antiviral activity. Interferon appears to be critical for some small molecular weight synthetic compounds, but does not appear to explain all the antiviral activity of certain large molecular weight polyanions. Whether there is a unified antiviral mechanism among different BRMs remains to be determined.

Synthetic immunoadjuvants: application to non-specific host stimulation and potentiation of vaccine immunogenicity

It is well recognized that immunoadjuvants mainly play two roles; non-specific stimulation of host resistance against infections and cancer, and the potentiation of vaccine immunogenicity. This article reviews the recent results of the development of synthetic immunoadjuvants in our laboratory with special reference to muramyldipeptide (MDP), trehalose dimycolate (TDM), lipid A, chitin and their related compounds. The usefulness of MDP derivative MDP-Lys(L18), which has recently gone on the market as a haematopoietic agent for restoration of leukopenia in cancer patients treated with radiotherapy and chemotherapy, is reviewed. The various approaches to application of synthetic immunoadjuvants to the potentiation of vaccine immunogenicity, including adjuvant formulation, are also discussed.

B30-MDP, a synthetic muramyl dipeptide derivative for tumour vaccination to enhance antitumour immunity and antimetastatic effect in mice

The effect of a muramyl dipeptide derivative (B30-MDP) on the augmentation of antitumour immunity against highly metastatic L5178Y-ML25 mouse lymphoma cells was examined in CDF1 (Balb/c x DBA/2) mice. Mice immunized with a mixture of X-irradiated tumour cells (10(3)) and B30-MDP (100 micrograms) on 7 days prior to challenge by viable tumour cells displayed a significant decrease in metastasis towards the target organs, liver and spleen, compared with that of untreated mice. Immunization of mice with the mixture on day 5 or 7 after tumour challenge, when the level of glutamic-pyruvic transaminase (GPT) and glutamic-oxaloacetic transaminase (GOT) in sera of mice inoculated with viable tumour cells was observed to be normal, caused less metastasis than immunization with X-irradiated tumour cells alone. Sensitization with X-irradiated tumour cells admixed with B30-MDP induced almost two times higher cytotoxicity of spleen cells against L5178Y-ML25 lymphoma cells than sensitization with X-irradiated tumour cells without B30-MDP. In contrast, cytotoxic activity of spleen cells against another target, L1210 lymphoma cells derived from BDF1 mice, was not observed by immunization with X-irradiated L5178Y-ML25 cells with or without B30-MDP. Specific lysis by splenic cells of the immunized mice against L5178Y-ML25 cells decreased to the normal level when T cells were deleted from the immunized spleen cells by the treatment of rabbit anti-mouse Thy1.2 antibody and rabbit complement. These results indicate that B30-MDP is able to augment a specific tumour immunity due to the enhancement of cytotoxicity mediated by T lymphocytes, and is useful as an immunopotentiating agent for active immunization of inactivated tumour cells.

Stimulation of host-defense mechanism with synthetic adjuvants and recombinant cytokines against viral infection in mice

The efficacy of synthetic immunoadjuvants and recombinant cytokines for the potentiation of host-resistance against virus infection was investigated using mouse models infected with Sendai virus and herpes simplex type 1 virus (HSV). The synthetic MDP derivative, MDP-Lys(L18), and recombinant cytokines, IL-1 beta, IFN-gamma, G-CSF and GM-CSF were shown to be effective for the stimulation of nonspecific protection against Sendai virus infection in mice. Both MDP-Lys(L18) and GM-CSF were effective for the protection against HSV infection in cyclophosphamide (CY)-treated mice. B30-MDP was suggested to be useful as an immunoadjuvant for the potentiation of antigenicity of recombinant or component vaccines.

Prophylactic activity of dihydroheptaprenol, a synthetic polyprenol derivative, against Sendai virus infection in mice

The effect of a chemically synthesized polyprenol derivative, dihydroheptaprenol (DHP), on the non-specific resistance of mice to Sendai virus infection was investigated. The mice that received 200 micrograms of DHP intranasally twice, at 3 days and 1 day before the infection, showed a significant protection against Sendai virus infection. Treatment of mice twice even with as much as 2000 micrograms of DHP through the subcutaneous route, however, had no protective effect against infection. Excess interferon and tumour necrosis factor production in intranasally DHP-treated mice was seen 1 day after the infection when compared with Sendai virus alone controls or with DHP alone controls. Variance analysis of these findings indicates a prophylactic activity of DHP in pulmonary viral infections.

Protective activity of recombinant cytokines against Sendai virus and herpes simplex virus (HSV) infections in mice

The efficacy of recombinant cytokines such as murine interferon-gamma (IFN-gamma), human granulocyte colony-stimulating factor (G-CSF), mouse granulocytic-macrophage colony-stimulating factor (GM-CSF) and human interleukin-1 beta (IL-1 beta) has been examined for augmentation of host resistance against Sendai virus and herpes simplex virus (HSV) infections. All four cytokines were found to protect mice against Sendai virus infection. IFN-gamma afforded protection when administered intranasally but not intravenously several days before the infection. Intranasal administration of G-CSF one day before the infection was the most effective administration route and timing. Intranasal administration of GM-CSF was found to afford protection 1 or 3 days before the infection. IL-1 beta demonstrated therapeutic activity against Sendai virus infection after intranasal administration on the same day as the infection. When each of the cytokines was administered subcutaneously four times daily into cyclophosphamide-treated mice before intravenous infection with HSV, only GM-CSF revealed any protective activity.