Uveitis induction in the rabbit by muramyl dipeptides

Conjunctival epitheliopathy induced by topical exposure to bacterial peptidoglycan, muramyl dipeptide

Noninfectious exudative conjunctivitis can be experimentally produced in rabbits by application of the apoptogenic bacterial cell wall peptidoglycan, muramyl dipeptide (MDP) to the ocular surface. The purpose of this study was to investigate the acute conjunctival cytopathology induced by unilateral ocular surface exposure to MDP. Hematoxylin and eosin staining assessed bilateral tear cytopathology and conjunctival histopathology. The caspases levels in conjunctival tissue and tears were measured in standard assays utilizing p-nitroanaline tagged caspase-specific substrates. Immunofluorescent antibody identified intracellular caspase-3, nuclear factor-κβ (NF-κβ), and oxidative DNA damage (8-OHdG; 8-oxo-2'-deoxyguanosine) in tear and conjunctiva cells. DNA extracted from conjunctival tissues and pooled tear fluids were visualized by ethydium bromide agarose gel electrophoresis. Onset of ipsilateral conjunctivitis was due to an epitheliopathy characterized by loss of conjunctival epithelial cell adherence, exuviation of conjunctival epithelial cells, and neutrophil infiltration. Caspase-3 levels were significantly higher in exuviated cells in ipsilateral than contralateral tear (p's ≤ 0.001) collected at 3-5 h post MDP. Significantly higher caspase-2, -3, -6, -8 and -9 (p's ≤ 0.03) levels were detected in ipsilateral than contralateral conjunctival tissue at 5 h. Polymeric DNA was detected in ipsilateral but not contralateral conjunctival tissue and tears. Caspase-3, NF-κβ, and 8-OHdG positive neutrophils were detected in bilateral conjunctiva and tear. The caspase-3/NF-κβ epithelial cells and polymeric DNA in conjunctival tissue and shedding of caspase positive cells and polymeric DNA into ipsilateral tears support MDP induction of acute programmed cell death in vivo. The results suggest that ipsilateral exudative conjunctivitis is due to acute caspase-mediated conjunctival epitheliopathy induced by topical exposure to the bacterial peptidoglycan MDP.

Exploration of Pattern Recognition Receptor Agonists as Candidate Adjuvants

Adjuvants are used to maximize the potency of vaccines by enhancing immune reactions. Components of adjuvants include pathogen-associated molecular patterns (PAMPs) and damage-associate molecular patterns (DAMPs) that are agonists for innate immune receptors. Innate immune responses are usually activated when pathogen recognition receptors (PRRs) recognize PAMPs derived from invading pathogens or DAMPs released by host cells upon tissue damage. Activation of innate immunity by PRR agonists in adjuvants activates acquired immune responses, which is crucial to enhance immune reactions against the targeted pathogen. For example, agonists for Toll-like receptors have yielded promising results as adjuvants, which target PRR as adjuvant candidates. However, a comprehensive understanding of the type of immunological reaction against agonists for PRRs is essential to ensure the safety and reliability of vaccine adjuvants. This review provides an overview of the current progress in development of PRR agonists as vaccine adjuvants, the molecular mechanisms that underlie activation of immune responses, and the enhancement of vaccine efficacy by these potential adjuvant candidates.

Structural Fine-Tuning of Desmuramylpeptide NOD2 Agonists Defines Their In Vivo Adjuvant Activity

We report on the design, synthesis, and biological evaluation of a series of nucleotide-binding oligomerization-domain-containing protein 2 (NOD2) desmuramylpeptide agonists with improved in vitro and in vivo adjuvant properties. We identified two promising compounds: 68, a potent nanomolar in vitro NOD2 agonist, and the more lipophilic 75, which shows superior adjuvant activity in vivo. Both compounds had immunostimulatory effects on peripheral blood mononuclear cells at the protein and transcriptional levels, and augmented dendritic-cell-mediated activation of T cells, while 75 additionally enhanced the cytotoxic activity of peripheral blood mononuclear cells against malignant cells. The C₁₈ lipophilic tail of 75 is identified as a pivotal structural element that confers in vivo adjuvant activity in conjunction with a liposomal delivery system. Accordingly, liposome-encapsulated 75 showed promising adjuvant activity in mice, surpassing that of muramyl dipeptide, while achieving a more balanced Th1/Th2 immune response, thus highlighting its potential as a vaccine adjuvant.

Interplay of oxidative stress and antioxidant bio markers in oil adjuvant Brucella melitensis vaccinated and challenged mice

The intracellular nature of Brucella leads to rise in oxidative stress due to bacterial invasion, particularly at the site of predilection spleen and lymph nodes. The present study aimed to evaluate the erythrocytic and tissue specific oxidative stress responses induced during oil adjuvant killed Brucella melitensis vaccination. The results of the study clearly implicated a significant increase in level of catalase, and superoxide dismutase (SOD) activity and lipid peroxidation (LPO), and total protein content in erythrocytes after vaccination. The activity of glutathione-S-transferase (GST) was unaltered during the period of experiment. The catalase activity and GSH content was significantly increased in lung and spleen tissues. The tissues GST levels increased significantly in all tissues, while tissue SOD level increased significantly only in lung tissues. Thus, it can be inferred that oil adjuvant based Brucella vaccine induces negligible signs of inflammatory pathophysiology and supports the development of significant level of protection against virulent Brucella challenge.

A novel vaccinological evaluation of intranasal vaccine and adjuvant safety for preclinical tests

Vaccines are administered to healthy humans, including infants, so the safety and efficacy must be very high. Therefore, evaluating vaccine safety in preclinical and clinical studies, according to World Health Organization guidelines, is crucial for vaccine development and clinical use. A change in the route of administration is considered to alter a vaccine's immunogenicity. Several adjuvants have also been developed and approved for use in vaccines. However, the addition of adjuvants to vaccines may cause unwanted immune responses, including facial nerve paralysis and narcolepsy. Therefore, a more accurate and comprehensive strategy must be used to develope next-generation vaccines for ensuring vaccine safety. Previously, we have developed a system with which to evaluate vaccine safety in rats using a systematic vaccinological approach and 20 marker genes. In this study, we developed a safety evaluation system for nasally administered influenza vaccines and adjuvanted influenza vaccines using these marker genes. Expression of these genes increased dose-dependent manner when mice were intranasally administered the toxicity reference vaccine. When the adjuvant CpG K3 or a CpG-K3-combined influenza vaccine was administered intranasally, marker gene expression increased in a CpG-K3-dose-dependent way. A histopathological analysis indicated that marker gene expression correlated with vaccine- or adjuvant-induced phenotypic changes in the lung and nasal mucosa. We believe that the marker genes expression analyses will be useful in preclinical testing, adjuvant development, and selecting the appropriate dose of adjuvant in nasal administration vaccines.

Preclinical Toxicology of Vaccines1

Immunity to targeted infectious diseases may be conferred or enhanced by vaccines, which are manufactured from recombinant forms as well as inactivated or attenuated organisms. These vaccines have to meet requirements for safety, quality, and efficacy. In addition to antigenic components, various adjuvants may be included in vaccines to evoke an effective immune response. To ensure the safety of new vaccines, preclinical toxicology studies are conducted prior to the initiation of, and concurrently with, clinical studies. There are five different types of preclinical toxicology study in the evaluation of vaccine safety: single and/or repeat dose, reproductive and developmental, mutagenicity, carcinogenicity, and safety pharmacology. If any adverse effects are observed in the course of these studies, they should be fully evaluated and a final safety decision made accordingly. Successful preclinical toxicology studies depend on multiple factors including using the appropriate study designs, using the right animal model, and evoking an effective immune response. Additional in vivo and in vitro assays that establish the identity, purity, safety, and potency of the vaccine play a significant role in assessing critical characteristics of vaccine safety.

The history of MF59(®) adjuvant: a phoenix that arose from the ashes

The first clinical trial of an MF59(®)-adjuvanted influenza vaccine (Novartis) was conducted 20 years ago in 1992. The product that emerged (Fluad(®), Novartis) was licensed first in Italy in 1997 and is now licensed worldwide in 30 countries. US licensure is expected in the coming years. By contrast, many alternative adjuvanted vaccines have failed to progress. The key decisions that allowed MF59 to succeed in such a challenging environment are highlighted here and the lessons that were learned along the way are discussed. MF59 was connected to vaccines that did not succeed and was perceived as a 'failure' before it was a success. Importantly, it never failed for safety reasons and was always well tolerated. Even when safety issues have emerged for alternative adjuvants, careful analysis of the substantial safety database for MF59 have shown that there are no significant concerns with widespread use, even in more 'sensitive' populations.

Repetitive peptide boosting progressively enhances functional memory CTLs

Cytotoxic T lymphocytes (CTLs) play a critical role in controlling intracellular pathogens and cancer cells, and induction of memory CTLs holds promise for developing effective vaccines against critical virus infections. However, generating memory CTLs remains a major challenge for conventional vector-based, prime-boost vaccinations. Thus, it is imperative that we explore nonconventional alternatives, such as boosting without vectors. We show here that repetitive intravenous boosting with peptide and adjuvant generates memory CD8 T cells of sufficient quality and quantity to protect against infection in mice. The resulting memory CTLs possess a unique and long-lasting effector memory phenotype, characterized by decreased interferon-γ but increased granzyme B production. These results are observed in both transgenic and endogenous models. Overall, our findings have important implications for future vaccine development, as they suggest that intravenous peptide boosting with adjuvant following priming can induce long-term functional memory CTLs.

Multiple caspases mediate acute renal cell apoptosis induced by bacterial cell wall components

The stimulus for caspase-mediated renal cell apoptosis in septic acute renal failure (ARF) is unclear. To demonstrate the nephrotoxic effects of bacterial cell wall components, the anti-cellular activity of bacterial muropeptides (muramyl dipeptides), peptidoglycans, and lipopolysaccharides was investigated in rabbit kidney cells. Changes in the cell membrane (APOPercentage™ dye uptake), caspase activities, and DNA degradation were quantified colorimetrically and using densitometric assays and their inhibition by caspase-specific and pan-caspase inhibitors was determined. The onset and levels of APOPercentage™ dye-positive rabbit kidney cells, caspase activities, and DNA degradation were closely associated. Specific caspase-1, -2, -3, -4, -8, -10, and -12 inhibitors reduced caspase-3 activity by ≥40%, but only caspase-3 and -8-specific inhibitors reduced apoptotic DNA levels. Pan-caspase inhibitor Q-VD-OPh was 10-fold more effective at inhibiting rabbit kidney cell death, caspase activation, and DNA degradation than caspase-family inhibitor Z-VAD-FMK. Apoptosis was inhibited effectively by both pan-caspase inhibitors when applied early during the stimulus-to-response period. Multiple initiator and effector caspases were activated suggesting extrinsic, intrinsic, and endoplasmic reticulum/stress apoptotic pathway stimulation in rabbit kidney cells treated with bacterial cell wall components. The results provide in vitro support for bacterial cell wall-induced apoptosis as a pathogenic mechanism of renal cell death in septic ARF and support the potential prophylactic use of pan-caspase inhibitors to suppress septic ARF.

Virus-like particle vaccines and adjuvants: the HPV paradigm

Complex antigen structures currently represent the most-studied approach for prophylactic as well as therapeutic vaccines. Different types of complex vaccines, including virus-like particles and virosomes, have been developed depending on the nature of the viral pathogen they are trying to replicate (enveloped vs naked) or the modality to express antigenic epitopes (i.e., the binding of envelope protein on liposomic structures). The complex structure of these vaccines provides them with some adjuvanted properties, not uniformly present for all virus-like particle types. The further inclusion of specific adjuvants in vaccine preparations can modify the presentation modality of such particles to the immune system with a specific Th1 versus Th2 polarization efficacy. A paradigm of the relevance of these new adjuvants are the immunological results obtained with the inclusion of monophosphoryl lipid A adjuvant in the formulation of L1-based human papillomavirus-naked virus-like particles to reduce a Th1 cellular immunity impairment, peculiar for alum-derived adjuvants, along with the induction of highly enhanced humoral and memory B-cellular immunity.

Effect of muramyl peptides on mitochondrial respiration

Muramyl peptides have been shown to exert several biological activities including potentiation of humoral and cell-mediated immunity and stimulation of natural resistance. The mode of action of muramyl peptides has not been elucidated fully and the immunological activities of some derivatives have been associated with toxic effects, including pyrogenicity and inflammatory reactions. Nevertheless, the impact of muramyl peptides on mitochondrial respiration has never been addressed. In this study, the in vitro effects of muramyl peptides on rat liver mitochondria were examined. Toxic muramyl peptides induced a significant decrease in respiratory control ratio versus non-toxic analogues. These results were confirmed by in vivo studies in mice and were extended to mitochondria isolated from spleens. Our data address, for the first time, the effect of muramyl peptides on mitochondrial bioenergetics. Further studies are required to reveal the mechanism of mitochondrial toxicity in relation to the damaging effects of toxic muramyl peptides.

Intracameral Toxicity of Bacterial Components Muramyl Dipeptide and Staurosporine: Ciliary Cyst Formation, Epithelial Cell Apoptosis and Necrosis

The uveitogenic bacterial cell wall component muramyl dipeptide (MDP) is apoptogenic in rabbit kidney cells. The purpose of this investigation was to assess the cytotoxic activity of MDP and staurosporine (STSP; induces cultured corneal and lens cells apoptosis) in rabbit ciliary body tissue. Anterior uveitis was determined by clinical symptoms and increased aqueous humor (AH) protein. Ciliary body tissue was assessed for histological changes, caspase-3 activity, dye uptake, distribution of immunoreactive caspase-3 and DNA ladders at 4 and 6 hours postinjection. Increases in caspase-3 activity, APOPercentage dye uptake, and localization of immunoreactive caspase-3 in ciliary epithelial cells were associated with ciliary cysts of detached nonpigmented epithelial (NPE) cells, as well as apoptotic and necrotic DNA ladders in ciliary body tissues from eyes injected with MDP and/or STSP. The results suggest that intracameral injection of the bacterial components MDP and STSP can induce acute endophthalmic changes in uveal tissue including formation of ciliary body, NPE and pigmented epithelial (PE) cell apoptosis, and ciliary body tissue necrosis.

NOD2, the gene responsible for familial granulomatous uveitis, in a mouse model of uveitis

PURPOSE

NOD2 plays an important role in the recognition of intracellular bacteria through its ability to sense the components of bacterial peptidoglycan (PGN), namely muramyl dipeptide (MDP) and muramyl tripeptide (MTP). Specific mutations in the human NOD2 gene cause Blau syndrome, an autosomal dominant form of uveitis, arthritis, and dermatitis. As a first step toward understanding the role of NOD2 in the pathogenesis of uveitis, the authors developed a mouse model of MDP-dependent uveitis.

METHODS

BALB/c mice and mice deficient in L-selectin or NOD2 received intravitreal injection of MDP, MTP, or PGN. The intravascular response within the iris and cellular infiltration was quantified by intravital microscopy and histologic assessment.

RESULTS

MDP induced an acute, ocular inflammatory response, wherein rolling and adhering leukocytes within the vasculature were significantly increased within 6 hours after MDP treatment. A minor increase in cellular infiltration occurred at 12 hours after MDP treatment. The adhesion molecule L-selectin participated in MDP-induced vascular inflammation because L-selectin knockout mice showed a significant decrease in the number of rolling cells. Importantly, NOD2 plays an essential role in ocular inflammation induced by MDP, as indicated by the fact that uveitis did not develop in Nod2 knockout mice in response to MDP. Nod2 knockout mice also showed abolished ocular inflammation in response to MTP but not to PGN treatment.

CONCLUSIONS

These findings demonstrate a novel mouse model of uveitis, wherein NOD2 plays an essential role in inflammation induced by the minimal components of PGN. Thus, innate immune responses mediated by NOD2 may participate in the development of uveitis in response to bacterial products.

MF59 is a safe and potent vaccine adjuvant that enhances protection against influenza virus infection

In preclinical studies, MF59 adjuvant offered improved protection against influenza virus challenge and significantly reduced the viral load in the lungs of challenged mice. In humans, MF59 is a safe and potent vaccine adjuvant that has been licensed in more than 20 countries (Fluad [Novartis Vaccines and Diagnostics Inc., MA, USA]). The safety profile of an MF59-adjuvanted vaccine is well established through a large safety database. MF59 adjuvant has had a significant impact on the immunogenicity of influenza vaccines in the elderly and in adults who are chronically ill. MF59 has also been shown to have a significant impact on the immunogenicity of pandemic influenza vaccines. MF59 allows for broader cross-reactivity against viral strains not included in the vaccine. MF59 has been shown to be more potent for both antibody and T-cell responses than aluminum-based adjuvants. MF59 has broad potential to be used as a safe and effective vaccine adjuvant for a wide range of vaccine types.

Vaccine adjuvants revisited

The development of new adjuvants for human vaccines has become an expanding field of research in the last thirty years, for generating stronger vaccines capable of inducing protective and long-lasting immunity in humans. Instead of such efforts, with several adjuvant strategies approaching to requirements for their clinical application, limitations like adjuvant toxicity remain to be fully surpassed. Here we summarize the current status of adjuvant development, including regulatory recommendations, adjuvant requirements, and adjuvant categories like mineral salts, tensoactive compounds, microorganism-derived adjuvants, emulsions, cytokines, polysaccharides, nucleic acid-based adjuvants, and a section dedicated to particulate antigen delivery systems. The mechanisms of adjuvanticity are also discussed in the light of recent findings on Toll-like receptors' biology and their involvement on immune activation.

Clinical safety of HIV lipopeptides used as vaccines in healthy volunteers and HIV-infected adults

BACKGROUND

HIV-1 lipopeptides have been developed by the French National Agency for AIDS Research (ANRS) for use as candidate vaccine against HIV since 1994. Between 1996 and 2005, four different lipopeptide constructs were tested alone or in combination with recombinant canarypox HIV vaccines in 10 trials conducted in France. The aim of this study was to review clinical safety of HIV lipopeptides.

METHODS

A meta-analysis based on individual subject data examined clinical safety data collected in eight preventive trials and two therapeutic trials enrolling 200 HIV-1-uninfected healthy volunteers and 48 HIV-1-infected patients.

RESULTS

Of 248 trial participants, eight (3.2%) did not complete follow-up: seven among the 200 healthy volunteers, and one among the 48 HIV-1 infected patients. During the 354 person-years of follow-up, 860 lipopeptides injections were administered. Local reactions were common. However, in trials where lipopeptides were tested without adjuvant and appropriate diluents, none of the vaccinees experienced severe local response. Systemic reactions were generally mild and transient. No grade 4 reaction was reported; 18 subjects experienced grade 3 systemic events related to the vaccination, mainly asthenia, fever, headache and arthralgia. Multivariate analysis showed that female sex, number of injections and diluent (more reactions in 5% glucose alone than in combination with Tris-HCl buffer) significantly increased systemic reactions related to the vaccination.

CONCLUSION

These data demonstrate that reactogenicity and systemic safety of HIV lipopeptides vaccine are acceptable both in healthy volunteers and HIV-infected adults.

Novel human polysaccharide adjuvants with dual Th1 and Th2 potentiating activity

Pure soluble, recombinant and synthetic antigens, despite their better tolerability, are unfortunately often much less immunogenic than live or killed whole organism vaccines. Thus, the move towards the development of safer subunit vaccines has created a major need for more potent adjuvants. In particular, there is an urgent need for adjuvants capable of boosting cellular (Th1) immunity but without unacceptable toxicity. The adjuvant activity of aluminium compounds (aluminium phosphate or hydroxide) was first described by Glenny and colleagues in 1926. Surprisingly, despite the description of over one hundred adjuvants in the scientific literature, alum remains the only adjuvant approved for human use in the USA. Unfortunately, alum has no effect on cellular immunity and is faced with increasing concerns regarding potential for cumulative aluminium toxicity. Why then has alum not been replaced in human vaccines? Despite the enormous number of candidates, potency has invariably been associated with increased toxicity, and this more than anything else has precluded their use, particularly in prophylactic vaccines where safety issues are paramount. Hence, there is a major unmet need for a safe efficacious adjuvant capable of boosting cellular plus humoral immunity. The extensive data on inulin-based adjuvants indicate that these are excellent candidates to replace alum as the adjuvant of choice for many vaccines. Particular advantages offered by inulin-based adjuvants is that they induce cellular in addition to humoral immunity and offer excellent safety, tolerability, ease of manufacture and formulation. Thus, adjuvants based on inulin have enormous potential for use in vaccines against both pathogens and cancer.

Surface calreticulin mediates muramyl dipeptide-induced apoptosis in RK13 cells

Calreticulin (CRT) is a binding protein for apoptotic N-acetylmuramyl-L-alanyl-D-isoglutamine (L,D-MDP) or peptidoglycan in RK(13) cells. CRT on RK(13) cell surface (srCRT) forms complex(es) with tumor necrosis factor receptor 1 (TNFR1) and TNFR-associated death domain (TRADD) protein of the cell membrane. CRT polyclonal or monoclonal antibody binding to RK(13) srCRT dose-dependently inhibited L,D-MDP-induced apoptosis. In RK(13) cells, L,D-MDP up-regulated the TNFR1.TRADD complex of the plasma membrane and subsequently induced cytosolic TRADD-Fas-associated death domain protein complex. Biotinylated srCRT was capable of calcium-dependent binding of Sepharose-immobilized L,D-MDP or peptidoglycan. However, Toll-like receptors TLR-2 and TLR-4, Nod2, and CD14 of RK(13) cells did not specifically bind Sepharose-immobilized L,D-MDP. High concentrations (5-40 mm) of EGTA dose-dependently inhibited free L,D-MDP binding to purified RK(13) cell CRT and promoted free L,D-MDP dissociation from RK(13) cell CRT.MDP complex. Different concentrations of EGTA (0-40 mm) added to Dulbecco's modified essential medium with 1.8 mm calcium or phosphate-buffered saline with 0.18 mm calcium have different effects on medium free calcium concentrations but have identical inhibiting effects on L,D-MDP-induced apoptosis. More inhibition of the L,D-MDP-induced apoptotic DNA ladders and caspase-3 activity in RK(13) cells was obtained with EGTA pretreatment (83%) than just EGTA + L,D-MDP (47%). The knocking down of srCRT by antisense oligonucleotide CRTAS121 (250 nmol/ml) and stealth small interfering RNA CRT_siR479 (150 pm/ml) for 2 days (44 and 66%, respectively), resulted in the inhibition of L,D-MDP-induced caspase-3 activity (47 and 65%, respectively). The results suggest that (a) the binding of L,D-MDP to srCRT is calcium-dependent, i.e. on srCRT-bound calcium, and (b) it is srCRT, not TLR-2, TLR-4, Nod2 or CD14, that mediates L,D-MDP-induced RK(13) cell apoptosis through activating the TNFR1. TRADD-Fas-associated death domain protein apoptotic pathway.

Vaccine adjuvants: current state and future trends

The problem with pure recombinant or synthetic antigens used in modern day vaccines is that they are generally far less immunogenic than older style live or killed whole organism vaccines. This has created a major need for improved and more powerful adjuvants for use in these vaccines. With few exceptions, alum remains the sole adjuvant approved for human use in the majority of countries worldwide. Although alum is able to induce a good antibody (Th2) response, it has little capacity to stimulate cellular (Th1) immune responses which are so important for protection against many pathogens. In addition, alum has the potential to cause severe local and systemic side-effects including sterile abscesses, eosinophilia and myofascitis, although fortunately most of the more serious side-effects are relatively rare. There is also community concern regarding the possible role of aluminium in neurodegenerative diseases such as Alzheimer's disease. Consequently, there is a major unmet need for safer and more effective adjuvants suitable for human use. In particular, there is demand for safe and non-toxic adjuvants able to stimulate cellular (Th1) immunity. Other needs in light of new vaccine technologies are adjuvants suitable for use with mucosally-delivered vaccines, DNA vaccines, cancer and autoimmunity vaccines. Each of these areas are highly specialized with their own unique needs in respect of suitable adjuvant technology. This paper reviews the state of the art in the adjuvant field, explores future directions of adjuvant development and finally examines some of the impediments and barriers to development and registration of new human adjuvants.

Stereo-isomer specific induction of renal cell apoptosis by synthetic muramyl dipeptide (N-acetylmuramyl-L-alanyl-D-isoglutamine)

The cytotoxicity of bacterial cell wall components, muramyl dipeptide (synthetic N-acetylmuramyl-L-alanyl-D-isoglutamine; L,D-MDP) and lipopolysaccharide (LPS), was investigated in several kidney cell lines. MDP and LPS were toxic to rabbit and monkey kidney cells, MDP was toxic to canine kidney cells, but not to human or porcine kidney cells. Notably, L,D-MDP was >100-fold more cytotoxic/microg than the D,D-MDP and L,L-MDP, as well as LPS. L,D-MDP and analogs containing L,D-MDP were the most widely cytotoxic of the MDP tested. The MDP-induced cytotoxicity was characterized as apoptosis by DAPI staining and DNA laddering. The acute rabbit kidney (RK13) cell apoptosis (cell death in < 5 h) induced by apical or basal application of MDP was associated with glutamate (Glu) release, decreased gamma-glutamyltranspeptidase (GGT) and acidosis and was suppressed by Indomethacin, Naproxen and Curcumin. The cytotoxic activity of L,D-MDP was decreased significantly by 24 h incubation in human sera. Aged (> 2 year-old) rabbits that apparently failed to quickly clear and excrete a uveitogenic dose of MDP within 24 h died in I week. The results indicate that minute amounts (5 ng/ml) of MDP containing L-alanyl-D-isoglutamine can induce renal cell apoptosis in vitro and support MDP-induced kidney cytotoxicity in rabbits. Also, the results indicate that MDP in sera can be detected utilizing the RK13 cell bioassay and that failure to rapidly clear and excrete L,D-MDP is associated with uveitis and death in aged rabbits.

The development and use of vaccine adjuvants

Interest in vaccine adjuvants is intense and growing, because many of the new subunit vaccine candidates lack sufficient immunogenicity to be clinically useful. In this review, I have emphasized modern vaccine adjuvants injected parenterally, or administered orally, intranasally, or transcutaneously with licensed or experimental vaccines in humans. Every adjuvant has a complex and often multi-factorial immunological mechanism, usually poorly understood in vivo. Many determinants of adjuvanticity exist, and each adjuvanted vaccine is unique. Adjuvant safety is critical and can enhance, retard, or stop development of an adjuvanted vaccine. The choice of an adjuvant often depends upon expensive experimental trial and error, upon cost, and upon commercial availability. Extensive regulatory and administrative support is required to conduct clinical trials of adjuvanted vaccines. Finally, comparative adjuvant trials where one antigen is formulated with different adjuvants and administered by a common protocol to animals and humans can accelerate vaccine development.

Improving vaccine performance with adjuvants

New vaccines are presently under development and in testing for the control of infectious diseases, including human immunodeficiency virus (HIV) and tuberculosis. Several of these vaccines are composed of synthetic, recombinant, or highly purified subunit antigens. Subunit vaccines are designed to include only the antigens required for protective immunization and to be safer than whole-inactivated or live-attenuated vaccines. However, the purity of the subunit antigens and the absence of the self-adjuvanting immunomodulatory components associated with attenuated or killed vaccines often result in weaker immunogenicity. Immunologic adjuvants are agents that enhance specific immune responses to vaccines. Formulation of vaccines with potent adjuvants is an attractive approach for improving the performance of vaccines composed of subunit antigens. Adjuvants have diverse mechanisms of action and should be selected for use on the basis of the route of administration and the type of immune response (antibody, cell-mediated, or mucosal immunity) that is desired for a particular vaccine.

The effect of Syntex adjuvant formulation (SAF-m) on humoral immunity to the influenza virus in the mouse

Syntex adjuvant in its microfluidized form (SAF-m) was equal to or superior to Freund's complete adjuvant in stimulating an enhanced hemagglutination inhibition (HI) antibody response in mice to trivalent influenza virus vaccine (TIV). There was an average 16-fold increase in HI titer for the three components of the vaccine with no significant differences among strains. The increased serum antibodies correlated with an increase in protection against infection. The threonyl-MDP (t-MDP) component of the adjuvant played no role in this activity. The vehicle, in contrast, was so effective that it could be diluted 1:202 (in the presence of (t-MDP) and still retain a statistically significant effect. Vaccine and adjuvant could be stored together at 4 degrees C for 2 years without a statistically significant change in potency. Mice were given a priming immunization with TIV, PBS, or adjuvanted TIV (AIV). A year later, the mice were boosted with heterotypic TIV or AIV. The nature of the priming immunization made no difference in the strong antibody response to an AIV boost. However, priming significantly improved the response to TIV with AIV being the best primer. The enhancement in the antibody response to AlShanghai of the unprimed (PBS) elderly mice caused by AIV (14-fold improvement over TIV) was similar to that in young mice. Female mice had antibody titers which overall were 2.6-fold higher than those of males (P < 0.0001) for AIV and TIV.

Enhancement by muramyl peptides of the protective response of interferon-alpha/beta against encephalomyocarditis virus infection

The use of interferon-alpha (IFN-alpha) in the treatment of infectious diseases has shown limited efficacy and dose-limiting toxicity. We have selected safe immunomodulators of the muramyl peptide family with the potential of enhancing the efficacy of IFN-alpha without resulting in increased toxicity. One of these synthetic muramyl dipeptide (MDP) derivatives, namely murabutide which is in a clinical stage of development, has been recently found to synergize with IFN-alpha 2a in the selective induction of anti-inflammatory mediators and to enhance the biological activities of the therapeutic cytokine. The present study was performed to assess the antiviral activity of such muramyl peptides and a possible potentiation of the antiviral activity of IFN-alpha/beta by associated therapy using the classical assay of Encephalomyocarditis virus (EMCV) infection. In vitro, pretreatment of Moloney Sarcoma virus (MSV)-transformed cell line with MDP derivatives followed by treatment with IFN-alpha/beta showed a synergistic protection against the cytopathogenic effect of a subsequent EMCV infection. None of the MSV cultures could be protected by stimulation with muramyl peptides alone. In vivo, all of the muramyl peptide derivatives tested were found to be more potent than the parent molecule MDP in inducing protection against death or in the prolongation of the mean survival time of infected mice. Sequential administration of suboptimal doses of exogenous IFN-alpha/beta and muramyl peptides established a strong antiviral state and considerably improved the protective effect of the cytokine, frequently leading to an abortive infection. Our findings suggest that combination therapy with safe muramyl peptides and IFN-alpha/beta could constitute a highly effective and new regimen for the treatment of viral infections in humans.

Immunologic adjuvants for modern vaccine formulations

Optimization of the immunogenicity of many new-generation vaccine formulations, including combination vaccines, will require the use of immunologic adjuvants other than the aluminum compounds in today's licensed vaccines. The selection of adjuvants for use in vaccine formulation may be as critical as the choice of the vaccine antigens themselves in providing optimal efficacy for the target populations, vaccine compliance, and cost. Adjuvants have diverse mechanisms of action and must be selected for use based on the immune responses desired for a particular candidate vaccine. Recent advances in the number and variety of adjuvants available for clinical evaluation coupled with the increased understanding of their mechanisms of action encourage the inclusion of adjuvants as part of rational vaccine design. Finally, the proposed standardized methods to evaluate adjuvant safety should be implemented for human candidate vaccines formulated with novel adjuvants.

Immunopharmacological activities and clinical development of muramyl peptides with particular emphasis on murabutide

Certain immunopharmacological activities of muramyl peptides have been associated with inflammatory and undesirable side-effects typically observed following the administration of the prototype molecule muramyl dipeptide. This activity is now demonstrated not to be linked to a direct activation of inflammatory processes in endothelial cells. Neither MDP nor other structural derivatives were able to induce inflammatory cytokines release or E-selectin gene expression in cultured human umbilical vein endothelial cells. However, oral administration of muramyl peptides has been reported to induce certain biological effects, including the downregulation of anamnestic, antigen-specific IgE responses, which are not observed following parenteral administration. We elaborate on these findings and extend them to show the efficacy of a new muramyl peptide in suppressing polyclonally induced serum IgE levels in anti-IgD-treated mice. The comparative effects of muramyl peptides, selected for clinical development, on the induction of cytokines in human whole blood are then presented at the level of mRNA accumulation and protein secretion. Moreover, the cytokine profile induced in vitro and in vivo by the combination of the safe immunostimulant, Murabutide, with interferon-alpha is examined. This combination reveals a selective and beneficial synergistic activity and induces anti-inflammatory cytokines in the absence of synergistic toxicity. The potential and the implications for the use of a therapeutic combination of an immunostimulant with a cytokine are discussed.

The role of adjuvants in retroviral vaccines

The global HIV epidemic continues unchecked. Reports to the World Health Organization's Global Programme on AIDS indicate that more than 14 million persons have become infected with HIV and more than two million have died with AIDS. The spread of AIDS has generated a worldwide mandate for the development of safe and effective vaccines against HIV. Vaccines have been the most effective defense against other viral diseases such as polio and smallpox. However, the development of a vaccine against HIV-1 is a formidable task due to the variation of the virus, inadequate animal models of HIV disease, and the lack of correlates of protective immunity. Several candidate HIV vaccines are composed of synthetic, recombinant, or highly purified subunit antigens. Vaccines composed of subunit antigens generally are considered to be safer than traditional whole-killed or live-attenuated vaccines. However, purified subunit vaccines often are inherently less immunogenic than traditional vaccines. Immunologic adjuvants are agents that act generally to enhance specific immune responses to vaccine antigens. Formulation of experimental HIV vaccines with potent immunologic adjuvants is an attractive approach for amplifying and directing immune responses to highly purified antigens. Alum adjuvants, consisting of aluminum salts, first described in the 1920s, remain the only adjuvants in U.S.-licensed vaccine formulations. Novel adjuvants now undergoing preclinical and clinical testing with experimental subunit vaccine include detoxified lipid A, adjuvant emulsions, liposomes, biodegradable microspheres, muramyl peptides, and saponins. Adjuvants have been shown to elicit cytotoxic T-cell responses as well as antibody to subunit antigens.(ABSTRACT TRUNCATED AT 250 WORDS)

Relevance of the guinea-pig necrotic inflammation footpad reaction to safety concerns with MDP-based adjuvants

The guinea-pig necrotic inflammatory reaction described by Nagao and Tanaka was investigated to determine its possible relevance to tuberculin-positive individuals who may receive MDP-based adjuvants. The reaction was induced by a preparatory footpad injection of Mycobacterium tuberculosis in Freund's incomplete adjuvant (FIA) followed three weeks later by a provocative gluteal injection of muramyl dipeptide (MDP). Increased footpad swelling and necrosis occurred within 24 h. The reaction was also caused to a significantly lesser degree by a gluteal injection of the threonyl-MDP component of Syntex adjuvant SAF-m. Elicitation of the reaction in responsive animals was absolutely dependent on the presence of both FIA and M. tuberculosis at the reaction site. Animals injected in the right footpad with FIA plus M. tuberculosis and in the left footpad with M. tuberculosis alone responded to the provocative injection with necrosis in the right footpad only. The reaction therefore appears to have little potential relevance to the vaccination of tuberculin-positive humans.

Adjuvants and immune enhancement

Adjuvants increase cell-mediated and humoral immune responses to specific antigens. Used with recombinant viral antigens, they can elicit the production of T lymphocytes that lyse target cells, expressing the antigen in a genetically restricted fashion. Adjuvants can augment the production of interferon-gamma, thereby favoring the production of protective antibody isotopes, such as immunoglobulin G2a in the mouse. Modern adjuvants display the efficacy of Freund's complete adjuvant without its side effects. One such adjuvant is Syntex adjuvant formulation, a synthetic analogue of muramyl dipeptide in a microfluidized squalane/squalene-in-water emulsion. Monophosphoryl lipid A in a similar lipid emulsion is also effective. Immune-stimulating complexes of saponin and antigens elicit potent cell-mediated and humoral responses. A purified saponin component has adjuvant activity with reduced side effects; liposomes also can have adjuvant activity. Administering antigens in adjuvants can overcome low responsiveness in very young and old experimental animals and in those that are genetically low responders. Adjuvants are likely components of a new generation of recombinant and subunit vaccines.

Enhancers of nonspecific immunity induce nitric oxide synthase: induction does not correlate with toxicity or adjuvancy

A range of bacterial products and related synthetic compounds, either alone or in combination, enhance nonspecific resistance to infection and tumors. These compounds, which vary in their other properties such as pyrogenicity, toxicity and adjuvancy, were used to assess the hypothesis that nonspecific resistance is mediated by induction of the L-arginine: nitric oxide (NO) pathway. The results obtained show that agents which stimulate nonspecific immunity, such as endotoxin, muramyl dipeptide (MDP) and combinations of monophosphoryl lipid A (MPL) with either trehalose dimycolate (TDM) or MDP cause a substantial induction of Ca(2+)-independent NO synthase in murine lung. In contrast, agents which do not stimulate nonspecific resistance, such as either MPL or TDM alone or threonyl MDP (ThrMDP), do not induce NO synthase. This difference in the ability of MDP and ThrMDP to induce NO synthase in the lung in vivo was also manifest in peritoneal macrophages in vivo as well as being evident in the greater than 100-fold greater potency of MDP in inducing the enzyme in vitro in lung slices. In contrast to the good correlation between induction of NO synthase and induction of nonspecific resistance, no correlation was observed with either the toxic effects of these agents or their adjuvancy.

Polypeptide profiles of normal and inflamed rabbit aqueous humor: identification of catabolic products of immunoglobulin G in the normal eye

The anterior segment of the eye is isolated from the bloodstream by anatomic barriers. These barriers break down during inflammation elicited by muramyl dipeptide (MDP), a component of the cell walls of bacteria. The protein composition of normal aqueous humor and inflamed aqueous were characterized using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. The presence of transferrin, albumin, IgG and IgM were demonstrated in normal and inflamed aqueous. Normal aqueous additionally contained seven polypeptides (35, 31, 29, 25, 22, 21 and 19 kDa, respectively) that were not observed in inflamed aqueous. Four of these peptides (31, 29, 25 and 19 kDa) were identified as fragments of IgG heavy chains based on their reactivity with anti-IgG antibodies and staphylococcal protein A. Immunoglobulin catabolism has been noted to occur in tissues diffusely throughout the body; this is the first report of it occurring in the eye. This phenomenon appears to be circumvented on breakdown of the blood-aqueous barrier. These observations may relate to the immunoprivilege of the eye and its modulation in inflammation.

Immunological adjuvants: desirable properties and side-effects

Adjuvants can be used with recombinant antigens to elicit cell-mediated immunity and antibodies of protective isotypes (IgG2a in the mouse and IgG1 in primates). Adjuvants should not produce reactions at injection sites, be pyrogenic or induce anterior uveitis or arthritis. Among 130 analogs of muramyl dipeptides tested, N-acetylmuramyl-L-threonyl-D-isoglutamine showed the greatest separation of potency as an adjuvant from potency in the production of side-effects. A stable emulsion of squalane and the Pluronic polymer L-121 provides a versatile vehicle for targeting of antigens to antigen-presenting cells. The combination of this emulsion with the threonyl analog of MDP is termed Syntex Adjuvant Formulation. This formulation increases the efficacy of influenza, hepatitis B virus, herpes simplex virus, lentivirus and tumor vaccines in experimental animals.

Role of bacterial debris in inflammatory diseases of the joint and eye

Several distinct rheumatic conditions (including Lyme arthritis, Reiter's syndrome and rheumatic fever) as well as certain forms of the blinding disease, uveitis, may share a common etiology. In each instance specific bacterial pathogens may infect a distant site, which on interaction with the immune system, leads to a sterile inflammation in the joint or eye. These "reactive" conditions may result, in some cases, from prior localization of non-viable bacterial remnants (including the cell wall or peptidoglycan) or alternatively "dormant" fastidious bacteria in the affected joint or eye where they act as persisting antigens. Classical culture techniques, would not detect the presence of these putative microbial antigens. Alternative approaches for detection of ubiquitous components of bacteria in the host (using appropriate chemical, molecular and immunological techniques) are discussed.

Modulation of the blood-aqueous barrier by gram positive and gram negative bacterial cell wall components in the rat and rabbit

Acute anterior uveitis in man is related to Gram negative bacterial infection occurring at sites distant to the eye. This could involve intraocular localization of inflammatory bacterial cell wall constituents. Modulation of the blood-aqueous barrier in rabbit and rat, by muramyl dipeptide (the monomer of peptidoglycan) and lipopolysaccharide (and its monomer lipid A) was studied. The rabbit eye was found to be highly susceptible to MDP and LPS, although without cellular infiltration. In contrast the rat eye was demonstrated to be totally refractory to MDP. The response to LPS in the rat was modest, required high dosages and ocular changes were slow to occur, but cellular infiltration was readily apparent. Since MDP is found in Gram positive (as well as Gram negative) bacterial cell walls it is hypothesized that Gram positive bacteria might also play a role in causing uveitis in man.

Enhancement of antibody responses to influenza B virus haemagglutinin by use of a new adjuvant formulation

Mice and guinea pigs were immunized with the haemagglutinin (HA) of influenza B-USSR/100 virus, either in Syntex Adjuvant Formulation-1 (SAF-1) or in saline. Antibody titres were determined by ELISA, haemagglutination inhibition and virus neutralization. Animals immunized with HA in SAF-1 had significantly higher antibody titres than did animals immunized with HA in saline. Both 3-week-old and 13 1/2-month-old mice had greater and more uniform antibody responses to HA in SAF-1 than to HA in saline.

Stimulant effect of the immunomodulator MTP-PE on proliferation of monocytic cells in the guinea pig

The effect of a single subcutaneous injection of various doses of the lipophilic muramyl tripeptide MTP-PE on cell proliferation was investigated in autoradiographs of histological sections of various organs of the guinea pig. The animals either received first MTP-PE in saline and then one 3H-thymidine pulse 1 h prior to sacrifice, or they were prelabeled with 3H-thymidine and then received MTP-PE. The number of proliferating cells increased up to between two and fivefold (marginally after 0.3 mg/kg and maximally after 30 mg/kg MTP-PE), but differed in the various organs. In addition, the time of the maximal increase varied between 5 h and 72 h after MTP-PE treatment and also depended on the organ. The majority of proliferating cells were of the monocyte lineage seen in conjunction with the vascular system. They were apparently promonocytes still capable of proliferation. Evidence for this conclusion is derived from (i) the distribution of 1 h-pulse-labeled cells in the various organ compartments in relation to the stimulated proliferation of the bone-marrow cells, and (ii) the distribution of the prelabeled, mainly bone-marrow derived cells, to the various organs. The augmented proliferation of the monocyte lineage is preceded by a dose-dependent, short-lasting increase in the proliferation of some epithelia and also by an increase in body temperature and a transient change in plasma proteins. These effects are part of a limited inflammatory reaction and may contribute to the immunostimulation.