Lipopolysaccharide and monophosphoryl lipid A differentially regulate interleukin-12, gamma interferon, and interleukin-10 mRNA production in murine macrophages

Regional immune mechanisms enhance efficacy of an autologous cellular cancer vaccine with intraperitoneal administration

Widespread peritoneal dissemination is common in patients with gynecologic or gastrointestinal cancers. Accumulating evidence of a central role for regional immunity in cancer control indicates that intraperitoneal immunotherapy may have treatment advantages. This study delineates immune mechanisms engaged by intraperitoneal delivery of a cell-based vaccine comprised of silicified ovarian cancer cells associated with enhanced survival. Vaccine trafficking from the site of injection to milky spots and other fat-associated lymphoid clusters was studied in syngeneic cancer models using bioluminescent and fluorescent imaging, microscopy, and flow cytometry. Spectral flow cytometry was used to phenotype peritoneal immune cell populations, while bioluminescent imaging of cancer was used to study myeloid and T cell dependency, systemic immunity, and vaccine efficacy in models of disseminated high-grade serous ovarian and DNA mismatch-repair proficient microsatellite-stable colorectal cancer. Following intraperitoneal vaccination of mice with ovarian cancer, vaccine cells were rapidly internalized by myeloid cells, with subsequent trafficking to fat-associated lymphoid clusters. Tumor clearance was confirmed to be T cell-mediated, leading to the establishment of local and systemic immunity. Combination immune checkpoint inhibitor and vaccine therapy in mice with advanced disease, characterized by an established suppressive tumor microenvironment, increased the number of mice with non-detectable tumors, however, change in tumor burden compared to vaccine monotherapy was not significant. Vaccination also resulted in tumor clearance in mouse models of metastatic colorectal cancer. This study demonstrates that intraperitoneal vaccine delivery has the potential to enhance vaccine efficacy by activating resident immune cells with the subsequent establishment of protective systemic anti-tumor immunity.

Lipid A modification of colistin-resistant Klebsiella pneumoniae does not alter innate immune response in a mouse model of pneumonia

Polymyxin resistance in carbapenem-resistant Klebsiella pneumoniae bacteria is associated with high morbidity and mortality in vulnerable populations throughout the world. Ineffective antimicrobial activity by these last resort therapeutics can occur by transfer of mcr-1, a plasmid-mediated resistance gene, causing modification of the lipid A portion of lipopolysaccharide (LPS) and disruption of the interactions between polymyxins and lipid A. Whether this modification alters the innate host immune response or carries a high fitness cost in the bacteria is not well established. To investigate this, we studied infection with K. pneumoniae (KP) ATCC 13883 harboring either the mcr-1 plasmid (pmcr-1) or the vector control (pBCSK) ATCC 13883. Bacterial fitness characteristics of mcr-1 acquisition were evaluated. Differentiated human monocytes (THP-1s) were stimulated with KP bacterial strains or purified LPS from both parent isolates and isolates harboring mcr-1. Cell culture supernatants were analyzed for cytokine production. A bacterial pneumonia model in WT C57/BL6J mice was used to monitor immune cell recruitment, cytokine induction, and bacterial clearance in the bronchoalveolar lavage fluid (BALF). Isolates harboring mcr-1 had increased colistin MIC compared to the parent isolates but did not alter bacterial fitness. Few differences in cytokines were observed with purified LPS from mcr-1 expressing bacteria in vitro. However, in a mouse pneumonia model, no bacterial clearance defect was observed between pmcr-1-harboring KP and parent isolates. Consistently, no differences in cytokine production or immune cell recruitment in the BALF were observed, suggesting that other mechanisms outweigh the effect of these lipid A mutations in LPS.

Vaccine-Induced Immunity Elicited by Microneedle Delivery of Influenza Ectodomain Matrix Protein 2 Virus-like Particle (M2e VLP)-Loaded PLGA Nanoparticles

This study focused on developing an influenza vaccine delivered in polymeric nanoparticles (NPs) using dissolving microneedles. We first formulated an influenza extracellular matrix protein 2 virus-like particle (M2e VLP)-loaded with poly(lactic-co-glycolic) acid (PLGA) nanoparticles, yielding M2e5x VLP PLGA NPs. The vaccine particles were characterized for their physical properties and in vitro immunogenicity. Next, the M2e5x VLP PLGA NPs, along with the adjuvant Alhydrogel® and monophosphoryl lipid A® (MPL-A®) PLGA NPs, were loaded into fast-dissolving microneedles. The vaccine microneedle patches were then evaluated in vivo in a murine model. The results from this study demonstrated that the vaccine nanoparticles effectively stimulated antigen-presenting cells in vitro resulting in enhanced autophagy, nitric oxide, and antigen presentation. In mice, the vaccine elicited M2e-specific antibodies in both serum and lung supernatants (post-challenge) and induced significant expression of CD4+ and CD8+ populations in the lymph nodes and spleens of immunized mice. Hence, this study demonstrated that polymeric particulates for antigen and adjuvant encapsulation, delivered using fast-dissolving microneedles, significantly enhanced the immunogenicity of a conserved influenza antigen.

In vitro effects of monophosphoryl lipid A and Poly I:C combination on equine cells

BACKGROUND

Toll-like receptor (TLR) agonists have been used as adjuvants to modulate immune responses in both animals and humans.

OBJECTIVES

The objective of this study was to evaluate the combined effects of the TLR 4 agonist monophosphoryl lipid A (MPL) and the TLR 3 agonist polyinosinic:polycytidylic acid (Poly I:C) on equine peripheral blood mononuclear cells (PBMCs), monocyte-derived dendritic cells (MoDCs), and bone marrow-derived mesenchymal stromal cells (BM-MSCs).

METHODS

The PBMCs, MoDCs, and BM-MSCs collected from three mixed breed horses were treated with MPL, Poly I:C, and their combination. The mRNA expression of interferon gamma (IFN-γ), interleukin (IL)-1β, IL-4, IL-6, IL-8, IL-12p40, tumor necrosis factor alpha (TNF-α), vascular endothelial growth factor (VEGF), and monocyte chemoattractant protein-1 (MCP-1) was determined using real-time polymerase chain reaction.

RESULTS

The combination of MPL and Poly I:C significantly upregulated immunomodulatory responses in equine cells/ without cytotoxicity. The combination induced greater mRNA expression of pro-inflammatory cytokines IFN-γ and IL-6 than MPL or Poly I:C stimulation alone in PBMCs. In addition, the combination induced significantly higher mRNA expression of IL-1β, IL-6, and IL-12p40 in MoDCs, and IL-8, MCP-1, and VEGF in BM-MSCs compared to stimulation with a single TLR agonist.

CONCLUSIONS

The combination of MPL and Poly I:C can be used as a potential adjuvant candidate for vaccines to aid in preventing infectious diseases in horses.

The Regulatory Roles of Ezh2 in Response to Lipopolysaccharide (LPS) in Macrophages and Mice with Conditional Ezh2 Deletion with LysM-Cre System

The responses of macrophages to lipopolysaccharide (LPS) might determine the direction of clinical manifestations of sepsis, which is the immune response against severe infection. Meanwhile, the enhancer of zeste homologue 2 (Ezh2), a histone lysine methyltransferase of epigenetic regulation, might interfere with LPS response. Transcriptomic analysis on LPS-activated wild-type macrophages demonstrated an alteration of several epigenetic enzymes. Although the Ezh2-silencing macrophages (RAW264.7), using small interfering RNA (siRNA), indicated a non-different response to the control cells after a single LPS stimulation, the Ezh2-reducing cells demonstrated a less severe LPS tolerance, after two LPS stimulations, as determined by the higher supernatant TNF-α. With a single LPS stimulation, Ezh2 null (Ezh2flox/flox; LysM-Crecre/−) macrophages demonstrated lower supernatant TNF-α than Ezh2 control (Ezh2fl/fl; LysM-Cre−/−), perhaps due to an upregulation of Socs3, which is a suppressor of cytokine signaling 3, due to the loss of the Ezh2 gene. In LPS tolerance, Ezh2 null macrophages indicated higher supernatant TNF-α and IL-6 than the control, supporting an impact of the loss of the Ezh2 inhibitory gene. In parallel, Ezh2 null mice demonstrated lower serum TNF-α and IL-6 than the control mice after an LPS injection, indicating a less severe LPS-induced hyper-inflammation in Ezh2 null mice. On the other hand, there were similar serum cytokines after LPS tolerance and the non-reduction of serum cytokines after the second dose of LPS, indicating less severe LPS tolerance in Ezh2 null mice compared with control mice. In conclusion, an absence of Ezh2 in macrophages resulted in less severe LPS-induced inflammation, as indicated by low serum cytokines, with less severe LPS tolerance, as demonstrated by higher cytokine production, partly through the upregulated Socs3.

Activating toll-like receptor 4 after traumatic brain injury inhibits neuroinflammation and the accelerated development of seizures in rats

Toll-like receptor 4 (TLR4) signaling plays a detrimental role in traumatic brain injury (TBI) pathology. Pharmacologic or genetic inactivating TLR4 diminish TBI inflammation and neurological complications. Nonetheless, TLR4 priming alleviates TBI inflammation and seizure susceptibility. We investigated impact of postconditioning with TLR4 agonist monophosphoryl lipid A (MPL) on TBI neuroinflammation and epileptogenesis in rats. TBI was induced in temporo-parietal cortex of rats by Controlled Cortical Impact device. Then rats received a single dose (0.1 μg/rat) of MPL by intracerebroventricular injection. After 24 h, CCI-injured rats received intraperitoneal injection of pentylenetetrazole 35 mg/kg once every other day until acquisition of generalized seizures. The injury size, number of survived neurons, and brain protein level of TNF-α, TGF-β, IL-10, and arginase1 (Arg1) were determined. Astrocytes and macrophage/microglia activation/polarization was assessed by double immunostaining with anti GFAP/Arg1 or anti Iba1/Arg1 antibodies. The CCI-injured rats developed generalized seizures after 5.9 ± 1.3 pentylenetetrazole injections (p < 0.001, compared to 12.3 ± 1.4 injections for sham-operated rats). MPL treatment returned the accelerated rate of epileptogenesis in TBI state to the sham-operated level. MPL did not change damage volume but attenuated number of dead neurons (p < 0.01). MPL decreased TNF-α overexpression (6 h post-TBI p < 0.0001), upregulated expression of TGF-β (48 h post-TBI, p < 0.0001), and IL-10 (48 h post-TBI, p < 0.0001) but did not change Arg1 expression. GFAP/Arg1 and Iba1/Arg1 positive cells were detected in TBI area with no significant change following MPL administration. MPL administration after TBI reduces vulnerability to seizure acquisition through down regulating neural death and inflammation, and up-regulating anti-inflammatory cytokines. This capacity along with the clinical safety, makes MPL a potential candidate for development of drugs against neurological deficits of TBI.

Adjuvants: friends in vaccine formulations against infectious diseases

Infectious diseases represent a major cause of deaths worldwide. No vaccine or effective treatment exists nowadays, especially against intracellular pathogens. The increase in multiple drug and superbug antibiotic resistance strains, excessive medication, or misuse of drugs has prompted the search for other safe and effective alternatives. Consistent with this, adjuvants (Latin word "adjuvare": "help or aid") co-administered (Exo) in vaccines have emerged as a promising alternative to initiate and boost an innate, downstream signal that led to adaptative immune response. Nowadays, a promising model of strong immunogens and adjuvants at mucosal sites are the microbial bacterial toxins. Other adjuvants that are also used and might successfully replace aluminum salts in combination with nanotechnology are CpG-ODN, poly IC, type I IFNs, mRNA platforms. Therefore, in the present review, we focused to revisit the old to the new adjuvants compounds, the properties that make them friends in vaccine formulations against infectious diseases.

Natural and synthetic carbohydrate-based vaccine adjuvants and their mechanisms of action

Modern subunit vaccines based on homogeneous antigens offer more precise targeting and improved safety compared with traditional whole-pathogen vaccines. However, they are also less immunogenic and require an adjuvant to increase the immunogenicity of the antigen and potentiate the immune response. Unfortunately, few adjuvants have sufficient potency and low enough toxicity for clinical use, highlighting the urgent need for new, potent and safe adjuvants. Notably, a number of natural and synthetic carbohydrate structures have been used as adjuvants in clinical trials, and two have recently been approved in human vaccines. However, naturally derived carbohydrate adjuvants are heterogeneous, difficult to obtain and, in some cases, unstable. In addition, their molecular mechanisms of action are generally not fully understood, partly owing to the lack of tools to elucidate their immune-potentiating effects, thus hampering the rational development of optimized adjuvants. To address these challenges, modification of the natural product structure using synthetic chemistry emerges as an attractive approach to develop well-defined, improved carbohydrate-containing adjuvants and chemical probes for mechanistic investigation. This Review describes selected examples of natural and synthetic carbohydrate-based adjuvants and their application in synthetic self-adjuvanting vaccines, while also discussing current understanding of their molecular mechanisms of action.

Maternal regulation of inflammatory cues is required for induction of preterm birth

Infection-driven inflammation in pregnancy is a major cause of spontaneous preterm birth (PTB). Both systemic infection and bacterial ascension through the vagina/cervix to the amniotic cavity are strongly associated with PTB. However, the contribution of maternal or fetal inflammatory responses in the context of systemic or localized models of infection-driven PTB is not well defined. Here, using intraperitoneal or intraamniotic LPS challenge, we examined the necessity and sufficiency of maternal and fetal Toll-like receptor (TLR) 4 signaling in induction of inflammatory vigor and PTB. Both systemic and local LPS challenge promoted induction of inflammatory pathways in uteroplacental tissues and induced PTB. Restriction of TLR4 expression to the maternal compartment was sufficient for induction of LPS-driven PTB in either systemic or intraamniotic challenge models. In contrast, restriction of TLR4 expression to the fetal compartment failed to induce LPS-driven PTB. Vav1-Cre-mediated genetic deletion of TLR4 suggested a critical role for maternal immune cells in inflammation-driven PTB. Further, passive transfer of WT in vitro-derived macrophages and dendritic cells to TLR4-null gravid females was sufficient to induce an inflammatory response and drive PTB. Cumulatively, these findings highlight the critical role for maternal regulation of inflammatory cues in induction of inflammation-driven parturition.

Synthesis of monophosphoryl lipid A using 2-naphtylmethyl ethers as permanent protecting groups

Lipid A, which is a conserved component of lipopolysaccharides of gram-negative bacteria, has attracted considerable interest for the development of immuno-adjuvants. Most approaches for lipid A synthesis rely on the use of benzyl ethers as permanent protecting groups. Due to the amphiphilic character of lipid A, these compounds aggregate during the hydrogenation step to remove benzyl ethers, resulting in a sluggish reaction and by-product formation. To address this problem, we have developed a synthetic approach based on the use of 2-naphtylmethyl ether (Nap) ethers as permanent protecting group for hydroxyls. At the end of a synthetic sequence, multiple of these protecting groups can readily be removed by oxidation with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ). Di-allyl N,N-diisopropylphosphoramidite was employed to install the phosphate ester and the resulting allyl esters were cleaved using palladium tetrakistriphenylphosphine. The synthetic strategy allows late stage introduction of different fatty acids at the amines of the target compound, which is facilitated by Troc and Fmoc as orthogonal amino-protecting groups.

Monophosphoryl lipid A pretreatment suppresses sepsis- and LPS-induced proinflammatory cytokine production in the medullary thick ascending limb

Sepsis is the leading cause of acute kidney injury in critically ill patients. Tumor necrosis factor-α (TNF-α) has been implicated in the pathogenesis of septic kidney injury; however, the sites and mechanisms of renal TNF-α production during sepsis remain to be defined. In the present study, we showed that TNF-α expression is increased in medullary thick ascending limbs (MTALs) of mice with sepsis induced by cecal ligation and puncture. Treatment with lipopolysaccharide (LPS) for 3 h in vitro also increased MTAL TNF-α production. Sepsis and LPS increased MTAL TNF-α expression through activation of the myeloid differentiation factor 88 (MyD88)-IL-1 receptor-associated kinase 1-ERK signaling pathway. Pretreatment with monophosphoryl lipid A (MPLA), a nontoxic immunomodulator that protects against bacterial infection, eliminated the sepsis- and LPS-induced increases in MTAL TNF-α production. The suppressive effect of MPLA on TNF-α was mediated through activation of a phosphatidylinositol 3-kinase-dependent pathway that inhibits MyD88-dependent ERK activation. This likely involves MPLA-phosphatidylinositol 3-kinase-mediated induction of Tollip, which negatively regulates the MyD88-ERK pathway by inhibiting activation of IL-1 receptor-associated kinase 1. These regulatory mechanisms are similar to those previously shown to mediate the effect of MPLA to prevent sepsis-induced inhibition of MTAL [Formula: see text] absorption. These results identify the MTAL as a site of local TNF-α production in the kidney during sepsis and identify molecular mechanisms that can be targeted to attenuate renal TNF-α expression. The ability of MPLA pretreatment to suppress MyD88-dependent ERK signaling in the MTAL during sepsis has the dual beneficial effects of protecting tubule transport functions and attenuating harmful proinflammatory responses.

Migration Gene Expression of Human Umbilical Cord Mesenchymal Stem Cells: A Comparison between Monophosphoryl Lipid A and Supernatant of Lactobacillus acidophilus

The capacity of human umbilical cord mesenchymal stem cells (hUMSCs) for migration and homing is very important in regenerative medicine. A detoxified derivative of lipopolysaccharides (LPS) that lacks many of the endotoxic properties of LPS is monophosphoryl lipid A (MPLA). Effects of MPLA on the induction of MSCs migration, have not yet been studied. Also, studies have shown that supernatant of Lactobacillus acidophilus (SLA) culture medium, can stimulate the proliferation of macrophages and lymphocytes in vitro by affecting the properties of the chemotaxis and angiogenesis. Our present study aimed to understanding of the migration of hUMSCs during treatment with MPLA and SLA, separately. HUMSCs were isolated from human umbilical cord and were characterized by investigating surface markers (CD105, CD90, anti-CD29, CD45, and CD34) and their differentiation into adipogenic and osteogenic lineages. HUMSCs were treated with MPLA (10^-3 µg/ml) and SLA (3 µl/ml). The morphological changes were not observed in both treated MSCs. Expression levels of migration markers were determined by quantitative reverse transcription PCR analysis on 2, 4, 6 days after treatment. Results showed that VEGF and MMP-2 but not CXCR-4 was increased in the presence of both treatments. Also, SLA led to a decrease and increase of the expression of VLA-4 and VCAM-1, respectively, while MPLA increased both VLA-4 and VCAM-1 expression.Therefore, it can be suggested that MPLA has more prominent results than SLA, but both treatments can probably be considered as an inducing factor in migration.

Type I IFN, Ly6C+ cells, and Phagocytes Support Suppression of Peritoneal Carcinomatosis Elicited by a TLR and CLR Agonist Combination

Metastatic cancer involving spread to the peritoneal cavity is referred to as peritoneal carcinomatosis and has a very poor prognosis. Our previous study demonstrated a Toll-like receptor and C-type lectin receptor agonist pairing of monophosphoryl lipid A (MPL) and trehalose-6,6'-dicorynomycolate (TDCM) effectively inhibits tumor growth and ascites development following TA3-Ha and EL4 challenge through a mechanism dependent on B-1a cell-produced natural IgM and complement. In this study, we investigated additional players in the MPL/TDCM-elicited response. MPL/TDCM treatment rapidly increased type I IFN levels in the peritoneal cavity along with myeloid cell numbers, including macrophages and Ly6C^hi monocytes. Type I IFN receptor (IFNAR1^-/-) mice produced tumor-reactive IgM following MPL/TDCM treatment, but failed to recruit Ly6C⁺ monocytes and were not afforded protection during tumor challenges. Clodronate liposome depletion of phagocytic cells, as well as targeted depletion of Ly6C⁺ cells, also ablated MPL/TDCM-induced protection. Cytotoxic mediators known to be produced by these cells were required for effects. TNFα was required for effective TA3-Ha killing and nitric oxide was required for EL4 killing. Collectively, these data reveal a model whereby MPL/TDCM-elicited antitumor effects strongly depend on innate cell responses, with B-1a cell-produced tumor-reactive IgM and complement pairing with myeloid cell-produced cytotoxic mediators to effectively eradicate tumors in the peritoneal cavity.

Increased in vitro migration of human umbilical cord mesenchymal stem cells toward acellular foreskin treated with bacterial derivatives of monophosphoryl lipid A or supernatant of Lactobacillus acidophilus

Migration and homing are known as critical steps toward regeneration of damaged tissues via cell therapies. Among various cellular sources of stem cells, the umbilical cord has been thus recognized as an interesting one endowed with high benefits. Accordingly, the main objective of the present study was to determine whether monophosphoryl lipid A (MPLA) or supernatant of Lactobacillus acidophilus (SLA) could increase migration of human umbilical cord mesenchymal stem cells (hUMSCs) toward acellular foreskin or not. In this study, the hUMSCs were isolated and cultured through acellular MPLA- or SLA-treated foreskin. Expression of some migration genes (i.e., VCAM-1, MMP-2, VLA-4, CXCR-4, and VEGF) was also investigated using quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR). Moreover; vimentin, cytokeratin 5 (CK5), and matrix metalloproteinases-2 (MMP-2) were detected via immunohistochemistry (IHC) analysis. The hUMSCs in the presence of MPLA- or SLA-treated foreskin showed more tissue tropism compared with those in the control group. Besides, the scanning electron microscopy (SEM) results established that the hUMSCs had more migratory activity in the presence of MPLA- or SLA-treated foreskin than the untreated one. The IHC analysis results correspondingly indicated that expression of vimentin, CK5, and MMP-2 proteins had augmented in both treatments compared with those in the control group. It was concluded that MPLA had revealed more prominent results than SLA, even though both treatments could be regarded as inducing factors in migration. Ultimately, it was suggested to introduce the use of MPLA and probiotic components as a promising approach to improve therapies in regenerative medicine.

Monophosphoryl lipid A induces protection against LPS in medullary thick ascending limb through induction of Tollip and negative regulation of IRAK-1

LPS inhibits HCO3- absorption in the medullary thick ascending limb (MTAL) through a Toll-like receptor 4 (TLR4)-myeloid differentiation factor 88 (MyD88)-extracellular signal-regulated kinase (ERK) pathway that is upregulated by sepsis. Pretreatment with the nontoxic immunomodulator monophosphoryl lipid A (MPLA) prevents inhibition by LPS through activation of a TLR4-TIR-domain-containing adaptor-inducing interferon-β (TRIF)-phosphatidylinositol 3-kinase (PI3K) pathway that prevents LPS-induced ERK activation. Here, we identified the molecular mechanisms that underlie the protective inhibitory interaction between the MPLA-PI3K and LPS-ERK pathways. Treatment of mouse MTALs with LPS in vitro increased phosphorylation of IL-1 receptor-associated kinase (IRAK)-1, a critical mediator of LPS signaling downstream of TLR4-MyD88. Activation of ERK by LPS was eliminated by a selective IRAK-1 inhibitor, establishing IRAK-1 as the upstream mediator of ERK activation. Pretreatment of MTALs with MPLA in vitro prevented LPS-induced IRAK-1 activation; this effect was dependent on PI3K. Treatment of MTALs with MPLA increased expression of Toll-interacting protein (Tollip), an inducible protein that negatively regulates LPS signaling by inhibiting IRAK-1. The MPLA-induced increase in Tollip protein level was prevented by PI3K inhibitors. In coimmunoprecipitation experiments, MPLA increased the amount of Tollip stably bound to IRAK-1, an interaction that inhibits IRAK-1 activation. These results support a mechanism whereby MPLA increases Tollip expression in the MTAL through a PI3K-dependent pathway. Tollip, in turn, inhibits LPS-induced TLR4 signaling by suppressing activation of IRAK-1, thereby preventing activation of ERK that inhibits HCO3- absorption. These studies show that MPLA induces reprogramming of MTAL cells that protects against LPS stimulation and identify IRAK-1 and Tollip as new therapeutic targets to prevent renal tubule dysfunction in response to infectious and inflammatory stimuli.

Monophosphoryl lipid A prevents impairment of medullary thick ascending limb [Formula: see text] absorption and improves plasma [Formula: see text] concentration in septic mice

Metabolic acidosis is the most common acid-base disorder in septic patients and is associated with increased mortality. Previously, we demonstrated that sepsis induced by cecal ligation and puncture (CLP) impairs [Formula: see text] absorption in the medullary thick ascending limb (MTAL) by 1) decreasing the intrinsic [Formula: see text] absorptive capacity and 2) enhancing inhibition of [Formula: see text] absorption by LPS through upregulation of Toll-like receptor (TLR) 4 signaling. Both effects depend on ERK activation. Monophosphoryl lipid A (MPLA) is a detoxified TLR4 agonist that enhances innate antimicrobial immunity and improves survival following sepsis. Pretreatment of MTALs with MPLA in vitro prevents LPS inhibition of [Formula: see text] absorption. Here we examined whether pretreatment with MPLA would protect the MTAL against sepsis. Vehicle or MPLA was administered to mice 48 h before sham or CLP surgery, and MTALs were studied in vitro 18 h postsurgery. Pretreatment with MPLA prevented the effects of sepsis to decrease the basal [Formula: see text] absorption rate and enhance inhibition by LPS. These protective effects were mediated through MPLA stimulation of a Toll/IL-1 receptor domain-containing adaptor-inducing IFN-β-(TRIF)-dependent phosphatidylinositol 3-kinase-Akt pathway that prevents sepsis- and LPS-induced ERK activation. The effects of MPLA to improve MTAL [Formula: see text] absorption were associated with marked improvement in plasma [Formula: see text] concentration, supporting a role for the kidneys in the pathogenesis of sepsis-induced metabolic acidosis. These studies support detoxified TLR4-based immunomodulators, such as MPLA, that enhance antimicrobial responses as a safe and effective approach to prevent or treat sepsis-induced renal tubule dysfunction and identify cell signaling pathways that can be targeted to preserve MTAL [Formula: see text] absorption and attenuate metabolic acidosis during sepsis.

Specific features of human monocytes activation by monophosphoryl lipid A

We deciphered the mechanisms of production of pro- and anti-inflammatory cytokines by adherent human blood mononuclear cells (PBMC) activated by lipopolysaccharide (LPS) or monophosphoryl lipid A (MPLA). Both LPS and MPLA induced tumor necrosis factor (TNF) production proved to be dependent on the production of interleukin-1β (IL-1β). Of note, MPLA induced IL-1β release in human adherent PBMCs whereas MPLA was previously reported to not induce this cytokine in murine cells. Both LPS and MPLA stimulatory effects were inhibited by Toll-like receptor-4 (TLR4) antagonists. Only monocytes activation by LPS was dependent on CD14. Other differences were noticed between LPS and MPLA. Among the different donors, a strong correlation existed in terms of the levels of TNF induced by different LPSs. In contrast, there was no correlation between the TNF productions induced by LPS and those induced by MPLA. However, there was a strong correlation when IL-6 production was analyzed. Blocking actin polymerization and internalization of the agonists inhibited MPLA induced TNF production while the effect on LPS induced TNF production depended on the donors (i.e. high TNF producers versus low TNF producers). Finally, conventional LPS, tolerized adherent PBMCs to TLR2 agonists, while MPLA primed cells to further challenge with TLR2 agonists.

Monophosphoryl lipid A enhances nontypeable Haemophilus influenzae-specific mucosal and systemic immune responses by intranasal immunization

OBJECTIVE

Acute otitis media (AOM) is one of the most common infectious diseases in children. Nontypeable Haemophilus influenzae (NTHi) is Gram-negative bacteria that are considered major pathogens of AOM and respiratory tract infections. In this study, we used monophosphoryl lipid A (MPL), a toll-like receptor (TLR) 4 agonist, as an adjuvant to induce mucosal immune responses against NTHi to enhance bacterial clearance from the nasopharynx.

METHODS

Mice were administered 10 μg outer membrane protein (OMP) from NTHi and 0, 10, or 20 μg MPL intranasally once a week for 3 weeks. Control mice were administered phosphate-buffered saline alone. After immunization, these mice were challenged with NTHi. At 6 and 12 h after bacterial challenge, the mice were killed and nasal washes and sera were collected. The numbers of NTHi- and OMP-specific antibodies were quantified by enzyme-linked immunosorbent assay.

RESULTS

The MPL 10 and 20 μg group produced a significant reduction in the number of bacteria recovered from the nasopharynx at 12 h after bacterial challenge compared to the control group. OMP-specific IgA titers were also augmented in the MPL groups compared to the control and OMP groups.

CONCLUSION

MPL is suitable for eliciting effective mucosal immune responses against NTHi in the nasopharynx. These results demonstrate the possibility of an adjuvant that involves stimulation of the innate immune system by TLR4 agonists such as MPL for mucosal vaccination.

Monophosphoryl lipid A induces protection against LPS in medullary thick ascending limb through a TLR4-TRIF-PI3K signaling pathway

Monophosphoryl lipid A (MPLA) is a detoxified derivative of LPS that induces tolerance to LPS and augments host resistance to bacterial infections. Previously, we demonstrated that LPS inhibits [Formula: see text] absorption in the medullary thick ascending limb (MTAL) through a basolateral Toll-like receptor 4 (TLR4)-myeloid differentiation factor 88 (MyD88)-ERK pathway. Here we examined whether pretreatment with MPLA would attenuate LPS inhibition. MTALs from rats were perfused in vitro with MPLA (1 µg/ml) in bath and lumen or bath alone for 2 h, and then LPS was added to (and MPLA removed from) the bath solution. Pretreatment with MPLA eliminated LPS-induced inhibition of [Formula: see text] absorption. In MTALs pretreated with MPLA plus a phosphatidylinositol 3-kinase (PI3K) or Akt inhibitor, LPS decreased [Formula: see text] absorption. MPLA increased Akt phosphorylation in dissected MTALs. The Akt activation was eliminated by a PI3K inhibitor and in MTALs from TLR4^-/- or Toll/IL-1 receptor domain-containing adaptor-inducing IFN-β (TRIF)^-/- mice. The effect of MPLA to prevent LPS inhibition of [Formula: see text] absorption also was TRIF dependent. Pretreatment with MPLA prevented LPS-induced ERK activation; this effect was dependent on PI3K. MPLA alone had no effect on [Formula: see text] absorption, and MPLA pretreatment did not prevent ERK-mediated inhibition of [Formula: see text] absorption by aldosterone, consistent with MPLA's low toxicity profile. These results demonstrate that pretreatment with MPLA prevents the effect of LPS to inhibit [Formula: see text] absorption in the MTAL. This protective effect is mediated directly through MPLA stimulation of a TLR4-TRIF-PI3K-Akt pathway that prevents LPS-induced ERK activation. These studies identify detoxified TLR4-based immunomodulators as novel potential therapeutic agents to prevent or treat renal tubule dysfunction in response to bacterial infections.

Signal integration in lipopolysaccharide (LPS)-stimulated murine macrophages

Using a panel of LPS-inducible genes, selected for the capacity of their products to contribute to endotoxicity, normal macrophages were compared to macrophages deficient in CD14, CD11b/CD18, or TLR4 to elicit gene expression in response to Escherichia coli LPS or the LPS mimetic, Taxol. All genes were TLR4-dependent. At low doses of LPS or Taxol, all genes were also CD14-dependent; however, IP-10 and ICSBP remained poorly inducible even at much higher concentrations. A distinct subset of genes (COX-2, IL-12 p40, and IL-12 p35) was CD11b/CD18-dependent. NF-κB translocation and MAPK phosphorylation were dysregulated in receptor-deficient macrophages. In contrast to E. coli LPS, a Porphyromonas gingivalis LPS preparation was found to be TLR2-, rather than TLR4-dependent, and resulted in differential expression of genes within the panel. These data suggest that: (i) TLR4 is necessary, but not sufficient, to induce the full repertoire of genes examined; (ii) CD14 and CD11b/CD18 facilitate signaling for induction of select subsets of genes that are also TLR4-dependent; and (iii) signaling through TLR2 versus TLR4 differs quantitatively/qualitatively. These data support an LPS signaling complex on murine macrophages that minimally includes CD14, CD11b/CD18, and TLR4 to respond to E. coli LPS to elicit the full spectrum of gene expression.

Effect of inflammatory and antiinflammatory stimuli on acyloxyacyl hydrolase gene expression and enzymatic activity in murine macrophages

Acyloxyacyl hydrolase (AOAH) is an enzyme found in macrophages and neutrophils that specifically cleaves the acyloxyacyl moieties of lipopolysaccharide (LPS), thus rendering it non-toxic for human cells. In the present study, we demonstrate that LPS augments AOAH mRNA expression (10-20-fold) in murine macrophages. Following LPS treatment (100 ng/m]), AOAH mRNA was induced by 2 h, peaked at 6 h, and was sustained over 72 h. Optimal induction of AOAH mRNA was observed with as little as 0.1 ng/ml LPS. LPS also induced a concomitant increase in AOAH enzymatic activity in cytosolic extracts from murine macrophages and the ability of macrophages to deacylate LPS was not diminished in endotoxin-tolerized macrophages. LPS-stimulated AOAH mRNA expression was cycloheximide sensitive, indicating that de novo protein synthesis is required for AOAH mRNA production. Moreover, AOAH mRNA expression was also induced by IFN-γ. LPS-stimulated mRNA expression was not suppressed by either dexamethasone or IL-10. Finally, intraperitoneal challenge of mice with 25 μg of LPS resulted in increases in AOAH mRNA in both the lung (∼3-fold) and in the liver (∼6-fold). A possible role for LPS-inducible AOAH in the elimination of LPS is discussed.

The Power of Asymmetry: Architecture and Assembly of the Gram-Negative Outer Membrane Lipid Bilayer

Determining the chemical composition of biological materials is paramount to the study of natural phenomena. Here, we describe the composition of model gram-negative outer membranes, focusing on the predominant assembly, an asymmetrical bilayer of lipid molecules. We also give an overview of lipid biosynthetic pathways and molecular mechanisms that organize this material into the outer membrane bilayer. An emphasis is placed on the potential of these pathways as targets for antibiotic development. We discuss deviations in composition, through bacterial cell surface remodeling, and alternative modalities to the asymmetric lipid bilayer. Outer membrane lipid alterations of current microbiological interest, such as lipid structures found in commensal bacteria, are emphasized. Additionally, outer membrane components could potentially be engineered to develop vaccine platforms. Observations related to composition and assembly of gram-negative outer membranes will continue to generate novel discoveries, broaden biotechnologies, and reveal profound mysteries to compel future research.

Artificial bacterial biomimetic nanoparticles synergize pathogen-associated molecular patterns for vaccine efficacy

Antigen-presenting cells (APCs) sense microorganisms via pathogen-associated molecular patterns (PAMPs) by both extra- and intracellular Toll-like Receptors (TLRs), initiating immune responses against invading pathogens. Bacterial PAMPs include extracellular lipopolysaccharides and intracellular unmethylated CpG-rich oligodeoxynucleotides (CpG). We hypothesized that a biomimetic approach involving antigen-loaded nanoparticles (NP) displaying Monophosphoryl Lipid A (MPLA) and encapsulating CpG may function as an effective "artificial bacterial" biomimetic vaccine platform. This hypothesis was tested in vitro and in vivo using NP assembled from biodegradable poly(lactic-co-glycolic acid) (PLGA) polymer, surface-modified with MPLA, and loaded with CpG and model antigen Ovalbumin (OVA). First, CpG potency, characterized by cytokine profiles, titers, and antigen-specific T cell responses, was enhanced when CpG was encapsulated in NP compared to equivalent concentrations of surface-presented CpG, highlighting the importance of biomimetic presentation of PAMPs. Second, NP synergized surface-bound MPLA with encapsulated CpG in vitro and in vivo, inducing greater pro-inflammatory, antigen-specific T helper 1 (Th1)-skewed cellular and antibody-mediated responses compared to single PAMPs or soluble PAMP combinations. Importantly, NP co-presentation of CpG and MPLA was critical for CD8(+) T cell responses, as vaccination with a mixture of NP presenting either CpG or MPLA failed to induce cellular immunity. This work demonstrates a rational methodology for combining TLR ligands in a context-dependent manner for synergistic nanoparticulate vaccines.

Pre-treatment of C57BL6/J mice with the TLR4 agonist monophosphoryl lipid A prevents LPS-induced sickness behaviors and elevations in dorsal hippocampus interleukin-1β, independent of interleukin-4 expression

Peripheral administration of lipopolysaccharide (LPS) elevates production of pro-inflammatory cytokines, and motivates the expression of sickness behaviors. In this study, we tested the ability of an LPS-derived adjuvant, monophosphoryl lipid A (MPLA), to prevent LPS-induced sickness behaviors in a burrowing paradigm. Testing occurred over a three-day period. Animals received a single injection of either MPLA or saline the first two days of testing. On day three, animals received either LPS or saline. Tissue from the dorsal hippocampus was collected for qRT-PCR to assess expression of IL-1β and IL-4. Results indicate that, during the pre-treatment phase, administration of MPLA induces an immune response sufficient to trigger sickness behaviors. However, we observed that animals pre-treated with MPLA for two days were resistant to LPS-induced sickness behaviors on day three. Results from the qRT-PCR analysis indicated that LPS-treated animals pre-treated with MPLA expressed significantly less IL-1β compared to LPS-treated animals pre-treated with saline. However, we did not observe a significant difference in IL-4 expression between groups. Therefore, results indicate that under the given parameters of the study, MPLA pre-treatment protects against LPS-induced sickness behaviors, at least in part, by decreasing expression of the pro-inflammatory cytokine IL-1β.

Influence of Brucella abortus lipopolysaccharide as an adjuvant on the immunogenicity of HPV-16 L1VLP vaccine in mice

Brucella abortus lipopolysaccharide (LPS) has less toxicity and no pyrogenic properties in comparison with other bacterial LPS. It is a toll-like receptor 4 agonist and has been shown to have the potential use as a vaccine adjuvant. In this study, the immunostimulatory properties of LPS from smooth and rough strains of B. abortus (S19 and RB51) as adjuvants were investigated for the human papillomavirus type 16 (HPV16) L1 virus-like particles (L1VLPs) vaccines. C57BL/6 mice were immunized subcutaneously three times either with HPV-16 L1VLPs alone, or in combination with smooth LPS (S-LPS), rough LPS (R-LPS), aluminum hydroxide or a mixture of them as adjuvant. The humoral immunity was evaluated by measuring the specific and total IgG levels, and also the T-cell immune response of mice was evaluated by measuring different cytokines such as IFN-γ, TNF-α, IL-4, IL-10 and IL-17. Results showed that serum anti-HPV16 L1VLP IgG antibody titers was significantly higher in mice immunized with a combination of VLPs and R-LPS or S-LPS compared with other immunized groups. Co-administration of HPV-16 L1VLPs with R-LPS elicited the highest levels of splenocytes cytokines (IFN-γ, IL-4, IL-17 and TNF-α) and also effectively induced improvement of a Th1-type cytokine response characterized with a high ratio of IFN-γ/IL-10. The data indicate that B. abortus LPS particularly RB51-LPS enhances the immune responses to HPV-16 L1VLPs and suggests its potential as an adjuvant for the development of a potent prophylactic HPV vaccine and other candidate vaccines.

MPLA inhibits release of cytotoxic mediators from human neutrophils while preserving efficient bacterial killing

Monophosphoryl lipid A (MPLA) is a lipopolysaccharides (LPS) derivative associated with neutrophil-dependent anti-inflammatory outcomes in animal models of sepsis. Little is known about the effect of MPLA on neutrophil function. This study sought to test the hypothesis that MPLA would reduce release of cytotoxic mediators from neutrophils without impairing bacterial clearance. Neutrophils were isolated from whole blood of healthy volunteers. The effects of MPLA and LPS on autologous serum-opsonised Pseudomonas aeruginosa killing by neutrophils and phagocytosis of autologous serum-opsonised zymosan were examined. Neutrophil oxidative burst, chemotaxis, enzyme and cytokine release as well as Toll-like receptor 4 (TLR4) expression were assessed following exposure to LPS or MPLA. LPS, but not MPLA, induced significant release of superoxide and myeloperoxidase from neutrophils. However, MPLA did not impair neutrophil capacity to ingest microbial particles and kill P. aeruginosa efficiently. MPLA was directly chemotactic for neutrophils, involving TLR4, p38 mitogen-activated protein kinase and tyrosine and alkaline phosphatases. LPS, but not MPLA, impaired N-formyl-methionyl-leucyl phenylalanine-directed migration of neutrophils, increased surface expression of TLR4, increased interleukin-8 release and strongly activated the myeloid differentiation primary response 88 pathway. Phosphoinositide 3-kinase inhibition significantly augmented IL-8 release from MPLA-treated neutrophils. The addition of MPLA to LPS-preincubated neutrophils led to a significant reduction in LPS-mediated superoxide release and TLR4 surface expression. Collectively, these findings suggest that MPLA directs efficient chemotaxis and bacterial killing in human neutrophils without inducing extracellular release of cytotoxic mediators and suggest that MPLA warrants further attention as a potential therapeutic in human sepsis.

Inefficient TLR4/MD-2 heterotetramerization by monophosphoryl lipid A

Synthetic forms of E. coli monophosphoryl lipid A (sMLA) weakly activate the MyD88 (myeloid differentiation primary response protein) branch of the bifurcated TLR4 (Toll-like receptor 4) signaling pathway, in contrast to diphosphoryl lipid A (sDLA), which is a strong activator of both branches of TLR4. sMLA's weak MyD88 signaling activity is apparent downstream of TLR4/MyD88 signaling as we show that sMLA, unlike sDLA, is unable to efficiently recruit the TNF receptor-associated factor 6 (TRAF6) to the Interleukin-1 receptor-associated kinase 1 (IRAK1). This reduced recruitment of TRAF6 explains MLA's lower MAPK (Mitogen Activated Protein Kinase) and NF-κB activity. As further tests of sMLA's ability to activate TLR4/Myeloid differentiation factor 2 (MD-2), we used the antibody MTS510 as an indicator for TLR4/MD-2 heterotetramer formation. Staining patterns with this antibody indicated that sMLA does not effectively drive heterotetramerization of TLR4/MD-2 when compared to sDLA. However, a F126A mutant of MD-2, which allows lipid A binding but interferes with TLR4/MD-2 heterotetramerization, revealed that while sMLA is unable to efficiently form TLR4/MD-2 heterotetramers, it still needs heterotetramer formation for the full extent of signaling it is able to achieve. Monophosphoryl lipid A's weak ability to form TLR4/MD-2 heterotetramers was not restricted to synthetic E. coli type because cells exposed to a biological preparation of S. minnesota monophosphoryl lipid A (MPLA) also showed reduced TLR4/MD-2 heterotetramer formation. The low potency with which sMLA and MPLA drive heterotetramerization of TLR4/MD-2 contributes to their weak MyD88 signaling activities.

Recognition of lipid A variants by the TLR4-MD-2 receptor complex

Lipopolysaccharide (LPS) is a component of the outer membrane of almost all Gram-negative bacteria and consists of lipid A, core sugars, and O-antigen. LPS is recognized by Toll-like receptor 4 (TLR4) and MD-2 on host innate immune cells and can signal to activate the transcription factor NFκB, leading to the production of pro-inflammatory cytokines that initiate and shape the adaptive immune response. Most of what is known about how LPS is recognized by the TLR4-MD-2 receptor complex on animal cells has been studied using Escherichia coli lipid A, which is a strong agonist of TLR4 signaling. Recent work from several groups, including our own, has shown that several important pathogenic bacteria can modify their LPS or lipid A molecules in ways that significantly alter TLR4 signaling to NFκB. Thus, it has been hypothesized that expression of lipid A variants is one mechanism by which pathogens modulate or evade the host immune response. Additionally, several key differences in the amino acid sequences of human and mouse TLR4-MD-2 receptors have been shown to alter the ability to recognize these variations in lipid A, suggesting a host-specific effect on the immune response to these pathogens. In this review, we provide an overview of lipid A variants from several human pathogens, how the basic structure of lipid A is recognized by mouse and human TLR4-MD-2 receptor complexes, as well as how alteration of this pattern affects its recognition by TLR4 and impacts the downstream immune response.

Immunomodulatory Activity of Lactococcus lactis A17 from Taiwan Fermented Cabbage in OVA-Sensitized BALB/c Mice

From fermented Taiwan foods, we have isolated numerous lactic acid bacteria (LAB) of plant origin and investigated their biological activities. This study aimed to investigate the immunomodulatory effect and mechanism of Lactococcus lactis A17 (A17), isolated from Taiwan fermented cabbage, on ovalbumin (OVA)-sensitized mice. Human peripheral blood mononuclear cells were used to verify immune responses of A17 by IFN-γ production. Live (A17-A) and heat-killed A17 (A17-H) were orally administered to OVA-sensitized BALB/c mice to investigate their effects on immunoglobulin (Ig) and cytokine production. The mRNA expression of Toll-like receptors (TLR) and nucleotide binding oligomerization domain (NOD)-like protein receptors in spleen cells was analyzed by real-time RT-PCR. Both live and heat-killed A17 modulate OVA-induced allergic effects. B-cell response was modulated by diminishing IgE production and raising OVA-specific IgG2a production, while T-cell response was modulated by increasing IFN-γ production and decreasing IL-4 production. The mRNA expression of NOD-1, NOD-2, and TLR-4 was down-regulated by A17 as well. This is the first report to describe a naïve Lactococcus lactis A17 strain as a promising candidate for prophylactic and therapeutic treatments of allergic diseases via oral administration. Our results suggest the ameliorative effects of A17 may be caused by modulating NOD-1 NOD-2, and TLR-4 expression.

The yin and yang of human Beta-defensins in health and disease

Rapidly evolving research examining the extended role of human beta-defensins (hBDs) in chemoattraction, innate immune-mediated response, and promotion of angiogenesis suggest that the collective effects of hBDs extend well beyond their antimicrobial mechanism(s). Indeed, the numerous basic cellular functions associated with hBDs demonstrate that these peptides have dual impact on health, as they may be advantageous under certain conditions, but potentially detrimental in others. The consequences of these functions are reflected in the overexpression of hBDs in diseases, such as psoriasis, and recently the association of hBDs with pro-tumoral signaling. The mechanisms regulating hBD response in health and disease are still being elucidated. Clearly the spectrum of function now attributed to hBD regulation identifies these molecules as important cellular regulators, whose appropriate expression is critical for proper immune surveillance; i.e., expression of hBDs in proximity to areas of cellular dysregulation may inadvertently exacerbate disease progression. Understanding the mechanism(s) that regulate contextual signaling of hBDs is an important area of concentration in our laboratories. Using a combination of immunologic, biochemical, and molecular biologic approaches, we have identified signaling pathways associated with hBD promotion of immune homeostasis and have begun to dissect the inappropriate role that beta-defensins may assume in disease.

Phytol-derived novel isoprenoid immunostimulants

This review describes the adjuvanticity of novel diterpenoids (synthetic phytol derivatives) compared to some commercially available adjuvants. The efficacy of the phytol-derived immunostimulants was evaluated in terms of their ability to activate innate immunity, amplify various antigen-specific immune responses, and engender immunological memory with no discernible adverse effects in both competent and immune-deficient mice. The profile that emerges out of these studies reveals that the phytol derivatives are excellent immunostimulants, superior to a number of commercial adjuvants in terms of long-term memory induction and activation of both innate and acquired immunity. Additionally, the phytol-derived compounds have no cumulative inflammatory or toxic effects even in immuno-compromised mice.

The Toll-like receptor 4 agonist monophosphoryl lipid a augments innate host resistance to systemic bacterial infection

Monophosphoryl lipid A (MPLA) is a Toll-like receptor 4 (TLR4) agonist that is currently used as a vaccine adjuvant in humans. In this study, we evaluated the effect of MPLA treatment on the innate immune response to systemic bacterial infections in mice. Mice treated with MPLA after burn injury showed improved survival and less local and systemic dissemination of bacteria in a model of Pseudomonas aeruginosa burn wound infection. Prophylactic treatment with MPLA significantly enhanced bacterial clearance at the site of infection and reduced systemic dissemination of bacteria despite causing attenuation of proinflammatory cytokine production during acute intra-abdominal infection caused by cecal ligation and puncture. Administration of MPLA at 1 h after CLP also improved bacterial clearance but did not alter cytokine production. MPLA treatment increased the numbers of granulocytes, double-positive myeloid cells, and macrophages at sites of infection and increased the percentage and total numbers of myeloid cells mediating phagocytosis of bacteria. Depletion of Ly6G(+) neutrophils, but not macrophages, eliminated the ability of MPLA treatment to improve bacterial clearance. The immunomodulatory effects of MPLA were absent in TLR4-deficient mice. In conclusion, these studies show that MPLA treatment significantly augments the innate immune response to bacterial infection by enhancing bacterial clearance despite the attenuation of proinflammatory cytokine production. The enhanced bacterial clearance is mediated, in part, by increased numbers of myeloid cells with effective phagocytic functions at sites of infection and is TLR4 dependent.

Pathogen-associated molecular patterns on biomaterials: a paradigm for engineering new vaccines

Vaccine development has progressed significantly and has moved from whole microorganisms to subunit vaccines that contain only their antigenic proteins. Subunit vaccines are often less immunogenic than whole pathogens; therefore, adjuvants must amplify the immune response, ideally establishing both innate and adaptive immunity. Incorporation of antigens into biomaterials, such as liposomes and polymers, can achieve a desired vaccine response. The physical properties of these platforms can be easily manipulated, thus allowing for controlled delivery of immunostimulatory factors and presentation of pathogen-associated molecular patterns (PAMPs) that are targeted to specific immune cells. Targeting antigen to immune cells via PAMP-modified biomaterials is a new strategy to control the subsequent development of immunity and, in turn, effective vaccination. Here, we review the recent advances in both immunology and biomaterial engineering that have brought particulate-based vaccines to reality.

A composite MyD88/CD40 switch synergistically activates mouse and human dendritic cells for enhanced antitumor efficacy

The in vivo therapeutic efficacy of DC-based cancer vaccines is limited by suboptimal DC maturation protocols. Although delivery of TLR adjuvants systemically boosts DC-based cancer vaccine efficacy, it could also increase toxicity. Here, we have engineered a drug-inducible, composite activation receptor for DCs (referred to herein as DC-CAR) comprising the TLR adaptor MyD88, the CD40 cytoplasmic region, and 2 ligand-binding FKBP12 domains. Administration of a lipid-permeant dimerizing ligand (AP1903) induced oligomerization and activation of this fusion protein, which we termed iMyD88/CD40. AP1903 administration to vaccinated mice enabled prolonged and targeted activation of iMyD88/CD40-modified DCs. Compared with conventionally matured DCs, AP1903-activated iMyD88/CD40-DCs had increased activation of proinflammatory MAPKs. AP1903-activated iMyD88/CD40-transduced human or mouse DCs also produced higher levels of Th1 cytokines, showed improved migration in vivo, and enhanced both antigen-specific CD8+ T cell responses and innate NK cell responses. Furthermore, treatment with AP1903 in vaccinated mice led to robust antitumor immunity against preestablished E.G7-OVA lymphomas and aggressive B16.F10 tumors. Thus, the iMyD88/CD40 unified "switch" effectively and safely replaced exogenous adjuvant cocktails, allowing remote and sustained DC activation in vivo. DC "licensing" through iMyD88/CD40 may represent a mechanism by which to exploit the natural synergy between the TLR and CD40 signaling pathways in DCs using a single small molecule drug and could augment the efficacy of antitumor DC-based vaccines.

Generation and characterisation of therapeutic tolerogenic dendritic cells for rheumatoid arthritis

OBJECTIVES

Tolerogenic dendritic cells (tolDCs) constitute a promising experimental treatment for targeting autoreactive T cells in autoimmune diseases, including rheumatoid arthritis (RA). The authors' goal is to bring tolDC therapy for RA to the clinic. Here the authors address key translational issues related to the manufacturing of tolDCs from RA patients with current good manufacturing practice (cGMP)-compliant reagents, the stability of tolDCs, and the selection of suitable quality control markers.

METHODS

Human monocyte-derived tolDCs were established from RA patients and healthy controls (HCs) using the immunosuppressive drugs dexamethasone and vitamin D₃, and the cGMP-grade immunomodulator, monophosphoryl lipid A, in the cGMP-compliant medium, CellGroDC. The functionality of tolDCs and tolDC-modulated autologous CD4 T cells was determined by flow cytometry, [³H]thymidine incorporation and ELISA.

RESULTS

Clinical-grade tolDCs established from patients with RA exhibit a typical tolerogenic phenotype of reduced costimulatory molecules, low production of proinflammatory cytokines and impaired stimulation of autologous antigen-specific T cells, comparable to HC tolDCs. Toll-like receptor 2 (TLR-2) was highly expressed by tolDCs but not mature DCs. Furthermore, tolDCs suppressed mature DC-induced T cell proliferation, interferon γ and interleukin 17 production, and rendered T cells hyporesponsive to further stimulation. Importantly, tolDCs were phenotypically stable in the absence of immunosuppressive drugs and were refractory to further challenge with proinflammatory mediators.

CONCLUSIONS

tolDCs established from patients with RA are comparable to those derived from healthy donors. TLR-2 was identified as an ideal marker for quality control of tolDCs. Potently tolerogenic and highly stable, these tolDCs are a promising cellular therapeutic for tailored immunomodulation in the treatment of RA.

Differential induction of innate immune responses by synthetic lipid a derivatives

Recent studies have indicated that lipopolysaccharides (LPS) isolated from particular bacterial strains can bias innate immune responses toward different signal transduction pathways thereby eliciting unique patterns of cytokines. Heterogeneity in the structure of lipid A (the active component of LPS) and possible contaminations with other inflammatory components have made it difficult to confirm these observations and dissect molecular motifs that may be responsible for modulatory properties. To address these issues, we have examined, for the first time, the ability of a range of well defined synthetic lipid As and isolated LPS and lipid A preparations to induce the production of a wide range of cytokines in three different mouse cell types. It was found that, for a given compound, the potencies of production of the various cytokines differed significantly. An additive model, in which a chemical change in the structure of a compound effects the potencies of all cytokines in the same manner, could describe the potencies of the cytokines for all compounds. Thus, no evidence was found that the structure of lipid A can modulate the pattern of cytokine production. In addition, the statistical analysis showed that the relative ordering of the potencies of the compounds was identical in the different cell types and that structural features such as the presence of a 3-deoxy-D-manno-octulosonic acid moiety, anomeric phosphate, lipid length, and acylation pattern were important for pro-inflammatory activity. Finally, it was found that transcriptional and post-transcription control mechanisms determine potencies and efficacies of cytokine production in cell-specific manners.

New insights for development of a safe and protective RSV vaccine

Respiratory Syncytial Virus (RSV) is the leading cause of pneumonia and bronchiolitis in infants and children <1 year old, resulting in significant morbidity and mortality worldwide. There is currently no RSV vaccine. In the 1960s, a formalin-inactivated RSV (FI-RSV) vaccine trial led to exacerbated disease upon natural infection of vaccinees, including two deaths. The causes involved in the disastrous results of these vaccine trials are still unclear but they remain the engine for searching new avenues to develop a safe vaccine that can provide long-term protection against this important pathogen. This article reviews some of the early history of RSV vaccine development,as well as more recent information on the interaction between RSV and the host innate and adaptive immune responses. A safe and efficacious vaccine for RSV will require "re-education" of the host immune response against RSV to prevent vaccine-enhanced or severe RSV disease.

Chemical synthesis and proinflammatory responses of monophosphoryl lipid A adjuvant candidates

Lipopolysaccharides (LPS), which are structural components of the outer surface membrane of Gram-negative bacteria, trigger innate immune responses through activation of Toll-like receptor 4 (TLR4). Such responses may be exploited for the development of adjuvants and in particular monophosphoryl lipid A (MPLA) obtained by controlled hydrolysis of LPS of Salmonella minnesota, exhibits low toxicity yet possesses beneficial immuno-stimulatory properties. We have developed an efficient synthetic approach for the preparation of a major component of MPLA (1), which has as a key feature the use of allyloxycarbonates (Alloc) as permanent protecting groups for the C-3 and C-4 hydroxyls of the proximal glucosamine unit. The latter protecting groups greatly facilitated deprotection of the fully assembled compound. Furthermore, the amino functions were protected as N-2,2,2-trichloroethoxycarbamates (Troc), which performed efficient neighboring group participation to give selectively 1,2-trans-glycosides and could easily be removed under mild conditions without affecting the permanent Alloc carbonates and anomeric dimethylthexylsilyl (TDS) ether. The synthetic methodology was also employed for the preparation of a monophosphoryl lipid A (2) derivative that has the anomeric center of the proximal sugar modified as a methyl glycoside. Compound 1 was not able to induce cytokine production in mouse macrophages whereas methyl glycoside 2 displayed activity, however it has a lower potency and efficacy than lipid A obtained by controlled hydrolysis S. minnesota. This indicates compound 2 is an attractive candidate for adjuvant development and that 1 is not the active substance of MPLA obtained by controlled hydrolysis of LPS.

Selective activation of the p38 MAPK pathway by synthetic monophosphoryl lipid A

TLR4 stimulation by lipopolysaccharide can cause both MAL/MyD88- and TRAM/TRIF (Toll IL-1 receptor domain-containing adaptor-inducing IFNbeta)-dependent signaling events. Monophosphoryl lipid A (MPLA), a low toxicity derivative of endotoxic lipopolysaccharide, enhances antibody responses, T cell expansion, and recall responses against antigens without causing excessive inflammatory side effects. Previously, we proposed that TRIF-biased activation of TLR4 by MPLA is responsible for its reduced toxicity while retaining potent adjuvant effects. However, some TRIF-associated genes, such as MCP-1, are only weakly expressed, and some MyD88-associated inflammatory and anti-inflammatory cytokines, such as tumor necrosis factor alpha and interleukin-10, are strongly activated after MPLA stimulation despite weak NF-kappaB but strong IRF3 activation. We now report that synthetic derivatives of MPLA retained TRIF bias as compared with synthetic diphosphoryl lipid A, indicating a change in a single phosphoryl group is sufficient for TRIF-biased TLR4 stimulation. We extend our previous observations by showing that sMLA induces strong p38 MAPK but weak JNK activation, resulting in high IP-10 (interferon-inducible protein 10), tumor necrosis factor alpha, and interleukin-10 but low MCP-1 transcript levels. Results of this study identify a novel biochemical mechanism for regulation of sMLA-induced gene expression.

Inflammasome-activating nanoparticles as modular systems for optimizing vaccine efficacy

Innate immune system activation is a critical step in the initiation of an effective adaptive immune response; therefore, activation of a class of innate pathogen receptors called pattern recognition receptors (PRR) is a central feature of many adjuvant systems. It has recently been shown that one member of an intracellular PRR, the NLRP3 inflammasome, is activated by a number of classical adjuvants including aluminum hydroxide and saponins [Eisenbarth SC, Colegio OR, O'Connor W, Sutterwala FS, Flavell RA. Crucial role for the Nalp3 inflammasome in the immunostimulatory properties of aluminium adjuvants. Nature 2008;453(June (7198)):1122-6; Li H, Willingham SB, Ting JP, Re F. Cutting edge: inflammasome activation by alum and alum's adjuvant effect are mediated by NLRP3. J Immunol 2008;181(July (1)):17-21]. Inflammasome activation in vitro requires signaling of both the Toll-like receptor (TLR) and NLRP3 in antigen-presenting cells. Here we present a class of nanomaterials endowed with these two signals for rapid optimization of vaccine design. We constructed this system using a simple approach that incorporates lipopolysaccharides (LPS) onto the surface of nanoparticles constructed from a biocompatible polyester, poly(lactic-co-glycolic acid) (PLGA), loaded with antigen. We demonstrate that LPS-modified particles are preferentially internalized by dendritic cells compared to uncoated nanoparticles and the system, when administered to mice, elicits potent humoral and cellular immunity against a model antigen, ovalbumin. Wild-type macrophages pulsed with LPS-modified nanoparticles resulted in production of the proinflammatory cytokine IL-1beta consistent with inflammasome activation. In comparison, NLRP3-deficient and caspase-1-deficient macrophages showed negligible production of IL-1beta. Furthermore, when endocytosis and lysosomal destabilization were inhibited, inflammasome activity was diminished, supporting the notion that nanoparticles rupture lysosomal compartments and behave as 'danger signals' [Hornung V, Bauernfeind F, Halle A, Samstad EO, Kono H, Rock KL, et al. Silica crystals and aluminum salts activate the NALP3 inflammasome through phagosomal destabilization. Nat Immunol 2008;9(August (8)):847-56]. The generality of this vaccination approach is tested by encapsulation of a recombinant West Nile envelope protein and demonstrated by protection against a murine model of West Nile encephalitis. The design of such an antigen delivery mechanism with the ability to stimulate two potent innate immune pathways represents a potent new approach to simultaneous antigen and adjuvant delivery.

Vaccine adjuvants: current challenges and future approaches

For humans, companion animals, and food producing animals, vaccination has been touted as the most successful medical intervention for the prevention of disease in the twentieth century. However, vaccination is not without problems. With the development of new and less reactogenic vaccine antigens, which take advantage of molecular recombinant technologies, also comes the need for more effective adjuvants that will facilitate the induction of adaptive immune responses. Furthermore, current vaccine adjuvants are successful at generating humoral or antibody mediated protection but many diseases currently plaguing humans and animals, such as tuberculosis and malaria, require cell mediated immunity for adequate protection. A comprehensive discussion is presented of current vaccine adjuvants, their effects on the induction of immune responses, and vaccine adjuvants that have shown promise in recent literature.

Lipid A-induced responses in vivo

The lipid A analogs used in preclinical studies and clinical trials are not naturally-occurring forms of lipid A; they are synthetic molecules produced to be less toxic than lipid A itself and they do not reproduce the effects of natural lipid A molecules especially in vivo. The responses induced by lipid A analogs are summarized in this chapter: their fate in the blood stream and their toxicity as well as the lipid A tolerance and the tumor immune responses they induce. Lipid A is not found in the mammalian organism under normal circumstances so its use in cancer therapy raises important questions as to its different effects in vivo and its toxicity, particularly in cancer patients. Lipid A has to be injected intravenously (i.v.) to study its effects. Injections of chemically synthesized lipid A in humans and in animals produce sepsis symptoms, such as tachycardia, tachypnea, hyper or hypothermia and leukocytosis or leukopenia. Similar manifestations are observed after injection of purified lipopolysaccharide (LPS), which is why lipid A is usually thought of as the active part of LPS. While lipid A injection is therefore expected to induce reactions similar to septic shock, the lipid A molecules used to treat cancer are not natural forms but analogs, produced by chemical synthesis or genetic engineering, specifically selected for their low toxicity. The in vivo effects of such low-toxicity lipid A analogs are summarized in this chapter.

Putting endotoxin to work for us: monophosphoryl lipid A as a safe and effective vaccine adjuvant

The development of non-infectious subunit vaccines greatly increases the safety of prophylactic immunization, but also reinforces the need for a new generation of immunostimulatory adjuvants. Because adverse effects are a paramount concern in prophylactic immunization, few new adjuvants have received approval for use anywhere in the developed world. The vaccine adjuvant monophosphoryl lipid A is a detoxified form of the endotoxin lipopolysaccharide, and is among the first of a new generation of Toll-like receptor agonists likely to be used as vaccine adjuvants on a mass scale in human populations. Much remains to be learned about this compound's mechanism of action, but recent developments have made clear that it is unlikely to be simply a weak version of lipopolysaccharide. Instead, monophosphoryl lipid A's structure seems to have fortuitously retained several functions needed for stimulation of adaptive immune responses, while shedding those associated with pro-inflammatory side effects.