Lipopeptide adjuvants in combination treatment

Immunogenicity of anthrax recombinant peptides and killed spores in goats and protective efficacy of immune sera in A/J mouse model

Anthrax is primarily recognized as an affliction of herbivores with incubation period ranging from three to five days post-infection. Currently, the Sterne live-spore vaccine is the only vaccine approved for control of the disease in susceptible animals. While largely effective, the Sterne vaccine has several problems including adverse reactions in sensitive species, ineffectiveness in active outbreaks and incompatibility with antibiotics. These can be surmounted with the advent of recombinant peptides (non-living) next generation vaccines. The candidate vaccine antigens comprised of recombinant protective antigen (PA), spore-specific antigen (bacillus collagen-like protein of anthracis, BclA) and formaldehyde inactivated spores (FIS). Presently, little information exists on the protectivity of these novel vaccine candidates in susceptible ruminants. Thus, this study sought to assess the immunogenicity of these vaccine candidates in goats and evaluate their protectivity using an in vivo mouse model. Goats receiving a combination of PA, BclA and FIS yielded the highest antibody and toxin neutralizing titres compared to recombinant peptides alone. This was also reflected in the passive immunization experiment whereby mice receiving immune sera from goats vaccinated with the antigen combination had higher survival post-challenge. In conclusion, the current data indicate promising potential for further development of non-living anthrax vaccines in ruminants.

Innate Immune Responses in Leprosy

Leprosy is an infectious disease that may present different clinical forms depending on host immune response to Mycobacterium leprae. Several studies have clarified the role of various T cell populations in leprosy; however, recent evidences suggest that local innate immune mechanisms are key determinants in driving the disease to its different clinical manifestations. Leprosy is an ideal model to study the immunoregulatory role of innate immune molecules and its interaction with nervous system, which can affect homeostasis and contribute to the development of inflammatory episodes during the course of the disease. Macrophages, dendritic cells, neutrophils, and keratinocytes are the major cell populations studied and the comprehension of the complex networking created by cytokine release, lipid and iron metabolism, as well as antimicrobial effector pathways might provide data that will help in the development of new strategies for leprosy management.

A purified recombinant lipopeptide as adjuvant for cancer immunotherapy

Synthetic lipopeptides have been widely used as vaccine adjuvants to enhance immune responses. The present study demonstrated that the tryptic N-terminal fragment of the lipoprotein rlipo-D1E3 (lipo-Nter) induces superior antitumor effects compared to a synthetic lipopeptide. The lipo-Nter was purified and formulated with protein or peptide vaccines to determine if lipo-Nter could be used as a novel adjuvant and could induce antitumor immunity in a cervical cancer model. Purified lipo-Nter activated the maturation of bone marrow-derived dendritic cells (BM-DCs), leading to the secretion of TNF-α through TLR2/6 but not TLR1/2. A recombinant mutant HPV16 E7 (rE7m) protein was mixed with lipo-Nter to immunize the mice; the anti-E7 antibody titers were increased, and the T helper cells were skewed toward the Th1 fate (increased IL-2 and decreased IL-5 secretion). Single-dose injection of rE7m and lipo-Nter inhibited tumor growth, but the injection of rE7m alone did not. Accordingly, lipo-Nter also enhanced the antitumor immunity of the E7-derived peptide but not the synthetic lipopeptide (Pam3CSK4). We demonstrated that the lipo-Nter of a bacterial-derived recombinant lipoprotein is a novel adjuvant that could be used for the development of a new generation of vaccines.

Deciphering PDT-induced inflammatory responses using real-time FDG-PET in a mouse tumour model

Dynamic positron emission tomography (PET), combined with constant infusion of 2-deoxy-2-[¹⁸F]fluoro-d-glucose (FDG), enables real-time monitoring of transient metabolic changesin vivo, which can serve to understand the underlying physiology.

Therapeutic impact of toll-like receptors on inflammatory bowel diseases: a multiple-edged sword

Recent studies have begun to define the mechanisms through which Toll-like receptors (TLRs) regulate intestinal homeostasis in health and disease. Current therapies for inflammatory bowel diseases (IBDs) mostly aim at interrupting the inflammatory cascade through agents that regulate TH1 or TH2 cytokine responses. As recognition grows for TLR dysfunction to play a role in IBD pathogenesis, TLRs could provide another valid interventional target for novel therapy development. However, seemingly contradictory results from studying different murine models of colitis have so far confounded whether therapeutically useful modulation of TLRs is best accomplished by activating, inhibiting, or rather a combination of both at different stages of mucosal disease. This review evaluates potential strategies as well as their rationale and future prospects.

Using distinct molecular signatures of human monocytes and dendritic cells to predict adjuvant activity and pyrogenicity of TLR agonists

We present a systematic study that defines molecular profiles of adjuvanticity and pyrogenicity induced by agonists of human Toll-like receptor molecules in vitro. Using P₃CSK₄, Lipid A and Poly I:C as model adjuvants we show that all three molecules enhance the expansion of IFNγ⁺/CD4⁺ T cells from their naïve precursors following priming with allogeneic DC in vitro. In contrast, co-culture of naive CD4⁺ T cells with allogeneic monocytes and TLR2/TLR4 agonists only resulted in enhanced T cell proliferation. Distinct APC molecular signatures in response to each TLR agonist underline the dual effect observed on T cell responses. Using protein and gene expression assays, we show that TNF-α and CXCL10 represent DC-restricted molecular signatures of TLR2/TLR4 and TLR3 activation, respectively, in sharp contrast to IL-6 produced by monocytes upon stimulation with P₃CSK₄ and Lipid A. Furthermore, although all TLR agonists are able to up-regulate proIL-1β specific gene in both cell types, only monocyte activation with Lipid A results in detectable IL-1β release. These molecular profiles, provide a simple screen to select new immune enhancers of human Th1 responses suitable for clinical application.

Induction of apoptosis in human leukemia K562 cells by cyclic lipopeptide from Bacillus subtilis natto T-2

A new cyclic lipopeptide (CLP) purified from Bacillus subtilis natto T-2 dose dependently inhibited growth in human leukemia K562 cells. The results of fluorescent staining indicated that CLP brought about apoptosis in K562 cells. Flow cytometric analysis also demonstrated that CLP caused dose-dependent apoptosis of K562 cells through cell arrest at G1 phase. Western blotting revealed that CLP-induced apoptosis in K562 cells was associated with caspase-3 and poly(ADP-ribose)polymerase (PARP) protein. It is estimated that CLP inhibited proliferation in K562 cells by inducing apoptosis.

Cytotoxic T lymphocyte response induced by an improved synthetic lipopeptide vaccine against cervical cancer

AIM

To explore cytotoxic T lymphocyte (CTL) response induced by the lipopeptide vaccine against cervical cancer.

METHODS

The immunological effect inducing CD8+ T cell-mediated cytotoxicity was investigated in human leukocyte antigen (HLA)-A2 transgenic mice and peripheral blood mononuclear cells (PBMC) of healthy HLA-A2.1+blood donor. The activity of specific CTL was measured by using a standard 4 h( 51)Cr release assay. The content of major histocompatibility complex (MHC) I on T2 cells and the expression of immune molecules on dendritic cells (DC) were detected by flow cytometry, and the concentrations of interleukin (IL)-12 and interferon-gamma were determined by ELISA.

RESULTS

The lipopeptide induced a strong epitope-specific CTL response both in vivo (transgenic mice) and in vitro (human PBMC). This CTL induction was critically dependent on the presence of the helper T lymphocyte epitope in transgenic mice, and the presence of a lipid tail bypassed the need for an adjuvant. The stability and persistence of the antigenic complex formed with the lipopeptide increased in comparison with the CTL parental peptide. The lipopeptide could induce the production of IL-12 in DC, but not the maturation of DC directly.

CONCLUSION

The combination of CTL and the T helper epitope and lipid molecule can remarkably improve the immunogenicity of the CTL peptide, the mechanism of which is associated with an increase in the stability and persistence of the antigenic complex formed with the lipopeptide and in the production of IL-12 in DC induced by the lipopeptide. The lipopeptide can be considered a more effective vaccine type for human being.

Lipopeptide structure determines TLR2 dependent cell activation level

Bacterial lipoproteins/peptides are composed of di-O-acylated-S-(2,3-dihydroxypropyl)-cysteinyl residues N-terminally coupled to distinct polypeptides, which can be N-acylated with a third fatty acid. Using a synthetic lipopeptide library we characterized the contribution of the lipid portion to the TLR2 dependent pattern recognition. We found that the two ester bound fatty acid length threshold is beyond eight C atoms because almost no response was elicited by cellular challenge with analogues carrying shorter acyl chains in HEK293 cells expressing recombinant human TLR2. In contrast, the amide bound fatty acid is of lesser importance. While two ester-bound palmitic acids mediate a high stimulatory activity of the respective analogue, a lipopeptide carrying one amide-bound and another ester-bound palmitic acid molecule was inactive. In addition, species specific LP recognition through murine and human TLR2 depended on the length of the two ester bound fatty acid chains. In conclusion, our results indicate the responsibility of both ester bound acyl chains but not of the amide bound fatty acid molecule for the TLR dependent cellular recognition of canonical triacylated LP, as well as a requirement for a minimal acyl chain length. Thus they might support the explanation of specific immuno-stimulatory potentials of different microorganisms and provide a basis for rational design of TLR2 specific adjuvants mediating immune activation to distinct levels.

Synthetic bacterial lipopeptide analogs: structural requirements for adjuvanticity

Modern vaccines aim at conferring immune protection, independently of the nature of the etiological agent causing the disease. These new therapeutics are based on highly purified antigenic moieties that offer potential advantages over traditional vaccines, including a high degree of safety and the capacity of eliciting highly specific immune responses. In spite of these advantages however, subunit vaccines tend to be poorly immunogenic in vivo, and require the coadministration of adjuvants that indirectly enhance cellular immunity. Thus, recombinant vaccines development is dependent on the design of new molecules, non-immunogenic per se, but endowed with immune modulatory properties. Synthetic analogs of bacterial lipoproteins were described more than a decade ago, but their capacity to act as adjuvants has been only recently dissected. These low molecular weight non-immunogenic molecules can be reproducibly synthetized, are safe, and of easy handling and administration. Furthermore, new experimental data from our laboratory reveal their powerful adjuvant effect on human HLA-I/II restricted T cell responses and identify the molecular and cellular requirements for optimal adjuvanticity.