The identification of plant lectins with mucosal adjuvant activity

Lectin-modified drug delivery systems - Recent applications in the oncology field

Chemotherapy with cytotoxic drugs remains the core treatment for cancer but, due to the difficulty to find general and usable biochemical differences between cancer cells and normal cells, many of these drugs are associated with lack of specificity, resulting in side effects and collateral cytotoxicity that impair patients' adherence to therapy. Novel cancer treatments in which the cytotoxic effect is maximized while adverse effects are reduced can be implemented by developing targeted therapies that exploit the specific features of cancer cells, such as the typical expression of aberrant glycans. Modification of drug delivery systems with lectins is one of the strategies to implement targeted chemotherapies, as lectins are able to specifically recognize and bind to cancer-associated glycans expressed at the surface of cancer cells, guiding the drug treatment towards these cells and not affecting healthy ones. In this paper, recent advances on the development of lectin-modified drug delivery systems for targeted cancer treatments are thoroughly reviewed, with a focus on their properties and performance in diverse applications, as well as their main advantages and limitations. The synthesis and analytical characterization of the cited lectin-modified drug delivery systems is also briefly described. A comparison with free-drug treatments and with antibody-modified drug delivery systems is presented, emphasizing the advantages of lectin-modified drug delivery systems. Main constraints and potential challenges of lectin-modified drug delivery systems, including key difficulties for clinical translation of these systems, and the required developments in this area, are also signalled.

Plant-derived immuno-adjuvants in vaccines formulation: a promising avenue for improving vaccines efficacy against SARS-CoV-2 virus

The SARS-CoV-2 outbreak has posed a plethora of problems for the global healthcare system and socioeconomic burden. Despite valiant efforts to contain the COVID-19 outbreak, the situation has deteriorated to the point that there are no viable preventive therapies to treat this disease. The case count has skyrocketed globally due to the newly evolved variants. Despite vaccination drives, the re-occurrence of recent pandemic waves has reinforced the importance of innovation/utilization of immune-booster to achieve appropriate long-term vaccine protection. Plant-derived immuno-adjuvants, which have multifaceted functions, can impede infections by boosting the immune system. Many previous studies have shown that formulation of vaccines using plant-derived adjuvant results in long-lasting immunity may overcome the natural tendency of coronavirus immunity to wane quickly. Plant polysaccharides, glycosides, and glycoprotein extracts have reportedly been utilized as enticing adjuvants in experimental vaccines, such as Advax, Matrix-M, and Mistletoe lectin, which have been shown to be highly immunogenic and safe. When employed in vaccine formulation, Advax and Matrix-M generate long-lasting antibodies, a balanced robust Th1/Th2 cytokine profile, and the stimulation of cytotoxic T cells. Thus, the use of adjuvants derived from plants may increase the effectiveness of vaccines, resulting in the proper immunological response required to combat COVID-19. A few have been widely used in epidemic outbreaks, including SARS and H1N1 influenza, and their use could also improve the efficacy of COVID-19 vaccines. In this review, the immunological adjuvant properties of plant compounds as well as their potential application in anti-COVID-19 therapy are thoroughly discussed.

In-silico structural inhibition of ACE-2 binding site of SARS-CoV-2 and SARS-CoV-2 Omicron spike protein by lectin antiviral dyad system to treat COVID-19

Spike glycoprotein of SARS-CoV-2 binds ACE-2 receptors via its receptor-binding-domain (RBD) and mediates virus-to-host cell fusion. Recently emerged omicron variant of SARS-CoV-2 possess around 30 mutations in spike protein where N501Y tremendously increases viral infectivity and transmission. Lectins interact with glycoproteins and mediate innate immunity displaying antiviral, antibacterial and anticarcinogenic properties. In this study, we analysed the potential of lectin, and lectin-antibody (spike-specific) complex to inhibit the ACE-2 binding site of wild and N501Y mutated spike protein by utilizing in-silico molecular docking and simulation approach. Docking of lectin at reported ACE-2 binding spike-RBD residues displayed the ZDock scores of 1907 for wild and 1750 for N501Y mutated spike-RBD. Binding of lectin with antibody to form proposed dyad complex gave ZDock score of 1174 revealing stable binding. Docking of dyad complex with wild and N501Y mutated spike-RBD, at lectin and antibody individually, showed high efficiency binding hence, effective structural inhibition of spike-RBD. MD simulation of 100ns of each complex proved high stability of complexes with RMSD values ranging from 0.2 -1.5nm. Consistent interactions of lead ACE-2 binding spike residues with lectin during simulation disclosed efficient structural inhibition by lectin against formation of spike RBD-ACE-2 complex.Hence, lectins along with their ability to induce innate immunity against spike glycoprotein can structurally inhibit the spike-RBD when given as lectin-antibody dyad system and thus can be developed into a dual effect treatment against COVID-19. Moreover, the high binding specificity of this system with spike-RBD can be exploited for development of diagnostic and drug-delivery systems.

Immunostimulant plant proteins: Potential candidates as vaccine adjuvants

The COVID-19 pandemic is shaking up global scientific structures toward addressing antibiotic resistance threats and indicates an urgent need to develop more cost-effective vaccines. Vaccine adjuvants play a crucial role in boosting immunogenicity and improving vaccine efficacy. The toxicity and adversity of most adjuvant formulations are the major human immunization problems, especially in routine pediatric and immunocompromised patients. The present review focused on preclinical studies of immunoadjuvant plant proteins in use with antiparasitic, antifungal, and antiviral vaccines. Moreover, this report outlines the current perspective of immunostimulant plant protein candidates that can be used by researchers in developing new generations of vaccine-adjuvants. Future clinical studies are required to substantiate the plant proteins' safety and applicability as a vaccine adjuvant in pharmaceutical manufacturing.

Immunoadjuvant and Humoral Immune Responses of Garlic (Allium sativum L.) Lectins upon Systemic and Mucosal Administration in BALB/c Mice

Dietary food components have the ability to affect immune function; following absorption, specifically orally ingested dietary food containing lectins can systemically modulate the immune cells and affect the response to self- and co-administered food antigens. The mannose-binding lectins from garlic (Allium sativum agglutinins; ASAs) were identified as immunodulatory proteins in vitro. The objective of the present study was to assess the immunogenicity and adjuvanticity of garlic agglutinins and to evaluate whether they have adjuvant properties in vivo for a weak antigen ovalbumin (OVA). Garlic lectins (ASA I and ASA II) were administered by intranasal (50 days duration) and intradermal (14 days duration) routes, and the anti-lectin and anti-OVA immune (IgG) responses in the control and test groups of the BALB/c mice were assessed for humoral immunogenicity. Lectins, co-administered with OVA, were examined for lectin-induced anti-OVA IgG response to assess their adjuvant properties. The splenic and thymic indices were evaluated as a measure of immunomodulatory functions. Intradermal administration of ASA I and ASA II had showed a four-fold and two-fold increase in anti-lectin IgG response, respectively, vs. the control on day 14. In the intranasal route, the increases were 3-fold and 2.4-fold for ASA I and ASA II, respectively, on day 50. No decrease in the body weights of animals was noticed; the increases in the spleen and thymus weights, as well as their indices, were significant in the lectin groups. In the adjuvanticity study by intranasal administration, ASA I co-administered with ovalbumin (OVA) induced a remarkable increase in anti-OVA IgG response (~six-fold; p < 0.001) compared to the control, and ASA II induced a four-fold increase vs. the control on day 50. The results indicated that ASA was a potent immunogen which induced mucosal immunogenicity to the antigens that were administered intranasally in BALB/c mice. The observations made of the in vivo study indicate that ASA I has the potential use as an oral and mucosal adjuvant to deliver candidate weak antigens. Further clinical studies in humans are required to confirm its applicability.

Scientific Opinion on development needs for the allergenicity and protein safety assessment of food and feed products derived from biotechnology

This Scientific Opinion addresses the formulation of specific development needs, including research requirements for allergenicity assessment and protein safety, in general, which is urgently needed in a world that demands more sustainable food systems. Current allergenicity risk assessment strategies are based on the principles and guidelines of the Codex Alimentarius for the safety assessment of foods derived from 'modern' biotechnology initially published in 2003. The core approach for the safety assessment is based on a 'weight-of-evidence' approach because no single piece of information or experimental method provides sufficient evidence to predict allergenicity. Although the Codex Alimentarius and EFSA guidance documents successfully addressed allergenicity assessments of single/stacked event GM applications, experience gained and new developments in the field call for a modernisation of some key elements of the risk assessment. These should include the consideration of clinical relevance, route of exposure and potential threshold values of food allergens, the update of in silico tools used with more targeted databases and better integration and standardisation of test materials and in vitro/in vivo protocols. Furthermore, more complex future products will likely challenge the overall practical implementation of current guidelines, which were mainly targeted to assess a few newly expressed proteins. Therefore, it is timely to review and clarify the main purpose of the allergenicity risk assessment and the vital role it plays in protecting consumers' health. A roadmap to (re)define the allergenicity safety objectives and risk assessment needs will be required to inform a series of key questions for risk assessors and risk managers such as 'what is the purpose of the allergenicity risk assessment?' or 'what level of confidence is necessary for the predictions?'.

Promising Plant-Derived Adjuvants in the Development of Coccidial Vaccines

Coccidial parasites cause medical and veterinary diseases worldwide, frequently leading to severe illness and important economic losses. At present, drugs, chemotherapeutics and prophylactic vaccines are still missing for most of the coccidial infections. Moreover, the development and administration of drugs and chemotherapeutics against these diseases would not be adequate in livestock, since they may generate unacceptable residues in milk and meat that would avoid their commercialization. In this scenario, prophylactic vaccines emerge as the most suitable approach. Subunit vaccines have proven to be biologically safe and economically viable, allowing researchers to choose among the best antigens against each pathogen. However, they are generally poorly immunogenic and require the addition of adjuvant compounds to the vaccine formulation. During the last decades, research involving plant immunomodulatory compounds has become an important field of study based on their potential pharmaceutical applications. Some plant molecules such as saponins, polysaccharides, lectins and heat shock proteins are being explored as candidates for adjuvant/carriers formulations. Moreover, plant-derived immune stimulatory compounds open the possibility to attain the main goal in adjuvant research: a safe and non-toxic adjuvant capable of strongly boosting and directing immune responses that could be incorporated into different vaccine formulations, including mucosal vaccines. Here, we review the immunomodulatory properties of several plant molecules and discuss their application and future perspective as adjuvants in the development of vaccines against coccidial infections.

Humoral immune and adjuvant responses of mucosally-administered Tinospora cordifolia immunomodulatory protein in BALB/c mice

Background

In traditional medicine, guduchi (Tinospora cordifolia) is considered as an adaptogen with immunomodulatory prowess. A 25 kDa protein from guduchi stem has been characterized as an immunomodulatory protein (ImP).

Objectives

The aim of this study was to evaluate the intrinsic immunogenicity of guduchi ImP and adjuvant activity using ovalbumin (OVA) as antigen in BALB/c mice.

Materials and Methods

Mice were given guduchi ImP (30 and 60 μg) by intranasal administration to respective groups (n = 6) on days 1, 14 and thereafter weekly till day 42. Immunogenic response was monitored by serum IgG/IgA levels (days 14, 35 and 50). The adjuvant activity was measured by serum anti-OVA IgG/IgA responses to administration of 30 μg OVA with guduchi ImP. The effect of guduchi ImP on the spleen status was examined by splenic weight (day 50).

Results

Guduchi ImP administration displayed a significant increase in anti-guduchi ImP IgG (5–7 fold) and anti-guduchi ImP IgA (3–4 fold) on day 50 vs. control. Guduchi ImP showed a significant increase in anti-OVA IgG (6–7 fold) and anti-OVA IgA (4–5 fold) on day 50 vs. control. The splenic index of guduchi ImP group increased significantly in both the immune and adjuvant response groups; however, the splenic index in the adjuvant response group was markedly higher.

Conclusion

The results indicate that guduchi ImP is a strong immunogen by itself and enhances the immunogenicity of mucosally-administered antigen in BALB/c mice. Based on the results of this animal study, it appears that guduchi ImP shows a potential for future studies in humans.

•

Evaluated the immune responses of guduchi immunomodulatory protein (ImP) in BALB/c mice.

•

Guduchi ImP (30/60 μg) given intranasally on days 1, 14; thereafter, weekly till day 42.

•

Increase in anti-guduchi ImP IgG (5–7 fold) and anti-guduchi ImP IgA (3–4 fold) on day 50.

•

Increase in ovalbumin-specific IgG (6–7 fold) and IgA (4–5 fold) on day 50 vs. control.

•

Splenic index of guduchi ImP group increased in the immune/adjuvant response groups.

Recent advances on biodegradable polymeric carrier-based mucosal immunization: an overview

Mucosal administration of vaccine is most prevalent way to induce desired immunity against various types of antigen and microbial in central and in addition, the peripheral blood in most external mucosal surface. Mucosal delivery of vaccine provides both humoral and cellular responses against mucosal infection. Mucosa, which are exposed to heavy loads of commensal and pathogenic microorganism, are one of the main region where infections are built up, also, thus have frontline status in immunity, making mucosa perfect site for vaccines application. The nasal route is favoured over parenteral route due to ease of administration, protection of antigen from degradation and induces sIgA which is not produced by systemic immunity. Natural and synthetic polymers are utilized to get nanoparticles carrier systems for development of nasal mucosal antibodies. The present review summarized the recent development in the field of vaccine delivery by means of mucoadhesive polymeric carriers. This review also describes the recent patent conceded for mucosal immunization utilizing these polymeric carriers.

Alleviation of cyclophosphamide-induced immunosuppression in Wistar rats by onion lectin (Allium cepa agglutinin)

ETHNOPHARMACOLOGICAL RELEVANCE

In various traditional medicines, onion has been classified as an immune-boosting food. Recent studies have claimed this property due to the presence of bioactive organosulfur compounds, prebiotic fructo-oligosaccharides and an immunomodulatory protein, lectin (Allium cepa agglutinin; ACA) (Prasanna and Venkatesh, 2015. Characterization of onion lectin (Allium cepa agglutinin) as an immunomodulatory protein inducing Th1-type immune response in vitro. Int. Immunopharmacol. vol. 26, pp. 304-313).

AIM OF THE STUDY

The aim of this study was to evaluate the immunoprotective properties of ACA in normal and cyclophosphamide (CP; 100μg/kg)-induced immunosuppressed Wistar rats.

MATERIALS AND METHODS

Wistar rats were administrated different doses of ACA (1, 10, and 100μg) to respective groups in normal as well as immunosuppressed animals. The effect of ACA on the status of immune organs was assessed by examining the splenic and thymic indices, and histopathological changes. The biomarkers for humoral immunity (serum IgG and IgA levels) and serum pro-inflammatory markers (COX-2, TNF-α and IL-10) were measured by ELISA.

RESULTS

ACA showed immunoprotective properties by significantly promoting the restoration of lymphoid cell count by ~6 fold vs. model control (immunosuppressed animals) and promotes the immune response significantly (~1.5-fold) in CP-induced immunosuppressed animals compared to model control; production of pro-inflammatory molecules (COX-2 and nitric oxide) and expression levels of immune regulatory molecule (TNF-α) were elevated in a dose-dependent manner.

CONCLUSIONS

The observed in vivo results suggest that ACA has the potential to be used as a nutritional therapeutic to boost the immune status of immunosuppressed subjects brought about by CP administration.

Biochemical and Immunological Characterization of Truncated Fragments of the Receptor-Binding Domains of C. difficile Toxin A

Clostridium difficile is an emerging pathogen responsible for opportunistic infections in hospitals worldwide and is the main cause of antibiotic-associated pseudo-membranous colitis and diarrhea in humans. Clostridial toxins A and B (TcdA and TcdB) specifically bind to unknown glycoprotein(s) on the surface of epithelial cells in the host intestine, disrupting the intestinal barrier and ultimately leading to acute inflammation and diarrhea. The C-terminal receptor-binding domain (RBD) of TcdA, which is responsible for the initial binding of the toxin to host glycoproteins, has been predicted to contain 7 potential oligosaccharide-binding sites. To study the specific roles and functions of these 7 putative lectin-like binding regions, a consensus sequence of TcdA RBD derived from different C. difficile strains deposited in the NCBI protein database and three truncated fragments corresponding to the N-terminal (residues 1–411), middle (residues 296–701), and C-terminal portions (residues 524–911) of the RBD (F1, F2 and F3, respectively) were designed and expressed in Escherichia coli. In this study, the recombinant RBD (rRBD) and its truncated fragments were purified, characterized biologically and found to have the following similar properties: (a) are capable of binding to the cell surface of both Vero and Caco-2 cells; (b) possess Toll-like receptor agonist-like adjuvant activities that can activate dendritic cell maturation and increase the secretion of pro-inflammatory cytokines; and (c) function as potent adjuvants in the intramuscular immunization route to enhance immune responses against weak immunogens. Although F1, F2 and F3 have similar repetitive amino acid sequences and putative oligosaccharide-binding domains, they do not possess the same biological and immunological properties: (i) TcdA rRBD and its fragments bind to the cell surface, but only TcdA rRBD and F3 internalize into Vero cells within 15 min; (ii) the fragments exhibit various levels of hemagglutinin (HA) activity, with the exception of the F1 fragment, which demonstrates no HA activity; and (iii) in the presence of alum, all fragments elicit various levels of anti-toxin A-neutralizing antibody responses, but those neutralizing antibodies elicited by F2 did not protect mice against a TcdA challenge. Because TcdA rRBD, F1 and F3 formulated with alum can elicit immune protective responses against the cytotoxicity of TcdA, they represent potential components of future candidate vaccines against C. difficile-associated diseases.

Characterization of onion lectin (Allium cepa agglutinin) as an immunomodulatory protein inducing Th1-type immune response in vitro

Onion (Allium cepa), a bulb crop of economic importance, is known to have many health benefits. The major objective of the present study is to address the immunomodulatory properties of onion lectin (A. cepa agglutinin; ACA). ACA was purified from onion extract by D-mannose-agarose chromatography (yield: ~1 mg/kg). ACA is non-glycosylated and showed a molecular mass of ~12 kDa under reducing/non-reducing SDS-PAGE; glutaraldehyde cross-linking indicated that ACA is a non-covalent tetramer of ~12 kDa subunits. Its N-terminal sequence (RNVLLNNEGL; UniProt KB Accn. C0HJM8) showed 70-90% homology to mannose-specific Allium agglutinins. ACA showed specific hemagglutination activity of 8200 units/mg and is stable in the pH range 6-10 and up to 45° C. The immunomodulatory activity of ACA was assessed using the macrophage cell line, RAW264.7 and rat peritoneal macrophages; at 0.1 μg/well, it showed a significant increase (6-8-fold vs. control) in the production of nitric oxide at 24h, and significantly stimulated (2-4-fold vs. control) the production of pro-inflammatory cytokines (TNF-α and IL-12) at 24h. ACA (0.1 μg/well) enhanced the proliferation of murine thymocytes by ~4 fold (vs. control) at 24h; however, ACA does not proliferate B cell-enriched rat splenocytes. Further, it significantly elevated the expression levels of cytokines (IFN-γ and IL-2) over the control in murine thymocytes. Taken together, purified ACA induces a Th1-type immune response in vitro. Though present in low amounts, ACA may contribute to the immune-boosting potential of the popular spice onion since considerable amounts are consumed on a daily basis universally.

Development and characterization of LTA-appended chitosan nanoparticles for mucosal immunization against hepatitis B

The present study was aimed at exploring the targeting potential of LTA-anchored chitosan nanoparticles (CH-NP) specifically to M cell following oral immunization. The lectinized CH-NP exhibited 7-29% coupling capacity depending upon the amount of glutaraldehyde added. Induction of the mucosal immunity was assessed by estimating secretory IgA level in the salivary, intestinal and vaginal secretions, and cytokine (IL-2 and IFN-γ) levels in the spleen homogenates. The results demonstrated that LTA-anchored CH-NP elicited strong humoral and cellular responses and hence could be a competent carrier-adjuvant delivery system for oral mucosal immunization against Hepatitis B.

Granzyme B-dependent proteolysis acts as a switch to enhance the proinflammatory activity of IL-1α

Granzyme B is a cytotoxic lymphocyte-derived protease that plays a central role in promoting apoptosis of virus-infected target cells, through direct proteolysis and activation of constituents of the cell death machinery. However, previous studies have also implicated granzymes A and B in the production of proinflammatory cytokines, via a mechanism that remains undefined. Here we show that IL-1α is a substrate for granzyme B and that proteolysis potently enhanced the biological activity of this cytokine in vitro as well as in vivo. Consistent with this, compared with full-length IL-1α, granzyme B-processed IL-1α exhibited more potent activity as an immunoadjuvant in vivo. Furthermore, proteolysis of IL-1α within the same region, by proteases such as calpain and elastase, was also found to enhance its biological potency. Thus, IL-1α processing by multiple immune-related proteases, including granzyme B, acts as a switch to enhance the proinflammatory properties of this cytokine.

Flagellin produced in plants is a potent adjuvant for oral immunization

The aim of this study was to produce adjuvant with high biosafety, efficacy and low cost. Towards this goal, the plant Nicotiana benthamiana transient expression system was successfully used to express Salmonella typhimurium's flagellin (FljB). The yield of the expressed FljB was 280 mg per kg of fresh weight (FW) leaves. The lyophilized plant powder containing plant expressing FljB was mixed with ovalbumin (OVA) and used for oral immunization of BALB/c mice. The ELISA analysis showed higher and accelerated OVA-specific serum antibody responses in mice given the mixture when compared to animals receiving OVA alone. Furthermore, FljB elicited a mixed Th1/Th2 response as shown by the presence of specific anti-OVA IgG1, IgG2a and IgG2b isotypes. OVA-specific IgAs were also detected in mice given the mixture. Cell-mediated immune response to OVA was induced by FljB as determined by a spleen lymphocyte specific proliferation test. No immune response was generated against FljB. In conclusion, our results showed for the first time the production of FljB in plants and the efficient use of the crude lyophilized extract as an adjuvant for oral immunization.

Safety of higher dosages of Viscum album L. in animals and humans--systematic review of immune changes and safety parameters

BACKGROUND

Viscum album L extracts (VAE, mistletoe) and isolated mistletoe lectins (ML) have immunostimulating properties and a strong dose-dependent cytotoxic activity. They are frequently used in complementary cancer treatment, mainly to improve quality of life, but partly also to influence tumour growth, especially by injecting VAE locally and in high dosage. The question is raised whether these higher dosages can induce any harm or immunosuppressive effects.

METHODS

Systematic review of all experiments and clinical studies investigating higher dosages of VAE in animals and humans (Viscum album > 1 mg in humans corresponding to > 0.02 mg/kg in animals or ML > 1 ng/kg) and assessing immune parameters or infections or adverse drug reactions.

RESULTS

69 clinical studies and 48 animal experiments reported application of higher doses of VAE or ML and had assessed immune changes and/or harm. In these studies, Viscum album was applied in dosages up to 1500 mg in humans and 1400 mg/kg in animals, ML was applied up to 6.4 μg/kg in humans and in animals up to 14 μg/kg subcutaneously, 50 μg/kg nasally and 500 μg/kg orally. A variety of immune parameters showed fluctuating or rising outcomes, but no immunosuppressive effect. Side effects consisted mainly of dose-dependent flu-like symptoms (FLS), fever, local reactions at the injection site and various mild unspecific effects. Occasionally, allergic reactions were reported. After application of high doses of recombinant ML, reversible hepatotoxicity was observed in some cases.

CONCLUSIONS

Application of higher dosages of VAE or ML is not accompanied by immunosuppression; altogether VAE seems to exhibit low risk but should be monitored by clinicians when applied in high dosages.

Fructans from aged garlic extract produce a delayed immunoadjuvant response to ovalbumin antigen in BALB/c mice

Garlic (Allium sativum) is known for its innumerable biological activities including immunomodulation. Aged garlic extract (AGE), an odorless garlic preparation, has been shown to have superior immunomodulatory properties over raw garlic extract. Although garlic is a very rich source of fructans (17%, fresh weight basis), AGE contains only 0.22% of raw garlic fructans. Aged garlic fructans (AGF) have recently been shown to possess immunomodulatory activities in vitro. Natural adjuvants capable of eliciting better immune response of a model antigen are important in developing newer vaccines. In the present study, the adjuvant activity of AGF has been investigated in BALB/c mice using ovalbumin (OVA, 30 µg) as an experimental antigen. The body weights of animals did not change significantly indicating that the administration of garlic fructans is well-tolerated. AGF produce a significant humoral (serum IgG) response to OVA in BALB/c mice administered mucosally by either intranasal or oral route--a delayed response appearing on 50th day at a dose of 30 µg AGF by intranasal route. However, the serum IgG response was seen earlier on 35th day at a dose of 100 µg AGF by oral route. Higher concentrations of AGF (>50 µg) were inhibitory for adjuvant activity by intranasal administration. These observations indicate that AGF display immunoadjuvant activity for a test antigen though the humoral immune response is delayed.

In planta production of plant-derived and non-plant-derived adjuvants

Recombinant antigen production in plants is a safe and economically sound strategy for vaccine development, particularly for oral/mucosal vaccination, but subunit vaccines usually suffer from weak immunogenicity and require adjuvants that escort the antigens, target them to relevant sites and/or activate antigen-presenting cells for elicitation of protective immunity. Genetic fusions of antigens with bacterial adjuvants as the B subunit of the cholera toxin have been successful in inducing protective immunity of plant-made vaccines. In addition, several plant compounds, mainly plant defensive molecules as lectins and saponins, have shown strong adjuvant activities. The molecular diversity of the plant kingdom offers a vast source of non-bacterial compounds with adjuvant activity, which can be assayed in emerging plant manufacturing systems for the design of new plant vaccine formulations.

Investigation of lectinized liposomes as M-cell targeted carrier-adjuvant for mucosal immunization

In the present investigation hepatitis B surface antigen (HBsAg) encapsulated liposomes were developed and coupled with Ulex europaeus agglutinin 1 (UEA-1) to increase transmucosal uptake by M-cells of the Peyer's patches. The liposomes were characterized for shape, size, polydispersity and encapsulation efficiency. Bovine submaxillary mucin (BSM) was used as a biological model for the in vitro determination of lectin activity and specificity. Dual staining technique was used to investigate targeting of lectinized liposomes to the M-cells. Anti-HBsAg IgG response in serum and anti-HBsAg sIgA level in various mucosal fluids was estimated by using ELISA, following oral immunization with lectinized and non-lectinized liposomes in Balb/c mice. Additionally, interleukin-2 (IL-2) and interferon-γ (IFN-γ) level in the spleen homogenates was determined. The results suggest that lectinized liposomes were successfully developed, exhibited increased activity with BSM as compared to non-lectinized liposomes and α-l-fucose specificity of the lectinized liposomes was also maintained. The lectinized liposomes were predominantly targeted to the M-cells. The serum anti-HBsAg IgG titre obtained after 3 consecutive days oral immunizations with HBsAg encapsulated lectinized liposomes and boosting after third week was comparable with the titre recorded after single intramuscular prime and third week boosting with alum-HBsAg. Moreover, lectinized liposomes induced higher sIgA level in mucosal secretions and cytokines level in the spleen homogenates. The results showed that the developed surface modified liposomes could be a potential module for the development of effective mucosal vaccines.

Immunological Implications of the use of Plant Lectins for Drug and Vaccine Targeting to the Gastrointestinal Tract

Plant lectins are under consideration as targeting agents to enhance the efficacy of orally administered drugs and vaccines. A significant issue that must be considered is the immunogenicity of these molecules since an immune response to the targeting agent may interfere with its ability to interact with the epithelium. In contrast, the ability of certain lectins to activate the immune system may be exploited in the delivery of vaccines. We previously demonstrated that plant lectins vary widely in their immunogenicity and in particular that mistletoe lectins (ML) I, II and II (MLI, MLII, MLIII) are potent immunogens when administered nasotracheally. Here, we measured immune responses following oral delivery of the MLs and assessed their ability to enhance responses to a co-administered antigen to determine if the molecules possess adjuvant activity. Oral administration of the lectins induced potent lectin-specific systemic and mucosal antibody responses. In addition, each of the three lectins possessed adjuvant activity when delivered orally together with ovalbumin (OVA). The lectins enhanced both serum and mucosal antibody responses to the co-delivered antigen. This shows for the first time that MLI, MLII and MLIII possess adjuvant activity when administered orally and may provide a platform for the generation of effective mucosal adjuvants.

T(H)2 adjuvants: implications for food allergy

A persistent question for immunologists studying allergic disease has been to define the characteristics of a molecule that make it allergenic. There has been substantial progress elucidating mechanisms of innate priming of T(H)2 immunity in the past several years. These accumulating data demonstrate that T(H)2 immunity is actively induced by an array of molecules, many of which were first discovered in the context of antihelminthic immune responses. Similar intrinsic or associated activities are now known to account for the T(H)2 immunogenicity of some allergens, and may prove to play a role for many more. In this review, we discuss what has been discovered regarding molecules that induce innate immune activation and the pathways that promote T(H)2-polarized immune responses generally, and specifically what role these mechanisms may play in food allergy from models of food allergy and the study of T(H)2 gastrointestinal adjuvants.

Micro- and nanoparticle-based vaccines for hepatitis B

The incredible success of vaccinations in contributing to public health is undeniable. In fact, vaccines are the most cost-effective public health tool for disease prevention because their cost is less than the combined costs of treatment, hospitalization, and time loss from work. However, despite the availability of vaccines, cost per dose is a factor limiting the success of global vaccination campaigns, as are the limitations imposed by the need of delivering multiple vaccine doses. A number of approaches are being tested particularly for the delivery of subunit vaccines, and in recent years, a number of groups have devoted their efforts to develop nano/microparticles prepared from biodegradable and biocompatible polymers as vaccine delivery systems with the goal of inducing both humoral and cellular immune responses. Some important properties of biodegradable polymers are their documented safety history, biocompatibility, and an ability to provide controlled time/rate of antigen release and polymer degradation. The most extensively studied polymer used for encapsulating vaccine antigens is poly (lactide-co-glycolide acid) (PLGA). This chapter deals in brief with efforts targeting the use of PLGA micro-and nanoparticles for the delivery of hepatitis B surface antigen.

Oral vaccination: where we are?

As early as 900 years ago, the Bedouins of the Negev desert were reported to kill a rabid dog, roast its liver and feed it to a dog-bitten person for three to five days according to the size and number of bites [1] . In sixteenth century China, physicians routinely prescribed pills made from the fleas collected from sick cows, which purportedly prevented smallpox. One may dismiss the wisdom of the Bedouins or Chinese but the Nobel laureate, Charles Richet, demonstrated in 1900 that feeding raw meat can cure tuberculous dogs - an approach he termed zomotherapy. Despite historical clues indicating the feasibility of oral vaccination, this particular field is notoriously infamous for the abundance of dead-end leads. Today, most commercial vaccines are delivered by injection, which has the principal limitation that recipients do not like needles. In the last few years, there has been a sharp increase in interest in needle-free vaccine delivery; new data emerges almost daily in the literature. So far, there are very few licensed oral vaccines, but many more vaccine candidates are in development. Vaccines delivered orally have the potential to take immunization to a fundamentally new level. In this review, the authors summarize the recent progress in the area of oral vaccines.

Intranasal immunization with influenza virus and Korean mistletoe lectin C (KML-C) induces heterosubtypic immunity in mice

The mucosal adjuvanticity of Korean mistletoe lectin C (KML-C) was investigated in mice intranasally immunized with inactivated influenza virus (H1N1). Mucosal and systemic immune responses were compared to those induced with cholera toxin B subunit (CTB). KML-C increased influenza-specific antibodies with dominant IgG1 subclass in serum, IgG in genital secretions and IgA in saliva, and significantly enhanced influenza-specific lymphocyte proliferation and cytotoxic activity in spleens and in mediastinal lymph nodes. When KML-C was used as a mucosal adjuvant, mice were completely protected from mortality after the challenge with a homologous (H1N1) mouse-adapted influenza virus. After challenge with heterologous (H3N2) influenza virus the level of heterosubtypic immunity in KML-C-treated mice was comparable to that of mice that received CTB as adjuvant. These findings suggest that KML-C may be used as an effective mucosal adjuvant.

Phytic acid modulates in vitro IL-8 and IL-6 release from colonic epithelial cells stimulated with LPS and IL-1beta

Phytic acid (PA), a major fiber-associated component of wheat bran and legumes, is physiologically present in the human large gut. The aim of this study was to examine the role of PA in immunologic function of intestinal epithelial cells by analyzing its effect on interleukin (IL)-8 and IL-6 secretion by colonocytes and its role in the response of these cells to bacterial lipopolysaccharides (LPS) and IL-1beta. The human colon cell line Caco-2 was exposed to LPS isolated from two strains of Desulfovibrio desulfuricans, wild intestinal and type soil strains, as well as to LPS from E. coli. Cells were also treated with IL-1beta and with a combination of LPS and IL-1beta. PA had a suppressive effect on IL-8 basal release and it dose dependently reduced IL-8 secretion by colonocytes stimulated with LPS and IL-1beta. On the contrary, PA increased constitutive IL-6 secretion and exhibited differentiated effects on LPS responsiveness of cells depending on its concentration and LPS origin. PA was also an efficient down-regulator of IL-6 secretion stimulated by binary actions of LPS and IL-1beta. The ability of PA to modulate IL-8 and IL-6 release suggests that PA present in the intestinal milieu may exert immunoregulatory effects on colonic epithelium under physiological conditions or during microbe-induced infection/inflammation in order to maintain the colonic mucosa in a noninflammatory state or to counteract infection.

The role of adjuvants in the development of mucosal vaccines

It is well-established that most pathogens that cause infectious diseases enter the host via mucosal membranes of the respiratory, digestive and genital tracts. Some parenterally administered vaccines induce protection against mucosal pathogens. However, there is increasing evidence that mucosal protection is better afforded by mucosal vaccination, particularly for the induction of memory responses. Mucosal vaccines must pass several difficult hurdles before entering the host and inducing an effective and protective immune response. This review deals with present and past efforts in devising effective mucosal vaccines using delivery systems and immunopotentiating adjuvants for protein-based vaccines. The paper will conclude with the authors' opinion on how the field will or should progress in the future and what will be the required components of ideal future mucosal vaccines that can induce immunological memory.

Mucosal adjuvant properties of the Shigella invasin complex

The Shigella invasin complex (Invaplex) is an effective mucosal vaccine capable of protecting against Shigella challenge in animal models. The major antigenic constituents of Invaplex are the Ipa proteins and lipopolysaccharide. The cell-binding capacity of the Ipa proteins prompted the investigation into the adjuvanticity of Invaplex. Using ovalbumin (OVA) as a model antigen, intranasal immunization with OVA combined with Invaplex was found to enhance anti-OVA serum immunoglobulin G (IgG) and IgA responses and induce OVA-specific mucosal antibody responses at sites located both proximal and distal to the immunization site. The immune responses induced with OVA and Invaplex were comparable in both magnitude and duration to the immune responses induced after immunization with OVA and cholera toxin. The OVA-specific immune response was characterized by high levels of serum IgG1 and increased production of interleukin-4 (IL-4), IL-5, or IL-10 from lymphoid cells of immunized animals, suggesting a Th2 response. In addition to enhancing the immunogenicity of OVA, Invaplex-specific immune responses were also induced, indicating the potential for the development of a combination vaccine consisting of Invaplex and other immunogens. Preexisting Invaplex-specific immunity did not interfere with the capacity to enhance the immunogenicity of a second, unrelated vaccine antigen, suggesting that Invaplex could be used as a mucosal adjuvant in multiple vaccine regimens.

Lectin anchored stabilized biodegradable nanoparticles for oral immunization 1. Development and in vitro evaluation

The investigation comprises development of a stable and targeted formulation of HBsAg for the oral immunization against Hepatitis B. PLGA nanoparticles bearing HBsAg was prepared by double emulsion method. The antigen was protected from organic/aqueous interface by using protein stabilizer, trehalose. The acidic environment generated within PLGA nanoparticles was neutralized by co-encapsulation of a basic additive, Mg(OH)(2) which provides an additional stabilization to the antigen especially against acid induced antigen inactivation. Furthermore, lectin from Arachis hypogaea (PNA) was anchored on to the surface of the HBsAg loaded nanoparticles in order to enhance their affinity towards the antigen presenting cells of the Peyer's patches. The developed system was characterized for shape, size and loading efficiency. The antigen integrity was assessed by using SDS-PAGE followed by isoelectric focusing analysis. Bovine submaxillary mucin (BSM) was used as a biological model for in vitro ligand affinity determination and activity studies. The lectin anchored nanoparticles exhibited 52.18+/-4.73% loading while ligand density was estimated to be of 17.90+/-1.14 microg/mg. The results suggest that HBsAg can be successfully stabilized by co-encapsulation of an appropriate protein stabilizer, i.e. trehalose and a basic additive, Mg(OH)(2). The ligand-coupled nanoparticles demonstrated approximately four folds increase in degree interaction with the BSM as compared to plain nanoparticles. Additionally, the nanoparticles maintained their intrinsic sugar specificity as associated due to lectin (PNA).

Lectins and microparticles for enhanced oral vaccination

Oral administration is an attractive means of vaccination since it alleviates the need for injection and trained personnel. Furthermore, effective oral vaccination induces immune responses locally in the gastrointestinal tract, the site of colonisation and infection by many pathogens. However, since most proteins and peptides are degraded in the gut, do not interact specifically with the epithelium, or induce strong immune responses, this route of delivery is generally inefficient. Two of the most promising potential approaches are the use of lectins to target vaccines to the epithelium and the association of vaccines with biodegradable microparticles. This paper describes methods to assess the stability of vaccines and targeting molecules in the gastrointestinal tract, interaction with the mucosa, uptake into internal organs and induction of mucosal antibody responses.

Lectins as Bioactive Plant Proteins: A Potential in Cancer Treatment

Plant lectins, a unique group of proteins and glycoproteins with potent biological activity, occur in foods like wheat, corn, tomato, peanut, kidney bean, banana, pea, lentil, soybean, mushroom, rice, and potato. Thus, dietary intakes by humans can be significant. Many lectins resist digestion, survive gut passage, and bind to gastrointestinal cells and/or enter the circulation intact, maintaining full biological activity. Several lectins have been found to possess anticancer properties in vitro, in vivo, and in human case studies; they are used as therapeutic agents, preferentially binding to cancer cell membranes or their receptors, causing cytotoxicity, apoptosis, and inhibition of tumor growth. These compounds can become internalized into cells, causing cancer cell agglutination and/or aggregation. Ingestion of lectins also sequesters the available body pool of polyamines, thereby thwarting cancer cell growth. They also affect the immune system by altering the production of various interleukins, or by activating certain protein kinases. Lectins can bind to ribosomes and inhibit protein synthesis. They also modify the cell cycle by inducing non-apoptotic G1-phase accumulation mechanisms, G2/M phase cell cycle arrest and apoptosis, and can activate the caspase cascade. Lectins can also downregulate telomerase activity and inhibit angiogenesis. Although lectins seem to have great potential as anticancer agents, further research is still needed and should include a genomic and proteomic approach.

Transgene vaccination using Ulex europaeus agglutinin I (UEA-1) for targeted mucosal immunization against HIV-1 envelope

Receptor-mediated gene transfer using an M cell ligand has been shown to be an efficient method for mucosal DNA immunization. To investigate further into alternative M cell ligands, the plant lectin, Ulex europaeus agglutinin I (UEA-1), was tested. UEA-1 binds to human intestinal Caco-2 cells, and these cells can be transfected with poly-l-lysine (PL)-conjugated UEA-1 for expression of reporter cDNAs. When tested in vivo, mice nasally immunized with UEA-1-PL complexed to plasmid encoding HIV-1 envelope showed elevated systemic and mucosal antibody responses, and these were supported by tissue antibody-forming cells. Likewise, elevated envelope-specific CTLs were induced. Thus, UEA-1 mediated DNA delivery represents an alternative mucosal formulation for inducing humoral and cellular immunity against HIV-1.

Investigation of lectin-modified insulin liposomes as carriers for oral administration

The aim of this study was to design and characterize lectin-modified liposomes containing insulin and to evaluate the potential of these modified colloidal carriers for oral administration of peptide and protein drugs. Wheat germ agglutinin (WGA), tomato lectin (TL), or Ulex europaeus agglutinin 1 (UEA1) were conjugated by coupling their amino groups to carbodiimide-activated carboxylic groups of N-glutaryl-phosphatidylethanolamine (N-glut-PE). Insulin liposomes dispersions were prepared by the reverse-phase evaporation technique and modified with the lectin-N-glut-PE conjugates. Lectin-modified liposomes were characterized according to particles size, zeta potential and entrapment efficiency. The hypoglycemic effect indicated by pharmacological bioavailability of insulin liposomes modified with WGA, TL and UEA1 were 21.40, 16.71 and 8.38% in diabetic mice as comparison with abdominal cavity injection of insulin, respectively. After oral administration of the insulin liposomes modified with WGA, TL and UEA1 to rats, the relative pharmacological bioavailabilities were 8.47, 7.29 and 4.85%, the relative bioavailability were 9.12, 7.89 and 5.37% in comparison with subcutaneous injection of insulin, respectively. In the two cases, no remarkable hypoglycemic effects were observed with the conventional insulin liposomes. These results confirmed that lectin-modified liposomes promote the oral absorption of insulin due to the specific-site combination on GI cell membrane.