Liposomal presentation of antigens for human vaccines

Liposomal adjuvants for human vaccines

INTRODUCTION

Liposomes are well-known as drug carriers, and are now critical components of two of six types of adjuvants present in licensed vaccines. The liposomal vaccine adjuvant field has long been dynamic and innovative, and research in this area is further examined as new commercial products appear in parallel with new vaccines. In an arena where successful products exist the potential for new types of vaccines with liposomal adjuvants, and alternative liposomal adjuvants that could emerge for new types of vaccines, are discussed.

AREAS COVERED

Major areas include: virosomes, constructed from phospholipids and proteins from influenza virus particles; liposomes containing natural and synthetic neutral or anionic phospholipids, cholesterol, natural or synthetic monophosphoryl lipid A, and QS21 saponin; non-phospholipid cationic liposomes; and combinations and mixtures of liposomes and immunostimulating ingredients as adjuvants for experimental vaccines.

EXPERT OPINION

Liposomes containing monophosphoryl lipid A and QS21 have considerable momentum that will result soon in emergence of prophylactic vaccines to malaria and shingles, and possible novel cancer vaccines. The licensed virosome vaccines to influenza and hepatitis A will be replaced with virosome vaccines to other infectious diseases. Alternative liposomal formulations are likely to emerge for difficult diseases such as tuberculosis or HIV-1 infection.

High-Throughput Continuous Flow Production of Nanoscale Liposomes by Microfluidic Vertical Flow Focusing

Liposomes represent a leading class of nanoparticles for drug delivery. While a variety of techniques for liposome synthesis have been reported that take advantage of microfluidic flow elements to achieve precise control over the size and polydispersity of nanoscale liposomes, with important implications for nanomedicine applications, these methods suffer from extremely limited throughput, making them impractical for large-scale nanoparticle synthesis. High aspect ratio microfluidic vertical flow focusing is investigated here as a new approach to overcoming the throughput limits of established microfluidic nanoparticle synthesis techniques. Here the vertical flow focusing technique is utilized to generate populations of small, unilamellar, and nearly monodisperse liposomal nanoparticles with exceptionally high production rates and remarkable sample homogeneity. By leveraging this platform, liposomes with modal diameters ranging from 80 to 200 nm are prepared at production rates as high as 1.6 mg min(-1) in a simple flow-through process.

Application of surface-linked liposomal antigens to the development of vaccines that induce both humoral and cellular immunity

The first characteristic identified in surface-linked liposomal antigens was the ability to induce antigen-specific, IgE-selective unresponsiveness. These results remained consistent even when different coupling procedures were employed for antigens with liposomes or for liposomes with different lipid components. The potential usefulness of surface-linked liposomal antigens for application to vaccine development was further investigated. During this investigation, a significant difference was observed in the recognition of liposomal antigens by antigen-presenting cells between liposomes with different lipid components, and this difference correlated closely with the adjuvant activity of liposomes. In addition to this "quantitative" difference between liposomes with differential lipid components, a "qualitative" difference (i.e., a differential ability to induce cross-presentation) was observed between liposomes with different lipid components. Therefore, by utilizing the ability to induce cross-presentation, surface-linked liposomal antigens might be used to develop virus vaccines that would induce cytotoxic T lymphocyte (CTL) responses. We have successfully developed a liposome vaccine that is capable of inducing CTL responses against internal antigens of influenza viruses and thus removing virus-infected cells in the host. This CTL-based liposomal vaccine might be applicable to the development of vaccines against influenza and other viruses that frequently undergo changes in their surface antigenic molecules.

Poly D,L-lactide-co-glycolic acid-liposome encapsulated ODN on innate immunity in Epinephelus bruneus against Vibrio alginolyticus

The efficacy of poly D,L-lactide-co-glycolic acid (PLGA)-liposome (L) encapsulated oligodeoxynucleotides with unmethylated deoxycytidyl-deoxyguanosine motifs (CpG-ODNs) on innate and adaptive immune response and disease resistance in kelp grouper (Epinephelus bruneus) against Vibrio alginolyticus at weeks 1, 2, and 4 is reported. The superoxide dismutase (SOD), respiratory burst, and lysozyme activities significantly increased in E. bruneus when immunized with ODN, PLGA+ODN, L+ODN, and PLGA+L+ODN on weeks 2 and 4. The serum complement activity was significantly enhanced with L+ODN and PLGA+L+ODN on week 1 while it increased with PLGA+ODN, L+ODN, and PLGA+L+ODN on weeks 2 and 4. The antibody titre consistently was increased with PLGA or L encapsulated with ODN (PLGA+ODN, L+ODN, and PLGA+L+ODN) from weeks 1 to 4. The cumulative mortality was 20% each in PLGA+ODN administered groups and 15% each in ODN, L+ODN, and PLGA+L+ODN groups during a period of 30 days. The present study suggests that PLGA-liposome encapsulated ODN has the potential to modulate the immune system and can serve as a useful tool for further design of immunoprophylatic nano drug formulations against bacterial diseases.

Development of a cytotoxic T-lymphocyte-based, broadly protective influenza vaccine

The current vaccination strategy against influenza is to induce production of antibodies directed against the surface antigens of these viruses. However, frequent changes in the surface antigens of influenza viruses allow them to avoid antibody-mediated immunity. On the other hand, it is known that cytotoxic T-lymphocyte (CTL) populations directed against internal antigens of influenza A virus are broadly cross-reactive to influenza virus subtypes. The present authors have previously demonstrated that antigens chemically coupled to the surface of liposomes made using unsaturated fatty acids are cross-presented by APCs via MHC class I to CD8(+) T cells and induce antigen-specific CTLs. Based on this finding, a liposome vaccine that is capable of inducing CTL response against internal antigens of influenza viruses and removing virus-infected cells in the host has been developed. The CTL-based liposomal technique might be applicable for developing vaccines against influenza and other viruses, such as hepatitis C, HIV, and severe acute respiratory syndrome corona virus, which frequently change their surface antigenic molecules.

Liposomal adjuvants: preparation and formulation with antigens

Many preclinical and clinical results indicate that liposomal systems can serve as effective adjuvants to subunit vaccines by enabling the formulation and delivery of vaccine antigens and immunopotentiators. The adjuvant effect of liposomes usually depends on both the composition of the lipid vesicles and their physical association with the vaccine antigen. This chapter describes methods for the preparation and characterization of sterile small, mostly unilamellar, lipid vesicles and for their association with vaccine antigens. It gives also some recommendations for the optimization of liposomal vaccines in preclinical testing. The most common immunopotentiators used in liposomal adjuvants are also described.

Effects of intravenous and subcutaneous administration on the pharmacokinetics, biodistribution, cellular uptake and immunostimulatory activity of CpG ODN encapsulated in liposomal nanoparticles

We have previously demonstrated that the immune response to an unmethylated cytidine-guanosine (CpG)-containing oligonucleotide (ODN) is greatly enhanced when encapsulated in a lipid nanoparticle (LN-CpG ODN). In this study, the pharmacokinetics, biodistribution and cellular uptake of LN-CpG ODN following intravenous (i.v.) and subcutaneous (s.c.) administration was characterized and correlated with immunostimulatory activity. It is shown that, despite dramatic differences in tissue distribution profiles and considerable differences in uptake by CD11c-positive, CD11b-positive, Mac-3-positive and CD45R/B220-positive cells following i.v. and s.c. administration, the resultant immune response is very similar with respect to levels of cellular activation (DX5, Mac-3, CD11b, CD45/B220, CD4, CD8 and CD11c) and cytolytic activity of immune cells [natural killer (NK) cells and monocytes/macrophages] in the spleen and blood compartments. Some differences in response kinetics and antibody-dependent cellular cytotoxicity (ADCC) activity were noted in the peripheral blood NK cell population. Analyses of particle biodistribution and cell types involved in uptake leads to the conclusion that the inherent ability of antigen-presenting cells (APCs) to sequester LN-CpG ODN results in efficient uptake of the particle, even when present at very low concentrations, leading to similar responses following i.v. and s.c. administration. These results contrast with the behavior of free CpG ODN, for which distinctly different immune responses are observed following i.v. or s.c. administration.

Peptides coupled to the surface of a kind of liposome protect infection of influenza viruses

In our previous study, OVA conjugated on the surface of a liposome, we termed Oleoyl liposome, which consisted of dioleoyl phosphatidyl choline, dioleoyl phosphatidyl ethanolamine, dioleoyl phosphatidyl glycerol acid and cholesterol in a 4:3:7:2 molar ratio, induced OVA-specific IgG antibody production but not OVA-specific IgE antibody production that is detrimental to the host. Furthermore, OVA(257-264)-Oleoyl liposome elicited CTL responses in the presence of CpG and rejected E.G7 tumors in mice. In this study we tested whether a peptide-Oleoyl liposome conjugates are capable of inducing protection against viral growth. Subcutaneous inoculation of NP(366-374)-Oleoyl liposome with CpG inhibited growth of influenza viruses in lungs of mice. Thus, surface-linked liposomal peptide might serve as an effective vaccine without detrimental effects in the presence of immune potentiators.

Antigen Chemically Coupled to the Surface of Liposomes Are Cross-Presented to CD8+ T Cells and Induce Potent Antitumor Immunity

We have previously demonstrated that liposomes with differential lipid components display differential adjuvant effects when Ags are chemically coupled to their surfaces. In the present study, Ag presentation of liposome-coupled OVA was investigated in vitro, and it was found that OVA coupled to liposomes made using unsaturated fatty acid was presented to both CD4+ and CD8+ T cells, whereas OVA coupled to liposomes made using saturated fatty acid was presented only to CD4+ T cells. Confocal laser scanning microscopic analysis demonstrated that a portion of the OVA coupled to liposomes made using unsaturated, but not saturated fatty acid, received processing beyond the MHC class II compartment, suggesting that the degradation of OVA might occur in the cytosol, and that the peptides generated in this manner would be presented to CD8+ T cells via MHC class I. The ability to induce cross-presentation of an Ag coupled to liposomes consisting of unsaturated fatty acid was further confirmed by in vivo induction of CTL and by the induction of tumor eradication in mice; E.G7 tumors in mice that received combined inoculation with OVA(257-264)-liposome conjugates, CpG, and anti-IL-10 mAbs were completely eradicated. In those mice, the frequency of CD8+ T cells reactive with OVA(257-264) peptides in the context of H-2K(b) was significantly increased. These results suggested that, by choosing lipid components for liposomes, surface-coupled liposomal Ags might be applicable for the development of tumor vaccines to present tumor Ags to APCs and induce antitumor responses.

Induction of immune responses against glycosphingolipid antigens: comparison of antibody responses in mice immunized with antigen associated with liposomes prepared from various phospholipids

The immune responses of mice against glycosphingolipid (GSL) antigens and the effect of the phospholipid composition of liposomes on the immunogenicity in mice of liposome-associated GSL antigens were examined. The immunization with GSL antigen alone was unable to induce any detectable anti-GSL antibody responses. On the other hand, the immune responses against GSL antigens were detected after immunization with liposomes composed of dipalmitoylphosphatidylcholine (DPPC) (0.5 micromol), cholesterol (Chol) (0.5 micromol), Salmonella minnesota R595 lipopolysaccharides (LPS) (10 microg) and GSL (0.05 micromol) (DPPC-liposome). However, the administration with liposome composed of dimyristoylphosphatidylcholine (DMPC) (0.5 micromol), Chol (0.5 micromol), S. minnesota R595 LPS (10 microg) and GSL (0.05 micromol) and with liposomes composed of distearylphosphatidylcholine (DSPC) (0.5 micromol), Chol (0.5 micromol), and S. minnesota R595 LPS (10 microg) and GSL (0.05 micromol) was ineffective for the induction of the immune responses against GSL antigens. These results suggest that DPPC-liposome would serve effectively as a delivery vehicle for inducing immune responses against GSL antigen.

Protective effect of antiganglioside antibodies against experimental Trypanosoma brucei infection in mice

Liposome-associated ganglioside antigens (ganglioside GM1 or bovine brain gangliosides) were prepared to facilitate the potential protective efficacy for Trypanosoma brucei. Mice were immunized with liposome-associated ganglioside GM1 or bovine brain gangliosides intraperitoneally (i.p.). After immunization, significantly higher antigen-specific IgG and IgM antibodies were detected in sera than in the nonimmunized control group. When sera from immunized mice were analyzed for isotype distribution, antigen-specific IgG1, IgG2a, and IgG3 antibody responses were also noted. After immunization, mice were challenged i.p. with 1 x 10(2) cells of T. brucei. Sixty percentage of liposome-associated ganglioside GM1-immunized mice survived the infection, and all the mice immunized with bovine brain gangliosides-containing liposomes survived. However, all control mice died within 7 days after infection. These data demonstrate that liposomes containing ganglioside antigens have the potential usefulness for the induction of a protective immune response against T. brucei infection and suggest the possibility of developing vaccines that may ultimately be used for the prevention of trypanosomiasis.

Protection against experimental Aeromonas salmonicida infection in carp by oral immunisation with bacterial antigen entrapped liposomes

Liposome-entrapped atypical Aeromonas salmonicida antigen was prepared to investigate the potential protective efficacy for A. salmonicida infection. Carp (Cyprinus carpio) were immunised orally with liposome-entrapped A. salmonicida antigen. After immunisation, significantly higher antigen-specific antibodies were detected in serum, intestinal mucus and bile than non-immunised control group. Furthermore, immunised carp were challenged by immersion with 1 x 10(6) cfu ml(-1) of A. salmonicida for 60 min. Of the eight non-immunised carp, three carp died (62.5% survival), whereas five out of six (83.5%) immunised survived. Furthermore, the development of skin ulcers was significantly inhibited in carp immunised with liposomes containing A. salmonicida antigen. These results suggest that liposomes containing A. salmonicida antigen have the potential for the induction of a protective immune response against atypical A. salmonicida infection and also suggest the possibility of developing a vaccine that may ultimately be used for the prevention of fish diseases.

An Increased Adjuvanticity of Liposomes by the Inclusion of Phosphatidylserine in Immunization with Surface-Coupled Liposomal Antigen

BACKGROUND

Exposure of phosphatidylserine (PS) on apoptotic cells is known to result in the enhanced recognition of apoptotic cells by phagocytes. By the inclusion of PS in the lipid component of liposomes, increased liposome immune adjuvant activity was expected.

METHODS

In the present study, two different liposome preparations containing either PS, i.e. PS-liposome, or phosphatidylcholine (PC), i.e. PC-liposome, were made, and macrophage recognition, processing, and antigen presentation of surface-coupled liposomal antigen were compared.

RESULTS

When ovalbumin-liposome conjugates were added to a culture of macrophages, enhanced recognition and processing of ovalbumin by the macrophages were observed by the inclusion of PS in the liposomes. The results correlated well with those regarding macrophage antigen presentation of liposome-coupled ovalbumin. Furthermore, in vivo immunization in mice with ovalbumin-liposome conjugates made with PS-liposomes induced a significantly higher level of anti-ovalbumin IgG antibody production than was induced by ovalbumin-liposome conjugates made with PC-liposomes. IgE-selective unresponsiveness was induced by ovalbumin-liposome conjugates regardless of the lipid components of liposomes.

CONCLUSIONS

These results suggest that the inclusion of PS in liposomes enhances recognition and processing of surface-coupled liposomal antigen by macrophages, and increases liposome immune adjuvant activity.

Encapsulation into sterically stabilised liposomes enhances the immunogenicity of melanoma-associated Melan-A/MART-1 epitopes

Tumour-associated antigens (TAA)-specific vaccination requires highly immunogenic reagents capable of inducing cytotoxic T cells (CTL). Soluble peptides are currently used in clinical applications despite an acknowledged poor immunogenicity. Encapsulation into liposomes has been suggested to improve the immunogenicity of discrete antigen formulations. We comparatively evaluated the capacity of HLA-A2.1 restricted Melan-A/MART-1 epitopes in soluble form (S) or following inclusion into sterically stabilised liposomes (SSL) to be recognised by specific CTL, to stimulate their proliferation and to induce them in healthy donors' peripheral blood mononuclear cells (PBMC), as well as in melanoma-derived tumour-infiltrating lymphocytes (TIL). HLA-A2.1⁺, Melan-A/MART-1-NA-8 melanoma cells served as targets of specific CTL in 51Cr release assays upon pulsing by untreated or human plasma-treated soluble or SSL-encapsulated Melan-A/MART-1 27–35 (M27–35) or 26–35 (M26–35) epitopes. These reagents were also used to stimulate CTL proliferation, measured as 3H-thymidine incorporation, in the presence of immature dendritic cells (iDC), as antigen-presenting cells (APC). Induction of specific CTL upon stimulation with soluble or SSL-encapsulated peptides was attempted in healthy donors' PBMC or melanoma-derived TIL, and monitored by 51Cr release assays and tetramer staining. Na-8 cells pulsing with SSL M27–35 resulted in a five-fold more effective killing by specific CTL as compared with equal amounts of S M27–35. Encapsulation into SSL also provided a partial (50%) protection of M27–35 from plasma hydrolysis. No specific advantages regarding M26–35 were detectable in these assays. However, at low epitope concentrations (⩽100 ng ml⁻¹), SSL M26–35 was significantly more effective in inducing CTL proliferation than S M26–35, in the presence of iDC, as APC. Preincubation with iDC for 6 h virtually abolished the capacity of S M26–35 to stimulate specific CTL proliferation, but only partially affected that of SSL M26–35. Most importantly, SSL M26–35 was able to enhance the induction of specific CTL in healthy donors PBMC and in melanoma-derived TIL as compared to S M26–35. Taken together, our data indicate that encapsulation of TAA epitopes into SSL results in effective immunogenic formulations suitable for clinical use in active specific tumour immunotherapy.

Immunostimulating reconstituted influenza virosomes

Immunostimulating reconstituted influenza virosomes (IRIVs) are a liposomal carrier system. Influenza hemagglutinin and neuraminidase are intercalated into the lipid bilayer and give the IRIVs their fusogenic activity. The system is already registered for human use and allows a specific targetting of antigens to a cellular or a humoral immune response. IRIVs are able to deliver proteins, RNA/DNA, peptides and mimetics to immunocompetent cells.

New technology platforms in the development of vaccines for the future

The desire for improved quality of life in both industrialised and under-developed nations has led to the quest for greater understanding and subsequent prevention and treatment of diseases. Here we discuss some of the latest of modern medicine's approaches to vaccination and disease treatment. Our main subject of discussion being the novel antigen delivery systems termed immunopotentiating reconstituted influenza virosomes (IRIVs) and their use as vaccines. Particular attention is paid to the currently licensed Epaxal and Inflexal V, good examples of the improvements being made in vaccinology. Alternative uses of virosomes such as peptide delivery, cytosolic drug delivery and gene delivery are also considered, highlighting the flexibility of the IRIV formulation and method of action. The paper concludes with consideration of alternative novel approaches to vaccinology including bacterial carriers for DNA vaccines, recombinant MV vaccines and polysaccharide-protein conjugates.

Trends and developments in liposome drug delivery systems

Since the discovery of liposomes or lipid vesicles derived from self-forming enclosed lipid bilayers upon hydration, liposome drug delivery systems have played a significant role in formulation of potent drugs to improve therapeutics. Currently, most of these liposome formulations are designed to reduce toxicity and to some extent increase accumulation at the target site(s) in a number of clinical applications. The current pharmaceutical preparations of liposome-based therapeutics stem from our understanding of lipid-drug interactions and liposome disposition mechanisms including the inhibition of rapid clearance of liposomes by controlling size, charge, and surface hydration. The insight gained from clinical use of liposome drug delivery systems can now be integrated to design liposomes targeted to tissues and cells with or without expression of target recognition molecules on liposome membranes. Enhanced safety and heightened efficacy have been achieved for a wide range of drug classes, including antitumor agents, antivirals, antifungals, antimicrobials, vaccines, and gene therapeutics. Additional refinements of biomembrane sensors and liposome delivery systems that are effective in the presence of other membrane-bound proteins in vivo may permit selective delivery of therapeutic compounds to selected intracellular target areas.

Direct measurements of hemoglobin interactions with liposomes using EPR spectroscopy

Electron paramagnetic resonance (EPR) spectroscopy was used to compare the rates of autoxidation at 37 degrees C of acellular and liposome-encapsulated hemoglobin (LEH) crosslinked between alpha chains with bis (3,5-dibromosalicyl) fumarate (alphaalphaHb). This method avoids the difficulties inherent in using conventional ultraviolet-visible (UV-vis) spectroscopy caused by the high turbidity of liposome suspensions. Rate constants of 0.039/h and 0.065/h were obtained for the alphaalphaHb and LEH samples, respectively. Similar oxidation measurements with alphaalphaHb using UV-vis spectroscopy gave a rate constant comparable to that obtained with EPR spectroscopy. Indirect measurement of the oxidation kinetics of LEH utilizing extraction of alphaalphaHb with chloroform from partially oxidized LEH samples was unreliable because the amount of extractable hemoglobin was inversely proportional to the degree of oxidation. EPR measurements showed a shift in the g value and substantial enhancement in the intensity of the bis-histidine low-spin B complex for the encapsulated hemoglobin, indicating a perturbation of this low-spin complex. We suggest that lipid-associated perturbations are responsible for the enhancement of the oxidation observed with the LEH samples compared to the unencapsulated material.

Comparison of in vivo fate and immunogenicity of hepatitis B surface antigen incorporated in cationic and neutral liposomes

To compare cationic liposomes (CatL) and neutral liposomes (NeuL), as a vaccine carrier, the in vivo fate and immunogenicity of hepatitis B surface antigen (HBsAg), incorporated in CatL and NeuL, were investigated. CatL, composed of phosphatidyl choline (PC) and stearyl amine (SA) with a molar ratio of 9:1, showed a 2.5-fold higher incorporating efficiency of HBsAg than NeuL composed of PC alone. Most of HBsAg incorporated in both liposomes existed in an antibody-available form on the outer surface of liposomes. After intramuscular injection to rats, HBsAg in CatL resided at the injection site for a longer period than that in NeuL with terminal half lives of 52.5 and 42.9 h, respectively. However, HBsAg in NeuL was more efficiently taken up by the lymphatic organs and spleen than that in CatL. Furthermore, the group treated with HBsAg in NeuL showed earlier sero-conversion with higher anti-HBsAg titre than the group treated with HBsAg in CatL. Sero-conversion rates (SCRs) in both CatL- and NeuL-treated animals were 100% after every injection carried out, except the primary injection of CatL. These results demonstrate that CatL can enhance the retention of incorporated antigen at the injection site, compared with NeuL. However, the production of antibody by HBsAg in NeuL is more effective than that by HBsAg in CatL, probably due to the higher lymphatic targeting ability of NeuL. Thus, NeuL appears to be a better carrier for HBsAg than CatL.

Use of reconstituted influenza virus virosomes as an immunopotentiating delivery system for a peptide-based vaccine

Immunopotentiating reconstituted influenza virosomes (IRIV) were used as a delivery system for the synthetic peptide-based malaria vaccine SPf66. The reduced SPf66 peptide molecules containing terminal cysteine residues were covalently attached to phosphatidylethanolamine with the heterobifunctional crosslinker gamma-maleimidobutyric acid N-hydroxysuccinimide ester. The SPf66-phosphatidylethanolamine was incorporated into IRIV and BALB/c mice were immunized twice by intramuscular injection with peptide-loaded virosomes. Titres of elicited anti-SPf66 IgG were determined by ELISA. These titres were significantly higher and the required doses of antigen were lower, when mice had been preimmunized with a commercial whole virus influenza vaccine. After preimmunization with the influenza vaccine, SPf66-IRIV elicited far more consistently anti-SPf66 antibody responses than SPf(66)n adsorbed to alum. MoAb produced by four B cell hybridoma clones derived from a SPf66-IRIV-immunized mouse cross-reacted with Plasmodium falciparum blood stage parasites in immunofluorescence assays. All four MoAbs were specific for the merozoite surface protein-1 (MSP-1)-derived 83.1 portion of SPf66. Sequencing of their functionally rearranged kappa light chain variable region genes demonstrated that the four hybridomas were generated from clonally related splenic B cells. Biomolecular interaction analyses (BIA) together with these sequencing data provided evidence for the selection of somatically mutated affinity-matured B cells upon repeated immunization with SPf66-IRIV. The results indicate that IRIV are a suitable delivery system for synthetic peptide vaccines and thus have a great potential for the design of molecularly defined combined vaccines targeted against multiple antigens and development stages of one parasite, as well as against multiple pathogens.

Adjuvant activity of immunopotentiating reconstituted influenza virosomes (IRIVs)

Using immunopotentiating, reconstituted influenza virosomes (IRIV) as a delivery vehicle, a number of vaccines have been developed. In humans, IRIV-based vaccines containing hepatitis A and influenza antigens have been found to possess enhanced immunogenicity compared to alum-adsorbed vaccine for hepatitis A or commercial subunits or whole virion influenza vaccines. These vaccines were safe and did not engender any antiphospholipid antibodies against the liposome components of the IRIV. Hepatitis B, tetanus toxoid and diphtheria toxoid, and nucleic acids have also been incorporated into IRIVs. These vaccines are now undergoing clinical phase I testing. IRIVs are also being evaluated in phase I trials for their ability to deliver antigens by the intranasal route.