Liposome-encapsulated HIV-1 Gag p24 containing lipid A induces effector CD4+ T-cells, memory CD8+ T-cells, and pro-inflammatory cytokines

Liposomal lipid A is an effective adjuvant for the delivery of antigens and for the induction of both cellular and humoral immunity. In this study, we demonstrate that following the third immunization with HIV-1 Gag p24 encapsulated in liposomes containing lipid A [L(p24+LA)], central memory CD8+ T-cells were localized in the spleen and lymph nodes of mice while effector memory CD8+ T-cells and effector CD4+ T-cells were found in the PBMC. Effector CD4+ T-cells were also detected in the spleen and lymph nodes. The predominant cytokine secreted from splenic lymphocytes and lymph nodes was IFN-gamma. In contrast, IL-6 and IL-10 were the major cytokines produced from PBMC. The peptide stimulation indicated that the cytokine responses observed were T-cell specific. The results demonstrate the importance of the adjuvant liposomal lipid A for the induction of HIV-1 Gag p24 -specific CD8+ T-cells, effector CD4+ T-cells, and cytokines with a Th-1 type profile after immunization with L(p24+LA).

Anthrax LFn-PA Hybrid Antigens: Biochemistry, Immunogenicity, and Protection Against Lethal Ames Spore Challenge in Rabbits

We describe a novel hybrid anthrax toxin approach that incorporates multiple components into a single vaccine product. The key domains of protective antigen (PA) and lethal factor (LF) that may be critical for inducing protective immunity are combined into one recombinant molecule. Two LF N-terminal domain-PA hybrids, one with wild-type PA and another with furin cleavage-minus PA, were expressed in E. coli and purified in a native form. Both the hybrids bind to the extracellular domain of the host receptor, CMG2; the wild-type hybrid can be cleaved by furin exposing the LF interacting domain, allowing it to oligomerize into lethal toxin as well as translocation pore-like complexes. The hybrid antigens are immunogenic in Dutch-belted rabbits, eliciting strong PA-specific and LF-specific antibodies. However, the lethal toxin neutralizing antibody titers are 3-7 times lower than those elicited by PA-alum. The hybrid antigens conferred 100% (6/6) protection in rabbits challenged intranasally with a 100 LD(50) dose of Bacillus anthracis Ames strain spores.

HIV-1, lipid rafts, and antibodies to liposomes: implications for anti-viral-neutralizing antibodies (Review)

The human immunodeficiency virus type 1 (HIV-1) is an enveloped virus with a lipid bilayer that contains several glycoproteins that are anchored in, or closely associated with, the membrane surface. The envelope proteins have complex interactions with the lipids both on the host cells and on the target cells. The processes of budding from host cells and entry into target cells occur at sites on the plasma membrane, known as lipid rafts, that represent specialized regions that are rich in cholesterol and sphingolipids. Although the envelope glycoproteins are antigenic molecules that potentially might be used for development of broadly neutralizing antibodies in a vaccine to HIV-1, the development of such antibodies that have broad specificities against primary field isolates of virus has been largely thwarted to date by the ability of the envelope proteins to evade the immune system through various mechanisms. In this review, the interactions of HIV-1 with membrane lipids are summarized. Liposomes are commonly used as models for understanding interactions of proteins with membrane lipids; and liposomes have also been used both as carriers for vaccines, and as antigens for induction of antibodies to liposomal lipids. The possibility is proposed that liposomal lipids, or liposome-protein combinations, could be useful as antigens for inducing broadly neutralizing antibodies to HIV-1.

Lipid binding properties of 4E10, 2F5, and WR304 monoclonal antibodies that neutralize HIV-1

Two human mAbs (2F5 and 4E10), originally derived from HIV-1-infected patients, are important, but rare, mAbs that exhibit broad cross-clade neutralizing activities against HIV-1. In addition to peptide sequences on the gp41 envelope protein, both antibodies reportedly also bound specifically to several phospholipid antigens. However, the phospholipid binding property of 2F5 has been disputed and, because of uncertainly regarding phospholipid binding, the modeling of neutralizing mechanisms has been difficult. To explore this issue, we examined the binding of 4E10 and 2F5 to a broad range of lipid antigens by ELISA. 4E10 and 2F5 both bound to a variety of purified phospholipids, and 4E10 bound, but 2F5 did not bind, to cardiolipin. Both mAbs also bound to a sulfated glycolipid, sulfogalactosyl ceramide (sulfatide), and to two neutral glycolipids, galactosyl ceramide and glucosyl ceramide, but not to other galactosyl glycolipids. 4E10, but not 2F5, also bound to cholesterol, although both mAbs bound to squalene. Interestingly, 4E10, but not 2F5, exhibited striking binding to lipid A, the lipid moiety of Gram-negative bacterial lipopolysaccharide. The binding properties of 4E10 to phospholipids, sulfatide, cholesterol, squalene, and lipid A were similar to those of a neutralizing murine mAb (WR304) induced by liposomes containing phosphatidylinositol phosphate and lipid A, although WR304 did not bind to neutral glycolipids. The discovery of a binding specificity of 4E10 for lipid A, a widely used vaccine adjuvant, suggests that innate immunity stimulated by lipid A could have played a role for induction of multispecific antibodies that simultaneously recognize both HIV-1 protein and lipid antigens.

Antibodies induced by liposomal protein exhibit dual binding to protein and lipid epitopes

Natural polyreactive antibodies can accommodate chemically unrelated epitopes, such as lipids and proteins, in a single antigen binding site. Because liposomes containing lipid A as an adjuvant can induce antibodies directed against specific lipids, we immunized mice with liposomes containing lipid A together with a protein or peptide antigen to determine whether monoclonal antibodies generated after immunization would be specifically directed both to the liposomal lipid (either cholesterol or galactosylceramide) and also to the accompanying liposomal protein or peptide. Monoclonal antibodies were obtained that bound, by ELISA, to cholesterol and to recombinant gp140 envelope protein from HIV-1, or to galactosylceramide and to an HIV-1 envelope peptide. Surface plasmon resonance studies with the former antibody showed that the liposomal cholesterol and liposomal gp140 each contributed to the overall binding energy of the antibody to liposomes containing cholesterol and protein.

Depletion of cellular cholesterol interferes with intracellular trafficking of liposome-encapsulated ovalbumin

Cholesterol is a major constituent of plasma cell membranes and influences the functions of proteins residing in the membrane. To assess the role of cholesterol in phagocytosis and intracellular trafficking of liposomal antigen, macrophages were treated with inhibitors of cholesterol biosynthesis for various time periods and levels of cholesterol depletion were assessed by thin layer chromatography. In control macrophages, cholesterol was present in the plasma membrane and in intracellular stores, as visualised by staining with the cholesterol-binding compound filipin, whereas macrophages treated with cholesterol inhibitors failed to stain with filipin. However, these macrophages were still capable of phagocytosis as evidenced by their internalisation of fluorescent-labelled bacteria and liposome-encapsulated Texas red labelled-ovalbumin, L(TR-OVA). While fluorescent ovalbumin (OVA) was consistently transported to the Golgi in macrophages incubated with L(TR-OVA), in cells treated with cholesterol inhibitors, OVA remained spread diffusely throughout the cytoplasm. Even though the mean fluorescence intensity of MHC class I molecules on cholesterol inhibitor-treated macrophages was equivalent to that of the control macrophages, the amount of MHC class I-liposomal OVA-peptide complex detected on the cell surface of cholesterol inhibitor-treated macrophages, was only 45.6 +/- 7.4% (n = 4, mean +/- SEM) of control levels after intracellular processing of L(OVA). We conclude that cholesterol depletion does not eliminate phagocytosis or MHC class I surface expression, but does affect the trafficking and consequently the MHC class I antigen-processing pathway.

Animal models of complement-mediated hypersensitivity reactions to liposomes and other lipid-based nanoparticles

Intravenous injection of some liposomal drugs, diagnostic agents, micelles and other lipid-based nanoparticles can cause acute hypersensitivity reactions (HSRs) in a high percentage (up to 45%) of patients, with hemodynamic, respiratory and cutaneous manifestations. The phenomenon can be explained with activation of the complement (C) system on the surface of lipid particles, leading to anaphylatoxin (C5a and C3a) liberation and subsequent release reactions of mast cells, basophils and possibly other inflammatory cells in blood. These reactions can be reproduced and studied in pigs, dogs and rats, animal models which differ from each other in sensitivity and spectrum of symptoms. In the most sensitive pig model, a few miligrams of liposome (phospholipid) can cause anaphylactoid shock, characterized by pulmonary hypertension, systemic hypotension, decreased cardiac output and major cardiac arrhythmias. Pigs also display cutaneous symptoms, such as flushing and rash. The sensitivity of dogs to hemodynamic changes is close to that of pigs, but unlike pigs, dogs also react to micellar lipids (such as Cremophor EL) and their response includes pronounced blood cell and vegetative neural changes (e.g., leukopenia followed by leukocytosis, thrombocytopenia, fluid excretions). Rats are relatively insensitive inasmuch as hypotension, their most prominent response to liposomes, is induced only by one or two orders of magnitude higher phospholipid doses (based on body weight) compared to the reactogenic dose in pigs and dogs. It is suggested that the porcine and dog models are applicable for measuring and predicting the (pseudo)allergic activity of particulate "nanodrugs".

Calcium modulation of monoclonal antibody binding to phosphatidylinositol phosphate

The binding characteristics of two monoclonal antibodies (mAb) to phosphatidylinositol-4-phosphate (PIP) were examined: a murine IgM mAb to PIP; and a human IgG mAb (4E10) that binds both to HIV-1 envelope protein and also to neutral and anionic phospholipids, including PIP. Binding of each mAb to pure PIP was inhibited by Ca(2+) as determined by ELISA. When studied by surface plasmon resonance, liposomes containing PIP could be stripped (i.e., removed) by either Ca(2+) or phosphorylated haptens after binding of the liposomes to the murine anti-PIP antibody attached to a BIAcore chip. In contrast, the binding of liposomal PIP to 4E10 was irreversible and could not be stripped. We therefore conclude that Ca(2+) and phosphate can modulate the initial binding of both types of antibodies to PIP. However, 4E10 binds to liposomal PIP in a two-stage process involving first Ca(2+)-modulated binding to the PIP polar headgroup, followed by irreversible binding to liposomal hydrophobic groups.

Monoclonal antibodies to phosphatidylinositol phosphate neutralize human immunodeficiency virus type 1: role of phosphate-binding subsites

Both a murine monoclonal antibody to phosphatidylinositol phosphate (PIP) and a human monoclonal antibody (4E10) that is known to have broadly neutralizing capabilities against primary isolates of human immunodeficiency virus type 1 (HIV-1) bound to PIP, as determined by enzyme-linked immunosorbent assay. Each of the antibodies had antigen subsite binding specificities in aqueous medium for small phosphate-containing molecules and for inositol. The anti-PIP monoclonal antibody inhibited infection by two HIV-1 primary isolates in neutralization assays employing primary human peripheral blood mononuclear cells. The data suggest that PIP or related lipids having free phosphates could serve as targets for the neutralization of HIV-1.

Antibodies to lipids and liposomes: immunology and safety

Naturally occurring antibodies to phospholipids and cholesterol are widespread; they occur commonly during the course of acute infections; they are not causally related to the anti-phospholipid syndrome; they have been associated with other clinical entities only as an epiphenomenon; and they have not been implicated as causing any clinical syndrome or disease. There are theoretical and experimental reasons to believe that normal cells and tissues are protected from binding of antibodies to bilayer lipids by steric hindrance due to adjacent larger molecules, such as large or charged adjacent glycolipids or proteins on the cell surface. There are also reasons to believe that certain natural antibodies to lipids can even serve useful normal functions. Antibodies to liposomal lipids induced by liposomes containing lipid A appear to have characteristics that are similar or identical to naturally occurring antibodies to lipids, and it is therefore believed that such antibodies would not cause adverse clinical effects. Numerous Phase I and II human clinical trials of experimental vaccines containing liposomes and lipid A have shown a high level of safety.

Multicomponent anthrax toxin display and delivery using bacteriophage T4

We describe a multicomponent antigen display and delivery system using bacteriophage T4. Two dispensable outer capsid proteins, Hoc (highly antigenic outer capsid protein, 155 copies) and Soc (small outer capsid protein, 810 copies), decorate phage T4 capsid. These proteins bind to the symmetrically localized capsid sites, which appear following prohead assembly and expansion. We hypothesized that multiple antigens fused to Hoc can be displayed on the same capsid and such particles can elicit broad immunological responses. Anthrax toxin proteins, protective antigen (PA), lethal factor (LF), and edema factor (EF), and their functional domains, were fused to Hoc with an N-terminal hexa-histidine tag and the recombinant proteins were over-expressed in E. coli and purified. Using a defined in vitro assembly system, the anthrax-Hoc fusion proteins were efficiently displayed on T4 capsid, either individually or in combinations. All of the 155 Hoc binding sites can be occupied by one antigen, or they can be split among two or more antigens by varying their molar ratio in the binding reaction. Immunization of mice with T4 phage carrying PA, LF, and EF elicited strong antigen-specific antibodies against all antigens as well as lethal toxin neutralization titers. The triple antigen T4 phage elicited stronger PA-specific immune responses than the phage displaying PA alone. These features offer novel avenues to develop customized multicomponent vaccines against anthrax and other pathogenic diseases.

Assembly of human immunodeficiency virus (HIV) antigens on bacteriophage T4: a novel in vitro approach to construct multicomponent HIV vaccines

Bacteriophage T4 capsid is an elongated icosahedron decorated with 155 copies of Hoc, a nonessential highly antigenic outer capsid protein. One Hoc monomer is present in the center of each major capsid protein (gp23*) hexon. We describe an in vitro assembly system which allows display of HIV antigens, p24-gag, Nef, and an engineered gp41 C-peptide trimer, on phage T4 capsid surface through Hoc-capsid interactions. In-frame fusions were constructed by splicing the human immunodeficiency virus (HIV) genes to the 5' or 3' end of the Hoc gene. The Hoc fusion proteins were expressed, purified, and displayed on hoc(-) phage particles in a defined in vitro system. Single or multiple antigens were efficiently displayed, leading to saturation of all available capsid binding sites. The displayed p24 was highly immunogenic in mice in the absence of any external adjuvant, eliciting strong p24-specific antibodies, as well as Th1 and Th2 cellular responses with a bias toward the Th2 response. The phage T4 system offers new direction and insights for HIV vaccine development with the potential to increase the breadth of both cellular and humoral immune responses.

Correlation between lethal toxin-neutralizing antibody titers and protection from intranasal challenge with Bacillus anthracis Ames strain spores in mice after transcutaneous immunization with recombinant anthrax protective antigen

Transcutaneous immunization of mice with recombinant protective antigen (rPA) of Bacillus anthracis resulted in significantly higher lethal toxin-neutralizing antibody titers than did intramuscular injection of alum-adsorbed rPA. Immunized mice were partially protected against intranasal challenge with 235,000 (10 50% lethal doses) Ames strain B. anthracis spores. A highly significant correlation was observed between toxin-neutralizing antibody titer and survival after challenge. Future experiments with rabbits and nonhuman primates should confirm the significance of protection by this vaccine strategy.

Cerebrovascular involvement in liposome-induced cardiopulmonary distress in pigs

Intravenous administration of liposomes, including Doxil, can cause severe life-threatening hemodynamic changes in pigs. The reaction is due to complement activation, and it is characterized by massive pulmonary hypertension, systemic hypotension, and severe cardiac abnormalities including falling cardiac output, tachy-or bradycardia with arrhythmia. There were no data suggesting the involvement of cerebrovascular changes in this reaction; however, clinical observations allowed this hypothesis. Here we measured the accompanying changes during liposome infusion by monitoring pulsatile electrical impedance (rheoencephalogram- REG) on the skull (n=24 pigs, 57 trials, 19 types of liposomes). A transient but significant decrease of REG pulse amplitudes followed the injection of liposomes (78.43% in the total sample, and 91.66% in the Doxil subgroup; P=0.003, n=12), indicating the involvement of cerebrovascular reaction during liposome infusion.

In vitro binding of anthrax protective antigen on bacteriophage T4 capsid surface through Hoc-capsid interactions: a strategy for efficient display of large full-length proteins

An in vitro binding system is described to display large full-length proteins on bacteriophage T4 capsid surface at high density. The phage T4 icosahedral capsid features 155 copies of a nonessential highly antigenic outer capsid protein, Hoc, at the center of each major capsid protein hexon. Gene fusions were engineered to express the 83-kDa protective antigen (PA) from Bacillus anthracis fused to the N-terminus of Hoc and the 130-kDa PA-Hoc protein was expressed in Escherichia coli and purified. The purified PA-Hoc was assembled in vitro on hoc(-) phage particles. Binding was specific, stable, and of high affinity. This defined in vitro system allowed manipulation of the copy number of displayed PA and imposed no significant limitation on the size of the displayed antigen. In contrast to in vivo display systems, the in vitro approach allows all the capsid binding sites to be occupied by the 130-kDa PA-Hoc fusion protein. The PA-T4 particles were immunogenic in mice in the absence of an adjuvant, eliciting strong PA-specific antibodies and anthrax lethal toxin neutralizing antibodies. The in vitro display on phage T4 offers a novel platform for potential construction of customized vaccines against anthrax and other infectious diseases.

Human dendritic cells and macrophages exhibit different intracellular processing pathways for soluble and liposome-encapsulated antigens

The intracellular fates of soluble and liposomal antigens in human macrophages and dendritic cells are not well defined. Previous studies using murine macrophages have demonstrated that liposomal antigens can enter the MHC class I pathway. The Golgi complex is a major organelle in this pathway. Phagocytosis of the antigens is followed by translocation of antigen-derived peptides to the trans-Golgi where they can complex with MHC class I molecules. In contrast, soluble antigens are normally processed through the MHC class II pathway. Therefore, in the present study, ovalbumin and a synthetic Ebola peptide were used either in a soluble form or encapsulated in liposomes to investigate the intracellular trafficking and localization of these antigens to the Golgi complex in human macrophages and dendritic cells. While liposome-encapsulated antigens were transported to the trans-Golgi region in 59-78% of macrophages, soluble antigens remained diffuse throughout the cytoplasm with only 3-11% of the macrophages exhibiting trans-Golgi localization. The majority of dendritic cells localized both soluble (Ebola, 75%; ovalbumin, 84%) and liposomal antigens (58% and 65%), and irradiated Ebola virus to the trans-Golgi. These studies demonstrate that the intracellular fate of soluble and liposomal antigens can differ depending upon the antigen-presenting cell.

Complement activation-related cardiac anaphylaxis in pigs: role of C5a anaphylatoxin and adenosine in liposome-induced abnormalities in ECG and heart function

Cardiac anaphylaxis is a severe, life-threatening manifestation of acute hypersensitivity reactions to allergens and drugs. Earlier studies highlighted an amplifying effect of locally applied C5a on the process; however, the role of systemic complement (C) activation with C5a liberation in blood has not been explored to date. In the present study, we used the porcine liposome-induced cardiopulmonary distress model for 1) characterizing and quantifying peripheral C activation-related cardiac dysfunction; 2) exploring the role of C5a in cardiac abnormalities and therapeutic potential of C blockage by soluble C receptor type 1 (sCR1) and an anti-C5a antibody (GS1); and 3) elucidating the role of adenosine and adenosine receptors in paradoxical bradycardia, one of the symptoms observed in this model. Pigs were injected intravenously with different liposomes [Doxil and multilamellar vesicles (MLV)], zymosan, recombinant human (rhu) C5a, and adenosine, and the ensuing hemodynamic and cardiac changes (hypotension, tachy- or bradycardia, arrhythmias, ST-T changes, ventricular fibrillation, and arrest) were quantified by ranking on an arbitrary scale [cardiac abnormality score (CAS)]. There was significant correlation between CAS and C5a production by liposomes in vitro, and the liposome-induced cardiac abnormalities were partially or fully reproduced with zymosan, rhuC5a, adenosine, and the selective adenosine A1 receptor agonist cyclopentyl-adenosine. The use of C nonactivator liposomes or pretreatment of pigs with sCR1 or GS1 attenuated the abnormalities. The selective A1 blocker cyclopentyl-xanthine inhibited bradycardia without influencing hypotension, whereas the A(2) blocker 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM-24135) had no such effect. These data suggest that 1) systemic C activation can underlie cardiac anaphylaxis, 2) C5a plays a causal role in the reaction, 3) adenosine action via A1 receptors may explain paradoxical bradycardia, and 4) inhibition of C5a formation or action or of A1-receptor function may alleviate the acute cardiotoxicity of liposomal drugs and other intravenous agents that activate C.

Advances in vaccine delivery: transcutaneous immunisation

Needle-free delivery of vaccines has become a global priority. Transcutaneous immunisation (TCI), topical application of vaccine antigens to the skin, can elicit systemic antibody and T-cell responses, suggesting that this new technique may provide a means for vaccination without needles. TCI requires the use of an adjuvant such as cholera toxin added to a vaccine antigen, such as diphtheria toxoid, to induce antibodies to diphtheria toxoid. The adjuvant and antigen are thought to target Langerhans cells, potent antigen-presenting cells found in the superficial layers of the skin. TCI appears to be a highly practical technique for delivery of vaccines that provides unique access to the immune system.

Immunostimulatory CpG motifs induce CTL responses to HIV type I oligomeric gp140 envelope protein

In the present study we investigated the immunomodulatory effects of two adjuvants, liposomal lipid A [L(LA)] and CpG-containing oligodeoxynucleotides (CpG ODN), to the HIV-1 ogp140 envelope protein. Administration of each of these adjuvants separately with unencapsulated ogp140 resulted in low antibody titres. Encapsulation of ogp140 in liposomes containing lipid A resulted in a sixfold increase in anti-ogp140 antibodies. The antibody titres were further enhanced threefold by the addition of CpG ODN. Priming and boosting BALB/c mice with unencapsulated ogp140 with L(LA) or encapsulation in liposomes containing lipid A induced a mixed Th1/Th2 type of immune response. In contrast, immunization with L(ogp140 + LA) plus CpG ODN switched the immune response to a Th-1 response with elevated anti-ogp140 IgG2a antibodies and IFN-gamma levels. Both adjuvants induced excellent ogp140-specific proliferative and CTL responses. Therefore, for the induction of high titre antibodies, but not for cellular responses, the antigen and lipid A have to be present in the same liposomes. These results can have significant implications in directing the Th1 or Th2 differentiation of antigen-specific immune responses in the context of vaccine development.

Liposome-stabilized oil-in-water emulsions as adjuvants: increased emulsion stability promotes induction of cytotoxic T lymphocytes against an HIV envelope antigen

Protective or therapeutic immunity against HIV infection is currently believed to require both antibody and CTL responses against the envelope protein. In the present study, the adjuvant activity of a unique oil-in-water emulsion, in which liposomes containing lipid A (LA) and encapsulated antigen served as the emulsifying agent, was examined in mice using oligomeric gp140 (ogp140) derived from the HIV-1 envelope as the antigen. Emulsions rendered either highly stable or unstable by altering the ratio of liposomes to oil were used to examine the effect of stability of the emulsion on adjuvant activity. Stable and unstable emulsions had similar potencies for inducing both IgG antibodies to ogp140 and antigen-specific T-lymphocyte proliferation. Stable emulsions, but not unstable emulsions, induced antigen-specific CTL responses, possibly because of the depot effect of the stable emulsions. Furthermore, stable emulsions induced lower IgG2a/IgG1 ratios than the unstable emulsions. We conclude that stable liposomal oil-in-water emulsions provide an effective means of obtaining both antibody and CTL responses against an HIV envelope antigen.

Functional microtubules are required for antigen processing by macrophages and dendritic cells

Antigen-presenting cells readily phagocytose antigens and channel them through various membrane-bound organelles within the cell. In previous studies, we demonstrated that macrophages concentrated and localized particulate antigens to the trans-Golgi prior to displaying the MHC-class I-antigenic peptides on the cell surface. In this study, we evaluated the importance of cytoskeletal elements in the intracellular trafficking of soluble and liposome-encapsulated ovalbumin in murine bone marrow-derived macrophages and human dendritic cells. F-actin, as identified by staining with fluorescein phalloidin, was observed at the point of contact between soluble or liposomal antigen and the cell membrane, suggesting that a rearrangement of the cytoskeleton occurs to facilitate the uptake of the antigens. Cells were incubated with colchicine, a microtubule depolymerizing agent, or paclitaxel, a microtubule polymerizing agent, before the addition of Texas Red-labeled ovalbumin or liposome-encapsulated Texas Red-labeled ovalbumin. Colchicine disrupted the trans-Golgi, whereas the trans-Golgi complexes were intact in paclitaxel treated cells. In either paclitaxel or colchicine-treated macrophages, internalized liposomal ovalbumin was not concentrated in the area of the trans-Golgi as determined by staining with fluorescent ceramide. In contrast, soluble ovalbumin was concentrated in the region of the trans-Golgi in 15% of the dendritic cells treated with paclitaxel, whereas 6% of the dendritic cells were able to concentrate liposomal antigen. In colchicine-treated dendritic cells, both soluble and liposomal antigens were internalized but did not localize to the area of the trans-Golgi. These data suggest that trafficking of soluble and liposome-encapsulated ovalbumin requires a functional microtubule-dependent translocation system.

Causative factors behind poloxamer 188 (Pluronic F68, Flocor™)-induced complement activation in human sera

Poloxamer 188 is a complex polydisperse mixture of non-ionic macromolecules. Adverse non-IgE-mediated hypersensitivity reactions occur in some individuals following intravenous injection of poloxamer 188-based pharmaceuticals, presumably via complement activation. Here we have delineated potential causal chemical and biological interactive factors behind poloxamer 188-induced complement activation in human serum specimens. We identified the molecular constituents inherent in poloxamer 188 preparations and studied their effect on generation of the two complement split products, SC5b-9 and Bb. Poloxamer 188 activated complement at sub-micellar concentrations and the results indicated the potential involvement of all three known complement activation pathways. The poloxamer-induced rise of SC5b-9 in human sera was abolished in the presence of a recombinant truncated soluble form of complement receptor type 1, thus confirming the role of C3/C5 convertases in the activation process. Poloxamer 188-mediated complement activation is an intrinsic property of these macromolecules and was independent of the degree of sample polydispersity, as opposed to other non-polymeric constituents. Poloxamer 188 preparations also contained unsaturated chains of diblock copolymers capable of generating SC5b-9 in human sera; this effect was terminated following the removal of double bonds by catalytic hydrogenation. By quasi-elastic light scattering, we established interaction between poloxamer and lipoproteins; interestingly, poloxamer-induced rise in SC5b-9 was significantly suppressed when serum HDL and LDL cholesterol levels were increased above normal to mimic two relevant clinical situations. This observation was consistent with previously reported data from patients with abnormal or elevated lipid profiles where no or poor complement activation by poloxamer 188 occurred. Our findings could provide the basis of novel approaches to the prevention of poloxamer-mediated complement activation.

Detection of antibodies to squalene

An ELISA-based assay is described for the measurement of antibodies to squalene (SQE) in human serum and plasma. The assay was adapted from the previously described assay for murine antibodies to SQE (J. Immunol. Methods 267 (2002) 119). Like the murine SQE antibody assay, the human antibody assay used sterile cell culture 96-well plates coated with SQE (20 nmol/well). Phosphate-buffered saline (PBS)-0.5% casein was used as both a blocking agent and dilution buffer. The assay has a high through-put capacity and is reproducible and quantitative. This assay was used to evaluate samples from three different human cohorts. The first cohort was retired employees of the United States Army Medical Research Institute of Infectious Diseases (USAMRIID alumni). The mean age was 68 (N=40; range 58-82). Most were vaccinated with the U.S. licensed anthrax vaccine (AVA) and most had received several other vaccines through a USAMRIID special immunization program. The second cohort was of similar age (N=372; mean age 67; range 54-97) from the normal population of Frederick, MD and were not vaccinated with AVA. The third cohort (N=299) was from Camp Memorial Blood Center, United States Army Medical Department Activities, Fort Knox, KY. (No additional volunteer information is available.) Using this new ELISA method, antibodies to SQE were detected in all three of the cohorts. IgG antibodies to SQE were detected in 7.5% and 15.1% of the samples from the USAMRIID alumni and Frederick cohorts, respectively. These differences were not significantly different (chi((1))(2)=1.69, p=0.19). In contrast, no IgG antibodies to SQE were detected in the Fort Knox cohort which is significantly different than the Frederick cohort (chi((1))(2)=49.25, p<0.0001). IgM antibodies to SQE were detected in 37.5% and 32.3% of the samples from the USAMRIID and Frederick cohorts, respectively, but there was no significant difference between the cohorts. In the Fort Knox cohort, 19.4% of the samples were positive for IgM antibodies to SQE, which was significantly different from the Frederick cohort (chi((1))(2)=14.23, p=0.0002). Although the age of the volunteers from the Fort Knox cohort is unknown, the demographic of the donors at the blood bank volunteers is 85% 17-21 years of age. This suggested that the prevalence of antibodies to SQE may increase with age. This was confirmed with mouse studies in which the presence of antibodies was monitored as a function of time. No antibodies to SQE were detected in female BALB/c, B10.Br and C57BL/6 mice at 2 months of age, but they reached a maximum prevalence with 100% and 89% of animals testing positive for IgG and IgM antibodies to SQE, respectively, in the C57Bl/6 mice at 18 months of age. BALB/c and B10.Br mice also developed antibodies to SQE over time, but were at a lower prevalence than those observed in the C57BL/6 mice. Thirty-five of the 40 volunteers in the USAMRIID were vaccinated with AVA (mean no. doses=26; range 3-47). Comparison of the prevalence of antibodies to SQE from the AVA immunized group with the Frederick cohort revealed that there was no statistical differences for IgG (chi((1))(2)=2.3, p=0.13) or IgM (chi((1))(2)=0.33, p=0.56). When the data from the USAMRIID and Frederick cohorts were combined and analyzed for the presence of antibodies to SQE with respect to the sex of the volunteer, females (40.8%) were found to have a higher prevalence of IgM antibodies to SQE than men (28.4%) (chi((1))(2)=6.59, p=0.01). No significant difference was observed in the prevalence for IgG antibodies to SQE in females (17.7%) and males (12.5%). We conclude that antibodies to SQE occur naturally in humans; have an increased prevalence in females; are not correlated with vaccination with AVA; and appear to increase in prevalence with age.

Needle-free skin patch vaccination method for anthrax

Three immunizations of mice with recombinant protective antigen (rPA) by transcutaneous immunization (TCI) induced long-term neutralizing antibody titers that were superior to those obtained with aluminum-adsorbed rPA. In addition, rPA alone exhibited adjuvant activity for TCI. Forty-six weeks after completion of TCI, 100% protection was observed against lethal anthrax challenge.

Immunization with DNA through the skin

The skin has evolved as a barrier to prevent external agents, including pathogens, from entering the body. It has a complex and efficient immune surveillance system, which includes Langerhans cells and dendritic cells. By targeting the body's natural defense system, skin-DNA immunization attempts to produce an efficient immune response. Nucleic acid vaccines provide DNA for protein expression in a variety of cells, including keratinocytes, Langerhans cells, and dendritic cells, which are located in the two main areas of the skin, the epidermis (the most superficial layer) and the dermis. After maturation, Langerhans cells and dermal dendritic cells can migrate to local lymph nodes where presentation of antigens to T cells can occur and thus start a variety of immunologic responses. Dermal immunization methods described in this article target the epidermis, the dermis, or both and include: (a) stripping; (b) chemical modification; (c) trans-epidermal immunization (transcutaneous immunization or non-invasive vaccination of the skin); (d) gene gun technology; (e) electroporation; (f) intradermal injections; and (g) microseeding. These techniques all require the removal of hair, the circumvention or modification of the stratum corneum layer of the epidermis, and the addition of DNA or amplification of DNA signal. As the biology of the skin and the mechanisms of DNA vaccination are elucidated, these skin immunization techniques will be optimized. With refinement, skin-DNA immunization will achieve the goal of producing a reliable and efficacious immune response to a variety of pathogens.

Complement Activation During Hemorrhagic Shock and Resuscitation in Swine

Activation of the complement (C) cascade is known to play a key role in the adverse immune consequences of hemorrhagic trauma with subsequent shock and resuscitation. However, it is not clear whether hypovolemia per se, without trauma and resuscitation, can also lead to C activation. To address this question, we studied the presence, kinetics, and cause of C activation in a porcine model of hemorrhagic shock and resuscitation in the absence of trauma. Pigs were bled to and kept at 35 mmHg for 90 min, followed by hypotensive resuscitation with different fluids and, finally, with shed blood. The animals developed severe lactic acidosis between 30 and 90 min, which was accompanied by a trend for initial rise and subsequent 40% drop of CH50/mL, indicating massive C activation even before resuscitation, i.e., before reperfusion damage could have occurred. Resuscitation with plasma expanders caused 20% additional C consumption, whereas whole blood raised CH50/mL. Plasma C5a decreased initially and then significantly increased at 60 and 180 min, whereas thromboxane B2 showed a 3-fold increase at 30 and 60 min. Plasma LPS was also increased above baseline at 90 and 180 min. In in vitro studies with pig blood, spontaneous C5a formation, as well as zymosan-induced C consumption, was significantly enhanced under the conditions of lactic acidosis. Our data suggest that lactic acidosis, endotoxemia, and possibly other ischemia-related tissue alterations act in a vicious cycle in inducing C activation and, hence, aggravation of shock. The biphasic course of CH50/mL and C5a changes may reflect yet unrecognized physiological responses to hemorrhage-related C activation.

Complement activation following first exposure to pegylated liposomal doxorubicin (Doxil): possible role in hypersensitivity reactions

BACKGROUND

Pegylated liposomal doxorubicin (Doxil) has been reported to cause immediate hypersensitivity reactions (HSRs) that cannot be explained as IgE-mediated (type I) allergy. Previous in vitro and animal studies indicated that activation of the complement (C) system might play a causal role in the process, a proposal that has not been tested in humans to date.

PATIENTS AND METHODS

Patients with solid tumors (n = 29) treated for the first time with Doxil were evaluated for HSRs and concurrent C activation. HSRs were classified from mild to severe, while C activation was estimated by serial measurement of plasma C terminal complex (SC5b-9) levels. Increases in SC5b-9 were compared in patients with or without reactions, and were correlated with Doxil dose rate.

RESULTS

Moderate to severe HSRs occurred in 45% of patients. Plasma SC5b-9 at 10 min after infusion was significantly elevated in 92% of reactor patients versus 56% in the non-reactor group, and the rise was greater in reactors than in non-reactors. We found significant association between C activation and HSRs, both showing direct correlation with the initial Doxil dose rate.

CONCLUSIONS

C activation may play a key role in HSRs to Doxil. However, low-level C activation does not necessarily entail clinical symptoms, highlighting the probable involvement of further, as yet unidentified, amplification factors.

F(ab)'2-mediated neutralization of C3a and C5a anaphylatoxins: a novel effector function of immunoglobulins

High-dose intravenous immunoglobulin (IVIG) prevents immune damage by scavenging complement fragments C3b and C4b. We tested the hypothesis that exogenous immunoglobulin molecules also bind anaphylatoxins C3a and C5a, thereby neutralizing their pro-inflammatory effects. Single-cell calcium measurements in HMC-1 human mast cells showed that a rise in intracellular calcium caused by C3a and C5a was inhibited in a concentration-dependent manner by IVIG, F(ab)2-IVIG and irrelevant human monoclonal antibody. C3a- and C5a-induced thromboxane (TXB2) generation and histamine release from HMC-1 cells and whole-blood basophils were also suppressed by exogenous immunoglobulins. In a mouse model of asthma, immunoglobulin treatment reduced cellular migration to the lung. Lethal C5a-mediated circulatory collapse in pigs was prevented by pretreatment with F(ab)2-IVIG. Molecular modeling, surface plasmon resonance (SPR) and western blot analyses suggested a physical association between anaphylatoxins and the constant region of F(ab)2. This binding could interfere with the role of C3a and C5a in inflammation.

Induction and detection of antibodies to squalene. II. Optimization of the assay for murine antibodies

An improved high throughput assay for measuring murine antibodies to squalene (SQE) is described. The assay is highly reproducible and sensitive and can detect 80 ng/ml of antibody to SQE. The assay, an ELISA, is similar to our previously described assay in which plates containing PVDF membranes were used [J. Immunol. Methods 245 (2000) 1]. The PVDF plates worked well for detection of murine monoclonal antibodies (mAbs) to SQE, but substantial PVDF plate variation was observed, resulting in significant loss of signal and reproducibility between different lots of plates. In the new assay, the PVDF plates were replaced with Costar round bottom 96-well sterile tissue culture plates. These latter plates, which are not normally used for ELISA assay, gave high absorbances for monoclonal antibodies and anti-SQE serum binding to SQE and low absorbances for solvent-treated wells. Other commercially available polystyrene ELISA plates were unsuitable, in that either the background was high or the absorbance for antibodies binding to SQE was low, or both. This change in plate from PVDF to polystyrene allowed the use of an ELISA plate washer, which dramatically increased the throughput rate over the hand-washed PVDF plates. The improved assay also replaced fetal bovine serum (FBS), which contained SQE in lipoproteins, with fatty acid-free bovine serum albumin (BSA) as the blocker/diluent. Fifteen nanomoles of SQE were selected as the optimal amount of SQE to add to the wells. The binding of monoclonal antibodies and anti-SQE serum was dependent upon both the amount of antibody added to the wells and the amount of SQE added to the wells. Antibody concentration curves were hyperbolic in shape, as seen with most other antibodies. Antibody binding first increased with SQE amount and then reached a plateau around 10 nmol of SQE/well. At high SQE amounts (>75 nmol/well), antibody binding decreased with the amount of SQE added. Using 3H-SQE, the amount of SQE bound to the wells increased linearly, up to 50 nmol of SQE added. Approximately 90% of the added SQE bound to the well. When amounts greater than 100 nmol of SQE were added, the amount of SQE bound to the wells was greatly reduced to approximately 5-10% of the added SQE. The assay was highly reproducible both from lot to lot of plates and from experiment to experiment.

Induction of immune responses in mice and monkeys to Ebola virus after immunization with liposome-encapsulated irradiated Ebola virus: protection in mice requires CD4(+) T cells

Ebola Zaire virus (EBO-Z) causes severe hemorrhagic fever in humans, with a high mortality rate. It is thought that a vaccine against EBO-Z may have to induce both humoral and cell-mediated immune responses to successfully confer protection. Because it is known that liposome-encapsulated antigens induce both antibody and cellular responses, we evaluated the protective efficacy of liposome-encapsulated irradiated EBO-Z [L(EV)], which contains all of the native EBO-Z proteins. In a series of experiments, mice immunized intravenously with L(EV) were completely protected (94/94 mice) against illness and death when they were challenged with a uniformly lethal mouse-adapted variant of EBO-Z. In contrast, only 55% of mice immunized intravenously with nonencapsulated irradiated virus (EV) survived challenge, and all became ill. Treatment with anti-CD4 antibodies before or during immunization with L(EV) eliminated protection, while treatment with anti-CD8 antibodies had no effect, thus indicating a requirement for CD4(+) T lymphocytes for successful immunization. On the other hand, treatment with either anti-CD4 or anti-CD8 antibodies after immunization did not abolish the protection. After immunization with L(EV), antigen-specific gamma interferon (IFN gamma)-secreting CD4(+) T lymphocytes were induced as analyzed by enzyme-linked immunospot assay. Anti-CD4 monoclonal antibody treatment abolished IFN gamma production (80 to 90% inhibition compared to that for untreated mice). Mice immunized with L(EV), but not EV, developed cytotoxic T lymphocytes specific to two peptides (amino acids [aa] 161 to 169 and aa 231 to 239) present in the amino-terminal end of the EBO-Z surface glycoprotein. Because of the highly successful results in the mouse model, L(EV) was also tested in three cynomolgus monkeys. Although immunization of the monkeys with L(EV)-induced virus-neutralizing antibodies against EBO-Z caused a slight delay in the onset of illness, it did not prevent death.

Design and selection of vaccine adjuvants: animal models and human trials

The availability of hundreds of different adjuvants has prompted a need for identifying rational standards for selection of adjuvant formulations based on safety and sound immunological principles for human vaccines. Although many of the mechanisms of adjuvants have been elucidated, meaningful comparisons between different adjuvants derived from in vitro studies, or from studies using adjuvants in rodents or other animals, are often not predictive for safety, adjuvant effects, or vaccine efficacy in humans. A highly efficient and cost-effective method for comparison of adjuvants with a new antigen is to conduct multiple small-scale, phase 1, comparative studies in humans with a new antigen, using adjuvants previously found to be safe with other antigens in human trials. Studies in which highly immunogenic and safe adjuvant formulations have been evaluated in comparative adjuvant trials in humans using a single candidate vaccine antigen against malaria, HIV, and prostate cancer with multiple adjuvants are reviewed.

Safety and immunogenicity of a prototype enterotoxigenic Escherichia coli vaccine administered transcutaneously

Transcutaneous immunization (TCI) is a new method for vaccine delivery that has been shown to induce immunity relevant to enteric disease vaccines. We evaluated the clinical safety and immunogenicity of a recombinant subunit vaccine against enterotoxigenic Escherichia coli (ETEC) delivered by TCI. Adult volunteers received patches containing the recombinant ETEC colonization factor CS6, either with heat-labile enterotoxin (LT) or patches containing CS6 alone. The vaccine was administered at 0, 1, and 3 months, and serum antibodies and antibody-secreting cells (ASCs) were assessed. Among the 26 volunteers that completed the trial, there were no responses to CS6 in the absence of LT. In the groups receiving both CS6 and LT, 68 and 53% were found to have serum anti-CS6 immunoglobulin G (IgG) and IgA, respectively; 37 and 42% had IgG and IgA anti-CS6 ASCs. All of the volunteers receiving LT had anti-LT IgG, and 90% had serum anti-LT IgA; 79 and 37% had anti-LT IgG and IgA ASCs. Delayed-type hypersensitivity (DTH), suggesting T-cell responses, was seen in 14 of 19 volunteers receiving LT and CS6; no DTH was seen in subjects receiving CS6 alone. This study demonstrated that protein antigens delivered by a simple patch could induce significant systemic immune responses but only in the presence of an adjuvant such as LT. The data suggest that an ETEC vaccine for travelers delivered by a patch may be a viable approach worthy of further evaluation.

Potentiation of liposome-induced complement activation by surface-bound albumin

Large anionic multilamellar liposomes containing 71% membrane cholesterol (MLV) caused complement (C) activation in human serum in vitro, as reflected in significant rises in S protein-bound terminal complex (SC5b-9) and C3a-desarg levels. Increasing the albumin content in serum by 1-4 g/100 ml led to 50-100% further increase in MLV-induced C activation, while higher amounts of exogenous human serum albumin (HSA) gradually lost the capability to potentiate liposomal C activation. HSA alone had no influence on SC5b-9 formation at any level below 12%. Complement activation by liposomes and the potentiating effect of supplemental HSA were greatly reduced or eliminated in the absence of C1q or in the presence of 10 mM EGTA/2.5 mM Mg(2+), pointing to the involvement of the classical pathway. Potentiation of C activation by supplemental HSA was not unique to MLV-induced activation, as deposition of HSA on the membrane of "Centricon" ultrafiltration units also potentiated the C-activating effect of the polycarbonate membrane. Fatty acid (FA) or non-monomeric protein contamination in HSA were unlikely to be playing a role in the described effects, as 96% pure, FA-rich (Buminate) and 99% pure, FA-free HSA had identical effects on liposomal C activation. While highlighting a new modulatory mechanism on liposomal C activation, the above data raise the possibility that deposition of extravasated HSA at sites of tissue injury may serve a hitherto unrecognized proinflammatory function.

Role of complement activation in hypersensitivity reactions to doxil and hynic PEG liposomes: experimental and clinical studies

Pegylated liposomal doxorubicin (Doxil) and 99mTc-HYNIC PEG liposomes (HPL) were reported earlier to cause hypersensitivity reactions (HSRs) in a substantial percentage of patients treated i.v. with these formulations. Here we report that (1) Doxil, HPL, pegylated phosphatidylethanolamine (PEG-PE)-containing empty liposomes matched with Doxil and HPL in size and lipid composition, and phosphatidylglycerol (PG)-containing negatively charged vesicles were potent C activators in human serum in vitro, whereas small neutral liposomes caused no C activation. (2) Doxil and other size-matched PEG-PE and/or PG-containing liposomes also caused massive cardiopulmonary distress with anaphylactoid shock in pigs via C activation, whereas equivalent neutral liposomes caused no hemodynamic changes. (3) A clinical study showed more frequent and greater C activation in patients displaying HSR than in non-reactive patients. These data suggest that liposome-induced HSRs in susceptible individuals may be due to C activation, which, in turn, is due to the presence of negatively charged PEG-PE in these vesicles.