Fixed Dosing of Liposomal Amphotericin B in Morbidly Obese Individuals.

In this prospective study, we examined the pharmacokinetics of 1 and 2 mg/kg liposomal amphotericin B in 16 morbidly obese individuals (104-177 kg). Body size had no effect on clearance. We recommend a fixed dose in patients ≥100 kg (ie, 300 or 500 mg rather than the current dose of 3 and 5 mg/kg, respectively). Clinical Trials Registration NCT02320604.

Clinical Pharmacokinetics, Pharmacodynamics, Safety and Efficacy of Liposomal Amphotericin B.

Since its introduction in the 1990s, liposomal amphotericin B (LAmB) continues to be an important agent for the treatment of invasive fungal diseases caused by a wide variety of yeasts and molds. This liposomal formulation was developed to improve the tolerability of intravenous amphotericin B, while optimizing its clinical efficacy. Since then, numerous clinical studies have been conducted, collecting a comprehensive body of evidence on its efficacy, safety, and tolerability in the preclinical and clinical setting. Nevertheless, insights into the pharmacokinetics and pharmacodynamics of LAmB continue to evolve and can be utilized to develop strategies that optimize efficacy while maintaining the compound's safety. In this article, we review the clinical pharmacokinetics, pharmacodynamics, safety, and efficacy of LAmB in a wide variety of patient populations and in different indications, and provide an assessment of areas with a need for further clinical research.

Preclinical Safety, Tolerability, Pharmacokinetics, Pharmacodynamics, and Antifungal Activity of Liposomal Amphotericin B.

The improved safety profile and antifungal efficacy of liposomal amphotericin B (LAmB) compared to conventional amphotericin B deoxycholate (DAmB) is due to several factors including, its chemical composition, rigorous manufacturing standards, and ability to target and transit through the fungal cell wall. Numerous preclinical studies have shown that LAmB administered intravenously distributes to tissues frequently infected by fungi at levels above the minimum inhibitory concentration (MIC) for many fungi. These concentrations can be maintained from one day to a few weeks, depending upon the tissue. Tissue accumulation is dose-dependent with drug clearance occurring most rapidly from the brain and slowest from the liver and spleen. LAmB localizes in lung epithelial lining fluid, within liver and splenic macrophages and in kidney distal tubules. LAmB has been used successfully in therapeutic and prophylactic animal models to treat many different fungal pathogens, significantly increasing survival and reducing tissue fungal burden.

Comparison between liposomal formulations of amphotericin B.

Given the clinical success of commercial amphotericin B lipid products, investigators have begun making generic formulations of liposomal amphotericin B. Generic medicines are an attractive approach to help decrease the cost and accessibility to healthcare, provided that appropriate studies are performed to ensure bioequivalence with the parent product. This is of particular concern for liposomal drugs such as amphotericin B where liposomes are used as a carrier system to reduce the toxicity of the active agent. A favorable therapeutic profile for this form of the drug has to include the proper chemical composition along with strictly controlled manufacturing processes. Studies have shown that a comparison of liposomal amphotericin B products with different or the same chemical compositions, using different methods of production, will vary in size, and have significantly dissimilar in vitro and in vivo toxicities along with reduced efficacy. These results underscore the importance of establishing appropriate bioequivalence testing for liposome products to ensure uniformity of their therapeutic index.

Recombinant Aspergillus fumigatus antigens Asp f 3 and Asp f 9 in liposomal vaccine protect mice against invasive pulmonary aspergillosis.

Invasive pulmonary aspergillosis caused by the ubiquitous mold Aspergillus fumigatus is a major threat to immunocompromised patients, causing unacceptably high mortality despite standard of care treatment, and costing an estimated $1.2 billion annually. Treatment for this disease has been complicated by the emergence of azole resistant strains of A. fumigatus, rendering first-line antifungal therapy ineffective. The difficulties in treating infected patients using currently available drugs make immunotherapeutic vaccination an attractive option. Here, we demonstrate the efficacy of VesiVax® adjuvant liposomes, consisting of a combination of two individual liposome preparations, to which two recombinant A. fumigatus surface antigens, Asp f 3 and Asp f 9 (VesiVax® Af3/9), have been chemically conjugated. Using a murine model, we demonstrate that VesiVax® Af3/9 is protective against infection by azole resistant strains of A. fumigatus in both steroid-suppressed and neutropenic mice as quantified by improved survival and reduced fungal burden in the lungs. This protection correlates with upregulation of IL-4 produced by splenocytes, and the presence of Asp f 3 and Asp f 9 specific IgG2a antibodies in the serum of mice given VesiVax® Af3/9. Furthermore, mice given VesiVax® Af3/9 with a subsequent course of liposomal amphotericin B (AmBisome®) had improved survival over those given either treatment alone, indicating a benefit to VesiVax® Af3/9 vaccination even in the case of infections that require follow-up antifungal treatment. These data demonstrate that prophylactic vaccination with VesiVax® Af3/9 is a promising method of protection against invasive pulmonary aspergillosis even as the changing face of the disease renders current therapies ineffective.

Liposomal amphotericin B and echinocandins as monotherapy or sequential or concomitant therapy in murine disseminated and pulmonary Aspergillus fumigatus infections.

Monotherapy and combination therapy were compared using optimal doses of liposomal amphotericin B, micafungin, or caspofungin in Aspergillus fumigatus pulmonary and disseminated infections. Mice were challenged intravenously (2.8 x 10(4) to 5.7 x 10(4) conidia) or intranasally (5.8 x 10(7) conidia) with A. fumigatus. Drugs (5, 10, or 15 mg/kg of body weight) were given for 3 or 6 days as single, concomitant, or sequential therapy (i.e., days 1 to 3 and then days 4 to 6). Mice were monitored for survival, and tissues were assayed for fungal burden and drug concentrations. Treatments starting 24 h postchallenge significantly prolonged survival in disseminated aspergillosis (P < 0.002), but only liposomal amphotericin B treatments or treatments beginning with liposomal amphotericin B increased survival to 100% in the pulmonary aspergillosis model. Fungi in kidneys and spleens (disseminated) and lungs (pulmonary) were significantly decreased (P < or = 0.04) by liposomal amphotericin B, liposomal amphotericin B plus echinocandin, or liposomal amphotericin B prior to echinocandin. In the disseminated infection, liposomal amphotericin B and micafungin (10 or 15 mg/kg) had similar kidney drug levels, while in the spleen, 5 and 15 mg/kg liposomal amphotericin B gave higher drug levels than micafungin (P < 0.02). In the pulmonary infection, drug levels in lungs and spleen with 5-mg/kg dosing were significantly higher with liposomal amphotericin B than with caspofungin (P < or = 0.002). In summary, treatment of A. fumigatus infections with liposomal amphotericin B plus echinocandin or liposomal amphotericin B prior to echinocandin was as effective as liposomal amphotericin B alone, and a greater decrease in the fungal burden with liposomal amphotericin B supports using liposomal amphotericin B prior to echinocandin.

Effect of testosterone and estrogen supplementation on the resistance to systemic Candida albicans infection in mice.

Candida species are the 4th leading cause of nosocomial infections in the US affecting both men and women. Since males of many species can be more susceptible to infections than females, we investigated whether male mice were more susceptible to systemic Candida albicans (C. albicans) infection and if sex hormones were responsible for sex-dependent susceptibility to this infection. Non-gonadectomized or gonadectomized mice were supplemented with sustained release 5α-dihydrotestosterone (5αDHT) or 17-ß-estradiol (E2) using subcutaneous pellet implantation. Mice were challenged intravenously with 5 × 105 C. albicans/mouse seven days after pellet implantation and monitored for survival and weight change. We observed that male mice were more susceptible to systemic C. albicans infection than female mice while gonadectomized male mice were as resistant to the C. albicans infection as female mice. 5αDHT supplementation of gonadectomized female or male mice increased their susceptibility to the yeast infection while E2 supplementation of gonadectomized male mice did not increase their resistance to the infection. Overall, our results strongly suggest that testosterone plays an important role in decreasing resistance to systemic C. albicans infection.

The VesiVax system: a method for rapid vaccine development.

The VesiVax system is based upon the concept that highly potent vaccines can be designed by engineering proteins that are capable of stably inserting themselves into liposomes. Such a nanoscale liposomal particle can then serve as an immunogen for vaccine development. The VesiVax vaccine technology platform is designed to make it relatively easy to engineer and produce new vaccines quickly. Vaccines based on the VesiVax system have been designed against the influenza virus and herpes simplex type 2 virus, the causative agents of the "flu" and genital herpes, respectively. Both vaccines have been tested in animal models and have demonstrated significant protective efficacy from challenge with lethal doses of virus. Assays of the immunological parameters suggest that both T and B cell responses can be elicited by VesiVax vaccines. The safety profile of the VesiVax vaccines is expected to be much better than that of vaccines prepared by conventional techniques. Taken together, the inherent flexibility of the VesiVax platform is expected to facilitate the rapid development of new vaccines which are effective at stimulating protective immune responses.

The Viscoelastic Properties of the Fungal Cell Wall Allow Traffic of AmBisome as Intact Liposome Vesicles.

The fungal cell wall is a critically important structure that represents a permeability barrier and protective shield. We probed Candida albicans and Cryptococcus neoformans with liposomes containing amphotericin B (AmBisome), with or without 15-nm colloidal gold particles. The liposomes have a diameter of 60 to 80 nm, and yet their mode of action requires them to penetrate the fungal cell wall to deliver amphotericin B to the cell membrane, where it binds to ergosterol. Surprisingly, using cryofixation techniques with electron microscopy, we observed that the liposomes remained intact during transit through the cell wall of both yeast species, even though the predicted porosity of the cell wall (pore size, ~5.8 nm) is theoretically too small to allow these liposomes to pass through intact. C. albicans mutants with altered cell wall thickness and composition were similar in both their in vitro AmBisome susceptibility and the ability of liposomes to penetrate the cell wall. AmBisome exposed to ergosterol-deficient C. albicans failed to penetrate beyond the mannoprotein-rich outer cell wall layer. Melanization of C. neoformans and the absence of amphotericin B in the liposomes were also associated with a significant reduction in liposome penetration. Therefore, AmBisome can reach cell membranes intact, implying that fungal cell wall viscoelastic properties are permissive to vesicular structures. The fact that AmBisome can transit through chemically diverse cell wall matrices when these liposomes are larger than the theoretical cell wall porosity suggests that the wall is capable of rapid remodeling, which may also be the mechanism for release of extracellular vesicles.IMPORTANCE AmBisome is a broad-spectrum fungicidal antifungal agent in which the hydrophobic polyene antibiotic amphotericin B is packaged within a 60- to 80-nm liposome. The mode of action involves perturbation of the fungal cell membrane by selectively binding to ergosterol, thereby disrupting membrane function. We report that the AmBisome liposome transits through the cell walls of both Candida albicans and Cryptococcus neoformans intact, despite the fact that the liposome is larger than the theoretical cell wall porosity. This implies that the cell wall has deformable, viscoelastic properties that are permissive to transwall vesicular traffic. These observations help explain the low toxicity of AmBisome, which can deliver its payload directly to the cell membrane without unloading the polyene in the cell wall. In addition, these findings suggest that extracellular vesicles may also be able to pass through the cell wall to deliver soluble and membrane-bound effectors and other molecules to the extracellular space.

Liposomal amphotericin B for the treatment of visceral leishmaniasis.

During the past decade, liposomal amphotericin B has been used with increasing frequency to treat visceral leishmaniasis (VL). The World Health Organization convened a workshop to review current knowledge and to develop guidelines for liposomal amphotericin B use for VL. In Europe, liposomal amphotericin B is widely used to treat VL. In Africa and Asia, the VL disease burden is high and drug access is poor; liposomal amphotericin B is available only through preferential pricing for nonprofit groups in East Africa. Clinical trials and experience demonstrate high efficacy and low toxicity for liposomal amphotericin B (total dose, 20 mg/kg) in immunocompetent patients with VL. Combination trials in areas with antileishmanial drug resistance, and treatment and secondary prophylaxis trials in VL-human immunodeficiency virus-coinfected patients, are important to safeguard the current armamentarium and to optimize regimens. The public health community should work to broaden access to preferential liposomal amphotericin B pricing by public sector VL treatment programs.

Effect of tissue penetration on AmBisome efficacy.

Amphotericin B reformulated into the liposomal formulation known as AmBisome (amphotericin B, hydrogenated soy phosphatidylcholine, cholesterol and dimyristoyl phosphatidylglycerol) can be safely administered at dosages 15 times higher than the conventional drug with the same broad spectrum of activity. Increased doses demonstrate non-linear clearance with saturation of the reticuloendothelial system (RES) and redistribution of the drug into non-RES tissues. The efficacy of this liposomal amphotericin B formulation appears to be related both to improved tissue penetration in the lungs, brain, kidneys, liver and spleen along with sustained bioactivity of therapeutic drug levels in these target tissues.

Effect of Delta-9-tetrahydrocannabinol on mouse resistance to systemic Candida albicans infection.

Delta-9-tetrahydrocannabinol (Δ9-THC), the psychoactive component of marijuana, is known to suppress the immune responses to bacterial, viral and protozoan infections, but its effects on fungal infections have not been studied. Therefore, we investigated the effects of chronic Δ9-THC treatment on mouse resistance to systemic Candida albicans (C. albicans) infection. To determine the outcome of chronic Δ9-THC treatment on primary, acute systemic candidiasis, c57BL/6 mice were given vehicle or Δ9-THC (16 mg/kg) in vehicle on days 1-4, 8-11 and 15-18. On day 19, mice were infected with 5×10(5) C. albicans. We also determined the effect of chronic Δ9-THC (4-64 mg/kg) treatment on mice infected with a non-lethal dose of 7.5×10(4) C. albicans on day 2, followed by a higher challenge with 5×10(5) C. albicans on day 19. Mouse resistance to the infection was assessed by survival and tissue fungal load. Serum cytokine levels were determine to evaluate the immune responses. In the acute infection, chronic Δ9-THC treatment had no effect on mouse survival or tissue fungal load when compared to vehicle treated mice. However, Δ9-THC significantly suppressed IL-12p70 and IL-12p40 as well as marginally suppressed IL-17 versus vehicle treated mice. In comparison, when mice were given a secondary yeast infection, Δ9-THC significantly decreased survival, increased tissue fungal burden and suppressed serum IFN-γ and IL-12p40 levels compared to vehicle treated mice. The data showed that chronic Δ9-THC treatment decreased the efficacy of the memory immune response to candida infection, which correlated with a decrease in IFN-γ that was only observed after the secondary candida challenge.

Characterization of the murine Th2 response to immunization with liposomal M2e influenza vaccine.

While the current influenza vaccine strategy is dependent on eliciting neutralizing antibodies to the hemagglutinin (H or HA) surface glycoprotein, antigenic drifts and occasional antigenic shifts necessitate constant surveillance and annual updates to the vaccine components. The ectodomain of the matrix 2 (M2e) channel protein has been proposed as a universal vaccine candidate, although it has not yet been shown to elicit neutralizing antibodies. Utilizing a liposome-based vaccine technology, an M2e vaccine (L-M2e-HD/MPL) was tested and shown to stimulate the production of anti-M2e antibodies which precipitated with whole virus and inhibited viral cell lysis by multiple type A strains of influenza virus using a novel in vitro assay. The anti-M2e antibodies also conferred complete protection following passive transfer from L-M2e-HD/MPL vaccinated mice to naïve mice challenged with H1N1 virus. Significantly higher levels of IL-4 compared to IFN-γ were secreted by the splenocytes of L-M2e-HD/MPL vaccinated mice incubated with M2e. In addition, depletion of CD4 cells or CD4 cells plus CD8 cells from L-M2e-HD/MPL vaccinated mice using monoclonal antibodies markedly decreased the level of protection of the vaccine when compared to just CD8 depletion of L-M2e-HD/MPL vaccinated mice. These results suggest that the protective immune response elicited by this vaccine is mediated primarily by a Th2 mechanism.

Comparison of the physicochemical, antifungal, and toxic properties of two liposomal amphotericin B products.

Small unilamellar amphotericin B liposomes can reduce the toxicity of amphotericin B. In this study, we compared the physical, antifungal, pharmocokinetic, and toxic properties of two liposomal amphotericin B products, AmBisome and Anfogen, that have the same chemical composition but are manufactured differently. In vitro tests included determinations of the MICs and the concentrations causing the release of 50% of the intracellular potassium from red blood cells (K50 values) to assess toxicity. The 50% lethal dose (LD50) was evaluated by using uninfected C57BL/6 mice and single intravenous (i.v.) doses of 1 to 100 mg/kg of body weight. Multiple i.v. dosing over 18 days was performed with 0.5, 1.0, or 5.0 mg of Anfogen/kg or 1.0, 5.0, or 25 mg of AmBisome/kg to evaluate chronic toxicity. DBA/2 mice were infected intranasally with 2.5 x 10(6) Aspergillus fumigatus conidia, treated for 3 or 4 days with 3.0, 5.0, or 7.5 mg of Anfogen/kg or 3, 5, 7.5, or 15 mg of AmBisome/kg, and evaluated to assess the toxicity of the drugs to the kidneys (by measurement of blood urea nitrogen and creatinine levels and histopathology) and the drug efficacy. The median particle size was 77.8 nm for AmBisome and 111.5 nm for Anfogen. In vitro K(50) values were significantly lower for Anfogen (0.9 mug/ml) than for AmBisome (20 microg/ml), and the LD50 of AmBisome was >100 mg/kg, versus 10 mg of Anfogen/kg. There was significant renal tubular necrosis in uninfected and infected mice given Anfogen but no tubular necrosis in AmBisome-treated mice. AmBisome at 7.5 or 15 mg/kg was also more efficacious than 7.5 mg of Anfogen/kg for the treatment of pulmonary aspergillosis, based on survival and weight loss data and numbers of CFU per gram of lung. In conclusion, the efficacy and toxicity of these two liposomal amphotericin B products were significantly different, and thus, the products were not comparable.

Effects of dosing regimen on accumulation, retention and prophylactic efficacy of liposomal amphotericin B.

OBJECTIVES: We hypothesized that effective prophylactic treatment of fungal infections would require adequate drug penetration and retention at potential infection sites. Using a mouse model, we examined liposomal amphotericin B (L-AmB) biodistribution, cell localization and retention in kidneys, lungs, liver and spleen to evaluate effective dosing regimens for prophylaxis of Candida glabrata and Candida albicans infections. METHODS: Following treatment of mice with cumulative doses of L-AmB (60-225 mg/kg), a bioassay was done to determine tissue drug concentrations 12 h to 6 weeks post-treatment. Immunohistochemical staining with anti-amphotericin B antibodies was used for cellular drug localization. Mice were treated prophylactically with 15-90 mg/kg L-AmB and challenged intravenously 1-7 days later with C. glabrata or they were given a total of 60 mg/kg as daily or intermittent dosing followed by intravenous challenge with C. albicans 3 or 6 weeks later. RESULTS: On the basis of microg/g tissue, the relative amount of drug was in the order spleen > liver > kidneys > lungs. Amphotericin B levels were maintained above the MIC for many fungi for 1 week in lungs and for as long as 6 weeks in kidneys and spleen. Drug localized in kidney tubular epithelial cells and in macrophages of liver and spleen. In prophylactic models, fungal burden was reduced by several 1000-fold or was undetectable within target tissues (kidneys, spleen). CONCLUSIONS: These observations underscore the importance of including drug tissue levels to obtain a better understanding of L-AmB efficacy. The sustained concentrations of bioactive AmB in many tissues provide a further rationale for investigating L-AmB prophylactic regimens.

In vitro susceptibility of Staphylococcus aureus to thrombin-induced platelet microbicidal protein-1 (tPMP-1) is influenced by cell membrane phospholipid composition and asymmetry.

Thrombin-induced platelet microbicidal proteins (e.g. tPMP-1) are small cationic peptides released from mammalian platelets. As the cytoplasmic membrane (CM) is a primary target of tPMPs, distinct CM characteristics are likely to affect the cells' susceptibility profiles. In Staphylococcus aureus, CM surface charge and hydrophobicity are principally determined by the content and distribution of its three major phospholipid (PL) constituents: negatively charged phosphatidylglycerol (PG) and cardiolipin (CL) and positively charged lysyl-PG (LPG). PL composition profiles, and inner vs outer CM leaflet PL distributions, were compared in an isogenic tPMP-susceptible (tPMP(S)) and -resistant (tPMP(R)) S. aureus strain pair (ISP479C vs ISP479R respectively). All PLs were asymmetrically distributed between the outer and inner CM leaflets in both strains. However, in ISP479R, the outer CM leaflet content of LPG was significantly increased vs ISP479C (27.3+/-11.0 % vs 18.6+/-7.0 % respectively; P=0.05). This observation correlated with reduced binding of the cationic proteins cytochrome c, poly-L-lysine, tPMP-1 and the tPMP-1-mimetic peptide, RP1, to tPMP-1(R) whole cells and to model liposomal CMs with LPG content and distribution similar to that of tPMP-1(R) strains. Collectively, selected CM parameters correlated with reduced staphylocidal capacities of tPMP-1 against certain S. aureus strains, including relative increases in outer CM leaflet positive charge and reduced surface binding of cationic molecules. These findings offer new insights into mechanisms of antimicrobial peptide susceptibility and resistance in S. aureus.

Comparative efficacies, toxicities, and tissue concentrations of amphotericin B lipid formulations in a murine pulmonary aspergillosis model.

Invasive aspergillosis, an important cause of morbidity and mortality in immunosuppressed (IS) patients, is often treated with amphotericin B lipid formulations. In the present study, liposomal amphotericin B (L-AMB) and amphotericin B lipid complex (ABLC) were compared in treatment of murine pulmonary aspergillosis. Uninfected, IS mice were treated for 4 days with 1, 4, 8, or 12 mg L-AMB or ABLC/kg of body weight, and their lungs were analyzed by high-performance liquid chromatography for drug concentrations. IS mice intranasally challenged with Aspergillus fumigatus were treated with 12, 15, or 20 mg/kg L-AMB or ABLC and monitored for survival, fungal burden (CFU), and tissue drug concentration. Blood urea nitrogen (BUN) levels and kidney histopathology were determined for uninfected and infected mice given 15 or 20 mg/kg L-AMB or ABLC. The results showed that both drugs had therapeutic levels of drug (>3.0 microg/g) in the lungs of uninfected or infected mice, and 24 h after the last dose, ABLC levels were significantly higher than L-AMB levels (P < 0.02). L-AMB and ABLC at 12 mg/kg both produced 57% survival, but only L-AMB at 15 or 20 mg/kg further increased survival to 80 to 90%, with BUN levels and kidney morphology similar to those of controls. Survival at 15 or 20 mg/kg ABLC was not significantly different than that of controls, and BUN levels were significantly elevated, with tubular alterations in uninfected animals and acute necrosis in kidney tubules of infected animals. In conclusion, although both drugs were effective in prolonging survival at 12 mg/kg, the reduced nephrotoxicity of L-AMB increased its therapeutic index, allowing for its safe and effective use at 15 or 20 mg/kg.

Comparison of antifungal treatments for murine fusariosis.

OBJECTIVES: Fusarium solani infections are notoriously difficult to treat. We compared the efficacy of polyenes and an echinocandin in treating murine fusariosis to identify the optimal therapeutic regimen. METHODS: Neutropenic mice infected intravenously with F. solani were treated with amphotericin B (AmB), liposomal AmB (LAmB), amphotericin B lipid complex (ABLC), caspofungin acetate or a combination of LAmB and caspofungin. Treatment was initiated prior to infection (prophylactic therapy), 24 h post-infection (delayed therapy) or 2 days before infection and continued for 1 day after (continuous therapy). RESULTS: Prophylaxis only with LAmB significantly reduced brain or kidney fungal burden compared with placebo. No prophylactic treatment improved survival. LAmB levels in the kidneys were higher than ABLC or AmB levels, which were often undetectable. In the delayed therapy model, neither polyenes nor caspofungin improved survival. In the continuous therapy model, LAmB or LAmB plus caspofungin did not improve survival even though they did decrease fungal burden. In contrast, continuous caspofungin at 1 but not 5 mg/kg/day improved survival, but did not decrease fungal burden. Kidney inflammation and tissue necrosis were markedly decreased in mice treated with caspofungin compared with other treatments. CONCLUSIONS: These studies demonstrate a dissociation between survival and tissue fungal burden during murine fusariosis. Although prophylactic LAmB may be useful at reducing tissue fungal burden, polyenes had limited survival benefit for active fusariosis. Caspofungin at 1 but not 5 mg/kg/day mediated surprising improvements in survival during active fusariosis, despite lack of reduction in fungal burden. Further studies are warranted.

Protection against H1, H5, H6 and H9 influenza A infection with liposomal matrix 2 epitope vaccines.

The recent emergence of multiple avian influenza A subtypes that cause human disease (i.e., H5N1, H9N2 and H7N7), coupled with the fear that one of these strains might precipitate a new pandemic, underscores the need to develop new technological approaches to immunization which elicit protective immune responses against multiple subtypes of influenza A. In response to this demand, several matrix 2 protein ectodomain segments (M2eA) corresponding to the H1N1, H5N1 and H9N2 influenza strains were formulated using a novel liposome-based vaccine technology and evaluated as potential immunogens for developing a "universal" influenza vaccine. Mice immunized with liposomal M2eA survived homologous challenges with H1N1 (100% survival) or H9N2 (80% survival) influenza strains. There were significant reductions in their lung viral load as well as in immunized mice challenged with the H5N1 subtype. The mice vaccinated with an M2eA segment corresponding to the H1N1 and H6N2 (a reassortant influenza A virus carrying the M2eA from PR8/34) strains elicited elevated IgG ELISA antibody titers to this M2eA epitope segment and antiserum from these immunized mice provided passive protection (100% survival) to naïve mice receiving a lethal dose of H6N2 influenza virus. These results provide the first evidence that recombinant M2eA epitopes to multiple subtypes elicited immune protection against a homologous challenge and provides further evidence in favor of the development of a "universal" influenza vaccine based on M2eA.