Formulation of HIV-envelope protein with lipid vesicles expressing ganglioside GM1 associated to cholera toxin B enhances mucosal immune responses

Mucosal Vaccine Development Based on Liposome Technology

Immune protection against infectious diseases is most effective if located at the portal of entry of the pathogen. Hence, there is an increasing demand for vaccine formulations that can induce strong protective immunity following oral, respiratory, or genital tract administration. At present, only few mucosal vaccines are found on the market, but recent technological advancements and a better understanding of the principles that govern priming of mucosal immune responses have contributed to a more optimistic view on the future of mucosal vaccines. Compared to live attenuated vaccines, subcomponent vaccines, most often protein-based, are considered safer, more stable, and less complicated to manufacture, but they require the addition of nontoxic and clinically safe adjuvants to be effective. In addition, another limiting factor is the large antigen dose that usually is required for mucosal vaccines. Therefore, the combination of mucosal adjuvants with the recent progress in nanoparticle technology provides an attractive solution to these problems. In particular, the liposome technology is ideal for combining protein antigen and adjuvant into an effective mucosal vaccine. Here, we describe and discuss recent progress in nanoparticle formulations using various types of liposomes that convey strong promise for the successful development of the next generation of mucosal vaccines.

A review of nanotechnological approaches for the prophylaxis of HIV/AIDS

Successful treatment and control of HIV/AIDS is one of the biggest challenges of 21st century. More than 33 million individuals are infected with HIV worldwide and more than 2 million new cases of HIV infection have been reported. The situation demands development of effective prevention strategies to control the pandemic of AIDS. Due to lack of availability of an effective HIV vaccine, antiretroviral drugs and nucleic acid therapeutics like siRNA have been explored for HIV prophylaxis. Clinical trials shave shown that antiretroviral drugs, tenofovir and emtricitabine can offer some degree of HIV prevention. However, complete prevention of HIV infection has not been achieved yet. Nanotechnology has brought a paradigm shift in the diagnosis, treatment and prevention of many diseases. The current review discusses potential of various nanocarriers such as dendrimers, polymeric nanoparticles, liposomes, lipid nanocarriers, drug nanocrystals, inorganic nanocarriers and nanofibers in improving efficacy of various modalities available for HIV prophylaxis.

Antibody response to polyhistidine-tagged peptide and protein antigens attached to liposomes via lipid-linked nitrilotriacetic acid in mice

Particulate delivery systems enhance antibody responses to subunit antigens. However, covalent attachment of protein antigens can disrupt protein structure and mask critical epitopes, altering the antibody response to the antigen. In this report, we evaluate noncovalent metal chelation via nitrilotriacetic acid (NTA) as a nondestructive method to attach peptide and protein antigens to liposomes. Two model antigens, ovalbumin (OVA) and a peptide derived from the membrane-proximal region of HIV-1 gp41 (N-MPR), were polyhistidinylated and attached to liposomes via monovalent NTA (mono-NTA; K(D) [equilibrium dissociation constant], ∼10 μM), trivalent NTA (tris-NTA; K(D), ∼1 nM), or a covalent linkage. Attachment of N-MPR, but not OVA, to liposomes via an NTA lipid elicited stronger antibody responses in BALB/c mice than a formulation in which unassociated antigen was simply admixed with control liposomes lacking NTA. However, the tris-NTA linkage did not increase antibody responses to either N-MPR or OVA compared to the level for the mono-NTA linkage, despite the greater liposomal association of the antigen. For both antigens, covalently attaching them to a lipid elicited significantly stronger antibody responses than NTA-anchored antigens (OVA titer, 3.4 × 10(6) versus 1.4 × 10(6) to 1.6 × 10(6) [P < 0.001]; N-MPR titer, 4.4 × 10(4) versus 5.5 × 10(2) to 7.6 × 10(2) [P < 0.003]). The data indicate that NTA linkages may increase antibody titers to weak antigens such as N-MPR, but NTA-mediated attachment remains inferior to covalent conjugation. Moreover, enhancements in antigen-liposome affinity do not result in increased antibody titers. Thus, additional improvements of NTA-mediated conjugation technology are necessary to achieve an effective, nondestructive method for increasing the humoral response to antigens in particulate vaccines.

Molecular basis of the mucosal immune system: from fundamental concepts to advances in liposome-based vaccines

The mucosal immune system, the primary portal for entry of most prevalent and devastating pathogens, is guarded by the special lymphoid tissues (mucosally associated lymphoid tissues) for immunity. Mucosal immune infection results in induction of IgA-manifested humoral immunity. Cell-mediated immunity may also be generated, marked by the presence of CD4+ Th1 and CD8+ cells. Furthermore, the immunity generated at the mucosal site is transported to the distal mucosal site as well as to systemic tissues. An understanding of the molecular basis of the mucosal immune system provides a unique platform for designing a mucosal vaccine. Coadministration of immunostimulatory molecules further accelerates functioning of the immune system. Mimicking receptor-mediated binding of the pathogen may be achieved by direct conjugation of antigen with an immunostimulatory molecule or encapsulation in a carrier followed by anchoring of a ligand having affinity to the cells of the mucosal immune system. Nanotechnology has played a significant role in mucosal vaccine development and among the available options liposomes are the most promising. Liposomes are phospholipid bilayered vesicles that can encapsulate protein as well as DNA-based vaccines and offer coencapsulation of adjuvant along with the antigen. At the same, time ligand-conjugated liposomes augment interaction of antigen with the cells of the mucosal immune system and thereby serve as suitable candidates for the mucosal delivery of vaccines. This article exhaustively explores strategies involved in the generation of mucosal immunity and also provides an insight to the progress that has been made in the development of liposome-based mucosal vaccine.

Nanoparticles for nasal vaccination

The great interest in mucosal vaccine delivery arises from the fact that mucosal surfaces represent the major site of entry for many pathogens. Among other mucosal sites, nasal delivery is especially attractive for immunization, as the nasal epithelium is characterized by relatively high permeability, low enzymatic activity and by the presence of an important number of immunocompetent cells. In addition to these advantageous characteristics, the nasal route could offer simplified and more cost-effective protocols for vaccination with improved patient compliance. The use of nanocarriers provides a suitable way for the nasal delivery of antigenic molecules. Besides improved protection and facilitated transport of the antigen, nanoparticulate delivery systems could also provide more effective antigen recognition by immune cells. These represent key factors in the optimal processing and presentation of the antigen, and therefore in the subsequent development of a suitable immune response. In this sense, the design of optimized vaccine nanocarriers offers a promising way for nasal mucosal vaccination.

Low-dose tolerance is mediated by the microfold cell ligand, reovirus protein sigma1

Mucosal tolerance induction generally requires multiple or large Ag doses. Because microfold (M) cells have been implicated as being important for mucosal tolerance induction and because reovirus attachment protein sigma1 (psigma1) is capable of binding M cells, we postulated that targeting a model Ag to M cells via psigma1 could induce a state of unresponsiveness. Accordingly, a genetic fusion between OVA and the M cell ligand, reovirus psigma1, termed OVA-psigma1, was developed to enhance tolerogen uptake. When applied nasally, not parenterally, as little as a single dose of OVA-psigma1 failed to induce OVA-specific Abs even in the presence of adjuvant. Moreover, the mice remained unresponsive to peripheral OVA challenge, unlike mice given multiple nasal OVA doses that rendered them responsive to OVA. The observed unresponsiveness to OVA-psigma1 could be adoptively transferred using cervical lymph node CD4(+) T cells, which failed to undergo proliferative or delayed-type hypersensitivity responses in recipients. To discern the cytokines responsible as a mechanism for this unresponsiveness, restimulation assays revealed increased production of regulatory cytokines, IL-4, IL-10, and TGF-beta1, with greatly reduced IL-17 and IFN-gamma. The induced IL-10 was derived predominantly from FoxP3(+)CD25(+)CD4(+) T cells. No FoxP3(+)CD25(+)CD4(+) T cells were induced in OVA-psigma1-dosed IL-10-deficient (IL-10(-/-)) mice, and despite showing increased TGF-beta1 synthesis, these mice were responsive to OVA. These data demonstrate the feasibility of using psigma1 as a mucosal delivery platform specifically for low-dose tolerance induction.

Effectiveness of the B subunit of cholera toxin in potentiating immune responses to the recombinant hemagglutinin/adhesin domain of the gingipain Kgp from Porphyromonas gingivalis

The hemagglutinin/adhesin HArep domain is present in the gingipains HRgpA and Kgp and in the hemagglutinin HagA of Porphyromonas gingivalis and is felt to be important in the virulence of this bacterium. In the present study, we determined the immunogenicity of recombinant HArep from the gingipain Kgp (termed Kgp-rHArep) and the effectiveness of the B subunit of cholera toxin (CTB), compared to other adjuvants in potentiating a specific response to Kgp-rHArep following intranasal (i.n.) immunization of mice. Furthermore, we determined the effectiveness of anti-Kgp-rHArep antibodies in protection against P. gingivalis invasion of epithelial cells. Evidence is provided that Kgp-rHArep was effective in inducing immune responses following systemic or mucosal immunization. Kgp-rHArep induced both a Th1- and Th2-type response following i.n. immunization. Immunization of mice with Kgp-rHArep and CTB, either admixed or chemically conjugated to the antigen, via the i.n. route, resulted in a significant augmentation of the systemic and mucosal immune response to Kgp-rHArep, which was similar to or higher than the responses seen in mice immunized with antigen and the other adjuvants tested. CTB and the heat-labile toxin of Escherichia coli potentiated a Th1- and Th2-type response to Kgp-rHArep, whereas the adjuvant monophosphoryl lipid A preferentially promoted a Th1-type response to the antigen. Furthermore, anti-Kgp-rHArep antibodies were shown to protect against P. gingivalis invasion of epithelial cells in an in vitro system. These results demonstrate the effectiveness of certain mucosal adjuvants in potentiating and in altering the nature of the immune response to Kgp-rHArep following i.n. immunization, and provide evidence for the potential usefulness of Kgp-rHArep for the development of a vaccine against periodontal disease.

Mucosal AIDS vaccines

Debates are still being waged over what is the best strategy for developing a potent AIDS vaccine. All the obvious approaches to making AIDS vaccines have been tried in the past two decades without much success. It is clear that new thinking and a revision of prevailing dogmas needs to be in place if we really want a vaccine. Conventional envelope-based antibody-inducing vaccines do not appear to hold promise, and broadly-neutralizing antibodies are now being searched as an alternative to the failed approach with subunit vaccines. The current consensus is that cellular immune responses, especially those mediated by CD8 cytotoxic/suppressor (CTL) and CD4 helper T lymphocytes, are needed to control HIV. Vaccines capable of inducing cell-mediated responses are, therefore, considered critical for controlling the spread of HIV. DNA-based vaccines triggering CTL reaction are currently thought to be an answer, but will they fulfill the promise? In the following paragraphs, a critical assessment of the state of the art will be provided in an attempt to analyze what we know and still don't know. The focus of this review is primarily on mucosal vaccines-a relatively new area in AIDS research. The update on V-1 Immunitor, the first mucosal AIDS vaccine available commercially, is provided within this context. Some of the reviewed concepts may be disputable, but without departure from the uninspiring consensus no substantial progress in the AIDS vaccine field can be envisioned.

Mucosal immunization with virus-like particles of simian immunodeficiency virus conjugated with cholera toxin subunit B

To enhance the efficiency of antigen uptake at mucosal surfaces, CTB was conjugated to simian immunodeficiency virus (SIV) virus-like particles (VLPs). We characterized the immune responses to the Env and Gag proteins after intranasal administration. Intranasal immunization with a mixture of VLPs and CTB as an adjuvant elicited higher levels of SIV gp160-specific immunoglobulin G (IgG) in sera and IgA in mucosae, including saliva, vaginal-wash samples, lung, and intestine, as well as a higher level of neutralization activities than immunization with VLPs alone. Conjugation of CTB to VLPs also enhanced the SIV VLP-specific antibodies in sera and in mucosae to similar levels. Interestingly, CTB-conjugated VLPs showed higher levels of cytokine (gamma interferon)-producing splenocytes and cytotoxic-T-lymphocyte activities of immune cells than VLPs plus CTB, as well as an increased level of both IgG1 and IgG2a serum antibodies, which indicates enhancement of both Th1- and Th2-type cellular immune responses. These results demonstrate that CTB can be an effective mucosal adjuvant in the context of VLPs to induce enhanced humoral, as well as cellular, immune responses.

Enhancement of mucosal immunization with virus-like particles of simian immunodeficiency virus

Cholera toxin (CT) is the most potent known mucosal adjuvant, but its toxicity precludes its use in humans. Here, in an attempt to develop safe and effective mucosal adjuvants, we compared immune responses to simian immunodeficiency virus (SIV) virus-like particles (VLPs) after intranasal coimmunization with RANTES, CpG oligodeoxynucleotides (ODN), or CT. Antibody analysis demonstrated that RANTES and CpG ODN had capacities for mucosal adjuvanticity, i.e., for enhancing serum and vaginal antibodies specific to SIV Env, similar to those for CT. RANTES and CpG ODN skewed serum antibodies predominantly to the immunoglobulin G2a isotype. Most importantly, RANTES and CpG ODN were more effective than CT in increasing neutralizing titers of both serum and vaginal antibodies. After intranasal coadministration with VLPs, RANTES or CpG ODN also induced increased levels of gamma interferon (IFN-gamma)-producing lymphocyte and cytotoxic T-lymphocyte activities in both spleen and lymph nodes but did not increase the levels of interleukin-4-producing lymphocytes. The results suggest that RANTES and CpG ODN enhance immune responses in a T-helper-cell-type-1 (Th1)-oriented manner and that they can be used as effective mucosal adjuvants for enhancing both humoral and cellular immune responses in the context of VLPs, which are particulate antigens.

Nucleic acid vaccines: tasks and tactics

There are no adequate vaccines against some of the new or reemerged infectious scourges such as HIV and TB. They may require strong and enduring cell-mediated immunity to be elicited. This is quite a task, as the only known basis of protection by current commercial vaccines is antibody. As DNA or RNA vaccines may induce both cell-mediated and humoral immunity, great interest has been shown in them. However, doubt remains whether their efficacy will suffice for their clinical realization. We look at the various tactics to increase the potency of nucleic acid vaccines and divided them broadly under those affecting delivery and those affecting immune induction. For delivery, we have considered ways of improving uptake and the use of bacterial, replicon or viral vectors. For immune induction, we considered aspects of immunostimulatory CpG motifs, coinjection of cytokines or costimulators and alterations of the antigen, its cellular localization and its anatomical localization including the use of ligand-targeting to lymphoid tissue. We also thought that mucosal application of DNA deserved a separate section. In this review, we have taken the liberty to discuss these enhancement methods, whenever possible, in the context of the underlying mechanisms that might argue for or against these strategies.

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.