Effect of liposomal antigens on the priming and activation of the immune system by dendritic cells

Nanoparticle Vaccines Adopting Virus-like Features for Enhanced Immune Potentiation

Synthetic nanoparticles play an increasingly significant role in vaccine design and development as many nanoparticle vaccines show improved safety and efficacy over conventional formulations. These nanoformulations are structurally similar to viruses, which are nanoscale pathogenic organisms that have served as a key selective pressure driving the evolution of our immune system. As a result, mechanisms behind the benefits of nanoparticle vaccines can often find analogue to the interaction dynamics between the immune system and viruses. This review covers the advances in vaccine nanotechnology with a perspective on the advantages of virus mimicry towards immune potentiation. It provides an overview to the different types of nanomaterials utilized for nanoparticle vaccine development, including functionalization strategies that bestow nanoparticles with virus-like features. As understanding of human immunity and vaccine mechanisms continue to evolve, recognizing the fundamental semblance between synthetic nanoparticles and viruses may offer an explanation for the superiority of nanoparticle vaccines over conventional vaccines and may spur new design rationales for future vaccine research. These nanoformulations are poised to provide solutions towards pressing and emerging human diseases.

The immunogenicity of the liposome-associated outer membrane proteins (OMPs) of Moraxella catarrhalis

The outer membrane proteins (OMPs) are the most immunogenic and attractive of the Moraxella catarrhalis vaccine antigens that may induce the protective immune response. The aim of this study was to determine the effectiveness of two types of OMP-associated phosphatidylcholine (PC) liposomal formulations (OMPs-PC, PC-OMPs) and of Zwittergent-based proteomicelles (OMPs-Z) in potentiating an anti-OMP systemic immune response in mice. The immunogenicities of the above preparations were evaluated by assessing serum anti-OMP IgG and IgA reactivity in the post-immunized mouse antisera using ELISA and Western blotting. Additionally, the cross-reactivity of the most effective anti-OMP response was determined using heterologous sera from both humans and mice. Both the proteoliposomes and the proteomicelles showed high immunogenic properties and did not elicit any distinct quantitative differences in the antibody titer or qualitative differences in the pattern of the mouse antisera. The post-immunized mouse antisera predominantly recognized a approximately 60-kDa OMP of M. catarrhalis. That protein was also found to be a highly cross-reactive antigen interacting with a panel of pooled mouse antisera produced by immunization either with whole cells or the purified OMPs of heterologous M. catarrhalis strains. Furthermore, normal sera collected from healthy children were found to be preferentially reactive with the 60-kDa OMP. The serum-specific IgG, IgA and IgM were respectively detected via immunoblotting in 90%, 85% and 30% of heterologous human sera. This similar immunogenic effectiveness of both OMP-associated liposomal formulations could contribute to the practical use of such formulations in the future in human vaccination. Moreover, the highly cross-reactive 60-kDa OMP seems to be an important antigenic marker of M. catarrhalis, and, as it is responsible for the induction of an antibody-mediated and long-lasting immune response, studying it may partially aid us in understanding the relatively low degree of pathogenicity of the bacterium in immunocompetent individuals.

Leishmania major: Immune response in BALB/c mice immunized with stress-inducible protein 1 encapsulated in liposomes

Protection against leishmaniasis is depending upon generation of a Th1 type of immune response. Field trials of first generation Leishmania vaccine showed a limited efficacy even with multiple doses mainly due to lack of an appropriate adjuvant. In this study, susceptible BALB/c mice were immunized with rLmSTI1 encapsulated in liposomes to explore the extent of protection induced by Leishmania antigen encapsulated in the liposomes against challenge with Leishmania major. The results showed that s.c. immunization of BALB/c mice with liposomal rLmSTI1 induced a significant protection against challenge and a significant lower parasite burden in spleen up to 14 weeks after challenge. The protected animals showed a significantly smaller footpad thickness after challenge, and a higher level of anti-SLA IgG antibodies before and after challenge with a predominant IgG2a titer. The data supports the possibility of using liposomal Leishmania antigens as a vaccine.

Liposomal vaccines--targeting the delivery of antigen

Vaccines that can prime the adaptive immune system for a quick and effective response against a pathogen or tumor cells, require the generation of antigen (Ag)-specific memory T and B cells. The unique ability of dendritic cells (DCs) to activate naïve T cells, implies a key role for DCs in this process. The generation of tumor-specific CD8(+) cytotoxic T cells (CTLs) is dependent on both T cell stimulation with Ag (peptide-MHC-complexes) and costimulation. Interestingly, tumor cells that lack expression of T cell costimulatory molecules become highly immunogenic when transfected to express such molecules on their surface. Adoptive immunotherapy with Ag-pulsed DCs also is a strategy showing promise as a treatment for cancer. The use of such cell-based vaccines, however, is cumbersome and expensive to use clinically, and/or may carry risks due to genetic manipulations. Liposomes are particulate vesicular lipid structures that can incorporate Ag, immunomodulatory factors and targeting molecules, and hence can serve as potent vaccines. Similarly, Ag-containing plasma membrane vesicles (PMV) derived from tumor cells can be modified to incorporate a T cell costimulatory molecule to provide both TCR stimulation, and costimulation. PMVs also can be modified to contain IFN-gamma and molecules for targeting DCs, permitting delivery of both Ag and a DC maturation signal for initiating an effective immune response. Our results show that use of such agents as vaccines can induce potent anti-tumor immune responses and immunotherapeutic effects in tumor models, and provide a strategy for the development of effective vaccines and immunotherapies for cancer and infectious diseases.

Immunogenicity and protective efficacy of a recombinant filamentous haemagglutinin from Bordetella pertussis

Bordetella pertussis is the causative agent of whooping cough, a major childhood pathogen; acellular vaccines consisting of purified B. pertussis antigens such as filamentous haemagglutinin (FHA) are commonly used to prevent pertussis. Despite the importance of FHA in B. pertussis pathogenesis and its inclusion in most acellular vaccines, the functional importance of individual domains in the induction of protective immunity is largely unknown. In this study, we have purified a recombinant FHA protein from Escherichia coli consisting of a 42 kDa maltose binding domain of E. coli and the 43 kDa type I immunodominant domain of FHA. The fusion protein (Mal85) was purified from E. coli cell lysates via affinity chromatography with an amylose column. Mal85 was then delivered to BALB/c mice intranasally encapsulated in liposomes, formulated with Protollin(TM) or in conjunction with an immunostimulatory CpG oligonucleotide. Mice were also vaccinated intraperitoneally with alum-adsorbed Mal85. Sera from all treatment groups showed strong IgG responses to Mal85 and recognized native FHA. Specific salivary IgA was induced in mice vaccinated with Mal85 in liposomes, Protollin(TM) and delivered with CpG. Vaccination with Mal85 encapsulated in liposomes or formulated with Protollin(TM) provided protection against aerosol challenge with B. pertussis in BALB/c mice. These data indicate that the type I domain of FHA is a protective antigen in mice and may serve as a candidate for inclusion in new acellular pertussis vaccines.