Presentation of proteins encapsulated in sterically stabilized liposomes by dendritic cells initiates CD8+ T-cell responses in vivo

Nanovaccines: An effective therapeutic approach for cancer therapy

Cancer vaccines hold considerable promise for the immunotherapy of solid tumors. Nanomedicine offers several strategies for enhancing vaccine effectiveness. In particular, molecular or (sub) cellular vaccines can be delivered to the target lymphoid tissues and cells by nanocarriers and nanoplatforms to increase the potency and durability of antitumor immunity and minimize negative side effects. Nanovaccines use nanoparticles (NPs) as carriers and/or adjuvants, offering the advantages of optimal nanoscale size, high stability, ample antigen loading, high immunogenicity, tunable antigen presentation, increased retention in lymph nodes, and immunity promotion. To induce antitumor immunity, cancer vaccines rely on tumor antigens, which are administered in the form of entire cells, peptides, nucleic acids, extracellular vesicles (EVs), or cell membrane-encapsulated NPs. Ideal cancer vaccines stimulate both humoral and cellular immunity while overcoming tumor-induced immune suppression. Herein, we review the key properties of nanovaccines for cancer immunotherapy and highlight the recent advances in their development based on the structure and composition of various (including synthetic and semi (biogenic) nanocarriers. Moreover, we discuss tumor cell-derived vaccines (including those based on whole-tumor-cell components, EVs, cell membrane-encapsulated NPs, and hybrid membrane-coated NPs), nanovaccine action mechanisms, and the challenges of immunocancer therapy and their translation to clinical applications.

Nanovaccines for cancer immunotherapy

The past few decades have witnessed the booming field of cancer immunotherapy. Cancer therapeutic vaccines, either alone or in combination with other immunotherapies such as adoptive cell therapy or immune checkpoint blockade therapy, are an attractive class of cancer immunotherapeutics. However, cancer vaccines have thus far shown suboptimal efficacy in the clinic. Nanomedicines offer unique opportunities to improve the efficacy of these vaccines. A variety of nanoplatforms have been investigated to deliver molecular or cellular or subcellular vaccines to target lymphoid tissues and cells, thereby promoting the potency and durability of anti-tumor immunity while reducing adverse side effects. In this article, we reviewed the key parameters and features of nanovaccines for cancer immunotherapy; we highlighted recent advances in the development of cancer nanovaccines based on synthetic nanocarriers, biogenic nanocarriers, as well as semi-biogenic nanocarriers; and we summarized newly emerging types of nanovaccines, such as those based on stimulator of interferon genes agonists, cancer neoantigens, mRNA vaccines, as well as artificial antigen-presenting cells. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Protection induced by Leishmania Major antigens and the imiquimod adjuvant encapsulated on liposomes in experimental cutaneous leishmaniasis

There is a need for new, effective, and less expensive and toxic treatment for Leishmaniasis. It seems that the use of a suitable adjuvant and a delivery system is effective in inducing immune reactions for protection. Liposomes can be applied as immunoadjuvants to trigger immune reactions to different antigens. The adjuvant effects of imiquimod using DSPC liposomes containing SLA (soluble Leishmania antigens) were studied on the type and intensity of the produced immune reaction to the challenge of Leishmania major in BALB/c mice. Liposomes were produced by the lipid film procedure. BALB/C mice were immunized subcutaneously, three times at 2-week intervals and with various formulations. Lesion development and the parasite burden in the spleens and feet after the challenge with Leishmania major, Th1 cytokine (IFN-γ), and the IgG isotype titration were assessed to evaluate the induced immune reaction and the protection level. The group of mice immunized with Liposome DSPC +Imiquimod +SLA revealed less severe footpad swelling, being significantly different (P < .05) from other groups. A higher level of IgG2a and IFN-γ secretion was observed in the mice immunized with Liposome DSPC +Imiquimod +SLA than the control group. These observations imply that the DSPC liposome containing imiquimod induces the Th1 immune response that is protective against the challenge of Leishmania major.

Synthetic nanovaccines for immunotherapy

Although vaccination is historically one of the most successful strategies for the prevention of infectious diseases, development of vaccines for cancer and many chronic infections, such as HIV, malaria, and tuberculosis, has remained a challenge. Strong and long-lasting antigen-specific T cell responses are critical for therapy of these diseases. A major challenge in achieving a robust CD8+ T cell response is the requirement of spatio-temporal orchestration of antigen cross-presentation in antigen-presenting cells with innate stimulation. Here, we discuss the development of nanoparticle vaccine (nanovaccine) that modulates the innate immune system and enhances adaptive immunity with reduced toxicity. We address how nanovaccines can integrate multiple functions, such as lymph node targeting, antigen presentation, and stimulation of innate immunity, to achieve a robust T cell response for immunotherapy.

A semi-synthetic whole parasite vaccine designed to protect against blood stage malaria

Although attenuated malaria parasitized red blood cells (pRBCs) are promising vaccine candidates, their application in humans may be restricted for ethical and regulatory reasons. Therefore, we developed an organic microparticle-based delivery platform as a whole parasite malaria-antigen carrier to mimic pRBCs. Killed blood stage parasites were encapsulated within liposomes that are targeted to antigen presenting cells (APCs). Mannosylated lipid core peptides (MLCPs) were used as targeting ligands for the liposome-encapsulated parasite antigens. MLCP-liposomes, but not unmannosylated liposomes, were taken-up efficiently by APCs which then significantly upregulated expression of MHC-ll and costimulatory molecules, CD80 and CD86. Two such vaccines using rodent model systems were constructed - one with Plasmodium chabaudi and the other with P. yoelii. MLCP-liposome vaccines were able to control the parasite burden and extended the survival of mice. Thus, we have demonstrated an alternative delivery system to attenuated pRBCs with similar vaccine efficacy and added clinical advantages. Such liposomes are promising candidates for a human malaria vaccine.

STATEMENT OF SIGNIFICANCE

Attenuated whole parasite-based vaccines, by incorporating all parasite antigens, are very promising candidates, but issues relating to production, storage and safety concerns are significantly slowing their development. We therefore developed a semi-synthetic whole parasite malaria vaccine that is easily manufactured and stored. Two such prototype vaccines (a P. chabaudi and a P. yoelii vaccine) have been constructed. They are non-infectious, highly immunogenic and give good protection profiles. This semi-synthetic delivery platform is an exciting strategy to accelerate the development of a licensed malaria vaccine. Moreover, this strategy can be potentially applied to a wide range of pathogens.

Current advances in self-assembled nanogel delivery systems for immunotherapy

Since nanogels (nanometer-sized gels) were developed two decades ago, they were utilized as carriers of innovative drug delivery systems. In particular, immunological drug delivery via self-assembled nanogels (self-nanogels) owing to their nanometer size and molecular chaperon-like ability to encapsulate large biomolecules is one of the most well studied and successful applications of nanogels. In the present review, we focus on self-nanogel applications as immunological drug delivery systems for cancer vaccines, cytokine delivery, nasal vaccines, and nucleic acid delivery, including several clinical trials. Cancer vaccines were the first practical application of self-nanogels as vehicles for drug delivery. After successful pre-clinical studies, phase I clinical trials were conducted, and it was found that vaccines consisting of self-nanogels could be administered repeatedly to humans without serious adverse effects, and self-nanogel vaccines induced antigen-specific cellular and humoral immunity. Cytokine delivery via self-nanogels led to the sustained release of IL-12, suppressed tumor growth, and increased Th1-type immune responses. Cationic self-nanogels were effective in penetrating the nasal mucosa and resulted in successful nasal vaccines in mice and nonhuman primates. Cationic self-nanogels were also used for the intracellular delivery of proteins and nucleic acids, and were successfully used to knockdown tumor growth factor expression using short interfering RNA with the immunological effect. These studies suggest that self-nanogels are currently one of the most unique and attractive immunological drug delivery systems and are edging closer to practical use.

Expression and purification of half-smooth tongue sole (Cynoglossus semilaevis) CSDAZL protein

The csdazl gene is a sex related gene of half-smooth tongue sole (Cynoglossus semilaevis). Our research group have cloned full length cDNA of csdazl, and studied its expression pattern. To get the further information of csdazl, we constructed a prokaryotic expression plasmid, pET-32a-CSDAZL, expressed in Escherichia coli BL21 and purified the fusion protein by His Trap. In order to detect the biological activity of the fusion protein, we injected the protein with liposome into fish, and detected other sex-related genes' mRNA expression. The results showed that the expression levels of half-smooth tongue sole female-related genes Cyp19a and Foxl2 significantly decreased between 6 and 24 h; however, both genes' expressions returned to their normal levels 72 h after injection, indicating that recombinant CSDAZL protein could down-regulated the expression of female-related genes, Foxl2 and Cyp19a genes, implying that the fusion protein has biological activity and csdazl plays a role in sex differentiation by regulating sex related genes' expression.

Induction of protection against leishmaniasis in susceptible BALB/c mice using simple DOTAP cationic nanoliposomes containing soluble Leishmania antigen (SLA)

A suitable adjuvant and delivery system are needed to develop an effective vaccine against leishmaniasis. To induce a Th1 type of response and protection in BALB/c mice against Leishmania major infection, 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) nanoliposomes bearing an intrinsic adjuvanticity, were used as an antigen delivery system and immunoadjuvant for soluble Leishmania antigens (SLA). DOTAP liposomes containing different concentrations of SLA were prepared by using lipid film method followed by sonication. The prepared vesicles showed a diameter of about 100nm, a positive zeta potential and approximately 70% encapsulation efficiency of SLA. BALB/c mice were immunized subcutaneously (SC), three times in a 3-week interval with different concentrations of liposomal SLA (12.5, 25, and 50μg of SLA/50μl/mice), free SLA and as well as free liposome. The group of mice received 50μg of SLA in DOTAP-nanoliposomes showed a significantly (p<0.001) smaller footpad swelling and the lowest spleen and footpad parasite burden after the challenge. This group also showed the highest IFN-γ production compared to the other groups, lower IL-4 level and higher IgG2a antibody titer. Taken together, the results indicated that simple DOTAP nanoliposome containing 1μg/μl SLA are appropriate delivery systems to induce a Th1 type of immune response and protection against L. major infection in BALB/c mice.

VLPs and particle strategies for cancer vaccines

Effective delivery of tumor antigens to APCs is one of the key steps for eliciting a strong and durable immune response to tumors. Several cancer vaccines have been evaluated in clinical trials, based on soluble peptides, but results have not been fully satisfactory. To improve immunogenicity particles provide a valid strategy to display and/or incorporate epitopes which can be efficiently targeted to APCs for effective induction of adaptive immunity. In the present review, we report some leading technologies for developing particulate vaccines employed in cancer immunotherapy, highlighting the key parameters for a rational design to elicit both humoral and cellular responses.

In vivo anti-HIV activity of the heparin-activated serine protease inhibitor antithrombin III encapsulated in lymph-targeting immunoliposomes

Endogenous serine protease inhibitors (serpins) are anti-inflammatory mediators with multiple biologic functions. Several serpins have been reported to modulate HIV pathogenesis, or exhibit potent anti-HIV activity in vitro, but the efficacy of serpins as therapeutic agents for HIV in vivo has not yet been demonstrated. In the present study, we show that heparin-activated antithrombin III (hep-ATIII), a member of the serpin family, significantly inhibits lentiviral replication in a non-human primate model. We further demonstrate greater than one log(10) reduction in plasma viremia in the nonhuman primate system by loading of hep-ATIII into anti-HLA-DR immunoliposomes, which target tissue reservoirs of viral replication. We also demonstrate the utility of hep-ATIIII as a potential salvage agent for HIV strains resistant to standard anti-retroviral treatment. Finally, we applied gene-expression arrays to analyze hep-ATIII-induced host cell interactomes and found that downstream of hep-ATIII, two independent gene networks were modulated by host factors prostaglandin synthetase-2, ERK1/2 and NFκB. Ultimately, understanding how serpins, such as hep-ATIII, regulate host responses during HIV infection may reveal new avenues for therapeutic intervention.

Cationic liposomes containing soluble Leishmania antigens (SLA) plus CpG ODNs induce protection against murine model of leishmaniasis

Development of an effective vaccine against leishmaniasis is possible due to the fact that individuals cured from cutaneous leishmaniasis (CL) are protected from further infection. First generation Leishmania vaccines consisting of whole killed parasites reached to phase 3 clinical trials but failed to show enough efficacies mainly due to the lack of an appropriate adjuvant. In this study, an efficient liposomal protein-based vaccine against Leishmania major infection was developed using soluble Leishmania antigens (SLA) as a first generation vaccine and cytidine phosphate guanosine oligodeoxynucleotides (CpG ODNs) as an immunostimulatory adjuvant. 1, 2-Dioleoyl-3-trimethylammonium-propane was used as a cationic lipid to prepare the liposomes due to its intrinsic adjuvanticity. BALB/c mice were immunized subcutaneously (SC), three times in 2-week intervals, with Lip-SLA-CpG, Lip-SLA, SLA + CpG, SLA, or HEPES buffer. As criteria for protection, footpad swelling at the site of challenge and spleen parasite loads were assessed, and the immune responses were evaluated by determination of IFN-γ and IL-4 levels of cultured splenocytes, and IgG subtypes. The group of mice that received Lip-SLA-CpG showed a significantly smaller footpad swelling, lower spleen parasite burden, higher IgG2a antibody, and lower IL-4 level compared to the control groups. It is concluded that cationic liposomes containing SLA and CpG ODNs are appropriate to induce Th1 type of immune response and protection against leishmaniasis.

Recent advancements in cytotoxic T lymphocyte generation methods using carbohydrate-coated liposomes

Both tumor-specific CD4⁺ and CD8⁺ T cells have been identified, and the latter is known as a major effector of adaptive antitumor immune responses. Optimal antitumor immune responses are considered to require the concomitant activation of both CD8⁺ and CD4⁺ T cells and the additional selective activation of CD4⁺ T cells with helper, but not regulatory function. As optimal antitumor immune responses are generated by the concomitant activation of both T cell types, it is necessary for vaccine methods involving cytotoxic T-lymphocytes (CTLs) generation to possess a mechanism whereby antigen presenting cells can present administrated exogenous antigens on not only Major histocompatibility complex (MHC) class II, but also MHC class I molecules.

An autologous therapeutic dendritic cell vaccine transfected with total lung carcinoma RNA stimulates cytotoxic T lymphocyte responses against non-small cell lung cancer

OBJECTIVE

The development of immunotherapy for malignancy is greatly limited by the characteristic weak antigenicity of tumors. The primary goal of this study was to circumvent the isolation and purification of tumor-specific antigen determinants by producing a vaccine using lung tumor RNA-loaded dendritic cells (DCs), and to test the response against lung cancer.

METHODS

Total RNA was isolated from 18 lung carcinomas with positive carcinoembryonic antigen (CEA) and mucin-1 (MUC1) staining, as identified by immunohistochemistry. DCs and T-cells from peripheral blood mononuclear cells were generated in vitro, and then DCs in different stages were transfected with RNA using several different methods. The expression of CEA and MUC1 in RNA-transfected DCs was measured using flow cytometry. T-cells stimulated by DCs were harvested as effectors, and primary tumor cells cultured in vitro were used as targets. Cytotoxicity was determined by lactic dehydrogenase detection assay.

RESULTS

Immature RNA-transfected DCs significantly increased the expression of CEA and MUC1, compared to mature transfected DCs. RNA transfection via electroporation resulted in significantly greater CEA and MUC1 expression than did transfection via lipofection or passive pulsing. Lymphocytes stimulated by DCs transfected with lung tumor RNA initiated a cytotoxic T lymphocyte (CTL) tumor-specific response.

CONCLUSION

Immature DCs transfected with total lung carcinoma RNA by electroporation in vitro effectively stimulate antigen-specific CTL responses against tumor cells.

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.

Use of proteoliposome as a vaccine against Trypanosoma cruzi in mice

We have generated proteoliposomes carrying proteins of Trypanosoma cruzi for use as immunogens in BALB/c mice. T. cruzi trypomastigote and amastigote forms were sonicated and mixed with SDS, with 94% recovery of soluble proteins. To prepare proteoliposomes, we have used a protocol in which dipalmitoylphosphatidylcholine, dipalmitoyl-phosphatidylserine and cholesterol were incubated with the parasite proteins. BALB/c mice immunized with 20microg were able to generate antibodies which, in Western blotting, reacted with the proteins of T. cruzi. We further investigated the ability of peritoneal cells from immunized mice to arrest the intracellular replication of trypomastigotes, in vitro. After 72h of culture, the number of intracellular parasites in immunized macrophages decreased significantly, as compared to controls. Despite the fact that exposure of mice to T. cruzi proteins incorporated into proteoliposomes generate antibodies and activate macrophages, the immunized mice were not protected against T. cruzi intraperitoneal challenge.

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.

Clinical applications of virosomes in cancer immunotherapy

Cancer immunotherapy is increasingly accepted as a treatment option for advanced stage disease. The identification of tumour-associated antigens in 1991 has prompted the development of antigen-specific immunotherapeutic strategies for a variety of cancers. Many of them result in some immunological responses in cancer patients; however, clinical results were not observed concomitantly with immunological responses; therefore, further improvements in the field of immunotherapy are urgently needed. Virosomes are lipidic envelopes devoid of genetic information, but which retain the antigenic profile and fusogenic properties from their viral origin. Virosomes are versatile antigen carriers and can be engineered to perform various tasks in cancer immunotherapy. Preclinical data have fostered the development of innovative clinical protocols. Hence, immunopotentiating reconstituted influenza virosomes will be assessed in breast and melanoma immunotherapy, and may contribute to the development of clinically effective cancer vaccines and ultimately improve patient outcomes. The objective of this review is to provide an overview of the potential clinical applications of virosomes as innovative and potentially effective reagents in active specific cancer immunotherapy.

Exosome lipidomics unravels lipid sorting at the level of multivesicular bodies

Exosomes are part of the family of "bioactive vesicles" and appear to be involved in distal communications between cells. They vehiculate bioactive lipids and lipolytic enzymes and their biogenesis require specific lipids and a membrane reorganisation. Their biogenesis pathway could be a way to secrete enzymes involved in lipid signalling and to generate "particulate agonists". However, this pathway seems also to be used by pathogens such as HIV. This review will consider several aspects of lipidomics studies which might help to understand the fate and role of these fascinating vesicles.

Carrier-mediated delivery of peptidic drugs for cancer therapy

Protein and peptide drugs are used for treatment of a variety of ailments. However, their wider use has been hindered by issues such as poor bioavailability in vivo and the cost involved in producing these drugs. This review discusses the various carrier-mediated methods used for delivery of peptide and protein drugs, with emphasis on liposomal and microspherical drug delivery systems. A brief look at the types of peptidic drugs currently in use clinically, and a brief discourse on several novel ideas for better protein delivery systems for cancer therapy is included.

DNA Prime Followed by Protein Boost Enhances Neutralization and Th1 Type Immunity Against FMDV

Prime-boost strategy has been exhibited its potency to enhance immune responses, which would be important to the success to develop a vaccine against the foot-and-mouth disease virus (FMDV). An eukaryotic expression construct encoding the FMDV capsid VP1 protein with a recombinant VP1 protein or a commercial FMDV vaccine were tested in the prime-boost strategy in mice and cattle trials. The levels of induced specific antibodies, T cell proliferations, and DTH activities were significantly higher in the prime-boost groups than in those vaccinated with DNA, protein or FMDV vaccine alone. More importantly, the levels of neutralizing antibodies in the former groups were significantly higher than others and could last for at least four months in cattle trials. This study suggests that the prime-boost strategy significantly improves the effective immunity and may provide a longer protection against FMDV infection.

Non‐Viral Vector as Vaccine Carrier

Over the last several years, advances in gene-based delivery technology arising from the field of gene therapy have helped revitalize the field of vaccine development. Genetic vaccination encoding antigen from bacteria, virus, and cancer has shown promise in protective humoral and cellular immunity; however, the potential disadvantages of naked DNA vaccine have reduced the value of the approach. To optimize antigen delivery efficiency as well as vaccine efficacy, the non-viral vector as vaccine carrier, for example, the cationic liposome, has shown particular benefits to circumvent the obstacles that both peptide/protein- and gene-based vaccines have encountered. Liposome-mediated vaccine delivery provides greater efficacy and safer vaccine formulation for the development of vaccine for human use. The success of the liposome-based vaccine has been demonstrated in clinical trials and further human trials are also in progress.

Induction of neutralising antibodies restricts the use of human granulocyte/macrophage colony stimulating factor for vaccine studies in rhesus macaques

Granulocyte/macrophage-colony stimulating factor (GM-CSF) is a valuable adjuvant to enhance induction of cellular immune responses in rodents. Less information is available regarding its use as an adjuvant in primates or humans. We explored recombinant human GM-CSF for potential vaccine studies in rhesus macaques and focused on its effect on peripheral monocytes as progenitors of dendritic cells and its potential immunogenicity. Application of human GM-CSF to nine animals led to an average 32-fold increase in monocyte numbers. This was not observed upon re-treatment, which coincided with GM-CSF-specific neutralising antibodies. These also neutralised the activity of rhesus macaque GM-CSF. The data underscore the need to use species-specific GM-CSF for immunomodulation in primates.

pH-Triggered Microparticles for Peptide Vaccination

Improving vaccine delivery to human APCs is a way to increase the CTL response to vaccines. We report the use of a novel pH-triggered microparticle that exploits the ability of APCs to cross-present MHC I-restricted Ags that have been engulfed in the low pH environment of the phagosome. A model MHC class I-restricted peptide Ag from the influenza A matrix protein was encapsulated in spray-dried microparticles composed of dipalmitoylphosphatidylcholine and the pH-sensitive polymethacrylate Eudragit E100. Release of the peptide from the particle was triggered by a drop in pH to the acidity normally found in the phagosome. The particles were efficiently phagocytosed by human monocytes and dendritic cells with minimal cellular toxicity and no functional impairment. Encapsulation of the peptide in the microparticles resulted in efficient presentation of the peptide to CD8(+) T cells by human dendritic cells in vitro, and was superior to unencapsulated peptide or peptide encapsulated in an analogous pH-insensitive particle. Vaccination of human HLA-A*0201 transgenic mice with peptide encapsulated in pH-triggering microparticles resulted in priming of CTL responses. These microparticles can be modified to coencapsulate a range of adjuvants along with the Ag of interest. Encapsulation of MHC I epitopes in pH-triggered microparticles increases Ag presentation and may improve CD8(+) T cell priming to peptide vaccines against viruses and cancer.

A mixed Th1/Th2 response elicited by a liposomal formulation of Leishmania vaccine instructs Th1 responses and resistance to Leishmania donovani in susceptible BALB/c mice

In this study, we have developed a vaccine with Leishmania donovani promastigote membrane antigens (leishmanial antigens (LAg)) encapsulated in a liposome carrier formulated with distearyol (DSPC, transition temperature (Tc) = 54 degrees C) derivative of l-alpha-phosphatidyl choline, for immunizing BALB/c mice against progressive visceral leishmaniasis. This formulation could limit hepatosplenomegaly to almost normal levels and conferred strong levels of protection in both liver and spleen against challenge infection. Immunization with liposomal LAg activated peritoneal macrophages for enhanced leishmanicidal activity in association with NO production, and induced antibody as well as T-cell mediated immune responses. Production of both IFN-gamma and IL-4 by splenic T cells, and serum IgG1 and IgG2a, suggest induction of a mixed Th1/Th2 response following immunization. Experimental challenge corresponded with elevated DTH, and mitogen and antigen specific cellular responses. Increased production of NO and IFN-gamma by spleen cells, and down regulation of IL-4, demonstrate that an initial stimulation of a mixed Th1/Th2 response by vaccination instructs Th1 responses and resistance against a progressive infection by L. donovani.

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

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

Mechanisms of increased immunogenicity for DNA-based vaccines adsorbed onto cationic microparticles

Investigation into the mechanism of action of vaccine adjuvants provides opportunities to define basic immune principles underlying the induction of strong immune responses and insights useful for the rational development of subunit vaccines. A novel HIV vaccine composed of plasmid DNA-encoding p55 gag formulated with poly-lactide-co-glycolide microparticles (PLG) and cetyl trimethyl ammonium bromide (CTAB) elicits both serum antibody titers and cytotoxic lymphocyte activity in mice at doses two orders of magnitude lower than those required for comparable response to plasmid DNA in saline. Using this model, we demonstrated the increase in potency requires the DNA to be complexed to the PLG-CTAB microparticles. Furthermore, the PLG-CTAB-DNA formulation increased the persistence of DNA at the injection site, recruited mononuclear phagocytes to the site of injection, and activated a population of antigen presenting cells. Intramuscular immunization with the PLG-CTAB-DNA complex induced antigen expression at both the injection site and the draining lymph node. These findings demonstrate that the PLG-CTAB-DNA formulation exhibits multiple mechanisms of immunopotentiation.

Effective induction of CD8+ T-cell response using CpG oligodeoxynucleotides and HER-2/neu-derived peptide co-encapsulated in liposomes

CpG oligodeoxynucleotides (CpG ODN) have been shown to have potent adjuvant activity for a wide range of antigens. Of particular interest is their improved activity when closely associated with the antigen. The purpose of this study is to determine the potential benefit of liposomes as a co-delivery vehicle to enhance the adjuvant activity of CpG ODN for a HER-2/neu-derived peptide to induce CD8+ T-cell response. Immunization studies were performed to evaluate the effectiveness of the liposomal vaccine in BALB/c mice. Mice were immunized with p63-71 encapsulated in liposomes alone or in combination with CpG ODN, as well as p63-71 alone in saline or with peptide-pulsed dendritic cells (DC) as controls. Enzyme-linked immunospot assay (ELISPOT) assay was performed to measure the frequency of splenocytes secreting IFN-gamma as a means to determine the antigen-specific response. It was found that immunization using p63-71 co-encapsulated with CpG ODN within the same liposomes enhanced the antigen-specific IFN-gamma response by more than 100-fold when compared with mice immunized with p63-71 alone. Immunization using free CpG ODN plus p63-71 encapsulated in liposomes or p63-71 and CpG ODN encapsulated in separate liposomes could not achieve the same effect. Using CD8 as a second marker and intracellular flow cytometric analysis, it was found that the IFN-gamma response was contributed by CD8+ T-cells, confirming the induction of cytotoxic T-lymphocytes (CTL) by this vaccination method. This indicates that a close association of HER-2/neu peptide and CpG ODN inside liposomes enhances the CTL epitope delivery and induces CD8+ mediated immune response. These results suggest that a vaccinal approach using liposome delivery system carrying in self-tumoral epitope and CpG ODN as adjuvant may have important implications for cancer therapy.

Dendritic cell-based immunotherapy

Dendritic cell (DC)-based vaccinations represent a promising approach for the immunotherapy of cancer and infectious diseases as DCs play an essential role in initiating cellular immune responses. A number of clinical trials using ex vivo-generated DCs have been performed so far and only minor toxicity has been reported. Both the induction of antigen-specific T cells and clinical responses have been observed in vaccinated cancer patients. Nevertheless, DC-based immunotherapy is still in its infancy and there are many issues to be addressed such as antigen loading procedures, DC source and maturational state, migration properties, route, frequency, and dosage of DC vaccination. The increasing knowledge of DC biology should be used to improve the efficacy of this new therapy.

Lipid-protamine-DNA-mediated antigen delivery to antigen-presenting cells results in enhanced anti-tumor immune responses

Vaccination with antigenic peptides encoding tumor antigens has the potential to be an effective treatment for cancer. To induce tumor-specific cellular immune responses, a peptide antigen must be presented by antigen-presenting cells (APCs) to T-cells in the lymphatic tissues. Effective in vivo delivery of peptide antigens to APCs has been problematic. Here we use a model antigen from the HPV16 E7 protein to formulate LPD/E7 particles that upon iv administration are internalized by CD11c(+) and CD11b(+) cells in the marginal zone of the spleen. Either iv or sc vaccination with LPD/E7 particles induces E7-specific CTL responses stronger than those obtained using previously described liposome/peptide strategies and prevents the establishment of E7-expressing tumors. Furthermore, the administration of LPD/E7 particles to tumor-bearing mice caused complete tumor regression in 100% of the treated animals. Based on these studies, the entrapment of peptide antigens inside LPD particles may be an effective and generally applicable strategy for the enhancement of peptide vaccine potency.

Expression of a functional eotaxin (CC chemokine ligand 11) receptor CCR3 by human dendritic cells

Critical to the function of Ag-presenting dendritic cells (DCs) is their capacity to migrate to lymphoid organs and to sites of inflammation. A final stage of development, termed maturation, yields DCs that are strong stimulators of T cell-mediated immunity and is associated with a remodeling of the cell surface that includes a change in the levels of expression of many molecules, including chemokine receptors. We show in this study that CCR3, a chemokine receptor initially discovered on eosinophils, is also expressed by human DCs that differentiate from blood monocytes, DCs that emigrate from skin (epidermal and dermal DCs), and DCs derived from CD34+ hemopoietic precursors in bone marrow, umbilical cord blood, and cytokine-elicited peripheral blood leukapheresis. Unlike other chemokine receptors, such as CCR5 and CCR7, the expression of CCR3 is not dependent on the state of maturation. All DC subsets contain a large intracellular pool of CCR3. The surface expression of CCR3 is not modulated following uptake of particulate substances such as zymosan or latex beads. CCR3 mediates in vitro chemotactic responses to the known ligands, eotaxin and eotaxin-2, because the DC response to these chemokines is inhibited by CCR3-specific mAbs. We postulate that expression of CCR3 may underlie situations where both DCs and eosinophils accumulate in vivo, such as the lesions of patients with Langerhans cell granulomatosis.

Current methods for loading dendritic cells with tumor antigen for the induction of antitumor immunity

The immunotherapy of cancer is predicated on the belief that it is possible to generate a clinically meaningful antitumor response that provides patient benefit, such as improvement in the time to progression or survival. Indeed, immunotherapeutics with dendritic cells (DC) as antigen-presenting delivery vehicles for cell-based vaccines have already improved patient outcome against a wide range of tumor types (1-9). This approach stimulates the patient's own antitumor immunity through the induction or enhancement of T-cell immunity. It is generally believed that the activity of cytotoxic T lymphocytes (CTL), the cells directly responsible for killing the tumor cells in vivo, are directed by DC. Therefore, the goal of many current designs for DC-based vaccines is to induce strong tumor-specific CTL responses in patients with cancer. In practice, most studies for DC-based cancer vaccine development have focused on the development of methods that can effectively deliver exogenous tumor antigens to DC for cross-priming of CD8+ T cells through the endogenous MHC class I processing and presentation pathway (10). To date, many methods have been developed or evaluated for the delivery of defined and undefined tumor antigens to DC. This review provides a brief summary on these methods, the techniques used in these methods, as well as the advantages and disadvantages of each method.

Presentation of a major histocompatibility complex class 1-binding peptide by monocyte-derived dendritic cells incorporating hydrophobized polysaccharide-truncated HER2 protein complex: implications for a polyvalent immuno-cell therapy

Recognition of the essential role of dendritic cells (DCs) as professional antigen-presenting cells has prompted investigators to search for methods to use DCs as natural adjuvants in immunotherapy. A number of antigenic oligopeptides, recognized by CD8(+) cytotoxic T lymphocytes (CTLs) specific for cancer cells, have been applied in clinical trials using DCs. Such a monovalent vaccine with a single epitope for a particular type of HLA class 1 molecule would be effective. However, a polyvalent vaccine might be more potent. We designed a novel protein delivery system consisting of hydrophobized polysaccharides complexed with target proteins. The truncated HER2 protein encompassing 147 N-terminal amino acids, including the 9-mer HER2p63-71 peptide (HER2p63), TYLPTNASL, the human homologue of an antigenic murine tumor rejection peptide, was prepared. We report here that HLA-A2402(+) DCs could incorporate hydrophobized polysaccharide-truncated HER2 protein complexes and process the protein to present major histocompatibility complex class 1-binding HER2p63 peptide. The complexes enter DCs by phagocytosis, and then the truncated protein is processed through a pathway similar to that for endogenous proteins. DCs sensitized by these complexes primed and boosted HER2p63-specific CD8(+) T cells in the context of HLA-A2402. Vaccination with DCs incorporating these complexes completely suppressed lung metastases in a HER2-expressing murine tumor model. We also generated 3 CD4(+) clones reactive with different HER2- derived 25-mer peptides from lymph node cells in mice treated with CHP/HER2-147. Thus, hydrophobized polysaccharide-protein complexes are promising candidates for the construction of polyvalent vaccines.

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

Dendritic cells (DCs) are recognized as the sole professional antigen-presenting cells capable of priming naive T cells of the helper and cytotoxic phenotypes. This property is presently exploited with success in vaccinal strategies against pathogens or tumor cells that otherwise escape immune recognition, but the repeated infusions of ex vivo expanded and sensitized DCs are usually required to achieve protection. In this paper, we demonstrate that liposomal antigens can efficiently relay and propagate the action of DCs, inducing a strong long-term response against their associated antigen. Their effect is mainly achieved by improving the ex vivo loading of DCs and by efficiently channeling the activation stimulus into the induction of effector function. This is demonstrated by the sustained immunoglobulin production as well as by the sustained lymphoproliferation and the increased cytokine secretion that can be achieved upon restimulation of DC-primed immune cells with limited amount of liposomal antigenic material. Being well-tolerated and easily prepared, liposomal antigens could therefore be expected to significantly contribute to the efficiency and to a more general utilization of the highly promising but rather cumbersome DC-based immunotherapies.

New perspectives in dendritic cell-based cancer immunotherapy

Dendritic cells are professional antigen-presenting cells with the unique capacity to initiate primary immune responses. Recently, several procedures to generate large numbers of dendritic cells from circulating precursors, including peripheral blood monocytes and CD34+ stem cells, have been developed. Stimulation with antigen-loaded dendritic cells was shown to break tolerance to tumour-associated antigens and to induce antitumour cytotoxic immune responses in vivo. Hence, numerous attempts to optimise delivery of tumour antigens to dendritic cells, as well as routes and schedules of administration to cancer patients, are currently under way. The first dendritic cell clinical studies have indicated this form of vaccination as feasible and safe; furthermore, in some cases, objective clinical responses were observed, even in patients heavily pretreated with standard chemo/radiotherapy approaches. These preliminary data, although encouraging, require further extensive investigations, which should address the technical and biological problems of manipulating human dendritic cells, as well as the clinical settings which could benefit from an immunotherapeutic approach.