Two human immunodeficiency virus vaccinal lipopeptides follow different cross-presentation pathways in human dendritic cells

Palmitoylated antigens for the induction of anti-tumor CD8+ T cells and enhanced tumor recognition

Induction of tumor-specific cytotoxic CD8⁺ T cells (CTLs) via immunization relies on the presentation of tumor-associated peptides in major histocompatibility complex (MHC) class I molecules by dendritic cells (DCs). To achieve presentation of exogenous peptides into MHC class I, cytosolic processing and cross-presentation are required. Vaccination strategies aiming to induce tumor-specific CD8⁺ T cells via this exogenous route therefore pose a challenge. In this study, we describe improved CD8⁺ T cell induction and in vivo tumor suppression of mono-palmitic acid-modified (C16:0) antigenic peptides, which can be attributed to their unique processing route, efficient receptor-independent integration within lipid bilayers, and continuous intracellular accumulation and presentation through MHC class I. We propose that this membrane-integrating feature of palmitoylated peptides can be exploited as a tool for quick and efficient antigen enrichment and MHC class I loading. Importantly, both DCs and non-professional antigen-presenting cells (APCs), similar to tumor cells, facilitate anti-tumor immunity by efficient CTL priming via DCs and effective recognition of tumors through enhanced presentation of antigens.

Development of an epitope-based HIV-1 vaccine strategy from HIV-1 lipopeptide to dendritic-based vaccines

INTRODUCTION

Development of a safe, effective and globally affordable Human Immunodeficiency Virus strain 1 (HIV-1) vaccine offers the best hope for future control of the HIV-1 pandemic. However, with the exception of the recent RV144 trial, which elicited a modest level of protection against infection, no vaccine candidate has shown efficacy in preventing HIV-1 infection or in controlling virus replication in humans. There is also a great need for a successful immunotherapeutic vaccine since combination antiretroviral therapy (cART) does not eliminate the reservoir of HIV-infected cells. But to date, no vaccine candidate has proven to significantly alter the natural history of an individual with HIV-1 infection. Areas covered: For over 25 years, the ANRS (France Recherche Nord&Sud Sida-HIV hépatites) has been committed to an original program combining basic science and clinical research developing an epitope-based vaccine strategy to induce a multiepitopic cellular response against HIV-1. This review describes the evolution of concepts, based on strategies using HIV-1 lipopeptides towards the use of dendritic cell (DC) manipulation. Expert commentary: Understanding the crucial role of DCs in immune responses allowed moving from the non-specific administration of HIV-1 sequences with lipopeptides to DC-based vaccines. These DC-targeting strategies should improve HIV-1 vaccine efficacy.

Double adjuvanting strategy for peptide-based vaccines: trimethyl chitosan nanoparticles for lipopeptide delivery

Aim: To develop novel polymer-based nanoscale delivery system for lipopeptide-based vaccine against group A Streptococcus (GAS). Materials & methods: Four types of lipopeptide antigen-loaded polymeric nanoparticles (NP) were prepared. NP were accessed for their capacity to be taken up by dendritic cells; effect on dendritic cell maturation; ability to induce mucosal and systemic immunity; and capability to induce antibody responses that opsonize GAS bacteria. Results & discussion: The combination of adjuvanting properties of lipopeptides and dextran/trimethyl chitosan-based NP had a synergistic effect on humoral immunity, and the produced antibodies showed high opsonic activity against clinical GAS isolates. Conclusion: Biocompatible NP-bearing trimethyl chitosan and dextran are efficient as mucosal adjuvants for the intranasal delivery of lipopeptide-based vaccines.

Depletion of tumor-associated macrophages enhances the anti-tumor immunity induced by a Toll-like receptor agonist-conjugated peptide

It has been reported that lipopeptides can be used to elicit cytotoxic T lymphocyte (CTL) responses against viral diseases and cancer. In our previous study, we determined that mono-palmitoylated peptides can enhance anti-tumor responses in the absence of adjuvant activity. To investigate whether di-palmitoylated peptides with TLR2 agonist activity are able to induce anti-tumor immunity, we synthesized a di-palmitic acid-conjugated long peptide that contains a murine CTL epitope of HPV E7_49–57 (Pam2IDG). Pam2IDG stimulated the maturation of bone marrow-derived dendritic cells (BMDCs) through TLR2/6. After immunization, Pam2IDG induced higher levels of T cell responses than those obtained with its non-lipidated counterpart (IDG). In the prophylactic model, Pam2IDG immunization completely inhibited tumor growth, whereas IDG immunization was unable to inhibit tumor growth. However, Pam2IDG immunization could not effectively inhibit the growth of established tumors. Therefore, we further investigated whether the depletion of immunosuppressive factors could improve the therapeutic effects of Pam2IDG. Our data indicate that treatment with Pam2IDG combined with clodronate/liposome delays tumor growth and increases the survival rate. We also observed that the therapeutic effects of Pam2IDG are improved by diminishing the function of tumor-associate macrophages (TAMs) and through the use of an IL10 receptor blocking antibody or a Cyclooxygenase 2 (Cox-2) inhibitor. In conclusion, the depletion of TAMs may enhance the anti-tumor immunity of a TLR2 agonist-conjugated peptide.

Self-adjuvanting lipoimmunogens for therapeutic HPV vaccine development: potential clinical impact

The goal of therapeutic HPV vaccines is the induction of cytotoxic T lymphocyte immunity against HPV-associated cancers. Recombinant proteins and synthetic peptides have high safety profiles but low immunogenicity, which limits their efficacy when used in a vaccine. Self-adjuvanting lipid moieties have been conjugated to synthetic peptides or expressed as lipoproteins to enhance the immunogenicity of vaccine candidates. Mono-, di- and tri-palmitoylated peptides have been demonstrated to activate dendritic cells and induce robust cellular immunity against infectious diseases and cancer. Recently, a platform technology using the high-yield production of recombinant lipoproteins with Toll-like receptor 2 agonist activity was established for the development of novel subunit vaccines. This technology represents a novel strategy for the development of therapeutic HPV vaccines. In this review, we describe recent progress in the design of therapeutic HPV vaccines using lipoimmunogens.

Long-term CD4(+) and CD8(+) T-cell responses induced in HIV-uninfected volunteers following intradermal or intramuscular administration of an HIV-lipopeptide vaccine (ANRS VAC16)

BACKGROUND

We have shown that the intradermal (ID) administration of an HIV-1 lipopeptide candidate vaccine (LIPO-4) is well tolerated in healthy volunteers, with one fifth the IM dose delivered by this route inducing HIV-1-specific CD8(+) T-cell responses of a magnitude and quality similar to those achieved by IM administration. In this long-term follow-up, we aimed to investigate the sustainability and epitopic breadth of the immune responses induced.

METHODS

In a prospective multicentre trial, 68 healthy volunteers were randomised to receive, at weeks 0, 4 and 12, either a 0.5 ml IM (500 μg of each lipopeptide; 35 volunteers) dose or a 0.1 ml ID (100 μg of each lipopeptide; 33 volunteers) dose of the LIPO-4 vaccine, in the deltoid region of the non-dominant arm. All 68 volunteers received the first two vaccinations, and 44 volunteers in the ID group and 22 in the IM group received the third. We describe here the long-term CD8(+) and CD4(+) T-cell immune responses, up to 48 weeks after the first immunisation.

RESULTS

Response frequency was highest at week 14 for CD4(+) T cells, at 85% (28/33) for the IM group and 61% (20/33) for the ID group (p=0.027), and at week 48 for CD8(+) T cells, at 36% (12/33) for the ID group and 31% (11/35) for the IM group (p=0.67). Response rates tended to be lower for volunteers receiving the third vaccination boost, whether IM or ID. Finally, we also observed a striking change in the specificity of the CD8(+) T-cell responses induced shortly (2 weeks) or several months (48 weeks) after LIPO-4 vaccination.

CONCLUSION

Lipopeptide vaccines elicited sustainable CD4(+) and CD8(+) T-cell responses, following IM or ID administration. CD8(+) T-cell responses had shifted and expanded to different epitopes after one year of follow-up. These results should facilitate the design of the next generation of prime-boost trials with repeated doses of lipopeptide vaccines.

Cytokine and gene transcription profiles of immune responses elicited by HIV lipopeptide vaccine in HIV-negative volunteers

OBJECTIVE

To dissect the biological mechanisms involved in the cellular responses to a candidate vaccine containing 5 HIV peptides coupled to a palmytoil tail (HIV-LIPO-5) in healthy volunteers, by using extensive immunogenicity assessments with different stimulation durations.

DESIGN

Immunogenicity substudy of a randomized phase II prophylactic HIV vaccine trial (ANRS VAC 18).

METHODS

HIV-LIPO-5 or placebo was administered at W0, W4, W12 and W24. Peripheral blood mononuclear cells from a subset of participants at W0 and W14 were stimulated with HIV-LIPO-5, Gag peptides contained in the vaccine and control peptides. ELISpot, lymphoproliferation, intracellular cytokine staining (ICS), cytokine multiplex and transcriptomic analyses were performed. Different time points and stimulation conditions were compared, controlling for test multiplicity.

RESULTS

Cultured ELISpot and lymphoproliferation responses were detected at W14. Ex-vivo ICS showed mainly interleukin (IL)-2-producing cells. Secretion of interferon (IFN)-γ, tumour necrosis factor (TNF)-α, IL-5 and IL-13 increased significantly after culture and Gag stimulation at W14 compared to W0. Metallothionein genes were consistently overexpressed after HIV-LIPO-5 stimulation at W0 and W14. At W14, significant probes increased substantially, including IFN-γ, CXCL9, IL2RA, TNFAIP6, CCL3L1 and IL-6. Canonical pathway analyses indicated a role of interferon signalling genes in response to HIV-LIPO-5.

CONCLUSION

HIV-LIPO-5 vaccination elicited Th1 and Th2 memory precursor responses and a consistent modulation in gene expression. The response profile before vaccination suggests an adjuvant effect of the lipid tail of HIV-LIPO-5. Our combined immunogenicity analyses allowed to identify a specific signature profile of HIV-LIPO-5 and indicate that HIV-LIPO-5 could be further developed as a prime in heterologous prime-boost strategies.

Lipoproteins are major targets of the polyclonal human T cell response to Mycobacterium tuberculosis

Most vaccines and basic studies of T cell epitopes in Mycobacterium tuberculosis emphasize water-soluble proteins that are secreted into the extracellular space and presented in the context of MHC class II. Much less is known about the role of Ags retained within the cell wall. We used polyclonal T cells from infected humans to probe for responses to immunodominant Ags in the M. tuberculosis cell wall. We found that the magnitude of response to secreted or cell wall intrinsic compounds was similar among healthy controls, patients with latent tuberculosis, and patients with active tuberculosis. Individual responses to secreted Ags and cell wall extract were strongly correlated (r(2) = 0.495, p = 0.001), suggesting that T cells responding to cell wall and secreted Ags are present at similar frequency. Surprisingly, T cell stimulatory factors intrinsic to the cell wall partition into organic solvents; however, these responses are not explained by CD1-mediated presentation of lipids. Instead, we find that molecules soluble in organic solvents are dependent upon MHC class II and recognized by IFN-γ-secreting CD4(+) T cells. We reasoned that MHC class II-dependent Ags extracting into lipid mixtures might be found among triacylated lipoproteins present in mycobacteria. We used M. tuberculosis lacking prolipoprotein signal peptidase A (lspA), an enzyme required for lipoprotein synthesis, to demonstrate loss of polyclonal T cell responses. Our results demonstrate the use of bacterial genetics to identify lipoproteins as an unexpected and immunodominant class of cell wall-associated Ags targeted by the polyclonal human T cell response to M. tuberculosis.

Design considerations for liposomal vaccines: influence of formulation parameters on antibody and cell-mediated immune responses to liposome associated antigens

Liposomes (phospholipid bilayer vesicles) are versatile and robust delivery systems for induction of antibody and T lymphocyte responses to associated subunit antigens. In the last 15 years, liposome vaccine technology has matured and now several vaccines containing liposome-based adjuvants have been approved for human use or have reached late stages of clinical evaluation. Given the intensifying interest in liposome-based vaccines, it is important to understand precisely how liposomes interact with the immune system and stimulate immunity. It has become clear that the physicochemical properties of liposomal vaccines - method of antigen attachment, lipid composition, bilayer fluidity, particle charge, and other properties - exert dramatic effects on the resulting immune response. Here, we present a comprehensive review of the physicochemical properties of liposomal vaccines and how they influence immune responses. A discussion of novel and emerging immunomodulators that are suitable for inclusion in liposomal vaccines is also presented. Through a comprehensive analysis of the body of liposomal vaccine literature, we enumerate a series of principles that can guide the rational design of liposomal vaccines to elicit immune responses of a desired magnitude and quality. We also identify major unanswered questions in the field, pointing the direction for future study.

Immunogenicity and safety of an HIV-1 lipopeptide vaccine in healthy adults: a phase 2 placebo-controlled ANRS trial

BACKGROUND

French National Agency for Research on AIDS and Viral Hepatitis's HIV-LIPO-5 vaccine includes five HIV-1 peptides, containing multiple CD8 and CD4 T-cell epitopes and coupled to a palmitoyl tail. Whether HIV-LIPO-5 immunogenicity varies with the dose is unknown.

METHODS

HIV-negative volunteers were randomized to receive HIV-LIPO-5 vaccine at 50 microg/lipopeptide (N = 32), 150 microg/lipopeptide (N = 32), 500 microg/lipopeptide (N = 33) or placebo (N = 34) at weeks 0, 4, 12 and 24. HIV-1-specific CD8 (interferon-gamma ELISpot on peripheral blood mononuclear cells cultured for 12 days) and CD4 responses (peripheral blood mononuclear cell lymphoproliferation) were assessed at baseline, after each injection and at week 48.

RESULTS

Local reactions were dose-dependent but no differences in systemic reactions appeared between groups. Sustained (at least on two separate occasions) CD8 response rates to at least one given HIV-1 pool were obtained in 22 of 32 (69%), 21 of 33 (64%) and 21 of 34 (62%) individuals for LIPO-5 50, 150 and 500 groups, respectively (P < or = 0.0001 for all comparisons to the placebo). Cumulative CD4 response rates were obtained in 15 of 32 (47%), 18 of 33 (55%) and 15 of 34 (44%) individuals (P < 0.0001 for all comparisons to placebo). At week 48, CD8 responses persisted in 47 of 91 (52%) HIV-LIPO-5 recipients.

CONCLUSION

Doses of 50, 150 and 500 microg of French National Agency for Research on AIDS and Viral Hepatitis's HIV-LIPO-5 vaccine were able to elicit HIV-specific sustained CD8 and CD4 T-cell responses in healthy adults. Safety is good and all doses appear appropriate in further 'prime-boost' trials.

Linear and branched glyco-lipopeptide vaccines follow distinct cross-presentation pathways and generate different magnitudes of antitumor immunity

BACKGROUND

Glyco-lipopeptides, a form of lipid-tailed glyco-peptide, are currently under intense investigation as B- and T-cell based vaccine immunotherapy for many cancers. However, the cellular and molecular mechanisms of glyco-lipopeptides (GLPs) immunogenicity and the position of the lipid moiety on immunogenicity and protective efficacy of GLPs remain to be determined.

METHODS/PRINCIPAL FINDINGS

We have constructed two structural analogues of HER-2 glyco-lipopeptide (HER-GLP) by synthesizing a chimeric peptide made of one universal CD4(+) epitope (PADRE) and one HER-2 CD8(+) T-cell epitope (HER(420-429)). The C-terminal end of the resulting CD4-CD8 chimeric peptide was coupled to a tumor carbohydrate B-cell epitope, based on a regioselectively addressable functionalized templates (RAFT), made of four alpha-GalNAc molecules. The resulting HER glyco-peptide (HER-GP) was then linked to a palmitic acid moiety, attached either at the N-terminal end (linear HER-GLP-1) or in the middle between the CD4+ and CD8+ T cell epitopes (branched HER-GLP-2). We have investigated the uptake, processing and cross-presentation pathways of the two HER-GLP vaccine constructs, and assessed whether the position of linkage of the lipid moiety would affect the B- and T-cell immunogenicity and protective efficacy. Immunization of mice revealed that the linear HER-GLP-1 induced a stronger and longer lasting HER(420-429)-specific IFN-gamma producing CD8(+) T cell response, while the branched HER-GLP-2 induced a stronger tumor-specific IgG response. The linear HER-GLP-1 was taken up easily by dendritic cells (DCs), induced stronger DCs maturation and produced a potent TLR- 2-dependent T-cell activation. The linear and branched HER-GLP molecules appeared to follow two different cross-presentation pathways. While regression of established tumors was induced by both linear HER-GLP-1 and branched HER-GLP-2, the inhibition of tumor growth was significantly higher in HER-GLP-1 immunized mice (p<0.005).

SIGNIFICANCE

These findings have important implications for the development of effective GLP based immunotherapeutic strategies against cancers.

Dendritic cell-based human immunodeficiency virus vaccine

Dendritic cells (DC) have profound abilities to induce and coordinate T-cell immunity. This makes them ideal biological agents for use in immunotherapeutic strategies to augment T-cell immunity to HIV infection. Current clinical trials are administering DC-HIV antigen preparations carried out ex vivo as proof of principle that DC immunotherapy is safe and efficacious in HIV-infected patients. These trials are largely dependent on preclinical studies that will provide knowledge and guidance about the types of DC, form of HIV antigen, method of DC maturation, route of DC administration, measures of anti-HIV immune function and ultimately control of HIV replication. Additionally, promising immunotherapy approaches are being developed based on targeting of DC with HIV antigens in vivo. The objective is to define a safe and effective strategy for enhancing control of HIV infection in patients undergoing antiretroviral therapy.

[From fundamental immunology to development of vaccinology]

In the last ten years research in vaccinology has been developed in the world to conceive new vaccine approaches against infections like HIV/AIDS. Jean-Gérard Guillet is a pioneer in the development of new vaccine strategies. From the first results he obtained in the late 80's on the presentation of antigenic peptides to T cells, he axed his work on the study of induction mechanisms of T cell mediated immune responses. The selection of antigenic peptides and the search to enhance antigen immunogenicity led him to elaborate lipopeptides as new vaccine formulae. The efficacy of these preparations was tested in animal models (mouse, macaque) and, thereafter, in humans with clinical trials promoted by the French National Agency for AIDS and viral hepatitis (ANRS). The study of T-cell induced responses in vaccinated volunteers was implemented following the creation of two facilities, an immuno-monitoring platform and the Clinical Investigation Centre Cochin-Pasteur, a structure specialized in vaccinology.

Antigen crosspresentation by human plasmacytoid dendritic cells

Crosspresentation is a specialized function of myeloid dendritic cells (mDCs), allowing them to induce CD8+ T cell responses against exogenous antigens that are not directly produced in their cytotosol. Human plasmacytoid DCs (pDCs) are not considered so far as able to perform crosspresentation. We showed here that purified human pDCs crosspresented vaccinal lipopeptides and HIV-1 antigens from apoptotic cells to specific CD8+ T lymphocytes. Apoptotic debris were internalized by phagocytosis and the lipopeptide LPPol reached nonacidic endosomes. This crosspresentation was amplified upon influenza virus infection. Importantly, the efficiency of crosspresentation by pDCs was comparable to that of mDCs. This property of human pDCs needs to be taken into account to understand the pathogenesis of infectious, allergic, or autimmune diseases and to help achieve desired responses during vaccination by targeting specifically either type of DCs.

Pathways utilized by dendritic cells for binding, uptake, processing and presentation of antigens derived from HIV-1

The outcome following HIV infection depends on the nature and durability of the HIV-specific T cell response induced initially. The activation of protective T cell responses depends upon dendritic cells (DC), antigen-presenting cells which have the capacity to process and present viral antigens. DC pulsed with aldrithiol-2-inactivated HIV and delivered in vivo were reported to induce immune responses and promote virologic control in chronically HIV-1-infected subjects. To gain an understanding of this phenomenon, we characterized the steps involved in the presentation of antigens derived from aldrithiol-2-treated vs. infectious HIV-1 by DC. Antigen presentation, on both MHC class I and II, was independent of DC-specific ICAM-3-grabbing integrin, DEC-205 and macrophage mannose receptor, C-type lectins expressed by the DC. Inhibitor studies showed that presentation on MHC class I was dependent on viral fusion in a CD4/coreceptor-dependent manner, both at the cell surface and within endosomes, and access to the classical endosomal processing pathway. MHC class II presentation of HIV-associated antigens was dependent on active endocytosis, probably receptor-mediated, and subsequent degradation of virions in acidified endosomes in the DC. Our study brings forth new facts regarding the binding, uptake, and processing of chemically inactivated virions leading to efficient antigen presentation and should aid in the design of more effective HIV vaccines.

Cytotoxic T lymphocyte response induced by an improved synthetic lipopeptide vaccine against cervical cancer

AIM

To explore cytotoxic T lymphocyte (CTL) response induced by the lipopeptide vaccine against cervical cancer.

METHODS

The immunological effect inducing CD8+ T cell-mediated cytotoxicity was investigated in human leukocyte antigen (HLA)-A2 transgenic mice and peripheral blood mononuclear cells (PBMC) of healthy HLA-A2.1+blood donor. The activity of specific CTL was measured by using a standard 4 h( 51)Cr release assay. The content of major histocompatibility complex (MHC) I on T2 cells and the expression of immune molecules on dendritic cells (DC) were detected by flow cytometry, and the concentrations of interleukin (IL)-12 and interferon-gamma were determined by ELISA.

RESULTS

The lipopeptide induced a strong epitope-specific CTL response both in vivo (transgenic mice) and in vitro (human PBMC). This CTL induction was critically dependent on the presence of the helper T lymphocyte epitope in transgenic mice, and the presence of a lipid tail bypassed the need for an adjuvant. The stability and persistence of the antigenic complex formed with the lipopeptide increased in comparison with the CTL parental peptide. The lipopeptide could induce the production of IL-12 in DC, but not the maturation of DC directly.

CONCLUSION

The combination of CTL and the T helper epitope and lipid molecule can remarkably improve the immunogenicity of the CTL peptide, the mechanism of which is associated with an increase in the stability and persistence of the antigenic complex formed with the lipopeptide and in the production of IL-12 in DC induced by the lipopeptide. The lipopeptide can be considered a more effective vaccine type for human being.

HLA-DR-restricted peptides identified in the Nef protein can induce HIV type 1-specific IL-2/IFN-gamma-secreting CD4+ and CD4+ /CD8+ T cells in humans after lipopeptide vaccination

We screened the Neflaiprotein to identify new HLA-DR-restricted epitopes, because this small protein is expressed early during infection, and specific CD4(+) T cells are critical for effective immunity in HIV-1 infection. We synthesized a set of peptides that covers the sequence of the Nef protein, and performed binding assays using 10 common HLA-DR molecules. We defined four large regions in this protein able to bind very efficiently to eight HLADR molecules. We took advantage of healthy volunteers immunized with an HIV-1 lipopeptide vaccine that contains three of the four HLA DR-restricted regions to investigate their capacities to stimulate T cells. In 11 vaccinated volunteers, typed for their class II molecules, we were able to correlate sequences of the vaccine displaying binding activities to specific HLA-DR molecules and the induction of CD4(+) T cell proliferation. To identify potential HLA-DR epitopes, we synthesized 31 15-mer peptides and showed that 26 bound to one or more HLA-DR molecules. Interestingly, 12 of the 26 15-mer peptides identified are included in the sequence of lipopeptides. We used IFN-gamma ELISPOT and flow cytometer assays to investigate the capacity of these potential CD4(+) T cell epitopes to induce specific T cell responses. We showed that seven of these peptides were able to stimulate HIV-specific T cell responses in five of six tested volunteers. These cells are Nef-specific CD4(+) and CD4(+) CD8(+) T cells secreting IL-2/INF-gamma or IL-2 alone. To conclude, these 26 Nef HLA-DR-restricted peptides could be helpful to better evaluate CD4(+) deficiencies in HIV infection and, for new vaccine designs.

New CD4+ and CD8+ T cell responses induced in chronically HIV type-1-infected patients after immunizations with an HIV type 1 lipopeptide vaccine

We showed that an anti-HIV lipopeptide vaccine injected to HIV-uninfected volunteers was well tolerated and able to induce a specific CD4(+) and CD8(+) T cell responses. The same vaccine was injected in HIV-1 chronically infected patients controlled by HAART to evaluate its immunogenicity. In this trial, 24 patients were immunized three times with a mixture of six lipopeptides (Nef 66-97, Nef 117-147, Nef 182-205, Gag 183-214, Gag 253-284, and Env 303-335) at 0, 3, and 6 weeks. We studied the HIV-1-specific CD4(+) T cell proliferative responses. The IFN-gamma secretion by activated CD8(+) T cells was evaluated, using an ex vivo ELISpot assay and 60 CD8(+) T cell epitopes derived from the vaccine. Before immunization (W0), anti-HIV CD4(+) T cell responses to Gag, Nef, and Env large peptides were detected in 7/23 (30%) analyzable patients. After three injections, 17/23 (74%) patients had a proliferative response and 16 of them induced new specific CD4(+) T cell responses. At W0, CD8(+) T cell responses to HIV-1 epitopes were detected in 6/23 (26%) patients. After vaccination, 16/23 (70%) patients showed CD8(+) T cell responses and 13 of these patients induced new T cell responses to 25 different HIV-1 epitopes. These HIV-1 epitopes were detected in patients with various HLA class I molecules (HLA-A2, -A3/A11, -A24, -B7 superfamily, -B8), as found in the majority of the white population. Lipopeptides induce new anti-HIV T cell responses in vaccinated infected patients and could be used as a new immunotherapy strategy. The majority of these responders induced specific new CD4(+) and CD8(+) T cell responses.

Overlapping synthetic peptides as vaccines

Several vaccine strategies aim to generate cell-mediated immunity (CMI) against microorganisms or tumors. While epitope-based vaccines offer advantages, knowledge of specific epitopes and frequency of major histocompatibility complex (MHC) alleles is required. Here we show that using promiscuous overlapping synthetic peptides (OSP) as immunogens generated peptide-specific CMI in all vaccinated outbred mice and in different strains of inbred mice; CMI responses also recognized viral proteins. OSP immunogens also induced CMI ex vivo in dendritic cell/T-cell cocultures involving cells from individuals with different HLA haplotypes. Thus, broad CMI was induced by OSP in different experimental settings, using different immunogens, without identifying either epitopes or MHC backgrounds of the vaccinees.

Cytotoxic capacity of hepatitis C virus (HCV)--specific lymphocytes after in vitro immunization with HCV-derived lipopeptides

BACKGROUND

Hepatitis C virus (HCV)-derived lipopeptides can induce epitope-specific immune responses in lymphocytes from HCV-naive individuals. We analyzed whether such T cells generated by in vitro immunization with HCV core-derived lipopeptides exert HCV-specific cytolytic activity.

METHODS

Using a sensitive flow cytometric cytotoxicity assay we characterized HCV-specific cytotoxicity in T cells generated in vitro with HCV core-derived 25-mer lipopeptides. In addition, we studied expressions of Fas ligand and perforin and interferon-gamma (IFN-gamma) secretion in HLA-A2-HCV(core_35-44) tetramer-positive T cells generated with lipopeptide amino acid 20-44 (LP20-44).

RESULTS

CD8+ T cells induced in vitro with HCV core-derived lipopeptides only infrequently exerted HCV-specific cytotoxicity, irrespective of whether antigen-coated T2 cells or autologous B lymphoblasts were used as targets. Detailed analysis of HLA-A2-HCV(core_35-44) tetramer-positive T cells generated with LP20-44 revealed that in vitro immunization resulted in T cells that secreted IFN-gamma after antigen-specific restimulation and that upregulated expression of Fas ligand but not of perforin.

CONCLUSIONS

Our data confirm at the functional level that HCV lipopeptides induce antigen-specific T lymphocytes that produce IFN-gamma but exert significant cytotoxicity in only a minority of experiments, probably because expression of cytolytic effector molecules is not enhanced in their granules.

Apoptotic cells at the crossroads of tolerance and immunity

Clearance of apoptotic cells by phagocytes can result in either anti-inflammatory and immunosuppressive effects or prostimulatory consequences through presentation of cell-associated antigens to T cells. The differences in outcome are due to the conditions under which apoptosis is induced, the type of phagocytic cell, the nature of the receptors involved in apoptotic cell capture, and the milieu in which phagocytosis of apoptotic cells takes place. Preferential ligation of specific receptors on professional antigen-presenting cells (dendritic cells) has been proposed to induce potentially tolerogenic signals. On the other hand, dendritic cells can efficiently process and present antigens from pathogen-infected apoptotic cells to T cells. In this review, we discuss how apoptotic cells manipulate immunity through interactions with dendritic cells.

Induction of effective and antigen-specific antitumour immunity by a liposomal ErbB2/HER2 peptide-based vaccination construct

Efficient delivery of tumour-associated antigens to appropriate cellular compartments of antigen-presenting cells is of prime importance for the induction of potent, cell-mediated antitumour immune responses. We have designed novel multivalent liposomal constructs that co-deliver the p63–71 cytotoxic T Lymphocyte epitope derived from human ErbB2 (HER2), and HA307–319, a T-helper (Th) epitope derived from influenza haemagglutinin. Both peptides were conjugated to the surface of liposomes via a Pam₃CSS anchor, a synthetic lipopeptide with potent adjuvant activity. In a murine model system, vaccination with these constructs completely protected BALB/c mice from subsequent s.c. challenge with ErbB2-expressing, but not ErbB2-negative, murine renal carcinoma (Renca) cells, indicating the induction of potent, antigen-specific immune responses. I.v. re-challenge of tumour-free animals 2 months after the first tumour cell inoculation did not result in the formation of lung tumour nodules, suggesting that long-lasting, systemic immunity had been induced. While still protecting the majority of vaccinated mice, a liposomal construct lacking the Th epitope was less effective than the diepitope construct, also correlating with a lower number of CD8⁺ IFN-γ⁺ T-cells identified upon ex vivo peptide restimulation of splenocytes from vaccinated animals. Importantly, in a therapeutic setting treatment with the liposomal vaccines resulted in cures in the majority of tumour-bearing mice and delayed tumour growth in the remaining ones. Our results demonstrate that liposomal constructs which combine Tc and Th peptide antigens and lipopeptide adjuvants can induce efficient, antigen-specific antitumour immunity, and represent promising synthetic delivery systems for the design of specific antitumour vaccines.

Processing and presentation of exogenous HLA class I peptides by dendritic cells from human immunodeficiency virus type 1-infected persons

Dendritic cells (DCs) loaded with viral peptides are a potential form of immunotherapy of human immunodeficiency virus type 1 (HIV-1) infection. We show that DCs derived from blood monocytes of subjects with chronic HIV-1 infection on combination antiretroviral drug therapy have increases in expression of HLA, T-cell coreceptor, and T-cell activation molecules in response to the DC maturation factor CD40L comparable to those from uninfected persons. Mature DCs (mDCs) loaded with HLA A*0201-restricted viral peptides of the optimal length (9-mer) were more efficient at activating antiviral CD8(+) T cells than were immature DCs or peptide alone. Optimal presentation of these exogenous peptides required uptake and vesicular trafficking and was comparable in DCs derived from HIV-1-infected and uninfected persons. Furthermore, DCs from HIV-1-infected and uninfected persons had similar capacities to process viral peptides with C-terminal and N-terminal extensions through their proteasomal and cytosolic pathways, respectively. We conclude that DCs derived from HIV-1-infected persons have similar abilities to process exogenous peptides for presentation to CD8(+) T cells as those from uninfected persons. This conclusion supports the use of DCs loaded with synthetic peptides in immunotherapy of HIV-1 infection.

Novel peptide-based HIV-1 immunotherapy

Therapeutic immunisation of human immunodeficiency virus type 1-infected individuals should be actively pursued in the first instance to augment highly active antiretroviral therapy regimens. Peptide-based immunotherapeutic strategies offer considerable advantages over conventional approaches, particularly regarding safety. Peptide design itself is becoming increasingly sophisticated, with the rapid evolution of bioinformatics tools that can analyse not only T cell epitopes, but also their potential for successful presentation on diverse human leukocyte antigen (HLA) class I or II following intracellular processing by antigen-presenting cells (APCs). By targeting conserved viral domains, peptides acquire improved reactivity to diverse viral strains. Dendritic cells represent a powerful route of administration, as they are the most potent APCs and can present exogenous peptides on both HLA class I and II through the process of cross-presentation. In this way, soluble peptides can thereby stimulate both CD4+ and CD8+ T cells.

Lipopeptide epitopes extended by an N?-palmitoyl-lysine moiety increase uptake and maturation of dendritic cells through a Toll-like receptor-2 pathway and trigger a Th1-dependent protective immunity

Lipopeptides, a form of peptide immunogens, are currently under intense investigation as human vaccines for many infectious pathogens and cancers. However, the cellular and molecular mechanisms of lipopeptide immunogenicity are only partially understood. We have investigated the influence of the lipid content on the immunogenicity of lipopeptides using the herpes simplex virus type 1 (HSV-1) gD(1-23) peptide as a model antigen. Totally synthetic lipopeptides were constructed by covalent attachment to the peptide backbone of either Nepsilon-palmitoyl-lysine (palmitoyl-lipidated peptide, palmitoyl-LP) or cholesterol-lysine (cholesterol-lipidated peptide, cholesterol-LP). Immunization of mice with the palmitoyl-LP, but not with its cholesterol-LP analog, induced a strong T cell-dependent protective immunity against lethal HSV-1 infection. Analysis of cytokine profiles and IgG2a/IgG1 ratios revealed that a dominant Th1-type immune response was stimulated by the palmitoyl-LP, as opposed to a Th2 response generated by its cholesterol-LP analog. The palmitoyl-LP was efficiently taken up in vitro by immature dendritic cells (DC) in a time- and dose-dependent manner, and induced phenotypic maturation and production of pro-inflammatory cytokines by DC. Finally, DC stimulated with the palmitoyl-LP induced antigen-specific T cell responses through the Toll-like receptor-2 pathway. These findings have important implications for the development of effective lipopeptide immunization strategies against infectious pathogens.

Long-term multiepitopic cytotoxic-T-lymphocyte responses induced in chimpanzees by combinations of Plasmodium falciparum liver-stage peptides and lipopeptides

Preclinical immunogenicity studies of 12 malaria peptides, selected from four Plasmodium falciparum antigens (Ags), namely, LSA1, LSA3, SALSA, and STARP, that are expressed at the pre-erythrocytic (sporozoite and liver) stages of the human parasite were carried out in chimpanzees. To strengthen their immunogenicity, six of these synthetic peptides were modified by the C-terminal addition of a single palmitoyl chain (lipopeptides) and delivered without adjuvant, whereas the remaining six unmodified peptides were emulsified and delivered by using Montanide ISA51 adjuvant. We have previously reported that these peptides and lipopeptides induce high B-cell and CD4(+)-T-helper responses in chimpanzees. In this report, we show their ability to induce multiepitopic and long-lasting antigen-specific CD8(+) cytotoxic-T-lymphocyte (CTL) responses. The magnitude, consistency, and memory of CTL responses generated by LSA3 peptides point to the strong immunogenicity of this liver-stage Ag. These findings support the screening strategy used to select the four P. falciparum pre-erythrocytic Ags and emphasize their valuable immunogenic properties. The successful immunization of nonhuman primates with combinations of corresponding peptides in a mineral oil emulsion (ISA51) and lipopeptides in saline provide a vaccine formulation that can be tested in humans.

Use of well-defined HIV-derived epitopes to evaluate CD4(+) and CD8(+) T cell responses in patients with chronic HIV-1 infection treated with HAART

Highly active antiretroviral therapy (HAART) is associated with a dramatic clinical benefit to HIV-infected patients through significant plasma viremia reduction and CD4(+) T cells increase. In previous reports, HIV-specific CD4(+) and/or CD8(+) T cell responses have been studied separately during HAART; therefore the relationship between these two virus-specific populations is currently not well understood. In this study, both HIV-specific CD4(+) and CD8(+) T cell responses were investigated using a large panel of well-defined T cell epitope peptides in 24 HIV-1-infected patients undergoing HAART, with undetectable viral load and CD4(+) T cell count >/= 350/mm(3). One-third of the patients had CD4(+) T cells able to proliferate when exposed to HIV-1 protein fragments but only two patients displayed polyclonal responses. In addition the majority (78%) of HAART-treated patients displayed no or monospecific CD8(+) T cell responses and the phenotypic analysis of these HIV-specific CD8(+) T cells demonstrated the absence of terminally differentiated effectors. In conclusion, the experimental approach used in this study shows that CD4(+) T cell responses may persist during HAART but are not associated with strong CD8(+) T cell responses

Primary immunisation of hepatitis C virus (HCV)-specific antibody producing B cells by lipidated peptides

We analysed whether hepatitis C virus (HCV)-specific antibody producing B lymphocytes can be induced in vitro with HCV-derived lipopeptides containing different T helper cell epitopes. HCV-specific antibody producing B cells were detected by ELISPOT at the single cell level. HCV-derived lipopeptides, but not their corresponding unlipidated peptides, induced B lymphocytes, which produced antibodies mainly reacting with the HCV-derived lipopeptides. The number of antigen-specific B cells was dependent on the number of added autologous T helper lymphocytes during the incubation period. Thus, HCV lipopeptides are more immunogenic than unmodified peptides and can induce HCV-reactive B lymphocytes in antigen-naïve lymphocytes.

Synthesis of Thiol-Reactive Lipopeptide Adjuvants. Incorporation into Liposomes and Study of Their Mitogenic Effect on Mouse Splenocytes

Synthetic analogues of triacylated and diacylated lipopeptides derived from the N-terminal domain of respectively bacterial and mycoplasmal lipoproteins are highly potent immunoadjuvants when administered either in combination with protein antigens or covalently linked to small peptide epitopes. Because of their amphipathic properties, lipopeptides, such as S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-N-palmitoyl-(R)-cysteinyl-alanyl-glycine (Pam(3)CAG), can be conveniently incorporated into liposomes and serve as anchors for antigens that are linked to them. To design vaccination constructs based on synthetic peptides and liposomes as vectors. we have accordingly synthesized a series of lipopeptides that differ by the number (Pam(3)C vs Pam(2)C) and nature of the acyl chains (palmitoyl vs oleoyl) and by the presence at their C-terminus of thiol-reactive functions, such as maleimide or bromoacetyl. When incorporated into liposomes, these latter functionalized lipopeptides allow, in aqueous media, a well controlled chemoselective conjugation of HS-peptides to the surface of the vesicles. Using a BALB/c mice splenocyte proliferation assay ([(3)H]thymidine incorporation), we have measured the lymphocyte activation potency of the different lipopeptides. We found that, compared to their free (emulsified) forms, the liposomal lipopeptides were endowed with enhanced mitogenic activities; i.e., up to 2 orders of magnitude for Pam(3)CAG which was more potent than Pam(2)CAG. The impact of functionalization on the cellular activity of Pam(3)CAG was dependent on the thiol-reactive group introduced: whereas the bromoacetyl derivative retained its full activity, the presence of a maleimide group virtually abolished the lymphocyte activation of the lipopeptide. Finally, the substitution of saturated palmitoyl chains by unsaturated oleoyl chains was inhibitory. Thus, thiol-reactive Ol(3)CAG derivatives were the least active mitogens in our assay. Taken together, our findings are of importance for the further optimization of antigen-specific liposomal-based synthetic vaccines; the bromoacetyl derivative of Pam(3)CAG should be a promising lipopeptide derivative serving as an anchor for peptide epitopes while retaining its lymphocyte activation activity.

HIV type 1-infected dendritic cells induce apoptotic death in infected and uninfected primary CD4 T lymphocytes

In addition to their essential role in adaptive immunity, dendritic cells (DCs) participate in innate immunity. In the context of measles virus (MV) or cytomegalovirus infections, they develop cytotoxic functions that may contribute in vivo to the elimination of virus-infected cells, but that also kill infected and noninfected T lymphocytes. Because the human immunodeficiency virus (HIV) induces T cell depletion through mechanisms that are still obscure, we investigated its ability to trigger DC cytotoxicity. When incubated with HIV, monocyte-derived DCs induced apoptosis in MDA-231 cells, which are sensitive to MV-induced DC cytotoxicity, and in uninfected as well as HIV-infected H9 CD4+ T cell lines. This apoptosis was inhibited by a mixture of FasL, TRAIL, TNF-alpha, and TWEAK inhibitors. Indeed, HIV infection induced or enhanced sensitivity to TRAIL, TNF-alpha, and TWEAK in H9 cells. Moreover, dendritic cells incubated with HIV-1 BAL or a wildtype HIV-1 isolate induced apoptosis in autologous primary CD4+ T lymphocytes, infected or not with a wild-type HIV-1 isolate. Therefore, induction of DC cytotoxicity by HIV may be relevant to in vivo HIV infection. Induction of cytotoxicity in DCs by HIV might contribute to HIV-associated T cell depletion through induction of apoptosis, especially in the early stages of infection. It may also contribute to elimination of infected cells in vivo, thereby enhancing cross-presentation of HIV by DCs. Therefore this new cytotoxic function of DCs may play an important role in innate and adaptive immunity during HIV infection.

An essential role for tripeptidyl peptidase in the generation of an MHC class I epitope

Most of the peptides presented by major histocompatibility complex (MHC) class I molecules require processing by proteasomes. Tripeptidyl peptidase II (TPPII), an aminopeptidase with endoproteolytic activity, may also have a role in antigen processing. Here, we analyzed the processing and presentation of the immunodominant human immunodeficiency virus epitope HIV-Nef(73-82) in human dendritic cells. We found that inhibition of proteasome activity did not impair Nef(73-82) epitope presentation. In contrast, specific inhibition of TPPII led to a reduction of Nef(73-82) epitope presentation. We propose that TPPII can act in combination with or independent of the proteasome system and can generate epitopes that evade generation by the proteasome-system.

Lipid vector for the delivery of peptides towards intracellular pharmacological targets

The ability of single-chain lipopeptides to gain access to cellular compartments other than those related to degradation/recycling was first deduced from their capacity to deliver peptide antigens into MHC-class I loading mechanisms. The ability of lipopeptides to escape complete endosome degradation was further illustrated by the selective inhibition of different protein kinase C isoenzymes and, more recently, the presentation of agonistic activity towards the interferon gamma receptor. Taken together, several independent results indicate that modification of a peptide by a single lipid chain confers upon it intracellular trafficking properties that can be used to deliver functional cargo peptides into living cells; the endoplasmic reticulum, cytosolic protease activity, sites of kinase activity, or even the signalling pathway associated with cytokine stimulation, all appear accessible to peptide modified by a single lipidic moiety. In this context, the interferon gamma receptor can be considered as a very discriminative pharmacological model, useful for the comparative evaluation of the cellular delivery of lipopeptides, as it allows the unambiguous tracking of their intact delivery into a wide range of cellular compartments. This model is now being used to probe the influence of the nature of the lipid moiety on the trafficking properties of lipopeptides.