Transloading of tumor antigen-derived peptides into antigen-presenting cells

TLR2-mediated activation of innate responses in the upper airways confers antiviral protection of the lungs

The impact of respiratory virus infections on global health is felt not just during a pandemic, but endemic seasonal infections pose an equal and ongoing risk of severe disease. Moreover, vaccines and antiviral drugs are not always effective or available for many respiratory viruses. We investigated how induction of effective and appropriate antigen-independent innate immunity in the upper airways can prevent the spread of respiratory virus infection to the vulnerable lower airways. Activation of TLR2, when restricted to the nasal turbinates, resulted in prompt induction of innate immune-driven antiviral responses through action of cytokines, chemokines, and cellular activity in the upper but not the lower airways. We have defined how nasal epithelial cells and recruitment of macrophages work in concert and play pivotal roles to limit progression of influenza virus to the lungs and sustain protection for up to 7 days. These results reveal underlying mechanisms of how control of viral infection in the upper airways can occur and support the implementation of strategies that can activate TLR2 in nasal passages to provide rapid protection, especially for at-risk populations, against severe respiratory infection when vaccines and antiviral drugs are not always effective or available.

How arginine derivatives alter the stability of lipid membranes: dissecting the roles of side chains, backbone and termini

Arginine (R)-rich peptides constitute the most relevant class of cell-penetrating peptides and other membrane-active peptides that can translocate across the cell membrane or generate defects in lipid bilayers such as water-filled pores. The mode of action of R-rich peptides remains a topic of controversy, mainly because a quantitative and energetic understanding of arginine effects on membrane stability is lacking. Here, we explore the ability of several oligo-arginines R[Formula: see text] and of an arginine side chain mimic R[Formula: see text] to induce pore formation in lipid bilayers employing MD simulations, free-energy calculations, breakthrough force spectroscopy and leakage assays. Our experiments reveal that R[Formula: see text] but not R[Formula: see text] reduces the line tension of a membrane with anionic lipids. While R[Formula: see text] peptides form a layer on top of a partly negatively charged lipid bilayer, R[Formula: see text] leads to its disintegration. Complementary, our simulations show R[Formula: see text] causes membrane thinning and area per lipid increase beside lowering the pore nucleation free energy. Model polyarginine R[Formula: see text] similarly promoted pore formation in simulations, but without overall bilayer destabilization. We conclude that while the guanidine moiety is intrinsically membrane-disruptive, poly-arginines favor pore formation in negatively charged membranes via a different mechanism. Pore formation by R-rich peptides seems to be counteracted by lipids with PC headgroups. We found that long R[Formula: see text] and R[Formula: see text] but not short R[Formula: see text] reduce the free energy of nucleating a pore. In short R[Formula: see text], the substantial effect of the charged termini prevent their membrane activity, rationalizing why only longer [Formula: see text] are membrane-active.

Prophylactic intranasal administration of a TLR2/6 agonist reduces upper respiratory tract viral shedding in a SARS-CoV-2 challenge ferret model

BACKGROUND

The novel human coronavirus SARS-CoV-2 is a major ongoing global threat with huge economic burden. Like all respiratory viruses, SARS-CoV-2 initiates infection in the upper respiratory tract (URT). Infected individuals are often asymptomatic, yet highly infectious and readily transmit virus. A therapy that restricts initial replication in the URT has the potential to prevent progression of severe lower respiratory tract disease as well as limiting person-to-person transmission.

METHODS

SARS-CoV-2 Victoria/01/2020 was passaged in Vero/hSLAM cells and virus titre determined by plaque assay. Challenge virus was delivered by intranasal instillation to female ferrets at 5.0 × 106 pfu/ml. Treatment groups received intranasal INNA-051, developed by Ena Respiratory. SARS-CoV-2 RNA was detected using the 2019-nCoV CDC RUO Kit and QuantStudio™ 7 Flex Real-Time PCR System. Histopathological analysis was performed using cut tissues stained with haematoxylin and eosin (H&E).

FINDINGS

We show that prophylactic intra-nasal administration of the TLR2/6 agonist INNA-051 in a SARS-CoV-2 ferret infection model effectively reduces levels of viral RNA in the nose and throat. After 5 days post-exposure to SARS-CoV-2, INNA-051 significantly reduced virus in throat swabs (p=<0.0001) by up to a 24 fold (96% reduction) and in nasal wash (p=0.0107) up to a 15 fold (93% reduction) in comparison to untreated animals.

INTERPRETATION

The results of our study support clinical development of a therapy based on prophylactic TLR2/6 innate immune activation in the URT, to reduce SARS-CoV-2 transmission and provide protection against COVID-19.

FUNDING

This work was funded by Ena Respiratory, Melbourne, Australia.

Geometry of a TLR2-Agonist-Based Adjuvant Can Affect the Resulting Antigen-Specific Immune Response

Targeted delivery of otherwise nonimmunogenic antigens to Toll-like receptors (TLRs) expressed on dendritic cells (DCs) has proven to be an effective means of improving immunogenicity. For this purpose, we have used a branched cationic lipopeptide, R₄Pam₂Cys, which is an agonist for TLR2 and enables electrostatic association with antigen for this purpose. Here, we compare the immunological properties of ovalbumin formulated with different geometrical configurations of R₄Pam₂Cys. Our results demonstrate that notwithstanding the presence of the same adjuvant, branched forms of R₄Pam₂Cys are more effective at inducing immune responses than are linear geometries. CD8⁺ T-cell-mediated responses are particularly improved, resulting in significantly higher levels of antigen-specific cytokine secretion and cytolysis of antigen-bearing target cells in vivo. The results correlate with the ability of branched R₄Pam₂Cys conformations to encourage higher levels of DC maturation and facilitate superior antigen uptake, leading to increased production of proinflammatory cytokines. These differences are not attributable to particle size because both branched and linear lipopeptides associate with antigen-forming complexes of similar size, but rather the ability of branched lipopeptides to induce more efficient TLR2-mediated cell signaling. Branched lipopeptides are also more resistant to trypsin-mediated proteolysis, suggesting greater stability than their linear counterparts. The branched lipopeptide facilitates presentation of antigen more efficiently to CD8⁺ T cells, resulting in rapid cell division and upregulation of early cell surface activation markers. These results as well as cognate recognition of Pam₂Cys by TLR2 indicate that the adjuvant's efficiency is also dependent on its geometry.

Induction of tumor-specific CTL responses using the C-terminal fragment of Viral protein R as cell penetrating peptide

The discovery of tumor-associated antigens recognized by T lymphocytes opens the possibility of vaccinating cancer patients with defined antigens. However, one of the major limitation of peptide-based vaccines is the low immunogenicity of antigenic peptides. Interestingly, if these epitopes are directly delivered into the cytoplasm of antigen presenting cells, they can be efficiently presented via the direct MHC class I presentation pathway. To improve antigen entry, one promising approach is the use of cell penetrating peptides (CPPs). However, most studies use a covalent binding of the CPP with the antigen. In the present study, we focused on the C-terminal domain of Vpr which was previously demonstrated to efficiently deliver plasmid DNA into cells. We provide evidence that the peptides Vpr55-91 and Vpr55-82 possess the capacity of delivering proteins and epitopes into cell lines as well as into human primary dendritic cells, without the necessicity for a chemical linkage. Moreover, immunization of HLA-A2 transgenic mice with Vpr55-91 as the sole adjuvant is able to induce antigen-specific cytotoxic T lymphocytes against multiple tumor epitopes.

Transport of a Fluorescent Analogue of Glucose (2-NBDG) versus Radiolabeled Sugars by Rumen Bacteria and Escherichia coli

Fluorescent tracers have been used to measure solute transport, but transport kinetics have not been evaluated by comparison of radiolabeled tracers. Using Streptococcus equinus JB1 and other bacteria, the objective of this study was to determine if a fluorescent analogue of glucose (2-NBDG) would be transported with the same kinetics and transporters as [(14)C]glucose. We uniquely modified a technique for measuring transport of radiolabeled tracers so that transport of a fluorescent tracer (2-NBDG) could also be measured. Deploying this technique for S. equinus JB1, we could detect 2-NDBG transport quantitatively and within 2 s. We found the Vmax of 2-NBDG transport was 2.9-fold lower than that for [(14)C]glucose, and the Km was 9.9-fold lower. Experiments with transport mutants suggested a mannose phosphotransferase system (PTS) was responsible for 2-NBDG transport in S. equinus JB1 as well as Escherichia coli. Upon examination of strains from 12 species of rumen bacteria, only the five that possessed a mannose PTS were shown to transport 2-NBDG. Those five uniformly transported [(14)C]mannose and [(14)C]deoxyglucose (other glucose analogues at the C-2 position) at high velocities. Species that did not transport 2-NBDG at detectable velocities did not possess a mannose PTS, though they collectively possessed several other glucose transporters. These results, along with retrospective genomic analyses of previous 2-NBDG studies, suggest that only a few bacterial transporters may display high activity toward 2-NBDG. Fluorescent tracers have the potential to measure solute transport qualitatively, but their bulky fluorescent groups may restrict (i) activity of many transporters and (ii) use for quantitative measurement.

Vaccine Potentiation by Combination Adjuvants

Adjuvants are crucial components of vaccines. They significantly improve vaccine efficacy by modulating, enhancing, or extending the immune response and at the same time reducing the amount of antigen needed. In contrast to previously licensed adjuvants, current successful adjuvant formulations often consist of several molecules, that when combined, act synergistically by activating a variety of immune mechanisms. These "combination adjuvants" are already registered with several vaccines, both in humans and animals, and novel combination adjuvants are in the pipeline. With improved knowledge of the type of immune responses needed to successfully induce disease protection by vaccination, combination adjuvants are particularly suited to not only enhance, but also direct the immune responses desired to be either Th1-, Th2- or Th17-biased. Indeed, in view of the variety of disease and population targets for vaccine development, a panel of adjuvants will be needed to address different disease targets and populations. Here, we will review well-known and new combination adjuvants already licensed or currently in development-including ISCOMs, liposomes, Adjuvant Systems Montanides, and triple adjuvant combinations-and summarize their performance in preclinical and clinical trials. Several of these combination adjuvants are promising having promoted improved and balanced immune responses.

Molecular cancer vaccines: Tumor therapy using antigen-specific immunizations

Vaccination against tumors promises selective destruction of malignant cells by the host's immune system. Molecular cancer vaccines rely on recently identified tumor antigens as immunogens. Tumor antigens can be applied in many forms, as genes in recombinant vectors, as proteins or peptides representing T cell epitopes.Analysis of various aspects indicates some advantage for peptide-based vaccines over the other modalities. Further refinements and extensively monitored clinical trials are necessary to advance molecular cancer vaccines from concepts into powerful therapy.

Adjuvant properties of Cytosine-phosphate-guanosine oligodeoxynucleotide in combination with various polycations in an ovalbumin-vaccine model

Oligonucleotides containing CpG motifs (cytosine-phosphate-guanosine oligodeoxynucleotide [CpG ODN]) display strong immunostimulatory effects, and polycations have been previously reported as cellular delivery system. In the present study, we investigated the adjuvant properties of combinations of a CpG ODN with various polycations (poly-arginine, poly-lysine, poly-histidine, or chitosan) in an ovalbumin vaccination model. We showed that, when combined to CpG ODN, poly-arginine and poly-histidine, but not poly-lysine or chitosan, enhanced efficiently both the IgG antibody production and the number of splenocytes secreting interferon-gamma after stimulation with a CD8+ T cell-restricted peptide. Interestingly, CpG ODN-poly-arginine, which was the most efficient, compared favorably to the complete Freund's adjuvant and aluminium salts and induced no local toxicity, making this combination a very attractive adjuvant for vaccines.

Dendritic cell acquisition of epitope cargo mediated by simple cationic peptide structures

In this study we evaluate the uptake by murine dendritic cells (DCs) of different synthetic, branched cationic peptide structures with a view to facilitating peptide epitope delivery. The level of cell uptake by fluorescenated peptides was measured by flow cytometry following quenching of extracellular fluorescence with trypan blue. Branched peptides containing either N-terminal arginine or N-terminal lysine residues were able to mediate cell entry but the peptide containing four arginine residues in a branching configuration (R4) was found to be superior not only to other branched peptides in translocating to the cell interior and also to a peptide containing four arginine residues arranged linearly. Fluorescenated R4 was found to be localized within intracellular vesicle-like compartments as well as being distributed throughout the cell cytoplasm. Uptake of R4 utilized an energy-dependent process that appeared to involve phosphatidylinositol-3-kinase and could induce intermediate levels of DC maturation. R4 when conjugated to a T-helper cell and CTL epitope construct was able to induce antigen-specific CD8+ T-cell mediated immune responses in mice when administered in adjuvant as were DCs that were pulsed with this construct and then matured with LPS. Fluorescenated R4 was also found to translocate into the interior of other cell types indicating that it may be useful for the delivery of peptide cargo into other specialized cells.

Therapeutic vaccination of chronic hepatitis C nonresponder patients with the peptide vaccine IC41

BACKGROUND & AIMS

IC41 is a synthetic peptide vaccine containing 7 relevant hepatitis C virus (HCV) T-cell epitopes and the T helper cell (Th)1/Tc1 adjuvant poly-L-arginine. IC41 has been shown to be safe and to induce HCV-specific interferon (IFN)-gamma-secreting CD4+ and CD8+ T cells in healthy volunteers. We aimed to investigate whether IC41 is able to induce HCV-specific T-cell responses also in chronic hepatitis C patients.

METHODS

Sixty HLA-A2-positive chronic HCV patients not responding to or relapsing from standard therapy were randomized in a double-blind phase II study into 5 groups to receive 6 vaccinations of IC41 (3 different dose groups), HCV peptides alone, or poly-L-arginine alone.

RESULTS

IC41 was well tolerated, and no drug-related serious adverse events or induction of hepatitis were observed. T-cell proliferation was recorded in up to 67% of patients in the 3 IC41 vaccine groups but only in 17% of patients treated with peptides alone. IFN-gamma enzyme-linked immunospot assay responses were observed exclusively in the IC41 groups with response rates up to 42%. There were 3 RNA responders with transient >1-log declines of HCV serum RNA associated with the strongest IFN-gamma enzyme-linked immunospot assay values within all 60 patients.

CONCLUSIONS

This study showed that the HCV peptide vaccine IC41 can induce HCV-specific Th1/Tc1 responses in a subset of difficult to treat HCV nonresponder patients despite persisting viremia. However, changes in HCV RNA occurred only in single patients. Because strongest T-cell responses were associated with HCV RNA decline, further studies with optimized vaccine regimens and combination therapies have been initiated.

Immunogenicity and safety of a novel therapeutic hepatitis C virus (HCV) peptide vaccine: A randomized, placebo controlled trial for dose optimization in 128 healthy subjects

As interferon/ribavirin-based standard therapy is curative in only about half of HCV patients, there remains an important need for alternatives including vaccines. The novel peptide vaccine IC41 consists of five synthetic peptides harboring HCV T cell epitopes and poly-L-arginine as synthetic adjuvant. In this randomized, placebo-controlled trial, 128 HLA-A2 positive healthy volunteers received four s.c. vaccinations of seven different doses IC41, HCV peptides alone, poly-l-arginine alone or saline solution, every 4 weeks. IC41 was safe and well tolerated. Mild to moderate local reactions were transient. Immunogenicity was assessed using T cell epitope specific [3H]-thymidine proliferation, IFN-gamma ELIspot and HLA-tetramer assays. IC41 induced responses in all dose groups. Higher responder rates were recorded in higher dose groups and increasing number of vaccinations were associated with higher responder rates and more robust responses. Poly-L-arginine was required for the aimed-for Th1/Tc1-type immunity (IFN-gamma secreting T cells).

IC31, a novel adjuvant signaling via TLR9, induces potent cellular and humoral immune responses

IC31, the combination of a novel immunostimulatory oligodeoxynucleotide containing deoxy-Inosine/deoxy-Cytosine (ODN1a) and the antimicrobial peptide KLKL(5)KLK, represents a promising novel adjuvant signaling via the TLR9/MyD88-dependent pathway of the innate immune system. In mice, IC31 induces potent peptide-specific type 1 cellular immune responses, as well as mainly type 1 dominated protein-specific cellular and humoral immune responses. In addition, cytotoxic T lymphocytes were induced, able to kill efficiently target cells in vivo. Activation of murine dendritic cells by IC31 induced efficiently proliferation of naïve CD4(+) TCR transgenic T cells (DO.11.10) as well as their differentiation into IFN-gamma- and IL-4-producing T cells in vitro.

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.

Delivery of bioactive molecules into the cell: the Trojan horse approach

In recent years, vast amounts of data on the mechanisms of neural de- and regeneration have accumulated. However, only in disproportionally few cases has this led to efficient therapies for human patients. Part of the problem is to deliver cell death-averting genes or gene products across the blood-brain barrier (BBB) and cellular membranes. The discovery of Antennapedia (Antp)-mediated transduction of heterologous proteins into cells in 1992 and other "Trojan horse peptides" raised hopes that often-frustrating attempts to deliver proteins would now be history. The demonstration that proteins fused to the Tat protein transduction domain (PTD) are capable of crossing the BBB may revolutionize molecular research and neurobiological therapy. However, it was only recently that PTD-mediated delivery of proteins with therapeutic potential has been achieved in models of neural degeneration in nerve trauma and ischemia. Several groups have published the first positive results using protein transduction domains for the delivery of therapeutic proteins in relevant animal models of human neurological disorders. Here, we give an extensive review of peptide-mediated protein transduction from its early beginnings to new advances, discuss their application, with particular focus on a critical evaluation of the limitations of the method, as well as alternative approaches. Besides applications in neurobiology, a large number of reports using PTD in other systems are included as well. Because each protein requires an individual purification scheme that yields sufficient quantities of soluble, transducible material, the neurobiologist will benefit from the experiences of other researchers in the growing field of protein transduction.

Regulation of the endogenous VEGF-A gene by exogenous designed regulatory proteins

We describe a facile method to activate or repress transcription of endogenous genes in a quantitative and specific manner by treatment with designed regulatory proteins (DRPs), in which artificial transcription factors (ATFs) are fused to cell-penetrating peptides (CPPs). Penetration of DRPs into cells is mediated by an N-terminal CPP fused to a nuclear localization signal; a DNA-binding domain and a transactivation domain follow. The DNA-binding domain was targeted to the vascular endothelial growth factor (VEGF)-A gene. An agonist DRP was rapidly taken up by cells and transported to the nucleus; soon after, the cells began transcribing the gene and secreting VEGF-A protein in a dose-dependent manner. Multiple copies of a short oligopeptide derived from a minimal transactivation domain of human beta-catenin was stronger than VP-16. The SRDX domain from the plant transcription factor, SUPERMAN, changed the DRP to a hypoxia-induced antagonist of VEGF-A. DRPs combine many of the potential benefits of transgenes with those of recombinant proteins.

Biological applications of protein transduction technology

The impermeable nature of the cell membrane to peptides, proteins, DNA and oligonucleotides limits the therapeutic potential of these biological agents. However, the recent discovery of short cationic peptides that cross the plasma membrane efficiently is opening up new possibilities for the intracellular delivery of such agents. These peptides are commonly referred to as protein transduction domains (PTDs) and are successfully used to transport heterologous proteins, peptides and other types of cargo into cells. Several recent reports have used the membrane transducing technology in vivo to deliver biologically active cargo into various tissues. This review discusses the structure of the most commonly used PTDs and how their ability to transduce membranes is used to regulate biological functions. It also considers future directions and the potential of this technology to move from the laboratory into the clinic.

Antennapedia transduction sequence promotes anti tumour immunity to epicutaneously administered CTL epitopes

The identification of tumor antigens has spurred the development of efficient adjuvants and novel delivery systems for cancer immunotherapy. To this end, a peptide-based vaccine consisting of the Antennapedia transduction sequence (ANTP) attached to an antigenic peptide was designed to enhance per-cutaneous delivery into cells of the epidermis and dermis. Here we show that the topical application of OVA(257-264) linked to ANTP in mice onto tape-stripped skin resulted in enhanced delivery of the antigen through the skin whereas OVA(257-264) alone remained distributed uniformly on the skin surface. This delivery correlated with an increase in the CTL response against OVA. When mixed with CpG oligodinucleotides (ODN), the recombinant antigen protected mice from tumor challenge. These data provide the first indication that in vivo use of a translocation sequence can enhance delivery of therapeutic peptides and increase anti-tumor immunity through a simple and safe mechanism involving enhanced penetration of the skin barrier.

Targeting dendritic cells for priming cellular immune responses

The cardinal role of dendritic cells (DC) in priming adaptive immunity and in orchestrating immune responses against all classes of pathogens and also against tumors is well established. Their unique potential both to maintain self-tolerance and to initiate protective immune responses against foreign and/or dangerous structures is based on the functional diversity and flexibility of these cells. Tissue DC lining antigenic portals such as mucosal surfaces and the skin are specialized to take up a wide array of compounds including proteins, lipids, carbohydrates, glycoproteins, glycolipids and oligonucleotides, particles carrying such structures and apoptotic or necrotic cells. This process is facilitated by specialized receptors with high endocytic capacity, which provides potential targets for delivering designed molecules. The best route for targeting B- and/or T cell epitopes, however, is still the subject of intense investigation. Immature DC, which reside in various tissues, can be activated by pathogens, stress and inflammation or modified metabolic products, which induce mobilization of cells to draining lymph nodes where they act as highly potent professional antigen presenting cells. This is brought about by the ability to present their accumulated intracellular content for both CD4+ helper (Th) and CD8+ cytotoxic/cytolytic T lymphocytes (Tc/CTL). Engulfed proteins are processed intracellularly and their peptide fragments are transported to the cell surface in the context of major histocompatibility complex encoded class I and II molecules for presentation to Th cells and CTLs, respectively. The T cell priming capacity of DC, however, depends not only on antigen presentation but also on other features of DC. Human monocyte-derived DC provide an excellent tool to study the internalizing, antigen-presenting and T cell-activating functions of DC at their immature and activated differentiation states. These biological activities of DC, however, are highly dependent on their migratory potential from the peripheral non-lymphoid tissues to the lymph nodes, on the expression of adhesion molecules, which support the interaction of DC with T lymphocytes, and the cytokines secreted by DC, which polarize immune responses to Th1-mediated cellular or Th2-mediated antibody responses. These results altogether demonstrate that monocyte-derived DC are useful candidates for in vitro or in vivo targeting of antigens to induce efficient adaptive immune responses against pathogens and also against tumors.

Peptides containing antigenic and cationic domains have enhanced, multivalent immunogenicity when bound to DNA vaccines

We explored strategies to codeliver DNA- and peptide-based vaccines in a way that enhances the immunogenicity of both components of the combination vaccine for T cells. Specific CD8(+) T cell responses to an antigenic peptide are primed when the peptide is fused to a cationic peptide domain that is bound to plasmid DNA or oligonucleotides (ODN; with or without CpG motifs). Plasmid DNA mixed with antigenic/cationic peptides or histones forms large complexes with different biological properties depending on the molar ratios of peptide/protein and polynucleotide. Complexes containing high (but not low) molar ratios of cationic peptide to DNA facilitate transfection (DNA uptake and expression of the plasmid-encoded product) of cells. In contrast, complexes containing low (but not high) molar ratios of cationic peptide to DNA prime potent multispecific T cell responses after a single intramuscular injection of the complexes. The general validity of this observation was confirmed mixing different antigenic/cationic peptides with different DNA vaccines. In these vaccine formulations, multispecific CD8(+) T cell responses specific for epitopes of the peptide- as well as the DNA-based vaccine were efficiently coprimed, together with humoral antibody responses to conformational determinants of large viral antigens encoded by the DNA vaccine. The data indicate that mixtures of DNA vaccines with antigenic, cationic peptides are immunogenic vaccine formulations particularly suited for the induction of multispecific T cell responses.

Gene transfer via reversible plasmid condensation with cysteine-flanked, internally spaced arginine-rich peptides

Nonviral gene transfer offers biosafety, stability, and expense advantages over viruses; however, it has suffered from poor efficiency. Because arginine-rich peptides facilitate uptake of macromolecules such as proteins, liposomes, and iron nanoparticles, we explored their potential in enhancing plasmid DNA delivery. In their unmodified form, known protein transduction sequences, including hepta-arginine and Tat(47-57), failed to support effective gene delivery. However, by flanking a core of consecutive arginines with amino- and carboxy-terminal cysteines in vitro gene transfer was observed. Furthermore, interspersing arginines with glycine and histidine residues achieved reversible plasmid condensation and dramatically increased transfection levels in a variety of cell types. Unlike most available cationic homopolymers that function only in vitro, these new peptides also increased gene expression in both murine and human tissue in vivo. Thus, cysteine-flanked, internally spaced arginine-rich (CFIS-R) peptides represent a new approach to efficient nonviral plasmid delivery using rationally designed protein transduction domains.

In vivo plasmid DNA electroporation generates exceptionally high levels of epitope-specific CD8+ T-cell responses

Based on observations that DBA/2 mice develop a highly specific response towards an HLA-Cw3-derived epitope, consisting entirely of CD8+CD62L-Vbeta10+ cells, we have established an in vivo mouse model for screening a variety of immunization approaches. Responder cells were readily detectable in small samples of the peripheral blood using three-color FACS analysis. This permitted multiple, sequential determination of CD8+ T-cell responses in living animals at a very high degree of precision. In vivo electroporation delivery of expression construct plasmids, outclassed the other approaches tested. Dominant, specific responses were induced already upon a single administration. Both the peak and the longevity of the response resembled those that are generated by the most active viral infections. The induced CTLs rejected epitope-bearing tumor cells in vivo and released interferon-gamma upon stimulation with the correct MHC::peptide combination in vitro. The potent in vivo response was not influenced by known modulators of the innate immune system, such as CpG DNA and LPS content. In vivo electroporation thus deserves consideration in the future in antitumor and antiviral immunization approaches, where CD8+ T cells play a predominant role.

Poly-L-arginine synergizes with oligodeoxynucleotides containing CpG-motifs (CpG-ODN) for enhanced and prolonged immune responses and prevents the CpG-ODN-induced systemic release of pro-inflammatory cytokines

This study describes an entirely synthetic vaccine composed of antigenic peptides (T cell epitopes), oligodeoxynucleotides containing CpG-motifs (CpG-ODN) and poly-L-arginine (pR). CpG-ODN are known to be potent inducers of predominantly type 1-like immune responses, while polycationic amino acids, like pR, facilitate the uptake of antigens into antigen presenting cells (APCs). We demonstrate that the application of peptides and pR/CpG-ODN results in strongly enhanced peptide-specific immune responses as compared to the application of peptides with either of the immunomodulators alone. High numbers of antigen-specific T cells can be observed even after only one injection of the vaccine for a remarkably long period of time (at least 372 days). Furthermore, the potentially harmful systemic release of pro-inflammatory cytokines induced upon injection of CpG-ODN is inhibited. Thus, the combined application of CpG-ODN and pR may represent a novel vaccine strategy in humans.

Induction of specific immune responses by polycation-based vaccines

The s.c injection of tumor Ag-derived, MHC class I-binding peptides together with cationic poly-amino acids (e.g., poly-L-arginine; pR) has been shown to protect animals against a challenge with tumor cells expressing the respective peptide(s). Given our only restricted knowledge about immunogenic tumor-associated peptides, we sought to determine whether this pR-based vaccination protocol would also induce protective cancer immunity if large proteins were used instead of peptide epitopes. We found that the intracutaneous administration of the model Ag beta-galactosidase (beta-gal) together with pR (referred to as pR-based protein vaccine; pR-PV) was significantly more potent in protecting mice against the growth of beta-gal-expressing RENCA cells than the protein alone. Coadministration of pR enhanced both the beta-gal-induced specific humoral and CD8 response. The protective effect required CD8(+), but neither CD4(+) T lymphocytes nor beta-gal-specific Abs. beta-Gal priming of protective CD8(+) T lymphocytes was found to be CD4(+) T cell-independent, to take place within the draining lymph nodes, and to be accomplished by day 5 after vaccination. Ablation of the injection sites as early as 1.5 h after pR-PV administration still led to protection in a large proportion of the animals, indicating that certain protein Ags administered intradermally in the context of polycations are quickly transported to the draining nodes, where they induce molecular and cellular events resulting in the helper-independent priming and expansion of Tc1 cells. However, optimal protection required the prolonged presence of the injection site, suggesting that pR-PV injection facilitates the formation of a cutaneous depot of Ag-charged cells capable of migration and T cell activation.

Intracellular delivery of monoclonal antibodies

With some exceptions, antibodies do not have the ability to penetrate cell membranes and act intracellularly. Their usefulness in research and medicine would be considerably enhanced if they had the intrinsic ability to act on intracellular targets. We report here that covalently linking poly-L-arginine (average molecular weight 10750, ca. 68 residues) to the oligosaccharide moiety of the CH2 region of an immunoglobulin makes possible penetration into the cytoplasm and, and in some cases into the nucleus of cells. We demonstrate this with five antibodies and seven cell lines. Retention of specificity is demonstrated by ELISA with an anti-HIV Gag antibody and intracellularly with a monoclonal anti-tubulin antibody. As the antibodies are covalently modified, they have the potential to be used in intact animals.

Dendritic cell delivery of plasmid DNA. Applications for controlled genetic immunization

Positive human clinical data using biolistic-mediated gene transfer (i.e., gene gun) to administer a nucleic acid-based Hepatitis B vaccine has validated genetic immunization as an effective clinical vaccine modality. Although the precise mechanism of action has yet to be determined, preclinical studies using jet injection have indicated that direct targeting of resident antigen presenting cells (Langerhan's cells) in the skin as the primary immunological driving force for the potent and long-lived immune response. Moreover, positive results with topical delivery of genetic vaccines and ex vivo loading of dendritic cells with antigen has strengthened the movement toward directly targeting antigen presenting cells as a means to amplify, control, and mediate the immunological consequences of prophylactic and/or therapeutic genetic vaccines. Despite these encouraging results with the gene gun, it is unclear whether this technology will translate into commercially available vaccines due to potential product development barriers such as cost and convenience. It is clear that safety concerns in using genetic approaches to treat and prevent disease have highlighted the need for strict product requirements for genetic vaccines. A plausible strategy to meet these requirements is to combine controlled plasmid delivery systems with tissue-specific gene expression systems.

Defined synthetic vaccines

Although vaccines have proven very successful in preventing certain infectious diseases, progress in the field has been slowed by the tediousness of developing classical vaccines consisting of whole pathogens. Thus, there is great need for improvement in several areas: firstly, the range of diseases which can be treated has to be expanded. Secondly, antigens have to be defined to make the use of whole pathogens as antigen obsolete. And thirdly, new adjuvants have to be developed which show low toxicity, high potency and are also able to drive the immune response in the desired direction. Ideally, a vaccine would only consist of well-characterized, synthetic materials. This review summarizes the different approaches for the development of completely defined synthetic vaccines.

The design, synthesis, and evaluation of molecules that enable or enhance cellular uptake: peptoid molecular transporters

Certain proteins contain subunits that enable their active translocation across the plasma membrane into cells. In the specific case of HIV-1, this subunit is the basic domain Tat(49-57) (RKKRRQRRR). To establish the optimal structural requirements for this translocation process, and thereby to develop improved molecular transporters that could deliver agents into cells, a series of analogues of Tat(49-57) were prepared and their cellular uptake into Jurkat cells was determined by flow cytometry. All truncated and alanine-substituted analogues exhibited diminished cellular uptake, suggesting that the cationic residues of Tat(49-57) play a principal role in its uptake. Charge alone, however, is insufficient for transport as oligomers of several cationic amino acids (histidine, lysine, and ornithine) are less effective than Tat(49-57) in cellular uptake. In contrast, a 9-mer of l-arginine (R9) was 20-fold more efficient than Tat(49-57) at cellular uptake as determined by Michaelis-Menton kinetic analysis. The d-arginine oligomer (r9) exhibited an even greater uptake rate enhancement (>100-fold). Collectively, these studies suggest that the guanidinium groups of Tat(49-57) play a greater role in facilitating cellular uptake than either charge or backbone structure. Based on this analysis, we designed and synthesized a class of polyguanidine peptoid derivatives. Remarkably, the subset of peptoid analogues containing a six-methylene spacer between the guanidine head group and backbone (N-hxg), exhibited significantly enhanced cellular uptake compared to Tat(49-57) and even to r9. Overall, a transporter has been developed that is superior to Tat(49-57), protease resistant, and more readily and economically prepared.

Cellular uptake and in situ binding of a peptide agonist for calmodulin

We have used the method of inverted hydropathy to develop peptides that interact with EF hands of calmodulin (CaM). Previously we have shown these peptides specifically interact with their desired target in a productive manner, in that they activated CaM in the absence of Ca(2+). Therefore, we sought to determine whether these peptides would enter cells, remain intact, and interact with CaM in the interior of the cell. Using several techniques we have demonstrated cellular uptake, stability, and an intracellular interaction with CaM with fluorescein-labeled and radiolabeled peptides in Jurkat T cells. The results suggest that these peptides may be useful in the study and the manipulation of Ca(2+)-mediated pathways in cells.

Stimulatory and inhibitory differentiation of human myeloid dendritic cells

Dendritic cells (DCs) play a critical obligate role in presenting antigens to T cells for activation. In the process, upon antigen capture, DCs undergo maturation and become more stimulatory. Human myeloid DCs can be generated from various sources, including blood, bone marrow, and CD34(+) stem cells. As such, plastic-adherent monocytes from circulation have served as a ready source for generating myeloid DCs in culture in granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) for translational research in active specific immunotherapy, especially in cancer, with the belief that they are essentially stimulatory or "immunogenic." Here we show that in vitro cultures of plastic-adherent circulating monocytes in GM-CSF and IL-4 followed by further maturation in interferon-gamma plus bacterial superantigens (DC maturing agents) can give rise to two diametrically opposite types of DCs-one stimulatory and another inhibitory. The stimulatory DCs express higher amounts of costimulatory molecules, synthesize IL-12, and efficiently stimulate naive allogeneic T cells in mixed lymphocyte reaction (MLR). The inhibitory DCs, in contrast, express lower concentrations of the critical costimulatory molecules, synthesize large amounts of IL-10, and are nonstimulatory in allogeneic primary MLR. Moreover, while the stimulatory DCs further amplify proliferation of T cells in lectin-driven proliferation assays, the inhibitory DCs totally block T cell proliferation in similar assays, in vitro. Most interestingly, neutralization of the endogenously derived IL-10 with anti-IL-10 antibody in DC cultures repolarizes the inhibitory DCs toward stimulatory phenotype. Accordingly, these observations have important implications in translational research involving myeloid DCs.

HLA class I expression on human cancer cells. Implications for effective immunotherapy

Early studies demonstrated the role of cytotoxic T cells as an immune defence mechanism against tumour cells. The demonstration of tumour antigen peptides and their presentation to T cells on major histocompatibility complex class I molecules highlighted the importance of these molecules in effective anti-tumour responses. It is well established that many tumours escape T cell recognition by loss or down regulation of class I molecule expression on the cell surface of tumour cells. Tumours which have lost class I expression are immunoselected and as a result have a propensity for growth and metastatic spread. With the development of cancer vaccine strategies for clinical use, there will be a future role for histocompatibility laboratories in determining class I expression on tumour cells in individual patients. These studies of expression will require not just the demonstration of total class I expression but the demonstration of locus and allele specific class I molecules involved in the relevant tumour peptide presentation. These studies will be pivotal in tailoring individual patient therapies. The identification of appropriate monoclonal antibody reagents for class I expression and techniques used on different kinds of tissue sections will be a component of the forthcoming 13th International Histocompatibility Workshop.

Cell-free tumor antigen peptide-based cancer vaccines

The central role that tumor antigen-derived peptides play in induction of antitumor immunity makes them ideal candidates for peptide-based cancer vaccines. We have demonstrated that "transloading" is an efficient strategy for importing short peptide ligands into antigen-presenting cells in vitro. Postulating that the transloading procedure might effect peptide uptake by antigen-presenting cells in vivo as well, we tested this approach for the generation of peptide-based cancer vaccines. In the P815 mastocytoma system, we vaccinated mice by s.c. injection of a single, known natural peptide derived from JAK-1 kinase. Whereas vaccination with peptide alone or mixed with incomplete Freund's adjuvant was ineffective, application of the peptide in conjunction with the polycation poly-L-lysine protected a significant number of animals against tumor challenge. Dependent upon the type of poly-L-lysine applied, protection against tumor take was comparable to that achieved with irradiated whole-cell vaccines, genetically modified to secrete granulocyte-macrophage colony-stimulating factor. In the murine melanoma M-3, a combination of four putative tumor antigen-derived peptides was tested as a cancer vaccine. Administered in combination with polycations, these peptides evoked potent antitumor immunity that could not be obtained with the peptides alone or peptides emulsified in incomplete Freund's adjuvant. However, peptide-polycation vaccines applied to the M-3 model were not as efficient as cellular control vaccines, consisting of irradiated interleukin 2 or granulocyte-macrophage colony-stimulating factor-secreting tumor cells.