Bordetella pertussis adenylate cyclase delivers chemically coupled CD8+ T-cell epitopes to dendritic cells and elicits CTL in vivo

Bioengineering of Bordetella pertussis Adenylate Cyclase Toxin for Antigen-Delivery and Immunotherapy

The adenylate cyclase toxin (CyaA) is one of the major virulence factors of Bordetella pertussis, the causative agent of whooping cough. CyaA is able to invade eukaryotic cells where, upon activation by endogenous calmodulin, it synthesizes massive amounts of cAMP that alters cellular physiology. The CyaA toxin is a 1706 residues-long bifunctional protein: the catalytic domain is located in the 400 amino-proximal residues, whereas the carboxy-terminal 1306 residues are implicated in toxin binding to the cellular receptor, the αMβ₂ (CD11b/CD18) integrin, and subsequently in the translocation of the catalytic domain across the cytoplasmic membrane of the target cells. Indeed, this protein is endowed with the unique capability of delivering its N-terminal catalytic domain directly across the plasma membrane of eukaryotic target cells. These properties have been exploited to engineer the CyaA toxin as a potent non-replicating vector able to deliver antigens into antigen presenting cells and elicit specific cell-mediated immune responses. Antigens of interest can be inserted into the CyaA protein to yield recombinant molecules that are targeted in vivo to dendritic cells, where the antigens are processed and presented by the major class I and class II histocompatibility complexes (MHC-I and II). CyaA turned out to be a remarkably effective and versatile vaccine vector capable of inducing all the components of the immune response (T-CD4, T-CD8, and antibody). In this chapter, we summarize the basic knowledge on the adenylate cyclase toxin and then describe the application of CyaA in vaccinology, including some recent results of clinical trials of immunotherapy using a recombinant CyaA vaccine.

Bordetella Pertussis virulence factors in the continuing evolution of whooping cough vaccines for improved performance

Despite high vaccine coverage, whooping cough caused by Bordetella pertussis remains one of the most common vaccine-preventable diseases worldwide. Introduction of whole-cell pertussis (wP) vaccines in the 1940s and acellular pertussis (aP) vaccines in 1990s reduced the mortality due to pertussis. Despite induction of both antibody and cell-mediated immune (CMI) responses by aP and wP vaccines, there has been resurgence of pertussis in many countries in recent years. Possible reasons hypothesised for resurgence have ranged from incompliance with the recommended vaccination programmes with the currently used aP vaccine to infection with a resurged clinical isolates characterised by mutations in the virulence factors, resulting in antigenic divergence with vaccine strain, and increased production of pertussis toxin, resulting in dampening of immune responses. While use of these vaccines provide varying degrees of protection against whooping cough, protection against infection and transmission appears to be less effective, warranting continuation of efforts in the development of an improved pertussis vaccine formulations capable of achieving this objective. Major approaches currently under evaluation for the development of an improved pertussis vaccine include identification of novel biofilm-associated antigens for incorporation in current aP vaccine formulations, development of live attenuated vaccines and discovery of novel non-toxic adjuvants capable of inducing both antibody and CMI. In this review, the potential roles of different accredited virulence factors, including novel biofilm-associated antigens, of B. pertussis in the evolution, formulation and delivery of improved pertussis vaccines, with potential to block the transmission of whooping cough in the community, are discussed.

Adenylate cyclase toxin-mediated delivery of the S1 subunit of pertussis toxin into mammalian cells

The adenylate cyclase toxin (ACT) of Bordetella pertussis internalizes its catalytic domain into target cells. ACT can function as a tool for delivering foreign protein antigen moieties into immune effector cells to induce a cytotoxic T lymphocyte response. In this study, we replaced the catalytic domain of ACT with an enzymatically active protein moiety, the S1 (ADP-ribosyltransferase) subunit of pertussis toxin (PT). The S1 moiety was successfully internalized independent of endocytosis into sheep erythrocytes. The introduced polypeptide exhibited ADP-ribosyltransferase activity in CHO cells and induced clustering typical to PT. The results indicate that ACT can act as a vehicle for not only epitopes but also enzymatically active peptides to mammalian cells.

Smart adjuvants

Although vaccine adjuvants have been used for almost a century, alum is the only adjuvant licensed by the US FDA for human vaccine use. Many adjuvants studied to date have generalized inflammatory properties and lack specificity in terms of targeting immune compartments and cell populations. Indeed, such adjuvants have often been crude in formulation, their effects usually restricted to T-helper 2-type immunity and their use limited owing to inherent toxicity. However, recent advances in immunology have resulted in a number of potential adjuvant candidates that are able to modulate the immune response in a more controlled and specific manner. These novel adjuvants are attractive for inclusion in current and future vaccine strategies since they have better-defined mechanisms of action. In this article, we review several compounds that target specific immune components, such as cells, receptors or signaling pathways, and have termed such reagents 'smart adjuvants'.

Pertussis toxin and adenylate cyclase toxin: key virulence factors of Bordetella pertussis and cell biology tools

Pertussis toxin and adenylate cyclase toxin are two important virulence factors of Bordetella pertussis, the bacterial cause of the respiratory disease pertussis or whooping cough. In addition to studies on the structure, function and role in pathogenesis of these two toxins, they are both used as cell biology tools for a variety of applications owing to their ability to enter mammalian cells, perform enzymatic activities and modify cell signaling events. In this article, recent data from the research literature that enhance our understanding of the nature of these two toxins, their role in the pathogenesis of B. pertussis infection and disease, particularly in modulating host immune responses, and their use as tools for other areas of research will be outlined.

Improving administration regimens of CyaA-based vaccines using TRAP assays to detect antigen-specific CD8(+) T cells directly ex vivo

Vaccination with recombinant adenylate cyclase of Bordetella pertussis (CyaA) carrying antigen is a promising approach to target antigen-presenting cells. We have used Trogocytosis Analysis Protocol (TRAP) assays to monitor immune responses raised by different vaccination regimens with recombinant CyaA carrying the ovalbumin antigen. We find that the intradermal, intramuscular or subcutaneous routes are all superior to intravenous injections, and actually lead to a sufficiently high frequency of reactive CTL to be detected and characterized directly ex vivo by TRAP assay or other standard assays. Finally, for all routes, we find a clear boosting effect upon re-injection of the vaccine.

Branched and linear lipopeptide vaccines have different effects on primary CD4+ and CD8+ T-cell activation but induce similar tumor-protective memory CD8+ T-cell responses

We compared murine T-cell responses to synthetic lipopeptide vaccines in which the TLR2 ligand Pam(2)Cys was attached to co-linear CD4+ and CD8+ T-cell epitopes of ovalbumin (OVA) in a linear or branched configuration. Mice received OVA-specific transgenic CD8+ and CD4+ T-cells followed by one injection of vaccine. Although the branched lipopeptide was more potent in activating OVA-specific CD4+ and CD8+ T-cells in the primary response, both vaccines induced cytolytic T lymphocytes (CTL) that expressed perforin, granzyme A-C, and IFN-gamma mRNAs and conferred long-term protection of most mice against challenge with OVA-expressing tumor cells. OVA epitope display was reduced in tumors that developed in some mice, suggesting CD8+ T-cell dependent selection.

Traffic of proteins and peptides across membranes for immunosurveillance by CD8(+) T lymphocytes: a topological challenge

Cytotoxic CD8(+) T lymphocytes kill infected cells that display major histocompatibility complex (MHC) class I molecules presenting peptides processed from pathogen proteins. In general, the peptides are proteolytically processed from newly made endogenous antigens in the cytosol and require translocation to the endoplasmic reticulum (ER) for MHC class I loading. This last task is performed by the transporters associated with antigen processing (TAP). Sampling of suspicious pathogen-derived proteins reaches beyond the cytosol, and MHC class I loading can occur in other secretory or endosomal compartments besides the ER. Peptides processed from exogenous antigens can also be presented by MHC class I molecules to CD8(+) T lymphocytes, in this case requiring delivery from the extracellular medium to the processing and MHC class I loading compartments. The endogenous or exogenous antigen can be processed before or after its transport to the site of MHC class I loading. Therefore, mechanisms that allow the full-length protein or processed peptides to cross several subcellular membranes are essential. This review deals with the different intracellular pathways that allow the traffic of antigens to compartments proficient in processing and loading of MHC class I molecules for presentation to CD8(+) T lymphocytes and highlights the need to molecularly identify the transporters involved.

Protein toxins: intracellular trafficking for targeted therapy

The immunotoxin approach is based on the use of tumor-targeting ligands or antibodies that are linked to the catalytic (toxic) moieties of bacterial or plant protein toxins. In this review, we first discuss the current state of clinical development of immunotoxin approaches describing the results obtained with the two toxins most frequently used: diphtheria and Pseudomonas toxin-derived proteins. In the second part of the review, a novel concept will be presented in which the roles are inverted: nontoxic receptor-binding toxin moieties are used for the targeting of therapeutic and diagnostic compounds to cancer or immune cells. The cell biological basis of these novel types of toxin-based therapeutics will be discussed, and we will summarize ongoing preclinical and clinical testing.