Page 313 - Clinical Immunology_ Principles and Practice ( PDFDrive )

294 ParT TwO Host Defense Mechanisms and Inflammation

New Mucosal Adjuvants and Delivery Systems immunostimulatory sequences consisting of short palindromic
nucleotides located around a CpG dinucleotide core (e.g., CpG
CLINICaL rELEVaNCE motifs). CpG motifs bind to intracellular TLR9 and induce
Examples of Mucosal Adjuvants and Delivery cytokine secretion (i.e., IL-6, IFN-α, IFN-β, IFN-γ, IL-12, and
IL-18) by a variety of immune cells. CpG motifs can enhance
Systems for the Induction of Targeted Immunity both systemic and mucosal immune responses when given nasally
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Genetically Engineered Bacterial Toxins to mice, and injection of bacterial DNA or CpG motifs with
• Examples are derivatives of the enterotoxin cholera toxin (CT) and a DNA vaccine or with a protein antigen promotes Th1-type
heat-labile toxin (LT-I) from Escherichia coli. responses even in mice with preexisting Th2-type immunity.
Stimulation of TLR3 by dsRNA results in the production of
Nucleic acid Toll-Like receptor (TLr) Ligands type I IFNs (i.e., IFN-α/β), which stimulate antibody responses
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• These sequences typically contain a transcription unit designed to to injected vaccines. The synthetic TLR3 ligand polyinosinic–
express the antigen in question that is coupled to an adjuvant/mitogen polycytidylic acid (poly I:C) has been shown to enhance CD8
unit, such as CpG motifs. responses to an experimental nasal influenza vaccine in mice
and promote heterosubtypic protection via stimulation of TLR3
Mucosal Cytokines and Innate Factors as adjuvants 36
• Mucosal delivery of specific cytokines or innate factors can reduce signaling by nonhematopoietic radioresistant cells.
the risk of adverse systemic effects while targeting the immune Mucosal Cytokines and Innate Factors as Adjuvants
response to the mucosa.
Mucosal delivery of cytokines offers a means to prevent the
Transgenic Plants adverse effects associated with the large and repeated parenteral
• Plants, such as potatoes, bananas, and rice, can be engineered to doses often required for the effective targeting of tissues and
express both B- and T-cell antigen epitopes, providing a simple delivery organs. For example, nasal delivery permits acquisition of sig-
system for oral vaccination or oral tolerance induction. nificant serum levels of IL-12 at one-tenth the dose required for
1
inhibition of serum IFN-γ by parenteral administration. Earlier
studies have shown that nasal administration of tetanus toxoid
Nontoxic Derivatives of Bacterial Enterotoxins with IL-12 as adjuvant induced high titers of sIgA antibody
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To circumvent the toxicity of enterotoxins, mutants of CT (mCT) responses in the GI tract, vaginal washes, and saliva. Similar
and LT (mLT) molecules were generated by site-directed muta- results were reported when mice were nasally immunized with
genesis in the active site of the A subunit of CT or LT, or in the soluble influenza H1 and N1 proteins and IL-12. Related studies
protease sensitive loop of LT. These mutants induced comparable showed that mucosally administered IL-12 can redirect antigen-
levels of antigen-specific serum IgG and sIgA antibodies as specific Th2-type responses toward the Th1 type or promote
wild-type CT and significantly higher levels than those induced mixed Th1- and Th2-type responses, depending on the mucosal
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by recombinant CT-B. One of the mutants also induces Th2-type route and timing of delivery. 1
responses through a preferential inhibition of Th1-type CD4 T FMS-like tyrosine kinase 3 ligand (FL) binds to the FMS-like
cells. mLT molecules, whether possessing a residual ADP– tyrosine kinase receptor Flt3/Flk2. FL mobilizes and stimulates
ribosyltransferase activity (e.g., LT-72R) or totally devoid of it myeloid and lymphoid progenitor cells, DCs, and NK cells.
(e.g., LT-7 K and LT-6 K3), can also function as mucosal adjuvants Although FL dramatically augments numbers of DCs in vivo, it
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for nasal vaccine antigen in mice. As LT induces a mixed CD4 fails to induce their activation. Treatment of mice by systemic
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Th1- and Th2-type response, one might envisage the use of FL injection can induce marked increases in the numbers of
mLTs when both Th1- and Th2-type responses are desired. DCs in both systemic (i.e., spleen) and mucosal lymphoid tissues
The use of GM1-receptor binding holotoxins as nasal mucosal (i.e., iLP, PPs, and mesenteric lymph nodes). Although this increase
adjuvants is currently not recommended because of the risk for in mucosal DCs can, in some cases, initially enhance induction
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their accumulation in the CNS. However, nontoxic mCT could of oral tolerance, it favors the induction of immune responses
overcome these potential problems. To this end, a model adjuvant by mucosal or systemic vaccines. Nasal administration of plasmid
has been developed by combining the ADP-ribosylating ability or adenovirus encoding FL cDNA (pFL or Ad-FL) with protein
of native CT (nCT) with a dimer of an Ig-binding fragment, D, antigens was shown to induce antigen-specific sIgA and protective
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of Staphylococcus aureus protein A. This CTA1-DD molecule immunity. 39-41 Thus FL cDNA may be an alternative to costly
directly binds to B cells of all isotypes, but not to MØs or DCs. treatments with FL protein.
Despite the lack of a mucosal binding element, the B cell–targeted
CTA1-DD molecule is as strong an adjuvant as nCT. Notably, Transgenic Plants
CTA1-DD promoted a balanced Th1/Th2 response with little Edible plants have been engineered to synthesize and assemble
effect on IgE antibody production. CTA1-DD did not induce one or more antigens that retain both T- and B-cell epitopes,
inflammatory changes in the nasal mucosa and, most importantly, thereby inducing systemic and mucosal immune responses in
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did not bind to or accumulate in the OBs or the CNS. CTA1-DD both mice and humans. 42,43 To circumvent potential denaturation
is an example of the use of nonganglioside targeting adjuvants of the plant antigen during cooking, recombinant bananas that
and delivery systems as new tools for the development of safe can accumulate up to 1 mg of vaccine antigen per 10 g of banana
and effective nasal vaccines. were developed. Most recently, the CT-B subunit has been
expressed under the control of the rice seed storage protein
Nucleic Acid Toll-Like Receptor Ligands glutelin promoter (MucoRice-CT-B). Oral feeding of powdered
Toll-like receptor 3 (TLR3) and TLR9 recognize the pathogen- MucoRice-CT-B to mice and nonhuman primates resulted in
associated microbial pattern double-stranded RNA (dsRNA) and the induction of both systemic and mucosal antibody responses
unmethylated DNA, respectively (Chapter 3). The latter contains for protection against CT. 44-46