Insights from Natural Infection-Derived Immunity to Cholera Instruct Vaccine Efforts

Center for Vaccine Development, Department of Pediatrics and Medicine, University of Maryland, School of Medicine, Baltimore, Maryland, USA.
Clinical and vaccine Immunology: CVI (Impact Factor: 2.47). 09/2012; 19(11):1707-11. DOI: 10.1128/CVI.00543-12
Source: PubMed


Diarrhea caused by Vibrio cholerae O1 (and occasionally O139) remains a notable disease burden in much of the developing world, affecting several million individuals and leaving an estimated toll of > 100,000 deaths annually (1).…

  • [Show abstract] [Hide abstract]
    ABSTRACT: Immunoglobulin A (IgA) is the most heterogeneous of immunoglobulin isotypes, as it occurs in a variety of molecular forms as well as subclasses and allotypes. However, the patterns of heterogeneity vary significantly between different species of mammals and birds. In humans, chimpanzees, gorillas, and gibbons, there are two unique subclasses (IgA1 and IgA2), whereas most other animals that have been investigated have only one, with the remarkable exception of the lagomorphs (rabbits and their allies), which have 13 IgA subclasses. Two, possibly more, allotypes of human IgA2 appear to represent different combinations of constant-region domains of the α-heavy chains. In humans and other primates, the predominant molecular form of circulating (serum) IgA is monomeric, in contrast to the pIgA that is produced in mucosal tissues and transported into the secretions as S-IgA. Further levels of heterogeneity arise from the variable number and composition of the oligosaccharide side-chains present on α-heavy chains. S-IgA antibodies to various viruses can effectively neutralize them. While inhibition of viral binding to cellular receptors is a plausible mechanism in many cases, inhibition of viral replication may occur by other means, depending upon the epitope specificity, isotype, and concentration of antibody as well as the virus and cells involved.
    No preview · Chapter · Dec 2005
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Introduction Cholera toxin B subunit (CTB) is a component of an internationally licensed oral cholera vaccine. The protein induces neutralizing antibodies against the holotoxin, the virulence factor responsible for severe diarrhea. A field clinical trial has suggested that the addition of CTB to killed whole-cell bacteria provides superior short-term protection to whole-cell-only vaccines; however, challenges in CTB biomanufacturing (i.e., cost and scale) hamper its implementation to mass vaccination in developing countries. To provide a potential solution to this issue, we developed a rapid, robust, and scalable CTB production system in plants. Methodology/Principal Findings In a preliminary study of expressing original CTB in transgenic Nicotiana benthamiana, the protein was N-glycosylated with plant-specific glycans. Thus, an aglycosylated CTB variant (pCTB) was created and overexpressed via a plant virus vector. Upon additional transgene engineering for retention in the endoplasmic reticulum and optimization of a secretory signal, the yield of pCTB was dramatically improved, reaching >1 g per kg of fresh leaf material. The protein was efficiently purified by simple two-step chromatography. The GM1-ganglioside binding capacity and conformational stability of pCTB were virtually identical to the bacteria-derived original B subunit, as demonstrated in competitive enzyme-linked immunosorbent assay, surface plasmon resonance, and fluorescence-based thermal shift assay. Mammalian cell surface-binding was corroborated by immunofluorescence and flow cytometry. pCTB exhibited strong oral immunogenicity in mice, inducing significant levels of CTB-specific intestinal antibodies that persisted over 6 months. Moreover, these antibodies effectively neutralized the cholera holotoxin in vitro. Conclusions/Significance Taken together, these results demonstrated that pCTB has robust producibility in Nicotiana plants and retains most, if not all, of major biological activities of the original protein. This rapid and easily scalable system may enable the implementation of pCTB to mass vaccination against outbreaks, thereby providing better protection of high-risk populations in developing countries.
    Full-text · Article · Mar 2013 · PLoS Neglected Tropical Diseases
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Ricin is a member of the ubiquitous family of plant and bacterial AB toxins that gain entry into the cytosol of host cells through receptor-mediated endocytosis and retrograde traffic through the trans-Golgi network (TGN) and endoplasmic reticulum (ER). While a few ricin toxin-specific neutralizing monoclonal antibodies (MAbs) have been identified, the mechanisms by which these antibodies prevent toxin-induced cell death are largely unknown. Using immunofluorescence confocal microscopy and a TGN-specific sulfation assay, we demonstrate that 24B11, a MAb against ricin’s binding subunit (RTB), associates with ricin in solution or when prebound to cell surfaces and then markedly enhances toxin uptake into host cells. Following endocytosis, however, toxin-antibody complexes failed to reach the TGN; instead, they were shunted to Rab7-positive late endosomes and LAMP-1-positive lysosomes. Monovalent 24B11 Fab fragments also interfered with toxin retrograde transport, indicating that neither cross-linking of membrane glycoproteins/glycolipids nor the recently identified intracellular Fc receptor is required to derail ricin en route to the TGN. Identification of the mechanism(s) by which antibodies like 24B11 neutralize ricin will advance our fundamental understanding of protein trafficking in mammalian cells and may lead to the discovery of new classes of toxin inhibitors and therapeutics for biodefense and emerging infectious diseases.
    Full-text · Article · Feb 2014 · mBio
Show more