Yersinia pestis (plague) vaccines

Anti-LcrV antibody inhibits delivery of Yops by Yersinia pestis KIM5 by directly promoting phagocytosis

LcrV of Yersinia pestis is a major protective antigen proposed for inclusion in subunit plague vaccines. One way that anti-LcrV antibody is thought to protect is by inhibiting the delivery of toxins called Yops to host cells. The present study characterizes the relation between this inhibition and the phagocytosis of the bacteria. J774A.1 cells were infected with Y. pestis KIM5 in the presence of a protective polyclonal anti-LcrV antibody or a nonprotective polyclonal anti-YopM antibody, and delivery of YopH and YopE into the cytoplasm was assayed by immunoblotting. The ability to inhibit the delivery of these Yops depended upon having antibody bound to the cell surface; blocking conditions that prevented the binding of antibody to Fc receptors prevented the inhibition of Yop delivery. Anti-LcrV antibody also promoted phagocytosis of the yersiniae, whereas F(ab')(2) fragments did not. Further, anti-LcrV antibody could not inhibit the delivery of Yops into cells that were unable to phagocytose due to the presence of cytochalasin D. However, Yops were produced only by extracellular yersiniae. We hypothesize that anti-LcrV antibody does not directly inhibit Yop delivery but instead causes phagocytosis, with consequent inhibition of Yop protein production in the intracellular yersiniae. The prophagocytic effect of anti-LcrV antibody extended to mouse polymorphonuclear neutrophils (PMNs) in vitro, and PMNs were shown to be critical for protection: when PMNs in mice were ablated, the mice lost all ability to be protected by anti-LcrV antibody.

LcrV plague vaccine with altered immunomodulatory properties

Yersinia pestis, the causative agent of plague, secretes LcrV (low-calcium-response V or V antigen) during infection. LcrV triggers the release of interleukin 10 (IL-10) by host immune cells and suppresses proinflammatory cytokines such as tumor necrosis factor alpha and gamma interferon as well as innate defense mechanisms required to combat the pathogenesis of plague. Although immunization of animals with LcrV elicits protective immunity, the associated suppression of host defense mechanisms may preclude the use of LcrV as a human vaccine. Here we show that short deletions within LcrV can reduce its immune modulatory properties. An LcrV variant lacking amino acid residues 271 to 300 (rV10) elicited immune responses that protected mice against a lethal challenge with Y. pestis. Compared to full-length LcrV, rV10 displayed a reduced ability to release IL-10 from mouse and human macrophages. Furthermore, the lipopolysaccharide-stimulated release of proinflammatory cytokines by human or mouse macrophages was inhibited by full-length LcrV but not by the rV10 variant. Thus, it appears that LcrV variants with reduced immune modulatory properties could be used as a human vaccine to generate protective immunity against plague.

Immunization of mice with YscF provides protection from Yersinia pestis infections

BACKGROUND

Yersinia pestis, the causative agent of plague, is a pathogen with a tremendous ability to cause harm and panic in populations. Due to the severity of plague and its potential for use as a bioweapon, better preventatives and therapeutics for plague are desirable. Subunit vaccines directed against the F1 capsular antigen and the V antigen (also known as LcrV) of Y. pestis are under development. However, these new vaccine formulations have some possible limitations. The F1 antigen is not required for full virulence of Y. pestis and LcrV has a demonstrated immunosuppressive effect. These limitations could damper the ability of F1/LcrV based vaccines to protect against F1-minus Y. pestis strains and could lead to a high rate of undesired side effects in vaccinated populations. For these reasons, the use of other antigens in a plague vaccine formulation may be advantageous.

RESULTS

Desired features in vaccine candidates would be antigens that are conserved, essential for virulence and accessible to circulating antibody. Several of the proteins required for the construction or function of the type III secretion system (TTSS) complex could be ideal contenders to meet the desired features of a vaccine candidate. Accordingly, the TTSS needle complex protein, YscF, was selected to investigate its potential as a protective antigen. In this study we describe the overexpression, purification and use of YscF as a protective antigen. YscF immunization triggers a robust antibody response to YscF and that antibody response is able to afford significant protection to immunized mice following challenge with Y. pestis. Additionally, evidence is presented that suggests antibody to YscF is likely not protective by blocking the activity of the TTSS.

CONCLUSION

In this study we investigated YscF, a surface-expressed protein of the Yersinia pestis type III secretion complex, as a protective antigen against experimental plague infection. Immunization of mice with YscF resulted in a high anti-YscF titer and provided protection against i.v. challenge with Y. pestis. This is the first report to our knowledge utilizing a conserved protein from the type III secretion complex of a gram-negative pathogen as a candidate for vaccine development.

Emerging infectious diseases: a 10-year perspective from the National Institute of Allergy and Infectious Diseases

Advances in infectious disease research over the past 10 years have allowed breakthroughs in the

diagnosis, prevention, and treatment of infectious disease.

Although optimists once imagined that serious infectious disease threats would by now be conquered, newly emerging (e.g., severe acute respiratory syndrome [SARS]), reemerging (e.g., West Nile virus), and even deliberately disseminated infectious diseases (e.g., anthrax bioterrorism) continue to appear throughout the world. Over the past decade, the global effort to identify and characterize infectious agents, decipher the underlying pathways by which they cause disease, and develop preventive measures and treatments for many of the world's most dangerous pathogens has resulted in considerable progress. Intramural and extramural investigators supported by the National Institute of Allergy and Infectious Diseases (NIAID) have contributed substantially to this effort. This overview highlights selected NIAID-sponsored research advances over the past decade, with a focus on progress in combating HIV/AIDS, malaria, tuberculosis, influenza, SARS, West Nile virus, and potential bioterror agents. Many basic research discoveries have been translated into novel diagnostics, antiviral and antimicrobial compounds, and vaccines, often with extraordinary speed.

Yersinia pestis V protein epitopes recognized by CD4 T cells

Pneumonic plague, an often-fatal disease for which no vaccine is presently available, results from pulmonary infection by the bacterium Yersinia pestis. The Y. pestis V protein is a promising vaccine candidate, as V protein immunizations confer to mice significant protection against aerosolized Y. pestis. CD4 T cells play central roles during vaccine-primed immune responses, but their functional contributions to Y. pestis vaccines have yet to be evaluated and optimized. Toward that end, we report here the identification of three distinct epitopes within the Y. pestis V protein that activate CD4 T cells in C57BL/6 mice. To our knowledge, these are the first identified CD4 T-cell epitopes in any Y. pestis protein. The epitopes are restricted by the I-A(b) class II major histocompatibility complex molecule and are fully conserved between Y. pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica. Immunizing mice with a V protein-containing vaccine or with short peptides containing the identified epitopes primes antigen-specific production of interleukin 2 and gamma interferon by CD4 T cells upon their restimulation in vitro. Consistent with prior studies documenting protective roles for CD4 T cells during Y. enterocolitica infection, vaccinating mice with a 16-amino-acid peptide encoding one of the epitopes suffices to protect against an otherwise lethal Y. enterocolitica challenge. The identification of these epitopes will permit quantitative assessments of V-specific CD4 T cells, thereby enabling researchers to evaluate and optimize the contribution of these cells to vaccine-primed protection against pneumonic plague.

A strategic vaccine facility for the UK

This paper describes a proposed Strategic Vaccine Facility (SVF) to provide a capability to the UK to deal with new and emerging disease threats. It would underpin the vaccine manufacturing industry by developing expertise and technology to enable rapid manufacture of small batches of vaccines for emergency use against agents, such as bioterrorist agents and emerging diseases. It would have a rare ability to work with dangerous pathogens under containment, allowing the production of inactivated and live vaccines, which would be difficult in a conventional plant. The facility's output will include vaccine candidates and manufacturing protocols for transfer to industry, small vaccine batches for emergency use or clinical trials, and vaccine reference standards. It would also be available for manufacturing small batches of experimental and public health vaccines for the UK and the developing world, allowing clinical trials to be undertaken against key diseases.