PLAGVAC

Yersinia pestis, the causative agent of plague, killed millions of humans during three pandemics and is among the deadliest bacteriological agents affecting man. Plague has recently been included in the list of re-emerging diseases and Y. pestis is classified as a potential biological weapon for terrorist use. Because antibiotic resistant strains of Y. pestis have been observed or could be engineered for evil use, vaccination against plague might become the only means to fight against the disease. No safe and effective plague vaccine is currently available. Most efforts made in the recent years were focused on subunit formulations combining the capsular F1 antigen and the V antigen (LcrV). Such vaccines however require the use of an adjuvant such as the controversial Aluminium hydroxyde, and repeated injections to protect, and this protection can be easily circumvented by genetical engineering Y. pestis for bioterrorist use. We followed a vaccine strategy based on oral vaccination with a live, attenuated strain of Yersinia pseudotuberculosis, as this species is genetically almost identical to Y. pestis, but of much lower pathogenicity and higher genomic stability. We have recently constructed an attenuated Y. pseudotuberculosis strain, designated V674TnF1, by deletion of genes coding for three essential virulence factors from the IP32953 strain which genome is known. It was also induced to stably produce the Y. pestis F1 pseudocapsule to increase its immunogenicity. Upon a single oral vaccination, this strain confers 100% protection against a lethal pneumonic plague challenge with a dose of up to 3000 x LD50 of the fully virulent Y. pestis CO92 strain. V674TnF1 also provides 100% protection against bubonic plague, even when an infectious dose of 104 x LD50 is administered. To our knowledge, the protection against bubonic and pneumonic plague conferred by a single dose of V674TnF1 is probably one of the most efficient -if not the most efficient- ever reported. A patent application procedure is currently ongoing. The present project consist in achieving the steps preliminary to clinical trials in humans. These are 1) the production of a clinical-grade form of the vaccine strain, by reconstructing the vaccine strain without antibiotics –resistance cassettes, as previously used to construct the V674Tn-F1 strain. 2) the verification that the new strain, which will be named V.Yptb-F1, retained the desired vaccinial properties. This implies that it has a strong attenuation of virulence, the ability to persist in vivo in the gut, and the ability to induce a humoral and cellular immune response resulting in 100% protection of animals against bubonic and pneumonic plague. 3) the setup of assays able to predict protective immunity by the measurement of immunological parameters named “correlates of immunity“, whic can be Yersinia pestis-specific antibodies or cell populations. 4) the evaluation of the human immune response in humanized mice, induced by vaccination, to confer protection against plague, before starting clinical trials in humans, by vaccinating and evaluating humanized HIS mice. 5) to protect the intellectual property of the vaccine and the development of scenarios to exploit the potential commercial value of the vaccine, by collaborations with the industry.