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EU Influenza Research  


Prove the mucosal adjuvanticity of LT mutants with influenza antigens for intranasal immunization

EC contribution: € 1.003.359
Duration: 36 months
Type: DM
Starting date: 1st February 2000

Mucosal administration of antigens is a global priority and is recommended by the 5th Framework Programme of the European Union. Many approaches have been adopted to develop vaccines that can be delivered without using syringes and that induce immune response at the mucosal sites that are often the portal of entry of pathogens. Here we propose to manufacture GMP lots of the mucosal adjuvants LTK63 and LTR72, two non-toxic derivatives of E. coli enterotoxin obtained by site-directed mutagenesis, and to test them in a clinical setting in human adult volunteers to obtain proof of concept that these molecules can be effectively used to adjuvant mucosal vaccines for human use. As a model, for this demonstration project we have chosen the influenza vaccine for intranasal administration.

Escherichia coli
Delivery of vaccines by mucosal route is one of the major goals of today's research. The advantage of easier delivery combined with the possibility of neutralizing pathogens at their portal of entry have made mucosal immunization one of the major targets of the European Union, WHO, and the US NIH. Furthermore, mucosal delivery by eliminating the use of syringes, would increase compliance and decrease the risk of spread of infectious diseases that has been reported by improper use of syringes during vaccination. In spite of the obvious advantages offered by mucosal vaccination, and the success obtained in this area in animal models in recent years, mucosal vaccines are not yet a reality, and it remains unclear whether they can be used for human vaccination. It is therefore mandatory to obtain proof of concept of the feasibility in humans of mucosal vaccines.

Most vaccines are unable to induce an immune response when delivered at mucosal sites. In order to make them immunogenic, strong mucosal adjuvants are required. In animals, the most potent mucosal adjuvants are the E. coli enterotoxin (LT) and cholera toxin (CT). Unfortunately, these two toxins cannot be used in humans and therefore their use as mucosal adjuvants has been restricted to animal studies. Recently, by site-directed mutagenesis, mutants of LT have been obtained (fig. 1) which are either completely non toxic, or with greatly reduced toxicity. Preclinical studies have shown that these mutants still act as mucosal adjuvants when used in animal models, and that the LT mutants are generally more active than the CT mutants. Two particular LT mutants, LTK63 and LTR72, that are completely non toxic or with very low residual activity, respectively (fig. 2), showed a good safety and adjuvanticity profile in preclinical studies, suggesting that they could be proposed for human studies.

A primary objective of the present project is to obtain proof of concept that LTK63 and LTR72, which are considered to be among the most promising mucosal adjuvants available today, are safe when mucosally administered to humans and enhance the immune response to antigens that are co-administered. The vaccine that will be used in this proof of principle study will be a subunit influenza vaccine including, in addition to H3N2 and B influenza antigens also an antigen, H5N3, against a potentially pandemic strain

A second objective is to prove that the intranasally delivered influenza vaccine induces protective levels of immunity comparable to those elicited by conventional influenza vaccines parenterally administered.

A third objective is to demonstrate that an effective pandemic vaccine can also be administered by the mucosal route.

The overall objective of the proposal is to demonstrate that mucosal vaccines, which have been very promising in animal models but have made very slow progress in their development for human use, can be an effective alternative for vaccine delivery.
If successful, this project will also pave the way for the development of other mucosal vaccines using the same or similar technologies.

Expected results

  1. Manufacturing of GMP lots of LTK63 and LTR72.
  2. Manufacturing of GMP lots of subunit influenza antigens.
  3. Combination of a mucosal adjuvant with influenza antigens, with and without an ad hoc delivery system, in a vaccine formulation to be delivered intranasally.
  4. Testing in human adult volunteers the safety and immunogenicity of the several mucosal vaccine formulations.
  5. Clinical comparison of the selected mucosal vaccine formulation with the conventional influenza vaccine for parenteral use.

Potential applications
Overall, we expect to obtain proof of concept that LTK63 and LTR72 can be used for the development of safe and immunogenic influenza vaccines for human use. The results deriving from this project will also be useful to potentially open the way to the clinical development of many other mucosal vaccines, including the development of vaccines against traveler's diarrhea, which could be targeted by recombinant LT mutants produced in E. coli.

Key words
Control of infectious diseases, pre-clinical development of vaccines, transdisease vaccinology

Project coordinator

Audino Podda
Chiron SpA
Via Fiorentina, 1 IT - 53100 Siena, Italy
T: (+39) 0577 243496
F: (+39) 0577 243551

List of partners (listed countrywise)

IT – University of Siena - Ist. Igiene, Siena
IE – Department of Biochemistry, Trinity College, Dublin
UK – PHLS Central Public Health Laboratory, London
IT – University of Milano - Ist. Virologia, Milan
SE – Department of Medical Microbiology, University of Göteborg