The potent IFN-γ inducing fusion antigen Ag85B-ESAT-6 (85B6) is a lead subunit candidate to improve current vaccination against Mycobacterium tuberculosis (Mtb). The recombinant M. bovis BCG strain Myc3504 was constructed to secrete 85B6. It was based on commercial BCG strain Moreau Rio de Janeiro (BCGMoWT) which remains available for human oral administration. Myc 3504 induced higher levels of 85B6-specific IFN-γ circulating T-cells as compared to BCGMoWT. A novel needle-free mucosal immunization regimen combining oral prime with Myc3504 or BCGMoWT with intranasal boost with LTK-63-adjuvanted 85B6 was compared to subcutaneous prime-boost immunization. Strikingly whereas parenteral immunization induced sustained levels of 85B6-specific IFN-γ secretion by circulating T-cells, mucosal regimens induced barely detectable IFN-γ. Despite this, mice and guinea pigs immunized with the mucosal regimens were as efficiently protected against aerosol Mtb challenge as parenterally immunized animals. After Mtb challenge, anti-ESAT-6 IFN-γ responses sharply increased in non-vaccinated mice as a hallmark of infection. Parenterally immunized mice that controlled Mtb infection, displayed anti-ESAT-6 IFN-γ responses as high as non-immunized infected mice, compromising the possible use of ESAT-6 as a diagnostic tool. Interestingly, in mucosally immunized mice that were equally protected, post-challenge ESAT-6-specific IFN-γ T-cell response remained low.
Bibliographical noteFunding Information:
This work was supported by the European Commission (Mucosal Vaccines for Poverty Related Diseases) European Union Contract LSHP-CT-2003-503240. We are grateful to Jes Dietrich and Peter Andersen for constructive discussions and constant interest in the work. We greatly thank Dominique Buzoni-Gatel for critical reading of the manuscript. We thank Rino Rappuoli and Donata Medaglini for support. We are grateful to Giuseppe Del Juidice and Priscille Brodin for sharing reagents with us. We acknowledge Charlotte Fjordager for her technical advice on the ELISPOT assay and the support of the staff in the Biological Investigations Group at CEPR, HPA, Porton Down.
- Tuberculosis vaccines