Title:
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Immune responses induced by Mycobacterium bovis BCG, and modified vaccinia virus Ankara expressing mycobacterial antigen 85A, when delivered as mucosal or systemic vaccinations to non-human primates
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Vaccination is the most effective way to control a global disease such as tuberculosis
(TB); however, conventional intradermal (ID) injection of the licensed TB vaccine,
BCG, provides only limited protection. Mucosal delivery of vaccines to pulmonary
surfaces is a loqical approach to generate a protective immune response at the
primary site of infection.
Non-human primate (NHP) models have been used to compare the safety and
immunogenicity of mucosal and ID TB vaccination strategies using BCG and
modified vaccinia virus Ankara expressing TB antigen 85A (MVA85A). Mucosal
vaccination strategies were well tolerated and induced potent antigen-specific CD4
and CD8 T-cell responses, including polyfunctional T-cells in the lung and peripheral
immune compartment. Systemic immune responses induced by mucosal BCG
revaccination and MVA85A boost vaccination were relatively transient, whereas
antigen-specific responses detected in mucosal tissues and bronchoalveolar lavage
(BAL) samples were more persistent. Unlike ID vaccination, aerosol vaccination with
MVA85A did not induce a detectable serum anti-vector antibody response.
Polyfunctional CD4 T-cells were detected in BAL and peripheral blood mononuclear
cells (PBMC) following aerosol and ID BCG vaccination. The immunogenicity of
aerosol-delivered BCG was dose dependent and consisted of both Th 1 and Th 17
cytokine responses. The aerosol BCG-induced T -cell response measured in BAL
and PBMC was significantly delayed relative to ID-vaccination, with a similar trend
apparent in serum anti-PPD IgG levels. Mucosal CD4 and CD8 populations were
polarised toward an effector memory phenotype, whereas frequencies of peripheral
central memory T-cells increased significantly, and remained elevated, following
aerosol vaccination. Expression of the 04131 integrin lung homing markers remained
consistently high on C04 and C08 T-cells isolated from BAL, and varied on
peripheral T -cells.
These studies indicate, that delivery of TB vaccines to the pulmonary surfaces is
practical and safe, with the potential to target the cell-mediated immune response to
the lung. The comparison of aerosol and ID BCG vaccination highlighted differences
in the mycobacteria-specific immune response that may contribute to the enhanced
protection previously reported from aerosol BCG studies, and will inform future
investigations of mucosal TB vaccination strategies.
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