Oral Vaccination with Subunit Vaccines Protects Animals against Aerosol Infection withMycobacterium tuberculosis

Abstract

Immunity against Mycobacterium tuberculosis depends largely on activation of cell-mediated responses, and gamma interferon has been shown to play a crucial role in this process in both humans and animal models. Since the lung is normally the organ in which infection is initiated and is the major site of pathology, immune responses in the lung play a significant role in restricting initial infection with M. tuberculosis. The aim of the present study was to stimulate efficient immunity in the lung by targeting the gut mucosa. Detoxified monophosphoryl lipid A (MPL) has been shown to be a relatively nontoxic adjuvant which efficiently promotes the induction of type 1 responses when it is given by the traditional subcutaneous route. We have therefore compared subcutaneous immunization of mice to oral immunization by using a model subunit vaccine carrying two immunodominant proteins from M. tuberculosis, in combination with MPL-based adjuvants. While less effective when used to prime a response, a heterologous priming and boosting vaccination strategy employing oral boosting induced significant systemic type 1 responses which equaled and surpassed those attained by subcutaneous immunization protocols. Moreover, the increased immune responses observed correlated with the induction of substantial protection against subsequent aerosol infection with virulent M. tuberculosis at levels comparable to, or better than, those obtained by multiple subcutaneous vaccinations. These results demonstrate that booster vaccinations via mucosal surfaces, by combining efficient subunit vaccines with the potent adjuvant MPL, may be an effective method of addressing some of the shortcomings of current vaccination strategies.

Combination of the Cationic Surfactant Dimethyl Dioctadecyl Ammonium Bromide and Synthetic Mycobacterial Cord Factor as an Efficient Adjuvant for Tuberculosis Subunit Vaccines

“…The antigen preparations were kept at Ϫ80°C until use. Both Ag85B-ESAT-6 and ESAT-6 have been titrated across the range of 0.01 to 100 g and were used in these studies at 1 and 10 g per immunization, respectively, which are doses repeatedly shown to induce strong immune responses in previous studies by our group (11,22,38,47).…”

“…Cells were cultured with antigen in vitro for 72 h before staining. Although not a direct ex vivo picture of the immune status in the mice, earlier studies had shown that this protocol improved the sensitivity of the assay for detecting even small differences in cell populations among groups (unpublished data) over that of the shorter stimulation that was previously used (22). After 72 h of incubation, cells were stained for the surface expression of CD4 and CD8 in addition to intracellular IFN-␥.…”

Single Mucosal, but Not Parenteral, Immunization with Recombinant Adenoviral-Based Vaccine Provides Potent Protection from Pulmonary Tuberculosis

“…Detrimental immunopathology that may be caused by direct application of live mycobacterial vaccines at the mucosal site, especially at the respiratory tract, is of particular safety concern (5,9). Furthermore, although promising, recombinant plasmid DNA or protein/subunit vaccines, when given parenterally, are unable to elicit superior protection over BCG vaccine (15)(16)(17) and when given mucosally cannot lead to effective immune activation (17)(18)(19)(20). Therefore, the development of safe and efficacious respiratory mucosal TB vaccines has remained a major challenge to TB vaccinologists.…”

Mucosal Administration of Ag85B-ESAT-6 Protects against Infection withMycobacterium tuberculosisand Boosts Prior Bacillus Calmette-Guérin Immunity

“…Regarding the Ag part of a mucosal vaccine against TB, we recently showed that vaccination with a fusion protein consisting of Ag85B and ESAT-6 (Ag85B-ESAT-6) promoted a strong immune response, which was highly protective against TB in the mouse, guinea pig, and nonhuman primate models (22)(23)(24)(25)(26). However, Ag85B-ESAT-6 has never been examined as an i.n.…”