Biomedical Sciences ETDs

Publication Date

5-1-2016

Abstract

Currently, over one-third of the global population is infected with tuberculosis (TB), one of the world's most deadly infectious diseases. The current vaccine against TB, Bacille Calmette-Guérin (BCG), is a live attenuated vaccine that is intradermally administered in over 150 countries around the world. Despite its widespread use, the vaccine has a variable protective efficacy of 0-80%, with the lowest efficacy rates in regions of the world where TB is most prevalent. This variability is partially due to environmental mycobacteria (EM) found in soil and water sources in areas of the world where BCG efficacy is poor. The research hypothesis of this work is that pulmonary BCG vaccination in EM-exposed hosts will be protective against TB. To test our hypothesis, we divided our research into three aims. In Chapter 2, we will focus on the first two research aims of this work which show: 1) Oral tolerance to EM is responsible for BCG protective variability, and 2) Pulmonary immunization is necessary for protective efficacy in individuals exposed to EM. To determine if the route of EM exposure played a role in immunosuppression against BCG, we exposed mice chronically, by either the oral or intradermal (ID) route, to Mycobacterium avium, a specific species of EM. Here we show the role of EM exposure route in the suppression of the murine immune response to BCG using flow cytometry and ELISA methodologies to determine a tolerant immunophenotype. This data suggests oral tolerance as a plausible mechanism for EM interference with ID BCG vaccination. Lastly, we use pulmonary immunization to generate a robust immune response to BCG in the lung airway, where EM immunity has not been generated. We again exposed mice chronically to M. avium by the oral route to mimic human exposure. Next, mice were vaccinated either by the ID route with BCG Pasteur to mimic the current BCG vaccination regimen or by the pulmonary route. We demonstrate that pulmonary BCG immunization is protective in EM-exposed mice later challenged with TB. Our data indicate that mucosal vaccination against TB by the pulmonary route may increase BCG vaccine efficacy by avoiding the immunosuppressive inference generated by chronic exposure to EM. In Chapter 3, we describe our third research aim, which shows that factorial design of excipients created a temperature-stable dry powder BCG that was suitable for pulmonary administration. First, dry powder formulations were assessed for storage temperature and moisture stability using a factorial design of excipients. Three optimal dry powder formulations were selected based on stability and flow characteristics, and these powders were spray-dried with live BCG to yield dry powders with a size in the range of 1-5 µm. BCG dry powders have been and will continue to be assessed for viability and shelf-life. This spray-dried live BCG is predicted to be highly stable and antigenic, providing the ideal inhalable vaccine delivery platform for EM-exposed mouse vaccination.

Keywords

Tuberculosis, Infectious disease, Mycobacteria, BCG, Vaccine, Dry powder, Pulmonary

Document Type

Dissertation

Language

English

Degree Name

Biomedical Sciences

Level of Degree

Doctoral

Department Name

Biomedical Sciences Graduate Program

First Advisor

Muttil, Pavan

First Committee Member (Chair)

Hall, Pamela

Second Committee Member

Cannon, Judy

Third Committee Member

Chackerian, Bryce

Fourth Committee Member

Timmins, Graham

Available for download on Monday, May 14, 2018

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