Investigation of mutant Mycobacterium smegmatis as a vector for a Tuberculosis vaccine

Tuberculosis (TB) is a disease caused by Mycobacterium tuberculosis (M.tb.). M.tb relies on a large repertoire of evasion strategies including secretion of proteins that alter host signaling and trafficking. M.tb possess the specialized type VII secretion system (T7SS), which has been demonstrated to aid in altering host pathways and promote bacterial survival. M. tb contains a total of five T7SS, called ESX-1 to ESX-5. ESX-1 is the most studied system and despite being dispensable for in vitro growth the system is required for virulence. The other ESX systems are much less characterized. The ESX-3 locus is ubiquitously present in all mycobacterial species and is regulated by iron and zinc; also it has been shown that esx-3 is involved in siderophore mycobactin based iron uptake. EspG, a protein encoded by the esx-3 locus, has been demonstrated to be involved in protein secretion and iron uptake. Recently, a mutant strain of M. smegmatis lacking esx-3, complemented with M. tb esx-3 has shown promise as a vaccine candidate, but the mechanism by which it activates the adaptive immune system is still unclear. We studied how the mutant M. smegmatis generate a different immune response than the wild type. We performed survival assays and checked cytokine profiles to assess the mechanism. We have observed growth impairment of the mutant when compared to the wild type. Thus, the interplay between the various immune responses towards eradicating the infection will be investigated during the course of this study, to generate better vaccines.