PROJECT SUMMARY The purpose of this R01 application is to investigate whether memory immunity induced in mice after vaccination with different types of candidates [rBCG, protein fusion in adjuvant, live attenuated mutant] induce similar or different subsets of CD4 memory T cells. Then, in a second series of studies, we will determine if this makes any difference if the vaccinated animal is then infected with newly emerging virulent clinical isolates of Mycobacterium tuberculosis which we have recently demonstrated differ in terms of their fitness, as well as their capacity to elicit regulatory T cells capable of interfering with protective immunity. These are practical issues in the field that are, as yet, not being addressed. Most of the proposed studies will be performed in the Flow Cytometry Core facility within our Level-III building at CSU [the PI is the Director] and will employ flow cytometry and high speed cell sorting, as well as our more usual highly standardized animal modeling techniques. Even if we do not see major differences in terms of the overall generation of memory T cell responses, the study outcomes may still reveal which type of vaccine “works best” [such head to head studies have not been done as yet, and this may spur the field to use these approaches to better prioritize current candidates].