Generation of heterogeneous memory T cells by live attenuated tularemia vaccine in humans

There is very limited evidence concerning the phenotype, function, and homing characteristics of memory T (TM) cells elicited by vaccination against intracellular bacteria in humans. Here we studied TM subsets elicited by exposure to Francisella tularensis in humans as a model of immunity to intracellular bacteria. To this end, TM cells were evaluated in two groups: (1) subjects immunized with live attenuated tularemia vaccine by skin scarification and (2) tularemia naturally infected subjects. In both groups the immune responses were mediated by CD4+ and CD8+ effector TM cells, mostly CD45RA−CD62L− and CD45RA+CD62L−. Based on the expression of CD27, integrins α4/β7, and α4/β1, it is likely that some of these TM cells have lytic potential and the ability to enter both mucosal and non-mucosal sites. Thus, regardless of whether by immunization or natural exposure, tularemia antigens elicited a broad spectrum of specific TM subsets with diverse homing characteristics.