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 (T_M) cells elicited by vaccination against intracellular bacteria in humans. Here we studied T_M subsets elicited by exposure to Francisella tularensis in humans as a model of immunity to intracellular bacteria. To this end, T_M 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 T_M cells, mostly CD45RA⁻CD62L⁻ and CD45RA⁺CD62L⁻. Based on the expression of CD27, integrins α₄/β_7, and α₄/β₁, it is likely that some of these T_M 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 T_M subsets with diverse homing characteristics.