Francisella-primed T cells shift toward glycolysis during control of intramacrophage bacterial growth.

Correlates that predict protection against intracellular pathogens, including the highly pathogenic bacterium Francisella, are of interest to evaluate novel candidate vaccines and to facilitate clinical trials. We have previously established an in vitro co-culture assay that measures the control of intramacrophage bacterial replication by immune T cells and serves as a functional correlate. Moreover, this assay is a tool to identify additional molecular correlates of protection and to better understand protective T cell responses against Francisella. To study the role of metabolic shifts in protective T cell responses, we used co-cultures to profile the metabolic activities of macrophages and lymphocytes from mice vaccinated with F. tularensis Live Vaccine Strain (LVS). Previous studies indicated that LVS infection of macrophages dysregulates macrophage metabolism and limits glycolysis. Here, we show that co-cultures of LVS-infected macrophages with LVS-primed lymphocytes, which controlled intramacrophage bacterial growth, exhibited more glycolysis than co-cultures containing naïve cells. Further, LVS-primed lymphocytes exhibited a significant loss of respiratory capacity over time, consistent with a transition to an effector T cell state. Gene expression analyses of splenic T cells recovered from co-cultures revealed a set of metabolic genes that were not only upregulated in glycolytic LVS-primed T cells but could also be detected in total primed splenocytes and peripheral blood lymphocytes. Taken together, we find that LVS-primed effector T cells override bacterial-induced metabolic dysregulation in macrophages to control bacterial infection. These results support future studies exploring the use of metabolic intermediates as potential correlates of protection.IMPORTANCECurrently, there are no licensed vaccines against the deadly bacterium Francisella tularensis, which causes the disease called tularemia in people and in many animals. F. tularensis is also a potential bioterrorism agent. In this study, we showed that metabolic activity measurements of cells from mice immunized with a candidate tularemia vaccine correlated well with protection against disease. These results suggest a new approach to developing lab tests that can predict successful vaccination before undertaking a clinical trial.