Activities of Murine Peripheral Blood Lymphocytes Provide Immune Correlates That Predict Francisella tularensis Vaccine Efficacy

Abstract

We previously identified potential correlates of vaccine-induced protection against Francisella tularensis using murine splenocytes and further demonstrated that the relative levels of gene expression varied significantly between tissues. In contrast to splenocytes, peripheral blood leukocytes (PBLs) represent a means to bridge vaccine efficacy in animal models to that in humans. Here we take advantage of this easily accessible source of immune cells to investigate cell-mediated immune responses against tularemia, whose sporadic incidence makes clinical trials of vaccines difficult. Using PBLs from mice vaccinated with F. tularensis Live Vaccine Strain (LVS) and related attenuated strains, we combined the control of in vitro Francisella replication within macrophages with gene expression analyses. The in vitro functions of PBLs, particularly the control of intramacrophage LVS replication, reflected the hierarchy of in vivo protection conferred by LVS-derived vaccines. Moreover, several genes previously identified by the evaluation of splenocytes were also found to be differentially expressed in immune PBLs. In addition, more extensive screening identified additional potential correlates of protection. Finally, expression of selected genes in mouse PBLs obtained shortly after vaccination, without ex vivo restimulation, was different among vaccine groups, suggesting a potential tool to monitor efficacious vaccine-induced immune responses against F. tularensis. Our studies demonstrate that murine PBLs can be used productively to identify potential correlates of protection against F. tularensis and to expand and refine a comprehensive set of protective correlates.

Aerosol prime-boost vaccination provides strong protection in outbred rabbits against virulent type A Francisella tularensis

“…tularensis is a facultative intracellular bacterium, cellular immune responses are thought to be of prime importance in protection. Indeed, experiments in mice have shown that T cell production of IFN-γ or control of bacterial replication in infected macrophages are associated with protection [ 24 , 25 ]. A recent paper has shown that cell-mediated immune responses can also be seen in human PBMC from LVS recipients bolstering the potential for measuring cellular immune responses in a clinical trial [ 26 ].…”

The Diversity Outbred Mouse Population Is an Improved Animal Model of Vaccination against Tuberculosis That Reflects Heterogeneity of Protection

“…protection (29)(30)(31)(32), but we recognized that inbred mouse models may be limited by lack of genetic diversity; we therefore initiated studies in DO mice in part to extend that work. Using the only currently licensed tuberculosis vaccine, we found that the DO population readily controlled systemic BCG bacterial burdens (Fig.…”

Monophosphoryl Lipid A Enhances Efficacy of a Francisella tularensis LVS-Catanionic Nanoparticle Subunit Vaccine against F. tularensis Schu S4 Challenge by Augmenting both Humoral and Cellular Immunity

“…Functional assays utilizing coculture of F. tularensis infected BMDM and splenocytes from immunized mice were performed as previously described (35,38). Briefly, bone marrow was harvested from immunologically naive mice and cultured for 1 week in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% conditioned medium from the LADMAC cell line as a source of macrophage colony-stimulating factor (M-CSF), as well as 10% fetal bovine serum (FBS) (Atlanta Biologicals, Flowery Branch, GA), 200 mM L-glutamine (Gibco, Grand Island, NY), and 10 mM HEPES buffer (Sigma).…”

“…Previous studies have shown that treatment of macrophages with IFN-␥ results in macrophage activation and killing of intracellular organisms (35,38). Therefore, in the same coculture system, the ability of the splenocytes to control intramacrophage replication of F. tularensis LVS was analyzed.…”

“…3. Two weeks after final immunization, splenocytes were harvested from naive mice or mice that had been immunized with VϩMPL, LVS-V, or LVS-VϩMPL, and these cells were cocultured with F. tularensis LVS-infected bone marrow-derived macrophages (BMDM), as described previously (35,38). After 72 h of coculture, the nonadherent cells were analyzed by flow cytometry, using a gating strategy for discriminating subsets of T cells (Fig.…”