Live mucosal vaccination stimulates potent protection via varied CD4+ and CD8+ T cell subsets against wild-type Brucella melitensis 16M challenge

Abstract

Re-emerging zoonotic pathogen Brucella spp. continues to impact developing countries and persists in expanding populations of wildlife species in the US, constantly threatening infection of our domestic herds. The development of improved animal and human vaccines remains a priority. In this study, immunity to a novel live attenuated B. melitensis strain, termed znBM-mC, was characterized. An oral prime, intranasal (IN) boost strategy conferred exquisite protection against pulmonary challenge, with wild-type (wt) B. melitensis providing nearly complete protection in the lungs and spleens from brucellae colonization. Vaccination with znBM-mC showed an IFN-γ+ CD8+ T-cell bias in the lungs as opposed to Rev 1-vaccinated mice showing IFN-γ+ CD4+ T-cell inclination. Lung CD4+ and CD8+ effector memory T cells (TEMs) increased over 200-fold; and lung CD4+ and CD8+ resident memory T cells (TRMs) increased more than 250- and 150-fold, respectively. These T cells served as the primary producers of IFN-γ in the lungs, which was essential for vaccine clearance and the predominant cytokine generated pre-and post-challenge with wt B. melitensis 16M; znBM-mC growth could not be arrested in IFN-γ−/− mice. Increases in lung TNF-α and IL-17 were also induced, with IL-17 being mostly derived from CD4+ T cells. Vaccination of CD4−/−, CD8−/−, and B6 mice with znBM-mC conferred full protection in the lungs and spleens post-pulmonary challenge with virulent B. melitensis; vaccination of IL-17−/− mice resulted in the protection of the lungs, but not the spleen. These data demonstrate the efficacy of mucosal vaccine administration for the generation of protective memory T cells against wt B. melitensis.

Activation of mucosal immunity as a novel therapeutic strategy for combating brucellosis

“…This finding disputes the idea that route of vaccination is the only factor, but the mutant is also an important consideration. These collective findings demonstrate that immune protection can be achieved with either CD4 + or CD8 + T cells, but eliciting memory responses proximal the site of infection, e.g., the stimulation of TRMs, are more apt to protect, possibly preventing or limiting brucellae dissemination as suggested by the ΔznuA B. melitensis (Clapp et al, 2016), znBAZ (Wang et al, 2020), and znBM-mC (Goodwin et al, 2022) studies.…”

“…Mucosal vaccination with znBAZ or znBM-mC stimulated robust CD8 + and CD4 + TRM responses in the lungs to facilitate protection against pulmonary wt challenge, and may have prevented further brucellae dissemination (Wang et al, 2020;Goodwin et al, 2022). Thus, the stimulation of alternative immune pathways is beneficial, and may improve vaccine efficacy warranting further testing.…”

“…Essential sources of IFN-γ include CD4 + ( Murphy et al, 2001 ; Vitry et al, 2012 ; Yingst et al, 2013 ; Vitry et al, 2014 ; Yang et al, 2016 ), CD8 + T cells ( Clapp et al, 2011 ; Durward-Diioia et al, 2015 ; Clapp et al, 2016 ; Yang et al, 2016 ; Wang et al, 2020 ), or both ( Araya et al, 1989 ; Hanot Mambres et al, 2016 ; Goodwin et al, 2022 ). NK cells also provide IFN-γ to activate macrophages and DCs ( Dornand et al, 2004 ; Bhagyaraj et al, 2021 ).…”

“…As a result, both CD4 + and CD8 + TRMs were elicited to greater levels subsequent to znBAZ vaccination than the level seen in those mice similarly vaccinated with RB51 ( Wang et al, 2020 ). In a similar vein, the same genetic mutations were performed to generate the ΔznuA Δ norD B. melitensis mutant carrying the mCherry reporter gene (znBM-mC; Goodwin et al, 2022 ). As accomplished with znBAZ vaccination, CD4 + and CD8 + TRMs were induced in the lungs of mice orally primed, nasally boosted with znBM-mC ( Table 1 ), but TEMs and TCMs were also detected ( Goodwin et al, 2022 ).…”

“…In a similar vein, the same genetic mutations were performed to generate the ΔznuA Δ norD B. melitensis mutant carrying the mCherry reporter gene (znBM-mC; Goodwin et al, 2022 ). As accomplished with znBAZ vaccination, CD4 + and CD8 + TRMs were induced in the lungs of mice orally primed, nasally boosted with znBM-mC ( Table 1 ), but TEMs and TCMs were also detected ( Goodwin et al, 2022 ). This evidence suggests that the mode of vaccination can contribute to types of IFN-γ + and polyfunctional T cells, as well as to the TRMs induced, but cannot diminish the influence of the Brucella ’s mutations used to develop these strains.…”