Nasal Vaccination Induces Innate Lymphoid Cells (ILC1s) and NK Cells to Initiate the Lung IFN-γ Cascade That Supports Adaptive T Cells Responses to Brucella

Brucellosis is the most common zoonotic disease worldwide, usually transmitted from Brucella-infected livestock after consumption of contaminated foods or by aerosol exposure.  There are no vaccines for humans, and current livestock vaccines are only ~70% efficacious. To address this void, we developed a live, double-mutant Brucella melitensis (BMDM) vaccine that confers sterile immunity after mucosal vaccination. Protection is IFN-γ-dependent since IFN-γ^-/- mice succumb to infection. We hypothesize that BMDM’s potency is linked to ILC and NK cell stimulation to drive Th1-type responses.  To test this hypothesis, mice, nasally vaccinated with BMDM, were evaluated for innate and adaptive immune cell influx into the lungs. By 3 days post-vaccination, IFN-γ-producing ILCs, NK cells, and γδ T cells increased in the lungs by 2-, 3-, and 3-fold, respectively. By 5 days, the NK cells and ILCs contracted, and CD4⁺ and CD8⁺ T cells increased 2- and 5-fold, respectively; γδ T cells remained unchanged.  By 2 wks, CD8⁺ T cells were the dominant IFN-γ source, being 15-fold > naive lungs. The CD4⁺ and CD8⁺ T cell percentages were also impacted after wild-type BM challenge.  Unprotected and RB51 (rough mutant)-vaccinated mice showed no differences in their percentages of lung CD4⁺ and CD8⁺ T cells unlike challenged BMDM-vaccinated lungs showing 30% fewer CD4⁺ T cells and an equal percentage of CD8⁺ T cells resulting in a net increase in CD8⁺ T cells.  Thus, the vaccine composition and the route of its delivery impact the types of innate and adaptive immune cells responsive to immunization and challenge.