Fig. 6. WT mice depleted of CD4+ and CD8 + T-cells and CD8^−/− mice are protected by repNP vaccination.

On D5 p.i., groups of mice (N = 6) from Fig. 3 were euthanized and evaluated for cellular immune responses to infection via (a) IFNу ELISpot shown as cumulative responses against peptides spanning the entire CCHFV NP (SFC: spot forming cells). For T-cell depletion study, WT C57BL6/J mice were (b) vaccinated with Sham or repNP RNA on day −28 relative to lethal CCHFV challenge. On days −5, −2, and +5 relative to CCHFV challenge, mice were treated with isotype or αCD4 and αCD8 antibody to deplete mice of T-cell populations. On D0, groups of mice were evaluated for immunological response to vaccine or treated with MAR1−5A3 antibody and infected with a lethal dose of 100 TCID₅₀ CCHFV strain UG3010. Mice (N = 8) were (c) weighed daily and monitored for (d) survival until day 14 p.i., On D5 p.i., groups of mice (N = 6) were evaluated for (e) depletion of CD4+ and CD8 + T-cell populations via Flow Cytometry. Antibody treatment achieved a 96.3% depletion of CD4 + T-cells and 98.5% depletion of CD8 + T-cells. In the second study, groups of WT C57BL6/J and CD8^−/− mice were vaccinated and infected as above. Mice (N = 8) were (f) weighed daily and monitored for (g) survival until day 14 p.i. Dashed lines indicate limit of detection. Data shown as mean plus standard deviation. Significance was calculated using one-way ANOVA; ns P > 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. Exact p-values: (d) both P = 0.0002, (g) both P = 0.0002.