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. 2024 Oct 10;20(10):e1012566.
doi: 10.1371/journal.ppat.1012566. eCollection 2024 Oct.

Humoral and T-cell-mediated responses to an insect-specific flavivirus-based Zika virus vaccine candidate

Affiliations

Humoral and T-cell-mediated responses to an insect-specific flavivirus-based Zika virus vaccine candidate

Danielle L Porier et al. PLoS Pathog. .

Abstract

Flaviviruses represent a significant global health threat and relatively few licensed vaccines exist to protect against them. Insect-specific flaviviruses (ISFVs) are incapable of replication in humans and have emerged as a novel and promising tool for flavivirus vaccine development. ISFV-based flavivirus vaccines have shown exceptional safety, immunogenicity, and efficacy, however, a detailed assessment of the correlates of protection and immune responses induced by these vaccines are still needed for vaccine optimization. Here, we explore the mechanisms of protective immunity induced by a previously created pre-clinical Zika virus (ZIKV) vaccine candidate, called Aripo/Zika (ARPV/ZIKV). In brief, immunocompromised IFN-αβR-/- mice passively immunized with ARPV/ZIKV immune sera experienced protection after lethal ZIKV challenge, although this protection was incomplete. ARPV/ZIKV-vaccinated IFN-αβR-/- mice depleted of CD4+ or CD8+ T-cells at the time of ZIKV challenge showed no morbidity or mortality. However, the adoptive transfer of ARPV/ZIKV-primed T-cells into recipient IFN-αβR-/- mice resulted in a two-day median increase in survival time compared to controls. Altogether, these results suggest that ARPV/ZIKV-induced protection is primarily mediated by neutralizing antibodies at the time of challenge and that T-cells may play a comparatively minor but cumulative role in the protection observed. Lastly, ARPV/ZIKV-vaccinated Tcra KO mice, which are deficient in T-cell responses, experienced significant mortality post-challenge. These results suggest that ARPV/ZIKV-induced cell-mediated responses are critical for development of protective immune responses at vaccination. Despite the strong focus on neutralizing antibody responses to novel flavivirus vaccine candidates, these results suggest that cell-mediated responses induced by ISFV-based vaccines remain important to overall protective responses.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Passive transfer of ARPV/ZIKV-induced antibodies partially protects naïve mice.
Four-week-old C57BL/6J mice were vaccinated as previously described. At 30 days post-vaccination, sera were pooled according to immunization group and injected into naïve 8–9 week-old IFN-αβR-/- mice. (a) One day prior to challenge, mice were bled to quantify the amount of ZIKV-specific nAb circulating in the blood. Dotted lines indicate the lower 20-fold and upper 640-fold limits of detection (LOD). Mice were challenged with ZIKV, except for the unchallenged group. Mice were then monitored for (b) survival and (c) weight change post-challenge. (d) Sera were collected for 1–4 days post-challenge (dpc) to quantify viremia. LOD is 100 pfu/mL. (a, d) Columns represent mean values, and symbols represent individual data points. (c) Symbols represent mean values. Error bars indicate SD of the mean. Asterisks indicate significance compared to healthy mice (unchallenged controls), unless otherwise indicated: not significant (ns), p ≤ 0.033 (*), p ≤ 0.0002 (***), p ≤ 0.0001 (****).
Fig 2
Fig 2. Depletion of T-cells in ARPV/ZIKV-vaccinated mice at challenge show neutralizing antibodies offer complete protection from ZIKV challenge.
Four-week-old IFN-αβR-/- mice were vaccinated as previously described. Beginning 27 days post-vaccination (dpv), T-cell depleting antibodies were administered according to depletion group (anti-CD4+, anti-CD8+, both, or isotype depletion). Mice were challenged with ZIKV at 30 dpv. Mice were monitored for (a-c) survival and (d-f) weight change post-challenge. (g-i) Sera were collected for 1–4 days post-challenge to quantify viremia. LOD is 100 pfu/mL. (d-f) Symbols represent mean values. (g-i) Columns represent mean values, and symbols represent individual data points. Error bars indicate SD of the mean. Asterisks indicate significance compared to isotype depleted control mice, unless otherwise indicated: not significant (ns), p ≤ 0.033 (*).
Fig 3
Fig 3. Depletion of T-cells in ARPV/ZIKV-vaccinated immunocompetent mice at challenge did not significantly impact clinical outcomes.
Four-week-old C57BL/6J mice were vaccinated as previously described. Regimens of in vivo T-cell depletion monoclonal antibody were administered according to depletion group (anti-CD4+, anti-CD8+, both, or isotype depletion). At 30 days post-vaccination, mice were challenged with ZIKV. Mice were then monitored for (a) survival and (b) weight change post-challenge. (c) Sera were collected for 1–4 days post-challenge. LOD is 100 pfu/mL. (b) Symbols represent mean values. (c) Columns represent mean values, and symbols represent individual data points. Error bars indicate SD of the mean. Asterisks indicate significance compared to isotype depleted control mice, unless otherwise indicated: not significant (ns), p ≤ 0.002 (**), p ≤ 0.0002 (***), p ≤ 0.0001 (****).
Fig 4
Fig 4. Adoptive transfer of ARPV/ZIKV-primed T-cells to naïve mice pre-challenge resulted in increased median survival times.
Single-cell suspensions of CD4+ or CD8+ T-cells were prepared from the spleens of C57BL/6J mice 30 days after vaccination, then injected into naïve IFN-αβR-/- mice 24 hours before challenge. Mice were then monitored for survival (a, b) and weight change (c, d). (c, d) Symbols represent mean values. Error bars indicate SD of the mean. Asterisks indicate significance compared to the “no transfer” group, unless otherwise indicated: not significant (ns), p ≤ 0.033 (*), p ≤ 0.002 (**), p ≤ 0.0002 (***), p ≤ 0.0001 (****).
Fig 5
Fig 5. T-cells are critical for the development of an effective immune response to ARPV/ZIKV vaccination.
Four-week-old mice with deficient B-cell responses (muMt-), deficient T-cell responses (Tcra KO), or both (Rag1 KO) were vaccinated as previously described. At 30 days post-vaccination, all mice were challenged with ZIKV. Tcra KO mice (a-b), muMt- mice (c-d), and Rag1 KO mice (e-f) were then monitored for survival and weight change. (g-i) Sera were collected for 1–4 days post-challenge to quantify viremia. Dotted lines indicate the 100 pfu/mL limit of detection (LOD). (b, d, f) Symbols represent mean values. (g-i) Columns represent mean values, and symbols represent individual data points. Error bars indicate SD of the mean. Asterisks indicate significance compared to sham-vaccinated control mice, unless otherwise indicated: not significant (ns), p ≤ 0.033 (*), p ≤ 0.002 (**).

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