Immune activation alters cellular and humoral responses to yellow fever 17D vaccine

Abstract

Background: Defining the parameters that modulate vaccine responses in African populations will be imperative to design effective vaccines for protection against HIV, malaria, tuberculosis, and dengue virus infections. This study aimed to evaluate the contribution of the patient-specific immune microenvironment to the response to the licensed yellow fever vaccine 17D (YF-17D) in an African cohort.

Methods: We compared responses to YF-17D in 50 volunteers in Entebbe, Uganda, and 50 volunteers in Lausanne, Switzerland. We measured the CD8+ T cell and B cell responses induced by YF-17D and correlated them with immune parameters analyzed by flow cytometry prior to vaccination.

Results: We showed that YF-17D-induced CD8+ T cell and B cell responses were substantially lower in immunized individuals from Entebbe compared with immunized individuals from Lausanne. The impaired vaccine response in the Entebbe cohort associated with reduced YF-17D replication. Prior to vaccination, we observed higher frequencies of exhausted and activated NK cells, differentiated T and B cell subsets and proinflammatory monocytes, suggesting an activated immune microenvironment in the Entebbe volunteers. Interestingly, activation of CD8+ T cells and B cells as well as proinflammatory monocytes at baseline negatively correlated with YF-17D-neutralizing antibody titers after vaccination. Additionally, memory T and B cell responses in preimmunized volunteers exhibited reduced persistence in the Entebbe cohort but were boosted by a second vaccination.

Conclusion: Together, these results demonstrate that an activated immune microenvironment prior to vaccination impedes efficacy of the YF-17D vaccine in an African cohort and suggest that vaccine regimens may need to be boosted in African populations to achieve efficient immunity.

Trial registration: Registration is not required for observational studies.

Funding: This study was funded by Canada's Global Health Research Initiative, Defense Threat Reduction Agency, National Institute of Allergy and Infectious Diseases, Bill & Melinda Gates Foundation, and United States Agency for International Development.

Figure 1. CONSORT diagram for (A) Lausanne and (B) Entebbe cohorts.

Figure 2. Differences in viremia after YF-17D vaccination in Lausanne and Entebbe.

(A) Vaccination schedule in the 2 cohorts and longitudinal sample collection time points used in this study. (B) Number of naive and boosted volunteers with or without detectable viremia in the plasma by quantitative RT-PCR 3 and 7 days after YF-17D vaccination. Numbers of subjects in each group are indicated within the bar graphs. VL, viral load. (C) YF-17D viral load measured in the plasma of naive vaccinees by quantitative RT-PCR 3 and 7 days after vaccination in Lausanne (white squares) and Entebbe (black dots).

Figure 3. Differences in innate cells between Lausanne and Entebbe cohorts.

(A) Frequency of exhausted CD16⁺ HLA-DR⁺ NK cells in CD3^– NKp46⁺ CD56⁺ NK cells at day 0, 3, and 7 after vaccination in Lausanne and Entebbe cohorts. (B) Frequency of activated CD16^– NK cells in CD3^– NKp46⁺ CD56⁺ NK cells secreting IFN-γ⁺ after ex vivo restimulation stained by intracellular cytokine staining at day 0, 3, and 7 after vaccination in Lausanne and Entebbe cohorts. (C) Frequency of CD14⁺ CD16⁺ inflammatory monocytes at baseline in Lausanne and Entebbe cohorts. White squares represent data points from the Lausanne cohort, and black dots represent data points from the Entebbe cohort.

Figure 4. Baseline differences in T cell subsets between Lausanne and Entebbe cohorts.

(A) Frequency of CD4 T cell memory subset distribution at baseline in Lausanne and Entebbe cohorts for central memory (TCM), transitional memory (TTM), and effector memory CD4 T cells (TEM), defined by expression of CCR7, CD27, and CD45RA. (B) Frequency of memory CD8 T cell subset distribution at baseline in Lausanne and Entebbe cohorts for transitional memory, effector memory, and terminally differentiated CD8 T cells (TEMRA), defined by expression of CCR7, CD27, and CD45RA. (C) Frequency of activated cells expressing PD-1 within the memory CD4 T cells at baseline in Lausanne and Entebbe cohorts. (D) Frequency of activated cells expressing ICOS within the memory CD4 T cells at baseline in Lausanne and Entebbe cohorts. (E) Frequency of activated cells expressing CD38 and HLA-DR within the memory CD8 T cells at baseline in Lausanne and Entebbe cohorts. (F) Frequency of Treg CD4 T cells, defined as CD3⁺CD4⁺CD45RA^–CD25⁺IL-7R^–Foxp3⁺, at baseline in Lausanne and Entebbe cohorts. White squares represent data points from the Lausanne cohort, and black dots represent data points from the Entebbe cohort.

Figure 5. Baseline differences in B cell subsets between Lausanne and Entebbe cohorts.

(A) Frequency of tissue-like memory B cell (CD19⁺CD27^–CD21^–) and activated memory B cell (CD19⁺CD27⁺CD21^–) subsets at baseline in Lausanne and Entebbe cohorts. (B) Frequency of naive (CD19⁺CD27^–CD21⁺) and resting memory B cell (CD19⁺CD27⁺CD21⁺) subsets at baseline in Lausanne and Entebbe cohorts. (C) Frequency of IgM⁺ and IgG⁺ memory B cell subsets at baseline in Lausanne and Entebbe cohorts. (D) Frequency of plasmablasts (CD38⁺ CD27⁺) in total B cells at baseline in Lausanne and Entebbe cohorts. White squares represent data points from the Lausanne cohort, and black dots represent data points from the Entebbe cohort.

Figure 6. Differences in A2/NS4B-specific CD8 T cells and NAb titers after YF-17D vaccination between Lausanne and Entebbe cohorts.

(A) Frequency of A2/NS4B-specific CD8 T cells in HLA-A*0201 vaccinees from Lausanne (white squares) and Entebbe (black dots) after vaccination. (B) Correlation between YF-17D NAb titers and frequency of A2/NS4B-specific CD8 T cells in both cohorts after vaccination. Gray dots depict samples from the Entebbe cohort. (C) YF-17D NAb titers in vaccinees from Lausanne (white squares) and Entebbe (black dots) after vaccination. Boosted individuals in both cohorts are depicted in gray. (D and E) YF-17D NAb titers in subjects with (white triangles) or without (black triangles) detectable viremia after vaccination (D) in the Lausanne cohort and (E) in the Entebbe cohort.

Figure 7. Negative associations between baseline immune activation and YF-17D vaccine response.

(A) Negative correlation between the frequency of CD38⁺ CD21⁺ CD27^– B cells at baseline and the YF-17D NAb titers in both cohorts. (B) Negative correlation between the frequency of tissue-like memory B cells at baseline and the YF-17D NAb titers in both cohorts. (C) Negative correlation between the expression level of PD-1 on memory CD8 T cells at baseline and the YF-17D NAb titers in both cohorts. (D) Negative correlation between the frequency of CD14⁺ CD16⁺ monocytes at baseline and the YF-17D NAb titers in both cohorts. Black dots represent data points from the Entebbe cohort, and white dots represent data points from the Lausanne cohort. (E) Negative correlation between the IL-10 secretion in the supernatant of PBMCs at baseline stimulated for 24 hours with YF-17D and the NAb titers in the Entebbe cohort. (F) Negative correlation between the absolute monocyte count at baseline and the YF-17D NAb titers in the Entebbe cohort.

Figure 8. Quality of the memory T and B cell responses after YF-17D vaccination in the Lausanne and Entebbe cohorts.

(A) Frequency of persisting A2/NS4B-specific CD8 T cell clonotypes at 2 time points after first vaccination in the Lausanne cohort and after first and boosted vaccination in the Entebbe cohort. (B) YF-17D NAb titers in the sera of boosted vaccinees in Lausanne and Entebbe cohorts longitudinally at baseline (day 3 or 0), day 7, and 1 year or day 84 after vaccination. Empty squares represent data points from the Lausanne cohort, and black dots represent data points from the Entebbe cohort. (C) Negative association between the NAb levels detected at baseline in Lausanne and Entebbe cohorts and the magnitude of NAb boosting after YF-17D revaccination. Red dots depict Lausanne subjects. (D) In the boosted subjects from Entebbe, NAb titers against YF-17D could not be detected at baseline when the first vaccination was 7 years or more in the past. (E) Number of boosted vaccinees with or without detectable viremia in the plasma after YF-17D vaccination in Lausanne and Entebbe cohorts. Numbers of subjects in each group are indicated within the bar graphs.