Dynamics of the CD8 T-cell response following yellow fever virus 17D immunization

Abstract

Management of yellow fever is focused on the prevention of illness by the use of the yellow fever virus (YFV) 17D vaccine. The role of neutralizing antibodies in protection is generally accepted with YFV-specific T cells likely contributing to the control of viral replication. We studied CD8(+) T-cell responses to four defined human leucocyte antigen-B35-restricted epitopes in YFV vaccine recipients as a model of the kinetics of cytotoxic T-lymphocyte responses to an acute human viral infection. Multiple features of these epitope-specific responses were analysed after vaccination including magnitude, cytokine production, phenotype and T-cell receptor repertoire. Peak peptide-specific interferon-gamma (IFN-gamma) responses of almost 1% of CD8(+) T cells were seen as early as 2 weeks post-vaccination; however, dominant responses varied between donors. Peptide-specific responses were still detectable at 54 months post-vaccination. Tetramer-positive cells, at high frequencies, were detected as early as 7-9 days, before detectable IFN-gamma-producing cells, suggesting a defect in the functional capacity of some antigen-specific cells early post-vaccination. The predominant memory phenotype of the tetramer-positive population was a differentiated effector (CD45RA(+) CCR7(-) CD62L(-)) phenotype. The T-cell receptor Vbeta analysis revealed a diverse oligoclonal repertoire in tetramer-positive T-cell populations in two individuals. These characteristics of the YFV-specific T-cell response could contribute to vaccine effectiveness.

Figure 1

Kinetics of interferon-γ (IFN-γ) response to human leucocyte antigen (HLA) B35 restricted yellow fever virus (YFV) epitopes in YFV 17D vaccinated individuals. Intracellular cytokine staining (ICS) assays were performed on peripheral blood mononuclear cell (PBMC) obtained from three YFV vaccine recipients (Donor A, B and C) at various time-points post-immunization and results were analysed by flow cytometry. Connected line represents the cumulative responses for the epitopes measured at each time-point. Frequencies represent the percentage of IFN-γ-producing CD3⁺ CD8⁺ cells (minus the background staining of unstimulated samples).

Figure 2

Kinetics of phenotypic marker expression by yellow fever virus (YFV) tetramer-positive population over the post-vaccination period. Serial peripheral blood mononuclear cells from three YFV 17D-vaccinated donors were analysed as described in the Materials and methods section with all events gated on a CD3⁺ CD8⁺ population and then on the tetramer-positive population. Values shown represent the number of tetramer-positive CD8⁺ T cells expressing the indicated phenotypic markers at each time-point (a) NS1 tetramer-positive population in Donor A, (b) NS2b tetramer-positive population in Donor B, (c) E tetramer-positive population in Donor C. CCR7⁺ CD45RA staining not performed in this donor.

Figure 3

Representative phenotypic marker staining of yellow fever virus (YFV)-specific cells in Donor A, B and C. Donor A, B and C peripheral blood mononuclear cells (PBMC) taken at specified time-points post-vaccination were stained for CD8, for tetramer-positive cells and then for combinations of phenotypic markers. (a) NS1 tetramer-positive cells from Donor A PBMC taken 46 months post-vaccination stained with the CDRA and CCR7 markers, (b) NS2b tetramer-positive cells from Donor B PBMC taken 7 days post-vaccination stained with CD45RO and CD45RA markers (c) E tetramer-positive cells from Donor C taken 2 months post-vaccination stained with CD27 and CD28 markers

Figure 4

Analysis of T-cell receptor (TCR) Vβ usage in NS1 and E tetramer-positive populations after yellow fever virus (YFV) 17D vaccination. (a) Immune cells from Donor A at four post-vaccination time-points were stained with NS1 tetramer and with antibodies to CD8 and a panel of Vβ families; (b) immune cells from Donor C at three post-vaccination time-points were stained with E tetramer and antibodies to CD8 and a panel of Vβ families. Data are summarized in a pie chart where each slice of the pie represents the proportion of CD8 T cells expressing a particular Vβ subtype. Individual Vβ subsets shown represented at least 8% of the total Vβ subsets detected at any one time-point. All other Vβ subsets were grouped in the Other category. Results are from one experiment.