Fifteen patients using different immunosuppressive drugs and 30 healthy individuals vaccinated 0–22 years ago were included. The serological response was measured using the plaque reduction neutralization test (PRNT). CD8+ and CD4+ T-cell responses were measured following proliferation and re-stimulation with YFV peptide pools. Phenotypic characteristics and cytokine responses of CD8+ T-cells were determined using class I tetramers.
The geometric mean titre of neutralizing antibodies was not different between the groups (p = 0.77). The presence of YFV-specific CD4+ and CD8+ T-cell did not differ between patients and healthy individuals (15/15, 100.0% vs. 29/30, 96.7%, p = 0.475). Time since vaccination correlated negatively with the number of YFV-specific CD8+ T-cells (r = −0.66, p = 0.0045). Percentages of early-differentiated memory cells increased (r = 0.67, p = 0.017) over time.
These results imply that YF vaccination is effective despite certain immunosuppressive drug regimens. An early-differentiated memory-like phenotype persisted, which is associated with effective expansion upon re-encounter with antigen, suggesting a potent memory T-cell pool remains.