RESUMEN
BACKGROUND: Improved vaccination strategies against tuberculosis are needed, such as approaches to boost immunity induced by the current vaccine, BCG. Design of these strategies has been hampered by a lack of knowledge of the kinetics of the human host response induced by neonatal BCG vaccination. Furthermore, the functional and phenotypic attributes of BCG-induced long-lived memory T-cell responses remain unclear. METHODS: We assessed the longitudinal CD4 T-cell response following BCG vaccination of human newborns. The kinetics, function, and phenotype of these cells were measured using flow cytometric whole-blood assays. RESULTS: We showed that the BCG-specific CD4 T-cell response peaked 6-10 weeks after vaccination and gradually waned over the first year of life. Highly activated T-helper 1 cells, predominantly expressing interferon γ, tumor necrosis factor α, and/or interleukin 2, were present at the peak response. Following contraction, BCG-specific CD4 T cells expressed high levels of Bcl-2 and displayed a predominant CD45RACCR7 central memory phenotype. However, cytokine and cytotoxic marker expression by these cells was more characteristic of effector memory cells. CONCLUSIONS: Our findings suggest that boosting of BCG-primed CD4 T cells with heterologous tuberculosis vaccines may be best after 14 weeks of age, once an established memory response has developed.