The PPD-specific T-cell clonal response in UK and Malawian subjects following BCG vaccination: a new repertoire evolves over 12 months.

Mycobacterium bovis bacille Calmette Guerin vaccination protects against pulmonary tuberculosis in the United Kingdom but not in Malawi. We investigated whether a difference in the clonal T-cell response to BCG vaccination might account for this. The results of clonal analysis were compared to those obtained by skin testing and in a whole blood interferon gamma assay. Pre-vaccination antigen specific T-cell clones were detected, but the majority of clones present 12 months after vaccination were not present earlier. The magnitude of the clonal response did not correlate well with results of the other assays. These data indicate that single assays may not be reliable and that a stable memory T-cell repertoire is slow to develop.