The in vitro cellular response to TT is proportional to the number of CD4⁺CD45RA⁺RO⁻ naive T cells.

●—●, Number of CD4⁺CD45RA⁺RO⁻ naive T cells at the time of the first vaccination and at the time of the third vaccination (for the second time point, no data were available for P1 [patient number 1], whereas for P7 and P8 data show the values of approximately 6 months after the third vaccination). The bars show the stimulation index (cpm response/cpm background) of patient cells normalized to the stimulation index of a normal control stimulated with TT in the same experiment. In all experiments, the same 2 normal controls, who had not been recently immunized, were used. In different experiments, responses of the normal controls varied between 35.10³ and 173.10³ cpm (90 ± 60.10³), whereas the cpm in cultures without antigen (patients as well as normal controls) never exceeded 1200.