Proliferative T-cell responses in surviving patients. Proliferative responses to (A) PHA and (B) tetanus toxoid. As in Figure 2, only 4 years of follow-up are shown. The most recent PHA response for patient DIG001 is 223 303 cpm at 8 years after transplantation. The most recent tetanus toxoid response for patient DIG001, at 7 years, had fallen to background levels. The mean PHA response of the normal control assay done in parallel with these assays (n = 77) was 162 249 cpm (the range including 1 SD was 67 507 cpm to 389 958 cpm). The mean tetanus toxoid response of the healthyl control individual run in parallel with these assays (n = 27) was 26 161 cpm (the range including 1 SD was 6597 cpm to 103 750 cpm). The mean medium background for the patients' PHA assays (n = 87) was 361 cpm (the range including 1 SD was 153 cpm to 853 cpm). The mean patient background for the tetanus toxoid assays (n = 36) was 1221 cpm (the range including 1 SD was 402 cpm to 3717 cpm).