We have recently demonstrated that
telomerase activity is increased and telomere length shortened in lymphocytes from peripheral blood of patients with
cutaneous T-cell lymphoma. In order to determine which cell type has increased
telomerase activity and shortened telomere length, CD4+, CD8+, CLA+ CD3+ and CLA- CD3+ T cells were isolated from peripheral blood of 25 patients, including 15 patients with
mycosis fungoides and 10 patients with
parapsoriasis. Eleven healthy individuals were used as controls; CD19+ B cells were separated from each individual as an internal control. The results showed that the increased
telomerase activity was significantly predominating in the CD4+ T-cell subset. Significantly shortened telomere length was found in CD4+ and CD8+ T-cell subsets from the patients compared with the same cell subsets obtained from healthy individuals. However, no difference was observed between the subsets; CD19+ B cells collected from patients and healthy control individuals had similar
telomerase activity and telomere length which was significantly different from the values found in T cells. The telomere length was significantly shorter in CLA+ CD3+ subset than in CLA- CD3+ subset. Interestingly, increased
telomerase activity and shortened telomere length was also detected in CD4+ T cells from patients with
parapsoriasis indicating that alteration of
telomerase activity and telomere length in CD4+ T cells is an early event in the pathogenesis of
cutaneous T-cell lymphoma. Thus, the results indicate that a significant high level of
telomerase activity and shortened telomere length frequently occur in T cells of patients with CTCL and may reflect
tumorigenesis.