• chronic myelogenous leukaemia;
  • naive T lymphocyte;
  • flow cytometry;
  • CD28;
  • lymphocyte subsets

Summary. In chronic myelogenous leukaemia (CML), clonal change occurs in all myeloid and B-cell lineages, but very rarely T-cell lineages. A detailed three-colour cytometric analysis of peripheral lymphocytes was performed in 22 patients with chronic-phase CML (CP-CML). CD45 gating analysis was used to discriminate between lymphocytes and basophils. The peripheral lymphocyte pool was comprised of a significant proportion of naive CD4 cells, defined by a CD4+45RA+ phenotype [47·0 ± 19·6% (mean ± SD) of the total CD4+ cells], and naive CD8 cells, defined by a CD8+CD45RA+CD28+ phenotype (35·1 ± 19·7% of total CD8+ cells), even in patients with long disease duration. The percentage of CD8 naive T cells showed inverse correlation with age, whereas no correlation was observed with disease duration. Possible explanations for the preservation of naive lymphocytes include (1) that the naive T cells differentiated from co-existing normal stem cells or (2) that long-lived naive T cells persisted from the CML onset and expanded peripherally (thymus independent). Either mechanism or a combination of both mechanisms might contribute to maintaining the naive compartment size.