Prevalence of genetically defined tumor cells in CD7 as well as CD26 positive and negative circulating T-cell subsets in Sézary syndrome

For diagnosis and monitoring of Sézary syndrome flow cytometric quantification of CD7− and CD26− T-cells is widely used. Because antigen loss is a characteristic but not disease-specific finding we investigated the significance of this approach. Therefore we analyzed the prevalence of tumor cells in FACS-sorted CD7+/− as well as CD26+/− circulating T-cells applying a clone-specific qualitative and quantitative T-cell receptor PCR. Tumor cells varied considerably in the CD7+ and CD7− cell subset but were largely confined to the CD26− population. We conclude that quantification of CD26− T-cells reflects the tumor cell amount more accurate and should be preferred in the clinical setting.