Intraclonal heterogeneity for CD158k and TCR Vβ expression in patients 1 and 13 and cell sorting analysis. (Ai) Patient 13 showed 2 distinct TCRαβ^dim and TCRαβ^bright circulating T-cell populations. Two-color flow cytometry showed that CD158k⁺ cells were present within both T-cell populations. (Aii) GeneScan Analysis applied to sorted populations revealed that the TCRαβ^dim population only disclosed clonal TCR Vβ5, TCR Vβ15, and TCR Vβ23. In contrast, the TCRαβ^bright population had a profile similar to that of whole PBMCs, including clonal TCR Vβ5, Vβ23, and Vβ15, suggesting that malignant and nonmalignant T-cell clones were present in the TCRαβ^bright and TCRαβ^dim subsets. (Bi) Two-color flow cytometry revealed heterogeneity for CD158k expression within the malignant TCR Vβ17 population in patient 1. A proportion of Vβ17⁺ cells did not express CD158k. A minor Vβ17^dim subpopulation could be recognized within the TCR Vβ17⁺ CD158k⁺ population (arrowhead). (Bii) Through RT-PCR, CD158k mRNA was detected at significant levels in the TCR Vβ17⁺ CD158k⁺ population; negative results were obtained in the TCR Vβ17⁺ CD158k^– population.