Transcriptomic landscape of CD8+ and CD4 + T-LGL leukemia revealed the distinct impact of STAT3 and STAT5B activating mutations

The biological basis of the high clinical heterogeneity of T-LGL Leukemia (T-LGLL) is not completely understood and effective therapies for this disease are lacking. Through RNA-Sequencing of purified T-LGLs we reveal gene expression profiles and pathway dysregulations in the major patient subgroups, defined by CD8+ or CD4+ phenotype and STAT3/STAT5B mutational status. Overall, T-LGLL patients exhibited a marked transcriptome dysregulation compared to controls. This was more pronounced in the most symptomatic CD8 + STAT3-mutated patients, which emerged as a distinct biological entity, separated from the other disease subgroups. Particularly, CD8 + STAT3-mutated cases displayed extensive down-regulation of genes, ultimately resulting in the de-repression of proliferation and cell cycle pathways. Among genes up-regulated in CD8 + STAT3-mutated cases we found VCAM1, the transcriptional repressor EZH2 and the p53-regulator MDM2 proto-oncogene, as well as the leukemogenesis-associated PVT1 up-regulation, representing the first report of a long-non-coding RNA alterations in leukemic T-LGLs. The impact of STAT5B mutations on T-LGLs transcriptome was more limited and the overexpression of the PIM1 serine/threonine kinase proto-oncogene was identified as one of the most relevant features of STAT5B-mutated CD4 + T-LGLL. This study significantly advances our understanding of T-LGLL pathogenesis, uncovering new oncogenic mechanisms within the distinct molecular subtypes of the disease.