Single-Cell RNA Sequencing Unveils the Clonal and Transcriptional Landscape of Cutaneous T-Cell Lymphomas

Purpose: Clonal malignant T lymphocytes constitute only a fraction of T cells in mycosis fungoides skin tumors and in the leukemic blood of Sezary syndrome, the classic types of cutaneous T-cell lymphomas. However, lack of markers specific for malignant lymphocytes prevents distinguishing them from benign T cells, thus delaying diagnosis and the development of targeted treatments. Here we applied single-cell methods to assess the transcriptional profiles of both malignant T-cell clones and reactive T lymphocytes directly in mycosis fungoides/Sezary syndrome patient samples. Experimental Design: Single-cell RNA sequencing was used to profile the T-cell immune repertoire simultaneously with gene expression in CD3(+) lymphocytes from mycosis fungoides and healthy skin biopsies as well as from Sezary syndrome and control blood samples. Transcriptional data were validated in additional advanced-stage mycosis fungoides/Sezary syndrome skin and blood samples by immunofluorescence microscopy. Results: Several nonoverlapping clonotypes are expanded in the skin and blood of individual advanced-stage mycosis fungoides/Sezary syndrome patient samples, including a dominant malignant clone as well as additional minor malignant and reactive clones. While we detected upregulation of patient-specific as well as mycosis fungoides- and Sezary syndromespecific oncogenic pathways within individual malignant clones, we also detected upregulation of several common pathways that included genes associated with cancer cell metabolism, cell-cycle regulation, de novo nucleotide biosynthesis, and invasion. Conclusions: Our analysis unveils new insights into mycosis fungoides/Sezary syndrome pathogenesis by providing an unprecedented report of the transcriptional profile of malignant T-cell clones in the skin and blood of individual patients and offers novel prospective targets for personalized therapy.

Automated summary

This study used single-cell methods to investigate the transcriptional profiles of malignant T-cell clones and reactive T lymphocytes in mycosis fungoides/Sezary syndrome patient samples. The study found that there are several expanded clonotypes in the skin and blood of individual patients, as well as upregulation of common pathways associated with cancer cell metabolism, cell-cycle regulation, de novo nucleotide biosynthesis, and invasion. These findings provide new insights into the pathogenesis of mycosis fungoides/Sezary syndrome and potential targets for personalized therapy.