Single-cell RNA sequencing comparison of CD4+, CD8+ and T-cell receptor γδ+ cutaneous T-cell lymphomas reveals subset-specific molecular phenotypes

Background: Malignant clones of primary cutaneous T-cell lymphomas (CTCL) can show a CD4+, CD8+ or T-cell receptor γδ+ phenotype, but their individual impact on tumor biology and skin lesion formation remains ill-defined. We perform a comprehensive molecular characterization of CD4+ vs. CD8+ and TCR-γ/δ+ CTCL lesions. Methods: We performed scRNA-seq of 18 CTCL skin biopsies to compare classic CD4+ advanced-stage mycosis fungoides (MF) with TCR-γ/δ+ MF and primary cutaneous CD8+ aggressive epidermotropic cytotoxic T-cell lymphoma (Berti’s lymphoma). Results: Malignant clones of TCR-γ/δ+ MF and Berti’s lymphoma showed similar clustering patterns distinct from CD4+ MF, along with increased expression of cytotoxic markers such as NKG7, CTSW, GZMA, and GZMM. Only advanced-stage CD4+MF clones expressed central memory T-cell markers (SELL, CCR7, LEF1), alongside B1/B2 blood involvement, whereas TCR-γ/δ+ MF and Berti’s lymphoma harbored a more tissue-resident phenotype (CD69, CXCR4, NR4A1) without detectable cells in the blood. CD4+ MF and TCR-γ/δ+ MF skin lesions harbored strong type 2 immune activation across myeloid cells, while Berti’s lymphoma was more skewed towards type 1 immune responses. Both CD4+ MF and TCR-γ/δ+ MF lesions showed upregulation of keratinocyte hyperactivation markers such as S100As and KRT16 genes. This increase was entirely absent in Berti’s lymphoma, possibly reflecting an aberrant keratinocyte response to invading tumor cells, that could contribute to the formation of the typical ulcero-necrotic lesions within this entity. Conclusions: Our scRNAseq profiling study reveals specific molecular patterns associated with distinct CTCL subtypes.