In vivo modelling of cutaneous T-cell lymphoma: The role of SOCS1

A novel knockout mouse model to assess the impact of one-copy loss of Hnrnpk in CD4 + T cells in chronically inflamed skin as a prelude to CTCL

Cutaneous T-cell lymphomas (CTCLs), particularly Mycosis fungoides (MF), frequently exhibit deletions and reduced expression of HNRNPK in CD4 + T cells. To enable in vivo studies, we developed a conditional Hnrnpk knockout mouse that thrives, facilitating the investigation of HNRNPK's role in CTCL onset. We generated mice with a floxed Hnrnpk allele, then crossbred them with Cd4CreERT2 mice to generate Hnrnpk flox Cd4CreERT2 mice, all in BL6 background. PCR confirmed the targeted deletion of Hnrnpk in CD4 + T cells after tamoxifen i.p. injection. Skin allergic reactions were induced with oxazolone, and Cre was activated in skin-infiltrating CD4 + T cells using tamoxifen topically after the first allergic skin reaction. The mice exhibited no immediately obvious phenotype. Flow cytometry and histopathological analysis were conducted on blood and skin samples collected throughout the experiment. Following 20 weeks of sustained allergic reactions, inflammation persisted over 20 weeks after challenges ceased, demonstrating early CTCL characteristics such as chronic skin inflammation, CD3 + CD4 + T cell infiltration, and stable peripheral blood parameters. This mouse model provides experimental access to the complex microenvironment and immune responses involved in early inflammatory stages, providing opportunities for further research into the role of HNRNPK in CTCL and the development of effective therapeutic interventions for this challenging malignancy.

Therapeutic Targeting of the Janus Kinase/Signal Transducer and Activator of Transcription Pathway in Cutaneous T-Cell Lymphoma

Background/Objectives: Cutaneous T-cell lymphoma (CTCL) is a rare group of non-Hodgkin lymphomas characterized by the clonal expansion of malignant T cells. While current treatments can alleviate symptoms and significant progress has been made in treating leukemic CTCL, a definitive cure remains elusive. Dysregulation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway is a key driver of CTCL pathogenesis. As a result, therapeutic strategies targeting JAK/STAT signaling have gained momentum, with the increasing use of JAK inhibitors and other agents that effectively suppress this pathway. These immune-modulating therapies have broad effects on physiological processes, inflammation, and the pathological changes associated with both inflammatory diseases and cancers. Several JAK inhibitors, originally FDA-approved for inflammatory conditions, are now being investigated for cancer treatment. Methods: In this paper, a brief review of the literature on JAK/STAT pathway dysregulation in CTCL is provided, highlighting both clinical and preclinical studies involving JAK inhibitors and other agents that target this pathway. Results: Specifically, we focus on six JAK inhibitors currently under clinical investigation-golidocitinib, ruxolitinib, cerdulatinib, tofacitinib, upadacitinib, and abrocitinib. Additionally, we discuss preclinical studies that explore the mechanisms underlying JAK/STAT pathway inhibition in CTCL. Furthermore, we review reported cases in which CTCL relapsed or emerged following JAK inhibitor treatment. Conclusions: Collectively, these findings support the potential clinical utility of targeting the JAK/STAT pathway in CTCL. However, further research is needed to evaluate safety risks, minimize adverse effects, and optimize these therapeutic strategies.

Pathogenic variants of mycosis fungoides identified using next-generation sequencing

Mycosis fungoides (MF), the predominant form of cutaneous T-cell lymphoma (CTCL), poses diagnostic challenges due to its clinical and histological resemblance to benign skin disorders. Delayed diagnosis contributes to therapeutic delays, prompting exploration of advanced diagnostics tools. Next-generation sequencing (NGS) may enhance disease detection by identifying pathogenic variants common to CTCL but absent in benign inflammatory disorders. We aim to discuss novel and common pathogenic variants in CTCL to enhance the utility of NGS as a diagnostic adjunct. This pilot study employed (NGS) to identify pathogenic variants in 10 MF cases. Cases were selected based on PCR-confirmed T-cell receptor clonality, with adequate DNA for NGS. GatorSeq NGS Panel, Illumina NextSeq500, and QIAGEN Clinical Insight QCI software facilitated sequencing, analysis, and variant interpretation. NGS revealed eight novel mutations in genes including HLA-DRB1, AK2, ITPKB, HLA-B, TYRO3, and CHD2. Additionally, previously reported MF-associated mutations such as DNMT3A, STAT5B, and SOCS1 (mouse study only) were detected as well. Detected variants were involved in apoptotic, NF-kB, JAK-STAT, and TCR signaling pathways, providing insights into MF pathogenesis. Mutations in genes like APC, AK2, TYRO3, and ITPKB that regulate tumor proliferation and apoptosis were noted. MF cases were associated with HLA gene mutations. NGS may enhance MF diagnosis, as the detection of pathogenic variants, particularly those known to occur in MF, favors a neoplastic diagnosis over an inflammatory diagnosis. Continuing this work may lead to the discovery of therapeutic targets.

"Next top" mouse models advancing CTCL research

This review systematically describes the application of in vivo mouse models in studying cutaneous T-cell lymphoma (CTCL), a complex hematological neoplasm. It highlights the diverse research approaches essential for understanding CTCL's intricate pathogenesis and evaluating potential treatments. The review categorizes various mouse models, including xenograft, syngeneic transplantation, and genetically engineered mouse models (GEMMs), emphasizing their contributions to understanding tumor-host interactions, gene functions, and studies on drug efficacy in CTCL. It acknowledges the limitations of these models, particularly in fully replicating human immune responses and early stages of CTCL. The review also highlights novel developments focusing on the potential of skin-targeted GEMMs in studying natural skin lymphoma progression and interactions with the immune system from onset. In conclusion, a balanced understanding of these models' strengths and weaknesses are essential for accelerating the deciphering of CTCL pathogenesis and developing treatment methods. The GEMMs engineered to target specifically skin-homing CD4+ T cells can be the next top mouse models that pave the way for exploring the effects of CTCL-related genes.

Socs1-knockout in skin-resident CD4+ T cells in a protracted contact-allergic reaction results in an autonomous skin inflammation with features of early-stage mycosis fungoides

Recent detailed genomic analysis of mycosis fungoides (MF) identified suppressor of cytokine signaling 1 (SOCS1), an inhibitor of JAK/STAT signaling, as one of the frequently deleted tumor suppressors in MF, and one-copy deletion of SOCS1 was confirmed in early-stage MF lesions. To better understand the functional role of SOCS1 in the genesis of MF, we used a genetically engineered mouse model emulating heterozygous SOCS1 loss in skin resident CD4+ T cells. In these mice an experimentally induced contact-allergic reaction was maintained for 20 weeks. Ten weeks after discontinuing contact-allergic challenges, only the skin with locally one-copy deletion of Socs1 in CD4+ T cells still showed high numbers of CD3+/CD4+ Socs1 k.o. cells in the dermis (p ＜ 0.0001) with prevalent Stat3 activation (p ＜0.001). And in one out of 9 mice, this had progressed to far more dramatic increases, including the thickened epidermis, and with an explosive growth of Socs1 k.o. T cells in circulation; indicative of cutaneous lymphoma. Hence, we show that Socs1 mono-allelic loss in CD4+ T cells locally in protractedly inflamed skin results in autonomous skin inflammation with features of early-stage MF.