Pierre Wolkenstein

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder in which cutaneous neurofibromas (cNFs) represent one of the most common and burdensome manifestations. No approved pharmacological treatment exists. Preclinical studies are essential to evaluate candidate therapies, but reliable outcome and endpoint measures for cNFs in animal models remain limited. We developed and validated a standardized methodology to assess drug efficacy in the Prss56Cre Nf1-KO mouse model which recapitulates key features of cNFs. In this model, Nf1 inactivation and tdTomato (Tom) reporter expression were specifically targeted to Schwann cells (SCs) responsible for cNF development. This approach enables real-time monitoring, isolation, and manipulation of tumor SCs at any time. We defined macroscopic (tumor count, total Tom ⁺ fluorescent surface area, fluorescence intensity) and microscopic (cell-type composition defined by immunolabeling with a panel of specific markers, area quantification) endpoints, developed dedicated ImageJ scripts for automated image analysis, and compared the results with those obtained using the conventional manual method. Both automated measurements showed excellent reproducibility (ICC = 1) and strong correlation with manual analysis (Spearman’s coefficient > 0.90), while significantly reducing analysis time (up to 100-fold faster). Bland–Altman analyses confirmed the absence of systematic bias compared with manual scoring. The standardized image naming and metadata integration further facilitated data consolidation and statistical analysis. This validated approach provides a reliable, reproducible, and time-efficient framework for evaluating drug effects on cNFs in preclinical studies. It establishes a foundation for robust efficacy testing of candidate therapies, facilitates cross-study comparability, and accelerates therapeutic development and clinical translation.

Neurofibromatosis type 1 (NF1) is a genetic disorder that predisposes individuals to the development of plexiform neurofibromas (pNF), benign tumors of the

Background: Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease affecting approximately 1% of the global population. Its pathogenesis involves both aberrant keratinization and autoinflammation, but the temporal relationship between these processes remains unclear. Objectives: To investigate the role of HF stem cell (HF‐SC) fate in the early pathogenesis of HS. Methods: We performed single‐cell RNA sequencing of HF cell populations from HS patients and healthy donors. We then analysed HF cell composition isolated from perilesional skin of 49 HS patients and integrated these data with clinical phenotypes to define disease endotypes. Results: Our data revealed two distinct differentiation trajectories of HF stem cells (HF‐SCs): one leading to interfollicular epidermis (IFE) basal cells enriched in inflammatory pathways, and another giving rise to outer root sheath (ORS) cells associated with keratinization. In HS lesions, both populations displayed altered inflammatory phenotypes and were closely linked to immune cell infiltration, pointing to a role in disease heterogeneity. By integrating clinical features with HF cell composition from 49 HS patients, we identified three major endotypes: (i) an inflammatory subtype, marked by T cell infiltration and an expansion of IFE basal cells; (ii) a keratinizing subtype, characterized by ORS enrichment and minimal inflammation; and (iii) a mixed subtype, exhibiting features of follicular remodelling, fistula formation and variable immune involvement. Conclusions: These findings provide novel insights into the epithelial‐immune interactions that drive HS and support a stratified therapeutic approach tailored to distinct epithelial dysfunctions.

Background: In drug reaction with eosinophilia and systemic symptoms (DRESS), cutaneous tests help to identify the responsible drug. However, uncertainty may persist and drug provocation tests (DPTs) could enable contraindications for essential drugs to be avoided. Objectives: To report the experience of DPTs in a series of DRESS patients managed in a referral centre for severe drug reactions. Methods: We performed a single‐centre retrospective study (October 2015–October 2021) of patients referred for an allergological work‐up after DRESS. Results: Seventy‐five patients were included (49 females, mean age 55 years, 212 suspected drugs). Cutaneous tests, realised in all patients, were positive in 38, and DPTs were performed in 39 patients (65 drugs: 41 suspected and 24 alternative drugs, all with negative cutaneous tests). DPTs were performed regardless of DRESS severity or RegiSCAR score, at full dose (FD) for 40 drugs and graduated dose (from 1/100 FD) for 25 drugs. The objective was always to avoid contra‐indications or to propose alternative drugs. Mild reactions occurred following challenge with 13 drugs (all suspected drugs), of which 6 could be continued. DPTs were more often positive when more drugs were suspected or reintroduced, but less often when a high‐notoriety drug was suspected and avoided. Conclusions: DPTs can be considered in DRESS by experienced teams to avoid unnecessary contraindications for essential drugs.

About half of patients with the genetic disease Neurofibromatosis type 1 (NF1) develop benign nerve sheath tumors, called plexiform neurofibromas (pNFs). Despite important advances in understanding the pathogenesis of pNFs, mainly due to the plethora of dedicated mouse models, the mechanisms responsible for the initiation of this process remain poorly understood. Here, we used a Nf1 -KO mouse model targeting biallelic loss of Nf1 in boundary cap cells on a wild type and heterozygous Nf1 background to explore the early events driving pNFs development. All mutants develop subcutaneous hyperplastic nerves with some progressing into pNFs from one year of age. We discovered that skin trauma accelerates this process, highlighting the role of inflammation. While skin trauma has no effect on control subcutaneous nerves, in the mutant nerves on a wildtype background, we observed an expansion of mutant Schwann cells expressing a profibrotic program. A similar response was observed in the mutant nerves on a heterozygous background without skin trauma, highlighting the impact of Nf1 heterozygosity in the nerve micro-environment on the development of pNFs.

Hidradenitis suppurativa (HS) is a severe skin disorder affecting 1% of the global population, with a complex and poorly understood pathogenesis involving aberrant keratinization and autoinflammation. It remains unclear whether autoinflammatory events precede or follow hyperkeratotic changes in hair follicle (HF) epithelia. Using single-cell RNA sequencing, we characterized HF cell populations in HS patients and investigated their role in disease pathogenesis. We uncovered two distinct differentiation trajectories of HF stem cells (HF-SCs): one leading to interfollicular epidermis (IFE) basal cells enriched in inflammatory pathways, and another giving rise to outer root sheath (ORS) cells associated with keratinization. In HS lesions, both populations displayed altered inflammatory phenotypes and were closely linked to immune cell infiltration, pointing to a role in disease heterogeneity. By integrating clinical features with HF cell composition from 49 HS patients, we identified three major endotypes: (i) an inflammatory subtype, marked by T cell infiltration and an expansion of IFE basal cells; (ii) a keratinizing subtype, characterized by ORS enrichment and minimal inflammation; and a mixed subtype, exhibiting features of follicular remodeling, fistula formation, and variable immune involvement. These findings provide novel insights into the epithelial-immune interactions that drive HS and support a stratified therapeutic approach tailored to the specific HF dysfunctions of each patient subgroup. Abstract Figure: