Interleukin-15 is a hair follicle immune privilege guardian.

Introduction

Alopecia areata (AA) is the most common inflammatory hair disease. Current therapies do not suppress disease reoccurance. Interferon gamma (IFNg) is a key pathogenic cytokine that drives AA. Interleukin 15 (IL-15) can activate IFNg secreting cells and may be a potential therapeutic target. This study asked whether IL-15 or its receptor (IL-15R) is expressed abnormally in AA patients, prevents immune privilege (IP) collapse and if it could be used to treat AA.

Main Points

• Analysis of immunohistochemically (IHC) labelled human scalp skin biopsies showed the number of perifollicular IL-15+ cells was significantly increased in both lesion and non-lesional areas of skin from AA patients compared to normal skin. The majority of these cells were shown to be T cells, which are known to require IL-15 for survival / differentiation.
• However, IL-15, IL-15Rα, and IL-15Rγ protein expression was decreased within the hair follicles (HF) of the AA patients suggesting impaired IL-15/IL-15R signalling. This may suggest that AA patients have a reduced sensitivity to IL-15 stimulation or it may be a reaction to the increase in perifollicular IL-15+ cells.
• However, IP collapse in AA was reduced by IL15 in in vivo studies.
• IL-15 up-regulated the expression of two HF-IP guardians, TGFβ2 and IGF-1, and reduced IFNg induced IP collapse. NK cells were also stimulated to produce IL-10 and reduce any IFNg induced inflammation
• In vivo, in a humanised AA mouse model, treatment with rhIL-15 showed more regrowth of hair shafts compared to vehicle-treated, alopecic scalp skin. IL-15 in scalp cultures also reduced the expression of major histocompatibility complex-class-I-related chain A, which is normally associated with IP collapse.

Conclusion

• The authors show that IL-15 itself does not appear to promote AA.
• Others have also shown IL-15 to promote hair growth, be anti-apoptotic, and protect other organ populations, although it may increase CD8 or CD4 T cells which cause hair toxicity. These have been inhibited by Jak blockers, that block the IL-15Rγ chain in patients, stimulating hair growth. The inhibition is transitory as it may also inhibit IL-15-dependent, protective immunoinhibitory cells. The authors suggest in the resulting relapsing disease, following Jak inhibitor treatment, IL-15Rα signalling is defective and agonists may be more beneficial.

EPISTEM SERVICES

IHC

• This data demonstrates how IHC can be used to determine the biological effects of exposure to Test Articles in the ex vivo hair follicle model. Epistem have pioneered the use of the hair follicle to measure DNA damage, protein or RNA changes induced by chemotherapy, or other agents, in preclinical and clinical situations. All histology/IHC or gene expression services are performed in-house in Epistem GCLP-accredited labs.
• In pre-clinical proof of concept models freshly plucked hairs can be maintained ex vivo in the presence of Test Articles and effects on protein or RNA measured. Biomarkers characteristic of target engagement can be identified. Hairs collected during clinical trials can similarly be analysed. Pharmacodynamic (PD) biomarker responses can be correlated with PK.
• Analytical services include quantification of IHC labelled hair sections (e.g. gH2AX, pChk1) either manually or semi-automated using the Aperio Scanscope CS2.
• The team have a wealth of experience in developing and troubleshooting IHC protocols for both automated (Ventana Discovery Ultra) and manual applications.

Organoids

• Epistem also offers organoid models of intestinal toxicity.

Laser Capture Microdissection

• Epistem also offers RNA‑friendly laser capture microdissection of target cell populations in order to identify specific target cell gene expression changes.