Evidence that a neutrophil-keratinocyte crosstalk is an early target of IL-17A inhibition in psoriasis

Abstract

The response of psoriasis to antibodies targeting the interleukin (IL)-23/IL-17A pathway suggests a prominent role of T-helper type-17 (Th17) cells in this disease. We examined the clinical and immunological response patterns of 100 subjects with moderate-to-severe psoriasis receiving 3 different intravenous dosing regimens of the anti-IL-17A antibody secukinumab (1 × 3 mg/kg or 1 × 10 mg/kg on Day 1, or 3 × 10 mg/kg on Days 1, 15 and 29) or placebo in a phase 2 trial. Baseline biopsies revealed typical features of active psoriasis, including epidermal accumulation of neutrophils and formation of microabscesses in >60% of cases. Neutrophils were the numerically largest fraction of infiltrating cells containing IL-17 and may store the cytokine preformed, as IL-17A mRNA was not detectable in neutrophils isolated from active plaques. Significant clinical responses to secukinumab were observed 2 weeks after a single infusion, associated with extensive clearance of cutaneous neutrophils parallel to the normalization of keratinocyte abnormalities and reduction of IL-17-inducible neutrophil chemoattractants (e.g. CXCL1, CXCL8); effects on numbers of T cells and CD11c-positive dendritic cells were more delayed. Histological and immunological improvements were generally dose dependent and not observed in the placebo group. In the lowest-dose group, a recurrence of neutrophils was seen in some subjects at Week 12; these subjects relapsed faster than those without microabscesses. Our findings are indicative of a neutrophil-keratinocyte axis in psoriasis that may involve neutrophil-derived IL-17 and is an early target of IL-17A-directed therapies such as secukinumab.

Keywords: IL-17A; neutrophils; psoriasis; secukinumab.

Figure 1

Psoriasis Area and Severity Index (PASI) response rates over time in subjects receiving secukinumab or placebo. (a) % change in PASI from Baseline. (b) ≥75% reduction from Baseline in PASI (PASI75). (c) ≥90% reduction from Baseline in PASI (PASI90).

Figure 2

Changes in epidermal and inflammatory parameters in skin lesions during treatment with secukinumab or placebo (a–f; data from all patients). (a–f) Mean values for (a) epidermal thickness in mm (normal 0.1–0.2 mm), (b) parakeratosis, (c) epidermal microabscesses of neutrophils, (d) numbers of myeloperoxidase (MPO)-positive neutrophils, (e) CD3-positive T cells and (f) CD11c-positive dendritic cells. Means for (b–f) derived from semi-quantitative scoring system [see the Materials and methods section and Fig. S2; normal = 0, except for CD3 and CD11c (0–1)]. Solid lines indicate mean changes in Psoriasis Area and Severity Index (PASI). (g, h) Mean log₂-transformed NanoString counts of expression levels of (g) inflammatory cytokines and (h) epidermal markers in the same biopsies. BL, Baseline; PBO, placebo; all graph titles in g) and h) indicate genes, e.g. CXCL8, DSC2, IFNG, KRT16, TNF indicate genes encoding IL-8, desmocollin-2, IFN-γ, keratin-16, TNF-α. Error bars are ± standard error of the mean.

Figure 3

Representative immunohistochemistry of skin biopsies from psoriatic lesions and analysis of IL17A expression in peripheral blood and skin leucocyte subsets. (a) Baseline evaluation of IL-17 in a subject from the secukinumab 1 × 10 mg/kg cohort shows prominent staining in epidermal Munro’s microabscesses (oval outline) and spongiform pustules of Kogoj (arrow, top row). Epidermal IL-17 staining was cleared at Week 2, but still evident in dermal T cells and mast cells at Week 12 (middle and bottom rows). (Control sections are shown in Fig. S5.) (b) Immunofluorescence double labelling for IL-17 (green) and myeloperoxidase (MPO; red) with DAPI counterstain confirming IL-17 staining of neutrophils in Munro’s microabscesses (top row), spongiform pustules of Kogoj (arrowhead, bottom left) and neutrophils in dermal vessels (arrow, bottom right). (c) Levels of IL-17A, CD3E, CD1c and proteinase-3 (PR3; to identify neutrophils) mRNA in peripheral blood cells of subjects with psoriasis (n = 4, top row) and healthy donors (n = 3, bottom row). IL-17A mRNA was not detected in more than 95% pure granulocyte fractions (Gran), but observed at low levels in T lymphocytes. Quantification cycle (Cq) for β2-microglobulin (B2M) between 19 and 24 for all samples shown; not detectable: Cq >45. (d) Levels of IL-17A, CD3E, CD1c, MPO (to identify cutaneous neutrophils), and tryptase (to identify cutaneous mast cells) mRNA in cells isolated from psoriatic plaques. One representative experiment of 4 is shown. Samples were run in duplicate for each probe, and quantification was based on ΔΔCq calculations. Arithmetic means ± standard deviation of different donors (a) and of triplicate determinations of individual samples (b) are shown. DC, dendritic cell; Mono, mononuclear; PSOR, psoriasis.