Single‐cell RNA sequencing analysis of a COVID‐19–associated maculopapular rash in a patient with psoriasis treated with ustekinumab

Coronavirus disease 2019 (COVID‐19) primarily affects the respiratory system but extrapulmonary manifestations, including the skin, have been well documented. However, transcriptomic profiles of skin lesions have not been performed thus far. Here, we present a single‐cell RNA sequencing analysis in a patient with COVID‐19 infection with a maculopapular skin rash while on treatment with the interleukin (IL)‐12/IL‐23 blocker ustekinumab for his underlying psoriasis. Results were compared with healthy controls and untreated psoriasis lesions. We found the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) viral entry receptors ACE2 and TMPRSS2 in keratinocytes of the patient with COVID‐19, while ACE2 expression was low to undetectable in psoriasis lesions and healthy skin. Among all cell types, ACE2+ keratinocyte clusters showed the highest levels of transcriptomic dysregulation in COVID‐19, expressing type 1–associated immune markers such as CXCL9 and CXCL10. In line with a generally type 1–skewed immune microenvironment, cytotoxic lymphocytes showed increased expression of the IFNG gene and other T‐cell effector genes, while type 2, type 17, or type 22 T‐cell activation was largely absent. Conversely, downregulation of several anti‐inflammatory mediators was observed. This first transcriptomic description of a COVID‐19–associated rash identifies ACE2+ keratinocytes displaying profound transcriptional changes, and inflammatory immune cells that might help to improve the understanding of SARS‐CoV‐2–associated skin conditions.

swollen endothelial layer, vessels engulfed with red blood cells, and perivascular infiltrates of mainly CD8+ T cells and eosinophils. 5 Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) entry receptors were described in keratinocytes and endothelial cells of healthy control (HC) skin 6,7 and sweat glands of COVID-19-infected patients. 8 However, mechanisms of skin rash development remain to be elucidated, and molecular investigations are still missing.

| RE SULTS
Here, we describe a 49-year-old male patient with moderate to severe chronic plaque-type psoriasis who had complete clearance of his skin disease during ustekinumab treatment (45 mg every 3 months).
Also, psoriasis harbored the disease-characteristic CCL27 downregulation, in contrast to COVID-19 ( Figure S1). Among canonical T-cell polarizing cytokines being expressed in the COVID-19 sample, we only found the prototypic type 1 cytokine IFNG to be upregu-

| DISCUSS ION
This is the first transcriptomic characterization of a COVID-19associated skin eruption. We can assume that we did not merely observe a psoriasis flare, as both the clinical presentation as maculopapular rash and the absence of type 17-associated mediators are inconsistent with a classic psoriatic lesion. Also, CCL27, typically downregulated in psoriasis, 11 was significantly upregulated in the COVID-19 sample. The observed strong type 1 immune activation is commonly found in virus-induced exanthemas, 10 supporting an association with SARS-CoV-2. Nevertheless, ongoing treatment with ustekinumab has most likely profoundly altered the skin immune microenvironment. 12 Thus, inferences about general mechanisms of viral rash development need to be made with great caution. However, the overall mild disease course supports the previous notion that cytokine- entry receptors TMPRSS2 and ACE2 by keratinocytes, with ACE2 being induced by COVID-19, consistent with prior reports. 6 While ACE2 expression was previously reported in psoriatic keratinocytes, 15 expression was much higher in our COVID-19 sample, with only scattered signals in psoriasis. Overall, one might speculate that ACE2 induction only happens in certain susceptible individuals subsequently developing a COVID-19 rash, a hypothesis that mandates further investigation in larger sample sets. Interestingly, cells with the highest degree of genomic dysregulation were found in the ACE2-expressing keratinocyte population, suggesting a direct cytopathic effect of the virus.
In line with the absence of viral entry receptors in endothelial cells in our sample, we did not observe the vasculitic changes that have been described for some COVID-19 skin manifestations. 7 This finding suggests that the distribution of viral entry receptors might directly influence the pattern of COVID-19 skin changes, mandating further investigations. Overall, these data shed new light on potential mechanisms of SARS-CoV-2-associated skin lesions, which could help guide future studies on the pathogenesis of viral rashes.

ACK N OWLED G M ENTS
We thank the Biomedical Sequencing Facility (BSF) at the Research Center for Molecular Medicine CeMM in Vienna for assistance with next-generation sequencing.

FU N D I N G I N FO R M ATI O N
This work was funded by a research grant to PMB from the LEO Foundation (grant number LF-OC-20-000621).

CO N FLI C T O F I NTE R E S T S TATE M E NT
PT has received speaker fees from Novartis, Lilly, and FotoFinder, and unrestricted grants from Lilly. CJ has received personal fees