Brian S. Kim, MD, said at MedscapeLive’s annual Las Vegas Dermatology Seminar, held virtually this year.
Recent years have brought enormous progress in understanding how chronic itch in patients with atopic dermatitis (AD) is mediated by type 2 cytokines, including interleukin-13, IL-4, and IL-31, as well as by Janus kinase (JAK) signaling. This has led to development of potent therapies targeting these mediators, including dupilumab (Dupixent) and the investigational agents tralokinumab, lebrikizumab, abrocitinib, upadacitinib, baricitinib, and the IL-31 inhibitor nemolizumab.
“This is now one of the most active areas in the field of dermatology,” observed Dr. Kim, a dermatologist and codirector of the Center for the Study of Itch and Sensory Disorders at Washington University in St. Louis.
He has figured prominently in this effort. He and his coinvestigators conducted translational studies in mouse models which unraveled key mechanisms by which the immune system responsible for skin inflammation in AD communicates with the nervous system to trigger the neural sensation of itch. He also led a phase 2 randomized trial in 307 patients with AD, which demonstrated that the investigational JAK1/JAK2 inhibitor ruxolitinib cream markedly improved itch within 36 hours, well before subsequent improvement in skin inflammation – and the topical JAK inhibitor did so with minimal systemic absorption.
Compared with chronic itch, much less research attention has been devoted to the phenomenon of acute itch flares superimposed upon the chronic itch of AD. These acute-on-chronic itch flares are a common feature of the disease. In a soon-to-be-published study of 159 AD patients in the placebo arm of a clinical trial, Dr. Kim and coinvestigators found that 26% exhibited a pattern of acute itch flares during the course of a single month. During the next month, 3.1% of patients under study went from an acute-on-chronic itch pattern in month 1 to a nonflare pattern, 20% went from a nonflare pattern in month 1 to acute itch flares in month 2, and 23% of the overall study population retained their pattern of acute itch flares through both months.
Brian Kim, MD, department of dermatology, Washington University St. Louis, and codrector of the Center for the Study of Itch.
“This does not seem to be just a static phenotype, but rather these patients can evolve over time. And we think that this can be driven by allergen-specific IgE,” according to Dr. Kim.
Indeed, the investigators found that patients with allergen-specific IgE in their serum were roughly twice as likely to exhibit the acute-on-chronic itch flare pattern than those without allergen-specific IgE.
The classical thinking has been that IgE binds to its receptors on mast cells, causing mast cell degranulation and release of histamine and other itch-inducing molecules. Yet antihistamines have proven notoriously ineffective for the treatment of AD.
Circulating basophils capable of working their way into inflamed skin also have IgE receptors. Dr. Kim and colleagues have shown that allergen-specific IgE in mice binds to those receptors, causing the basophils to degenerate, releasing itch-promoting chemicals. They have subsequently carried over this work into the clinical arena.
“We’ve found that patients with atopic dermatitis have significantly higher expression of receptors for IgE in their basophils than in the basophils of healthy controls, indicating perhaps that the basophils in patients with atopic dermatitis are much more prone to stimulation by allergen by way of IgE. This is a new concept that we’re exploring,” Dr. Kim said.
“We haven’t really known before what IgE does in atopic dermatitis, but it turns out that it may actually play a very important role in triggering acute flares of itch,” the dermatologist explained. “What’s been surprising is that the IgE activity is not mediated so much by mast cells, which are tissue-resident; the predominant means appears to be that IgE acts on basophils. That then creates release not of histamine, but of leukotriene C4, which is a very potent pruritogen. This may be responsible for those acute itch flares.”
Asked during an audience Q&A how allergen-specific IgE–mediated basophil activation might be targeted therapeutically in order to prevent acute-on-chronic itch flares in patients with AD, Dr. Kim mentioned two possibilities. One is treatment with potent anti-IgE agents, which to date have not been adequately tested for their antipruritic prowess in AD.
“Also, there’s another molecule that seems to be relatively basophil-selective and -specific that’s just been discovered by my colleague Xinzhong Dong at Johns Hopkins University [in Baltimore] – called MRGPRX2 – that may actually be a potentially viable way to go after basophils, maybe even by depleting them if you had an antibody against that,” Dr. Kim said. He was a coinvestigator in Dr. Dong’s recent study characterizing MRGPRX2, the mast-cell-expressed Mas-related G-protein–coupled receptor activator.
Dr. Kim reported receiving research funding from Cara Therapeutics and LEO Pharma, holding a patent for the use of JAK inhibitors in chronic itch, and serving as a consultant to numerous pharmaceutical companies.
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