Speaker- John E. Harris

Vitiligo affects over 1% of the global population, with half of the patients diagnosed before the age of 20, highlighting concerns about the long-term use of treatments, such as oral Janus kinase (JAK) inhibitors, in pediatric populations. The management of vitiligo involves not only inducing remission but also maintaining it and preventing relapses, raising questions about the safety and efficacy of prolonged treatment. As investigators investigate vitiligo, they are concurrently exploring other autoimmune disorders, including type 1 diabetes, lupus, Hashimoto's thyroiditis, pernicious anemia, and Addison's disease. 

Vitiligo treatment has a long and varied history, with records dating back to 1400 BC in ancient Indian medical texts, which highlighted the social stigma associated with the condition, particularly its impact on marriage prospects. Early treatment methods were unconventional, involving cow urine, cow dung, elephant dung, and cobra bones. It is believed that the microbiome may have changed over time, altering responses to these treatments. Bavachi seeds combined with sunlight were used thousands of years ago, while more drastic measures like arsenic and sulfuric acid were employed about a century ago to reduce the appearance of vitiligo. In the 1950s, Psoralen Combined with Ultraviolet A (PUVA) therapy was rediscovered, and monobenzone began to be used as a depigmenting agent. The first Food & Drug Administration (FDA) approved treatment for vitiligo was monobenzone, which was approved in the 1980s, followed by punch grafting techniques in the same decade. In 1997, there were modern vitiligo treatment including topical immunosuppressants, narrowband Ultraviolet B (UVB) phototherapy, and surgical interventions. In 2022 ruxolitinib, a JAK inhibitor, became the first FDA-approved targeted therapy for vitiligo. The approval of ruxolitinib is expected to revolutionize vitiligo management.

The study strategy in the laboratory emphasizes an integrated approach that combines basic science utilizing a mouse model of vitiligo, a translational study involving patient tissues, and clinical trials aimed at elucidating the mechanisms underlying vitiligo and developing novel treatments. Dr. Jillian Richmond, a postdoctoral investigator in the lab, began her investigation by observing patients who experience relapses upon cessation of therapy. Her findings revealed that mouse vitiligo lesions accumulate resident memory T cells, which infiltrate the epidermis, adhere via specific adhesion molecules, and persist indefinitely. These T cells are integral to maintaining vitiligo and become inactive when treatment is started. Further investigations demonstrated that these resident memory T cells are also present in human skin and rely on interleukin-15 (IL-15) as a critical trophic factor for survival. When IL-15 is blocked, these cells are eliminated from the skin of mice with vitiligo, preventing disease relapse. The observation laid the groundwork for an ongoing clinical trial, which was sponsored by the National Institutes of Health (NIH), utilizing an IL-15 antibody. Additionally, a therapeutic company that Insight acquired two years ago is making progress in developing an IL-15 receptor antibody. The role of Cluster of Differentiation 8 T (CD8 T) cells in driving vitiligo is significant; these cells infiltrate the skin, target melanocytes, and produce interferon-gamma (IFN-γ). The cytokine activates signaling pathways in surrounding keratinocytes, producing chemokines like C-X-C Motif Chemokine Ligand 10 (CXCL10), which attract additional T cells and further exacerbate vitiligo progression. Some of these CD8 T cells differentiate into resident memory T cells, where they can reactivate upon encountering newly emigrating melanocytes, continuing the cycle of IFN-γ production. While conventional therapies and JAK inhibitors can temporarily inactivate these T cells, leading to improvement and repigmentation of melanocytes, the cessation of therapy results in the reactivation of these memory cells, prompting disease recurrence. However, the investigators have determined that blocking the IL-15 receptor can effectively erase the memory of these T cells. 

The study focused on identifying novel pathways that could be therapeutically targeted for treating vitiligo. Investigators employed suction blistering to sample affected and unaffected skin and normal skin from individuals with vitiligo. The cellular components extracted from these blisters were analyzed using advanced methodologies, including flow cytometry and single-cell Ribonucleic acid (RNA) sequencing. Notably, the fluid obtained from these blisters contained chemokines such as CXCL9 and CXCL10, which presented a significant opportunity for discovering additional targeted therapeutic pathways. The study team received a P50 award from the National Institutes of Health (NIH), establishing a center for study translation focused on vitiligo. Their overarching strategy involved comprehensively characterizing all identified pathways to understand their functional roles, as inhibiting specific pathways might aid in treating the disease. However, investigators acknowledged the possibility that inhibiting certain pathways in vitiligo might not yield beneficial outcomes, emphasizing the need to explore the mechanistic underpinnings of these pathways to identify effective treatment modalities. The team comprised experts including Michael Garber, Jillian Richman, Sally Kent, Larry Stern, and Long Kai. Using transcriptomics to analyze gene expression profiles in the skin enables them to determine which genes were activated, their localization, and the specific cell types responsible for their expression. The approach enhanced dermatologists’ understanding of the cellular dynamics involved in skin biopsies, which could be challenging to discern through conventional clinical observations. Histological examination of skin biopsies from vitiligo patients revealed the presence of CD8 T cells infiltrating the lesions, which activated Signal Transducer and Activator of Transcription 1 (STAT1) and secreted various chemokines, which marked a pioneering insight into the mechanisms of vitiligo, where T cells directly attacked melanocytes and expressed genes that facilitated the process. The investigators leveraged the technology to validate new therapeutic targets, gained deeper insights into the disease's driving mechanisms, and explored options beyond JAK inhibitors to develop innovative therapies for vitiligo.

The study focused on developing novel therapeutics for vitiligo, emphasizing the translation of mechanistic knowledge into opportunities for new treatments. It highlighted the contributions of Craig Mello, who discovered RNA interference (RNAi). The groundbreaking technology allows short double-stranded RNA to enter cells and target specific mRNA, leading to the degradation of protein complexes that may contribute to the pathogenesis of vitiligo. Small interfering RNA (siRNA), a technology capable of targeting any gene in the human genome, took 20 years to develop due to its inherent instability. Anastasia Khvorova enhanced the chemistry of siRNA to improve its stability, potency, and delivery to specific organs and cells within the body. Chi, a postdoctoral investigator, aimed to create siRNAs specifically for the skin, targeting JAK1. He screened the mRNA for JAK1 and identified a sequence that could degrade it, effectively causing its disappearance in both human and mouse models. Following this, he injected the siRNA into the footpads of mice. Compared to controls, the mice injected with interferon-gamma showed reduced production of CXCL9 and CXCL10, indicating that the treatment effectively inhibited interferon-gamma signaling within the tissue. The subsequent step involved testing the siRNA in human skin using surgically discarded samples. A fluorescent dye was applied to the siRNA before injection into the skin, allowing it to diffuse and knock out JAK1 in the epidermis and dermis. The knockout demonstrated in vivo relevance for treating animals with vitiligo. The technology was tested in porcine skin; the siRNA effectively knocked out JAK1 in both skin layers, reduced interferon gamma signaling, and exhibited a duration of action exceeding four weeks. The innovative approach has been validated in live mice, human skin ex vivo, and live pigs whose skin shares similarities. 

The challenge of effectively delivering siRNA into human skin for treating vitiligo presents significant obstacles, particularly given the need for monthly treatment regimens. Investigators have developed a transdermal delivery system utilizing ceramic stars to overcome the issue and create micro-perforations in the stratum corneum. The approach facilitated the direct application of water-soluble drugs, enabling the siRNA to knock down JAK1 effectively. Preliminary tests in live pig models have yielded promising results, suggesting that the method could be developed into a topical treatment administered 12 times a year. Another innovative strategy was proposed by Dr. John Stanley, who studied pemphigus patients and discovered that antibodies binding to desmoglein 3, without causing blister formation, could deliver therapeutic agents precisely where needed. Chao, an antibody engineer, further advanced the concept, engineering a bispecific antibody that combined an interferon gamma-blocking antibody with an antibody derived from a pemphigus patient targeting desmoglein 3. The bispecific antibody demonstrated the ability to neutralize interferon gamma while specifically binding to desmoglein 3 in keratinocytes, mirroring the functionality of the parent antibody. In mouse models, the bispecific antibody remained anchored within the skin, effectively protecting the injected footpad from depigmentation. Conversely, the untethered antibody became systemic and protected both footpads. However, the desmoglein 3-targeting antibody did not exhibit any therapeutic effects on vitiligo. Additionally, investigators explored using infrared light with an antibody to deliver a cytotoxic chemical to bound T cells. The method aimed to address T cell-driven inflammatory skin diseases. The antibody disperses throughout the body, binds to T cells, and activates the chemical upon exposure to infrared light, which leads to targeted T cell apoptosis in the treated area. In experiments, human T cells treated with the drug and exposed to increasing light doses exhibited a dose-dependent increase in cell death. Biopsies of human skin containing T cells that received the drug treatment followed by light exposure showed successful elimination of T cells while preserving the integrity of melanocytes.

In summary, the development of new treatments for vitiligo a condition primarily driven by T cells, including interferon-gamma and IL-15 signalling. Proposed approaches include conventional antibodies, antibody-drug conjugates with light, bispecific antibodies, and siRNA. There is optimism surrounding the future availability of oral JAK inhibitors, biologics, and siRNA bispecific antibodies.

33, European Academy of Dermatology and Venereology Congress, 25-28 September 2024, Amsterdam