The research team, led by Min-Ji Kim and Kyung-Sun Kang of Seoul National University together with Seunghee Lee, created what they call vascularized skin assembloids, or VSAs. The strategy builds on two earlier stem-cell technologies. Skin organoids grown from human induced pluripotent stem cells can recapitulate epidermal and dermal differentiation and even generate appendages such as hair follicles, melanocytes and neurons. Blood vessel organoids, likewise derived from pluripotent stem cells, self-assemble into endothelial networks with lumina and mural support cells. Each system on its own, however, falls short of real skin. Skin organoids often develop inverted polarity, with the epidermis facing inward, and can undergo ectopic cartilage formation, while neither model on its own provides the vascular and immune components needed to model inflammation.

The assembloid approach sidesteps these problems by treating the two organoid types as building blocks rather than finished products. The researchers first optimized the extracellular matrix in which the blood vessel organoids were embedded, testing different ratios of Matrigel to collagen. Expression of the endothelial genes PECAM1 and CDH5, markers of vascular density and junctional organization, peaked at a one-to-three Matrigel-to-collagen ratio, while alpha-SMA, a marker of aberrant mural-cell activation, rose in collagen-rich matrices. With this optimized composition in hand, the team cut mature, cyst-like skin organoids into eight pieces each and placed them onto pre-vascularized matrix, then cultured the combined tissues at an air–liquid interface for several weeks.

Over 28 days, the fused structures underwent a striking transformation. Initially the skin organoid fragments and vascular matrix retained distinct boundaries, but within a week the skin tissue spread across the vascularized surface. By day 15 the construct had thickened and consolidated, and by day 28 branched CD31-positive vascular networks had arborized extensively through the dermal compartment. Gene-expression analysis tracked this maturation, with PECAM1 and CDH5 rising steadily while the barrier genes filaggrin and loricrin were significantly upregulated by the end of the culture period. Three-dimensional reconstructions showed that the vascular networks maintained relatively uniform vessel diameters, and hair-follicle-like structures were frequently found sitting adjacent to vessels, echoing the intimate spatial relationship between skin appendages and blood supply in native tissue. The vascularized constructs also secreted more vascular endothelial growth factor and nitric oxide than non-vascularized controls, indicating genuine endothelial activity rather than passive decoration.

Single-cell RNA sequencing confirmed that the assembloids had gained cellular complexity, not just structural features. Compared with conventional skin organoids, VSAs contained increased proportions of cells expressing endothelial markers such as PECAM1, CDH5, KDR, VWF and CLDN5, as well as perivascular markers including PDGFRB, RGS5 and ACTA2. Enrichment analysis of genes upregulated in the assembloids pointed to programs of endothelial proliferation and migration, vasculature development, angiogenesis, basement membrane organization and cytokine response. Histology reinforced the picture: the assembloids developed a defined KRT5-positive basal layer and KRT10-positive suprabasal layer, expressed filaggrin and loricrin more prominently than ordinary skin organoids, and restricted penetration of Lucifer Yellow dye largely to the outer epidermis, evidence of a more mature barrier. When transplanted onto wounds in immunodeficient mice, the grafts persisted for four weeks, and their human CD31-positive vessels connected with mouse host vasculature and became accessible to an intravenously injected lectin, suggesting the engineered vessels can be incorporated into a living circulatory system.

The most consequential addition, however, was immunological. The team incorporated mononuclear cells isolated from umbilical cord blood into the assembloids and challenged the system with lipopolysaccharide, a bacterial endotoxin. In vascularized constructs, the immune cells migrated into the upper dermis and clustered near CD31-positive vascular structures, whereas in matched avascular organoids the infiltrating cells rarely progressed beyond the lower dermis. Molecular readouts told the same story: after LPS stimulation, vascularized assembloids with immune cells showed markedly higher expression of the adhesion molecules ICAM1 and VCAM1 and the inflammatory cytokines IL-6 and TNF-alpha than any other condition, with ICAM1 upregulation localized to the endothelial structures themselves. In other words, the vasculature was not merely a passive conduit but an active participant in recruiting and activating immune cells, exactly as it does in inflamed human skin.

With an immune-responsive, vascularized skin model in hand, the researchers turned to atopic dermatitis. They applied house dust mite extract, a major environmental allergen, to the epidermal surface of the assembloids in three treatments spaced two days apart. The response was dramatic and reproducible. Transcriptomic profiling separated treated and control samples cleanly, revealing activation of inflammatory, cornification and type 2 immune-regulation programs, along with TNF and IL-17 signalling pathways. Crucially, when the team compared their treated assembloids with published gene-expression data from skin biopsies of atopic dermatitis patients, the patterns partially paralleled each other: both showed elevated type 2 and alarmin-associated genes such as IL33, IL4R, CCL17 and CCL26, keratinocyte stress markers including KRT16, S100A8 and S100A9, and adhesion and infiltration mediators such as CXCL8 and ICAM1. At the tissue level, allergen exposure thickened the epidermis, reduced filaggrin, raised KRT16 and drove immune cells along vascular structures into the upper dermis. Flow cytometry identified CD4-positive and CD8-positive T cells, CD14-positive myeloid cells and CD11c-positive HLA-DR-positive antigen-presenting-like populations, with a rightward shift in HLA-DR intensity suggesting myeloid activation. The treated assembloids also secreted elevated levels of TSLP, CCL17, IL-4, IL-13, VEGF and nitric oxide.

The final test was pharmacological, and here the model passed with a precision that will excite drug developers. The team applied upadacitinib, a JAK1 inhibitor, and dupilumab, an antibody that blocks the IL-4 receptor alpha subunit, two drugs with proven efficacy in moderate-to-severe atopic dermatitis. Both agents reduced allergen-induced epidermal hyperplasia, restored expression of the barrier proteins filaggrin, loricrin and claudin-1, suppressed TSLP and KRT16, and reduced the infiltration of CD4-positive T cells into the upper dermis. Mechanistically, house dust mite exposure strongly increased phosphorylation of STAT6, the central transcription factor downstream of IL-4 and IL-13 signalling, and both drugs significantly diminished this activation, along with the expression of STAT6 target genes including TARC, MDC, CCL26 and POSTN. Cytokine profiling showed broad suppression of the allergen-induced mediators IL-33, ST2, IL-4, IL-13, CCL17, RANTES, VCAM1 and VEGF. The responses matched the known mechanisms of action of both therapeutics, which is precisely what a preclinical screening platform should do.

The authors are candid about the limits of their system. The vascular networks, while organized and associated with basement membrane and perivascular cells, do not yet form a fully mature, perfusable artery-vein-capillary hierarchy, because the static air–liquid culture lacks blood flow and haemodynamic cues; integrating microfluidic perfusion could change that. Definitive lymphatic vessels were not observed, the immune compartment derives from cord blood rather than skin-resident cells and lacks bona fide Langerhans cells and tissue-resident memory T cells, and the allergen model captures an acute response rather than the chronic, relapsing reality of clinical atopic dermatitis. Even so, the achievement is substantial: a modular, human-cell-derived skin model that assembles epithelium, dermis, vessels and immune cells in a tunable way, reproduces key molecular features of a common allergic disease, and responds to real drugs in a mechanism-consistent manner. Beyond disease modelling, the preformed vascular networks suggest future roles in regenerative medicine, from wound healing to bioengineered skin grafts, where vascularization remains the central bottleneck. For a field long forced to choose between oversimplified dishes and imperfect animal models, vascularized skin assembloids offer a third option that looks increasingly like the real thing.

Subject of Research: Vascularized, immune-integrated human skin assembloids for modelling atopic dermatitis and drug testing in vitro

Article Title: Vascularized human skin assembloids model compartmental skin organization and immune responsiveness in vitro

Article References: Kim, M.-J., Lee, S., & Kang, K.-S. (2026). Vascularized human skin assembloids model compartmental skin organization and immune responsiveness in vitro. Experimental & Molecular Medicine. https://doi.org/10.1038/s12276-026-01840-x

Image Credits: AI Generated

DOI: 10.1038/s12276-026-01840-x

Keywords: skin assembloids, organoids, atopic dermatitis, vascularization, immune cells, house dust mite, upadacitinib, dupilumab, STAT6 signalling, induced pluripotent stem cells, skin barrier, inflammatory skin disease

The study, conducted by researchers at Pfizer Japan, IQVIA Solutions Japan, and Pfizer Inc., built a hybrid model combining a decision tree for the initial induction phase with a Markov framework for maintenance and all subsequent lines of therapy. Patients who failed their first advanced therapy were assumed to switch to an alternative agent, then to a basket of remaining drugs, and eventually to best supportive care if they continued to lose response. The simulated population mirrored Japanese trial participants newly starting advanced therapy, with a mean age of 42.4 years and a mean body weight of 59.7 kilograms. Efficacy and safety inputs came from a Bayesian network meta-analysis covering ten advanced therapies, supplemented with Japan-specific costs drawn from a nationwide claims database and adjusted to 2025 price levels.

The economics were evaluated from the perspective of the Japanese payer, with both costs and quality-adjusted life years discounted at an annual rate of 2.0 percent, in line with national health technology assessment guidelines. The willingness-to-pay threshold was set at JPY 7,500,000 per QALY, roughly USD 49,547, the benchmark used in Japan’s system for designated intractable diseases, a category to which ulcerative colitis belongs. Only serious infections were modelled as adverse events, a choice consistent with previous economic evaluations in this therapeutic area, because they drive the greatest costs and quality-of-life impairment while safety profiles across the drug classes remain broadly similar.

The central result was striking in its clarity. Among all 79 sequences evaluated, starting with etrasimod and following with upadacitinib produced the greatest lifetime health benefit, a total of 17.801 quality-adjusted life years. Four strategies anchored the efficiency frontier, the curve tracing the most efficient options at each cost level: infliximab followed by ustekinumab, infliximab followed by etrasimod, infliximab followed by upadacitinib, and etrasimod followed by upadacitinib. Each successive step along the frontier bought more health at an incremental cost-effectiveness ratio comfortably below the Japanese threshold, culminating in etrasimod followed by upadacitinib at JPY 6,684,442 per QALY, which remained cost-effective and delivered the most value overall.

The mechanistic logic behind the winning sequence is instructive. The network meta-analysis showed that upadacitinib, an oral JAK inhibitor, achieved the highest remission and response rates among patients who had already been exposed to advanced therapy, making it a particularly powerful second-line option. Etrasimod, which traps lymphocytes in lymph nodes by modulating the S1P receptor on their surface and thereby blunts intestinal inflammation while preserving systemic immune surveillance, showed favorable efficacy and safety across multiple endpoints in treatment-naïve patients. Pairing the two oral agents in that order therefore maximized cumulative quality-adjusted survival, and etrasimod outperformed ozanimod, its identically priced oral counterpart, on maintenance response, remission, and serious infection rates in the comparative evidence underpinning the model.

Sensitivity analyses revealed where the conclusion could shift. When infliximab and adalimumab biosimilars were introduced into the model, the picture changed materially. Because biosimilar infliximab costs JPY 13,860 per 100-milligram vial compared with JPY 35,981 for the originator, a first-line biosimilar infliximab sequence followed by upadacitinib became the most cost-effective strategy, pushing the etrasimod-upadacitinib combination above the threshold. Yet the authors caution that real-world biosimilar uptake in Japanese ulcerative colitis remains around 20 percent, and a survey found that 85 percent of Japanese inflammatory bowel disease patients were unaware biosimilars even existed. Under Japan’s high-cost medical expense benefit program, out-of-pocket costs are so constrained that patients have little financial incentive to switch.

Other scenario analyses tested alternative assumptions about disease progression and treatment intensity. Allowing dose escalation of tofacitinib, upadacitinib, and ustekinumab during maintenance left etrasimod followed by upadacitinib as the most cost-effective sequence, though with a narrower margin. Assuming patients never transitioned from later-line therapy to best supportive care shifted the optimal sequence to etrasimod followed by ustekinumab. Applying higher colectomy rates, informed by Japanese national database studies, moved infliximab followed by upadacitinib to the top. The fragility of the base-case result was further underlined by the one-way sensitivity analysis, in which placebo-arm maintenance parameters and infliximab’s relative efficacy had the largest influence on the incremental net monetary benefit.

The study carries important caveats that temper any temptation to treat its ranking as clinical gospel. Efficacy estimates derive from a network meta-analysis of trials published through November 2022, and such analyses for ulcerative colitis are known to suffer from heterogeneity in prior biologic exposure, baseline disease activity, and outcome definitions. Real-world evidence, which now exists for several of the agents, was excluded because of incomparability across studies. Serious infections were the only adverse event modelled, leaving unquantified risks such as major cardiovascular events, venous thromboembolism, herpes zoster, and malignancy, factors that matter greatly in real treatment choices. Utility values came largely from non-Japanese populations, and the transition rate from late-line therapy to best supportive care was borrowed from a United States claims database.

There is also the question of who conducted the analysis. All clinical authors are Pfizer employees or contractors funded by Pfizer Japan, and the company financed the research and publication. The acknowledged conflicts do not invalidate the mathematics, but they do mean the framing of etrasimod, a Pfizer drug, as the preferred starting point deserves independent scrutiny, particularly given how sensitive the results were to pricing assumptions around cheaper biosimilars.

For clinicians and policymakers, the study’s value lies less in crowning a single winner than in demonstrating that sequencing choices carry quantifiable economic and health consequences over a lifetime of disease. The authors themselves stress that the findings should complement, not dictate, clinical judgement, alongside patient age, comorbidities, pregnancy plans, and personal preference. As Japan’s ulcerative colitis population grows, having expanded roughly 1.4-fold over eight years, and as real-world data accumulate on the newer oral agents, future updates of this model will be needed to confirm whether the etrasimod-then-upadacitinib pathway truly delivers the best value in everyday practice rather than in simulation.

Subject of Research: Cost-effectiveness modeling of advanced therapy sequences for moderately to severely active ulcerative colitis in Japan

Article Title: Comparative Cost-Effectiveness of Advanced Treatment Sequences for Moderately to Severely Active Ulcerative Colitis in Japan

Article References: Kamei, K., Enami, M., Matsuda, H., Yamagami, K., Dai, Y., Hoshi, M., Law, E. H., & Yuasa, A. (2026). Comparative Cost-Effectiveness of Advanced Treatment Sequences for Moderately to Severely Active Ulcerative Colitis in Japan. Advances in Therapy. https://doi.org/10.1007/s12325-026-03757-3

Image Credits: AI Generated

DOI: 10.1007/s12325-026-03757-3

Keywords: ulcerative colitis, cost-effectiveness, etrasimod, upadacitinib, infliximab, S1P receptor modulators, JAK inhibitors, network meta-analysis, QALY, Japan, biosimilars, treatment sequencing

The journey to that outcome began in April 2023, when the patient arrived complaining of progressive pain in the small joints of his hands and wrists, his hips, and chronic low back pain with roughly thirty minutes of morning stiffness. His blood tests showed marked inflammation: an erythrocyte sedimentation rate of 49 millimeters per hour and C-reactive protein at 29.4 milligrams per liter, both far above normal. Yet his rheumatoid factor, anti-CCP antibodies, and HLA-B27 were all negative. Ultrasound confirmed synovial swelling in his hand joints, and with no visible skin lesions, his physicians reasonably diagnosed seronegative rheumatoid arthritis. Methotrexate plus the TNF inhibitor etanercept brought only partial relief, and liver enzyme elevations forced the methotrexate to be abandoned. Etanercept alone failed, adalimumab failed, and the inflammatory fire kept burning.

By June 2024, computed tomography and magnetic resonance imaging revealed bilateral sacroiliitis—inflammation of the joints linking the spine to the pelvis—prompting a revised diagnosis of ankylosing spondylitis with high disease activity on both scoring systems. Treatment switched again, this time to ixekizumab, a monoclonal antibody that neutralizes interleukin-17A, a central cytokine in spondyloarthritis. The drug helped, but not enough; inflammation persisted and painkillers remained a daily necessity. Because the patient carried a heavy burden of metabolic syndrome—obesity, hypertension, diabetes, hyperlipidemia, hyperuricemia, and fatty liver disease—his clinicians had deliberately avoided JAK inhibitors, fearing metabolic side effects. The breakthrough came two months later, when pitting nail changes appeared and careful, repeated questioning, corroborated by family members, uncovered a forgotten diagnosis of childhood psoriasis that had been quiescent for more than two decades.

That long-dormant history, plus the nail dystrophy and inflammatory joint disease, satisfied the 2006 CASPAR classification criteria with a score of four points. The diagnosis became psoriatic arthritis, and the treatment team added upadacitinib at fifteen milligrams daily to the continuing ixekizumab. The response was rapid and complete: articular symptoms resolved, C-reactive protein and sedimentation rate normalized, and the ankylosing spondylitis disease activity score plummeted from 3.06 to 0.94 on the CRP-based measure and from 3.25 to 1.2 on the ESR-based measure, indicating low disease activity. Ten months later, the patient reported no adverse reactions. In an unexpected twist, his metabolic parameters improved substantially, with better blood pressure, blood glucose, lipids, and uric acid—likely reflecting restored physical activity, weight loss, and the dominant anti-inflammatory effect of effective disease control overriding the lipid-raising potential intrinsic to JAK1 inhibition.

The immunological rationale for pairing these two drug classes is grounded in the tangled biology of psoriatic arthritis itself. The disease is driven by interconnected cascades: dendritic cells and macrophages release IL-23, which fuels Th17 cells and sustains the IL-17/IL-22 axis, while the JAK-STAT pathway serves as the intracellular conduit for a host of pro-inflammatory signals including interferons, IL-6, and IL-12/23. Blocking a single cytokine, the authors argue, can be circumvented by compensatory upregulation of alternative pathways and by JAK-STAT activation persisting within tissue-resident cells such as synovial fibroblasts, osteoclasts, and entheseal cells. Dual blockade collapses this redundancy, suppressing two arms of the inflammatory network simultaneously. It may also permit lower drug doses and forestall the escape mechanisms that limit single-agent therapy, an appealing proposition in a disease where no trial has ever pushed ACR20 response rates above sixty percent.

To contextualize their case, the researchers conducted a scoping review following PRISMA-ScR guidelines, systematically searching PubMed from January 2000 through September 2025 and screening more than two thousand records. Sixteen studies met inclusion criteria, encompassing dozens of individual patients treated with combinations spanning TNF inhibitors, IL-12/23 and IL-23 blockers, IL-17 inhibitors, JAK inhibitors, the phosphodiesterase inhibitor apremilast, and the TYK2 inhibitor deucravacitinib. Most reported meaningful clinical improvement, and several recent case series pairing oral JAK or TYK2 inhibitors with biologics achieved minimal disease activity without adverse events. The history of the field, however, carries warnings. Early combination attempts in rheumatoid arthritis, such as etanercept with anakinra or abatacept, were abandoned for insufficient efficacy and heightened infection risk, and ABT-122, an engineered antibody designed to block both TNF and IL-17 in a single molecule, failed to outperform adalimumab and was discontinued for psoriatic arthritis.

Safety remains the central question hanging over the entire approach. Combining two immunosuppressants raises the theoretical specter of synergistic infection risk, and the published literature documents tuberculosis, herpes zoster flares, skin infections, and respiratory infections among patients on dual biologic regimens. The authors emphasize that the true incidence of serious infections, cardiovascular events, venous thromboembolism, and malignancy under combination therapy cannot be quantified from isolated case reports, which are also vulnerable to publication bias favoring successful outcomes. Their own case encountered no infectious complications, but the follow-up period, while adequate to demonstrate efficacy, remains too short to establish long-term safety. Rigorous controlled trials with extended surveillance, they conclude, are an essential prerequisite before combination therapy can move from desperate rescue strategy to standard practice.

Beyond the therapeutic lesson, the case exposes what the authors call a critical blind spot in diagnostic paradigms. Neither the 2010 ACR/EULAR criteria for rheumatoid arthritis nor the ASAS criteria for axial spondyloarthritis incorporate structured screening for remote or dormant psoriasis. HLA-B27 negativity, present in this patient, is atypical for ankylosing spondylitis, where roughly ninety percent of patients carry the marker, but entirely compatible with psoriatic arthritis, where prevalence sits between twenty and thirty percent—a subtle clue that went unrecognized for over a year. The authors propose a standardized screening protocol for all patients with seronegative inflammatory arthritis: persistent, structured questioning about childhood and remote skin conditions with family verification, systematic examination of the nails and occult sites such as the scalp, umbilicus, and intergluteal cleft, and a low threshold for sacroiliac imaging. They further argue that electronic health records should flag historical psoriasis diagnoses for rheumatologists, and that patients with long-standing psoriasis deserve periodic joint screening even after their skin clears.

The patient, reflecting on his own sixteen-month odyssey through three diagnoses and multiple medications, described the frustration of partial responses and unrelenting painkiller dependence, followed by the near-immediate disappearance of pain and stiffness once the second drug was added. The research team frames the case as evidence that refractory psoriatic arthritis, particularly in patients whose diagnosis was delayed and whose disease spans both axial and peripheral joints, may respond to dual IL-17 and JAK pathway blockade where monotherapy fails. Their agenda for the field is explicit: randomized controlled trials with endpoints covering joints, skin, spine, and entheses; biomarker studies to identify which patients truly need dual targeting rather than empirical trial and error; long-term registries to pin down the safety profile; and de-escalation studies to learn whether remission, once achieved, can be held on less intensive therapy. Until such data arrive, the case stands as a compelling proof of concept—and a reminder that in inflammatory arthritis, the skin’s history can hold the key to both the diagnosis and the cure.

Subject of Research: Combined IL-17 inhibitor and JAK inhibitor therapy for refractory psoriatic arthritis

Article Title: Combination Treatment of IL‐17 Inhibitor and JAK Inhibitor in Psoriatic Arthritis: A Case Report and Scoping Review

Article References: Pang, M., Li, L., Zhang, Q., & Zhao, M. (2026). Combination Treatment of IL‐17 Inhibitor and JAK Inhibitor in Psoriatic Arthritis: A Case Report and Scoping Review. Immunity, Inflammation and Disease, 14(9), Article e70515. https://doi.org/10.1002/iid3.70515

Image Credits: AI Generated

DOI: 10.1002/iid3.70515

Keywords: psoriatic arthritis, ixekizumab, upadacitinib, IL-17 inhibitor, JAK inhibitor, combination therapy, biologics, tsDMARDs, sacroiliitis, seronegative arthritis, metabolic syndrome, CASPAR criteria