A preprint by Lunger et al. reports macrophage engineering through constitutively active synthetic cytokine receptors to induce polarization states that are unobtainable with natural cytokine receptors.

Bone regeneration is a complex, tightly regulated process involving coordinated interactions of immune and stromal cells. Early phases of healing rely on the timely clearance of debris, a task primarily carried out by macrophages and osteoclasts. However, the sequence of events leading to the presence of osteoclasts at the fracture site and how this is shaped by local tissue microenvironments remains poorly understood, particularly at single-cell and spatial resolution. Using single-cell RNA sequencing and multi-epitope ligand cartography, we mapped the spatial organization of distinct cell compartments engaged in early fracture healing in both young and aged female mice at the start of healing. Surprisingly, we found that young mice exhibited an increased presence of activated osteoclasts at day 7, concentrated within the cortical niche. This compartment was also characterized by a spatially restricted immune response with a selective accumulation of distinct macrophage types jointly interacting with neutrophils and stromal cells. This raised the possibility that local cell organization influences osteoclast precursor differentiation. We identified a fracture-associated Spp1hi macrophage subset enriched at the cortex, which represented a transitional monocyte-derived state that expressed early osteoclast differentiation transcripts and gave rise to osteoclasts ex vivo. Neutrophils preceded fracture-associated Spp1hi macrophage accumulation and may promote their recruitment through chemotactic signaling. This coordination was less pronounced in aged mice despite preserved transcriptional states. In parallel, stromal cells in young animals displayed higher expression of essential niche factors, further supporting local osteoclastogenesis at the cortex. Together, our findings identify a distinct macrophage state that contains cells with osteoclast differentiation potential and reveal early, cortex-specific niche activity supporting osteoclastogenesis. This provides a new framework for understanding the initiation of spatial immune-stromal interactions for the early stages of regeneration.

Abstract Memory-like or precursor exhausted (Tpex) CD8+ T cells are a critical reservoir in chronic infections and cancer, yet the signals sustaining their cytokine production remain unclear. Here, we identify KLRF1 as part of a CD4–CD8 communication axis that supports cytokine production in late-differentiated human CD8+ T cells. KLRF1 is upregulated in late-differentiated CD8+ T cells, and neutralizing KLRF1 reduces TNF and IFN-γ production. Differentiated CD4+ T cells express the KLRF1 ligand AICL, and in co-culture only AICL+ - not AICL⁻ - CD4+ T cells enhance cytokine output in CD8+ T cells. Using spatial proteomics of lung adenocarcinoma and adjacent tissue, we found that CD4+ AICL+ and CD8+ KLRF1+ T cells are enriched and spatially interacting in non-tumor regions, whereas both populations are reduced within tumor tissue. Single-cell RNA-seq of tissue samples and scRNA/ATAC analyses of circulating immune cells further showed that CD8+KLRF1+ T cells display a Tpex-like transcriptional and chromatin-accessibility profile. Together, these data identify the AICL–KLRF1 axis as a CD4+–CD8+ communication pathway that supports cytokine competence in late-differentiated CD8+ T cells.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex, multisystemic disorder mostly triggered by viral infections, with core symptoms including post-exertional malaise (PEM), fatigue, pain, and cognitive dysfunction. Its prevalence has increased significantly in the context of the coronavirus disease 2019 (COVID-19) pandemic. Despite its severity and impact on patients' quality of life, ME/CFS remains poorly understood. On May 12 and 13, 2025, the 3rd International Conference hosted by the Charité Fatigue Center brought together nearly 200 researchers from various disciplines on-site, and around 3,700 participants online to discuss recent advances in ME/CFS research, diagnostics, clinical care, and therapeutic trials. The program featured 33 lectures by international experts on key topics such as post-COVID syndrome (PCS), care structures, and pathophysiological mechanisms including cardiovascular dysregulation, immune dysregulation, autoimmune mechanisms, and metabolic dysfunction. In addition, results from clinical trials addressing disease mechanisms, including those specifically targeting autoantibodies, were presented. While public awareness and funding opportunities have increased in the wake of the pandemic and the emergence of PCS, ME/CFS remains severely underresearched. Sustained and adequately funded research efforts are urgently required to advance understanding, identify diagnostic markers, and develop targeted therapeutic interventions.

Type 2 diabetes is linked to systemic inflammation driven by metabolic stress and aging. Although pancreatic inflammation associated with these factors is well documented, the dynamics of immune cell populations and their molecular changes remain poorly understood. We characterized immune cell alterations in the pancreas and pancreatic islets during Western diet (WD) feeding and aging using imaging mass cytometry (IMC) and single-cell RNA sequencing (scRNA-seq). Spatial and transcriptional analyses were performed to define immune cell subtype composition, activation states, and inferred cell-cell communication programs under metabolic and age-related stress conditions. Our analyses identified expansion of an F4/80low macrophage subtype and activated effector-like CD8+ T cells throughout the pancreas during WD feeding and aging. Within pancreatic islets, single-cell RNA sequencing identified a type I interferon-responsive macrophage population with low F4/80 expression that expanded during overnutrition. Notably, the type I interferon responses elicited by these stressors diverged: aging was associated with a more canonical type I interferon response, whereas overnutrition induced a broader response that included STAT3-associated transcriptional programs. We further provide evidence for enhanced cytokine-mediated communication between macrophages and a CD8+ cytotoxic T-cell population under overnutrition and aging. These findings show that metabolic stress and aging remodel pancreatic inflammation through overlapping but distinct immune mechanisms, involving expansion of F4/80low macrophages, activation of divergent type I interferon programs, and enhanced macrophage-CD8+ T-cell communication. Together, these findings suggest that distinct therapeutic approaches may be required to preserve islet function in type 2 diabetes driven by metabolic stress versus aging.

Insufficient healing of the Achilles tendon remains a frequent clinical challenge, creating a need for early markers that identify patients at risk of impaired healing. To examine whether adaptive immunity contributes to these outcomes, we analyzed T cell subsets in blood and hematoma collected during surgery. Patients with a higher CD4+/CD8+ T cell ratio at surgery reported more pain, showed reduced functional recovery, and greater tendon strain after 12 months. Conversely, elevated CD8+ T cell levels, and the CD28-/CD57+ memory subset, coincided with more favorable outcomes. We then investigated how these cells affect tendon healing by co-culturing human tenocytes with CD4+ or CD8+ T cells. Exposure to CD4+ T cells increased collagen type 3, IL-17 receptors and matrix metalloproteinases expression, indicating a shift toward impaired extracellular matrix organization. These results suggest that the CD4+/CD8+ T cell balance may serve as a prognostic marker and that modulating CD4+ T cell activity or IL-17 signaling could improve tendon repair.

Insufficient healing of the Achilles tendon remains a frequent clinical challenge, creating a need for early markers that identify patients at risk of impaired healing. To examine whether adaptive immunity contributes to these outcomes, we analyzed T cell subsets in blood and hematoma collected during surgery. Patients with a higher CD4+/CD8+ T cell ratio at surgery reported more pain, showed reduced functional recovery, and greater tendon strain after 12 months. Conversely, elevated CD8+ T cell levels, and the CD28-/CD57+ memory subset, coincided with more favorable outcomes. We then investigated how these cells affect tendon healing by co-culturing human tenocytes with CD4+ or CD8+ T cells. Exposure to CD4+ T cells increased collagen type 3, IL-17 receptors and matrix metalloproteinases expression, indicating a shift toward impaired extracellular matrix organization. These results suggest that the CD4+/CD8+ T cell balance may serve as a prognostic marker and that modulating CD4+ T cell activity or IL-17 signaling could improve tendon repair.

In a subset of children and adolescents, SARS-CoV-2 infection induces a severe acute hyperinflammatory shock1 termed multisystem inflammatory syndrome in children (MIS-C) at four to eight weeks after infection. MIS-C is characterized by a specific T cell expansion2 and systemic hyperinflammation3. The pathogenesis of MIS-C remains largely unknown. Here we show that acute MIS-C is characterized by impaired reactivation of virus-reactive memory T cells, which depends on increased serum levels of the cytokine TGFβ resembling those that occur during severe COVID-19 (refs. 4,5). This functional impairment in T cell reactivity is accompanied by the presence of TGFβ-response signatures in T cells, B cells and monocytes along with reduced antigen-presentation capabilities of monocytes, and can be reversed by blocking TGFβ. Furthermore, T cell receptor repertoires of patients with MIS-C exhibit expansion of T cells expressing TCRVβ21.3, resembling Epstein-Barr virus (EBV)-reactive T cell clones capable of eliminating EBV-infected B cells. Additionally, serum TGFβ in patients with MIS-C can trigger EBV reactivation, which is reversible with TGFβ blockade. Clinically, the TGFβ-induced defect in T cell reactivity correlates with a higher EBV seroprevalence in patients with MIS-C compared with age-matched controls, along with the occurrence of EBV reactivation. Our findings establish a connection between SARS-CoV-2 infection and COVID-19 sequelae in children, in which impaired T cell cytotoxicity triggered by TGFβ overproduction leads to EBV reactivation and subsequent hyperinflammation.

Immune evasion by escape mutations subverts immunity against SARS-CoV-2. A role of pan-coronavirus immunity for more durable protection is being discussed, but has remained understudied. We here investigated the effects of age, mutations, and homo-/heterologous vaccination regimens on the dominant pan-coronavirus-specific cellular and humoral epitope iCope after SARS-CoV-2 infection and vaccination in detail. In older individuals, the quantitatively and qualitatively reduced iCope-reactive CD4+ T cell responses with narrow TCR repertoires could not be enhanced by vaccination and were further compromised by emerging spike mutations. In contrast, pan-coronavirus-reactive humoral immunity was affected only by mutations and not by age. Our results reveal a distinct deficiency of the dichotomous layer of pan-coronavirus immunity in the older, critical for long-term protection against SARS-CoV-2 variants.

Advanced age is the most important risk factor for severe disease or death from COVID-19, but a thorough mechanistic understanding of the molecular and cellular underpinnings is lacking. Multi-omics analysis of 164 samples from SARS-CoV-2-infected persons aged 1 to 84 years reveals a rewiring of type I interferon (IFN) signaling with a gradual shift from signal transducer and activator of transcription 1 (STAT1) to STAT3 activation in monocytes, CD4+ T cells, and B cells with increasing age. Diversion of IFN signaling is associated with increased expression of inflammatory markers, enhanced release of inflammatory cytokines, and delayed contraction of infection-induced CD4+ T cells. A shift from IFN-responsive germinal center B (GCB) cells toward CD69high GCB and atypical B cells during aging correlates with immunoglobulin (Ig)A production in children, whereas complement-fixing IgG predominates in adults. Our data provide a mechanistic basis for inflammation-prone responses to infections and associated pathology during aging.

Myocarditis, characterized by inflammatory cell infiltration, can have multiple etiologies, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection or, rarely, mRNA-based coronavirus disease 2019 (COVID-19) vaccination. The underlying cellular and molecular mechanisms remain poorly understood. In this study, we performed single-nucleus RNA sequencing on left ventricular endomyocardial biopsies from patients with myocarditis unrelated to COVID-19 (Non-COVID-19), after SARS-CoV-2 infection (Post-COVID-19) and after COVID-19 vaccination (Post-Vaccination). We identified distinct cytokine expression patterns, with interferon-γ playing a key role in Post-COVID-19, and upregulated IL16 and IL18 expression serving as a hallmark of Post-Vaccination myocarditis. Although myeloid responses were similar across all groups, the Post-Vaccination group showed a higher proportion of CD4+ T cells, and the Post-COVID-19 group exhibited an expansion of cytotoxic CD8+ T and natural killer cells. Endothelial cells showed gene expression changes indicative of vascular barrier dysfunction in the Post-COVID-19 group and ongoing angiogenesis across all groups. These findings highlight shared and distinct mechanisms driving myocarditis in patients with and without a history of SARS-CoV-2 infection or vaccination. Maatz, Lindberg et al. identify molecular alterations and immune response changes in endomyocardial biopsies from patients with myocarditis after COVID-19 infection, after anti-COVID-19 vaccination or from non-COVID-related causes.

The majority of patients recovers from severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) coronavirus disease 2019 (COVID-19) without obvious sequelae, but a significant proportion suffers long-term consequences which have been termed post COVID syndrome (PCS). Despite a wide range of considerations on treatment options in PCS and a significant number of trials initiated, only very few results from randomized controlled trials are currently available. In conclusion, there is an evident medical need to identify treatments for patients with PCS. The primary objective of the platform trial RAPID is to assess the impact of different PCS treatments on the overall physical function of patients. Designed as a master protocol, RAPID contains all information that is generic to this adaptive platform trial. Current and future study treatments are specified in intervention-specific appendices (ISA). The first ISA, RAPID_REVIVE is presented in this manuscript. General sections of the master protocol are named as such. RAPID_REVIVE is a double-blind, placebo-controlled, phase II clinical trial evaluating antiviral PCS treatment with vidofludimus calcium (IMU-838). Patients are randomized at a 1:1 ratio to 45 mg/day vidofludimus calcium (22.5 mg for the first 7 days) or placebo during an initialization phase and thereafter using a response-adaptive randomization procedure. The trial includes a screening period of 7 days, a double-blind treatment period of 56 days and a follow-up period of 28 days. The primary outcome is the intra-patient change in physical function measured by the Short Form-36 Physical Function (SF-36-PF) from baseline to day 56. Secondary endpoints include mental and physical health, intensity of fatigue, severity of mental disorder symptoms, and cognitive function. PCS is a major problem for global health care and the identification of treatment options is urgently needed. Currently, PCS patients are in a situation without evidence-based treatment options, and quality of life, and often mental health are significantly impaired. The purpose of RAPID is to establish an adaptive platform trial protocol which will concert and quicken clinical trials to evaluate the efficacy and safety of different potential treatments for PCS with the aim to expand the very limited evidence base for the treatment of PCS. EU Clinical Trials Register (CTIS) ID: 2024–511628-16–00 (RAPID_REVIVE). Registered on 18.03.2024.

Tissue fibrosis is characterised by the high-energy consumption associated with myofibroblast contraction. Although myofibroblast contraction relies on ATP production, the role of cellular metabolism in myofibroblast contraction has not yet been elucidated. Studies have so far only focused on myofibroblast contraction regulators, such as integrin receptors, TGF-β and their shared transcription factor YAP/TAZ, in a fibroblast-myofibroblast transition setting. Additionally, the influence of the regulators on metabolism and vice versa have been described in this context. However, this has so far not yet been connected to myofibroblast contraction. This review focuses on the known and unknown of how cellular metabolism influences the processes leading to myofibroblast contraction and vice versa. We elucidate the signalling cascades responsible for myofibroblast contraction by looking at FMT regulators, mechanical cues, biochemical signalling, ECM properties and how they can influence and be influenced by cellular metabolism. By reviewing the existing knowledge on the link between cellular metabolism and the regulation of myofibroblast contraction, we aim to pinpoint gaps of knowledge and eventually help identify potential research targets to identify strategies that would allow switching tissue fibrosis towards tissue regeneration.

Dexamethasone is a life-saving treatment for severe COVID-19, yet its mechanism of action is unknown, and many patients deteriorate or die despite timely treatment initiation. Here, we identify dexamethasone treatment-induced cellular and molecular changes associated with improved survival in COVID-19 patients. We observed a reversal of transcriptional hallmark signatures in monocytes associated with severe COVID-19 and the induction of a monocyte substate characterized by the expression of glucocorticoid-response genes. These molecular responses to dexamethasone were detected in circulating and pulmonary monocytes, and they were directly linked to survival. Monocyte single-cell RNA sequencing (scRNA-seq)-derived signatures were enriched in whole blood transcriptomes of patients with fatal outcome in two independent cohorts, highlighting the potential for identifying non-responders refractory to dexamethasone. Our findings link the effects of dexamethasone to specific immunomodulation and reversal of monocyte dysregulation, and they highlight the potential of single-cell omics for monitoring in vivo target engagement of immunomodulatory drugs and for patient stratification for precision medicine approaches.

Early identification of patients at risk for impaired tendon healing and corresponding novel therapeutic approaches are urgent medical needs. This study aimed to clarify the role of CD3+ T-cells during acute Achilles tendon (AT) healing. Blood and hematoma aspirate were taken from 26 patients during AT reconstruction, and additional blood samples were obtained during clinical follow-up at 6, 26 and 52 weeks after surgery. T-cell subsets were analyzed by flow cytometry using CD3, CD4, CD8, CD11a, CD57 and CD28 antibodies. Clinical follow-up included functional tests, MRI assessments, and subjective questionnaires. In vitro, the functional behavior of patient-derived tenocytes was investigated in co-cultures with autologous unpolarized CD4+ or CD8+ T-cells, or IFNy-polarized CD8+ or IL17-polarized CD4+ Tcells (n=5-6). This included alterations in gene expression (qPCR), MMP secretion (ELISA), migration rate (scratch wound healing assay) or contractility (collagen gels). Analysis revealed that elevated CD4+ T-cell levels and reduced CD8+ T-cell levels (increased CD4/CD8 ratio) in hematoma aspirate and pre-operative blood were associated with inferior clinical outcomes regarding pain and function at 26 and 52 weeks. Increased levels of CD8+ -memory T-cell subpopulations in blood 6 weeks after surgery were associated with less tendon elongation. In vitro, tenocytes showed increased MMP1/2/3 levels and collagen III/I ratio in co-culture with unpolarized and/or IL17-polarized CD4+ T-cells compared to unpolarized CD8+ T-cells. This coincided with increased IL17 receptor expression in tenocytes co-cultured with CD4+ T-cells. Exposure of tenocytes to IL17-polarized CD4+ T-cells decreased their migration rate and increased their matrix contractility, especially compared to IFNy-polarized CD8+ T-cells. The CD4+ /CD8+ T-cell ratio could serve as prognostic marker for early identification of patients with impaired AT healing potential. Local reduction of CD4+ T-cell levels or their IL17 secretion represent a potential therapeutic approach to improve AT healing and to prevent weakening of the tendon ECM.

In addition to acute hyperinflammatory responses, SARS-CoV-2 infections can have long-term effects on our immune system leading to, for example, post-acute sequelae of COVID-19 (PASC). In this issue of Cell, Cheong et al. show that severe infections via IL-6 induce persistent epigenetic signatures in hemopoietic stem cells and their myeloid progenitors associated with increased inflammatory potential.y

Disease-modifying therapies (DMTs) are widely used in neuroimmunological diseases such as multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD). Although these treatments are known to predispose patients to infections and affect their responses to vaccination, little is known about the impact of DMTs on the myeloid cell compartment. In this study, we use mass cytometry to examine DMT-associated changes in the innate immune system in untreated and treated patients with MS ( n = 39) or NMOSD ( n = 23). We also investigated the association between changes in myeloid cell phenotypes and longitudinal responsiveness to homologous primary, secondary, and tertiary SARS-CoV-2 mRNA vaccinations. Multiple DMT-associated myeloid cell clusters, in particular CD64 + HLADR low granulocytes, showed significant correlations with B and T cell responses induced by vaccination. Our findings suggest the potential role of myeloid cells in cellular and humoral responses following vaccination in DMT-treated patients with neuroimmunological diseases.