PURPOSE OF REVIEW:Autoimmune encephalitis (AE), paraneoplastic neurological syndromes (PNS), and glial antibody-mediated disorders (for example, AQP4-NMOSD) are traditionally classified based on the target antigens of their respective autoantibodies. However, recent insights from immunogenomics, single-cell sequencing, and neuropathology indicate that T cell programs substantially influence disease initiation, localization, and chronicity. This review highlights three emerging dimensions of T-cell involvement - circulating exhausted-like helper T-cell memory, intrathecal T-B cooperation, and parenchymal tissue-resident cytotoxicity - that offer new perspectives on clinical and pathological features across these disorders. RECENT FINDINGS:In AQP4-NMOSD, circulating exhausted-like CD4 + T cells may constitute a durable autoreactive memory reservoir capable of re-initiating plasmablast responses. In LGI1- and CASPR2-associated encephalitis, systemic and intrathecal CD4 + differentiation appears to support systemic antibody maturation and local plasmablast expansion, with emerging hints of some accompanying CD8 + -mediated tissue injury. In contrast, in PNS and intracellular antigen-associated AE, CD8 + T cell-mediated cytotoxicity dominates and is characterized by parenchymal CD8 + tissue-resident memory (TRM) signatures. SUMMARY:These T-cell dimensions may provide a useful framework for understanding clinical paradoxes - such as relapse despite B-cell depletion, persistent memory dysfunction in IgG4-AE, and therapeutic inefficacy in PNS - and suggest opportunities for therapeutic strategies targeting exhausted T-cell memory, intrathecal cooperation, or TRM stability.

IntroductionBlinatumomab (BLN) is a bispecific T-cell engager that has revolutionized the treatment of B-cell precursor acute lymphoblastic leukemia (BCP-ALL), significantly improving outcomes in both adults and children. By simultaneously binding to CD19 on B cells and CD3 on T cells, BLN triggers target cell-dependent T-cell activation, resulting in the cytolysis of CD19+ BCP-ALL cells. Despite the remarkable clinical advancements achieved with BLN, the immunological mechanisms underlying treatment response or failure remain poorly characterized. γδ T cells are attractive candidates for adoptive T-cell therapy due to potent cytotoxicity, capacity to present antigens, broad lysis of different tumor entities, and low alloreactivity. Because γδ T cells can also be redirected by BLN, we systematically studied BLN-driven effector functions in vitro in conventional αβ and unconventional γδ T cells from healthy donors.Materials and methodsWe evaluated cytotoxicity and cytokine/effector release in freshly isolated and in vitro-expanded αβ and γδ T cells from healthy adults against CD19+ BCP-ALL cell lines (NALM-6, HAL-01), and profiled dynamic phenotypic alterations by multiparametric flow cytometry.ResultsCD19+ targets were consistently reduced in the presence of BLN. Freshly isolated αβ, especially CD8+, displayed superior BLN-mediated effector functions as compared to γδ T cells, with donor-dependent variability in γδ killing. Notably, zoledronate-expanded Vγ9Vδ2 γδ T-cell lines achieved cytotoxicity comparable to PHA-expanded αβ cells. However, γδ T-cell-killing benefited from higher BLN concentration when challenged with high tumor load. In these in vitro healthy-donor T-cell cultures, BLN induced CD3 down-modulation in αβ T cells but not in γδ T cells, and αβ cultures released higher soluble Fas ligand, findings consistent with stronger early activation and suggestive of increased susceptibility to activation-associated apoptosis/AICD. Exploratory targeted single-cell transcriptomics (one donor) supported a pronounced activation/exhaustion program in αβ T cells and a comparatively stable effector-memory profile with low checkpoint expression in γδ T cells.DiscussionTogether, these in vitro data reveal subset-specific BLN responses and support the hypothesis that ex vivo-expanded Vγ9Vδ2 γδ T cells could complement BLN-mediated cytotoxicity, particularly under conditions of higher CD19 density and lower target burden. These findings provide a mechanistic framework for future testing of γδ T-cell/BLN combination strategies in patient-derived models and clinical studies.

The commensal yeast Candida albicans is a major inducer of human mucosal Th17 cells. How C. albicans drives Th17 cell responses at homeostasis, and whether such responses contribute to inflammatory diseases, remains poorly understood. Here, we showed that C. albicans-reactive Th17 cells targeted a limited set of proteins enriched in fungal extracellular vesicles. At homeostasis, these cells predominantly resided in the oral mucosa. However, T cell receptor profiling revealed shared clonotypes across oral and gut tissues, with C. albicans being a major driver of this repertoire overlap. In patients with Crohn’s disease, C. albicans-specific Th17 cells with features of oral priming were enriched in intestinal tissues, where they retained their focused antigen specificity but acquired pathogenic Th17 cell traits. Together, our results reveal a stable, antigen-restricted C. albicans Th17 subset that is shared across mucosal sites and undergoes functional adaptation in the inflamed intestine. These cells represent a potential target for immune modulation in Crohn’s disease.

The activation of human Vδ2 γδ T cells by phosphoantigens (pAg) strictly depends on transmembrane butyrophilin (BTN) molecules, specifically BTN3A isoforms and BTN2A1. Several bacteria, including M. tuberculosis, produce potent pAg and thus trigger a strong activation of Vδ2 T cells. The antigen-specific activation of CD4 and regulatory (Treg) T cells can be monitored by the rapid upregulation of CD154 and CD137, respectively. We have previously established that CD137 is also rapidly upregulated on Vδ2 T cells upon stimulation with pAg. In the present study, we have used antagonistic anti-BTN3A/2A1 antibodies to dissect the pAg-dependent and pAg-independent activation of Vδ2 T cells by various microbes. While the activation of Vδ2 T cells by pAg and aminobisphosphonate zoledronate was completely blocked by anti-BTN3A/2A1 antibodies, only partial inhibition was observed for activation with M. tuberculosis and other bacteria as analyzed by CD137/CD154 upregulation and intracellular interferon-γ expression. Similarly, anti-TCR antibody 7A5 and Lck inhibitor emodin had only a minimal inhibitory effect on activation by bacteria but strongly reduced pAg activation of Vδ2 T cells. Further studies revealed a crucial role of IL-18 in the BTN/TCR-independent early activation of Vδ2 T cells by bacteria. Neutralizing anti-IL-18 antibodies and inflammasome inhibition did not affect pAg activation of Vδ2 T cells but strongly reduced their activation by bacteria. Our results identify a BTN/TCR-independent but IL-18 and inflammasome-dependent activation pathway of Vδ2 T cells, which might be relevant for the role of Vδ2 T cells during bacterial infections.

Autoreactive CD4+ cells control the immune response in chronic autoimmune diseases but remain difficult to track. The ex vivo characterization of autoreactive T cells is essential to understand their function and how they adapt to chronic autoimmunity. Neuromyelitis optica spectrum disorder is a prototypic autoimmune disease of the central nervous system targeting aquaporin-4 (AQP4). AQP4-specific CD4+ T cells are centrally involved in disease development. However, their functional and molecular properties are poorly characterized. We combined HLA-tetramer- and antigen-reactive T cell enrichment and scRNA sequencing to characterize ex vivo AQP4-specific CD4+ T cells isolated from blood of patients and healthy donors. Surprisingly, in AQP4-antibody+ NMOSD patients, autoreactive T cells showed reduced proliferative capacity and pro-inflammatory cytokines. Instead, exhaustion-associated co-inhibitory receptors were co-expressed together with FOXP3. The proliferative blockade of autoreactive T cells was reversed in vitro by checkpoint inhibition. The same exhaustion-like phenotype was demonstrated in autoimmune hepatitis and bullous pemphigoid. We identified a new exhaustion-like T cell phenotype and a potential role of FOXP3 for the regulation of chronic autoreactivity in human autoimmune disease. Our data suggest CD4+ T cell exhaustion as a common mechanism of adaptation to chronic self-stimulation across disease types with important implications for their therapeutic targeting Basic Autoimmunity (BA)

Neurodegenerative dementias including Alzheimer disease severely impair cognitive and social abilities and are a major cause of mortality with no causal treatment yet. Autoimmune mechanisms have been increasingly considered to contribute to disease progression, e.g. by enhancing protein misfolding or pro-inflammatory immune responses. Understanding this contribution may lead to novel treatment options beyond removing neurodegeneration-associated proteins. We hypothesized that CD4+ TH cells against synaptic proteins may play a role in dementia, given the profound changes of synaptic proteins in the disease. We investigated TH cell frequencies and phenotypes after antigen-reactive T cell enrichment (ARTE) using three important synaptic antigens known to play a role in cognitive function, N-Methyl-D-Aspartate receptor (NMDAR), Leucine-rich, glioma inactivated 1 (LGI1) and metabotropic glutamate receptor 5 (mGluR5). Our data revealed that synaptic autoantigen-specific TH cells occurred in all cohorts and were similarly frequent in patients with dementia and sex- and age-matched controls. However, they were significantly reduced compared to young healthy subjects, indicating strong age-related effects (‘immune senescence’). Compared to the ubiquitously available Candida albicans antigen, synaptic autoantigen-specific TH cell responses were strongly driven by IFNγ-producing T cells, expression of which markedly decreased with age. Patients with dementia had significantly less IL-17-producing synaptic autoantigen-specific TH cells than aged healthy controls. This first direct ex vivo quantitative and qualitative analysis of circulating T cells autoreactive to three synaptic autoantigens in dementia shows no correlation with cognitive impairment. It suggests that synaptic autoantigen-specific TH cells decline with age and are not a major driver of dementia development.

Background Recently, autoantibodies directed against the epithelial adhesion protein integrin alpha V beta 6 have been identified that are strongly associated with ulcerative colitis (UC). We aimed to elucidate whether anti-integrin alpha V beta 6 (anti-alpha V beta 6) is present in primary sclerosing cholangitis (PSC), its associated inflammatory bowel disease, or other cholestatic liver diseases and their persistence after proctocolectomy.Methods We detected anti-alpha V beta 6 by an enzyme-linked immunosorbent assay in sera collected at 2 German tertiary centers, including healthy controls (N = 62), UC (N = 36), Crohn's disease (CD, N = 65), PSC-inflammatory bowel diseases (IBD) (78 samples from N = 41 patients), PSC without IBD (PSC, 41 samples from N = 18 patients), primary biliary cholangitis (PBC, N = 24), autoimmune hepatitis (AIH, N = 32), secondary sclerosing cholangitis (SSC, N = 12), and metabolic dysfunction-associated steatotic liver disease (MASLD, N = 24). In addition, sera after proctocolectomy were studied (44 samples/N = 10 patients). Immunofluorescent analyses were performed in tissue samples from liver, large bile duct from surgical resections, and colon of PSC patients.Results Anti-alpha V beta 6 occurred in 91% of UC, 17% of CD, 73% of PSC-IBD, 39% of PSC, 4% of PBC, 14% of AIH, and 0% of healthy controls, SSC, or MASLD. Integrin alpha V beta 6 is selectively expressed in disease-associated epithelia of both bile duct and colon. Anti-alpha V beta 6 levels correlate moderately with intestinal disease activity in PSC-IBD, but only weakly with biliary disease.Conclusions Anti-alpha V beta 6 frequently occurs in patients suffering from PSC, especially in PSC-IBD. Anti-alpha V beta 6 levels positively correlate to IBD activity in PSC-IBD, but may also occur in the absence of clinically manifest IBD in PSC. Graphical Abstract

The development of the human immune system lasts for several years after birth. The impact of this maturation phase on the quality of adaptive immunity and the acquisition of immunological memory after infection at a young age remains incompletely defined. Here, using an antigen-reactive T cell (ARTE) assay and multidimensional flow cytometry, we profiled circulating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-reactive CD3(+)CD4(+)CD154(+) T cells in children and adults before infection, during infection, and 11 months after infection, stratifying children into separate age groups and adults according to disease severity. During SARS-CoV-2 infection, children younger than 5 years old displayed a lower antiviral CD4(+) T cell response, whereas children older than 5 years and adults with mild disease had, quantitatively and phenotypically, comparable virus-reactive CD4(+) T cell responses. Adults with severe disease mounted a response characterized by higher frequencies of virus-reactive proinflammatory and cytotoxic T cells. After SARS-CoV-2 infection, preschool-age children not only maintained neutralizing SARS-CoV-2-reactive antibodies postinfection comparable to adults but also had phenotypically distinct memory T cells displaying high inflammatory features and properties associated with migration toward inflamed sites. Moreover, preschool-age children had markedly fewer circulating virus-reactive memory B cells compared with the other cohorts. Collectively, our results reveal unique facets of antiviral immunity in humans at a young age and indicate that the maturation of adaptive responses against SARS-CoV-2 toward an adult-like profile occurs in a progressive manner.

Pro-inflammatory autoantigen-specific CD4+ T helper (auto-Th) cells are central orchestrators of autoimmune diseases (AIDs). We aimed to characterize these cells in human AIDs with defined autoantigens by combining human leukocyte antigen (HLA)-tetramer-based and activation-based multidimensional ex vivo analyses. In aquaporin4-antibody-positive neuromyelitis optica spectrum disorder (AQP4-NMOSD) patients, auto-Th cells expressed CD154, but proliferative capacity and pro-inflammatory cytokines were strongly reduced. Instead, exhaustion-associated co-inhibitory receptors were expressed together with FOXP3, the canonical regulatory T cell (Treg) transcription factor. Auto-Th cells responded in vitro to checkpoint inhibition and provided potent B cell help. Cells with the same exhaustion-like (ThEx) phenotype were identified in soluble liver antigen (SLA)-antibody-autoimmune hepatitis and BP180-antibody-positive bullous pemphigoid, AIDs of the liver and skin, respectively. While originally described in cancer and chronic infection, our data point to T cell exhaustion as a common mechanism of adaptation to chronic (self-)stimulation across AID types and link exhausted CD4+ T cells to humoral autoimmune responses, with implications for therapeutic targeting.

Allergies result from an antigen-specific loss of tolerance against innocuous foreign substances. Allergen immunotherapy (AIT) aims to reverse the pathogenic response and to re-establish physiological tolerance. However, the tolerogenic mechanisms that prevent allergy in healthy and act during AIT are still obscure. Foxp3 expressing ‘regulatory’ CD4 T cells (Tregs) are essential mediators of tolerance against allergens. It remains controversial which antigen specificity of Tregs is required to prevent allergy and the role of allergen-specific Tregs during AIT. Recent work provided precise insight into physiological T cell responses against environmental and food compounds. This identified Treg responses mainly against peptides and proteins not involved in immune pathology, revealing an unexpected role of Treg antigen specificity for tolerance. This review will focus on antigen-specific Treg responses against food and airborne allergens, and the impact of the technological approach utilized for antigen-specific Treg characterization is discussed, with critical points to be addressed in future research.