OTULIN haploinsufficiency predisposes to environmentally directed inflammation.

Recently, OTULIN haploinsufficiency was linked to enhanced susceptibility to Staphylococcus aureus infections accompanied by local necrosis and systemic inflammation. The pathogenesis observed in haploinsufficient patients differs from the hyperinflammation seen in classical OTULIN-related autoinflammatory syndrome (ORAS) patients and is characterized by increased susceptibility of dermal fibroblasts to S. aureus alpha toxin-inflicted cytotoxic damage. Immunological abnormalities were not observed in OTULIN haploinsufficient patients, suggesting a non-hematopoietic basis. In this research report, we investigated an Otulin+/- mouse model after in vivo provocation with lipopolysaccharide (LPS) to explore the potential role of hematopoietic-driven inflammation in OTULIN haploinsufficiency. We observed a hyperinflammatory signature in LPS-provoked Otulin+/- mice, which was driven by CD64+ monocytes and macrophages. Bone marrow-derived macrophages (BMDMs) of Otulin+/- mice demonstrated higher proinflammatory cytokine secretion after in vitro stimulation with LPS or polyinosinic:polycytidylic acid (Poly(I:C)). Our experiments in full and mixed bone marrow chimeric mice suggest that, in contrast to humans, the observed inflammation was mainly driven by the hematopoietic compartment with cell-extrinsic effects likely contributing to inflammatory outcomes. Using an OTULIN haploinsufficient mouse model, we validated the role of OTULIN in the regulation of environmentally directed inflammation.

From dentistry to immunology: navigating challenges and building a career in neuroimmunology.

This Commentary recounts an academic journey from dentistry to neuroimmunology, highlighting pivotal moments such as a PhD fraught with challenges and an unexpected postdoctoral experience in France. My decision to settle in Belgium for a postdoc and subsequent transition to an assistant professorship at KU Leuven reflects resilience, adaptability and a commitment to both scientific exploration and family life. Balancing career uncertainties, motherhood and academic achievements, it encapsulates a trajectory shaped by a passion for neuroimmunology.

A Pilot Study to Develop Paraneoplastic Cerebellar Degeneration Mouse Model.

Modeling paraneoplastic neurological diseases to understand the immune mechanisms leading to neuronal death is a major challenge given the rarity and terminal access of patients' autopsies. Here, we present a pilot study aiming at modeling paraneoplastic cerebellar degeneration with Yo autoantibodies (Yo-PCD). Female mice were implanted with an ovarian carcinoma cell line expressing CDR2 and CDR2L, the known antigens recognized by anti-Yo antibodies. To boost the immune response, we also immunized the mice by injecting antigens with diverse adjuvants and immune checkpoint inhibitors. Ataxia and gait instability were assessed in treated mice as well as autoantibody levels, Purkinje cell density, and immune infiltration in the cerebellum. We observed the production of anti-Yo antibodies in the CSF and serum of all immunized mice. Brain immunoreaction varied depending on the site of implantation of the tumor, with subcutaneous administration leading to a massive infiltration of immune cells in the meningeal spaces, choroid plexus, and cerebellar parenchyma. However, we did not observe massive Purkinje cell death nor any motor impairments in any of the experimental groups. Self-sustained neuro-inflammation might require a longer time to build up in our model. Unusual tumor antigen presentation and/or intrinsic, species-specific factors required for pro-inflammatory engagement in the brain may also constitute strong limitations to achieve massive recruitment of antigen-specific T-cells and killing of antigen-expressing neurons in this mouse model.

Brain regulatory T cells.

The brain, long thought to be isolated from the peripheral immune system, is increasingly recognized to be integrated into a systemic immunological network. These conduits of immune-brain interaction and immunosurveillance processes necessitate the presence of complementary immunoregulatory mechanisms, of which brain regulatory T cells (Treg cells) are likely a key facet. Treg cells represent a dynamic population in the brain, with continual influx, specialization to a brain-residency phenotype and relatively rapid displacement by newly incoming cells. In addition to their functions in suppressing adaptive immunity, an emerging view is that Treg cells in the brain dampen down glial reactivity in response to a range of neurological insults, and directly assist in multiple regenerative and reparative processes during tissue pathology. The utility and malleability of the brain Treg cell population make it an attractive therapeutic target across the full spectrum of neurological conditions, ranging from neuroinflammatory to neurodegenerative and even psychiatric diseases. Therapeutic modalities currently under intense development include Treg cell therapy, IL-2 therapy to boost Treg cell numbers and multiple innovative approaches to couple these therapeutics to brain delivery mechanisms for enhanced potency. Here we review the state of the art of brain Treg cell knowledge together with the potential avenues for future integration into medical practice.

CTLA4-Ig Effectively Controls Clinical Deterioration and Immune Condition in a Murine Model of Foxp3 Deficiency.

PURPOSE: FOXP3 deficiency results in severe multisystem autoimmunity in both mice and humans, driven by the absence of functional regulatory T cells. Patients typically present with early and severe autoimmune polyendocrinopathy, dermatitis, and severe inflammation of the gut, leading to villous atrophy and ultimately malabsorption, wasting, and failure to thrive. In the absence of successful treatment, FOXP3-deficient patients usually die within the first 2 years of life. Hematopoietic stem cell transplantation provides a curative option but first requires adequate control over the inflammatory condition. Due to the rarity of the condition, no clinical trials have been conducted, with widely unstandardized therapeutic approaches. We sought to compare the efficacy of lead therapeutic candidates rapamycin, anti-CD4 antibody, and CTLA4-Ig in controlling the physiological and immunological manifestations of Foxp3 deficiency in mice. METHOD: We generated Foxp3-deficient mice and an appropriate clinical scoring system to enable direct comparison of lead therapeutic candidates rapamycin, nondepleting anti-CD4 antibody, and CTLA4-Ig. RESULTS: We found distinct immunosuppressive profiles induced by each treatment, leading to unique protective combinations over distinct clinical manifestations. CTLA4-Ig provided superior breadth of protective outcomes, including highly efficient protection during the transplantation process. CONCLUSION: These results highlight the mechanistic diversity of pathogenic pathways initiated by regulatory T cell loss and suggest CTLA4-Ig as a potentially superior therapeutic option for FOXP3-deficient patients.

Molecular and cognitive signatures of ageing partially restored through synthetic delivery of IL2 to the brain.

Cognitive decline is a common pathological outcome during aging, with an ill-defined molecular and cellular basis. In recent years, the concept of inflammaging, defined as a low-grade inflammation increasing with age, has emerged. Infiltrating T cells accumulate in the brain with age and may contribute to the amplification of inflammatory cascades and disruptions to the neurogenic niche observed with age. Recently, a small resident population of regulatory T cells has been identified in the brain, and the capacity of IL2-mediated expansion of this population to counter neuroinflammatory disease has been demonstrated. Here, we test a brain-specific IL2 delivery system for the prevention of neurological decline in aging mice. We identify the molecular hallmarks of aging in the brain glial compartments and identify partial restoration of this signature through IL2 treatment. At a behavioral level, brain IL2 delivery prevented the age-induced defect in spatial learning, without improving the general decline in motor skill or arousal. These results identify immune modulation as a potential path to preserving cognitive function for healthy aging.

Regulatory T-cell stability and functional plasticity in health and disease.

FOXP3-expressing regulatory T cells (Treg ) are indispensable for immune homeostasis and tolerance, and in addition tissue-resident Treg have been found to perform noncanonical, tissue-specific functions. For optimal tolerogenic function during inflammatory disease, Treg are equipped with mechanisms that assure lineage stability. Treg lineage stability is closely linked to the installation and maintenance of a lineage-specific epigenetic landscape, specifically a Treg -specific DNA demethylation pattern. At the same time, for local and directed immune regulation Treg must possess a level of functional plasticity that requires them to partially acquire T helper cell (TH ) transcriptional programs-then referred to as TH -like Treg . Unleashing TH programs in Treg , however, is not without risk and may threaten the epigenetic stability of Treg with consequently pathogenic ex-Treg contributing to (auto-) inflammatory conditions. Here, we review how the Treg -stabilizing epigenetic landscape is installed and maintained, and further discuss the development, necessity and lineage instability risks of TH 1-, TH 2-, TH 17-like Treg and follicular Treg .

Brain-resident regulatory T cells and their role in health and disease.

Regulatory T cells (Tregs) control inflammation and maintain immune homeostasis. The well-characterised circulatory population of CD4+Foxp3+ Tregs is effective at preventing autoimmunity and constraining the immune response, through direct and indirect restraint of conventional T cell activation. Recent advances in Treg cell biology have identified tissue-resident Tregs, with tissue-specific functions that contribute to the maintenance of tissue homeostasis and repair. A population of brain-resident Tregs, characterised as CD69+, has recently been identified in the healthy brain of mice and humans, with rapid population expansion observed under a number of neuroinflammatory conditions. During neuroinflammation, brain-resident Tregs have been proposed to control astrogliosis through the production of amphiregulin, polarize microglia into neuroprotective states, and restrain inflammatory responses by releasing IL-10. While protective effects for Tregs have been demonstrated in a number of neuroinflammatory pathologies, a clear demarcation between the role of circulatory and brain-resident Tregs has been difficult to achieve. Here we review the state-of-the-art for brain-resident Treg population, and describe their potential utilization as a therapeutic target across different neuroinflammatory conditions.

Astrocyte-targeted gene delivery of interleukin 2 specifically increases brain-resident regulatory T cell numbers and protects against pathological neuroinflammation.

The ability of immune-modulating biologics to prevent and reverse pathology has transformed recent clinical practice. Full utility in the neuroinflammation space, however, requires identification of both effective targets for local immune modulation and a delivery system capable of crossing the blood-brain barrier. The recent identification and characterization of a small population of regulatory T (Treg) cells resident in the brain presents one such potential therapeutic target. Here, we identified brain interleukin 2 (IL-2) levels as a limiting factor for brain-resident Treg cells. We developed a gene-delivery approach for astrocytes, with a small-molecule on-switch to allow temporal control, and enhanced production in reactive astrocytes to spatially direct delivery to inflammatory sites. Mice with brain-specific IL-2 delivery were protected in traumatic brain injury, stroke and multiple sclerosis models, without impacting the peripheral immune system. These results validate brain-specific IL-2 gene delivery as effective protection against neuroinflammation, and provide a versatile platform for delivery of diverse biologics to neuroinflammatory patients.

AAV-mediated delivery of an anti-BACE1 VHH alleviates pathology in an Alzheimer's disease model.

Single domain antibodies (VHHs) are potentially disruptive therapeutics, with important biological value for treatment of several diseases, including neurological disorders. However, VHHs have not been widely used in the central nervous system (CNS), largely because of their restricted blood-brain barrier (BBB) penetration. Here, we propose a gene transfer strategy based on BBB-crossing adeno-associated virus (AAV)-based vectors to deliver VHH directly into the CNS. As a proof-of-concept, we explored the potential of AAV-delivered VHH to inhibit BACE1, a well-characterized target in Alzheimer's disease. First, we generated a panel of VHHs targeting BACE1, one of which, VHH-B9, shows high selectivity for BACE1 and efficacy in lowering BACE1 activity in vitro. We further demonstrate that a single systemic dose of AAV-VHH-B9 produces positive long-term (12 months plus) effects on amyloid load, neuroinflammation, synaptic function, and cognitive performance, in the AppNL-G-F Alzheimer's mouse model. These results constitute a novel therapeutic approach for neurodegenerative diseases, which is applicable to a range of CNS disease targets.

Intratumoral DNA-based delivery of checkpoint-inhibiting antibodies and interleukin 12 triggers T cell infiltration and anti-tumor response.

To improve the anti-tumor efficacy of immune checkpoint inhibitors, numerous combination therapies are under clinical evaluation, including with IL-12 gene therapy. The current study evaluated the simultaneous delivery of the cytokine and checkpoint-inhibiting antibodies by intratumoral DNA electroporation in mice. In the MC38 tumor model, combined administration of plasmids encoding IL-12 and an anti-PD-1 antibody induced significant anti-tumor responses, yet similar to the monotherapies. When treatment was expanded with a DNA-based anti-CTLA-4 antibody, this triple combination significantly delayed tumor growth compared to IL-12 alone and the combination of anti-PD-1 and anti-CTLA-4 antibodies. Despite low drug plasma concentrations, the triple combination enabled significant abscopal effects in contralateral tumors, which was not the case for the other treatments. The DNA-based immunotherapies increased T cell infiltration in electroporated tumors, especially of CD8+ T cells, and upregulated the expression of CD8+ effector markers. No general immune activation was detected in spleens following either intratumoral treatment. In B16F10 tumors, evaluation of the triple combination was hampered by a high sensitivity to control plasmids. In conclusion, intratumoral gene electrotransfer allowed effective combined delivery of multiple immunotherapeutics. This approach induced responses in treated and contralateral tumors, while limiting systemic drug exposure and potentially detrimental systemic immunological effects.

The potential anti-inflammatory and anti-nociceptive effects of rat hemopressin (PVNFKFLSH) in experimental arthritis.

Inflammatory arthritis, such as rheumatoid arthritis (RA), stands out as one of the main sources of pain and impairment to the quality of life. The use of hemopressin (PVNFKFLSH; Hp), an inverse agonist of type 1 cannabinoid receptor, has proven to be effective in producing analgesia in pain models, but its effect on neuro-inflammatory aspects of RA is limited. In this study, antigen-induced arthritis (AIA) was evoked by the intraarticular (i.art.) injection of methylated bovine serum albumin (mBSA) in male Sprague Dawley rats. Phosphate buffered saline (PBS)-injected ipsilateral knee joints or AIA contralateral were used as control. Nociceptive and inflammatory parameters such as knee joint oedema and leukocyte influx and histopathological changes were carried out in addition to the local measurement of interleukins (IL) IL-6, IL-1ß, tumor necrosis factor-α and the immunoreactivity of the neuropeptides substance P (SP) and calcitonin gene related peptide (CGRP) in the spinal cord (lumbar L3-5 segments) of AIA rats. For 4 days, AIA rats were treated daily with a single administration of saline, Hp injected (10 or 20 µg/day, i.art.), Hp given orally (20 µg/Kg, p.o.) or indomethacin (Indo; 5 mg/Kg, i.p.). In comparison to the PBS control group, the induction of AIA produced a significant and progressive mono-arthritis condition. The degree of AIA severity progressively compromised the normal walking pattern and impaired mobility over the next four days in relation to PBS-injected rats or contralateral knee joints. In AIA rats, the reduction of the distance between footprints and disturbances of gait evidenced signs of nociception. This response worsened at day 4, and a loss of footprint from the ipsilateral hind paw was evident. Daily treatment of the animals with Hp either i.art. (10 and 20 µg/knee) or p.o. (20 µg/Kg) as well as Indo (5 mg/Kg, i.p.) ameliorated the impaired mobility in a time-dependent manner (P < 0.05). In parallel, the AIA-injected ipsilateral knee joints reach a peak of swelling 24 h after AIA induction, which persisted over the next four days in relation to PBS-injected rats or contralateral knee joints. There was a significant but not dose-dependent inhibitory effect produced by all dosages and routes of Hp treatments on AIA-induced knee joint swelling (P < 0.05). In addition, the increased synovial levels of MPO activity, total leukocytes number and IL-6, but not IL-1ß, were significantly reduced by the lower i.art. dose of Hp. In conclusion, these results successfully demonstrate that Hp may represent a novel therapeutic strategy to treat RA, an effect which is unrelated to the proinflammatory actions of the neuropeptides CGRP and SP.

Tumor necrosis factor receptor-associated factor 6 interaction with alpha-synuclein enhances cell death through the Nuclear Factor-kB pathway.

BACKGROUND: Parkinson's disease (PD) is a neurodegenerative disease characterized by intracellular inclusions named Lewy bodies (LB), and alpha-synuclein (asyn) is the major component of these protein aggregates. The precise physiological and pathological roles of asyn are not fully understood. Nevertheless, asyn present in LB is ubiquitinated but fails to reach the 26S proteasome. The mutation A30 P is related to an aggressive and early-onset form of PD. Tumor necrosis factor receptor-associated factor 6 (TRAF6) is an E3 ubiquitin ligase, and it interacts and ubiquitinates the asyn in atypical chains (lysine K6, K27, K29, and K33). Methods: Here, we investigated the role of TRAF6 interaction with asyn and the involvement of nuclear factor κB (NF-κB), a key transcription factor in pro-inflammatory signaling pathway activation. RESULTS AND CONCLUSION: We demonstrated that TRAF6 binds to both WT and the mutant form A30 P asyn in an SH-SY5Y cell model. Additionally, the interaction between TRAF6 and WT asyn induced an increase in the activation of NF-κB, leading to changes in TNF, IL-1ß and IL-10 levels and culminating in reduced cell viability. Interestingly, the activation of NF-κB and gene regulation were not found in A30 P asyn. These data point to a novel role of TRAF6 in the pathophysiology of PD.

Immunological Bases of Paraneoplastic Cerebellar Degeneration and Therapeutic Implications.

Paraneoplastic cerebellar degeneration (PCD) is a rare immune-mediated disease that develops mostly in the setting of neoplasia and offers a unique prospect to explore the interplay between tumor immunity and autoimmunity. In PCD, the deleterious adaptive immune response targets self-antigens aberrantly expressed by tumor cells, mostly gynecological cancers, and physiologically expressed by the Purkinje neurons of the cerebellum. Highly specific anti-neuronal antibodies in the serum and cerebrospinal fluid represent key diagnostic biomarkers of PCD. Some anti-neuronal antibodies such as anti-Yo autoantibodies (recognizing the CDR2/CDR2L proteins) are only associated with PCD. Other anti-neuronal antibodies, such as anti-Hu, anti-Ri, and anti-Ma2, are detected in patients with PCD or other types of paraneoplastic neurological manifestations. Importantly, these autoantibodies cannot transfer disease and evidence for a pathogenic role of autoreactive T cells is accumulating. However, the precise mechanisms responsible for disruption of self-tolerance to neuronal self-antigens in the cancer setting and the pathways involved in pathogenesis within the cerebellum remain to be fully deciphered. Although the occurrence of PCD is rare, the risk for such severe complication may increase with wider use of cancer immunotherapy, notably immune checkpoint blockade. Here, we review recent literature pertaining to the pathophysiology of PCD and propose an immune scheme underlying this disabling disease. Additionally, based on observations from patients' samples and on the pre-clinical model we recently developed, we discuss potential therapeutic strategies that could blunt this cerebellum-specific autoimmune disease.

Microglia Require CD4 T Cells to Complete the Fetal-to-Adult Transition.

The brain is a site of relative immune privilege. Although CD4 T cells have been reported in the central nervous system, their presence in the healthy brain remains controversial, and their function remains largely unknown. We used a combination of imaging, single cell, and surgical approaches to identify a CD69+ CD4 T cell population in both the mouse and human brain, distinct from circulating CD4 T cells. The brain-resident population was derived through in situ differentiation from activated circulatory cells and was shaped by self-antigen and the peripheral microbiome. Single-cell sequencing revealed that in the absence of murine CD4 T cells, resident microglia remained suspended between the fetal and adult states. This maturation defect resulted in excess immature neuronal synapses and behavioral abnormalities. These results illuminate a role for CD4 T cells in brain development and a potential interconnected dynamic between the evolution of the immunological and neurological systems. VIDEO ABSTRACT.

The potential anti-inflammatory and anti-nociceptive effects of rat hemopressin (PVNFKFLSH) in experimental arthritis

Inflammatory arthritis, such as rheumatoid arthritis (RA), stands out as one of the main sources of pain and impairment to the quality of life. The use of hemopressin (PVNFKFLSH; Hp), an inverse agonist of type 1 cannabinoid receptor, has proven to be effective in producing analgesia in pain models, but its effect on neuro-inflammatory aspects of RA is limited. In this study, antigen-induced arthritis (AIA) was evoked by the intraarticular (i.art.) injection of methylated bovine serum albumin (mBSA) in male Sprague Dawley rats. Phosphate buffered saline (PBS)-injected ipsilateral knee joints or AIA contralateral were used as control. Nociceptive and inflammatory parameters such as knee joint oedema and leukocyte influx and histopathological changes were carried out in addition to the local measurement of interleukins (IL) IL-6, IL-1β, tumor necrosis factor-α and the immunoreactivity of the neuropeptides substance P (SP) and calcitonin gene related peptide (CGRP) in the spinal cord (lumbar L3-5 segments) of AIA rats. For 4 days, AIA rats were treated daily with a single administration of saline, Hp injected (10 or 20 μg/day, i.art.), Hp given orally (20 μg/Kg, p.o.) or indomethacin (Indo; 5 mg/Kg, i.p.). In comparison to the PBS control group, the induction of AIA produced a significant and progressive mono-arthritis condition. The degree of AIA severity progressively compromised the normal walking pattern and impaired mobility over the next four days in relation to PBS-injected rats or contralateral knee joints. In AIA rats, the reduction of the distance between footprints and disturbances of gait evidenced signs of nociception. This response worsened at day 4, and a loss of footprint from the ipsilateral hind paw was evident. Daily treatment of the animals with Hp either i.art. (10 and 20 μg/knee) or p.o. (20 μg/Kg) as well as Indo (5 mg/Kg, i.p.) ameliorated the impaired mobility in a time-dependent manner (P < 0.05). In parallel, the AIA-injected ipsilateral knee joints reach a peak of swelling 24 h after AIA induction, which persisted over the next four days in relation to PBS-injected rats or contralateral knee joints. There was a significant but not dose-dependent inhibitory effect produced by all dosages and routes of Hp treatments on AIA-induced knee joint swelling (P < 0.05). In addition, the increased synovial levels of MPO activity, total leukocytes number and IL-6, but not IL-1β, were significantly reduced by the lower i.art. dose of Hp. In conclusion, these results successfully demonstrate that Hp may represent a novel therapeutic strategy to treat RA, an effect which is unrelated to the proinflammatory actions of the neuropeptides CGRP and SP

CD8+ T cell-mediated endotheliopathy is a targetable mechanism of neuro-inflammation in Susac syndrome.

Neuroinflammation is often associated with blood-brain-barrier dysfunction, which contributes to neurological tissue damage. Here, we reveal the pathophysiology of Susac syndrome (SuS), an enigmatic neuroinflammatory disease with central nervous system (CNS) endotheliopathy. By investigating immune cells from the blood, cerebrospinal fluid, and CNS of SuS patients, we demonstrate oligoclonal expansion of terminally differentiated activated cytotoxic CD8+ T cells (CTLs). Neuropathological data derived from both SuS patients and a newly-developed transgenic mouse model recapitulating the disease indicate that CTLs adhere to CNS microvessels in distinct areas and polarize granzyme B, which most likely results in the observed endothelial cell injury and microhemorrhages. Blocking T-cell adhesion by anti-α4 integrin-intervention ameliorates the disease in the preclinical model. Similarly, disease severity decreases in four SuS patients treated with natalizumab along with other therapy. Our study identifies CD8+ T-cell-mediated endotheliopathy as a key disease mechanism in SuS and highlights therapeutic opportunities.

IFN-γ is a therapeutic target in paraneoplastic cerebellar degeneration.

Paraneoplastic neurological disorders result from an autoimmune response against neural self-antigens that are ectopically expressed in neoplastic cells. In paraneoplastic disorders associated to autoantibodies against intracellular proteins, such as paraneoplastic cerebellar degeneration (PCD), current data point to a major role of cell-mediated immunity. In an animal model, in which a neo-self-antigen was expressed in both Purkinje neurons and implanted breast tumor cells, immune checkpoint blockade led to complete tumor control at the expense of cerebellum infiltration by T cells and Purkinje neuron loss, thereby mimicking PCD. Here, we identify 2 potential therapeutic targets expressed by cerebellum-infiltrating T cells in this model, namely α4 integrin and IFN-γ. Mice with PCD were treated with anti-α4 integrin antibodies or neutralizing anti-IFN-γ antibodies at the onset of neurological signs. Although blocking α4 integrin had little or no impact on disease development, treatment using the anti-IFN-γ antibody led to almost complete protection from PCD. These findings strongly suggest that the production of IFN-γ by cerebellum-invading T cells plays a major role in Purkinje neuron death. Our successful preclinical use of neutralizing anti-IFN-γ antibody for the treatment of PCD offers a potentially new therapeutic opportunity for cancer patients at the onset of paraneoplastic neurological disorders.

Inflammatory CNS disease caused by immune checkpoint inhibitors: status and perspectives.

Cancer treatment strategies based on immune stimulation have recently entered the clinical arena, with unprecedented success. Immune checkpoint inhibitors (ICIs) work by indiscriminately promoting immune responses, which target tumour-associated antigens or tumour-specific mutations. However, the augmented immune response, most notably the T cell response, can cause either direct neurotoxicity or, more commonly, indirect neurotoxic effects through systemic or local inflammatory mechanisms or autoimmune mechanisms. Consequently, patients treated with ICIs are susceptible to CNS disease, including paraneoplastic neurological syndromes, encephalitis, multiple sclerosis and hypophysitis. In this Opinion article, we introduce the mechanisms of action of ICIs and review their adverse effects on the CNS. We highlight the importance of early detection of these neurotoxic effects, which should be distinguished from brain metastasis, and the need for early detection of neurotoxicity. It is crucial that physicians are well informed of these neurological adverse effects, given the anticipated increase in the use of immunotherapies to treat cancer.