Multiple sclerosis (MS) is a complex inflammatory disease of the CNS resulting from an intricate interplay between genetic predisposition and environmental factors. Vitamin D (VD) deficiency is one of the established risk factors for MS. CD46 costimulation of CD4+ T cells induces a switch from Th1 to type I regulatory cells (Tr1), characterized by increased IL-10 production. This switch is impaired in MS T cells but can be restored by VD, which also strongly promotes expression of CD226 on CD46-activated T cells. The rs763361 polymorphism in the CD226 gene, resulting in a non-synonymous Gly307Ser variant, is associated with increased risk for MS. Herein, we show that expression of this CD226 risk allele disrupts the ability of CD46-activated T cells to operate the IFNγ/IL-10 switch upon VD exposure. Mechanistically, the risk variant impairs activation of the integrin LFA-1, which promotes the Tr1 phenotype. LFA-1-mediated Tr1 differentiation is also impaired in MS T cells expressing the CD226 risk allele upon CD46 and VD stimulation. Our study unveils how, in the context of MS susceptibility, a genetic polymorphism and an environmental factor act in concert to control the differentiation of Tr1 cells.

Tissue-resident memory T cells (Trms) are essential for regional immunity in non-lymphoid tissues. Although single-cell transcriptomics have revealed Trm heterogeneity in various diseases, the molecular mechanisms behind this diversity are unclear. To investigate this, we performed single-cell transcriptomic analysis of brain CD8+ T cells from mice chronically infected with Toxoplasma gondii. This analysis revealed a heterogeneous expression of the transcriptional regulator Id2 in brain Trms, correlating with different functional states. Using mixed bone marrow chimeras, we found that Id2 deficiency in T cells caused parasite-specific Trms to develop an altered phenotype with diminished effector functions and reduced expression of the key tissue-retention molecules CD49a, CXCR6, and CD103. Furthermore, Id2 loss in brain-infiltrating CD8+ T cells led to the accumulation of exhausted PD1+Tox+CD8+ Trm cells, while Id2 overexpression repressed T cell exhaustion. Overall, our study shows that Id2 levels dictate the acquisition of effector vs. exhausted phenotypes in CD8+ Trms during chronic CNS infection.

Preventing T cell migration to the central nervous system (CNS) has remarkable therapeutic effects in relapsing-remitting multiple sclerosis (RRMS) but is poorly effective against the progressive form (PMS). Disability progression in PMS likely results from an interplay between smoldering local inflammation and neurodegeneration. The mechanisms sustaining the chronicity of PMS are poorly understood. Here, we investigated the potential role of tissue-resident memory CD4 + T cells (CD4 + Trm cells) in sustaining chronic CNS autoimmunity. We showed that CD4 + Trm cells were present in the CNS of mice with chronic experimental autoimmune encephalomyelitis (EAE) and in brain tissues from persons with PMS. Using flow cytometry and immunohistofluorescence analysis, we revealed the presence of bona fide CD4 + Trm cells expressing characteristic Trm cell surface markers, including CD69, CXCR6, P2RX7, and CD49a, in the CNS of mice with EAE and in the brains of persons with PMS. These T cells also expressed the transcription factor Hobit in mice with chronic EAE. Single-cell transcriptomic analysis uncovered the transcriptional heterogeneity and inflammatory potential of CD4 + Trm cells, and, accordingly, these cells localized within CNS inflammatory lesions of mice with EAE and persons with PMS. Last, either genetic or pharmacological depletion of CD4 + Trm cells combined with antibody-mediated depletion of the recirculating CD4 + T cell compartment alleviated neurological signs during the chronic phase of EAE. Our results indicate that CD4 + Trm cells contribute to maintain a chronic inflammatory state in the CNS and suggest that therapeutic strategies for PMS should consider targeting the CNS-resident T cell compartment.

Multiple sclerosis (MS) is a complex inflammatory disease of the central nervous system (CNS), resulting from an intricate interplay between genetic predisposition and environmental factors. Vitamin D (VD) deficiency is one of the established risk factors for MS. CD46 costimulation of CD4+ T cells induces a switch from Th1 to type I regulatory cells (Tr1), characterized by increased IL-10 production. This switch is impaired in MS T cells but can be restored by VD, which also strongly promotes expression of CD226 on CD46-activated T cells. The rs763361 polymorphism in the CD226 gene, resulting in a non-synonymous Gly307Ser variant, is associated with increased risk for MS. Herein, we show that expression of this CD226 risk allele disrupts the ability of CD46-activated T cells to operate the IFNγ/IL-10 switch upon VD exposure. Mechanistically, the risk variant impairs activation of the integrin LFA-1, which sustains homotypic adhesion associated with acquisition of the Tr1 phenotype. LFA-1-mediated Tr1 differentiation is also impaired in MS T cells expressing the CD226 risk allele upon CD46 and VD stimulation. Our study unveils how, in the context of MS susceptibility, a genetic polymorphism and an environmental factor act in concert to control the differentiation of Tr1 cells.

By eliciting immune activation in the digestive tract, intestinal pathogens may perturb gut homeostasis. Some gastrointestinal infections can indeed increase the risk of developing post-infectious irritable bowel syndrome (PI-IBS). Intriguingly, the prevalent foodborne parasite Toxoplasma gondii has not been linked to the development of PI-IBS and the impact of this infection on colon homeostasis remains ill-defined. We show in a mouse model that latent T. gondii decreases visceral nociceptive responses in an opioid signaling-dependent manner. Despite the accumulation of Th1 and cytotoxic T cells in the colon of latently infected mice, the selective invalidation of enkephalin gene in T cells ruled out the involvement of T cell-derived enkephalins in hypoalgesia. These findings provide clues about how this widespread infection durably shapes the gut immune landscape and modifies intestinal physiological parameters. They suggest that in contrast to other gut microbes, T. gondii infection could be negatively associated with abdominal pain.

AbstractChronicT. gondiiinfection induces brain-resident CD8+ T cells (bTr) but their protective functions and differentiation cues remain undefined. Here, we used a mouse model of latent infection byT. gondiileading to effective CD8+ T cell-mediated parasite control. Thanks to antibody depletion approaches, we found that peripheral circulating CD8+ T cells are dispensable for brain parasite control during chronic stage, indicating that CD8+ bTr are sufficient to prevent brain parasite reactivation. We observed that the retention markers CD69, CD49a and CD103 are sequentially acquired by brain parasite-specific CD8+ T cells throughout infection, and that a majority of CD69/CD49a/CD103 triple-positive (TP) CD8+ T cells also express Hobit, a transcription factor associated with tissue residency. This TP subset develops in a CD4+ T cell-dependent manner, and is associated with effective parasite control during chronic stage. Conditional invalidation of TAP-mediated MHC class I presentation showed that presentation of parasite antigens by glutamatergic neurons and microglia regulate the differentiation of CD8+ bTr into TP cells. Single-cell transcriptomic analyses uponT. gondiilatency vs. encephalitis revealed that resistance to encephalitis is associated with the expansion of stem-like subsets of CD8+ bTr.In summary, parasite-specific brain-resident CD8+ T cells are functionally heterogeneous and autonomously ensure parasite control duringT. gondiilatent infection. Their differentiation is shaped by neuronal and microglial MHC I presentation. A more detailed understanding of local T cell-mediated immune surveillance of this common parasite is needed for harnessing brain-resident CD8+ T cells in order to enhance control of chronic brain infections.

Therapeutic options against multiple sclerosis (MS) preventing T cell migration to the central nervous system (CNS) have remarkable clinical effects against the relapsing-remitting (RRMS) form of the disease, while they are poorly effective against its progressive form (PMS). Disability progression in PMS is thought to result from an interplay between smoldering local inflammation and neurodegeneration. We postulated that an ongoing inflammatory process mediated by CNS-resident memory CD4+ T cells (CD4+ Trm) could contribute to promote disease chronicity independently of de novo recruitment of peripheral autoreactive T cells. Indeed, our results revealed the presence of bona fide CD4+ Trm expressing CD69, CXCR6, P2RX7, CD49a and the transcription factor Hobit in the CNS of mice with chronic experimental autoimmune encephalomyelitis (EAE) and in the brain of persons with PMS. Single-cell transcriptional analysis uncovered their transcriptional heterogeneity and inflammatory potential and, accordingly, CD4+ Trm preferentially localized within inflammatory lesions. Finally, depletion of both the recirculating and the CNS-resident CD4+ T cell compartments was required to alleviate neurological signs during the chronic phase of EAE. Our results, therefore, indicate that CD4+ Trm actively contribute to maintain a chronic inflammatory state in the CNS, promoting damage and/or preventing repair, and suggest that new therapeutic strategies for the treatment of PMS should consider targeting the CNS-resident T cell compartment.### Competing Interest StatementThe authors have declared no competing interest.

Chronic Toxoplasma gondii infection induces brain-resident CD8+ T cells (bTr), but the protective functions and differentiation cues of these cells remain undefined. Here, we used a mouse model of latent infection by T. gondii leading to effective CD8+ T cell-mediated parasite control. Thanks to antibody depletion approaches, we found that peripheral circulating CD8+ T cells are dispensable for brain parasite control during chronic stage, indicating that CD8+ bTr are able to prevent brain parasite reactivation. We observed that the retention markers CD69, CD49a, and CD103 are sequentially acquired by brain parasite-specific CD8+ T cells throughout infection and that a majority of CD69/CD49a/CD103 triple-positive (TP) CD8+ T cells also express Hobit, a transcription factor associated with tissue residency. This TP subset develops in a CD4+ T cell-dependent manner and is associated with effective parasite control during chronic stage. Conditional invalidation of Transporter associated with Antigen Processing (TAP)-mediated major histocompatibility complex (MHC) class I presentation showed that presentation of parasite antigens by glutamatergic neurons and microglia regulates the differentiation of CD8+ bTr into TP cells. Single-cell transcriptomic analyses revealed that resistance to encephalitis is associated with the expansion of stem-like subsets of CD8+ bTr. In summary, parasite-specific brain-resident CD8+ T cells are a functionally heterogeneous compartment which autonomously ensure parasite control during T. gondii latent infection and which differentiation is shaped by neuronal and microglial MHC I presentation. A more detailed understanding of local T cell-mediated immune surveillance of this common parasite is needed for harnessing brain-resident CD8+ T cells in order to enhance control of chronic brain infections.

Background and Objectives The rs763361 nonsynonymous variant in the CD226 gene, which results in a glycine-to-serine substitution at position 307 of the CD226 protein, has been implicated as a risk factor of various immune-mediated diseases, including multiple sclerosis (MS). Compelling evidence suggests that this allele may play a significant role in predisposing individuals to MS by decreasing the immune-regulatory capacity of Treg cells and increasing the proinflammatory potential of effector CD4 T cells. However, the impact of this CD226 gene variant on CD8 T-cell functions, a population that also plays a key role in MS, remains to be determined. Methods To study whether the CD226 risk variant affects human CD8 T-cell functions, we used CD8 T cells isolated from peripheral blood mononuclear cell of 16 age-matched healthy donors homozygous for either the protective or the risk allele of CD226. We characterized these CD8 T cells on T-cell receptor (TCR) stimulation using high-parametric flow cytometry and bulk RNAseq and through characterization of canonical signaling pathways and cytokine production. Results On TCR engagement, the phenotype of ex vivo CD8 T cells bearing the protective (CD226-307Gly) or the risk (CD226-307Ser) allele of CD226 was largely overlapping. However, the transcriptomic signature of CD8 T cells from the donors carrying the risk allele presented an enrichment in TCR, JAK/STAT, and IFN gamma signaling. We next found that the CD226-307Ser risk allele leads to a selective increase in the phosphorylation of the mitogen-activated protein kinases extracellular signal-regulated kinases 1 and 2 (ERK1/2) associated with enhanced phosphorylation of STAT4 and increased production of IFN gamma. Discussion Our data suggest that the CD226-307Ser risk variant imposes immune dysregulation by increasing the pathways related to IFN gamma signaling in CD8 T cells, thereby contributing to the risk of developing chronic inflammation.

Fig S1. IL-33 and St2 protein expression in sporadic colon cancer.

Supplementary Figure 1. Gating strategy and representative flow cytometric plots of MC38 tumors from WT and Il11ra-/- hosts. Supplementary Figure 2. IL-11 has no effect on tumor-infiltrating immune cells in MC38 and CT26 tumors from WT and Il11ra-/- hosts. Supplementary Figure 3. IL-11 has no effect on PMA/Iono-induced IFNγ and TNFα production by IL-11RA-deficient CD4+ T cells. Supplementary Figure 4. Single cell profiling of IL11RA and IFNG expression in intra-tumoral CD4+ T cells from colon cancer patients.

Fig S2. MC38 tumor growth is enhanced in St2-deficient hosts.

Supplementary Figure 5 from Immune Infiltration of Spontaneous Mouse Astrocytomas Is Dominated by Immunosuppressive Cells from Early Stages of Tumor Development

Supplementary Figure 4 from Immune Infiltration of Spontaneous Mouse Astrocytomas Is Dominated by Immunosuppressive Cells from Early Stages of Tumor Development

Fig S6. St2-deficiency did not alter Treg frequency in untreated naïve colons.

Suppl Table 1. Oligonucleotide Sequences

Supplementary Figure 3 from Immune Infiltration of Spontaneous Mouse Astrocytomas Is Dominated by Immunosuppressive Cells from Early Stages of Tumor Development

Fig S3. St2 is not expressed by Lgr5+ stem cells within the colon.

Supplementary Figure 2 from Immune Infiltration of Spontaneous Mouse Astrocytomas Is Dominated by Immunosuppressive Cells from Early Stages of Tumor Development

Supplementary Figure 1 from Immune Infiltration of Spontaneous Mouse Astrocytomas Is Dominated by Immunosuppressive Cells from Early Stages of Tumor Development