Cutting Edge: Effect of Disease-Modifying Therapies on SARS-CoV-2 Vaccine-Induced Immune Responses in Multiple Sclerosis Patients.

Multiple sclerosis (MS) is a demyelinating inflammatory disease of the CNS treated by diverse disease-modifying therapies that suppress the immune system. Severe acute respiratory syndrome coronavirus 2 mRNA vaccines have been very effective in immunocompetent individuals, but whether MS patients treated with modifying therapies are afforded the same protection is not known. This study determined that dimethyl fumarate caused a momentary reduction in anti-Spike (S)-specific Abs and CD8 T cell response. MS patients treated with B cell-depleting (anti-CD20) or sphingosine 1-phosphate receptor agonist (fingolimod) therapies lack significant S-specific Ab response. Whereas S-specific CD4 and CD8 T cell responses were largely compromised by fingolimod treatment, T cell responses were robustly generated in anti-CD20-treated MS patients, but with a reduced proportion of CD4+CXCR5+ circulating follicular Th cells. These data provide novel information regarding vaccine immune response in patients with autoimmunity useful to help improve vaccine effectiveness in these populations.

Cutting Edge: DOCK8 Regulates a Subset of Dendritic Cells That Is Critical for the Development of Experimental Autoimmune Encephalomyelitis.

Dedicator of cytokinesis 8 (DOCK8) is a guanine nucleotide exchange factor with an essential role in cytoskeletal rearrangement, cell migration, and survival of various immune cells. Interestingly, DOCK8-deficient mice are resistant to the development of experimental autoimmune encephalomyelitis (EAE). To understand if EAE resistance in these mice results from an alteration in dendritic cell (DC) functions, we generated mice with conditional deletion of DOCK8 in DCs and observed attenuated EAE in these mice compared with control mice. Additionally, we demonstrated that DOCK8 is important for the existence of splenic conventional DC2 and lymph node migratory DCs and further established that migratory DC, rather than resident DC, are essential for the generation and proliferation of pathogenic T cell populations upon immunization with myelin Ag in adjuvant. Therefore, our data suggest that limiting migratory DCs through DOCK8 deletion and possibly other mechanisms could limit the development of CNS autoimmunity.

Abatacept Targets T Follicular Helper and Regulatory T Cells, Disrupting Molecular Pathways That Regulate Their Proliferation and Maintenance.

Abatacept is a CTLA-4-Ig fusion protein that binds to the costimulatory ligands CD80 and CD86 and blocks their interaction with the CD28 and CTLA-4 receptors expressed by T cells, therefore inhibiting T cell activation and function. Abatacept has shown clinical efficacy in treating some autoimmune diseases but has failed to show clinical benefit in other autoimmune conditions. The reasons for these disparate results are not clear and warrant further investigation of abatacept's mode of action. Longitudinal specimens from the Immune Tolerance Network's A Cooperative Clinical Study of Abatacept in Multiple Sclerosis trial were used to examine the effects of abatacept treatment on the frequency and transcriptional profile of specific T cell populations in peripheral blood. We found that the relative abundance of CD4+ T follicular helper (Tfh) cells and regulatory T cells was selectively decreased in participants following abatacept treatment. Within both cell types, abatacept reduced the proportion of activated cells expressing CD38 and ICOS and was associated with decreased expression of genes that regulate cell-cycle and chromatin dynamics during cell proliferation, thereby linking changes in costimulatory signaling to impaired activation, proliferation, and decreased abundance. All cellular and molecular changes were reversed following termination of abatacept treatment. These data expand upon the mechanism of action of abatacept reported in other autoimmune diseases and identify new transcriptional targets of CD28-mediated costimulatory signaling in human regulatory T and Tfh cells, further informing on its potential use in diseases associated with dysregulated Tfh activity.

Th17 cells induce ectopic lymphoid follicles in central nervous system tissue inflammation.

Ectopic lymphoid follicles are hallmarks of chronic autoimmune inflammatory diseases such as multiple sclerosis (MS), rheumatoid arthritis, Sjögren's syndrome, and myasthenia gravis. However, the effector cells and mechanisms that induce their development are unknown. Here we showed that in experimental autoimmune encephalomyelitis (EAE), the animal model of MS, Th17 cells specifically induced ectopic lymphoid follicles in the central nervous system (CNS). Development of ectopic lymphoid follicles was partly dependent on the cytokine interleukin 17 (IL-17) and on the cell surface molecule Podoplanin (Pdp), which was expressed on Th17 cells, but not on other effector T cell subsets. Pdp was also crucial for the development of secondary lymphoid structures: Pdp-deficient mice lacked peripheral lymph nodes and had a defect in forming normal lymphoid follicles and germinal centers in spleen and lymph node remnants. Thus, Th17 cells are uniquely endowed to induce tissue inflammation, characterized by ectopic lymphoid follicles within the target organ.

A dominant function for interleukin 27 in generating interleukin 10-producing anti-inflammatory T cells.

Regulatory T cells (T(reg) cells) expressing the transcription factor Foxp3 are key in maintaining the balance of immune homeostasis. However, distinct induced T regulatory type 1 (Tr1) cells that lack Foxp3 expression also regulate T cell function, mainly by producing the immunosuppressive cytokine interleukin 10 (IL-10). However, the factors required for the induction of IL-10-producing suppressive T cells are not fully understood. Here we demonstrate that dendritic cells modified by T(reg) cells induced the generation of IL-10-producing Tr1 cells. The differentiation of naive CD4+ T cells into IL-10-producing cells was mediated by IL-27 produced by the T(reg) cell-modified dendritic cells, and transforming growth factor-beta amplified the generation of induced IL-10+ Tr1 cells by IL-27. Thus, IL-27 and transforming growth factor-beta promote the generation of IL-10-producing Tr1 cells.

Cutting Edge: Integrin α4 Is Required for Regulatory B Cell Control of Experimental Autoimmune Encephalomyelitis.

The neutralization of integrin α4 (Itga4) is currently used as treatment in multiple sclerosis. Although most studies have focused on its function on lymphocyte migration to the CNS, we have uncovered the importance of Itga4 for the generation of regulatory B cells in peripheral immune organs and their control of pathogenic T cell response and CNS pathology. Our study underscores the importance of looking at the dual role of B cells in CNS autoimmunity and provides important perspectives regarding the efficacy and side effects associated with Itga4 neutralization and other B cell-targeting therapies.

IL-7/IL-7 Receptor Signaling Differentially Affects Effector CD4+ T Cell Subsets Involved in Experimental Autoimmune Encephalomyelitis.

IL-17-producing CD4(+) T (Th17) cells, along with IFN-γ-expressing Th1 cells, represent two major pathogenic T cell subsets in experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis (MS). The cytokines and transcription factors involved in the development and effector functions of Th1 and Th17 cells have been largely characterized. Among them, IL-23 is essential for the generation of stable and encephalitogenic Th17 cells and for the development of EAE. The IL-7/IL-7R signaling axis participates in cell survival, and perturbation of this pathway has been associated with enhanced susceptibility to MS. A link between IL-23-driven pathogenic T cells and IL-7/IL-7R signaling has previously been proposed, but has not been formally addressed. In the current study, we showed that Th17 cells from mice with EAE express high levels of IL-7Rα compared with Th1 cells. Using mice that constitutively express IL-7Rα on T cells, we determined that sustained IL-7R expression in IL-23R-deficient mice could not drive pathogenic T cells and the development of EAE. IL-7 inhibited the differentiation of Th17 cells, but promoted IFN-γ and GM-CSF secretion in vitro. In vivo IL-7/anti-IL-7 mAb complexes selectively expanded and enhanced the proliferation of CXCR3-expressing Th1 cells, but did not impact Th17 cells and EAE development in wild-type and IL-23R-deficient mice. Importantly, high IL-7 expression was detected in the CNS during EAE and could drive the plasticity of Th17 cells to IFN-γ-producing T cells. Together, these data address the contribution of IL-23/IL-23R and IL-7/IL-7R signaling in Th17 and Th1 cell dynamics during CNS autoimmunity.

Cutting edge: the pathogenicity of IFN-γ-producing Th17 cells is independent of T-bet.

During the development of experimental autoimmune encephalomyelitis (EAE), the proportion of pathogenic and myelin-specific cells within CNS-infiltrating cytokine-producing Th cells is unknown. Using an IL-17A/IFN-γ double reporter mouse and I-A(b)/myelin oligodendrocyte glycoprotein 38-49 tetramer, we show in this study that IL-17(+)IFN-γ(+) Th cells, which are expanded in the CNS during EAE, are highly enriched in myelin oligodendrocyte glycoprotein-specific T cells. We further demonstrate that IL-23 is essential for the generation and expansion of IFN-γ-producing Th17 cells independently of the Th1-associated transcription factors T-bet, STAT1, and STAT4. Furthermore, Th17 and IL-17(+)IFN-γ(+) Th cells can induce CNS autoimmunity independently of T-bet. Whereas T-bet is crucial for Th1-mediated EAE, it is dispensable for Th17 cell-mediated autoimmunity. Our results suggest the existence of different epigenetic programs that regulate IFN-γ expression in Th1 and Th17 cells.

Myelin-specific regulatory T cells accumulate in the CNS but fail to control autoimmune inflammation.

Treatment with ex vivo-generated regulatory T cells (T-reg) has been regarded as a potentially attractive therapeutic approach for autoimmune diseases. However, the dynamics and function of T-reg in autoimmunity are not well understood. Thus, we developed Foxp3gfp knock-in (Foxp3gfp.KI) mice and myelin oligodendrocyte glycoprotein (MOG)(35-55)/IA(b) (MHC class II) tetramers to track autoantigen-specific effector T cells (T-eff) and T-reg in vivo during experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. MOG tetramer-reactive, Foxp3(+) T-reg expanded in the peripheral lymphoid compartment and readily accumulated in the central nervous system (CNS), but did not prevent the onset of disease. Foxp3(+) T cells isolated from the CNS were effective in suppressing naive MOG-specific T cells, but failed to control CNS-derived encephalitogenic T-eff that secreted interleukin (IL)-6 and tumor necrosis factor (TNF). Our data suggest that in order for CD4(+)Foxp3(+) T-reg to effectively control autoimmune reactions in the target organ, it may also be necessary to control tissue inflammation.

Self-antigen tetramers discriminate between myelin autoantibodies to native or denatured protein.

The role of autoantibodies in the pathogenesis of multiple sclerosis (MS) and other demyelinating diseases is controversial, in part because widely used western blotting and ELISA methods either do not permit the detection of conformation-sensitive antibodies or do not distinguish them from conformation-independent antibodies. We developed a sensitive assay based on self-assembling radiolabeled tetramers that allows discrimination of antibodies against folded or denatured myelin oligodendrocyte glycoprotein (MOG) by selective unfolding of the antigen domain. The tetramer radioimmunoassay (RIA) was more sensitive for MOG autoantibody detection than other methodologies, including monomer-based RIA, ELISA or fluorescent-activated cell sorting (FACS). Autoantibodies from individuals with acute disseminated encephalomyelitis (ADEM) selectively bound the folded MOG tetramer, whereas sera from mice with experimental autoimmune encephalomyelitis induced with MOG peptide immunoprecipitated only the unfolded tetramer. MOG-specific autoantibodies were identified in a subset of ADEM but only rarely in adult-onset MS cases, indicating that MOG is a more prominent target antigen in ADEM than MS.

Induction and effector functions of T(H)17 cells.

T helper (T(H)) cells constitute an important arm of the adaptive immune system because they coordinate defence against specific pathogens, and their unique cytokines and effector functions mediate different types of tissue inflammation. The recently discovered T(H)17 cells, the third subset of effector T helper cells, have been the subject of intense research aimed at understanding their role in immunity and disease. Here we review emerging data suggesting that T(H)17 cells have an important role in host defence against specific pathogens and are potent inducers of autoimmunity and tissue inflammation. In addition, the differentiation factors responsible for their generation have revealed an interesting reciprocal relationship with regulatory T (T(reg)) cells, which prevent tissue inflammation and mediate self-tolerance.

Control of T(reg) and T(H)17 cell differentiation by the aryl hydrocarbon receptor.

Regulatory T cells (T(reg)) expressing the transcription factor Foxp3 control the autoreactive components of the immune system. The development of T(reg) cells is reciprocally related to that of pro-inflammatory T cells producing interleukin-17 (T(H)17). Although T(reg) cell dysfunction and/or T(H)17 cell dysregulation are thought to contribute to the development of autoimmune disorders, little is known about the physiological pathways that control the generation of these cell lineages. Here we report the identification of the ligand-activated transcription factor aryl hydrocarbon receptor (AHR) as a regulator of T(reg) and T(H)17 cell differentiation in mice. AHR activation by its ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin induced functional T(reg) cells that suppressed experimental autoimmune encephalomyelitis. On the other hand, AHR activation by 6-formylindolo[3,2-b]carbazole interfered with T(reg) cell development, boosted T(H)17 cell differentiation and increased the severity of experimental autoimmune encephalomyelitis in mice. Thus, AHR regulates both T(reg) and T(H)17 cell differentiation in a ligand-specific fashion, constituting a unique target for therapeutic immunomodulation.

IL-21 and TGF-beta are required for differentiation of human T(H)17 cells.

The recent discovery of CD4(+) T cells characterized by secretion of interleukin (IL)-17 (T(H)17 cells) and the naturally occurring regulatory FOXP3(+) CD4 T cell (nT(reg)) has had a major impact on our understanding of immune processes not readily explained by the T(H)1/T(H)2 paradigm. T(H)17 and nT(reg) cells have been implicated in the pathogenesis of human autoimmune diseases, including multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease and psoriasis. Our recent data and the work of others demonstrated that transforming growth factor-beta (TGF-beta) and IL-6 are responsible for the differentiation of naive mouse T cells into T(H)17 cells, and it has been proposed that IL-23 may have a critical role in stabilization of the T(H)17 phenotype. A second pathway has been discovered in which a combination of TGF-beta and IL-21 is capable of inducing differentiation of mouse T(H)17 cells in the absence of IL-6 (refs 6-8). However, TGF-beta and IL-6 are not capable of differentiating human T(H)17 cells and it has been suggested that TGF-beta may in fact suppress the generation of human T(H)17 cells. Instead, it has been recently shown that the cytokines IL-1beta, IL-6 and IL-23 are capable of driving IL-17 secretion in short-term CD4(+) T cell lines isolated from human peripheral blood, although the factors required for differentiation of naive human CD4 to T(H)17 cells are still unknown. Here we confirm that whereas IL-1beta and IL-6 induce IL-17A secretion from human central memory CD4(+) T cells, TGF-beta and IL-21 uniquely promote the differentiation of human naive CD4(+) T cells into T(H)17 cells accompanied by expression of the transcription factor RORC2. These data will allow the investigation of this new population of T(H)17 cells in human inflammatory disease.

Cutting edge: loss of α4 integrin expression differentially affects the homing of Th1 and Th17 cells.

The neutralization of α4 integrin is currently used as treatment in several autoimmune diseases and is thought to prevent the entry of most immune cells in target tissues. In this study, we showed that selective deletion of α4 integrin in T cells did not prevent but delayed the development of experimental autoimmune encephalomyelitis. Whereas both Th1 and Th17 cells infiltrate the CNS of wild-type mice, T cells present in the CNS of mice lacking α4 integrin were mainly enriched in Th17 cells, suggesting that this T cell subset uses other integrins to access the CNS. In contrast, α4 integrin expression is important for Th1 cells to enter the CNS and for the stability of their Th1-associated genetic program. Therefore, our data suggest that anti-α4 integrin Ab treatment may be more efficient in the treatment of Th1- rather than Th17-mediated disease.

IL-21 initiates an alternative pathway to induce proinflammatory T(H)17 cells.

On activation, naive T cells differentiate into effector T-cell subsets with specific cytokine phenotypes and specialized effector functions. Recently a subset of T cells, distinct from T helper (T(H))1 and T(H)2 cells, producing interleukin (IL)-17 (T(H)17) was defined and seems to have a crucial role in mediating autoimmunity and inducing tissue inflammation. We and others have shown that transforming growth factor (TGF)-beta and IL-6 together induce the differentiation of T(H)17 cells, in which IL-6 has a pivotal function in dictating whether T cells differentiate into Foxp3+ regulatory T cells (T(reg) cells) or T(H)17 cells. Whereas TGF-beta induces Foxp3 and generates T(reg) cells, IL-6 inhibits the generation of T(reg) cells and induces the production of IL-17, suggesting a reciprocal developmental pathway for T(H)17 and T(reg) cells. Here we show that IL-6-deficient (Il6-/-) mice do not develop a T(H)17 response and their peripheral repertoire is dominated by Foxp3+ T(reg) cells. However, deletion of T(reg) cells leads to the reappearance of T(H)17 cells in Il6-/- mice, suggesting an additional pathway by which T(H)17 cells might be generated in vivo. We show that an IL-2 cytokine family member, IL-21, cooperates with TGF-beta to induce T(H)17 cells in naive Il6-/- T cells and that IL-21-receptor-deficient T cells are defective in generating a T(H)17 response.

Proinflammatory T helper type 17 cells are effective B-cell helpers.

T helper type 17 (TH17) cells are highly proinflammatory effector T cells that are characterized by the production of high amounts of IL-17A, IL-17F, IL-21, and IL-22. Furthermore, TH17 cells have been associated with a number of autoimmune diseases. However, it is not clear whether TH17 cells can also serve as effective helper cells. Here we show that TH17 cells can function as B-cell helpers in that they not only induce a strong proliferative response of B cells in vitro but also trigger antibody production with class switch recombination in vivo. Transfer of TH17 cells into WT or T-cell receptor alpha-deficient mice, which lack endogenous T cells, induces a pronounced antibody response with preferential isotype class switching to IgG1, IgG2a, IgG2b, and IgG3, as well as the formation of germinal centers. Conversely, blockade of IL-17 signaling results in a significant reduction in both number and size of germinal centers. Whereas IL-21 is known to help B cells, IL-17 on its own drives B cells to undergo preferential isotype class switching to IgG2a and IgG3 subtypes. These observations provide insights into the unappreciated role of TH17 cells and their signature cytokines in mediating B-cell differentiation and class switch recombination.

Diminished responses to mRNA-based SARS-CoV-2 vaccines in individuals with rheumatoid arthritis on immune-modifying therapies.

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disorder that causes debilitating swelling and destruction of the joints. People with RA are treated with drugs that actively suppress one or more parts of their immune system, and these may alter the response to vaccination against SARS-CoV-2. In this study, we analyzed blood samples from a cohort of patients with RA after receiving a 2-dose mRNA COVID-19 vaccine regimen. Our data show that individuals on the cytotoxic T lymphocyte antigen 4-Ig therapy abatacept had reduced levels of SARS-CoV-2-neutralizing antibodies after vaccination. At the cellular level, these patients showed reduced activation and class switching of SARS-CoV-2-specific B cells, as well as reduced numbers and impaired helper cytokine production by SARS-CoV-2-specific CD4+ T cells. Individuals on methotrexate showed similar but less severe defects in vaccine response, whereas individuals on the B cell-depleting therapy rituximab had a near-total loss of antibody production after vaccination. These data define a specific cellular phenotype associated with impaired response to SARS-CoV-2 vaccination in patients with RA on different immune-modifying therapies and help inform efforts to improve vaccination strategies in this vulnerable population.

Reciprocal developmental pathways for the generation of pathogenic effector TH17 and regulatory T cells.

On activation, T cells undergo distinct developmental pathways, attaining specialized properties and effector functions. T-helper (T(H)) cells are traditionally thought to differentiate into T(H)1 and T(H)2 cell subsets. T(H)1 cells are necessary to clear intracellular pathogens and T(H)2 cells are important for clearing extracellular organisms. Recently, a subset of interleukin (IL)-17-producing T (T(H)17) cells distinct from T(H)1 or T(H)2 cells has been described and shown to have a crucial role in the induction of autoimmune tissue injury. In contrast, CD4+CD25+Foxp3+ regulatory T (T(reg)) cells inhibit autoimmunity and protect against tissue injury. Transforming growth factor-beta (TGF-beta) is a critical differentiation factor for the generation of T(reg) cells. Here we show, using mice with a reporter introduced into the endogenous Foxp3 locus, that IL-6, an acute phase protein induced during inflammation, completely inhibits the generation of Foxp3+ T(reg) cells induced by TGF-beta. We also demonstrate that IL-23 is not the differentiation factor for the generation of T(H)17 cells. Instead, IL-6 and TGF-beta together induce the differentiation of pathogenic T(H)17 cells from naive T cells. Our data demonstrate a dichotomy in the generation of pathogenic (T(H)17) T cells that induce autoimmunity and regulatory (Foxp3+) T cells that inhibit autoimmune tissue injury.