ObjectiveAdult drug‐resistant epilepsy (DRE) is associated with significant morbidity. Infiltration of immune cells is observed in DRE epileptic foci; however, the relation between DRE and the peripheral immune cell compartment remains only partially understood. We aimed to investigate differences in immune cell populations, cytokines, and neurodegenerative biomarkers in the peripheral blood of subjects with epilepsy versus healthy controls, and in DRE compared to well‐controlled epilepsy (WCE).MethodsPeripheral blood mononuclear cells and serum from >120 age‐ and sex‐matched adults suffering from focal onset epilepsy and controls were analyzed by multipanel flow cytometry, multiplex immunoassays, and ultrasensitive single molecule array.ResultsUsing a data‐driven analytical approach, we identified that CD4 T cells in the peripheral blood are present in a higher proportion in DRE patients. Moreover, we observed that the frequency of CD4 T cells expressing proinflammatory cytokines interleukin (IL)‐17A, IL‐22, tumor necrosis factor, interferon‐γ, and granulocyte‐macrophage colony–stimulating factor, but not anti‐inflammatory cytokines IL‐10 and IL‐4, is elevated in the peripheral blood of DRE subjects compared to WCE. In parallel, we found that Th17‐related circulating proinflammatory cytokines are elevated, but Th2‐related cytokine IL‐4 is reduced, in the serum of epilepsy and DRE subjects. As Th17 cells can exert neurotoxicity, we measured levels of serum neurofilament light chain (sNfL), a marker of neuronal injury. We found significantly elevated levels of sNfL in DRE compared to controls, especially among older individuals.SignificanceOur data support that DRE is associated with an expansion of the CD4 Tcell subset in the peripheral blood and with a shift toward a proinflammatory Th17/Th1 CD4 Tcell immune profile. Our results further show that pathological levels of sNfL are more frequent in DRE, supporting a potential neurodegenerative component in adult DRE. With this work, we provide evidence for novel potential inflammatory and degenerative biomarkers in DRE.

Multiple sclerosis (MS) is characterized by the loss of myelin and of myelin-producing oligodendrocytes (OLs) in the central nervous system (CNS). Pro-inflammatory CD4+ Th17 cells are considered pathogenic in MS and are harmful to OLs. We investigated the mechanisms driving human CD4+ T cell-mediated OL cell death. Using fluorescent and brightfield in vitro live imaging, we found that compared to Th2-polarized cells, Th17-polarized cells show greater interactions with primary human OLs and human oligodendrocytic cell line MO3.13, displaying longer duration of contact, lower mean speed, and higher rate of vesicle-like structure formation at the sites of contact. Using single-cell RNA sequencing, we assessed the transcriptomic profile of primary human OLs and Th17-polarized cells in direct contact or separated by an insert. We showed that upon close interaction, OLs upregulate the expression of mRNA coding for chemokines and antioxidant/anti-apoptotic molecules, while Th17-polarized cells upregulate the expression of mRNA coding for chemokines and pro-inflammatory cytokines such as IL-17A, IFN-γ, and granzyme B. We found that secretion of CCL3, CXCL10, IFN-γ, TNFα, and granzyme B is induced upon direct contact in cocultures of human Th17-polarized cells with human OLs. In addition, we validated by flow cytometry and immunofluorescence that granzyme B levels are upregulated in Th17-polarized compared to Th2-polarized cells and are even higher in Th17-polarized cells upon direct contact with OLs or MO3.13 cells compared to Th17-polarized cells separated from OLs by an insert. Moreover, granzyme B is detected in OLs and MO3.13 cells following direct contact with Th17-polarized cells, suggesting the release of granzyme B from Th17-polarized cells into OLs/MO3.13 cells. To confirm granzyme B–mediated cytotoxicity toward OLs, we showed that recombinant human granzyme B can induce OLs and MO3.13 cell death. Furthermore, pretreatment of Th17-polarized cells with a reversible granzyme B blocker (Ac-IEPD-CHO) or a natural granzyme B blocker (serpina3N) improved survival of MO3.13 cells upon coculture with Th17 cells. In conclusion, we showed that human Th17-polarized cells form biologically significant contacts with human OLs and exert direct toxicity by releasing granzyme B.

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Epilepsy is a chronic neuronal disorder affecting ~65 millions people throughout the world. 1/3 of patients suffer from drug-resistant epilepsy (DRE). Objective to assess the relationship between different Th17 markers and the clinical course of epilepsy to uncover new potential immune biomarkers and therapeutic targets of interest for DRE. Approach Subjects between 19–55 years old with a focal diagnosed epilepsy were recruited at the CHUM epilepsy clinic. The profile of peripheral blood T lymphocytes from DRE patients (n=48) is compared to well-controlled epilepsy (WCE; n=30) and healthy controls (n=35). Peripheral blood mononuclear cells (PBMCs) were isolated by gradient density centrifugation before ex vivo analysis of surface markers (flow cytometry). Total CD4 T lymphocytes were magnetically isolated from PBMCs and stimulated overnight before analysis of cytokine expression or processed for RNA extraction before analysis of transcription factors expression by qRT-PCR. Results Our data suggest that antiepileptic drugs are associated with a relative ‘immunosuppression’, more pronounced in WCE. Epilepsy is associated with an altered distribution of immune cell populations with a higher CD4:CD8 ratio. A higher proportion of CD4 T lymphocytes from DRE subjects express CCR6 and CD161 compared to WCE. The proportion of CD4 T cells expressing pro-inflammatory cytokines from Th17/1 lineage (IL-17A, IL-22, IFN-γ, GM-CSF, TNFα) is higher in DRE than WCE, while anti-inflammatory cytokines (IL-4, IL-10) tend to be lower. Conclusion Our preliminary results suggest an increased frequency of pro-inflammatory Th17/1 lymphocytes and their related cytokines in DRE. Pro-inflammatory CD4 T cells could play a role in DRE.