Citations

Autoantibody-mediated diseases targeting one autoantigen provide a unique opportunity to comprehensively understand the development of disease-causing B cells and autoantibodies. Convention suggests that such autoreactivities are generated during germinal center reactions. Here, we explore earlier immune checkpoints, focusing on patients with contactin-associated protein-like 2 (CASPR2)–autoantibody encephalitis. In both disease and health, high (~0.5%) frequencies of unmutated CASPR2-reactive naïve B cells were identified. By contrast, CASPR2-reactive memory B cells were exclusive to patients, and their B cell receptors demonstrated affinity-enhancing somatic mutations with pathogenic effects in neuronal cultures and mice. The unmutated, precursor memory B cell receptors showed a distinctive balance between strong CASPR2 reactivity and very limited binding across the remaining human proteome. Our results identify permissive central tolerance, defective peripheral tolerance, and autoantigen-specific tolerance thresholds in humans as sequential steps that license CASPR2-directed pathology. By leveraging the basic immunobiology, we rationally direct tolerance-restoring approaches, with an experimental paradigm applicable across autoimmunity.

Abstract Autoimmunity affects 10% of the population. Within this umbrella, autoantibody-mediated diseases targeting one autoantigen provide a unique opportunity to comprehensively understand the developmental pathway of disease-causing B cells and autoantibodies. While such autoreactivities are believed to be generated during germinal centre reactions, the roles of earlier immune checkpoints in autoantigen-specific B cell tolerance are poorly understood. We address this concept in patients with CASPR2-autoantibody encephalitis and healthy controls. In both groups, comparable and high (∼0.5%) frequencies of unmutated CASPR2-reactive naïve B cells were identified. By contrast, CASPR2-reactive memory B cells were exclusive to patients, and their B cell receptors demonstrated affinity-enhancing somatic mutations with heterogenous binding kinetics. These effector molecules possessed epitope-dependent pathogenic effects in vitro neuronal cultures and in vivo. The unmutated common ancestors of these memory B cells showed a distinctive balance between strong CASPR2 reactivity and very limited binding across the remaining human proteome. Our results are the first to propose mechanisms underlying autoantigen-specific tolerance in humans. We identify permissive central tolerance, defective peripheral tolerance and heterogenous autoantibody binding properties as sequential pathogenic steps which licence CASPR2-directed pathology. By leveraging the basic immunobiology, we rationally direct tolerance-restoring approaches in CASPR2-antibody diseases. This paradigm is applicable across autoimmune conditions.

Intrathecal synthesis of central nervous system (CNS)-reactive autoantibodies is observed across patients with autoimmune encephalitis (AE), who show multiple residual neurobehavioral deficits and relapses despite immunotherapies. We leveraged two common forms of AE, mediated by leucine-rich glioma inactivated-1 (LGI1) and contactin-associated protein-like 2 (CASPR2) antibodies, as human models to comprehensively reconstruct and profile cerebrospinal fluid (CSF) B cell receptor (BCR) characteristics. We hypothesized that the resultant observations would both inform the observed therapeutic gap and determine the contribution of intrathecal maturation to pathogenic B cell lineages. From the CSF of three patients, 381 cognate-paired IgG BCRs were isolated by cell sorting and scRNA-seq, and 166 expressed as monoclonal antibodies (mAbs). Sixty-two percent of mAbs from singleton BCRs reacted with either LGI1 or CASPR2 and, strikingly, this rose to 100% of cells in clonal groups with ≥4 members. These autoantigen-reactivities were more concentrated within antibody-secreting cells (ASCs) versus B cells ( P < 0.0001), and both these cell types were more differentiated than LGI1- and CASPR2-unreactive counterparts. Despite greater differentiation, autoantigen-reactive cells had acquired few mutations intrathecally and showed minimal variation in autoantigen affinities within clonal expansions. Also, limited CSF T cell receptor clonality was observed. In contrast, a comparison of germline-encoded BCRs versus the founder intrathecal clone revealed marked gains in both affinity and mutational distances ( P = 0.004 and P < 0.0001, respectively). Taken together, in patients with LGI1 and CASPR2 antibody encephalitis, our results identify CSF as a compartment with a remarkably high frequency of clonally expanded autoantigen-reactive ASCs whose BCR maturity appears dominantly acquired outside the CNS.

Objective Myelin oligodendrocyte glycoprotein antibody‐associated disease (MOGAD) can be monophasic or relapsing, with early relapse being a feature. However, the relevance of early relapse on longer‐term relapse risk is unknown. Here, we investigate whether early relapses increase longer‐term relapse risk in patients with MOGAD. Methods A retrospective analysis of 289 adult‐ and pediatric‐onset patients with MOGAD followed for at least 2 years in 6 specialized referral centers. “Early relapses” were defined as attacks within the first 12 months from onset, with “very early relapses” defined within 30 to 90 days from onset and “delayed early relapses” defined within 90 to 365 days. “Long‐term relapses” were defined as relapses beyond 12 months. Cox regression modeling and Kaplan–Meier survival analysis were used to estimate the long‐term relapse risk and rate. Results Sixty‐seven patients (23.2%) had early relapses with a median number of 1 event. Univariate analysis revealed an elevated risk for long‐term relapses if any “early relapses” were present (hazard ratio [HR] = 2.11, p < 0.001), whether occurring during the first 3 months (HR = 2.70, p < 0.001) or the remaining 9 months (HR = 1.88, p = 0.001), with similar results yielded in the multivariate analysis. In children with onset below aged 12 years, only delayed early relapses were associated with an increased risk of long‐term relapses (HR = 2.64, p = 0.026). Interpretation The presence of very early relapses and delayed early relapses within 12 months of onset in patients with MOGAD increases the risk of long‐term relapsing disease, whereas a relapse within 90 days appears not to indicate a chronic inflammatory process in young pediatric‐onset disease. ANN NEUROL 2023;94:508–517

ObjectiveDrug‐resistant seizures are common in patients with leucine‐rich, glioma‐inactivated 1 (LGI1)‐IgG associated and contactin‐associated protein‐like 2 (CASPR2)‐IgG associated encephalitis. We performed the first randomized double‐blind placebo‐controlled trial to evaluate efficacy of intravenous immunoglobulin (IVIG) in reducing seizure frequency.MethodsOur enrollment goal was 30 LGI1/CASPR2‐IgG–seropositive adult patients with ≥2 seizures per week. Patients were randomized to receive IVIG (0.5g/kg day 1, 1g/kg day 2, 0.6g/kg weeks 3 and 5) or volume‐matched intravenous normal saline. Following the blinded phase, the nonresponders in the placebo group received IVIG. The primary clinical outcome was 50% reduction in seizure frequency from baseline to 5 weeks.ResultsAfter enrollment of 17 patients (LGI1‐IgG, 14; CASPR2‐IgG, 3) over 34 months, the study was terminated due to slow enrollment. Six of 8 patients in the IVIG group were responders, compared to 2 of 9 in the placebo group (p = 0.044, odds ratio = 10.5, 95% confidence interval = 1.1–98.9). For the LGI1‐IgG seropositive subgroup, 6 of 8 patients in the IVIG group were responders, compared to zero of 6 in the placebo group. Two LGI1‐IgG–seropositive patients receiving IVIG, but none receiving placebo, were seizure‐free at the end of the blinded phase. Four of the 6 patients entering the open‐label IVIG arm reported ≥50% reduction in seizure frequency. There were no correlations with LGI1/CASPR2‐IgG1–4 subclasses.InterpretationSuperiority of IVIG to placebo reached statistical significance for the primary endpoint for all patients and the subset with LGI1‐IgG. These results have to be interpreted with the caveat that the study did not reach its originally selected sample size. ANN NEUROL 2020;87:313–323