Anti-MOG antibodies are present in a subgroup of patients with a neuromyelitis optica phenotype

Neuromyelitis optica (NMO) is a clinically defined entity within the spectrum of inflammatory demyelinating diseases of the central nervous system (CNS) which is characterized by inflammatory attacks that are confined to the spinal cord and the optic nerves [1,2]. Limited forms of the disease are considered as NMO spectrum disorder (NMOSD) [3]. The finding of anti-aquaporin-4 (AQP4) antibodies in the majority of patients with NMO [4] and some patients with NMOSD has advanced our pathogenic understanding of the disease [5] and has directed the therapeutic approach towards a B cell-directed therapy [6]. However, 10% to 50% of NMO patients, depending on cohorts and assays used, are AQP4-negative [7]. Recent evidence suggests that some of the NMO cases are related to antibodies against myelin oligodendrocyte glycoprotein (MOG) [8-17].

Previously, we showed that anti-MOG antibodies are present in about 25% of pediatric patients with a first episode of acute demyelination and that these antibodies correlate with the disease course [18,19]. The aims of the present study were a) to analyze the presence of anti-MOG antibodies in an independent blinded cohort of patients with NMO/NMOSD and multiple sclerosis (MS) using the previously described cell-based assay (CBA) [18], b) to correlate antibody findings to clinical and magnetic resonance imaging (MRI) parameters of MOG-seropositive and AQP4-seropositive NMO patients and NMO patients with no detectable antibodies, and c) to characterize the long-term clinical outcome of the MOG-seropositive patients.

A total of 135 patients including patients with NMO/NMOSD (n = 48), relapsing-remitting MS (n = 48), and healthy donors (n = 39) were analyzed. NMO/NMOSD and MS patient samples were collected at the University Hospital, Strasbourg, France between 2006 and 2012. The clinical data were obtained retrospectively from the European Database for Multiple Sclerosis (EDMUS). Healthy donor samples were obtained from the blood donation center, Etablissement Français du Sang (EFS), Strasbourg, France. Diagnoses of NMO/NMOSD or MS were based on the revised Wingerchuk criteria or the McDonald criteria, respectively [2,20]. Baseline sera for the NMO and MS patients were collected within an average of 8 years (0 to 42 years) (MOG vs. AQP4 vs. seronegative: 17 (3 to 32), 6 (0 to 42), 7 (0 to 15) years) and 14 years (3 to 37 years) of the first inflammatory episode, respectively. The mean period of observation for the NMO/NMOSD patients was 19 years (3 to 35) for the MOG-positive patients, 11 years (3 to 44) for the AQP4-positive patients, and 9 years (2 to 17) for the seronegative patients. Anti-AQP4 antibodies were measured by two different methods: indirect immunofluorescence (iIF) and CBA. Anti-MOG antibodies in the sera were measured by flow cytometry using a CBA with full-length, human, native conformational MOG as previously described [18]. The analysis was carried out blinded. Anti-MOG antibody positivity was determined by the ratio of the geometric mean channel fluorescence (GMCF) of the MOG-transfected and the empty vector-transfected cell line. The cutoff was calculated to be 1.45 (mean GMCF ratio plus two standard deviations of the healthy donor control group measured in parallel). The study was approved by the local ethical committee of the University Hospital of Strasbourg (DC-2009-1002; CPP 09/40; DC-2014-2222), and all patients gave their informed consent for the study.

In total, 48 patients with NMO/NMOSD were included in the study: 4 of the 48 patients tested positive for anti-MOG antibodies, all of which were negative for anti-AQP4-antibodies (Figure 1). Tested with the iIF assay, 22 patients were positive for anti-AQP4-antibodies, while testing with the CBA revealed that 31 patients were anti-AQP4 antibody-positive (Figure 1A). Only one patient was tested positive with the iIF assay, but negative with the CBA. The remaining 13 patients were seronegative for both antibodies tested (Figure 1).

The median age at first attack was slightly younger in the MOG-seropositive group (31 years; range 15 to 55 years) compared to the age of the AQP4-seropositive group (38 years; range 15 to 60 years) or the seronegative group (36 years; range 23 to 53 years). Of note, two out of four of the MOG-seropositive patients had a disease onset in childhood (<18 years), whereas this was the case only in three out of thirty one of the AQP4-seropositive and none of the seronegative patients. In terms of clinical presentation, half of the MOG-seropositive (2/4) or AQP4-seropositive (16/31) patients and about two thirds (8/13) of the seronegative patients had an initial presentation with uni-/bilateral optic neuritis (ON) (Table 1). A quarter of the MOG-seropositive (1/4) and about a third of the AQP4-seropositive (10/31) and seronegative (4/13) patients had a disease manifestation with transverse myelitis (TM). Remarkably, the mean time to the second attack affecting a different CNS region was longer in the MOG-seropositive patients (11.3 years; range 1 to 30 years) as compared to the AQP4-seropositive (3.2 years; range 0 to 9 years) and seronegative (3.4 years; range 0 to 7 years) patients (Table 1). Oligoclonal bands (OCBs) were more often found in the MOG-seropositive patients (3/3, not available in 1) compared to the AQP4-seropositive (5/29, not available in 2) and seronegative (1/13) patients.

MOG-seropositive patients showed brain lesions during the disease course more frequently (2/4) as compared to AQP4-seropositive (5/31) and seronegative (1/13) patients. Follow-up brain MRI in two MOG-seropositive patients revealed juxtaventricular lesions in one patient, and lesions in the thalamus and corpus callosum in another patient fulfilling the Barkhof criteria (Figure 2). All of the patients had longitudinally extensive transverse myelitis (LETM) in the cervical and/or thoracic spinal cord.

Longitudinal follow-up samples, which were available in two patients with anti-MOG antibodies, showed fluctuating antibody levels over the follow-up period of 22 and 74 months (Figure 3). An increase of anti-MOG antibodies was associated in one patient (STB01) with an increased relapse frequency, but was independent of any disease activity in another patient (STB02) (Figure 3).