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Intravenous ofatumumab treatment of multiple sclerosis and related disorders: An observational study

Open AccessPublished:October 15, 2022DOI:https://doi.org/10.1016/j.msard.2022.104246

      Highlights

      • Annualized relapse rate was reduced from 1.03 at baseline to 0.38 during treatment.
      • Disability worsening was stabilized with a cumulated risk of 7% at 24 months.
      • Mild-moderate infusion-related reactions were common.

      Abstract

      Background

      Ofatumumab is an anti-CD20 monoclonal antibody approved for subcutaneous administration for the treatment of relapsing multiple sclerosis (MS), but intravenously administered ofatumumab has been investigated in a phase 2 trial and used off-label. The objective of the present study was to assess disease activity and side effects in relation to longer-term intravenous ofatumumab treatment of MS and related disorders.

      Methods

      We conducted a retrospective study of patients treated off-label with intravenous ofatumumab for MS, neuromyelitis optica spectrum disease (NMOSD) and myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) at the Danish Multiple Sclerosis Center. Data was retrieved from the Danish Multiple Sclerosis Registry and through medical chart review.

      Results

      Fifty patients were identified with a median treatment duration of 2.2 years. Annualized relapse rate decreased from 1.03 at baseline to 0.38 during ofatumumab treatment. At 24 months, the probability of having experienced a relapse was 55% and confirmed disability worsening 7%. Frequency of infusion-related reactions was 86% during the first infusion and 42% during the last infusion. Six experienced infections requiring hospitalization.

      Conclusion

      Our data indicate a reduction of relapse frequency, stabilization of disability worsening and an acceptable safety profile, although we observed a higher frequency of infusion reactions compared to data from other intravenously administered anti-CD20 monoclonal antibodies. The study supports a class effect of anti-CD20 monoclonal antibodies and the hypothesis that complement activation may be associated to a higher frequency of infusion related reactions.

      Graphical abstract

      Keywords

      Abbreviations

      ADCC
      Antibody-dependent cell-mediated cytotoxicity
      ARR
      Annualized relapse rates
      CDC
      Complement-dependent cytotoxicity
      CDI
      Confirmed disability improvement
      CDW
      Confirmed disability worsening
      DMSC
      Danish Multiple Sclerosis Center
      DMSR
      Danish Multiple Sclerosis Registry
      DMT
      Disease-modifying therapy
      MS
      Multiple sclerosis
      EDSS
      Expanded Disability Status Scale
      IRR
      Infusion-related reactions
      IV
      Intravenous
      MOGAD
      Myelin-oligodendrocyte glycoprotein associated disease
      NK
      Natural killer
      NMOSD
      Neuromyelitis optica spectrum disease
      RRMS
      Relapsing-remitting MS
      SC
      Subcutaneous

      1. Introduction

      Multiple sclerosis (MS), neuromyelitis optica spectrum disease (NMOSD) and myelin-oligodendrocyte glycoprotein associated disease (MOGAD) are inflammatory and demyelinating disorders of the central nervous system (
      • Wingerchuk D.M.
      • Lennon V.A.
      • Lucchinetti C.F.
      • Pittock S.J.
      • Weinshenker B.G.
      The spectrum of neuromyelitis optica.
      ;
      • Reich D.S.
      • Lucchinetti C.F.
      • Calabresi P.A.
      Multiple Sclerosis.
      ;
      • Höftberger R.
      • Guo Y.
      • Flanagan E.P.
      • Lopez-Chiriboga A.S.
      • et al.
      The pathology of central nervous system inflammatory demyelinating disease accompanying myelin oligodendrocyte glycoprotein autoantibody.
      ). B cells are implicated in the immunopathogenesis of these disorders, and targeting B cells with anti-CD20 monoclonal antibodies is an increasingly used treatment strategy for MS, NMOSD and MOGAD (
      • Graf J.
      • Mares J.
      • Barnett M.
      • Aktas O.
      • et al.
      Targeting B cells to modify MS, NMOSD, and MOGAD: Part 1.
      ,
      • Graf J.
      • Mares J.
      • Barnett M.
      • Aktas O.
      • et al.
      Targeting B cells to modify MS, NMOSD, and MOGAD: Part 2.
      ).
      The surface molecule CD20 is expressed by most B cells and a subset of proinflammatory T cells (
      • Von Essen M.R.
      • Ammitzbøll C.
      • Hansen R.H.
      • Petersen E.R.S.
      • et al.
      Proinflammatory CD20+ T cells in the pathogenesis of multiple sclerosis.
      ;
      • Sellebjerg F.
      • Blinkenberg M.
      • Sorensen P.S.
      Anti-CD20 monoclonal antibodies for relapsing and progressive multiple sclerosis.
      ). Ofatumumab is a fully human anti-CD20 monoclonal antibody which depletes CD20+ cells through complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC) (
      • Reagan J.L.
      • Castillo J.J.
      Ofatumumab for newly diagnosed and relapsed/refractory chronic lymphocytic leukemia.
      ).
      Subcutaneous (SC) ofatumumab was approved for relapsing forms of MS with active disease by the U.S. Food and Drug Administration in August 2020 and by the European Medicines Agency in March 2021 based on two phase III trials demonstrating its efficacy on reducing relapse rate, disability worsening and MRI lesion activity (
      • Hauser S.L.
      • Bar-Or A.
      • Cohen J.A.
      • Comi G.
      • et al.
      Ofatumumab versus teriflunomide in multiple sclerosis.
      ). Intravenous (IV) ofatumumab, however, has only been studied for MS in a phase II trial including 38 subjects with relapsing-remitting MS (RRMS). The study demonstrated the tolerability of two ofatumumab infusions two weeks apart, and a significant reduction in MRI lesion activity in comparison to placebo during the first 24 weeks after ofatumumab administration (
      • Sorensen P.S.
      • Lisby S.
      • Grove R.
      • Derosier F.
      • et al.
      Safety and efficacy of ofatumumab in relapsing-remitting multiple sclerosis: A phase 2 study.
      ). No phase III trial has been conducted, as focus has since shifted to SC ofatumumab administration.
      IV ofatumumab (brand name Arzerra®) was approved by the European Medicines Agency in 2010 for treatment of chronic lymphocytic leukemia. Until April 2019, when commercial marketing of the drug was terminated in Europe, selected patients with demyelinating disorders were treated off-label with IV ofatumumab at the Danish Multiple Sclerosis Center (DMSC). The objective of this study was to assess effectiveness and side effects of IV ofatumumab therapy in MS, NMOSD and MOGAD.

      2. Material and methods

      2.1 Study design

      We conducted a retrospective observational study of all patients who had received IV ofatumumab (Arzerra®, originally devoloped by Genmab, Copenhagen, Denmark; current marketing authorization holder Novartis Europharm Ltd., Camberley, UK) as treatment for MS, NMOSD or MOGAD at DMSC. Patients were identified through the Danish Multiple Sclerosis Registry (DMSR) (
      • Magyari M.
      • Joensen H.
      • Laursen B.
      • Koch-Henriksen N.
      The danish multiple sclerosis registry.
      ), and no timeframe restrictions were applied.

      2.2 Treatment and follow up

      The ofatumumab treatment regimen consisted of two induction infusions at a 2-weeks interval followed by a maintenance infusion every 6 months. Standard induction doses were 300 mg followed by 1000 or 300 mg, while maintenance dose was 1000 or 600 mg (before and after April 2016, respectively). Treatment with IV ofatumumab was terminated when marketing of Arzerra® was discontinued in 2019, and many patients treated with ofatumumab were subsequently switched to rituximab (maintenance dose 1000 mg) or ocrelizumab (maintenance dose 600 mg). Patients were pretreated with oral methylprednisolone, fexofenadine and paracetamol before infusions.
      At the DMSC, clinical evaluation including Expanded Disability Status Scale (EDSS) scoring is routinely scheduled every 6 months for patients on anti-CD20 monoclonal antibodies. The DMSR is regularly notified by clinicians during regular clinical visits. Immunoglobulin levels (IgA, IgG and IgM) and flowcytometric determination of blood lymphocyte subset counts (CD19+ B cells, CD3+ T cells, CD3+CD4+ T cells, CD3+CD8+ T cells and CD16+CD56+ natural killer (NK) cells) were routinely measured 1-4 weeks before each ofatumumab infusion series. For patients with MS, an MRI re-baseline scan of the brain and spinal cord is generally obtained within 3-6 months after changing or initiating disease-modifying therapy (DMT), and control brain MRI scans are conducted yearly thereafter.

      2.3 Data collection

      Baseline characteristics and blood test results were collected from the latest clinical visit prior to ofatumumab initiation. For relapses, we registered the summed number throughout the year prior to commencement of ofatumumab. Baseline cerebral MRI was defined as the latest scan within 12 months prior to ofatumumab initiation, and re-baseline was defined as the first scan after treatment start.
      From the DMSR, we retrieved demographic and clinical data such as sex, diagnosis, date of birth, date of disease onset and diagnosis, relapses and EDSS scores, information on cerebral MRI lesions, initiation and termination of ofatumumab treatment, and prior and subsequent DMT. Additionally, we reviewed electronic medical charts, imaging and laboratory results for participants who continually were affiliated with the DMSC at the time of chart review, cross-validating the data retrieved from the DMSR and collecting information on infections requiring hospitalization, infusion-related reactions (IRRs), immunoglobulin levels, T, B and NK cell counts and assessing for late onset neutropenia.

      2.4 Outcomes

      Primary outcome was clinical relapses the first year of ofatumumab treatment and annualized relapse rates (ARR) throughout treatment. ARR was calculated for patients who completed at least one year of ofatumumab treatment only and with follow-up from 6 months after the first infusion (re-baseline) until 6 months after the last infusion. Secondary outcomes with follow-up until 6 months after the last infusion were confirmed disability worsening (CDW) or improvement (CDI) for patients with ≥ 3 EDSS assessments, radiological disease activity (gadolinium contrast enhancement and new or enlarging T2 brain MRI lesions) and infections requiring hospitalization. Moreover, we assessed immunoglobulin levels and blood cell counts 4-8 months after each infusion series, late onset neutropenia until up to 2.5 years after termination of ofatumumab treatment, IRRs during the first three infusions and the last infusion and, for patients who were subsequently treated with rituximab or ocrelizumab, IRRs during the first rituximab or ocrelizumab infusion.
      CDW was defined as an increase in EDSS score confirmed after ≥ 6 months and meeting the following criteria: ≥1.5 points increase for patients with baseline EDSS score = 0, ≥1.0 points increase for baseline EDSS score >0 and ≤5.5, and ≥0.5 points increase for baseline EDSS score >5.5. CDI was defined as a decrease in EDSS score of ≥1 point and was only assessed for patients with baseline EDSS ≥2.0. Assessment of CDW and CDI required a minimum of 3 EDSS scorings within the follow-up period.
      B cell counts were truncated at 0.01 × 109 cells per liter, as this was the lower limit of detection until 2018. Patients who were treated with another CD20 depleting therapy prior to ofatumumab treatment were excluded from B cell count and IRR results during the first three infusions. IRRs were graded according to a modified version of the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE) version 5.0 (

      U.S. Department of Health and Human Services (2017) Common terminology criteria for adverse events (CTCAE) version 5.0.

      ). For immunoglobulin analyses, we excluded measurements during immunoglobulin replacement therapy.

      2.5 Statistical analyses

      Statistical analyses were performed depending on whether data followed a normal distribution or not, which was checked visually by histograms and QQ-plots and statistically by Shapiro-Wilk test. Continuous non-parametric data are reported as medians with their 1st and 3rd quartiles (Q1-Q3) or range, and categorical data as counts and percentages. Relapse rates before and on treatment were calculated using a generalized estimating equation with a negative binomial distribution and log link function. We assumed the working correlation structure to be unstructured. McNemar Test was used for comparing paired categorical data, and Pearson's Chi-squared test for unpaired categorical data. For survival data, we analyzed differences between survival curves by log-rank test and calculated hazard ratios where applicable. Mixed model analysis was used for repeated measures of continuous outcomes. In statistical analyses p<0.05 was considered significant. Analysis of ARR was performed using SAS version 9.4 (SAS Institute Inc., Cary, NC, USA). Analyses apart from ARR were conducted in R version 4.1.0 (

      Gerds, T.A. (2019) prodlim: product-limit estimation for censored event history analysis.

      ;

      Pinheiro, J., Bates, D., DebRoy, S., Sarkar, D., et al. (2021) nlme: linear and nonlinear mixed effects models description.

      ;
      R Core Team
      R: A language and environment for statistical computing.
      ), and graphs were made in R and GraphPad Prism version 9.0.0 (GraphPad Software, San Diego, CA, USA).

      2.6 Protocol approval

      The study was approved by the directors of the Neuroscience Center and the Department of Neurology, Copenhagen University Hospital – Rigshospitalet. According to Danish legislation non-interventional register-based studies require neither ethics approval nor informed patient consent. To comply with regulatory definitions for anonymization, results are only reported for groups comprising more than 3 patients. Where relevant, groups ≤3 were pooled.

      3. Results

      3.1 Patient characteristics

      Fifty eligible patients were identified and included, all of whom had been treated between February 2013 and April 2019. Forty-five patients were eligible for chart review, and 37 were subsequently treated with ocrelizumab (n=23) or rituximab (n=14) (Fig. 1).
      Fig 1
      Fig. 1Flow chart outlining patient eligibility and inclusion.
      Registry data was included for all 50 patients and includes relapses, EDSS changes, MRI data, initiation and termination of ofatumumab treatment, prior and subsequent DMT. Medical chart data was available for 45 patients and includes infections requiring hospitalization, infusion-related reactions, immunoglobulin levels, T, B and NK cell counts and late-onset neutropenia.
      Baseline characteristics are summarized in Table 1.
      Table 1Baseline characteristics
      MSNNMOSD/MOGADN
      Age at treatment start, yearsa45 (35-51)4250 (41-56)8
      Sex, female (%)35 (83%)427 (88%)8
      Disease duration, yearsa12 (7-16)426 (4-12)8
      Phenotype/disorder (%)428
       RRMS35 (83%)
       Progressive MS7 (17%)
       MOGAD4 (50%)
       NMOSD4 (50%)
      EDSSa4.0 (3.0-5.9)424.0 (3.3-4.4)8
      Number of DMT changes prior to starting ofatumumaba3.0 (3.0-5.0)422.0 (1.8-3.3)8
      Latest DMT prior to ofatumumab428
       Fingolimod17 (40%)
       Dimethyl fumarate8 (19%)
       Natalizumab10 (24%)
       Other5 (12%)6 (75%)
      Reason for switching to ofatumumab408
       Adverse effects9 (23%)
       Disease activity27 (68%)7 (88%)
       Other4 (10%)
      Relapses previous year, n (%)42
       None14 (33%)
       ≥ 128 (67%)
      ARRb1.10 (0.84-1.43)400.69 (0.35-1.36)8
      aMedian (Q1-Q3).
      bEstimate (95% confidence interval)
      Of the 50 patients included, 4/50 (8%) were diagnosed with NMOSD, 4/50 (8%) with MOGAD and 42/50 (84%) with MS, of which 35/42 (83%) had RRMS and 7/42 (17%) had progressive MS. Median age at treatment start was 46 years (Q1-Q3: 35-52 years), and median EDSS was 4.0 (Q1-Q3: 3.0-5.5). Throughout the year preceding ofatumumab initiation, 17/50 (34%) experienced no relapse.
      Baseline brain MRI results were available for 41/42 (98%) of patients with MS. New or enlarging lesions were present in 12/41 (29%), and contrast enhancing lesions in ≤3 of 25 scans with post-contrast sequences.
      Before ofatumumab treatment, ≤3 were untreated, ≤3 were treated with rituximab and 45/50 (90%) were treated with another DMT. Overall, the patients had switched DMT a median of 3 times (Q1-Q3: 2-5) prior to initiation of ofatumumab. The most frequent DMTs before switching to ofatumumab were natalizumab (11/50 or 22%), fingolimod (18/50 or 36%) and dimethyl fumarate (8/50 or 16%), and most frequent reasons for discontinuation were disease activity (34/48 or 71%) and adverse events (10/48 or 21%). Median wash-out periods were 1.6 months (Q1-Q3: 1.4-1.8) for natalizumab, 1.6 months (Q1-Q3: 1.2-2.6) for fingolimod, and 2.2 (Q1-Q3: 0.6-5.3) for dimethyl fumarate.

      3.2 Disease activity and disability worsening

      The first year after initiation of ofatumumab treatment, the relapse-free proportion of patients was 30/50 (60%), which was significantly different from the 34% the year preceding ofatumumab treatment (p=0.009). The second year of ofatumumab treatment, the relapse-free proportion of patients was 27/43 (63%). For patients who completed at least one year of ofatumumab treatment (n=48), the ARR was reduced with 63% (95% CI 47%-74%, p <0.0001) from 1.03 (95% CI 0.79-1.32) at baseline to 0.38 (95% CI 0.26-0.55) during treatment (median follow-up time from re-baseline = 2.1 years). Absolute rate difference was -0.64 (95% CI -0.89 to -0.40, p < 0.0001).
      For MS patients separately (n=40), the ARR was reduced with 63% (95% CI 46%-74%, p < 0.0001) from 1.10 (95% CI 0.84-1.43) at baseline to 0.41 (95% CI 0.28-0.60) on treatment. The absolute rate difference was -0.69 (95% CI -0.96 to -0.41, p <0.0001). For MOGAD and NMOSD patients (n=8), the ARR on treatment was 0.27 (95% CI 0.09-0.76). Due to the small sample size, we did not have enough power to reasonably estimate before-and-after differences for this population.
      Overall, 30/50 (60%) experienced at least one relapse during follow-up, 8/45 (18%) developed 6 months CDW, and ≤3/45 patients had CDI. For patients who experienced a relapse, median time to first relapse was 6 months (range 23 days-30 months) from treatment start. For MS patients, the probability of having experienced at least one relapse at 24 months was 54% (95% CI 38%-69%), and the probability of 6 months CDW was 8% (95% CI 0%-17%) at 24 months. The cumulative risk of CDW and relapse in MS over time is depicted in Fig. 2.
      Fig2
      Fig. 2Risk of relapse and disability worsening for patients with multiple sclerosis.
      Kaplan-Meier cumulative incidence curves showing A) the cumulative proportion of multiple sclerosis patients with relapse breakthrough over time, and B) the cumulative proportion of multiple sclerosis patients with six months confirmed EDSS worsening over time.
      On re-baseline MRI scans, 5/41 (12%) of MS patients had at least one new or enlarged brain lesion, and ≤3/10 had contrast enhancing lesions. From the re-baseline scan until 6 months after the last infusion, ≤3/29 MS patients developed a new or enlarging lesion. Median MRI follow up time (i.e. time between re-baseline scan until the last scan within follow up) was 1.9 years (Q1-Q3: 1.3-2.4 years).
      Outcomes related to clinical disease activity and worsening are summarized in Table 2.
      Table 2Intravenous ofatumumab treatment and disease activity
      TotalNMSNNMOSD/MOGADN
      Treatment duration, yearsa2.2 (1.8-2.6)502.1 (1.8-2.6)423.0 (2.3-3.7)8
      ARRb0.38 (0.26-0.55)480.41 (0.28-0.60)400.27 (0.09-0.76)8
       Incidence rate ratio0.37 (0.26-0.53)*0.37 (0.26-0.54)*
       Absolute difference-0.64 (-0.89 to -0.40)*-0.69 (-0.96 to -0.41)*
      Relapse-free, n (%)
       First 6 months34 (68%)5030 (71%)42
       Months 7-1238 (79%)4833 (83%)40
      Time to first relapse, monthsa6 (4-15)306 (5-17)253 (2-4)5
      Probability of relapse at 24 monthsb55% (41%-69%)5054% (38%-69%)42
      Time to CDW, monthsa28 (18-31)822 (18-29)6
      Probability of CDW at 24 monthsb7% (0%-14%)458% (0%-17%)38
      Reason for discontinuing ofatumumab50428
       Marketing terminated31 (62%)26 (62%)5 (63%)
       Adverse effects7 (14%)7 (17%)≤3
       Disease activity≤3≤3≤3
       Planning pregnancy≤3≤3≤3
       Other7 (14%)6 (14%)≤3
      aMedian (Q1-Q3).
      bEstimate (95% confidence interval).
      *p < 0.0001

      3.3 Adverse and side effects

      3.3.1 Immunoglobulin levels

      At baseline, 7/44 (16%) had IgG levels below the lower limit of normal (< 6.1 g/L) with a median level of 5.7 g/L (Q1-Q3: 5.0-5.8), 6/43 (14%) had low IgM (< 0.39 g/L) with a median level of 0.27 (Q1-Q3: 0.26-0.32), and ≤3 patients had low IgA (< 0.70 g/L). De novo low IgM was detected in 10/36 (28%), while ≤3 patients developed de novo IgA or IgG hypogammaglobulinemia during ofatumumab treatment. For patients with de novo IgM hypogammaglobulinemia, median treatment time to detection of low IgM was 18 months (Q1-Q3: 10-22), and lowest level was 0.31 g/L (Q1-Q3: 0.28-0.34).
      After a median treatment time of 11 months (Q1-Q3: 6-18) for IgG and 6 months (Q1-Q3: 5-6) for IgM, all patients with baseline low IgG or IgM levels either had worsening of the specific hypogammaglobulinemia or new episodes after an initial normalization. Median lowest levels were 5.5 g/L (Q1-Q3: 4.8-5.8 g/L) for IgG and 0.18 g/L (0.14-0.22) for IgM. Serial measurements of immunoglobulin levels are shown in Fig. 3.
      Fig 3
      Fig. 3Serum immunoglobulin levels.
      Serial immunoglobulin levels as measured within 4-8 months after each ofatumumab infusion series. Immunoglobulin A, G and M level is plotted on the y-axis against infusion series number on the x-axis. Dotted lines mark upper and lower limits of normal range.

      3.3.2 Blood cell counts

      Seventy-nine percent of patients (27/34) had complete B cell depletion after the first ofatumumab treatment series (i.e. ≤0.01 × 109 CD19+ B cells/l), 94% (32/34) after the second, and 94% (32/34) after the third treatment series. Median time of sampling was 5.7 months after the latest infusion series (Q1-Q3: 5.4-5.9) and 0.4 months before the next infusion series (Q1-Q3: 0.3-0.8). Of patients with incomplete B cell depletion after the first infusion series, 3/7 (43%) experienced a relapse during the first 6 months of ofatumumab treatment, and of patients with complete B cell depletion, 10/27 (37%) experienced a relapse (p=0.8).
      There were no cases of late onset neutropenia as assessed for up to 2.5 years after the last ofatumumab infusion (median follow up period 2.3 years, Q1-Q3: 2.1-2.4).
      Cell counts of CD3+ T cells, CD4+ T cells, CD8+ T cells and NK cells did not change significantly in relation to numbers of infusion series (p=0.38, 0.09, 0.27 and 0.20, respectively). Serial measurements of T, B and NK cell counts are shown in Fig. 4.
      Fig 4
      Fig. 4Blood lymphocyte subset counts.
      Serial blood cell counts as measured within 4-8 months after each ofatumumab infusion series. Dotted lines indicate upper and lower limits of normal ranges. 4A-D: median cell counts and interquartile ranges for A) CD3+ T cells B) CD8+ T cells, C) CD4+ T cells and D) natural killer cells. 4E: spaghetti plot depicting serial B cell counts for each patient. Line at 0.01 marks the lower limit of detection and complete B cell depletion.

      3.3.3 Infusion related reactions

      During the first ofatumumab infusion, 6/42 (14%) did not report IRRs, and 34/42 (81%) had moderate to severe IRRs, of which 18/34 (53%) were treated once with one therapeutic, 8/34 (24%) were treated twice or with two therapeutics, and 7/34 (21%) were treated at least three times during the infusion or with at least three therapeutics. There were no cases of life-threatening IRRs, and no patients needed hospitalization for IRRs. Frequency and grading of IRRs are shown in Table 3. The administered doses of the second infusions were available for 39 patients, of whom 28/39 (72%) received 300 mg. For the third infusion, 33/40 (83%) received 600 mg. All the patients who initially received 1000 mg doses were eventually switched to 600 mg maintenance doses.
      Table 3Frequency and severity of infusion related reactions.
      Grade0: None1: Mild2: Moderate3: Severe
      N (%)
      First infusion6 (14%)≤330 (71%)4 (10%)
      Second infusion29 (71%)5 (12%)7 (17%)0
      Third infusion12 (30%)≤325 (63%)0
      Last infusion26 (58%)4 (9%)15 (33%)0
      Grade 1: resolved spontaneously without need of intervention or infusion interruption; grade 2: responded to infusion interruption and/or therapy (e.g. antihistamine, methylprednisolone, acetaminophen, inhaled sympathomimetics); grade 3: lasted beyond completion of infusion or recurred after infusion.
      Of patients who were subsequently treated with rituximab, 7/14 (50%) experienced no IRRs during their last ofatumumab infusion, and 7/14 (50%) experienced mild to moderate reactions. When switching to rituximab, 9/14 (64%) experienced no IRRs during their first rituximab infusion, and 5/14 (36%) experienced mild to moderate reactions. Median number of ofatumumab infusions before switching to rituximab was 6.5 (Q1-Q3: 5.0-7.0). Of patients who switched from ofatumumab to ocrelizumab, 16/23 (70%) experienced no IRRs during their last ofatumumab infusion, and 7/23 (30%) experienced mild to moderate IRRs. During their first ocrelizumab infusion, 18/23 (78%) experienced no IRRs and 5/23 (22%) experienced mild to moderate IRRs. Median number of ofatumumab infusions before switching to ocrelizumab was 7 (Q1-Q3: 6-8). Overall, the patients who had IRRs after the last administration of ofatumumab were not the same as those who had IRRs after the first administration of rituximab or ocrelizumab, but the number of patients was too low to allow for a detailed analysis.

      3.3.4 Serious infections

      During ofatumumab treatment and until 6 months after the last infusion, 6/45 (13%) were admitted at least once to hospital because of an infection. Median time before acquiring the first infection requiring hospitalization was 16 months (Q1-Q3: 14-17), and ≤3 patients were admitted more than once due to an infection. Median duration of hospitalization was 4 days (Q1-Q3: 2.5-6.5 days), and all infections resolved on relevant treatment. Comparison between patients with and without hypogammaglobulinemia at baseline revealed no statistically significant differences. Hazard ratio for an infection requiring hospitalization was estimated to 2.43 (95% CI 0.45-13.30, p=0.3) for patients with low IgG (< 6.1 g/L) at baseline and 1.14 (95% 0.13-9.75, p=0.9) for patients with low IgM (< 0.39 g/L) at baseline.

      4. Discussion

      Data on IV ofatumumab treatment of demyelinating disorders is limited to a phase II trial of 38 RRMS patients of short duration. We identified 50 patients at the DMSC who had been treated off-label with IV ofatumumab and conducted the first real-world study of its use in patients with MS, MOGAD and NMOSD.
      We found a statistically significant change in relapse-free proportion of patients from 34% the year prior to commencement of IV ofatumumab treatment to 60% the first year of treatment. For patients with MS, the ARR decreased from 1.10 at baseline to 0.41 during treatment. This was a smaller reduction than that observed in the ASCLEPIOS I and II phase III trials of SC ofatumumab (
      • Hauser S.L.
      • Bar-Or A.
      • Cohen J.A.
      • Comi G.
      • et al.
      Ofatumumab versus teriflunomide in multiple sclerosis.
      ), where ARR was reduced from 1.2 to 0.11 and 1.3 to 0.10, respectively. At 24 months, the cumulated risk of 6 months CDW for the MS group was 8% (95% CI 0%-17%), which is in line with the ASCLEPIOS results (8.2% and 8.0%). However, these risks should be compared with high caution as the MS patients in the present study had a higher age (median 45 years) and EDSS score (median 4.0) at treatment start, and the population consisted of a heterogenous group of patients with both RRMS and secondary progressive MS, but also primary-progressive MS. Moreover, most had been treated with high-efficacy DMTs prior to switching to ofatumumab, including 24% treated with natalizumab and 40% with fingolimod, and yet; the reason for discontinuation of prior treatment was disease activity in 68% of cases, whereas 41% of the participants in the ASCLEPIOS trials received no DMT prior to enrollment, and for patients who did, interferon-beta was the most frequent DMT. Additionally, ASCLEPIOS required relapses to be accompanied by a clinically relevant increase in EDSS score or functional system scores, whereas relapses in clinical practice are less well-defined.
      Seventy-nine percent of patients had complete B cell depletion 4-8 months after the first ofatumumab infusion series. NK and T cell counts did not change overall in relation to number of infusions. As cell counts were assessed 4-8 months after each infusion series, we cannot exclude an earlier impact on these. Interestingly, a study of CD20 depletion with ublituximab found the proportion of NK and T cells to decrease immediately, but transiently, after the first infusion with a subsequent increase to baseline values after two weeks (
      • Lovett-Racke A.E.
      • Gormley M.
      • Liu Y.
      • Yang Y.
      • et al.
      B cell depletion with ublituximab reshapes the T cell profile in multiple sclerosis patients.
      ). We found no significant difference between proportion of patients with relapses during the first 6 months between patients with complete versus incomplete B cell depletion, but the longer-term impact could not be determined due to the low number of patients with incomplete depletion after the following infusion series. Moreover, as further cell phenotyping is not part of routine testing, potential changes in cell subsets, including memory B cells, relative frequencies and ratios were not assessed in this study.
      During the first ofatumumab infusion, 86% experienced IRRs. This is comparable to the phase II trial of IV ofatumumab for RRMS, where 90.9% of patients who received 300 mg ofatumumab as first infusion experienced drug-related adverse events on first infusion (
      • Sorensen P.S.
      • Lisby S.
      • Grove R.
      • Derosier F.
      • et al.
      Safety and efficacy of ofatumumab in relapsing-remitting multiple sclerosis: A phase 2 study.
      ), but somewhat higher than the frequencies reported for IV ocrelizumab (∼28%-35%) (
      • Kappos L.
      • Li D.
      • Calabresi P.A.
      • O'Connor P.
      • et al.
      Ocrelizumab in relapsing-remitting multiple sclerosis: a phase 2, randomised, placebo-controlled, multicentre trial.
      ;
      • Hauser S.L.
      • Bar-Or A.
      • Comi G.
      • Giovannoni G.
      • et al.
      Supplement to: ocrelizumab versus interferon beta-1a in relapsing multiple sclerosis.
      ;
      • Montalban X.
      • Hauser S.L.
      • Kappos L.
      • Arnold D.L.
      • et al.
      Supplement to: ocrelizumab versus placebo in primary progressive multiple sclerosis.
      ) and IV rituximab (42%-78.3%) (
      • Bar-Or A.
      • Calabresi P.A.J.
      • Arnlod D.
      • Markowitz C.
      • et al.
      Rituximab in relapsing-remitting multiple sclerosis: A 72-week, open-label, phase I trial.
      ;
      • Hauser S.L.
      • Waubant E.
      • Arnold D.L.
      • Vollmer T.
      • et al.
      B-cell depletion with rituximab in relapsing–remitting multiple sclerosis.
      ;
      • Hawker K.
      • O'Connor P.
      • Freedman M.S.
      • Calabresi P.A.
      • et al.
      Rituximab in patients with primary progressive multiple sclerosis: results of a randomized double-blind placebo-controlled multicenter trial.
      ), although no head-to-head studies have been conducted. Upon binding of ocrelizumab, CD20+ B cells are primarily depleted through ADCC, whereas ofatumumab and rituximab mainly exert their depletion through CDC. Ofatumumab, however, yields a greater CDC than rituximab and requires a much lower CD20 density for its CDC mediation (
      • Teeling J.L.
      • Mackus W.J.M.
      • Wiegman L.J.J.M.
      • van den Brakel J.H.N.
      • et al.
      The biological activity of human CD20 monoclonal antibodies is linked to unique epitopes on CD20.
      ;
      • Klein C.
      • Lammens A.
      • Schäfer W.
      • Georges G.
      • et al.
      Epitope interactions of monoclonal antibodies targeting CD20 and their relationship to functional properties.
      ). This might be of clinical importance, as complement activation is thought to have a role in triggering IRRs (
      • Van Der Kolk L.E.
      • Grillo-López A.J.
      • Baars J.W.
      • Hack C.E.
      • Van Oers M.H.J.
      Complement activation plays a key role in the side-effects of rituximab treatment.
      ;
      • Gelfand J.M.
      • Cree B.A.C.
      • Hauser S.L.
      Ocrelizumab and other CD20+ B-cell-depleting therapies in multiple sclerosis.
      ).
      Serum IgM concentrations showed a decreasing trend related to number of infusions, which is consistent with findings for CD20 depleting therapies in general (
      • Evertsson B.
      • Hoyt T.
      • Christensen A.
      • Nimer F.A.L.
      • Foley J.
      • Piehl F.
      A comparative study of tolerability and effects on immunoglobulin levels and CD19 cell counts with ocrelizumab vs low dose of rituximab in multiple sclerosis.
      ;
      • Kridin K.
      • Ahmed A.R.
      Post-rituximab immunoglobulin M (IgM) hypogammaglobulinemia.
      ;
      • Oksbjerg N.R.
      • Nielsen S.D.
      • Blinkenberg M.
      • Magyari M.
      • Sellebjerg F.
      Anti-CD20 antibody therapy and risk of infection in patients with demyelinating diseases.
      ). De novo low IgG and IgA was infrequent. The hazard ratios for infections requiring hospitalization in patients with low IgG and IgM at baseline were non-significant and had very wide confidence intervals. Thus, from this small sample we cannot make inferences about the association of immunoglobin levels and infections requiring hospitalization. The clinical significance of hypogammaglobulinemia in relation to CD20 depleting therapy in MS is still uncertain. Several studies have indicated that CD20-depletion can induce de novo IgG hypogammaglobulinemia in some patients, and that this may associate with increased infection risk (
      • Salzer J.
      • Svenningsson R.
      • Alping P.
      • Novakova L.
      • et al.
      Rituximab in multiple sclerosis: A retrospective observational study on safety and efficacy.
      ;
      • Evertsson B.
      • Hoyt T.
      • Christensen A.
      • Nimer F.A.L.
      • Foley J.
      • Piehl F.
      A comparative study of tolerability and effects on immunoglobulin levels and CD19 cell counts with ocrelizumab vs low dose of rituximab in multiple sclerosis.
      ;
      • Hauser S.L.
      • Kappos L.
      • Montalban X.
      • Craveiro L.
      • et al.
      Safety of ocrelizumab in patients with relapsing and primary progressive multiple sclerosis.
      ). On the other hand, other studies did not demonstrate an association between low immunoglobulin serum concentrations and risk of serious infections (
      • Hawker K.
      • O'Connor P.
      • Freedman M.S.
      • Calabresi P.A.
      • et al.
      Rituximab in patients with primary progressive multiple sclerosis: results of a randomized double-blind placebo-controlled multicenter trial.
      ;
      • Oksbjerg N.R.
      • Nielsen S.D.
      • Blinkenberg M.
      • Magyari M.
      • Sellebjerg F.
      Anti-CD20 antibody therapy and risk of infection in patients with demyelinating diseases.
      ). Some studies on rheumatologic cohorts have reported declines of total immunoglobulin levels and hypogammaglobulinemia to be risk factors of serious infections (
      • Besada E.
      • Koldingsnes W.
      • Nossent J.C.
      Long-term efficacy and safety of pre-emptive maintenance therapy with rituximab in granulomatosis with polyangiitis: Results from a single centre.
      ;
      • Boleto G.
      • Avouac J.
      • Wipff J.
      • Forien M.
      • et al.
      Predictors of hypogammaglobulinemia during rituximab maintenance therapy in rheumatoid arthritis: A 12-year longitudinal multi-center study.
      ), and one study found immunoglobulin replacement therapy to reduce the risk of serious infections (
      • Barmettler S.
      • Ong M.S.
      • Farmer J.R.
      • Choi H.
      • Walter J.
      Association of immunoglobulin levels, infectious risk, and mortality with rituximab and hypogammaglobulinemia.
      ).
      The most important limitations of our study are the retrospective nature, the small number of patients and the inherent heterogeneity of the patients included. Some of the patients received 1000 mg for their second infusions and initial maintenance infusions, which may have had an impact on efficacy and adverse effects. However, due to the small number of patients, this could not be validly assessed. Furthermore, there is a risk that the observed reduction in relapse rate is not solely attributable to treatment with ofatumumab but also to a regression-to-the-mean phenomenon. As most patients switched to ofatumumab due to disease breakthrough (71%) and had at least one relapse in the year prior (66%), these sampled patients will by study design have a high ARR, that might not reflect the true population mean ARR. The strengths are the long follow-up periods, continuous assessments and measurements and validation through thorough medical chart review. Additionally, the entire Capital Region of Denmark and Region Zealand use the same electronic medical record system. We thus had access to medical chart notes from hospitalizations and outpatient visits at other hospitals in the regions as well, minimizing the risk of reporting bias. As ofatumumab was an off-label treatment option, the results reflect a patient population for whom the treating neurologists had deemed approved treatment options exhausted, which reduces its generalizability. Accordingly, confounding by indication could compromise estimates of the effect size. Lastly, analyses were limited to overall descriptive trends. Further subgroup analyses examining the effect on disease activity in patients with RRMS, progressive MS, NMOSD and MOGAD separately were not performed due to the risk of type II errors but would be warranted.

      5. Conclusions

      The results indicate that IV ofatumumab treatment of demyelinating disorders reduces relapse rate and stabilizes disability worsening with an acceptable safety profile. Additionally, the study supports a class effect of anti-CD20 monoclonal antibody treatment of MS, but also suggests that IV treatment with monoclonal antibodies which uses complement activation as an important effector function may be associated to a higher frequency of IRRs.

      Study funding

      This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

      CRediT authorship contribution statement

      Sahla El Mahdaoui: Methodology, Investigation, Formal analysis, Writing – original draft. Jeppe Romme Christensen: Conceptualization, Methodology, Writing – review & editing. Melinda Magyari: Data curation, Methodology, Writing – review & editing. Malthe Faurschou Wandall-Holm: Methodology, Formal analysis, Writing – review & editing. Finn Sellebjerg: Conceptualization, Methodology, Writing – review & editing.

      Declaration of competing interest

      FS has served on scientific advisory boards for, served as consultant for, received support for congress participation or received speaker honoraria from Alexion, Biogen, Bristol Myers Squibb, Merck, Novartis, Roche and Sanofi Genzyme. His laboratory has received research support from Biogen, Merck, Novartis, Roche and Sanofi Genzyme. JRC has received speaker honoraria from Biogen. MM has served in scientific advisory board for Sanofi, Novartis, Merck, and has received honoraria for lecturing from Biogen, Merck, Novartis, Roche, Genzyme, Bristol Myers Squibb. SEM and MWH have no competing interests to declare.

      Acknowledgements

      The graphical abstract was created with BioRender.com.

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