Alzheimer's Targeted Treatments: Focus on Amyloid and Inflammation.

Alzheimer's disease (AD) is the major cause of dementia that is now threatening the lives of billions of elderly people on the globe, and recent progress in the elucidation of the pathomechanism of AD is now opening venue to tackle the disease by developing and implementing "disease-modifying therapies" that directly act on the pathophysiology and slow down the progression of neurodegeneration. A recent example is the success of clinical trials of anti-amyloid b antibody drugs, whereas other therapeutic targets, e.g., inflammation and tau, are being actively investigated. In this dual perspective session, we plan to have speakers from leading pharmas in the field representing distinct investments in the AD space, which will be followed by the comment from scientific leadership of the Alzheimer's Association who will speak on behalf of all stakeholders. Neuroscientists participating in the Society for Neuroscience may be able to gain insights into the cutting edge of the therapeutic approaches to AD and neurodegenerative disorders, and discuss future contribution of neuroscience to this field.

People get ready! A new generation of Alzheimer's therapies may require new ways to deliver and pay for healthcare.

The development of disease-modifying therapies (DMTs) for Alzheimer's disease (AD) has progressed over the last decade, and the first-ever therapies with potential to slow the progression of disease are approved in the United States. AD DMTs could provide life-changing opportunities for people living with this disease, as well as for their caregivers. They could also ease some of the immense societal and economic burden of dementia. However, AD DMTs also come with major challenges due to the large unmet medical need, high prevalence of AD, new costs related to diagnosis, treatment and monitoring, and uncertainty in the therapies' actual clinical value. This perspective article discusses, from the broad perspective of various health systems and stakeholders, how we can overcome these challenges and improve society's readiness for AD DMTs. We propose that innovative payment models such as performance-based payments, in combination with learning healthcare systems, could be the way forward to enable timely patient access to treatments, improve accuracy of cost-effectiveness evaluations and overcome budgetary barriers. Other important considerations include the need for identification of key drivers of patient value, the relevance of different economic perspectives (i.e. healthcare vs. societal) and ethical questions in terms of treatment eligibility criteria.

Improvement of the thalamocortical white matter network in people with stable treated relapsing-remitting multiple sclerosis over time.

Advanced imaging techniques (tractography) enable the mapping of white matter (WM) pathways and the understanding of brain connectivity patterns. We combined tractography with a network-based approach to examine WM microstructure on a network level in people with relapsing-remitting multiple sclerosis (pw-RRMS) and healthy controls (HCs) over 2 years. Seventy-six pw-RRMS matched with 43 HCs underwent clinical assessments and 3T MRI scans at baseline (BL) and 2-year follow-up (2-YFU). Probabilistic tractography was performed, accounting for the effect of lesions, producing connectomes of 25 million streamlines. Network differences in fibre density across pw-RRMS and HCs at BL and 2-YFU were quantified using network-based statistics (NBS). Longitudinal network differences in fibre density were quantified using NBS in pw-RRMS, and were tested for correlations with disability, cognition and fatigue scores. Widespread network reductions in fibre density were found in pw-RRMS compared with HCs at BL in cortical regions, with more reductions detected at 2-YFU. Pw-RRMS had reduced fibre density at BL in the thalamocortical network compared to 2-YFU. This effect appeared after correction for age, was robust across different thresholds, and did not correlate with lesion volume or disease duration. Pw-RRMS demonstrated a robust and long-distance improvement in the thalamocortical WM network, regardless of age, disease burden, duration or therapy, suggesting a potential locus of neuroplasticity in MS. This network's role over the disease's lifespan and its potential implications in prognosis and treatment warrants further investigation.

Dissonance in the face of Alzheimer's disease breakthroughs: clinician and lay stakeholder acceptance, concerns and willingness to pay for emerging disease-modifying therapies.

BACKGROUND: Introducing new disease-modifying therapies (DMTs) for Alzheimer's disease demands a fundamental shift in diagnosis and care for most health systems around the world. Understanding the views of health professionals, potential patients, care partners and taxpayers is crucial for service planning and expectation management about these new therapies. AIMS: To investigate the public's and professionals' perspectives regarding (1) acceptability of new DMTs for Alzheimer's disease; (2) perceptions of risk/benefits; (3) the public's willingness to pay (WTP). METHOD: Informed by the 'theoretical framework of acceptability', we conducted two online surveys with 1000 members of the general public and 77 health professionals in Ireland. Descriptive and multivariate regression analyses examined factors associated with DMT acceptance and WTP. RESULTS: Healthcare professionals had a higher acceptance (65%) than the general public (48%). Professionals were more concerned about potential brain bleeds (70%) and efficacy (68%), while the public focused on accessibility and costs. Younger participants (18-24 years) displayed a higher WTP. Education and insurance affected WTP decisions. CONCLUSIONS: This study exposes complex attitudes toward emerging DMTs for Alzheimer's disease, challenging conventional wisdom in multiple dimensions. A surprising 25% of the public expressed aversion to these new treatments, despite society's deep-rooted fear of dementia in older age. Healthcare professionals displayed nuanced concerns, prioritising clinical effectiveness and potential brain complications. Intriguingly, younger, better-educated and privately insured individuals exhibited a greater WTP, foregrounding critical questions about healthcare equity. These multifaceted findings serve as a guidepost for healthcare strategists, policymakers and ethicists as we edge closer to integrating DMTs into Alzheimer's disease care.

Longitudinal evaluation of serum MOG-IgG titers in MOGAD after initiation of maintenance immunoglobulin: A case series.

BACKGROUND: Myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) is a distinct demyelinating disease of the central nervous system. Immunoglobulin (Ig) has been used as a maintenance therapy to prevent relapses in MOGAD, but the impact of Ig on serum MOG-IgG titers is unclear. OBJECTIVE: To characterize the variation in serum MOG-IgG titers after initiation of Ig treatment in people with MOGAD. METHODS: We conducted a retrospective study of 10 patients with a diagnosis of MOGAD and available serum MOG-IgG titers before and after initiation of maintenance Ig treatment. RESULTS: We found that most of the patients remained MOG-IgG seropositive while on Ig treatment with a reduced or unchanged titer, despite a lack of disease activity. CONCLUSIONS: This case series suggests that the mechanism of action of Ig therapy in MOGAD is not exclusively dependent on MOG-IgG titer reduction.

Altered lymphocyte profiles and herpes zoster infections in patients with multiple sclerosis on natalizumab.

Cases of herpes zoster (HZ) in patients with MS on natalizumab (NTZ) have been documented. In this study, we assessed lymphocyte subsets in NTZ-treated patients with HZ compared to matched controls without HZ. Twenty unvaccinated patients developed HZ while on NTZ for an incidence rate of 12.3 per 1000 patient-years. These patients had lower CD8+% and higher CD4+:CD8+ ratios (p ⩽ 0.01) than non-HZ matched controls. Two patients with relapsing-remitting MS developed HZ twice while on NTZ. These findings underscore the importance of pre-NTZ HZ vaccination due to potential HZ risk.

Non-inferiority analysis of subcutaneous versus intravenous 300 mg monthly natalizumab administration: A post hoc analysis of the REFINE study.

To quantify the probability that monthly intravenous (IV) and subcutaneous (SC) natalizumab (NTZ) had similar efficacy in relapsing-remitting multiple sclerosis (RRMS), non-inferiority of efficacy of NTZ-SC versus NTZ-IV on combined MRI unique active lesions number (CUAL) was explored re-analysing the REFINE data set. Non-inferiority margins were selected equal to 25%/33%/50% fractions of the effect size of NTZ-IV versus placebo observed in the AFFIRM study. Ninety-nine RRMS were included. NTZ-SC resulted not inferior to NTZ-IV on CUAL for all margins at 2.5% significance level, and, in worst-case scenario, its effect over NTZ-IV did not exceed 3.5% (or 2.8%) of the effect of NTZ-IV versus placebo.

A US payer perspective health economic model assessing value of monitoring disease activity to inform discontinuation and re-initiation of DMT in multiple sclerosis.

OBJECTIVES: We evaluate the potential clinical and cost impacts of discontinuing disease-modifying therapy (DMT) in people with multiple sclerosis (PwMS) when age-related immunosenescence can reduce DMT efficacy while increasing associated risks. METHODS: A Markov model simulated clinical and cost impacts to the patient and payers when a proportion of eligible patients with relapsing remitting multiple sclerosis (RRMS) discontinue DMT. Eligibility was defined as age >55 years, an RRMS diagnosis of >5 years, and no history of relapses for 5 years. Increasing the proportion of eligible patients willing to discontinue therapy was also modeled. Clinical and cost inputs were from published literature. RESULTS: Difference in EDSS progression between eligible patients who did and did not attempt discontinuation was not significant. After 1 year of eligibility, per-patient costs were $96k lower in the cohort that attempted discontinuation; however a higher proportion of relapses were seen in this group. When the proportion of patients willing to discontinue DMT increased, clinical findings remained consistent while the average cost per patient decreased. CONCLUSION: While there are increased clinical and cost benefits as more eligible patients attempt discontinuation, the risk of relapses can increase. Timely disease monitoring is required to manage safe DMT discontinuation.

Iatrogenic myelodysplastic syndrome complicating multiple sclerosis: A case report.

After 1.5 years of treatment with dimethyl fumarate (DMF) for multiple sclerosis, preceded 8 years earlier by intravenous (IV) cladribine and 1 year earlier by natalizumab, our patient developed myelodysplastic syndrome (MDS). The initial manifestation was a severe drop in absolute neutrophil and lymphocyte counts. Repeat bone marrow biopsy demonstrated a new unbalanced translocation (between the chromosome 1 long arm and chromosome 7 short arm). This case report, to our knowledge, is the first linking iatrogenic MDS to DMF and cladribine, while also suggesting caution with immunosuppressants in multiple sclerosis patients.

Prediction of disease activity and treatment failure in relapsing-remitting MS patients initiating daily oral DMTs.

BACKGROUND: Limited data exist regarding treatment response prediction to oral disease-modifying therapies (DMTs) in multiple sclerosis (MS). OBJECTIVES: We assessed the capacity of available scoring systems to anticipate disease activity parameters in naïve relapsing-remitting MS (RRMS) patients initiating daily oral DMTs, hypothesizing that they exhibit different predictive potentials. METHODS: We conducted a retrospective study and applied the Rio Score (RS), modified Rio Score (mRS), and MAGNIMS Score 12 months after DMT initiation. At 36 months, we examined their ability to predict evidence of disease activity (EDA) components and treatment failure by logistic regression analysis. RESULTS: Notably, 218 patients (62.4% females) initiating dimethyl fumarate, teriflunomide, and fingolimod were included. At 36 months, the RS high-risk group predicted evidence of clinical activity (odds ratio (OR) 10 [2.7-36.9]) and treatment failure (OR 10.6 [3.4-32.5]) but did not predict radiological activity (OR 1.9 [0.7-5]). The mRS non-responders group did not predict EDA and treatment failure. RS, mRS, and MAGNIMS 0 categories showed significantly lower EDA and treatment failure than the remainder. CONCLUSION: Scoring systems present different predictive abilities for disease activity parameters at 36 months in MS patients initiating daily oral therapies, warranting further adjustments (i.e. introduction of fluid biomarkers) to depict disease activity status fully.

Torben Fog - A Danish pioneer in a multi-faceted spectrum of multiple sclerosis research.

Torben Fog was committed to multiple sclerosis (MS) research for more than four decades, starting before the defence of his thesis in 1948 and lasting until his death in 1987. His research was multi-facetted, making him one of the great pioneers in the study of essential parts of the pathology, immunology and treatment of MS. He has contributed with meticulous studies of the MS plaques, documenting the perivenous distribution of plaques in the spinal cord. He constructed a scoring system for the disability in MS and used a computer programme to calculate a total neurological deficit. Together with his co-workers, Fog in 1972 was the first to report the association between MS and the human leukocyte antigen system. Fog can be considered as the father of immunomodulatory therapy in MS, treating MS patients with the first transfer factor, and as early as 1980, he was the first to treat MS with intramuscular natural interferon.

Recent Advances in Clinical Trials in Multiple System Atrophy.

PURPOSE OF REVIEW: This review summarizes previous and ongoing neuroprotection trials in multiple system atrophy (MSA), a rare and fatal neurodegenerative disease characterized by parkinsonism, cerebellar, and autonomic dysfunction. It also describes the preclinical therapeutic pipeline and provides some considerations relevant to successfully conducting clinical trials in MSA, i.e., diagnosis, endpoints, and trial design. RECENT FINDINGS: Over 30 compounds have been tested in clinical trials in MSA. While this illustrates a strong treatment pipeline, only two have reached their primary endpoint. Ongoing clinical trials primarily focus on targeting α-synuclein, the neuropathological hallmark of MSA being α-synuclein-bearing glial cytoplasmic inclusions. The mostly negative trial outcomes highlight the importance of better understanding underlying disease mechanisms and improving preclinical models. Together with efforts to refine clinical measurement tools, innovative statistical methods, and developments in biomarker research, this will enhance the design of future neuroprotection trials in MSA and the likelihood of positive outcomes.

Amyloid-related imaging abnormalities (ARIA): radiological, biological and clinical characteristics.

Excess accumulation and aggregation of toxic soluble and insoluble amyloid-ß species in the brain are a major hallmark of Alzheimer's disease. Randomized clinical trials show reduced brain amyloid-ß deposits using monoclonal antibodies that target amyloid-ß and have identified MRI signal abnormalities called amyloid-related imaging abnormalities (ARIA) as possible spontaneous or treatment-related adverse events. This review provides a comprehensive state-of-the-art conceptual review of radiological features, clinical detection and classification challenges, pathophysiology, underlying biological mechanism(s) and risk factors/predictors associated with ARIA. We summarize the existing literature and current lines of evidence with ARIA-oedema/effusion (ARIA-E) and ARIA-haemosiderosis/microhaemorrhages (ARIA-H) seen across anti-amyloid clinical trials and therapeutic development. Both forms of ARIA may occur, often early, during anti-amyloid-ß monoclonal antibody treatment. Across randomized controlled trials, most ARIA cases were asymptomatic. Symptomatic ARIA-E cases often occurred at higher doses and resolved within 3-4 months or upon treatment cessation. Apolipoprotein E haplotype and treatment dosage are major risk factors for ARIA-E and ARIA-H. Presence of any microhaemorrhage on baseline MRI increases the risk of ARIA. ARIA shares many clinical, biological and pathophysiological features with Alzheimer's disease and cerebral amyloid angiopathy. There is a great need to conceptually link the evident synergistic interplay associated with such underlying conditions to allow clinicians and researchers to further understand, deliberate and investigate on the combined effects of these multiple pathophysiological processes. Moreover, this review article aims to better assist clinicians in detection (either observed via symptoms or visually on MRI), management based on appropriate use recommendations, and general preparedness and awareness when ARIA are observed as well as researchers in the fundamental understanding of the various antibodies in development and their associated risks of ARIA. To facilitate ARIA detection in clinical trials and clinical practice, we recommend the implementation of standardized MRI protocols and rigorous reporting standards. With the availability of approved amyloid-ß therapies in the clinic, standardized and rigorous clinical and radiological monitoring and management protocols are required to effectively detect, monitor, and manage ARIA in real-world clinical settings.

Cost and effectiveness of autologous haematopoietic stem cell transplantation and high-efficacy disease-modifying therapies in relapsing-remitting multiple sclerosis.

BACKGROUND: Autologous haematopoietic stem cell transplantation (AHSCT) is a highly effective one-off treatment for relapsing-remitting multiple sclerosis (RR-MS), potentially representing an optimal front-loading strategy for costs. OBJECTIVE: Exploring cost/effectiveness of AHSCT and high-efficacy disease-modifying treatments (HE-DMTs) in RR-MS, estimating costs at our centre in Italy, where National Health Service (NHS) provides universal health coverage. METHODS: Costs (including drugs, inpatient/outpatient management) for treatment with AHSCT and HE-DMTs were calculated as NHS expenditures over 2- and 5-year periods. Cost-effectiveness for each treatment was estimated as "cost needed to treat" (CNT), i.e. expense to prevent relapses, progression, or disease activity (NEDA) in one patient over n-years, retrieving outcomes from published studies. RESULTS: Costs of AHSCT and HE-DMTs were similar over 2 years, whereas AHSCT was cheaper than most HE-DMTs over 5 years (€46 600 vs €93 800, respectively). When estimating cost-effectiveness of treatments, over 2 years, mean CNT of HE-DMTs for NEDA was twofold that of AHSCT, whereas it was similar for relapses and disability. Differences in CNT were remarkable over 5 years, especially for NEDA, being mean CNT of HE-DMTs €382 800 vs €74 900 for AHSCT. CONCLUSIONS: AHSCT may be highly cost-effective in selected aggressive RR-MS. Besides priceless benefits for treated individuals, cost-savings generated by AHSCT may contribute to improving healthcare assistance at a population level.

Navigating the future of Alzheimer's care in Ireland - a service model for disease-modifying therapies in small and medium-sized healthcare systems.

BACKGROUND: A new class of antibody-based drug therapy with the potential for disease modification is now available for Alzheimer's disease (AD). However, the complexity of drug eligibility, administration, cost, and safety of such disease modifying therapies (DMTs) necessitates adopting new treatment and care pathways. A working group was convened in Ireland to consider the implications of, and health system readiness for, DMTs for AD, and to describe a service model for the detection, diagnosis, and management of early AD in the Irish context, providing a template for similar small-medium sized healthcare systems. METHODS: A series of facilitated workshops with a multidisciplinary working group, including Patient and Public Involvement (PPI) members, were undertaken. This informed a series of recommendations for the implementation of new DMTs using an evidence-based conceptual framework for health system readiness based on [1] material resources and structures and [2] human and institutional relationships, values, and norms. RESULTS: We describe a hub-and-spoke model, which utilises the existing dementia care ecosystem as outlined in Ireland's Model of Care for Dementia, with Regional Specialist Memory Services (RSMS) acting as central hubs and Memory Assessment and Support Services (MASS) functioning as spokes for less central areas. We provide criteria for DMT referral, eligibility, administration, and ongoing monitoring. CONCLUSIONS: Healthcare systems worldwide are acknowledging the need for advanced clinical pathways for AD, driven by better diagnostics and the emergence of DMTs. Despite facing significant challenges in integrating DMTs into existing care models, the potential for overcoming challenges exists through increased funding, resources, and the development of a structured national treatment network, as proposed in Ireland's Model of Care for Dementia. This approach offers a replicable blueprint for other healthcare systems with similar scale and complexity.

Stress testing the Centiloid: Precision and variability of PET quantification of amyloid pathology.

INTRODUCTION: Assessing the potential sources of bias and variability of the Centiloid (CL) scale is fundamental for its appropriate clinical application. METHODS: We included 533 participants from AMYloid imaging to Prevent Alzheimer's Disease (AMYPAD DPMS) and Alzheimer's Disease Neuroimaging Initiative (ADNI) cohorts. Thirty-two CL pipelines were created using different combinations of reference region (RR), RR and target types, and quantification spaces. Generalized estimating equations stratified by amyloid positivity were used to assess the impact of the quantification pipeline, radiotracer, age, brain atrophy, and harmonization status on CL. RESULTS: RR selection and RR type impact CL the most, particularly in amyloid-negative individuals. The standard CL pipeline with the whole cerebellum as RR is robust against brain atrophy and differences in image resolution, with 95% confidence intervals below ± 3.95 CL for amyloid beta positivity cutoffs (CL < 24). DISCUSSION: The standard CL pipeline is recommended for most scenarios. Confidence intervals should be considered when operationalizing CL cutoffs in clinical and research settings. HIGHLIGHTS: We developed a framework for evaluating Centiloid (CL) variability to different factors. Reference region selection and delineation had the highest impact on CL values. Whole cerebellum (WCB) and whole cerebellum plus brainstem (WCB+BSTM) as reference regions yielded consistent results across tracers. The standard CL pipeline is robust against atrophy and image resolution variation. Estimated within- and between-pipeline variability (95% confidence interval) in absolute CL units.

Response to Fingolimod in Multiple Sclerosis Patients Is Associated with a Differential Transcriptomic Regulation.

Fingolimod is an immunomodulatory sphingosine-1-phosphate (S1P) analogue approved for the treatment of relapsing-remitting multiple sclerosis (RRMS). The identification of biomarkers of clinical responses to fingolimod is a major necessity in MS to identify optimal responders and avoid the risk of disease progression in non-responders. With this aim, we used RNA sequencing to study the transcriptomic changes induced by fingolimod in peripheral blood mononuclear cells of MS-treated patients and their association with clinical response. Samples were obtained from 10 RRMS patients (five responders and five non-responders) at baseline and at 12 months of fingolimod therapy. Fingolimod exerted a vast impact at the transcriptional level, identifying 7155 differentially expressed genes (DEGs) compared to baseline that affected the regulation of numerous signaling pathways. These DEGs were predominantly immune related, including genes associated with S1P metabolism, cytokines, lymphocyte trafficking, master transcription factors of lymphocyte functions and the NF-kB pathway. Responder and non-responder patients exhibited a differential transcriptomic regulation during treatment, with responders presenting a higher number of DEGs (6405) compared to non-responders (2653). The S1P, NF-kB and TCR signaling pathways were differentially modulated in responder and non-responder patients. These transcriptomic differences offer the potential of being exploited as biomarkers of a clinical response to fingolimod.

Analysis of seroconversion following COVID-19 vaccination among multiple sclerosis patients treated with disease-modifying therapies in Poland.

CLINICAL RATIONALE FOR THE STUDY: The rapid spread of SARS-CoV-2 throughout the world has highlighted the importance of vaccinations to control the pandemic and to protect people at risk for severe disease courses. Disease-modifying therapies (DMT) in multiple sclerosis (MS), whether immunomodulatory or immunosuppressive, may affect the immune response. Therefore, the question arose as to whether these vaccinations would be effective. AIM OF THE STUDY: We planned a study to assess the immune response to SARS-CoV-2 vaccines by type of therapy. MATERIAL AND METHODS: Participants were recruited from 14 Polish MS centres. The data was obtained by neurologists using a questionnaire. We collected data on 353 MS patients (269 females, 84 males) who received complete primary SARS-CoV-2 vaccination. All persons with MS (PwMS) were treated with disease-modifying therapies. RESULTS: 305 out of 353 PwMS (86.4%) were positive for IgG Abs against SARS-CoV-2 S domain S1 Ag after vaccination. A strong immune response was noted in 129 PwMS (36.5%). The rate of seroconversion after SARS-CoV-2 vaccination in PwMS who received immunomodulatory DMTs (interferon beta, glatiramer acetate, teriflunomide, dimethyl fumarate, natalizumab) was 91.5%, in PwMS receiving immune reconstruction therapy (alemtuzumab, cladribine) was 92%, and in immunosuppressive DMTs (fingolimod, ocrelizumab), the seroconversion rate was 59%. CONCLUSIONS AND CLINICAL IMPLICATIONS: Our study shows that, in PwMS receiving immunomodulatory therapy, the immune response to vaccination is generally excellent. Even in immunosuppressive patients, seroconversion is satisfactory.

Vaccine-breakthrough SARS-CoV-2 infections in people with multiple sclerosis and related conditions: An observational study by the New York COVID-19 Neuro-Immunology Consortium (NYCNIC-2).

BACKGROUND: People with MS (PwMS) and related conditions treated with anti-CD20 and S1P modulating therapies exhibit attenuated immune responses to SARS-CoV-2 vaccines. It remains unclear whether humoral/T-cell responses are valid surrogates for postvaccine immunity. OBJECTIVE: To characterize COVID-19 vaccine-breakthrough infections in this population. METHODS: We conducted a prospective multicenter cohort study of PwMS and related CNS autoimmune conditions with confirmed breakthrough infections. Postvaccination antibody response, disease-modifying therapies (DMTs) at the time of vaccination, and DMT at the time of infection were assessed. RESULTS: Two hundred nine patients had 211 breakthrough infections. Use of anti-CD20 agents at time of infection was associated with increased infection severity (p = 0.0474, odds ratio (OR) = 5.923) for infections during the Omicron surge and demonstrated a trend among the total cohort (p = 0.0533). However, neither use of anti-CD20 agents at the time of vaccination nor postvaccination antibody response was associated with hospitalization risk. Anti-CD20 therapies were relatively overrepresented compared to a similar prevaccination-era COVID-19 cohort. CONCLUSION: Use of anti-CD20 therapies during vaccine breakthrough COVID-19 infection is associated with higher severity. However, the attenuated postvaccination humoral response associated with anti-CD20 therapy use during vaccination may not drive increased infection severity. Further studies are necessary to determine if this attenuated vaccine response may be associated with an increased likelihood of breakthrough infection.

High CD4+:CD8+ ratios with herpes zoster infections in patients with multiple sclerosis on dimethyl fumarate.

BACKGROUND: Dimethyl fumarate (DMF) depletes CD8+ and CD4+ T cells, and cases of herpes zoster (HZ) in patients with multiple sclerosis (MS) on DMF have been documented. OBJECTIVES: To evaluate lymphocyte subsets in patients with MS who developed HZ on DMF (Tecfidera) compared to matched controls who did not develop HZ. METHODS: We used linear mixed-effects models to test for differences in white blood cell count, lymphocyte percentage, absolute lymphocyte count, CD3+ percentage, absolute CD3+ count, CD4+ percentage, absolute CD4+ count, CD8+ percentage, absolute CD8+ count, and CD4+:CD8+ ratio over time in HZ and non-HZ groups. RESULTS: Eighteen patients developed HZ while on DMF. The linear mixed-effects model for CD4+:CD8+ ratio showed a significant difference between the HZ and non-HZ groups (p = 0.033). CD4+:CD8+ ratio decreased over time in the HZ group and increased over time in the non-HZ group. CONCLUSION: Patients with MS who develop HZ while on DMF have high CD4+:CD8+ ratios, suggesting an imbalance of CD4+ and CD8+ cells that may put a patient at risk for developing HZ while on DMF. This result emphasizes the need for lymphocyte subset monitoring (including CD4+:CD8+ ratios) on DMF, as well as vaccination prior to DMF initiation.