Изучение клинической полезности нееврофильтрованных световых цепочек для управления множественным склерозом.

Introduction

Multiple sclerosis (MS) is a chronic inflammatory and neurodegenerative disease that affects an estimated 2.8 million people globally. 1 Owing to the diverse phenotypes of MS and an array of disease-modifying therapies (DMTs) available, a personalized approach to treatment is necessary. 2 Personalization of care for people with MS (pwMS) requires prognostication at time of diagnosis; an initial treatment selection based on risk-benefit analysis and shared decision making; and, subsequently, an ongoing assessment of treatment response to promptly determine whether a treatment adjustment is needed. 2

Although traditional measures used to prognosticate and/or monitor disease in MS can include clinical demographics, assessment of acute inflammatory activity based on clinical relapses and presence or development of gadolinium-enhancing or new/enlarging T2 lesions on MRI, cognitive impairment measures, ophthalmologic testing, and disability progression measures, there are limitations to most of these methods. Radiologic assessment using MRI has been a mainstay in many practices, but it can be expensive and time-consuming and may be impractical for frequent repeat monitoring. In addition, the quality and consistency of serial MRI scans may vary and influence their interpretation. 3 Furthermore, some patients may be unable to obtain an MRI scan because of having metallic foreign bodies or intolerance to the scanner or contrast agent. Measures of disability progression have several limitations. For example, the Expanded Disability Status Scale (EDSS) score can be subjective 4 and nonlinear, may underestimate certain functional domains as higher scores are largely determined by ambulatory function, and can generally be insensitive for capturing ongoing CNS injury. 5

Certain putative biomarkers, such as neurofilament light chain (NfL) and glial fibrillary acidic protein (GFAP), have shown promise as measures for prognostication and the assessment of patient response to treatment. 2,6 In particular, there is a mounting body of evidence to support the use of NfL for predicting disease/disability progression and monitoring treatment response in cohorts of patients 7 ; however, the utility of NfL monitoring for individual patients in the clinic requires further exploration. This review aims to educate health care providers (HCPs) on the potential uses of NfL in clinical practice to optimize management of pwMS based on the most recent literature ( Figure 1 ).

Potential Uses of sNfL Measurements in the Clinical Management of Patients With MS

DMT = disease-modifying therapy; MS = multiple sclerosis; sNfL = serum neurofilament light chain.

Methods

A PubMed search was conducted to find applicable articles for inclusion. The following search terms were used: (1) (multiple sclerosis [Title]) AND (prognosis [Title]), (2) ([multiple sclerosis {Title}] AND [neurofilament light {Title/Abstract}]) AND (diagnos* [Title]), (3) (multiple sclerosis [Title]) AND ([neurofilament {Title}] OR NFL {Title}]) AND (practice [Title/Abstract]), (4) (multiple sclerosis [Title]) AND (neurofilament [Title]) OR NFL (Title) AND (clinical practice [Title/Abstract]), (5) (neurofilaments) AND (functions), (6) (neurofilament light [Title]) AND (reference[Title/Abstract]), (7) (multiple sclerosis [Title]) AND (neurofilament light [Title/Abstract]) AND (prognostic [Title/Abstract]), (8) (multiple sclerosis[Title]) AND (neurofilament [Title] OR NFL[Title]) AND (disease activity [Title]), (9) (multiple sclerosis [Title]) AND (neurofilament [Title]) OR (NfL [Title]) AND (outcomes [Title/Abstract]), (10) (neurofilament [Title]) OR (NfL[Title]) AND (assay [Title]), (11) (“neurofilament” [Title] OR “NFL” [Title]) AND (cost [Title/Abstract]), (12) (multiple sclerosis [Title]) AND (neurofilament [Title]) OR (NfL [Title]) AND body mass index [Title/Abstract]), (13) (multiple sclerosis [Title]) AND (neurofilament [Title]) OR (NfL [Title]) AND (comorbidities [Title/Abstract]), (14) (multiple sclerosis [Title]) AND (neurofilament [Title]) OR (NfL [Title]) AND (pregnancy [Title/Abstract]), and (15) (multiple sclerosis [Title]) AND (neurofilament [Title]) OR (NfL [Title]) AND (combination[Title/Abstract]).

Searches were limited to the article title only, English language, and publication after 2020; case study–type articles, letters, commentaries, and editorials were excluded. Additional articles of particular interest published before 2020 were included, as were references not included in the original PubMed searches that were recommended by the authors or were manually accessed if considered relevant to a statement in the review.

NfL in Physiologic and Pathologic Conditions

Neurofilaments are neuroaxonal cytoskeletal proteins that maintain cell homeostasis and provide mechanical and structural support to axons. 7,8 In mammals, neurofilaments are heteropolymers composed of 4 constituent subunits defined by their molecular weights: neurofilament heavy (190–210 kDa), medium (150 kDa), and light (68 kDa), as well as α-internexin and peripherin ( Figure 2 ). 8,9 In healthy individuals under normal conditions, low levels of neurofilament proteins, including NfL, are continuously released from both the CNS and peripheral neuroaxonal units into the extracellular space and these can reach the CSF and blood as part of normal tissue turnover. Several characteristics, including age, sex, and body mass index (BMI), can influence normal NfL levels, and abnormally increased NfL levels can be released because of neuroaxonal damage caused by neurologic and non-neurologic comorbidities. 10

Neurofilament Structure and Subunits and Mechanisms Leading to Increased NfL Concentrations in the CSF and Blood

α-int = α-internexin; E = glutamic acid-rich segments; KE = lysine-glutamic acid; KEP = lysine-glutamic acid-proline; KSP = lysine-serine-proline; NfH = neurofilament heavy chain; NfL = neurofilament light chain; NfM = neurofilament medium chain; SP = serine-proline.

Age is an important factor, with NfL levels rising in the CSF and blood in an age-dependent manner. 10,11 Levels of serum NfL (sNfL) are particularly variable in individuals aged older than 60 years, potentially due to comorbidities, increased neuronal apoptosis, and/or disruption of the blood-brain barrier. 10,11 A biphasic sNfL age dependency has also been demonstrated, with higher sNfL levels observed in infancy and adolescence than in childhood, 12 before the age-associated increase in adulthood. Studies have also shown that NfL levels are higher in healthy men compared with healthy women. 13,14 There is also a significant association between BMI and plasma NfL (pNfL) levels even after adjusting for age and sex, with pNfL decreasing by 0.02 pg/mL per unit of BMI in healthy controls. 15 In a study of stroke patients with diabetes mellitus, higher sNfL was also associated with race, cardiovascular disease history, elevated systolic blood pressure, decreased renal function measured by the estimated glomerular filtration rate, and poor glycemic control measured by hemoglobin A1C. 16

Compared with healthy controls, NfL levels are elevated in the CSF and blood of patients with a range of neurologic disorders, including MS 17,18 ; neurodegenerative diseases, such as dementia; and amyotrophic lateral sclerosis, 19 stroke, 20 and neurologic trauma, 21 all reflecting the neuroaxonal damage that occurs in these disease pathologies. In MS, elevated NfL can be the result of injury caused by focal relapse–related inflammatory processes and/or nonrelapse-related compartmentalized inflammation and neurodegenerative processes believed to underlie progressive disease biology, although the magnitude of increase is considerably higher in the context of focal relapse biology. 22 It is, therefore, not surprising that increases in NfL concentrations have been observed across the spectrum of MS clinical phenotypes, including patients with relapsing forms of MS (RMS) even at stages of clinically isolated syndrome 13 and presymptomatic MS, 23 as well as in progressive forms of MS, including secondary progressive MS (SPMS) and primary progressive MS (PPMS).

Potential Value of NfL in the Management of MS

Clinical Evidence for NfL as a Prognostic Marker

Baseline NfL levels have been shown in multiple prospective studies to predict short-term and long-term outcomes in pwMS. 22,24-26 For example, the prognostic value of baseline sNfL for on-study focal inflammatory disease activity and worsening in patients with RMS was explored in a protocol-planned analysis of the phase 3 ASCLEPIOS trials of ofatumumab (ASCLEPIOS I [ NCT02792218 ] and ASCLEPIOS II [ NCT02792231 ]). 24 Based on the median sNfL levels at baseline for the overall population of ASCLEPIOS I/II trials (9.3 pg/mL), patients were stratified into “high” (>9.3 pg/mL) and “low” (≤9.3 pg/mL) groups. Compared with low sNfL, high sNfL was found to be prognostic of increased on-study new focal inflammatory T2 lesion formation at years 1 and 2 and also of higher annual percentage decrease in whole brain volume, thalamic volume, and white matter volume. 24 These results are further supported by results of the phase 2 APLIOS study ( NCT03560739 ), which indicated that the prognostic value of baseline and time-matched sNfL for predicting on-study gadolinium-enhancing (Gd+) T1 lesions was comparable with the predictive ability of baseline Gd+ lesions. 26

In the phase 3 ORCHESTRA trials of the anti-CD20 ocrelizumab, including the OPERA I/II trials in RMS ( NCT01247324 / NCT01412333 ) and the ORATORIO trial in PPMS ( NCT01194570 ), elevated baseline NfL was found to have a prognostic relationship with MRI outcomes (brain volume, thalamic volume, and new/enlarging T2 lesions) in patients with RMS and patients with PPMS. 22 Baseline NfL was prognostic for clinical progression (24-week confirmed disability progression on the EDSS) in patients with RMS without disease activity and in patients with PPMS. 22 Baseline NfL level was also associated with exploratory measures of confirmed disability progression, such as progression independent of relapse activity, time to walking-aid dependence (EDSS score 6), and the Nine-Hole Peg Test (9HPT) in patients with RMS without disease activity and 9HPT in patients with PPMS. 22 In the EXPAND and INFORMS studies of the sphingosine 1-phosphate modulators siponimod in SPMS and fingolimod in PPMS, respectively, baseline NfL concentrations >30 pg/mL were also associated with significantly greater confirmed disability progression. 25 Although these findings raise the question as to whether NfL elevations may also capture injury from nonrelapsing progressive disease processes, there remains the possibility that subclinical focal inflammatory lesions (i.e., subclinical relapse biology) contributed to NfL elevations and disability worsening. In a subgroup of the ocrelizumab trial participants, persistently elevated NfL levels in patients already receiving ocrelizumab for approximately 1 year were also associated with an increased risk of future disease progression. 22 Because this patient population was being treated with a high-efficacy therapy during which relapse biology is generally absent, these results suggest that persistently high NfL in individuals in whom relapses are absent or relapse-associated inflammatory injuries are effectively suppressed by therapy may be used to identify, and possibly monitor, the presence of nonrelapsing progressive injury processes.

The potential use of NfL as a long-term predictive biomarker has also shown promise. The phase 3 Multiple Sclerosis Collaborative Research Group clinical trial and its long-term extension studies demonstrated that cNfL and sNfL levels are associated with long-term clinical outcomes in patients with relapsing-remitting multiple sclerosis (RRMS), such as brain parenchymal fraction change over 8 years, and were predictive of reaching an EDSS score ≥6 at year 8, with sNfL also being predictive at year 15. 27 In a prospective cohort study of patients who had an sNfL sample collected within 5 years of symptom onset and had >15 years of routine clinical follow-up, patients with low baseline sNfL levels were 4.3 times less likely to reach an EDSS score ≥4 during follow-up and were 7.1 times less likely to develop clinically progressive MS. 28 Patients with the highest baseline sNfL levels worsened more rapidly, with an EDSS annual rate of 0.16. 28 In a real-world cohort of 534 treatment-naïve pwMS with a clinical follow-up of ≤13.5 years, high baseline pNfL levels were associated with reduced cortical volumes in patients with stable T1 lesion volumes. 29 A 2022 meta-analysis of 5 studies with >4,000 patients also found that patients with “high” sNfL levels had a shorter time to reach EDSS score ≥4 but similar time to relapse compared with those with low NfL levels. 18 Finally, a retrospective, observational, case and control study in patients with RRMS found that baseline sNfL levels were prognostic of long-term disability. Patients who developed aggressive RRMS (EDSS score ≥6 at ≤15 years of follow-up) had significantly higher baseline sNfL levels than those who developed more benign RRMS (EDSS score ≤3 at ≥10 years of follow-up). 30 It is important to note that none of the above mentioned studies, with the exception of findings in the phase 3 ORCHESTRA trials, 22 could distinguish whether worsening outcomes reflected relapse-related injury vs nonrelapsing progressive injury.

NfL to Identify Treatment Responders

Because NfL concentration reflects neuroaxonal damage, stable or decreasing NfL levels while on treatment may provide evidence of decreased further injury in response to treatment. Conversely, NfL increase after treatment initiation could imply that the patient is a suboptimal responder. Multiple DMTs have been shown to maintain reduced NfL levels in a broad number of studies. 31 Larger reductions in NfL levels are generally seen with higher efficacy DMTs. 31 This may in part reflect patients starting high-efficacy therapies having higher baseline disease activity and, thus, higher baseline NfL levels, leading to larger relative decreases in NfL after treatment initiation. 31 Although most patients experience decreased cNfL levels in response to treatment, cNfL levels can remain elevated in some patients (∼10%–20%) despite the use of high-efficacy therapies, 32 potentially reflecting ongoing injury from nonrelapsing progressive disease, which is not substantially affected with currently approved DMTs.

Clinical Evidence for NfL as a Biomarker of Subclinical Disease Activity

NfL elevations may reveal subclinical disease activity in patients who appear clinically and even radiologically stable. In the previously mentioned APLIOS study, patients who developed new subclinical Gd+ T1 lesions at study week 4 (which were absent at baseline) had increased sNfL levels during the month preceding the week 4 MRI scan, indicating that sNfL assessment may capture subclinical disease activity that might otherwise be missed by infrequent MRI scans. 26 Although similar results were presented in a small study of 15 pwMS in whom rising sNfL levels were observed up to 5 months before new clinical relapses, 33 a larger recent study of 166 pwMS with frequent imaging and blood sampling indicated that initial increases in sNfL trailed the first observation of a Gd+ lesion. 34

There is also a mixed body of evidence linking sNfL and subclinical cognitive and neuropsychiatric symptoms, such as brain fog, fatigue, depression, and anxiety, which may partly reflect relatively small cohort sizes and study durations. In a study of 45 clinically stable pwMS, sNfL levels were not associated with cognitive or neuropsychiatric parameters. 35 sNfL was similarly found to be an unreliable marker for cognitive functioning in a study of 82 pwMS, only correlating with worse processing speed of the parameters assessed. 36 However, several other studies suggest an inverse relationship between elevated NfL and cognitive function 37-39 and provide supportive evidence for sNfL as a predictor of cognitive decline at least at the group level. 37-39 Ultimately, large-scale longer duration studies will be needed to validate the utility of sNfL as an injury marker related to clinical and subclinical cognitive and neuropsychiatric decline.

NfL in the Identification of Pseudorelapses

sNfL may prove quite useful in differentiating pseudorelapses from relapses. Because pseudorelapses involve worsening of existing neurologic symptom/s due to a non–MS-related stressor such as heat, infection, or exertion and are not believed to reflect an active neuroaxonal injury process, 40 a normal sNfL level may be reassuring and, in some cases, may help avoid unnecessary corticosteroid use and/or changes in DMTs.

NfL Use in Special Populations

NfL may also be used to monitor disease activity in special populations. For example, it has been suggested that sNfL can be used during family planning, with clinicians using NfL alongside traditional clinical measures to identify a period of stable disease activity for the patient to attempt conception. 41 Once pregnant, sNfL can be a useful and convenient tool for monitoring disease activity and may again be used to identify pseudorelapses because many symptoms associated with pregnancy, such as fatigue, bladder symptoms, and mobility problems, may overlap with those of an MS relapse. NfL may also be particularly useful in older patients to monitor disease activity when treatment is discontinued because of immunosenescence, although one must appropriately adjust for age-associated and comorbidity-associated NfL increases.

Assays for Measuring NfL

NfL levels can be measured from CSF and blood (serum or plasma) samples. NfL concentrations are 40-fold higher in the CSF than in the blood 8 ; however, CSF measurements are impractical for repeated monitoring of pwMS. Successful adaptation of assays to blood samples, including emerging techniques that are ultrasensitive to low concentrations of NfL in serum and plasma, now allows for rapid, simple, and minimally invasive clinical quantification of NfL. 8 sNfL measurements may be more amenable than plasma levels to frequent longitudinal testing because sNfL levels seem stable at room temperature and across multiple freeze-thaw cycles and do not require special collection or shipping techniques. 42 sNfL samples can provide higher NfL measurements than paired plasma samples, 43,44 which in part may reflect different matrix properties of serum vs plasma. Sources for laboratory analysis of sNfL available in the United States (as of October 2024) are summarized in the Table 45,46 , although this information is expected to change in line with the emergence of more platforms and participating laboratories. 42

Table Available NfL Assays Type of assay Biofluid Manufacturer Availability Ella Simple Plex Immunoassay System Serum, plasma, and CSF Bio-Techne desktop ELISA immunoassay system Commercially available Simoa single-molecule array Serum, plasma, and CSF Quanterix received FDA Breakthrough Device Designation a in April 2022 Commercially available Roche Diagnostics Elecsys NfL Immunoassay Serum and plasma LabCorp received FDA Breakthrough Device Designation in November 2023 Commercially available ADVIA Centaur/Atellica sNfL assay Siemens/Novartis Serum and plasma Siemens/Novartis received FDA Breakthrough Device Designation in March 2022 Used in research settings; commercial availability expected soon b Lumipulse G NfL Serum, plasma, and CSF Fujirebio Used in research settings R-PLEX Human Neurofilament L Assay Serum and CSF Meso Scale Discovery (MSD) Used in research settings Abbreviations: FDA = Food and Drug Administration; NfL = neurofilament light chain; sNfL = serum neurofilament light chain. Adapted from the Consortium of Multiple Sclerosis Centers (CMSC) 2024 Consensus Paper on Neurofilament Biomarkers in Multiple Sclerosis. a FDA Breakthrough Device Designation is a formal identification for medical devices that provide for more effective treatment or diagnosis of life-threatening or irreversibly debilitating diseases or conditions. The Breakthrough Program is intended to help patients have more timely access to medical devices by expediting their development, assessment, and review while preserving the statutory standards for premarket approval, 510(k) clearance, and De Novo marketing authorization. 45 b Commercially available in the European Union in late 2024. 46

Available NfL Assays

Abbreviations: FDA = Food and Drug Administration; NfL = neurofilament light chain; sNfL = serum neurofilament light chain.

Adapted from the Consortium of Multiple Sclerosis Centers (CMSC) 2024 Consensus Paper on Neurofilament Biomarkers in Multiple Sclerosis.

FDA Breakthrough Device Designation is a formal identification for medical devices that provide for more effective treatment or diagnosis of life-threatening or irreversibly debilitating diseases or conditions. The Breakthrough Program is intended to help patients have more timely access to medical devices by expediting their development, assessment, and review while preserving the statutory standards for premarket approval, 510(k) clearance, and De Novo marketing authorization. 45

Commercially available in the European Union in late 2024. 46

Challenges to Implementing and Interpreting NfL Measurements in Clinical Practice

Effect of Confounders on NfL Levels

Multiple variables and conditions other than MS may confound NfL interpretation in a clinical setting ( Figure 3 ). As mentioned previously, these include other neurologic conditions (i.e., neurodegenerative diseases, 19 stroke, 20 traumatic brain injury, 21 and peripheral neuropathy 47 ), as well as a range of non-neurologic conditions and factors (i.e., BMI and pregnancy). 15,48,49 A large real-world study found that factors significantly associated with elevated sNfL levels in pwMS include comorbid diabetes mellitus, smoking, and decreased renal function as determined by the estimated glomerular filtration rate. 49 After adjusting for age and sex, this study and another further found that higher BMI was significantly associated with lower NfL levels and this association was consistent across BMI categories. 15,49 Although NfL levels increase with age in pwMS as they do in healthy individuals, 50 it is unclear whether sex is a confounding factor in pwMS because studies to date have variably reported higher levels of NfL in men than in women with MS, 13,49 higher levels of NfL in women than in men with MS, 50 and no difference in levels between men and women with MS. 51

Confounding Factors Affecting the Interpretation of NfL Measurements

Issues With NfL Measurement and Interpretation

Regarding measuring NfL levels for clinical applications, there remains a lack of measurement standardization, which has led to significant variation in measured sNfL levels across different methods and assays. 52 This is in part driven by the lack of well-established reference ranges and diagnostic and prognostic cutoff values for each assay. One study found that the percentage of NfL measurements classified as “elevated” in pwMS can vary from 3.7% to 30.9% depending on the published reference resource used for classification. 53 Sample measurement and interpretation is further complicated because a clinically meaningful change in NfL has not yet been established and is likely to be context dependent. Although elevated NfL generally correlates with important MS outcomes, there is still a significant overlap in sNfL levels between pwMS and healthy controls. 3 This overlap presents a challenge when interpreting sNfL levels at the individual patient level, because measurements that include elevated NfL levels due to an MS-related injury may still fall within the normal range. Guidance is, therefore, still needed on how to best measure and interpret NfL levels for individual patients.

Cost and Access Barriers to Implementation of NfL in Clinical Practice

As an emerging technology, there are challenges that patients and HCPs may face in implementing the use of NfL testing. As with many new technologies, the current cost of NfL testing is relatively high compared with other blood tests. 3 This may be concerning for patients because it may be difficult to receive reimbursement from insurers. Although several assays have been given Breakthrough Device Designation, they have, to date, not yet been formally approved by the US Food and Drug Administration. However, adoption of routine sNfL analysis could reduce the need for frequent MRI by helping clinicians determine whether a follow-up MRI is required, ultimately reducing the cost of care. 42 Use of sNfL may also save costs if it prevents patients from staying on DMTs with suboptimal efficacy. 42

Availability of and access to compatible analysis instruments may also affect the use of some tests. For example, the Simoa assay currently requires the purchase of a specialty analyzer platform, which may limit test accessibility. However, ongoing projects developing immunoassays using the same Quanterix NfL antibodies as the Simoa platform aim to adapt the assay onto a routine analyzer platform, which would improve availability and accessibility of the tests. 46 Indeed, as interest in NfL as a biomarker of MS increases, the emergence of new assays that use existing platforms will likely drive down setup and testing costs and increase test accessibility.

Improving NfL Use in Clinical Practice

Implementation and proper interpretation of NfL measurements in practice would be aided by assay standardization and establishment of context-appropriate reference values. Absolute values of NfL can vary depending on the type of assay used and biofluid tested, 42 and lack of reference values or failure to correct for confounding variables can limit the proper utility of NfL as a biomarker for individual patients. As an example, in 1 study, although absolute levels >23 pg/mL or a >30% increase from baseline (taken during remission) corresponded to a 5–7-fold increase in MRI activity, 54 neither cutoff value remained significant in patients older than 50 years. 54 Establishing reference values across geographically and ethnically diverse populations will help ensure proper implementation in a global setting. An additional challenge is that group-level effects observed in NfL cohort studies, such as the compelling prognostic value of NfL in clinical trial data sets, translate only modestly to individual-level predictions in part because of large variability in individual patients' absolute values, especially when using a single cross-sectional measurement. 55

Ideally, baseline and longitudinal sNfL levels would be collected for pwMS, allowing patients to act as their own controls. However, analytical and biological variation will need to be taken into consideration when determining whether a change in a patient's sNfL levels is clinically significant. In healthy individuals, within-participant variation is positively correlated with the time interval between consecutive measurements. Biological variation estimates have been previously reported to be 3.1% when measuring sNfL on consecutive days 56 and 7%–10% for consecutive weeks. 57,58 Analytical variation ranged from 6.3% to 7.2%. 56,57 From these studies, the reference change value for NfL, which represents the change needed between consecutive measurements to exceed biological and analytical variation, is estimated to be approximately 23%–31%. 56,57

When baseline sNfL measurements are not available, transformation of absolute values to Z-scores or percentiles can begin to reliably correct for confounding factors, such as age and BMI. A reference database has been established by the Kuhle group using blood samples from >5,000 healthy people from which age-corrected and BMI-corrected reference values were derived. 59 The Z-scores produced were then compared against those of 1,313 pwMS from the Swiss MS Cohort and were further validated in an independent sample of 4,341 patients with MS from the Swedish MS registry. 59 A Z-score >1.5 was associated with a 3.15-fold increased risk of future clinical and radiologic disease activity for all pwMS, including those with no evidence of disease activity. 59 This study used only 1 assay for NfL analysis. 59 Standardization across assays as well as large-scale, multicenter studies incorporating different regions, ethnicities, and disease states will further help apply appropriate cutoff value.

Biomarker Combinations

In addition to the importance of considering NfL measurement and interpretation as complementary to traditional clinical and imaging assessments, NfL may eventually be best used in combination with other biomarkers. A recent study measuring 24 fluid biomarkers, including NfL, showed that combinations of ≤6 biomarkers measured in the CSF or serum provide incremental improvements in the prediction of MS prognosis. 55 Of 7 serum biomarkers that were found to be significantly differently expressed in pwMS vs controls, osteopontin was found to have the highest fold difference next to NfL. 55 Osteopontin is a cytokine expressed by various cell types including immune cells. 55 Osteopontin may, therefore, be complementary to NfL by providing insights into different cellular processes associated with disease activity in MS.

Elevated levels of GFAP have been shown to correlate with MS outcomes, 6,60,61 and implementing GFAP measurements in clinical practice is also being discussed. 61 GFAP is principally recognized as an astrocytic intermediate filament and can be released from activated and/or injured astrocytes into the CSF and blood. 62 Increased GFAP is more strongly associated with disease progression than relapse activity, whereas the inverse is true for increased NfL. 60,61,63 Combined measurement of GFAP and NfL may, therefore, eventually aid clinical practice by providing a more complete picture of subclinical disease processes involved in relapsing and nonrelapsing progressive MS. Other promising astrocytic markers that have been associated with progressive disease biology, such as CSF chitinase-3 like-protein-1 (CHI3L1), may be useful as part of a biomarker panel to capture disease activity. Evidence suggests that, although CHI3L1 and GFAP are both considered astrocytic markers, their levels may represent distinct pathologic processes because CHI3L1 levels are not well correlated with GFAP levels in pwMS. 64 Because serum levels of CHI3L1 do not differ significantly between pwMS and healthy controls, meaningful assessment of CHI3L1 levels in patients may require analysis of CSF (rather than blood samples), making it less practical than serum GFAP measurements. 64

Clinical and real-world evidence continues to support the use of blood biomarkers, such as NfL, in predicting disease activity/worsening and monitoring treatment response. The recent development of sensitive blood assays has increased the convenience and accessibility of sNfL testing. As commercial assays continue to be developed and standardized and large-scale, multicenter studies are completed to determine reference ranges and cutoff values across broad populations, sNfL measurements alone or in combination show increasing promise for incorporation into routine clinical practice and shift the current treatment paradigm toward more personalized precision medicine. When coupled with traditional clinical assessments and other biomarkers, measuring sNfL holds the promise of significantly improving patient care, particularly for patients who might experience barriers to access, such as those living in rural communities, those with financial limitations, or those with disabilities. Beyond its role in patient management, NfL may be used during clinical trial development (i.e., for stratifying patients with nonrelapsing progressive MS in the context of high-efficacy therapy). Future studies will, therefore, not only contribute to improving patient management but may also have a greater impact on therapeutic advances and improving outcomes in MS.