Increased serum NfL and GFAP levels indicate different subtypes of neurologic immune-related adverse events during treatment with immune checkpoint inhibitors

Abstract

Neurologic immune-related adverse events (nirAEs) represent rare, yet severe side effects associated with immune checkpoint inhibitor (ICI) therapy. Given the absence of established diagnostic biomarkers for nirAEs, we aimed to evaluate the diagnostic utility of serum Neurofilament Light Chain (NfL) and Glial Fibrillary Acidic Protein (GFAP). Fifty-three patients were included at three comprehensive cancer centers, of these 20 patients with manifest nirAEs and 11 patients with irHypophysitis. Controls included patients without any irAE (n = 8) and other irAEs (n = 14). Using a single-molecule enzyme-linked immunosorbent assay (Simoa), serum levels were measured prior to, during and after the manifestation of (n)irAEs in 80 samples. Symptom severity of the (n)irAEs was graded according to the Common Criteria for Adverse Events (CTCAE) version 5.0. Serum NfL levels were significantly higher in the nirAE group (n = 20) compared to irHypophysitis (n = 11; p = .0025) and controls (n = 22; p = .0384). Subgroup analysis demonstrated a significant elevation of NfL in nirAEs of the peripheral nerves (PNirAE) in contrast to neuromuscular syndromes (NMirAE) (p = .0260). GFAP levels were highest in patients with nirAE affecting the central nervous system (CNSirAE) compared to PNirAE and NMirAE (p = .0064). Symptom severity of nirAEs was associated with increased levels of NfL and GFAP (p = .0069, .0092). Individuals with elevated NfL levels exhibited less favorable outcomes of the (n)irAEs (p = .0199). Measurement of NfL and GFAP may be helpful for the differentiation of the broad spectrum of nirAEs and may serve as an indicator of symptom severity. Further investigation is needed to evaluate their potential as diagnostic and prognostic biomarkers.

Keywords: biomarker; immune checkpoint inhibitors; melanoma; neurological immune‐related adverse events; neurotoxicity.

FIGURE 1

Patient flow. Utilizing the MelAutim database, we identified patients with nirAEs across three centers in Germany: Berlin Charité, University Hospital Erlangen (UKER), and the University Hospital of Munich, LMU. More than 1000 patients were screened. Based on the predominant neurologic syndrome of the nirAEs, patients were categorized into three subgroups: Peripheral nerve/nerve root affection, PNirAE (n = 11), affection of the central nervous system, CNSirAE (n = 5), or affection of the neuromuscular junction and/or muscles, NMirAEs (n = 4). Cases with irHypophysitis (n = 11) were analyzed separately. Control cohorts consisted of patients with other irAEs (n = 14) or no irAEs (n = 8).

FIGURE 2

Serum NfL and GFAP levels in nirAE. (A) Serum NfL and GFAP levels in nirAE vs. other subgroups: Serum NfL levels were significantly higher in the nirAE group (n = 20) compared to irHypophysitis (n = 11, p = .0025, Kruskal–Wallis test with post‐hoc Dunn's testing) and other/no irAE control group (n = 22, p = .0384, Kruskal–Wallis test with post‐hoc Dunn's testing). GFAP levels did not significantly differ between groups, yet the nirAE subgroup exhibited a trend of higher GFAP levels. (B) Serum NfL and GFAP levels in different clinical manifestations of nirAE: Within nirAE subtypes (affected peripheral nerves/nerve roots: PNirAE, n = 11; central affection: CNSirAE, n = 5; or affection of the neuromuscular junction and/or muscles: NMirAE, n = 4) both PNirAE and CNSirAE showed increased NfL levels, while NMirAEs had lower NfL levels. Notably, PNirAE had significantly higher NfL levels than NMirAE (p = .0260, Kruskal–Wallis test with post‐hoc Dunn's testing). GFAP levels were significantly higher in CNSirAE compared to PNirAE (p = .0064, Kruskal–Wallis test with post‐hoc Dunn's testing). CNSirAE; affection of the central nervous system; GFAP: glial fibrillary acidic protein; NfL: neurofilament light chain; NMirAEs, affection of the neuromuscular junction and/or muscles; PNirAE; peripheral nerve/nerve root affection.

FIGURE 3

Analysis of clinical parameters and serum NfL and GFAP levels. (A) Correlation and linear regression analysis of age, and serum NfL and GFAP values: Age correlated significantly with GFAP levels in the subgroup of nirAE and irHypophysitis (n = 31, Spearman's r: 0.5207, p = .0027, confidence interval [CI] is given with 95% depicted with dotted lines and in between colored area). (B) Correlation and linear regression analysis of symptom severity and serum NfL and GFAP values: Symptom severity grading (CTCAE°) was available in 26 patients with nirAE or irHypophysitis and showed significant correlation with both NfL and GFAP serum concentrations (NfL: Spearman's r = 0.5207, p = .0069; GFAP: Spearman's r = 0.4600, p = .0092; for both regression analyses CI is given with 95%, depicted with dotted lines and in between colored area, red for NfL and blue for GFAP). (C) Group analysis between low‐grade (n)irAE (CTCAE° = 1–2) versus high‐grade (n)irAE (CTCAE° = 3–5) shows a significant difference for both NfL and GFAP levels (NfL: p = .0080, GFAP: p = .0487, Mann–Whitney U test). (D) Inter‐group analysis of prognostic implications of NfL and GFAP serum levels: Elevated NfL concentrations correlated with less favorable clinical outcomes in nirAE and irHypophysitis patients (outcome data was available in n = 21, categorized according to the following: Completely resolved symptoms, resolved with sequelae and persistent disability). Higher NfL levels were associated with less favorable outcomes: Group analysis between outcome parameters showed significant differences in their NfL levels between the status “completely resolved symptoms” versus “persistent disability” (p = .0387, Kruskal–Wallis test with post‐hoc Dunn's testing). There were no significant differences for GFAP levels. CI, confidence interval; CNSirAE, affection of the central nervous system; NfL, neurofilament light chain; GFAP, glial fibrillary acidic protein; NMirAEs, affection of the neuromuscular junction and/or muscles; PNirAE, peripheral nerve/nerve root affection.