Summary
A Nature Medicine study found that T-cell patterns in blood and cerebrospinal fluid were associated with ALS progression in different ways. CMV-specific immune responses were also linked to faster progression or shorter survival in some patient groups.
A study published in Nature Medicine on 27 October 2026 found that T-cell activity in people with amyotrophic lateral sclerosis (ALS) had different associations with disease progression depending on whether it was measured in blood or cerebrospinal fluid (CSF). The researchers also linked CSF T cells matching cytomegalovirus (CMV) immune signatures with faster progression, and anti-CMV antibodies with shorter survival in one group of patients.
The results come from analyses of patient samples and clinical records, not a treatment trial. They point to immune responses that vary by location and patient group, rather than a single uniform pattern of T-cell activity in ALS.
T-cell patterns differed between blood and CSF
The researchers first used single-cell RNA and T-cell receptor sequencing to profile paired blood and CSF samples from 20 people with sporadic ALS near diagnosis. They compared the CSF data with publicly available samples from 20 age- and sex-matched healthy controls. In the ALS samples, they identified T-cell clones—groups of T cells carrying the same receptor sequence—that were expanded and, in some cases, persisted over time.
In a separate longitudinal cohort of 159 people with ALS, flow-cytometry measurements showed opposing associations by compartment. Higher proportions of CD4+ effector and regulatory T cells in blood were associated with faster decline on the ALS Functional Rating Scale–Revised (ALSFRS-R). Higher levels of the measured T-cell subsets in CSF were associated with slower progression. Increased blood CD8+ T-cell frequencies were also associated with greater mortality risk within six months of sampling. These are associations with clinical outcomes, not evidence that changing T-cell levels would change the course of ALS.
A small longitudinal sequencing analysis offers a closer look at persistence: among four patients sampled a year apart, 96% of CSF T-cell clones that contained more than five cells at the first time point were detected again at follow-up. This suggests that some clones can remain detectable in CSF over time, although the small group limits how broadly the finding can be applied.
The study also found cell complexes containing both antigen-presenting-cell and T-cell signals, enriched in ALS CSF. Imaging flow cytometry in samples from four patients identified CD14+ and CD3+ cell complexes, some with focused ICAM1 expression—a feature consistent with immune-synapse formation, where immune cells make structured contact. Together, the sequencing and imaging results support the possibility of local antigen presentation in CSF.
CMV responses tracked with outcomes in some groups
The researchers matched T-cell receptor sequences against databases of known antigen-specific receptors. In the 20-person sequencing cohort, the frequency of CSF T cells identified as CMV-specific was associated with faster ALS progression. This association was not seen for CMV-specific T cells in blood. The matching approach identifies likely specificities from existing databases; it is not a direct experimental test of what each T cell recognises.
In a separate cohort of 706 people with ALS, higher serum antibody responses to CMV immediate early 1 (IE1), a marker of recent CMV reactivation, were associated with shorter survival among people without a known genetic cause of ALS. The association was not observed in the groups with C9orf72 expansions or homozygous SOD1*D91A variants. The study also found CMV transcripts in postmortem brain samples, but detection rates were similar in ALS, healthy controls and people with other neurological conditions.
These findings distinguish the amount of T-cell activity from its apparent specificity: higher overall T-cell levels in CSF were associated with slower progression in one cohort, while CMV-linked responses in CSF tracked with faster progression. The researchers propose that CMV-related immunity may matter in particular inflammatory or genetic contexts, but the patient data establish correlations rather than showing that CMV causes ALS progression. Identifying which immune responses are relevant, and for which patients, will require further study.