For decades, multiple sclerosis research and therapy development have centered on demyelination caused by peripheral immune attacks on oligodendrocytes. The April 2026 MedicalXpress report correctly notes that cortical neuron loss occurs in parallel yet has received less attention. However, it stops short of identifying the precise immune-mediated mechanism now revealed: infiltration of CD8+ tissue-resident memory T cells into cortical gray matter, where they directly induce neuronal apoptosis through perforin-granzyme B pathways, independent of myelin damage.

This observational study examined postmortem cortical tissue from 47 MS patients and 21 controls using single-cell RNA sequencing, spatial transcriptomics, and multiplex immunohistochemistry. No commercial conflicts of interest were declared. The researchers documented clonal expansion of CD8+ T cells expressing high levels of GZMB and PRF1 that physically contact cortical pyramidal neurons, triggering mitochondrial dysfunction and caspase-independent cell death. This builds on but significantly extends a 2021 Nature Reviews Neurology synthesis on gray matter pathology (review of 85 studies) and a 2023 longitudinal cohort study in The Lancet Neurology (n=1,842, industry-funded for drug monitoring) showing that current disease-modifying therapies reduce relapses yet fail to halt progressive cortical atrophy.

Original coverage missed the therapeutic implication: most approved MS drugs (anti-CD20, S1P modulators, interferons) primarily target circulating lymphocytes and do not adequately address compartmentalized CNS-resident CD8+ T cells behind an intact blood-brain barrier. This explains why cognitive decline and neurodegeneration continue despite suppression of new lesions. Patterns observed here parallel mechanisms in Rasmussen encephalitis and certain paraneoplastic syndromes, suggesting shared final pathways of T-cell-mediated neuronal killing.

The discovery opens targeted avenues including CNS-penetrant granzyme inhibitors, specific chemokine receptor blockers to prevent CD8+ residency, and combination neuroprotective regimens. Without addressing this axis, MS treatment will remain incomplete, focused on the wrong compartment and cell type for the most disabling aspect of the disease.