And the prediction held:
🔵 Ocrelizumab → TARGET depleted from blood
🔴 Natalizumab → TARGET enriched in blood
Two highly effective MS therapies with distinct mechanisms showing concordant effects on the same cellular state.
🔄 Independent therapeutic triangulation.
12/

🧠 But could we find the same phenotype in the MS brain?
In independent post-mortem datasets, TARGET was enriched in T cells from:
🔥 chronically inflamed lesion rims
🧠 perilesional white matter
vs lesion cores and healthy white matter.
10/

🧬 Next, we looked at TCR clonality.
TARGET was enriched in T cell clonotypes disproportionately expanded in the CSF — in both blood and CSF.
This supports a peripherally induced state primed for CNS trafficking, with subsequent clonal expansion within the CNS.
8/

💧 We first looked in CSF.
In an independent blood/CSF single-cell dataset:
🧠 In MS/CIS, TARGET was significantly enriched in memory T cells in CSF relative to blood
↔️ In healthy controls, no significant difference
Consistent with preferential CNS trafficking in MS.
7/

📈 Before treatment, TARGET was enriched in circulating memory T cells from people with more clinically aggressive relapsing MS.
But do these cells contribute to CNS pathology? 🧠
6/

🤔 Were TARGET cells simply depleted because some T cells express low levels of CD20?
The timing argued otherwise:
❌ No significant depletion two weeks after ocrelizumab
✅ Clear depletion months later
Most consistent with loss of B cell-dependent stimulation or support.
5/

🔥 We found a distinct T cell state depleted after B cell loss:
⚔️ proinflammatory–cytotoxic
🧬 non-canonical granzymes
🧭 trafficking
🏠 tissue-residency priming
♨️ chronic activation
We called it TARGET: Trafficking, Activated, Residency-Primed, Granzyme K-Effector T cells.
4/

🧮 To capture effects beyond conventional cell types, our analytical strategy:
🔬 quantified treatment-induced changes at single-cell resolution
🧬 defined continuous gene programs
🔗 used explainable machine learning to link these programs to treatment effects
3/

🔬 We started by asking:
What happens to the immune system in MS when B cells are removed?
Using longitudinal CITE-seq, we profiled 264,512 cells from treatment-naive people with MS before and during ocrelizumab.
2/

🧩 B cell depletion is highly effective in multiple sclerosis.
But why?
In our new @brain1878.bsky.social paper, we used ocrelizumab as a perturbation, uncovering a B cell-dependent T cell state linking peripheral immune activation to chronic CNS inflammation.
doi.org/10.1093/brain/awag303
🧵👇
1/