ACTRIMS 2025 Highlights
Tolebrutinib results offer real hope for people with smouldering MS and possibly how to identify high-risk subjects (PRL+) who are more likely to respond to tolebrutinib
The good thing about in-person meetings is that they give you time to reflect on the field and what needs to be done in the future. They also allow you to speak to colleagues and friends about MS and where things are going in the future. These are some of my initial thoughts after attending ACTRIMS 2025.
The MS field is fixated on effector mechanisms and measuring damage. Many talks and posters discussed how the immune system causes damage to the nervous system and how we measure the damage using immune markers, body fluid markers, electrophysiology, OCT (optical adherence tomography), MRI and PET imaging, clinical outcomes, or AI (machine and deep learning). However, I was disappointed that nobody mentioned neurological stress testing to measure resilience or reserve.
There was little discussion on what I call proximal events that lead to someone developing MS in the first place. There are two talks on EBV and MS. Dalia Rotstein (Toronto, Canada) extended the EBV prodrome to IM (infectious mononucleosis) itself, showing that IM triggers sickness behavior and excess healthcare utilisation. Could MS begin at the time of IM? This needs some deep thought but is a novel and intriguing concept. I will come back to this topic in future.
Another presentation using longitudinally collected samples implied that systemic EBV reactivation occurs in the three-month window before a relapse occurs (Abstract 1). The study did not report actual viral detection, only the B-cell gene transcription signature in response to EBV products. The presentation was very data-heavy, and I would need to digest the paper when it comes out before drawing premature conclusions. Another study showed that EBV-specific CD8+ cells are enriched in the spinal fluid of patients with MS (Abstract 2). This would imply that EBV is active in the CNS of pwMS, and the immune system responds to lytic EBV CNS infection. This data would be compatible with other EBV data and argues for testing CNS-penetrant EBV antivirals in MS.
There were excellent talks on the biology of myelination and remyelination and their complexity. The question I ask is, is remyelination a problem in MS? If you switch off the disease, for example, with alemtuzumab or AHSCT, patients remyelinate and recover function spontaneously. Indeed, the real issue is using their treatments early. Trying to remyelinate a damaged nervous system without curing someone of having MS is foolhardy. If the autoimmune target in MS is myelin or the oligodendrocyte, the cell that makes myelin, repairing these two components will invite further attacks on their integrity. It is like doing a kidney transplant in someone with an autoimmune kidney disease. In many autoimmune diseases of the kidney, the disease reoccurs in the transplanted kidney.
This is why remyelination therapies in isolation will not work. Similarly, targeting remyelination therapies a long time after the event, i.e. after the loss of neurons and axons, won’t work either. You need a surviving neuron and demyelinated axon to remyelinate it successfully. This is why remyelination and neurorestorative therapies are so many decades away. There are too many issues to overcome, the biggest being poor phase 3 trial design and the need to include the physiological stimulus to promote repair (rehabilitation) as part of the trial design.Another highlight was the role of microglia in MS pathology. Using new technologies, it is clear that the microglial response is very complicated. Microglia are mediators of damage and repair. So it will be a yin and yang. As paramagnetic rim lesions or PRLs are due to activated microglia, this topic will probably be the year's MS hot topic. It was great to see data from the relapsing and progressive tolebrutinib studies showing that the more PRLs you have, the worse your prognosis. Tolebrutinib is associated with a better outcome in subjects with PRLs, implying that this is how it probably works. Whether this treatment response is due to its effect on microglia or EBV is a moot point. I argue that the BTK inhibitors are working via EBV mechanisms and not necessarily via microglia. This post-hoc analysis tells us that tolebrutinib has a bioactive mechanism of action targeting CNS mechanisms. These results offer real hope for slowing down and preventing further damage in those with smouldering MS and possibly how to identify high-risk subjects (PRL+) who are more likely to respond to the treatment. I suspect these results will increase the need for detecting and monitoring for PRLs in routine clinical practice. Would you want to know how many PRLs you have in your brain?
Several talks discussed smouldering MS or at least referred to it. This included many posters and research presentations. It is clear that the term has now become sticky, as a large proportion of the MS community refers to the phenomenon of PIRA (progression independent of relapse activity) as smouldering MS.
There was no overt discussion on MS prevention at this meeting. I hope this becomes a significant focus in future meetings. If you have any questions about ACTRIMS, please feel free to ask.
Abstract 1
Background: Despite the efficacy of B-cell depletion therapies, relapsing-remitting multiple sclerosis (MS) remains a complex disease with ambiguity surrounding the cell and molecular mechanisms that cause relapses. Single-cell RNA sequencing (scRNA-seq) of clinical specimens provides a systematic framework for documenting cells and pathways in human diseases.
Objectives: The aims of this study are to 1. catalogue peripheral immune cells before, during, and after relapse, 2. reveal the earliest molecular mechanisms in the ontogeny of a relapse, and 3. identify and validate novel blood-based biomarkers of relapse.
Methods: We applied single cell RNA-sequencing (scRNA-seq) to 30 clinical blood samples from 6 RRMS patients and 6 age/sex matched healthy controls. Samples were drawn within 90 days before relapse, or during relapse, and paired with remission samples. A robust mixed-effects model was utilized to identify perturbed cell types and transcriptomic features associated with relapses. Cell-specific molecular features were characterized with minimal-bias signature-scoring and surface marker imputation. A set of prioritized, predictive biomarkers were derived from whole genome-sequencing, single cell gene expression, and imputed surface proteins. Finally, 309 bulk RNA-sequencing libraries of FACS-sorted CD3+, CD14+, and CD19+ cells were constructed from 71 additional MS patients at timepoints pre- and post-relapse to validate relapse features in an expanded cohort of patients.
Results: We observe a pre-relapse, pro-inflammatory transcriptional signature in MS patients up to 87 days prior to relapse. This signature, localized primarily within B cells, plasmacytoid dendritic cells (pDCs) and monocytes, is consistent with host response to reactivation (and lytic replication) of Epstein-Barr virus (EBV). The pre-relapse signature is attenuated in active relapse samples, which instead exhibit aberrant type 2 classical dendritic cell (cDC2) and CD8+ cytotoxic T cell features. The MS relapse-specific signatures are greater in magnitude than inter-patient heterogeneity observed in healthy controls.
Conclusions: Our data implicate a monocyte/dendritic cell response to EBV reactivation in B cells as one of the earliest events in the development of relapses in MS. The multi-omic cellular atlas offers a wealth of new blood-based biomarkers predictive of disease activity. Several of these pre-relapse mechanisms are potentially targetable with new and existing therapies, offering hope for more specific, personalized treatments for MS patients.
Abstract 2
Background: Multiple sclerosis (MS) is an immune-mediated CNS demyelinating disease. Epstein-Barr virus (EBV) has been implicated as a risk factor of MS. B cells, the target of EBV infection, play a critical role in MS disease mechanisms, along with the clonal expansion of CD8 T cells. However, how CD8 T cells respond to EBV-infected B cells in MS remains unclear.
Objectives: This study aimed to investigate the expanded subpopulation of CSF CD8 T cells linked to EBV-infected B cells in MS.
Methods: We performed bulk RNA sequencing (RNA-seq) of prospectively acquired cerebrospinal fluids (CSF) cell samples derived from 348 MS and 164 controls. We generated TCR repertoire library and performed weighted gene co-expression network analysis (WGCNA). We validated the major findings using cellular indexing of transcriptomes and epitopes (CITE-seq) data on CSF CD8 T cells from 13 MS patients and 5 controls and combined these with publicly available single cell RNA-seq data from MS CSF. An in vitro system using patient-matched peripheral blood mononuclear cells and lymphoblastoid cell lines (CSF-LCL) generated from CSF B cells assessed CD8 T cell responses to EBV-infected B cells.
Results: In CSF bulk RNA-seq, MS patients exhibited higher TCR clonality and specificity to EBV lytic proteins compared to controls. TCRs from MS patients showed greater clustering coefficient (i.e. TCR similarity) in complementarity-determining regions 3 (CDR3), particularly those predicted to target EBV antigens. Importantly, TCR clustering coefficient was associated with the expression of cytotoxic CD8 module genes in WGCNA, such as CD8A, GZMH, GZMK, and NKG7 and with interferon signaling module. scRNA-seq revealed a subpopulation of GZMK+GZMH+ double positive (DP) CD8 T cells expressing genes related to identified cytotoxicity and interferon signaling modules. These DP CD8 T cells had significantly higher predicted specificity for EBV proteins than other CD8 cells. In vitro PBMC co-culture with CSF-LCLs expanded autologous DP CD8 T cells, while these CD8 T cells exhibited some cytotoxicity to CSF-LCL.
Conclusions: Our study shows significant expansion of EBV-specific cytotoxic DP CD8 T cells in MS CSF, providing indirect evidence for the intrathecal EBV infection in MS.
Abstract 3
Background: Tolebrutinib is a brain-penetrant Bruton’s tyrosine kinase inhibitor (BTKi) that, in phase 3 pivotal trials, led to a 31% and 29% reduction in disability accumulation relative to placebo and teriflunomide in nrSPMS and RMS, respectively. MRI paramagnetic rim lesions (PRLs) are chronic active lesions associated with inflammation, demyelination, and axonal transection in the white matter and are correlated with disability accumulation and resistant to currently approved therapies. Because BTKi can modulate neuroinflammation driven by disease-associated microglia and B cells, we asked, in a post-hoc analysis, whether PRLs were associated with response to tolebrutinib.
Objectives: To evaluate PRLs observed at baseline as a prognostic and predictive biomarker for disability accumulation and treatment response in HERCULES and GEMINI.
Methods: HERCULES (NCT04411641), GEMINI 1 (NCT04410978), and GEMINI 2 (NCT04410991) were phase 3, double-blind trials of 60 mg tolebrutinib once daily. In HERCULES, participants were randomized 2:1 to receive tolebrutinib or placebo. In GEMINI, participants were randomized 1:1 to receive tolebrutinib or teriflunomide (14 mg once daily), each with matching placebo. 437 (39%) of the 1131 HERCULES participants and 631 (34%) of the 1873 GEMINI participants were from sites with imaging capabilities allowing evaluation of PRLs. Following prior studies, we analyzed the effect of tolebrutinib on time to onset of 6-month confirmed disability worsening (6-mo CDW) in participants with 0, 1-3, or ≥4 PRLs at baseline. PRLs were manually identified on SWI images generated from 3D-gradient echo phase images (6 echoes ranging from 4.9 to 41 ms, 0.8-mm isotropic resolution).
Results: Across both trials, 653 participants (61%) had PRLs, consistent with data from observational studies with high-sensitivity MRI sequences. In HERCULES, the proportion of participants with 0, 1-3, or ≥4 PRLs at baseline was 40%, 36%, and 24%, respectively, with similar proportions in GEMINI. In both HERCULES and GEMINI, the risk of 6-mo CDW increased as a function of baseline PRLs in the placebo and teriflunomide comparator groups, respectively. In HERCULES, tolebrutinib appeared to mitigate the risk of 6-mo CDW with greater effect in participants with more baseline PRLs, reducing the risk by 54% in participants with ≥4 PRLs. In GEMINI, a similar risk mitigation was observed with a 46% and 49% risk reduction in participants with 1-3 and ≥4 PRLs, respectively. In tolebrutinib-treated participants with PRLs in both HERCULES and GEMINI, the risk of 6-mo CDW was numerically similar to the corresponding risk in participants without PRLs.
Conclusions: This post-hoc analysis suggests that the impact of tolebrutinib treatment may be greater in those with higher number of PRLs, consistent with the CNS bioactive mechanism of action of tolebrutinib.
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Please note that the opinions expressed here are those of Professor Giovannoni and do not necessarily reflect the positions of Queen Mary University of London or Barts Health NHS Trust. The advice is intended as general and should not be interpreted as personal clinical advice. If you have problems, please tell your healthcare professional, who will be able to help you.
Email question: "PRLs, how are they identified? Is it a special request when doing MRI, or are they seen on routine MRIs? I’m not sure I have heard of them before……."
Paramagnetic rim lesions (PRLs) in multiple sclerosis are detected using susceptibility-weighted imaging (SWI) MRI sequences. These sequences allow visualisation of iron accumulation around specific lesions, appearing as a "rim" of high signal intensity on the image, indicating the presence of a PRL; these lesions are often best seen on high-field strength MRI scanners, such as 3T machines with appropriate imaging protocols. Please be aware that SWI sequences need to be requested and are currently not routine for MS disease monitoring.
Great summary (as always!). We had a small side-meeting discussing clinical trial strategies for remyelinating therapies. Being CMO of a company developing just such a therapy, I am obviously more optimistic than you regarding the possibility of having an approved remyelinating therapy to patients within a decade. I would also note that data from the ORATORIO study demonstrated that anti-CD20 was also pretty effective in reducing PRLs vs. placebo. Re EBV: there is no doubt that EBV infection plays a role in disease initiation (at least). It’s really unfortunate that no effort (with the exception of Patrick Küry in Dusseldorf) is being made toward understanding the potential role EBV in activation of HERV-env, a mechanism that could explain a lot of what we see.