Epstein-Barr Virus Link to MS Spurs New Vaccine and T-Cell Trials

A common teenage bout of mononucleosis can look, in hindsight, like the opening chapter of a multiple sclerosis (MS) diagnosis that does not arrive until a decade later. Epstein-Barr virus (EBV), the herpesvirus behind most mononucleosis cases, has emerged as a near-universal prerequisite for MS, and a review published in Lancet Neurology laid out how that link works at a cellular level and cataloged the therapies now being tested to interrupt it.¹

A Trigger, Not the Whole Story

EBV eventually infects roughly 90% of adults in mid-latitude regions, yet only about 0.1% of those carriers go on to develop MS, underscoring that the virus is necessary but not sufficient on its own. The strongest evidence for a causal role comes from a 20-year analysis of more than 10 million young adults in the US military, which found a 32-fold greater risk of MS among individuals who underwent EBV seroconversion compared with those who stayed seronegative, according to the review. A related analysis from the National Institutes of Health, drawing on the same military cohort, similarly concluded that most MS cases could theoretically be prevented by stopping EBV infection outright.²

The review's authors wrote that these findings "strongly support the concept that Epstein–Barr virus infection is, in most cases, necessary for the development of multiple sclerosis."¹

Genetics Narrow Who Is At Risk

Why so few EBV carriers develop MS appears to come down to a combination of genetic and immune factors. Carriers of the MHC class II allele HLA-DRB1*15:01 who also have MS tend to show elevated antibody levels against EBV nuclear antigen 1 (EBNA1), and the review noted that the allele and the antibody response act synergistically to raise MS susceptibility.

EBV infection also appears to reprogram B cells: a viral protein called EBNA2 binds several of the genetic risk loci already linked to MS, and infection promotes expansion of atypical, neuroinvasive B cells that migrate toward the central nervous system and are enriched in inflamed brain and spinal cord tissue in people with MS. Once inside the central nervous system, these B cells efficiently activate autoreactive T cells, and a separate viral protein, latent membrane protein 1, appears to help the infected B cells survive there longer than they otherwise would.

Vaccines Aim To Prevent Infection Before It Starts

Several prophylactic EBV vaccines designed to block the primary infection altogether have already completed or advanced through early testing in healthy volunteers: 2 gp350-based nanoparticle vaccines finished phase 1 and phase 1/2 testing in adults aged 18 to 29 and 18 to 25, respectively (NCT04645147; NCT05683834), while an mRNA vaccine encoding several EBV glycoproteins remains active in adolescents and adults aged 10 to 30 (NCT05164094) and a related mRNA candidate continues in adults aged 18 to 55 (NCT05831111).

On the treatment side, a therapeutic version of one of those mRNA vaccines is now recruiting adults with relapsing MS aged 18 to 55 (NCT06735248), and a single-center phase 1 trial of autologous EBV-specific T cells is recruiting people with MS aged 18 to 45 (NCT02912897). A phase 2 study of the antiviral tenofovir/emtricitabine in people with MS is enrolling by invitation (NCT05957913); a related add-on trial pairing an antiviral with anti-CD20 therapy was withdrawn before enrolling any participants, for funding reasons unrelated to safety or efficacy.

Not Every Approach Has Worked

Not every therapy aimed at EBV has panned out. A terminated phase 1/2 trial of adoptive transfer of EBV-specific T cells in people with progressive MS did not meet its primary end point of confirmed disability improvement at 12 months, even though a separate, earlier pilot study of a similar T-cell approach had produced sustained clinical improvement in 3 of 10 participants with progressive MS. The review's authors cautioned that overly ambitious primary end points, such as confirmed disability improvement on a single scale, might have led to underestimating the therapy's biological effect.

The review itself carries its own limits: it was based on a literature search of PubMed, medRxiv, and bioRxiv restricted to English-language articles published between January 2023 and February 2026, and it stopped short of resolving whether EBV drives ongoing disease progression after MS onset or acts only as an initial trigger.

What It Means for Clinicians and Patients

The practical takeaway is not yet a new prescription, since none of the EBV-targeted vaccines or cell therapies have reached approval. But the pipeline signals a shift toward addressing a root biological trigger of MS rather than only suppressing the immune response after the disease has already taken hold.

The review's authors called for larger randomized trials with outcome measures that go beyond the standard disability scale, including advanced imaging and fluid biomarkers capable of catching subtler signs of progression, and flagged pediatric MS as a population that could reveal how early in life the EBV-MS relationship actually begins. Results from the ongoing prevention and treatment trials are expected to clarify how much of MS risk, activity, and progression can ultimately be attributed to this common virus.

References

1. Lünemann JD, Münz C. Epstein-Barr virus and multiple sclerosis: from associations to mechanisms to potential therapies. Lancet Neurol. 2026;25(8):755-763. doi:10.1016/S1474-4422(26)00177-8

2. Doctrow B. Study suggests Epstein-Barr virus may cause multiple sclerosis. NIH Research Matters. National Institutes of Health. Published February 1, 2022. Accessed July 23, 2026. https://www.nih.gov/news-events/nih-research-matters/study-suggests-epstein-barr-virus-may-cause-multiple-sclerosis