Epstein-Barr virus lives inside 95% of adults on Earth. You probably caught it as a teenager — it causes mono, hides inside your immune cells, and stays dormant for life. A landmark 2022 Harvard study tracking 10 million U.S. military personnel found that EBV infection increases the risk of developing multiple sclerosis by 32 times. Among the small group who never caught EBV, almost none developed MS. The virus isn’t just associated with the disease — it appears to be required for it.
Now a team at UC San Francisco led by Dr. Joe Sabatino has caught EBV in the act. Published February 5th, 2026, in Nature Immunology, their study examined CD8+ killer T cells — the assassins of the immune system that most MS research had overlooked in favor of CD4+ helper T cells. In MS patients, these killers were 10 to 100 times more concentrated in the cerebrospinal fluid than in blood, compared to an even distribution in healthy controls. Many of them specifically targeted Epstein-Barr virus. Most critically, the team found one specific EBV gene active only in MS patients — silent in healthy carriers of the same virus.
The emerging picture is devastating in its elegance. EBV partially reactivates in the nervous systems of MS patients, expressing a gene that provokes a massive immune response. Killer T cells flood in to attack the virus, and in the process, they cause collateral damage to the myelin coating on nerve fibers — like calling an airstrike on a building because there’s one enemy combatant inside. A separate Stanford study found that part of the EBV protein mimics a brain protein called GlialCAM, suggesting molecular mimicry may compound the direct viral provocation.
The therapeutic implications are enormous. Moderna has an mRNA vaccine against EBV in Phase 1 clinical trials — if it works, vaccinating teenagers before they encounter EBV could potentially prevent MS within a generation. For the nearly one million Americans already living with MS, researchers are exploring therapies to suppress the specific viral gene or clear EBV-infected cells from the nervous system. After six decades of investigating EBV since its discovery in 1964, science is finally connecting the dots from “weird correlation” to specific gene, specific cells, and specific mechanism.