Researchers have identified serum CST5 as a predictive marker of resistance to anti-CD20 antibody therapy in multiple sclerosis (MS) patients. Proteomic profiling of patient sera suggests CST5 levels may stratify patients likely to respond to treatments like ocrelizumab, facilitating personalized therapy optimization. This discovery provides critical leverage for tailoring immunotherapies in MS, a disease with varying patient responses to B cell-depleting agents.