This is a clinical trial to see whether senolytic therapy is safe and feasible for patients with secondary progressive MS and whether treatment improves physical and thinking abilities. The study seeks to enroll adults with secondary progressive MS (SPMS), aged 50-85, who are not currently taking a MS disease-modifying therapy and have noticed their MS symptoms getting worse. People who join the study will take the medicines dasatinib and quercetin by mouth every two weeks for three months. These medicines work together to remove old, damaged cells that may cause inflammation and slow the repair of nerves. Participants will also be followed for one year from enrollment to monitor for treatment effects.