MIT researchers validated a physical marker—T-cell buoyant mass—to predict patient response to immune checkpoint blockade, outperforming tumor mutational burden (TMB) in a 28-patient melanoma study. The approach uses suspended microchannel resonator (SMR) technology to measure cell mass and infer immune fitness after activation. In the reported analysis, buoyant-mass stratification better matched responders’ outcomes than molecular-only metrics. If replicated in larger cohorts, the method could offer a scalable, non-genetic alternative for manufacturing and clinical decision-making—potentially improving both biomarker selection and cell-culture yield evaluation for cell therapy workflows.