MIT researchers reported validation of a new physical marker—measuring buoyant mass of T cells—as a predictor of response to immune checkpoint blockade. In a clinical study of 28 melanoma patients receiving ICB, buoyant-mass measurements predicted treatment response more accurately than tumor mutational burden. The approach uses suspended microchannel resonator (SMR) technology to quantify T-cell buoyancy relative to water, aiming to infer immune fitness—how likely T cells are to activate after expansion. The work suggests that non-molecular cell properties may integrate multiple biological signals that gene-based markers don’t capture. For cell therapy and immuno-oncology manufacturing, the paper also frames buoyant mass as a potential tool to improve cell culture productivity and decision-making beyond conventional genomics-driven biomarkers.