plasma treatment, the SPSM supports long-term spheroid culture (>14 days) with high viability (>95%) and minimal handling. Its utility is validated in cytotoxicity assays using doxorubicin (DOX) and chimeric antigen receptor (CAR) T cells, where label-free efficacy assessment based on spheroid size correlates with fluorescence staining in commercial ultralow attachment (ULA) plates. This platform provides a robust and quantitative approach for evaluating drug and immune cell therapies, readily adaptable for broader immuno-oncology investigations.