A new Nature Biotechnology approach, single-cell spatial pharmacobiology (SSP), mapped how systemically infused therapeutic antibodies behave inside patient tumors at single-cell resolution. Published work applied SSP to head-and-neck and pancreatic tumor samples from individuals treated in Phase 1 trials. Researchers reported spatial heterogeneity in both antibody delivery and target engagement, shaped by stromal barriers. The work combines in situ imaging of fluorescent antibodies with high-plex spatial proteomics—effectively turning distribution and engagement into measurable, cell-level pharmacodynamic signals. For drug developers, the study points toward a more rigorous way to connect dosing, tissue barriers, and on-target biology without relying solely on bulk readouts.