Dynamics of macrophage tumor infiltration

Long-term remission in cancer patients treated with ex vivo bona fide M1-induced macrophages has been poor, and the reasons behind this are not understood. Injected M1 macrophages must physically migrate to tumors to execute their role that leads to a therapeutic benefit. However, the trafficking of macrophages to tumors has not been rigorously studied. We hypothesized that trafficking capabilities of macrophages are impacted when naive M0 macrophages are converted into an M1 phenotype for macrophage therapy. To test this, we developed a three-dimensional assay comprising a tumor spheroid and macrophages to quantify macrophage tumor transport. Cell migration, permeability, and kinetics of tumor entry were quantitatively defined and compared between macrophage phenotypes. Our results demonstrate that compared to M0 macrophages, M1 macrophages migrate less efficiently toward the tumor spheroid and exhibit a fivefold lower tumor permeability. Live imaging data combined with unsupervised machine learning algorithms reveal that macrophage migration correlates with their shape transitions. Our studies highlight the importance of transport considerations in determining the efficacy of cell therapies. This study quantitatively demonstrates that the transport properties of macrophages in tumors depend on their phenotype.