Bites that kill: Understanding cancer cell fate after macrophage mediated trogocytosis

Macrophage therapies are an exciting avenue for targeted cancer cell killing in tumors. Macrophages phagocytose (that is, whole cell engulfment) of dying, dead, and abnormal cells. However, it's been observed that in solid tumors, macrophages primarily perform trogocytosis or nibbling, where they tear away portions of solid tumor cells. Trogocytosis in tumors is observed to be paradoxical: while it allows immune cells to strip away antigen from the cancer cell surface and thus allowing cancer progression. Conversely, it can cause cancer cell death, aiding immunotherapy. This dichotomous result raises the question of how to leverage trogocytosis in immunotherapy to be consistently lethal. We observe higher rates of trogocytosis compared to phagocytosis with Chimeric Antigen Receptor macrophages (CAR-M) when interacting with solid tumor cells. Our 3D tumor spheroid model constructed with SKOV3 cells shows a significant reduction in size with Her2CAR macrophages, with higher trogocytosis. I observe trogocytosed cancer cells to undergo apoptotic cell death via specific targeting by Her2CAR macrophages in 2D cell cultures. However, interestingly, death is not immediate in the co-cultures; instead, it happens following sustained trogocytic attack. In the first 2 hours of co-culture, when trogocytosis is significantly higher than phagocytosis, there's no cancer cell death. Our 3D tumor spheroid model also shows a reduction in spheroid diameter with Her2CAR macrophages after 5 days of co-culture. The cancer cell death can be blocked with a pan-caspase inhibitor Q-VD-Oph. The delayed cancer death suggests that trogocytosed cancer cells overcome initial, non-lethal loss of cell membrane; however, continual trogocytic attack renders cancer cells susceptible to apoptosis at later timepoints. Continuous loss of the cell membrane, followed by continual repair while maintaining homeostasis, is an energy-expensive process for the cancer cells. Thus accumulation of sustained stress in the trogocytosed cancer cells can ultimately push them to undergo apoptosis. I am currently investigating oxidative stress accumulation for activation of apoptosis in trogocytosed cells. Further, a change in transcriptomic profile for certain genes following 3-day co-culture with Her2CAR macrophages is also observed, suggesting the trogocytosed cells can alter their transcriptomic response to trogocytosis. Under current investigation is whether accumulated stress in trogocytosed cells causes this change in transcriptomic profile. CAR-M presents a promising avenue for targeting tumors. However, their efficacy in solid tumors needs to be improved. We observe continual trogocytosis pushes cancer cells to apoptosis at later timepoints. Thus, to make trogocytosis lethal in immunotherapy, understanding the trogocytosed cell response and investigating the fate of trogocytosed cells is essential.