Clearing a scar-driving macrophage reopened tumors to immunotherapy in mice

The biology sits in cellular senescence, a stress response that pushes a cell to permanently stop dividing ^[9]. That is often useful. It can shut damaged cells down before they turn cancerous, and it helps coordinate wound healing by sending signals that pull other cells to an injury ^[10]. The trouble starts when senescent cells do not clear once the repair is done. Lingering, they keep broadcasting the same signals, which now drive chronic inflammation and fibrosis ^[11]. "Senescence is a double-edged sword," said Scott Lowe, who chairs the Cancer Biology and Genetics Program at MSK's Sloan Kettering Institute ^[12][7].

So the hard part is precision. "The challenge has been how to target just the harmful cells while preserving the helpful ones," Lowe said ^[13]. The team's opening was a marker. Within macrophages, a small subset carried both the surface protein P-selectin and the hallmarks of senescence, a population they named MΦP+sen+ ^[14]. "What was striking was how consistently we found this specific population of macrophages in fibrotic tissue," said Clemens Hinterleitner, a co-first author ^[15][21]. Those cells sit in the fibrotic niches of liver and lung tumors and in scarred liver and lung tissue without cancer, and their presence tracks with worse immunotherapy responses in patients ^[16]. They both build the scar and suppress other immune cells ^[17]. "By sending out profibrotic and immunosuppressive signals, they essentially put up a wall that keeps the immune system from being able to do its job," said Valentin Barthet, a co-first author ^[18][21].

The engineered nanoparticles, about 1,000 times smaller than the width of a human hair, were built to carry a drug and clear that population selectively, with the aim of minimal toxicity to healthy cells ^[3][4]. The causal test ran in mice: in models of liver and lung fibrosis and of fibrotic liver and lung cancers, the work reduced scarring and enabled an immunotherapy response ^[19][22]. The human side of the paper is correlational. The team confirmed the same cells in tumor samples from lung cancer patients treated at MSK and in human lung and liver cancer datasets, where their presence lined up with poorer outcomes ^[20][16]. The human data cannot show whether removing the cells changes a patient's outcome; that step was done only in mice ^[19][20]. The report does not give the size of the effect in mice.

Lowe's case for the effort was plain. Immunotherapy "doesn't work for the vast majority of patients," he said, and "anything we can do to make it work better and for more people is worth pursuing" ^[8]. Because the same senescent macrophages appear in scarred tissue without cancer, the authors say the approach could reach other fibrotic and inflammatory diseases ^[6][16].