Macrophages (green) engulfing melanoma cells (purple). Keith et al. / Garvan Institute, CC BY-SA For the past 15 years or so, a class of drugs called immune checkpoint inhibitors have been used to treat melanoma – the most dangerous kind of skin cancer. For many patients, they produce remarkable results. For others, they do nothing. We still don’t really know why. But in new research published in the Journal of Experimental Medicine, we observed immune cells called macrophages attacking melanom