Indeed, recent studies have demonstrated that PD1 is expressed by various immune cells including T cells and a subset of myeloid cells.30 Based on CyTOF data, we found that PD1 is expressed not only by CTLs, but also by B cells, macrophages as well as granulocytes in the blood but not in the tumor (figure 3A), in line with previous publications.30–32 Thus, it is possible that anti-PD1 treatment affects PD1-expressing ‘on-target’ CTLs or other ‘off-target’ immune cell types, in a manner that ultimately contributes to tumor aggressiveness. The gene discussed is PDCD1; the disease is neoplasm.