PDCD1 and collagenous colitis: It is not therefore a true model for collagenous colitis, but the very strong association with PD1/PD‐L1 blockade suggests that a further understanding of the impact of the blockade of this axis, not only on T cells51, 52 but also on other immune cells, macrophages and mesenchymal cells—may shed further light on the pathogenesis of this rare disease.4, 9