Unlike haematological diseases where the gene (haemoglobin), cell (red blood cell) and clinical features (anaemia) map well onto each other, the cellular basis for most inflammatory diseases remains enigmatic. The Human Cell Atlas (HCA) was established to construct a map of the different cell types involved in forming human organs using single cell analysis with spatial analysis to locate their position in tissue. Using the principles of the HCA in an Arthritis Therapy Acceleration Programme (A-TAP) we have assessed how the cellular composition of tissue is affected following treatment with biologics such as anti TNF across a range of IMIDs including RA and IBD. This therapeutic cell atlas can be used to instruct and power experimental medicine studies where a common cell-based marker is used in Bayesian driven basket trials as a common outcome measure in the study.