When RA is limited via dietary uptake, HSC are activated to proliferate and differentiate.79 This is in line with findings that loss of the RA receptor retinoic acid receptor γ (RARγ) leads to decreased HSC number and increased differentiation.80 The same study also showed that RARγ activation increases the self‐renewing capacity of HSC.80 Besides regulating HSC dormancy directly, the BM stroma actively participates in the control of and response to RA levels. Here, RARG is linked to rheumatoid arthritis.