We therefore searched for the presence of CD1a and CXCR4 co-expressing cells in PBMC (n = 17) and BMMC (n = 5) derived from 13 therapy-naive LCH-patients with different clinical manifestation forms (3 multi-system, 4 poly-ostotic, 5 mono-ostotic and 1 diabetes insipidus); samples were collected at different time points that is, at onset (n = 14, one PBMC and one BMMC were collected from the same patient), after initiating any form of treatment (n = 2), after reaching non-active disease (n = 4) or at LCH reactivation (one PBMC and one BMMC sample from the same patient). This evidence concerns the gene CD1A and diabetes insipidus.