MPN is initiated and maintained from a mutated hematopoietic stem cell (HSC). The interplay between the MPN HSCs and the stem cell niche is increasingly recognized as crucial for the biology of the disease. Dr. Simon Méndez-Ferrer et al, previously demonstrated that nestin-positive mesenchymal stem cells (nestin+ MSCs) within the bone marrow niche are innervated by sympathetic nerve fibers and are important in regulating normal HSCs. New findings by Dr. Méndez-Ferrer's laboratory show that these nestin+ MSCs are strongly reduced in bone marrow from patients with MPN.