Prominence of nestin-expressing Schwann cells in bone marrow of patients with myelodysplastic syndromes with severe fibrosis.

Nestin-expressing stromal cells (NESCs) and Schwann cells in the bone marrow (BM) play crucial roles as a niche for normal hematopoietic stem cells in mice. It has been reported that both types of cells are decreased in myeloproliferative neoplasms in patients and also in a mouse model, whereas an increase in NESCs was reported in acute myeloid leukemia. It is thus of interest whether and how these BM stromal cells are structured in myelodysplastic syndromes (MDS). Here, we focused on NESCs and glial fibrillary acidic protein (GFAP)-expressing cells in the BM of MDS patients. We found a marked increase of NESCs in MDS with fibrosis (MDS-F) at a high frequency (9/19; 47.4%), but not in MDS without fibrosis (0/26; 0%). Intriguingly, in eight of the nine (88.9%) MDS-F cases with elevated NESCs, a majority of NESCs also expressed GFAP, with an additional increase in GFAP single-positive cells. Furthermore, in seven of them, we found a prominent structure characterized by neurofilament heavy chain staining surrounded by NESCs with GFAP expression. This structure may represent peripheral nerve axons surrounded by Schwann cells, and could be relevant to the pathophysiology of MDS-F.