 Dexter observed that mesenchymal stromal cells could maintain early HSCs "ex vivo", and both Lord and Gong showed that these cells localized to the endosteal margins in long bones.These studies and others supported the idea that bone cells create the HSC niche, and all the research that elucidated this specialized hematopoietic microenvironment stemmed from these landmark studies.Despite the vast work done in this field, there is still controversy over the origins of definitive HSCs.