On 2015 Mar 03, Dita Gratzinger commented:

We congratulate the authors on a comprehensive overview of this very complex and evolving field of research. Many of the crucial studies represent in vitro and mouse model research; we are characterizing the state of the intact bone marrow stroma in myelodysplastic syndromes. The authors state that

"Multiple data have shown that osteoprogenitors—MSPCs—exhibit normal morphology and frequency in the bone marrow of MDS patients, as well as undisturbed osteoblastic, adipocytic and chondrocytic differentiation potential in vitro."

We have recently published data, not available at the time this review was written, regarding the architecture and extent of the CD271+ mesenchymal stromal cell compartment in intact human bone marrow core biopsies Johnson RC, 2014, and in fact demonstrate an increase in the density of this compartment in higher grade MDS as compared to lower grade MDS and marrow from similarly aged cytopenic patients. We also found an association of high CD271+ mesenchymal stromal cell density with shorter overall survival among patients with MDS, independent of IPSS-R and history of transfusion. We acknowledge that it is not clear whether functionally described osteoprogenitors correspond to all or a subset of CD271+ mesenchymal stromal cells; however, as cited in your review, we have previously shown Flores-Figueroa E, 2012 that CD271+ mesenchymal stromal cells express CXCL12 and arborize extensively within marrow, in association with marrow vasculature, and are intimately associated with the majority of CD34+ hematopoietic stem/progenitor cells in intact human marrow, and are thus good candidates to represent a key functional component of the human bone marrow hematopoietic progenitor/stem cell niche.

On 2015 Mar 03, Dita Gratzinger commented:

We congratulate the authors on a comprehensive overview of this very complex and evolving field of research. Many of the crucial studies represent in vitro and mouse model research; we are characterizing the state of the intact bone marrow stroma in myelodysplastic syndromes. The authors state that

"Multiple data have shown that osteoprogenitors—MSPCs—exhibit normal morphology and frequency in the bone marrow of MDS patients, as well as undisturbed osteoblastic, adipocytic and chondrocytic differentiation potential in vitro."

We have recently published data, not available at the time this review was written, regarding the architecture and extent of the CD271+ mesenchymal stromal cell compartment in intact human bone marrow core biopsies Johnson RC, 2014, and in fact demonstrate an increase in the density of this compartment in higher grade MDS as compared to lower grade MDS and marrow from similarly aged cytopenic patients. We also found an association of high CD271+ mesenchymal stromal cell density with shorter overall survival among patients with MDS, independent of IPSS-R and history of transfusion. We acknowledge that it is not clear whether functionally described osteoprogenitors correspond to all or a subset of CD271+ mesenchymal stromal cells; however, as cited in your review, we have previously shown Flores-Figueroa E, 2012 that CD271+ mesenchymal stromal cells express CXCL12 and arborize extensively within marrow, in association with marrow vasculature, and are intimately associated with the majority of CD34+ hematopoietic stem/progenitor cells in intact human marrow, and are thus good candidates to represent a key functional component of the human bone marrow hematopoietic progenitor/stem cell niche.