Increased CD271+ CXCL12 Chemokine Overproducing Mesenchymal Stromal Cells Maintain Distinctive Association with CD34+ Hematopoietic Progenitor/Stem Cells in Myelodysplastic Syndrome
Authors: Flores-Figueroa Eugenia , Varma Sushama , Montgomery Kelli , Greenberg Peter L. , Gratzinger Dita 
Published: October 2019

Abstract
Abstract 2789

Background:
The bone marrow microenvironment provides a crucial hematopoietic niche for survival and differentiation of hematopoietic progenitor/stem cells (HPSCs). The dysfunctional microenvironment in myelodysplastic syndrome (MDS) may provide a new source of prognostic and diagnostic information and even provide insight into the pathophysiology of the disease. We used tissue microarray (TMA) techniques combined with semi-automated image acquisition using double immunofluorescence and confocal microscopy to methodically and quantitatively analyze the interrelationships among key components of the bone marrow microenvironment and their relationships to CD34+ hematopoietic progenitor/stem cells (HPSCs) in intact human bone marrow derived from archival diagnostic paraffin-embedded core biopsy specimens representing benign (NL), MDS, and acute myeloid leukemia (AML) diagnoses.

Methods:
Whole bone marrow core biopsies (13 NL, 11 MDS, 7 AML) and 1 mmTMA cores (5 NL, 6 MDS, 4 AML) were evaluated. The area occupied by stromal cell populations was assessed using freely available ImageJ software. Adjacency of CD34+ HPSCs to specific cell populations was manually quantitated on double immunofluorescent-stained whole TMA core images.

Results:
CD271 (low-affinity nerve growth factor receptor/pNGFR) highlights an extensive arborizing MSC population, whereas nestin and CD146 (melanoma cell adhesion molecule, MCAM) localize to specific vascular compartments. In MDS, CD271+ MSCs are markedly increased as compared to benign marrow (p=0.012), whereas there is no significant change in CD146, nestin, or CD163+ macrophage populations (Table 1). We document an intimate and conserved relationship of the CD271+ MSC population to CD34+ HPSCs and quantitate the preservation of this relationship in MDS (Fig 1, Table 2). Remarkably, the CD271+ MSC population is in intimate contact with the majority of CD34+ HPSCs (86% on average) across NL, MDS and AML marrows, whereas no significant contact is seen with nestin+ or CD146+ vascular elements. In benign bone marrow expression of the pro-survival chemokine CXCL12 is largely restricted to the vasculature, whereas in MDS and AML CD271+ MSCs abnormally express CXCL12.

Conclusions:
We propose that CD271+ MSCs are candidates for a pathophysiologic role in MDS, and are candidate prognostic/diagnostic markers. We hypothesize that the relationship of MDS and AML CD34+ blasts with abnormal CD271+ MSC likely exposes neoplastic CD34+ HPSCs to aberrant contact-dependent signaling via the chemokine CXCL12 or other signals. We propose that the increased, dysfunctional, and spatially disarranged CD271+ arborizing MSC infrastructure may contribute to the ineffective hematopoiesis that is a defining feature of MDS by promoting inappropriate proliferation/survival of CD34+ HPSCs and by failing to support trafficking of maturing hematopoietic cells to microenvironmental compartments where they receive specific contact-dependent signals.
CD34+ HPSCs are in intimate and conserved contact with CD271+ MSCs at baseline and in myeloid neoplasia. CD34+ HPSCs (red) are in intimate contact with NGFR+ arborizing stromal cells (green). Representative photomicrographs of benign (NL), low-grade myelodysplastic syndrome/5Q minus (RA5Q), and high grade myelodysplastic syndrome/refractory anemia with excess blasts 2 (RAEB2).

Disclosures:
Greenberg: amgen: Consultancy, Research Funding; onconova: Research Funding; glaxosmithkline: Research Funding; novartis: Consultancy, Research Funding.