Spatial gradients of blood vessels and hematopoietic stem and progenitor cells within the marrow cavities of the human skeleton

This report evaluates the spatial profile of blood vessel fragments (BVFs) and CD34⁺ and CD117⁺ hematopoietic stem and progenitor cells (HSPCs) in human cancellous bone. Bone specimens were sectioned, immunostained (anti-CD34 and anti-CD117), and digitally imaged. Immunoreactive cells and vessels were then optically and morphometrically identified and labeled on the corresponding digital image. The distance of each BVF, or CD34⁺ or CD117⁺ HSPC to the nearest trabecular surface was measured and binned in 50-μm increments. The relative concentration of HSPCs and BVFs within cancellous marrow was observed to diminish with increasing distance in the marrow space. On average, 50% of the CD34⁺ HSPC population, 60% of the CD117⁺ HSPC population, and 72% of the BVFs were found within 100 μm of the bone surfaces. HSPCs were also found to exist in close proximity to BVFs, which supports the notion of a shared HSPC and vessel spatial niche.