Background
Infantile haemangioma (IH), the most common tumour of infancy is a tumour of the vasculature, typically undergoes an initial proliferation phase, typified by aggressive angiogenesis, followed spontaneously by gradual involution with residual fibbrofatty tissue. Previous studies have demonstrated the expression the endothelial progenitor cell (EPCs) markers (CD34, CD133 & VEGFR-2) on the endothelium of IH micro-vessels, along with the abundance of these EPCs in the peripheral circulation of patients afflicted with IH. We propose that the endothelium of proliferating IH represents a primitive haemogenic endothelium phenotype with the capacity to give rise to primitive haemopoietic cells.
Aim
To investigate the expression of primitive mesoderm and haematopoietic markers and the ability for primitive erythropoiesis in IH.
Methods
Immunohistochemistry & RT-PCR was performed on 6 proliferating and 6 involuted IH specimens for the primitive mesoderm marker (brachyury), primitive haematopoietic markers (Tal-1, GATA-2, angiotensin converting enzyme (ACE) & CD133), and the erythropoiesis markers (erythropoietin receptor (EPOR) and HBZ).
6 proliferating IH specimens were grown as explants in vitro and erythropoietin + IL-3 were added to the explant derived cells for a total of 6 days. Cells were then extracted and stained for the erythrocyte marker (Glycophorin A) and HBZ.
Results
The endothelium of all proliferating IH lesions expressed Brachyury, Tal-1, GATA-2, ACE, CD133, EPOR & HBZ.
Cells derived from explants of proliferating IH specimens showed a biconcave morphology in the presence of EPO + IL-3, and confirmed to be primitive erythrocytes by the expression of gylcophorin A and HBZ.
Conclusion
The expression profile of primitive haematopoietic markers on the endothelium of IH. The functional capacity for cells derived from IH explants to undergo embryonic erythropoiesis infers a putative stem cell origin for IH, and a developmental anomaly nature of this tumour.