It has been shown that extracellular adenosine triphosphate potentiated the chemotactic response to bone marrow-derived human mesenchymal stem cells and increased their migration.26 Dibutyryl cAMP increased expression of SDF-1 in wound tissue and enhanced endothelial progenitor cell migration.27 A link between CXCR4 and the A2B-receptor has been shown by a study about human colorectal carcinoma cells.5 Adenosine, which is present in the extracellular fluid of tumours because of their hypoxia, acted through A2A- and A2B-receptors to upregulate CXCR4-expression on tumour cells. Here, CXCR4 is linked to colorectal carcinoma.