Cytokine Induced Changes in the Hematopoietic Stem Cell Trafficking Regulatory Peptidase CD26.

Hematopoietic stem cell transplantation (HSCT) serves as a successful treatment option for patients with malignant or non-malignant severe hematologic diseases. However, large numbers of transplantable donor cells are needed and patient survival is compromised when donor cell numbers are limited, as is the case when umbilical cord blood (CB) donor cells are utilized as a donor source for transplantation into adult patients. Given that CB is readily available, has a lower histocompatibility requirement, and has a reduced risk of graft vs. host disease (GVHD) there are advantages to utilizing CB for HSCT, in particular when an appropriate matched donor is not available. However, in the majority of cases potential recipients have been confined to children because in adults, the amount of CB collected appears to be a limiting factor. Given the promise of CB for HSCT there is significant potential and application for improvements in the efficiency of Hematopoietic Stem Cell (HSC) trafficking to the bone marrow (BM) in both scenarios. To facilitate our long term goal of improving HSCT efficiency, we have recently delineated a novel method by where the inhibition of peptidase CD26 on donor HSC and Progenitor Cells (HPC) increases the number of donor HSC/HPC trafficking to recipient’s BM, resulting in a significant increase in HSC transplant efficiency.

CD26 (DPPIV/dipeptidylpeptidase IV) is a membrane bound extracellular peptidase that cleaves dipeptides from the N-terminus of polypeptide chains. Natural substrates of CD26 protease activity include the pancreatic polypeptide family, the glucagon family, and the chemokine family. Since the removal of N-terminal amino acids from chemokines frequently result in significant changes in functional activity, proteolytic cleavage of chemokines has significant implications with respect to their ability to act on cells. We have previously shown that that suppression of CD26 activity, by the use of CD26 inhibitors or the use of CD26^−/− donor cells, increases the efficiency of HSC/HPC settlement and growth in the transplanted recipient. This translates into an increase in overall recipient survival in mice.

We report here the results of experiments that examine the ability of several cytokines to alter CD26 on the surface of CD34⁺CD38⁻ phenotypically defined HSC/HPC from CB. HSC isolated from CB were treated with varying dilutions of either Stem Cell Factor (SCF/steel factor/kit ligand), Granulocyte-Colony Stimulating Factor (G-CSF), Granulocyte Macrophage-Colony Stimulating Factor (GM-CSF), Erythropoietin (EPO), or Trombopoietin (TPO) during culture in IMDM, 20% FBS, 37°C, 5%CO₂ for 18 hours and then analyzed for changes in CD26. We observed significant dose dependent increases in the percentage of cells expressing CD26 and the amount of CD26 being expressed on each cell in samples treated with G-CSF, GM-CSF, and SCF as measured by multi-varient flow cytometric analysis. More modest changes in CD26 expression were observed during EPO and TPO treatment. Differential expression of CXCR4 was also noted. We feel these observations have important clinical implications with respect treatment of donor cells prior to transplantation and treatment of patients post HSCT.