Reduced CD26 Dipeptidylpeptidase IV Membrane Expression and Activity of CD34+ Cells from Patients with Myelofibrosis with Myeloid Metaplasia.

Myelofibrosis with Myeloid Metaplasia (MMM) is characterized by an abnormal constitutive mobilization of CD34+ stem/progenitor cells. The SDF-1alpha axis chemoactracts hematopoietic stem and progenitor cells and is thought to play a crucial role in the homing/mobilization of these cells from the bone marrow, interacting with its unique receptor CXCR4. CD26 (dipeptidylpeptidase IV/DPPIV) is an extracellular peptidase, present both as membrane-bound and as a catalitically active soluble form in plasma. It has the ability to cleave SDF-1alpha at its position-2 proline inducing significant changes in its receptor binding and/or functional activation, thus inhibiting normal SDF-1alpha induced migration. In this study we evaluated the expression of CD26/DPPIV in patients with MMM (N=63) and its functional activity (N=8). CD26/DPPIV cell surface expression was measured by flow cytometry on peripheral blood mononuclear cells (PBMNC) or on immunoselected circulating CD34 + cells. The CD26/DPPIV activity was measured in 96-well microplates using the chromogenic substrate gly-pro-p-nitoanilide. The proteolytic activity was determined by measurements of the amount of nitoanilide (pNA) formed in the supernatant at 405 nm. Absorbance was measured at 405 nm and the picomoles of pNA formed were calculated by comparison with a pNA standard curve. The CD26 expression on the membrane of PBMNC of patients with MMM was comparable to that found on PBMNC of normal controls (median 29.5 %, range 0.72–61.1; median 33.1 %, range 20.3–39.2, respectively). However, the percentage of circulating CD34+CD26+ cells was significantly reduced (P<0.05) in patients with MMM (median, 0.2 %, range 0–48.4%) with respect to normal controls (median 10.3 %, range 0–30.2%). The CD26/DPPIV activity evaluated on purified circulating CD34+ cells from patients with MMM was significantly lower (p<0.03) than that of CD34+ cells from normal controls (median 14.2 pmol, range 0–45.6; median 67.2 pmol, range 34.5–81.1, respectively). The same activity, evaluated on CD34− circulating cells was comparable between patients with MMM and normal controls. In addition, the peptidase activity mediated by the sCD26 was significantly lower (p<0.03) in patients with MMM (median value of absorbance, 409; range 281–681) than in controls (median 518, range 494–550). In summary, our data show that both CD26 expression and its peptidase activity are lower in circulating CD34+ cells of patients with MMM than in CD34+ cells of normal controls; similarly, a significant reduction of the activity of sCD26 peptidase, derived from all the CD26+ peripheral blood cells, was found in patients with MMM compared with controls. These novel findings suggest that not only modifications of CXCR4 expression but also an altered regulation of SDF-1 activity can affect the correct function of the CXCR4/SDF-1 alpha axis in patients with MMM.