Reversibility of low VLA-4, and CXCR-4 expression on peripheral blood CD34+ cells

Molecular mechanisms leading to mobilisation and homing of hematopoietic progenitor cells and stem cells probably involve a modulation of adhesion molecules expressed on these cells. This modulation could be induced by interactions between chemokines and their receptors, such as SDF-1 and CXCR-4. In the present study, we compared VLA-4 (α4/β1), VLA-5 (α5/β1) and CXCR-4 expression on peripheral blood CD34+ cells during a 3-day liquid culture in 10 % FBS αMEM and murine stromal MS-5 cell supernatant (containing high levels of SDF-1). CD34+ cells were purified from leukapheresis products after G-CSF mobilisation and tested for co-expression of α4, α5, β1 chains and CXCR-4 by direct immuno-fluorescence. An increased expression of α4 and β1 but not α5 was seen from d1, particularly with MS-5 cell supernatant and in a lesser extent with 10 % FBS αMEM. Values were respectively 146 and 113 % for α4, 148 and 121 % for β1 and 99 and 105 % for α5 as compared to d0 expression. CXCR-4 expression was maximally increased on d2 particularly with 10 % FBS αMEM (308 % of d0 expression) but this increase was less clear with MS-5 cell supernatant (233 % of d0 expression). Maximal VLA-4 expression reached levels which are originally observed on bone marrow CD34+ cells while the low levels of α5 were not modified. We are now investigating the precise role of SDF-1 in the modulating activity contained in such culture media.