Adhesion molecules on peripheral blood-derived CD34+ cells: effects of cryopreservation and short-term ex vivo incubation with serum and cytokines.

The homing of hematopoietic precursor cells (HPC) within the bone marrow is most likely to be mediated by specific adhesion via surface receptors to cellular and extracellular matrix (ECM) components and to be regulated by cytokines. We investigated the effects of serum and cytokines on the expression of adhesion molecules on cryopreserved and fresh peripheral blood-derived progenitor cells (PBPC) and on the adhesion of PBPC to various ECM proteins. PBPC were collected from patients by leukapheresis during G-CSF-supported recovery from conventional cancer chemotherapy. Freezing markedly reduced the fraction of CD34+ cells with L-selectin (CD62L) expression from 62 to 11% and also diminished the fluorescence intensity for the integrin subunits CD29 and CD49d on CD34+ cells. A 14 h incubation of thawed PBPC with serum induced re-expression of adhesion molecules. The addition of the cytokine cocktails (G-CSF + SCF + IL-3 + IL-11 or IL-4 + IL-1beta + IFN-gamma) or MGDF, however, exerted no effects in addition to serum alone. Furthermore, when compared to serum alone, the addition of cytokine cocktails or MGDF did not alter the fraction of fresh PB-CD34+ cells adhering to collagen I, collagen IV, fibronectin, laminin or vitronectin. HPC adhesion to ECM components might be refractory to short-term alterations of the cytokine environment. Alternatively, longer incubation times or other cytokines may be necessary to modulate the expression of adhesion molecules on hematopoietic progenitor cells or adhesion itself under ex vivo conditions.