FAS ANTIGEN (CD95) EXPRESSION IN PERIPHERAL-BLOOD PROGENITOR CELLS FROM PATIENTS WITH LEUKEMIA AND LYMPHOMA

Fas antigen (CD95) is a cell surface receptor belonging to the tumour necrosis factor/nerve growth factor superfamily and is able to induce apoptosis when triggered by its' natural ligand or an anti-Fas antibod y. Fas expression is low on CD34(+) bone marrow (BM) progenitor cells, but is increased by various cytokines in vitro. We investigated Fas e xpression on CD34(+) cells from 39 peripheral blood progenitor cell (P BPC) harvests and from 5 normal BM harvests by dual colour flow cytome try to determine if Fas expression was altered during mobilisation. By including calibrated microbeads during flow cytometry, we quantified the number of Fas antigen molecules per cell. A low percentage of PBPC (22%) and normal BM (23%) CD34(+) cells expressed Fas antigen. Fas ex pression varied on CD34(+) cells from different diseases and the highe st expression was found in ALL (52%). There was a significant three fo ld increase in the number of Fas molecules/cell expressed on CD34(+) c ells (PBPC 6,230 molecules/cell, BM 2,236; p = 0.0003). This level of expression was considerably less than that for CD3/CD19 lymphocytes (3 3,095 molecules/cell) and CD14 monocytes (47,467 molecules/cell) in th e PBPC harvest, In conclusion, mobilisation including the use of growt h of factors, has minimal effect on CD34 progenitor cell Fas expressio n.