Lectin‐induced increase in clonogenic growth of haematopoietic progenitor cells

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Abstract
The galactoside‐specific plant lectin, Viscum album agglutinin (VAA‐I) increases cellular parameters of natural host defence. It also binds to a variety of haematopoietic cells, including progenitors. We investigated whether VAA‐I has a stimulatory effect on haematopoietic progenitor cells. Peripheral blood progenitor cells from 7 healthy volunteers were cultured in a colony assay with VAA‐I plus erythropoietin (EPO) and stem cell factor (SCF). At 50 pg/ml VAA‐I induced a significant increase in the cytokine‐dependent clonogenic growth (52% in median, p<0.05). In another set of experiments purified CD34+ cells were isolated from the bone marrow aspirate of 4 patients with non‐metastatic breast cancer using fluorescence‐activated cell sorting. Binding to CD34+ cells was demonstrated by using directly fluorescence‐conjugated VAA‐I. Co‐incubation with d‐galactose significantly abrogated this effect. CD34+ cells were cultured in the presence of EPO, SCF, interleukin‐3, granulocyte/monocyte colony‐stimulating factor and granulocyte colony‐stimulating factor. VAA‐I alone had no measurable effect on the clonogenic growth of the isolated cells. However, at concentrations of 100 and 250 pg/ml VAA‐I increased the cytokine‐dependent proliferation and differentiation of CD34+ cells by a median of 75 and 85%, respectively. The results show that VAA‐I binds to haematopoietic progenitor cells and has a co‐stimulatory effect on their proliferation.