cDNA cloning of FRIL, a lectin from Dolichos lablab, that preserves hematopoietic progenitors in suspension culture

Ex vivo culture of hematopoietic stem cells is limited by the inability of cytokines to maintain primitive cells without inducing proliferation, diffe rentiation, and subsequent loss of repopulating capacity. We identified rec ently in extracts of kidney bean and hyacinth bean a mannose-binding lectin , called FRIL, and provide here evidence that this protein appears to satis fy properties of a stem cell preservation factor. FRIL was first identified based on its ability to stimulate NIH 3T3 cells transfected with Flt3, a t yrosine kinase receptor central to regulation of stem cells. Molecular char acterization from polypeptide sequencing and identification of the cDNA of hyacinth bean FRIL shows 78% amino acid identity with a mannose-binding lec tin of hyacinth beans. Treatment of primitive hematopoietic progenitors in suspension culture with purified hyacinth FRIL alone is able to preserve ce lls for 1 month without medium changes. In vitro progenitor assays for huma n hematopoietic cells cultured 3 weeks in FRIL displayed small blast-like c olonies that were capable of serial replating and persisted even in the pre sence of cytokines known to induce differentiation. These results suggest t hat FRIL is capable of preserving primitive progen itors in suspension cult ure for prolonged periods. FRIL's clinical utility involving procedures for stem cell transplantation, tumor cell purging before autologous transplant ation, and ex vivo cultures used for expansion and stem cell gene therapy c urrently are being explored.