The plant lectin FRIL supports prolonged in vitro maintenance of quiescenthuman cord blood CD34(+)CD38(-/low)/SCID repopulating stem cells

Objective. Ex vivo maintenance of human stem cells is crucial for many clin ical applications. Current culture methods rely on optimized combinations o f cytokines. Although these conditions provide some level of stem cell supp ort, they primarily induce proliferation and differentiation, resulting in reduced repopulation capacity. Materials and Methods. The recently identified legume lectin FRIL has been shown to preserve human cord blood progenitors up to a month in suspension culture without medium changes. To test whether FRIL also preserves human S CID repopulating stem cells (SRC), we cultured human CD34(+) cord blood cel ls in medium containing FRIL, with or without subsequent exposure to cytoki nes. and tested their repopulating potential. Results. We report that FRIL maintains SRC between 6 and 13 days in culture . Incubation of CD34(+) cells with FRIL results in significantly lower numb ers of cycling cells compared with cytokine-stimulated cells. CD34(+) cells first cultured with FRIL for 6 days and subsequently exposed to cytokines for an additional 4 days generated significantly more mononuclear and proge nitor cells and higher levels of engraftment in NOD/SCID mice compared with CD34(+) cells cultured with FRIL alone. Similar results were obtained with CD34(+)CD38(-/low) cells, including expansion of SRC that were cultured in FRIL followed by cytokine stimulation. Moreover, CD34(+) cells precultured with FRIL successfully engrafted primary and more importantly secondary re cipients with lymphoid and myeloid cells, providing further support that FR IL maintains SRC for prolonged periods. Conclusion. FRIL's ability to preserve quiescent primitive cells in a rever sible manner may significantly expand the time and range of ex vivo manipul ations of human stem cells for clinical applications. (C) 2000 Internationa l Society for Experimental Nematology. Published by Elsevier Science Inc.