Background: Used leuko-depletion filters (LDFs), containing billions of white blood cells (WBCs), are discarded. Because the steady-state blood contains low quantities of stem and progenitor cells that are retained in LDFs, the viability and the functional properties of mononuclear cells (MNCs) and CD 34+ cells recovered from LDFs were investigated.
Study design and methods: WBCs were recovered from LDFs by use of a closed system. MNCs and CD 34+ cells were isolated from freshly LDF-recovered WBCs or after their overnight incubation. The CD 34+ cells were enumerated, as well as the number of colony-forming unit (CFU)-granulocyte-macrophage, burst-forming unit-erythroid, and CFU-Mixed. The expansion in clinical-scale volume cultures (serum-free medium plus stem cell factor, granulocyte-colony-stimulating factor, and megakaryocyte growth and development factor) was performed starting from MNCs, freshly isolated CD 34+ cells, and CD 34+ cells isolated after overnight incubation of WBCs. The erythroid, megakaryocytic, eosinophilic, and monocyte-myelocytic lineage differentiation of LDF-recovered CD 34+ cells was challenged in liquid cultures by adding relevant cytokines.
Results: Nearly 450 x 10(3) viable CD 34+ cells were recovered per LDF. These cells exhibit unimpaired colony-forming ability. It is possible to expand these cells ex vivo, but their response to cytokines is different compared to mobilized peripheral blood and cord blood CD 34+ cells. Thus, further work is necessary to optimize their ex vivo expansion. These cells give rise to the mature cells and precursors of erythroid, megakaryocytic, eosinophilic, and monomyelocytic lineage in liquid cultures.
Conclusion: MNCs and CD 34+ cells recovered from the LDFs exhibit unimpaired functional capacities. Recent development of ex vivo technologies for expansion, retro-differentiation, and differentiation reinforces the value in cell therapy of these LDG-recovered peripheral blood progenitor cells that are routinely discarded.