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High-efficiency recovery of immature haematopoietic progenitor cells with extensive proliferative capacity from human cord blood cryopreserved for 10 years.

Cord blood is enriched with haematopoietic stem and progenitor cells which have high levels of proliferative, replating and expansion capacity in vitro. Cryopreserved cord blood stored for up to a few years has been used as a source of transplantable cells for related and unrelated allogeneic stem cell transplantation. Information on retrieval of immature and mature subsets of viable haematopoietic progenitor cells from long-term cryopreserved cord blood is not yet available. We therefore assessed the recovery of cord blood cells stored frozen in liquid nitrogen for up to 10 years. Calculations of efficiency of recovery were possible because the exact same culture conditions were used for pre-freeze and post-thaw cells with the serum and growth factors presently used being of similar potency to those used for the studies 10 years ago. High efficiency recovery of immature and mature progenitors was found even though a relatively unsophisticated freezing procedure had been used. Recovery of nucleated cells averaged 88% and that of granulocyte-macrophage (CFU-GM), erythroid (BFU-E) and multipotential (CFU-GEMM) progenitors averaged from 74 to 91% for different populations, with some samples in each category being recovered at 100%. Recovery of immature progenitors responsive to stimulation in vitro with a colony stimulating factor plus the potent co-stimulating cytokine, steel factor, was also demonstrated, although the per cent recovery of such cells could not be calculated directly as steel factor was not available 9-10 years ago when the cells were originally frozen. While the cell populations assayed are not considered to represent long-term narrow repopulating cells, the data presented demonstrate that cells with very high proliferative capacity can be stored long term in cryopreserved form.