Impact of Storage and Cryoprotectants on the Function of Cord Blood Hematopoietic Stem Cells

Abstract

Cord blood (CB) has emerged as a significant source of hematopoietic stem cells (HSC) for transplantation. Large distances between collection and processing sites combined with staff availability can lead to long processing delays of CB unit (CBU). Standard agencies limit CBU storage at room temperature (RT) to a maximum of 48 hours from collection to freezing. Slow-engraftment and graft failure are major issues related to CB transplantation. I hypothesized that prolonged storage at RT reduces the engraftment activities of CBU due to the loss in HSC numbers. I set to test my hypothesis by performing serial and limiting-dilution transplantation assays in immunodeficient mice. My results showed that the engraftment activity of CBU was significantly perturbed by prolonged storage (>40 hours) at RT. In line with my hypothesis, the transplantation assays suggested that the engraftment deficit originates from loss in HSC numbers. My findings provide results for CB banks to make an informed decision on how long CBU can be stored at RT before processing. Conversely, CBU must be cryopreserved before use, and loss of function can occur due to osmotic shock and mechanical damage from uncontrolled ice-crystal growth (ice-recrystallization) during freezing and thawing. Current cyroprotectants like dimethyl-sulfoxide fail to inhibit ice-recrystallization. However, a novel class of small ice-recrystallization inhibitor (IRI) molecules (N-aryl-D-aldonamides) have been developed. I hypothesized that supplementation of cryopreservation solution with IRIs will improve the post-thaw viability and engraftment activity of CBU. Herein, I identified two IRIs (IRI 2 and IRI 6) that improved the post-thaw recovery of hematopoietic clonogenic and multipotent progenitors. Moreover, supplementation of CB graft with IRI 2 was beneficial to engraftment and had no negative impact on the differentiation and self-renewal activities of HSCs. Taken together, my results demonstrate for the first time that IRI may be beneficial to the engraftment activity of HSC graft and support further investigation.