Published online May 26, 2020. doi: 10.4252/wjsc.v12.i5.359
Peer-review started: February 28, 2020
First decision: April 2, 2020
Revised: April 14, 2020
Accepted: April 28, 2020
Article in press: April 28, 2020
Published online: May 26, 2020
Peripheral blood stem cells (PBSC) are commonly cryopreserved awaiting clinical use for hematopoietic stem cell transplant (HSCT). Long term cryopreservation is commonly defined as five years or longer, and limited data exists regarding how long PBSC can be cryopreserved and retain the ability to successfully engraft. Our study examines the engraftment potential of long-term cryopreserved PBSC units. This could allow for PBSC units to be stored for a longer time without repeated viability testing and for these units to be utilized in clinical HSCT.
We investigated the viability and colony-forming unit capacity in vitro, and the in vivo engraftment potential of long-term cryopreserved PBSC units. This was done to gain an understanding of the viability of long-term cryopreserved PBSC units so that these long-term cryopreserved units could be used for clinical HSCT.
Our intention was to investigate if long-term cryopreserved PBSC units, which are being preserved in stem cell banks for many years, can be utilized with successful in vivo engraftment. This will help with gaining insight to the potential use of long-term cryopreserved PBSC units.
PBSC units were collected and frozen as per validated clinical protocols. The units were then thawed as per clinical standards of practice. Progenitor function was assessed with standard colony-forming assays. CD34-selected cells were transplanted into NOD/ SCID/IL-2Rγnull (NSG) mice and stem cell function was assessed.
Ten long-term cryopreserved PBSC units (mean of 17 years) demonstrated appropriate post-thaw viability of which nine had BFU-E growth and seven showed CFU-GM growth. Immunodeficient NSG mice (6-7 recipient mice/PBSC unit) were transplanted with 4 randomly selected PBSC units that were cryopreserved for up to 18 years, and all mice showed short-term and long-term engraftment and reconstitution of human myeloid and lymphoid cells. Moving forward it will be important to analyze the engraftment of long-term cryopreserved PBSC units in vivo on a larger scale.
This study demonstrates the appropriate long term engraftment of clinically collected and thawed PBSC units follow cryopreservation up to 17 years in immunodeficient mice. This is one of few studies that analyzes the in vivo engraftment potential of long-term cryopreserved PBSC units. This can allow institutions to safely increase the time of safe storage for PBSC units, without further viability testing of the units. These findings are beneficial for clinical programs, stem cell banks, and regulatory and accrediting agencies interested in product stability.
In summary, this study demonstrates that long-term cryopreserved PBSC can exhibit short- and long-term engraftment in immunodeficient mice with differentiation into multilineage phenotypes. Future research would be to expand studies to look at in vivo engraftment on a larger scale and ultimately to apply this to clinical transplantation in humans.