Viability and Engraftment of Hematopoietic Progenitor Cells (HPC) After Long Term Cryopreservation: Effect of Diagnosis and % Dimethylsulfoxide (DMSO) Concentration.

There are few reports of HPC viability after more than 9 y of storage. It has been suggested that HPC from myeloma patients (pts) may survive storage less well than those from other diseases. The appropriate concentration of DMSO for long term storage is unclear. Our program has collected and stored HPC since November 1989, changing from 5% DMSO to 10% DMSO in August 2000. We present a retrospective analysis of viability by diagnosis and DMSO concentration in pts who underwent autologous transplant using HPC after long-term storage (up to 17.8 y).

HPC were harvested and preserved using a controlled rate freezer and 5% or 10% DMSO, then stored in liquid nitrogen. Viability was tested by flow cytometry using unwashed samples and looking at propidium iodide or 7-AAD uptake within the CD34+ population. Data from 242 samples were analyzed (224 myeloma pts and 18 other diagnoses): 100 consecutively thawed samples with storage time <1 y (all 10% DMSO), 100 consecutive samples stored from 5-9 y ( 7 samples, 10% and 93 samples, 5% DMSO), and all samples stored and used for transplant after >9y (42 samples, 5% DMSO). No statistically significant difference was seen in viability between <1y and 5-9y, so these groups were combined and compared to >9y. White blood cell (WBC) and platelet engraftment were compared for the 2 groups using an unpaired t test.

Mean viability for the 0-9y and >9 y groups were 91.62% and 92.79% respectively, with no statistically significant difference in viability between groups (p=0.28). Using a 2-tailed t test, no difference was seen in viability based on diagnosis (p=0.19) or between 5% and 10% DMSO (p= 0.12). No difference was seen in WBC engraftment (p=0.28) or platelet engraftment between groups (p=0.57).

HPC collections remained viable after 17.8 years, the longest time reported for use after storage to date. No difference in viability was seen with 5% or 10% DMSO, or between myeloma and other diseases. Storage time did not affect engraftment.

No relevant conflicts of interest to declare.