PB2187: VIABILITY AND PROLIFERATIVE POTENTIAL OF AUTOGRAFT HEMATOPOIETIC STEM CELLS

Abstract

Background: Autograft cellularity is a fundamental condition for the timing of hematopoiesis recovery in patients with multiple myeloma (MM) after autologous hematopoietic stem cell transplantation (AutoSCT). Taking the number of CD34+ cells in a volume of 2x10/6/kg of the patient’s weight as a suboptimal value that provides fast and reliable graft engraftment, it remains unclear whether this number will be sufficient for subsequent transplantation, if tandem AutoHSCT assumes an interval of 6 months, and repeated - not earlier 36 months. Aims: Determination of the preservation of colony-forming (CFU) and CD34+ cells in the autograft of MM patients depending on the terms of their cryopreservation. Methods: A retrospective analysis of the results of the study of 127 samples of the product of leukocytapheresis was performed. The prepared cell suspension was placed in disposable CryoMacs Freesing bags and mixed with dimethyl sulfoxide to its final concentration of 7.5%. Freezing was carried out in a Cryo 560-16 Planer RLC programmed freezer. Containers with cell suspension were stored in liquid nitrogen. To assess the effect of the duration of the cryopreservation period on CFU, the numerical values of each sample were converted into percentages: the primary CFU values from each sample were taken as 100%, and the CFU values after the cryopreservation period were compared with them. Results: Depending on the terms of cryostorage, 3 groups were formed. Group 1: 83 samples, shelf life from 1 to 5.9 months. Group 2: 34 samples, shelf life from 6 to 10 months. Group 3: 10 samples, shelf life over 10 months. A trend towards a decrease in the number of colonies was revealed as the duration of the cryopreservation period increased. Thus, the number of CFU-totals decreased from 66% recorded after 1–5.9 months of storage, to 60% after 6–10 months and to 44% of the original number when stored for more than 10 months; p=0.131. The decrease in the number of colony-forming cells of granulomonocytopoiesis was distinct in cell suspension samples stored for more than 10 months, but also did not reach significant values: 64%, 58% and 37%, respectively; p=0.451. On the contrary, the decrease in the number of burst-forming cells of erythrocytopoiesis (BFU-E) after 10 months of cryostorage was significantly lower than at earlier periods of cell suspension thawing. So if the content of BFU-E after 1–5.9 and 6–10 months of storage was 65% and 57% of the initial amount, respectively, then after 10 months it was only 26%; p=0.01. When analyzing the preservation of CD34+ cells, a tendency was also found to decrease in their percentage as the duration of cryopreservation increased, but the difference did not reach a significant value: 77% during thawing after 1–5.9 months of cryopreservation, 49% after 6–10 months and 39% in case of cell suspension thawing after 10 months of storage; p=0.465. Despite the fact that in some patients with the maximum terms of cell suspension cryopreservation, the need for a larger number of doses of donor erythrocytes was recorded and there were longer terms for platelet recovery than in patients in the other two groups, the median values of the analyzed parameters did not differ. Summary/Conclusion: When planning the first and subsequent, repeated, AutoHSCT in MM patients, it is advisable to prepare an autograft with a greater than suboptimal cellularity due to a possible decrease in the number of CFU during long-term cryostorage of the cell suspension.