The Cell Loss after Thawing in Cord Blood Units

Umbilical cord blood (CB) are increasingly used for allogeneic transplantation as an alternative source to bone marrow or peripheral stem cell for patients who lack a human leucocyte antigen (HLA)-matched donor. Cell dose is one of the main determinant factor for selection of the unit and it has been shown to correlate with time and probability of engraftment. Cell doses available for selection of the unit are the ones evaluated before cryopreservation. Processing of the graft either with cryopreservation and/or thawing inevitably lead to cell loss but the data showing to what extent is very limited although this has great importance especially for the units with critical cell counts. To evaluate the extent of the cell loss after thawing and the effect of preservation duration on cell loss and the viability, we retrospectively analyzed our single center experience in a cohort of patients receivingunrelated CBT.

Sixty cord blood units used for unrelated CBT in fifty-eight patients in our Pediatric Stem Cell Transplantation Unit were included in the study. One of the patient was transplanted with double cord blood unit and one had recurrent CBT because of previous graft failure.

Median number of declared TNC per kilogram of recipient body weight was 16x107/kg (range: 3,16-59,1). After thawing the median TNC dose decreased to 11,1x107/kg (range:1,5-34), with median cell viability at 80%. The median TNC recovery was found as 70%. Median CD 34+ cell count declared by the banks per kilogram body weight of recipient was 6,0x105/kg (range: 0,5-37). The CD 34 cell count of one of the units used in a patient having double cord blood infusion was not available. The CD34 cell count of the other complementary unit was 0,48x105/kg. Since the total cell counts received bu the recipient was given, the CD34 cell count of the patient having double CB infusion was not included in statistical analysis. The median postthawed CD 34 cell count was 3,4 x105/kg (range: 0-21)and median CD34 cell recovery was %58.

The storage duration of the CB units in liquid nitrogen was available for 59 units and that was 52±30 months (range:3-130 months). Correlation analysis did not show any significant correlation between CB unit storage duration and viability (r=-0,2 p=0.07). Also any correlation between storage time and also TNC and CD34 cell recovery were not identified.

Our study indicated that approximately 30% of cell loss is expectable in cord blood transplantation because of either cryopreservation or thawing. It should be kept in mind while assessing acceptibility of cord blood units with limited cell counts