Peripheral blood stem cells (PBSC) storage conditions may influence cell quality and/or functionality, which may directly impact recipients'clinical outcomes. Thus, the Brazilian Health Regulatory Agency (ANVISA) demands validation of fresh storage times greater than 48 (forty-eight) hours, with technical-scientific evidence about the quality and safety of the product. The aim of this study was to verify the effects of longer fresh storage times in the viability and functionality of PBSC intended for Hematopoietic Progenitor Cells (HPC) transplantation.

Ten aliquots of PBSC units were analyzed. The samples were storage fresh at 2°C to 8°C. Measurements were performed immediately (I) and 72 h after PBSC collection storage (AS), by flow cytometry analysis and clonogenic assays. CD45+ and CD34+ cells viability, white blood cells (WBC) counts and CD34+ cell concentrations and colony forming units (CFU) were evaluated. All clonogenic assays were performed in duplicate with 1 × 104 cells/mL. The results of these assays were expressed as the arithmetical mean of the duplicates. A descriptive analysis and T-dependent test were performed (SPSS 15 software).

: According to the in-process controls, the median interval between the end of collection and temporary storage was 72 hours, with the maximum time being 91 hours and 48 minutes and the minimum storage time being 69 hours and 25 minutes. This variation in storage time is due to the end time of some collections that were longer than the laboratory's operating hours, so the samples had to be analyzed within the possibilities of the routine. Median viability of CD34+ cells immediately after collection was 100%, minimum viability was 98.8%, so all cases were in compliance with the laboratory quality indicator target. The median viability of CD34+ cells after fresh storage was 99.75%. There were two cases with viability below 98%, and the minimum viability was 97.1%. The average loss of viability of CD34+ cells in relation to the mean obtained in fresh samples was 0.66%. One case had a 2.99% loss of viability. Despite the significantly decreased CD45+ cells viability after storage (I: 98,3%; AS: 90,4%; p =< 0,0001), no significative changes were noted in CD34+ cell viability (I: 100%; AS: 99,75%), as well as in WBC (I: 248350/μl; AS: 242705/μl) and CD34+ cells (I: 5,24 × 106/kg; AS: 4,67 × 106/kg) concentrations. Moreover, no significant decrease in colony-forming unit numbers was observed in units stored for 72 hours (I: 34,5; AS: 21,5).

Despite the significant decrease in CD45+ cell viability after 72 hours storage, no significant changes were observed in CD34+ cell viability, as well as in WBC and CD34+ cell concentrations in the same period. These results are reinforced by the functional assays, in which no significant decrease in colony-forming unit numbers was observed and it also demonstrated that the cells maintain their proliferation and differentiation potential.

These results lead to the assumption that the fresh storage time of 72 hours had no significative impact in variables of concern (CD34+ cells and clonogenic assays) and thus does not impact the quality and safety of the product. Nonetheless, despite the strong recommendation of infusing fresh graft as soon as possible, our data suggest that, when necessary, it is safe to use PBSC until 72h after collection.