Stability Program for Hematopoietic Progenitor Products from Apheresis (HPC-A) at an Academic Institution

We perform stability testing on HPC-A products stored in vapor phase nitrogen from 1 week to 5 years. Stability is defined as CD34 viability of 70% or higher (±40% from baseline), and negative sterility results at 14 days. Potency is defined as 21 days or less to ANC engraftment if infused. We performed a comparison on frozen products from deceased patients or soon to be transplanted products stored for more than 10 years (group 3, n=7) or less than 10 years (group 2, n=10). The objective of our analysis was to establish a method to predict stability and potency, with clinical and economic implications. Thirteen patients were consented on an IRB approved protocol, and request for exemption was presented to the IRB for the remaining. Freshly isolated samples (group 1, n=3) provided control data. The demographic characteristics of the cellular products were matched between groups, except that older samples were volume reduced using the COBE-2991 device, (p=0.007). Samples in group 2 were stored for a median time of 3.6 years (range 0.42, 7.1), and samples in group 3 for 12.31 years (range10.12-14.34), respectively. We observed a post-thaw TNC decrease of 30% in group 2 and 36% in group 3 (p=0.9). CD34 counts decreased by 6.5% in group 2, and 11.37% in group 3 (p=0.7). We observed a 26% reduction of viable CD34 cells in group 2 vs. 34% in group 3 (p=0.1). All but two patients in group 3 received the first transplant, with products stored for a median of 2 days in group 1, 9 days in group two, and 137 days in group 3 (p=0.03). Cellular composition was consistent among products. All products engrafted ANCs within 12 days (p=0.5) and PLT within 17 days (p=0.4). Four patients in group 2 and 1 patient in group 3 received a second transplant. Median storage for group 2 was 3.6 years (0.42-7.09), compared with 12.3 years (10.12-14.34) in group 3 (p=1). All second transplants achieved prompt engraftment of both ANCs and PLT (≤12 d, p=0.2; 0.046, resp.). Regarding the ability of lineage depleted CD34 stem cells to form colonies in vitro, we collected data from 13 independent hematopoietic colony-forming unit assays. A statistically significant reduction in colony formation for both groups 2 and 3 was observed when compared with group 1. Other authors have reported successful engraftment in the absence of colony formation in vitro. Therefore, we decided to perform a functional evaluation of the aldehyde dehydrogenase (ALDH) enzyme activity using a commercially available flow cytometry kit in alternative. As expected, ALDH functionality correlated with CD34 viability (Pearson's coefficient: 0.4). (Figure 1). HPC-A products stored longer than 10 years resulted in efficient engraftment after the infusion of standard doses of viable CD34 cells. Viability assessed with 7-AAD is a simple and essential measure to assess the stability of frozen products, and the ALDH assay is an efficient adjunct to assess the functionality of CD34 stem cells.