Post-Thaw Viability of Cryopreserved Hematopoietic Progenitor Cell Grafts Influences Patients' Predisposition towards Infectious Complications in the Post-Transplant Period.

Abstract 4666

Cell viability in peripheral blood progenitor cell (PBPC) grafts and its influence on the clinical course following transplantation was evaluated in 81 consecutive transplantations (72 autologous, 9 allogeneic) performed in patients with hematological diseases. Viability of cells in PBPC grafts, assessed by trypan blue dye exclusion test immediately upon collection was 98.6±3.5%, after addition of dimethyl sulfoxide (DMSO) 73.3±21.8%, and post-thaw 65.2±16.1%. It did not differ significantly between patients with different diagnoses, gender, age, type of priming used, dose of G-CSF administered or number of CD34+ cells collected. However, grafts stored for more than 60 days showed lower post-thaw viability compared to the ones thawed in the 60 days following cryopreservation (56.6±15.2% vs. 67.6±15.5%, p=0.04). A strong, statistically significant correlation was found between pre-cryopreserved CD34+ cell dose and hematopoietic recovery in patients, expressed as time to reach ANC>1×10⁹/l and platelets >20×10⁹/l (R²=0.14 p=0.001, R²=0.12 p=0.005, respectively). Occurrence of febrile neutropenia and total number of febrile days did not differ significantly between patients depending on the dose of CD34+ cells infused. On the contrary, post-thaw graft viability did not influence engraftment time, but there was a predisposition towards infectious complications in the post-transplant period in patients receiving grafts with lower percentage of viable cells. These patients developed febrile neutropenia more often (72.2% vs. 50% of patients, p=0.05) and had more febrile days (2.4±2.6 vs. 1.5±2.3, p=0.05) following transplantation. Our results demonstrate that PBPC grafts are capable of long term engraftment regardless of the graft storage time or percentage of viable cells post-thaw, which confirms the robustness of CD34+ cells during the freeze/thaw procedures carried out in daily clinical practice. Granulocyte concentration in PBPC grafts could have an influence on infectious complications following transplantation. This is an intriguing finding that deserves further investigation on a larger number of patients, less heterogeneous in terms of underlying disease, type of transplantation or conditioning regimen used.