Long‐term cryopreservation of autologous stem cell grafts: a clinical and experimental study of hematopoietic and immunocompetent cells

BACKGROUND: Autologous stem cell transplantation (ASCT) is used in the treatment of several malignancies. Harvesting sufficient peripheral blood progenitor cells (PBPCs) for a potential second autotransplantation at the time of relapse several years after diagnosis is becoming an increasingly common practice. STUDY DESIGN AND METHODS: Cryopreserved PBPCs were prepared with different concentrations of dimethyl sulfoxide (DMSO; 2, 4, 5, and 10%) and stored for at least 5 years before the recovery of CD34+ cells and various T- and natural killer (NK)-cell subsets were analyzed by flow cytometry. Furthermore, clinical variables for myeloma patients having a second autotransplantation with long-term-stored autografts were evaluated. RESULTS: The number of viable CD34+ cells in long-term-stored grafts was higher when autografts were cryopreserved with 4 or 5% than with 2 and 10% DMSO. The number of viable CD34+ cells was reduced by 13.9% after 5 years of cryostorage in 5% DMSO. Lymphocyte viability was also higher with 4 or 5% DMSO. However, the frequencies of several T-cell subsets showed DMSO-dependent differences, whereas NK-cell subsets did not. Furthermore, after a second autotransplantation with long-term-stored PBPC grafts at the time of myeloma relapse (median storage time, 42 months) all 17 patients reached neutrophil counts exceeding 0.5 × 109/L and platelet counts exceeding 20 × 109/L within 15 days. There was no difference in engraftment between patients receiving autografts preserved with 5 and 10% DMSO. CONCLUSION: PBPC autografts can safely be stored for at least 5 years in 5% DMSO and used for ASCT.