Cryopreservation of Growth Factor-Mobilized Peripheral Blood Stem Cells Does Not Compromise Major Outcomes after Allogeneic Hematopoietic Cell Transplantation: A Single-Center Experience

Abstract

During the COVID-19 pandemic, cryopreservation of allogeneic donor stem cell products ensured availability of products at the start of conditioning for hematopoietic cell transplantation (HCT). Following recommendations from unrelated donor registries, including the National Marrow Donor Program (NMDP), many centers started to cryopreserve related donor peripheral blood stem cell (PBSC) products. Throughout the process, several centers have published outcomes with cryopreserved versus fresh products, some with conflicting results. Even though cryopreservation was initially considered only a temporary measure driven by the pandemic, potential advantages include greater flexibility of transplant timing. However, concern about detrimental effects of cryopreservation including increased risks of graft rejection, relapse and consequently mortality remained. The primary objective was to describe our center's experience comparing outcomes following PBSC transplantation with cryopreserved versus fresh grafts. This was an observational case study with retrospective review comparing cryopreserved grafts (N=213), to a recent historical cohort (controls) using fresh grafts (N=167). In multivariable analyses, the adjusted hazard ratio (fresh vs. cryo) we for overall mortality was HR= 1.20 (95% confidence interval (CI), 0.79-1.82; p=0.40), for non-relapse mortality HR=0.99 (95% CI, 0.55-1.77; p=0.98), and for relapse HR=0.94 (95% CI, 0.60 -1.48; p=0.80). The adjusted hazard ratio for platelet engraftment was HR=1.31 (95% CI, 1.05-1.63; p=.02) and the odds ratio of grades III-IV acute GVHD was OR=1.75 (95% CI 1.01-3.04; p=.05) with fresh compared to cryopreserved grafts. There was no demonstrable difference in the risk of chronic GHVD. Although longer-term follow-up is needed, these data provide preliminary reassurance that in the event of another pandemic or should the logistical need arise in individual patients, cryopreservation of PBSC products constitutes a reasonably safe alternative.