Impact of cryopreservation and transit times of allogeneic grafts on hematopoietic and immune reconstitution

Abstract

We sought to evaluate the impact of cryopreservation of unrelated donor (URD) peripheral blood stem cell (PBSC) grafts on engraftment, chimerism, and immune reconstitution in the context of the COVID-19 pandemic. We reviewed stem cell product characteristics and clinical outcomes in 101 patients receiving cryopreserved PBSCs from URDs between January 1, 2019 and 31 December, 2020, compared with 203 patients receiving fresh URD PBSCs. We observed no differences in 6-month overall survival, progression-free survival, or nonrelapse mortality. Patients receiving cryopreserved PBSCs had delayed platelet engraftment and impaired reconstitution of white blood cells and T-cell subsets at day 30. Thirty-four percent of patients receiving cryopreserved grafts had CD3 chimerism <50% at day 30 after transplantation, compared with 14% of patients receiving fresh PBSCs (P = .0002). At day 100, this difference persisted (CD3+ chimerism <50%: 17% of cryopreserved cohort vs 6% of fresh cohort; P = .016). Greater product age at infusion was associated with increased graft failure, independent of cryopreservation. Receipt of grafts >48 hours old at time of cryopreservation or infusion significantly increased the risk of graft failure (subdistribution hazard ratio = 4.57; 95% confidence interval, 1.71-12.3; P = .0025). Our data indicate that cryopreservation is associated with similar overall short-term clinical outcomes compared with fresh PBSC. However, patients must be monitored closely for increased risk of other potentially adverse outcomes, including graft failure and poor immune recovery, particularly for grafts with older overall age at infusion. Longer-term follow-up is needed to determine impact on relapse and survival.

Graphical abstract

Figure 1.

Graft ages. (A) Overall age of product (defined as time in hours from collection to end of processing) varied between fresh (red) and cryopreserved (blue) cohorts. Products in the cryopreserved group were more likely to be ≥48 hours old at end of processing, reflecting longer intervals at all stages: transit, holding, and processing times. Of cryopreserved products, 16.8% was >60 hours old at the end of processing compared with 2% of fresh products (P < .0001). (B) International products (blue) tended to be older than domestic products (red). This difference in length of transit time is particularly pronounced in the cryopreserved group, reflective of changes in transit time during the COVID-19 pandemic. Cryo, cryopreserved.

Figure 2.

Clinical outcomes of patients receiving cryopreserved vs fresh stem cell products. OS (A) and PFS (B) were similar in patients receiving fresh products (blue line) and cryopreserved products (red line). Patients receiving cryopreserved products had a 1-day delay in neutrophil engraftment (defined as first of 2 consecutive days of ANC > 500 cells per µL) (median 15 days vs 14 days; P = .02) (C) but slower platelet engraftment (defined as first of 3 consecutive days of platelet count >20 000) (median 24 days vs 18 days; P = .044) (D) compared with patients receiving fresh products. (E) Incidence of grade II to IV aGVHD was higher in patients receiving cryopreserved product compared with fresh (100-day cumulative incidence: 17% vs 9%; P = .014).

Figure 3.

Immune reconstitution. (A) Patients receiving cryopreserved stem cells (blue bars) had lower WBC and neutrophil count (ANC) at 30 days after transplant compared with patients receiving fresh (red bars) (median WBC 3850 cells per µL vs 6260 cells per µL; P = .0079, median ANC 2240 cells per µL vs 3300 cells per µL; P = .016). There were trends toward lower absolute lymphocyte (ALC) and monocyte (AMC) counts in patients receiving cryopreserved grafts, but these were not statistically significant. (B) Similarly, CD3⁺, CD4⁺ Tcon and Treg, and CD8⁺ subsets also had trends toward lower values in cryopreserved vs fresh.