Cryopreservation Impairs Engraftment in Bone Marrow Transplantation

Introduction: Due to the covid-19 pandemic, a recommendation was made, especially for non-related allogeneic hematopoietic stem cell transplantation (allo-HSCT), to cryopreserve hematopoietic stem cells products and start the conditioning regimen only after the product be received at the receptor service. There are conflicting data on how the procedure of cryopreservation (and thaw) of bone marrow affects outcomes. In this study we evaluated the primary graft failure incidence using cryopreserved bone marrow grafts compared to non-cryopreserved bone marrow grafts. We also evaluated transfusion needs during the first 30 days after transplant and the occurrence of severe adverse events (AEs) related to the product infusion, during covid-19 pandemic in a single Brazilian center.

Methods: From January 2020 to 30 June 2022, we retrospectively analyzed clinical and laboratory data from 9 cryopreserved (cryo) (all of them unrelated) and 15 non-cryopreserved (non-cryo) bone marrow grafts (2 of them unrelated), here defined as control group. Haploidentical transplants were excluded due to a higher risk of primary graft failure reported on this type of transplant. Children and adults with malignant and non-malignant disorders were included. We evaluated engraftment, red blood cells (RBC) and platelets (Pl) units transfused during the first 30 days, and adverse effects associated with product infusion. Neutrophil engraftment was defined as the first of 3 consecutive days with absolute neutrophil counts of ≥ 500/µL and primary graft failure was defined as failure to achieve a neutrophil engraftment by day 28 after bone marrow infusion. Results were given as median (range) and comparison between the groups was performed employing the Mann-Whitney U test. Percentages were compared with the chi-square or the Fisher exact test.

Results: Only two cryopreserved grafts have not been used (one patient died before the start of the conditioning regimen and the other did not receive the graft yet). Baseline characteristics were similar in both groups. The median (range) age was 21 (1-37) and 20 (6-32) years, with 42.86% and 40% under 18 years of age in the cryo and non-cryo groups, respectively. Also, 85.7% and 53.3% were male, and 14.3% and 13.3% had malignant disease (acute leukemia) in the cryo and non-cryo groups, respectively (Table 1). The numbers of infused total nuclear and CD34+ cells/kg in the cryo and non-cryo groups were not significantly different (p= 0.14, and p= 0.41, respectively) (Table 1). Three (42.8%) patients from the cryo group, all of them children (with osteopetrosis, aplastic anemia, and acute leukemia) did not achieve neutrophil engraftment by day 28, whereas all 15 patients from non-cryo group had hematologic recovery (RR= 4.75, 95% CI: 1.61-11.75; p= 0.02). Furthermore, there was a slight tendency toward delayed neutrophil engraftment in the cryo group: 21.5 (19-23) and 19.0 (15-28) days (p= 0.20).

The numbers of RBC and Pl units transfused during the first 30 days after product infusion were higher in the cryo than non-cryo group: RBC 5.0 (3-9) and 1.0 (0-4) (p< 0.0001); Pl 15.0 (7-18) and 5.0 (1-20) (p= 0.0014), respectively (Figure 1). Three patients (42.8%) had severe AEs (seizure, hypertension urgency associated with second-degree atrioventricular block: Mobitz type 1, and acute renal failure) during or right after bone marrow infusion, all of them in the cryo group (relative risk= 4.75, 95% CI: 1.61-8.43, p= 0.02). All of them recovered completely from AE.

Conclusions: Transplantation of cryopreserved bone marrow grafts seems to be associated with a higher risk of primary engraftment failure and, consequently, a higher transfusion needs, and with more severe adverse events related to the product infusion. Because of these findings and in spite of the ongoing pandemic, we recommend a careful evaluation of the necessity to adopt this practice.

Guerino-Cunha:Kite: Speakers Bureau; Janssen: Consultancy, Speakers Bureau; Novartis: Speakers Bureau.