Inferior Clinical Outcomes in Recipients of Cryopreserved Grafts Following Reduced Intensity Allogeneic Hematopoietic Cell Transplantation: A Single Center Report

ABSTRACT

Background: In 2020 cryopreservation of allogeneic donor apheresis products was implemented to overcome the challenges of donor availability and product transport related to the COVID-19 pandemic. Several studies have reported on allo-HCT outcomes with cryopreserved (cryo) grafts with conflicting findings regarding overall survival (OS), engraftment and hematopoietic recovery. Here, we report on the clinical post-HCT outcome in recipients of cryo grafts in our institution. Moreover, we compare the graft composition of cryo and fresh products by assessing the immunophenotype of hematopoietic stem cell (HSC) and lymphocyte subsets. Methods: Data collected from 29 patients who underwent allo-HCT with cryo PBSC (cryo group) from 03-08/2020 were compared to a control cohort of 60 consecutive patients, who received fresh PBSC allo-HCT (fresh group) from 06/2019 to 08/2020. Primary endpoints were OS and graft failure. Secondary endpoints were hematopoietic recovery and GvHD. Flow cytometry was performed on 5 available samples in the cryo group and compared to 4 prospectively collected fresh apheresis samples from allogeneic donors. Results: Conditioning intensity was equally distributed among both groups (cryo-69% RIC vs 31% MAC;fresh-65% RIC vs 35% MAC). Median post-collection (prefreeze) dose of CD34+ cells x106/kg differed in the two groups (7.3 cryo vs 9.2 fresh) with no differences in the dose of CD3+ cells x108/kg. All donor types, except UCB were included in the analysis. The cryo group included more HLA-matched unrelated donors (72.4 vs 41.7%), whereas the fresh group included more HLA-matched sibling (33.3 vs 6.9%) and slightly more haplo/HLAmismatched donors (25.0 vs 20.6%). 4 of 29 patients (13.8%) in the cryo group developed primary graft failure vs 1 of 60 patients (1.7%) in the fresh group (p = 0.03). All 4 cryo patients received HLA-matched unrelated grafts following RIC (3=Flu/Mel, 1=Flu/TBI), whereas the patient in the fresh cohort received a haploidentical graft, following MAC (Bu/Cy). Donor chimerism at 1 month for the RIC allo-HCT is shown in Fig. 1. We observed inferior OS in the cryo RIC group [Fig. 2;HR and 95% CI 4.20 (1.22, 14.4)], and slower recovery of neutrophils (p = 0.006) and platelets (p = 0.058). The incidence of acute GvHD was similar in the two groups. For all patients (n = 89), multivariate analysis performed for OS and graft failure after adjusting for donor type, patient age, gender, CD34 cell dose, and conditioning intensity supported the inferiority of cryo allo-HCT. Finally, flow cytometry analysis revealed significantly lower absolute counts of NK cells (CD3-CD56+) in cryo as compared to fresh apheresis samples (p = 0.0159), with no differences in CD4+ and CD8+ T-, B-(CD19+CD20 +), CD34+ cells and HSC (CD34+CD38-CD90 +CD45RA-). Conclusions: Our data show that the use of cryopreserved grafts following RIC allo-HCT led to inferior OS with increased rate of graft failure. Further studies are needed to determine a potential role of graft composition on cryo vs fresh allo-HCT outcomes.