Active infection at the time of CD34+ selected stem cell boost is associated with treatment failure and poor survival.

BACKGROUND: The use of CD34+ selected stem cell boost (SCB) post allogeneic hematopoietic cell transplant (alloHCT) has been increasing. Predictors of treatment failure following SCB, both in the context of poor graft function (PGF) or other settings, are not well-characterized. We report among the largest single center retrospective experiences of the use of SCB and evaluate potential predictors of response and outcomes. METHODS: 58 patients who underwent HCT between 2015 and 2022 and who received SCB were identified. The indication for SCB was predominantly PGF, defined as the presence of 2 or more cytopenias for at least two consecutive weeks beyond day +14 after alloHCT in the presence of ≤ 30% bone marrow cellularity and ≥ 90% donor myeloid chimerism in the absence of morphological disease. RESULTS: The median dose of infused CD34+ selected SCB products was 3.88 x 106 CD34+ cells/kg (range: 0.99-9.92). The median 2-year OS and NRM following SCB was 47% and 38%, respectively. The cumulative incidences of 6-month grade III-IV acute and 2-year moderate-severe chronic GVHD following SCB were 3.4% and 12%, respectively. Overall response (CR + PR) was attained in 36/58 (62%) patients, and in 69% with PGF. On multivariable analysis, an active infection at the time of SCB was the greatest predictor of poor response and survival (p=0.013) following SCB. CONCLUSION: SCB can restore hematopoiesis in the majority of patients, particularly for those with poor graft function in whom there is no active infection at infusion.

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

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.