Fresh Versus Cryopreserved Allograft Outcomes in Peripheral Blood Stem Cell Transplantations

Background: The emergence of the COVID-19 pandemic saw an increased use of cryopreserved (cryo) peripheral blood (PB) grafts for allogeneic hematopoietic stem cell transplantation (HSCT). Outcomes of patients receiving either fresh or cryo grafts have yielded heterogeneous results. Herein, we retrospectively compared the outcomes of patients receiving fresh and cryo grafts at a single center.(Table Presented)Methods: Between 2019 and 2021, we reviewed data from 380 patients;167 (44%) received a fresh, and 213 (56%) received a cryo graft. Patients underwent myeloablative or nonmyeloablative HSCT from either matched or mismatched, related or unrelated donors. Cell doses were determined by number of donor cells collected and recipient weight at infusion. Engraftment, disease risk (DR) and acute GVHD were classified based on established criteria. Donor chimerism was collected at approximately day 28 and day 80 after HSCT. Unadjusted and adjusted estimates of overall survival (OS), relapse, and non-relapse mortality (NRM) as a function of time were obtained. The adjusted odds (grades III-IV acute GVHD) and the adjusted cause-specific hazard of failure (all other outcomes) were compared between the 2 groups. with the use of logistic (Figure Presented) or Cox regression, respectively. These models were adjusted for various factors known to be associated with each outcome. Result(s): The characteristics of patients between the 2 groups are shown in Table 1. There was a higher proportion of patients with high/very high DR in the fresh graft group (Table 1). Median time to neutrophil engraftment was 17 and 18 days in fresh vs. cryo, respectively. The adjusted hazard ratio (HR) of neutrophil engraftment (fresh vs. cryo) was 1.07 (95% CI, 0.86-1.34, p=0.54). Median time to platelet engraftment was 13 and 15 days, respectively, and the adjusted HR of platelet engraftment was 1.32 (1.06-1.65, p=0.01). Day 28 chimerism data were available for 272 patients (113 fresh and 159 cryo). At day 28, donor CD3 chimerism was below 50% in 5 out of 113 (4.4%) and 17 out of 159 (10.7%) patients receiving fresh and cryo grafts, respectively (p= 0.06). At day 80, 3 out of 121 (2.5%) patients in the fresh group and 4 out of 165 (2.4%) in the cryo group had CD3 chimerism below 50%. The adjusted HRs (fresh vs. cryo) for death and NRM were 0.83 (0.54-1.28, p=0.40) and 0.71 (0.38-1.33, p=0.29), respectively (Figures 1 and 2). The adjusted HR for relapse was 0.65 (0.42-0.99, p=0.05) (Figure 3). The adjusted odds ratio (fresh vs. cryo) for grades III-IV GVHD was 1.65 (0.94-2.9, p=0.07). Conclusion(s): In this single-center retrospective study we observed numerically better outcomes with fresh grafts relative to cryo grafts for all examined endpoints with the exception of grades III-IV aGVHD, although none of the differences were definitive with the possible exception of relapse and platelet engraftment. Further studies are needed to confirm our observations.Copyright © 2023 American Society for Transplantation and Cellular Therapy

Cryopreservation for Allogeneic Hematopoetic Stem Cell Transplants Is Non-Inferior to Fresh Graft Products

Background: The use of cryopreservation for stem cell grafts for both autologous stem cell and allogeneic cord blood transplant has been utilized for years. For other allogeneic stem cell transplant sources, the use of fresh collected grafts has been preferred due to concerns that cryopreservation may result in impaired graft function. With the onset of the COVID-19 pandemic a shift was made at our institution to exclusive use of cryopreservation Methods: In this retrospective single-center analysis a total of 133 patients undergoing allogeneic stem cell transplant at the University of Minnesota between 1/2018-6/2021 for a variety of malignancies were included, with 62 patients receiving fresh stem cell product and 71 patients receiving frozen stem cell product. Univariate statistical analysis was performed. Result(s): There was no significant difference between the two groups with regards to product type, sex, age, diagnosis (acute leukemia vs other), disease risk index, conditioning regimen, Karnofsky score, co-morbidity index, or cell dose (Table 1). Donor type was notably different between the two groups (p<0.01): matched sibling grafts were more commonly used for fresh products than frozen (85% vs. 35%), while matched unrelated donors were used more frequently for frozen than for fresh products (54% vs. 6%). Use of frozen product was associated with delayed neutrophil and platelet engraftment compared to fresh (median days to engraftment 15 vs 12 for neutrophils, 23 vs 17 for platelets, p<0.01 for both). Two-year relapse rates were significantly lower for frozen products (4%) than fresh (24%) (Table 2). This may be partially attributable to differences in follow up between the groups, as fresh products had a total of 910 days of follow up vs 432 for frozen products (P<0.0001). The difference in follow up remained statistically significant if the data was censored at 730 days (P<0.0001). Of note, the use of frozen products was associated with a lower rate of chronic graft-versus-host disease at one year post-transplant (p<0.01). There was no significant difference in the rates of acute GVHD between the groups. There were significant differences in GVHD prophylaxis regimens between the fresh and frozen groups (p<0.01). (Figure Presented)Two-year overall survival did not differ between groups (p=0.96). Conclusion(s): Use of cryopreserved stem cell products is associated with similar efficacy and outcomes as those seen with the use of fresh stem cell products. Although the data presented here suggest novel finding of decreased risk of relapse and chronic GVHD with the use of frozen stem cell products, additional follow up may abrogate these differences. Regardless, the logistical benefits of cryopreservation make this an attractive option for continued use in allogeneic transplants and our data presented here suggests that cryopreserved products remain an appropriate option for allogeneic stem cell transplant.Copyright © 2023 American Society for Transplantation and Cellular Therapy

Factors Affecting the Need for a Second HPC(A) Collection in Unrelated Allogenic Transplants: Process Improvement Opportunity

Introduction: Matched unrelated donors (MUD) for hematopoietic progenitor cell (HPC) transplantation are facilitated through the National Marrow Donor Program. Most peripheral blood collections (HPC-A) are obtained in a single day apheresis collection. Extensive planning is required to coordinate the mobilization, collection, and shipment of the product with the conditioning and infusing at the transplant center. Typically, these products are infused fresh, although the COVID pandemic has necessitated cryopreservation in many instances. It was perceived that the number of two-day MUD collections was increasing at our institution. This study was performed to determine if this was true and to evaluate potential causes. Method(s): The project was considered a laboratory quality improvement project;IRB approval was not required per institutional guideline. Data was collected retrospectively for 120 HPC(A) MUD from August 2017-November 2020 including donor's age, weight, and sex, along with recipient to donor weight ratio. Each factor was analyzed against CD34 yield per day of collection. Result(s): Of the 120 donors, 5.6% collected over 2 days in 2017(n=1), 3.7 % (n=1, 2018), 3.6 % (n=1, 2019) with highest observation 17% (n=8) in 2020 (Image). Donor age, donor weight, donor sex, and recipient to donor weight ratio were compared to absolute CD34 yield. There was not a correlation seen between CD34 yield and donor age nor weight. However, donor sex along with recipient/donor weight ratio each showed a correlation in the number of collections required. Of those requiring a second day of collection, 73% were female while 27% were male. Two-day collections could be predicted with 83% accuracy in female with >1.09 recipient/donor weight ratio and male with > 1.49 recipient/donor weight ratio.(Figure Presented) Conclusion(s): The observed trend of increased 2-day NMDP collections coincided with an increase in frequency of female donors. Not surprisingly, higher recipient/donor weight was associated with a higher likelihood of 2-day collections. The size and scope of this study do not allow us to determine a definitive cause. However, it was noted these findings coincided with new donor selection guidelines prioritizing HLA-DP match potentially leading to an increase in female donors being selected. Unexpected two-day collection can have significant effects on transplantation. Developing a predictive algorithm with 83% accuracy allows for patient and staff preparation to anticipate the likelihood for additional collections. Having the product collected and received in advance, prior to patient conditioning improves logistics and removes some variability from scheduling. Larger, multicenter studies are required to determine if increased numbers of two-day collection of MUD are occurring at other centers and to the potential causesCopyright © 2023 American Society for Transplantation and Cellular Therapy

Cryopreservation of Unrelated Donor Stem Cell Grafts Is Associated with Lower Rates of Chronic Gvhd after Allogeneic Transplantation

Allogeneic hematopoietic stem cell transplantation (allo- HSCT) has traditionally involves administering fresh peripheral blood or bone marrow stem cells. At onset of the COVID-19 pandemic in March 2020, the National Marrow Donor Program (NDMP) mandated cryopreservation of all unrelated peripheral blood stem cell (PBSC) products to prevent interruptions in transplant plans by donor COVID-19 infection after recipient's start of conditioning chemotherapy. Since the lifting of this mandate, many centers have continued to cryopreserve grafts prior to initiation of conditioning, but the longer-term clinical outcomes of this practice including chronic graft versus host disease (cGVHD) rates of patients receiving cryopreserved stem cells have not been previously well described. Prior work has raised concern for a deleterious effect of cryopreservation on overall survival and non-relapse mortality (PMID: 33865804). However, heterogeneity in the patient population and reason for cryopreservation suggest that further study is needed to assess these outcomes. Here we report our single-institution experience of clinical outcomes using cryopreserved versus fresh URD PBSCs for allo-HSCT. We examined long-term outcomes in 387 patients who received unrelated donor (URD) PBSCs (136 cryopreserved, 251 fresh) between January 1, 2019 and July 31, 2021. The cohorts had similar baseline characteristics including donor/recipient age/sex, disease, conditioning regimen/intensity, and GVHD prophylaxis regimens. Two-year OS, PFS, relapse, NRM, and acute GVHD rates were not different between recipients of fresh versus cryopreserved PBSCs. Strikingly, 2-year incidence of cGVHD (28% vs 52%, p=0.00001) and moderate/severe cGVHD (9% vs 24%, p=0.00016) was substantially lower in recipients of cryopreserved PBSCs compared to fresh, respectively (Figure 1). This difference was only noted in patients receiving a GVHD prophylaxis regimen without post-transplantation cyclophosphamide (PTCY) (no PTCY 2-year cGVHD incidence cryopreserved vs fresh: 29% vs 57%, p=0.000016), moderate/severe cGVHD 16% vs 34%, p=0.0006) (Figure 2). For patients receiving a PTCY-containing GVHD prophylaxis regimen, there was no difference in cGVHD incidence (cGVHD cryopreserved vs fresh: 24% vs 27%, p=0.56, moderate/severe cGVHD 7% vs 9.3%, p=0.3, Figure 3). (Figure Presented) (Figure Presented) (Figure Presented) While survival and relapse rates are not different, cryopreservation is associated with a marked reduction in cGVHD rates in the setting of non-PTCy based GVHD prophylaxis. Larger multicenter or registry analyses are needed to confirm these observations and may prompt a re-assessment of the role of cryopreservation of stem cell products in clinical practice. If confirmed, it will be critical to understand the immunologic consequences of cryopreservation and how they might influence the clinical impact on chronic GVHDCopyright © 2023 American Society for Transplantation and Cellular Therapy

Why Are Patients Not Getting a Graft? An Intent-to-Transplant Analysis in the Times of Universal Coverage and Haploidentical Donors

Introduction: Allogeneic hematopoietic stem cell transplantation (alloHSCT) is a potentially curative option for patients with hematologic diseases. When considered candidates, patients face barriers to receive a transplant. Therefore, we aimed to analyze factors that limit or favor access to an alloHSCT in a population that has been HLA typed and therefore with a potential intent-to-transplant. Method(s): We retrospectively reviewed records from 2015 until the start of the COVID19 pandemic in two Mexican government- funded transplant centers and one private that have in-house HLA typing;in two of them, an outpatient transplant strategy is followed for most patients. HLA-typed patients who were potentially eligible for transplantation were included and their outcomes were assessed in an intent-to-transplant basis. We compared the outcomes of patients who underwent transplantation to those who did not and evaluated contributing barriers to access alloHSCT with multivariate logistic regression. Result(s): A total of n=374 patients were analyzed. The median age at HLA-typing was 35 years (IQR 23-47);59.3% had acute(Table Presented) leukemia, 17.4% bone marrow failure or myelodysplastic neoplasms, 13.1% lymphoma, 8% myeloproliferative neoplasms, 1.1% chronic lymphocytic leukemia and 1.1% multiple myeloma. Most patients (55.9%) had government insurance coverage. Median time from diagnosis to HLA-typing was 8 months (IQR 3-19). The majority had a potential donor (94.4%): 56.4% haploidentical, 37.4% a matched sibling donor and 0.5% an unrelated donor. Almost half of them received a transplant (n=185, 49.5%), the median time from HLA-typing to alloHSCT was 2 months (IQR 1-5.5). Disease activity or progression was the biggest barrier for transplantation;Table 1. Donor availability limited transplant access for 12.1% of patients. Access to transplantation was favored by private/out-of-pocket payment (OR 2.1 95% CI 1.3-3.4), and receiving care in the outpatient center (OR 6.4 95% CI 4-10.0), while HLA matching was not (OR 1.2 95% CI 0.8-1.8). Non-relapse mortality in alloHSCT was 21%. Median overall survival (OS) from the intent-to-transplant cohort was 16 months (CI 95% 12.4-19.6). An OS landmark analysis for patients alive at or beyond 2 months (the median time from HLA-typing to alloHSCT) showed prolonged survival in alloHSCT (30 vs 12 months, p <.001), Figure 1. By the time of the analysis 159 patients (42.5%) were still alive and 115 (30.7%) were event-free.(Figure Presented)Conclusion: The most frequent barrier to transplantation was the disease itself, followed by the transplant waitlist and comorbidities. Access to resources and an outpatient strategy or "center effect" favored alloHSCT. In the era of haploidentical transplantation, donor availability was a smaller issue. Efforts to improve timely referrals and access to effective pre-transplant therapies should be undertaken.Copyright © 2023 American Society for Transplantation and Cellular Therapy

Successful matched unrelated donor hematopoietic stem cell transplantation for infantile Wolman disease

Introduction: Wolman disease is a rare genetic disorder with an autosomal recessive inheritance. A mutation in the LIPA gene causes lysosomal acid lipase (LAL) deficiency results in lipid storage and adrenal insufficiency. Death in early infancy is due to liver failure. Patients and methods: We describe the clinical course of a three-month-old infant diagnosed with Wolman disease. A rapid mutational analysis confirmed a LIPA gene defect. Results: He underwent matched unrelated donor peripheral blood stem cell hematopoietic stem cell transplantation (HSCT) at 3 months of age, with a treosulfan-based conditioning, which resulted in engraftment with donor-derived hematopoietic cells. He required supportive care for sinusoidal obstruction syndrome and mucositis. He was administered low dose prednisolone for grade I skin graft versus host disease, and a complete donor chimerism was documented on several occasions. At one year post HSCT, his growth and development were optimal, and there was no hepatosplenomegaly. He is maintained on glucocorticoid and mineralocorticoid supplements for primary hypoaldosteronism. Conclusion: The case emphasizes the timely diagnosis and the potential for successful treatment of Wolman disease by HSCT. © 2022 Pediatric Hematology Oncology Chapter of Indian Academy of Pediatrics

Post-Transplantation Cyclophosphamide for the Prevention of Graft-Versus-Host Disease Should Not Limit Transplantation for Acute Lymphoblastic Leukemia in People with Trisomy 21

Introduction: Use of hematopoietic cell transplantation (HCT) in patients with trisomy 21 (+21) is infrequent given concerns about increased toxicity with cytotoxic chemotherapy.1 Due to increasing evidence of benefit from post-HCT cyclophosphamide (PTCy) for graft-vs.-host disease (GVHD) prophylaxis and lack of prior descriptions in patients with +21,2-4 we report on 2 patients with +21 and acute lymphoblastic leukemia (ALL) who underwent HCT with PTCy. Method(s): Retrospective data were collected from 2 patients with ALL and +21 who underwent allogeneic HCT with PTCybased GVHD prophylaxis from 2019 to 2021. Data collected included age, disease risk, HCT-CI, GVHD incidence, and survival. Result(s): Patient 1 is a 22-year-old male and patient 2 a 25-year-old female. Both had Ph-negative, B-cell ALL. Patient 1 had ETV6/RUNX1 rearrangement, del 12p, gain of X, and he had recurrence of measurable residual disease (MRD) after initial MRD-negative CR with two lines of therapy pre-HCT. Patient 2 had normal cytogenetics and relapsed disease with 4 prior lines of therapy. Both achieved MRD-negativity pre-HCT. Both received fludarabine and melphalan conditioning, and patient 1 also received thiotepa 2.5 mg/kg. PTCy was given on days +3 and 4 at 50 mg/kg with sirolimus and tacrolimus for GVHD prophylaxis. Patient 1 had a haploidentical donor and received one dose of rabbit ATG (1 mg/kg) on day +5. Patient 2 had a matched unrelated donor. There was no significant delay in engraftment of ANC (day 16-19) or platelets (day 15-16). Patient 2 developed acute GVHD at day 30 (stage I skin, stage II GI) that resolved with steroids which were tapered off by day 96 without recurrence. Sirolimus stopped at day 79 (pt 1) and 103 (pt 2) and tacrolimus was stopped at day 274 (pt 1) and 469 (pt 2). Patient 1 developed a sirolimus-induced pericardial effusion at day 84 which did not recur after sirolimus discontinuation. Patient 2 developed moyamoya 8 months post-HCT during tacrolimus taper without other GVHD symptoms. Response to steroids was noted, so tacrolimus was restarted for residual neurological deficit. Neither patient developed chronic GVHD or left ventricular ejection fraction decline, and neither patient had disease relapse at follow-up of 30 and 16 months respectively. Patient 2 developed COVID pneumonia 16 months post-HCT and died while in CR. Patient 1 remains alive, in CR, and off immunosuppression nearly 3 years post HCT. Conclusion(s): Allogeneic HCT with PTCy at standard doses did not appear prohibitively toxic in patients with +21 when administered after reduced-intensity conditioning. In this case series, GVHD rates seemed consistent with larger series in patients without +21. Moyamoya development is associated with autoimmunity in patients with +21 and hence may have been GVHD-related5. Trisomy 21 should not be a barrier to patients otherwise eligible for HCT, even with PTCy prophylaxis.Copyright © 2023 American Society for Transplantation and Cellular Therapy

Outcomes of Cryopreserved Vs Fresh Haploidentical Allogeneic Donor Grafts Using Post-Transplant Cyclophosphamide (PTCy) for Gvhd Prophylaxis

The World Health Organization (WHO) declared COVID-19 a pandemic in March 2020. Since then, logistical challenges arose regarding the procurement of allogeneic (allo) hematopoietic stem cell (HSC) donor grafts. Little data was available on transplant outcomes using cryo haploidentical (haplo) HSC grafts with post-transplant cyclophosphamide (PTCy) for GVHD prophylaxis. We retrospectively analyzed patients who received a first PTCy-based haplo hematopoietic stem cell transplant (Haplo HCT) at a single outpatient transplant center between January 2015 and December 2021. We identified 294 patients, 179 received a fresh graft and 115 received a cryo graft (Table 1). Both cohorts were similar in terms of median age, diagnoses, HCT-CI score and DRI. Out of 179 fresh haplo grafts, 160 (89.4%) were from peripheral blood stem cells (PBSC) and 19 (10.6%) were bone marrow grafts (BM). There were no cryo BM grafts used. Conditioning intensity were similar amongst both cohorts, with 43% myeloablative, 41.9% non-myeloablative and 15.1% RIC regimens used for fresh Haplo HCT and 39.1% myeloablative, 42.6% non-myeloablative and 18.3% RIC cryo Haplo HCT. Median time to engraftment was 16 days for fresh Haplo HCT and 17 days for cryo HCT (p=0.18). Median time to platelet engraftment was 27 days for fresh Haplo HCT and 27.5 days for cryo HCT (p=0.96). Since March 2020, only 8 transplants performed at our institution were from fresh haplo HSC grafts. Cryo grafts performed after March 2020 accounted for 73 (63.5%) of 115 total cryo Haplo HCT performed in the period reviewed. Using a Cox model to evaluate the effect of graft type and adjusting for significant variables, we found no difference in overall survival (OS), disease free survival (DFS), non-relapse mortality (NRM) and relapse rates between fresh and cryo Haplo HCT performed (Figure 1). While we found no difference in grades III-IV aGVHD (Table Presented) (Figure Presented) between fresh vs cryo Haplo HCT, we found a statistically significant higher incidence of grades II-IV aGVHD (p=0.033). There was no difference in all-grade cGVHD (p=0.53) or moderate- severe cGVHD (p=0.86) (Figure 2).(Figure Presented) The National Marrow Donor Program (NMDP) released a statement requiring cryopreservation of unrelated donor grafts at the start of the COVID-19 pandemic. The cryopreservation of all types of allo HSC grafts has been adopted by many transplant programs including ours. Our results mimic a CIBMTR analysis published at the start of the pandemic, where survival outcomes using fresh vs cryo haplo HSC grafts with PTCy as GVHD prophylaxis were similar. Contrary to other reports, we did not see differences in graft failure or rates of cGVHD between fresh and cryo Haplo HCT. The use of cryopreserved HSC grafts for Haplo HCT with PTCy results in favorable outcomes in an outpatient transplant setting. Further studies are needed to determine the cost-effectiveness of this practice in the post-pandemic era.Copyright © 2023 American Society for Transplantation and Cellular Therapy

The Stem Cell Unrelated Donor Search during Covid19

Background In Stem Cell Transplants approximately two thirds of donors are identified and used from unrelated donor registries. In January 2020, we considered the impact that Covid19 infections and restrictions would have on donor availability. We identified that we needed to change our practice to ensure we could continue the SCT procedures which are critical for patients. Methods In January 2020, the Joint United Kingdom Blood Transfusion and Transplantation Service Professional Advisory committee (JPAC) changed the Tissue and cell donor selection guidelines. The risk and restrictions of Covid19 caused significant challenges including logistical issues for product delivery. Donor deferrals at medical assessments increased from 14% to 29% and overall activity in the UK was 75% of usual provision. Best practice was established and agreed with the donor registries. As per NICE guidelines, cryopreservation of all stem cell products was recommended with fresh donations considered according to patient condition. Back up donors were identified where possible. All donors were tested for Covid 19 on day of medical and harvest to ensure effective screening. We carried out 58 stem cell procedures from unrelated donors in 2020 and 56 in 2021. This activity is comparable to previous years. We secured stem cell products from Germany, USA, Korea, Poland, Turkey, Greece, Switzerland, the Netherlands and the UK. We analysed our data to assess if any delays occurred. Ethical approval was not required for this service evaluation. Results SCT activity was maintained throughout Covid19 with only postponement of elective SCT's which was assessed to be in the patient's best interest. Discussion We were able to adapt our practice to the benefit of our patients in unique and challenging circumstances. Conclusion We implemented measures which enabled BMT activity to continue throughout the acute Covid19 period despite challenges with new variants and further restrictions.

Issues Faced by a Resource-Constrained Stem Cell Donor Registry and Impact of Coronavirus Disease 2019 on Their Functioning: A 9-Year Observational Study from a Single Registry in India

Background: Allogeneic hematopoietic stem cell transplantation activity is growing globally as one of the curative treatment options for many hematological diseases. A stem cell transplant registry plays an important role in such treatment. Setting up a functional stem cell donor registry is quite challenging with several issues such as resources, donor recruitment, donor attrition, ethnicity, lack of support, and impact of coronavirus disease 2019 (COVID-19). Aim(s): The aim of the current study was to present the experience of a resource-constrained registry in India as well as the effect of COVID-19 on its operations. Settings and Design: The present study was a descriptive study which was designed to study the functioning of a resource-constrained registry from north India. Material(s) and Method(s): The study data for the period of 2012-2020 pertaining to donor recruitment, number of searches, number of matched donors, number of transplants performed, and donor attrition was collected from the registry software "Prometheus." Statistical Analysis: Descriptive statistics such as frequency and percentage was used. Result(s): During the past 9 years of operation, the registry has faced several issues pertaining to lack of funds, donor recruitment, donor attrition, and COVID-19 has exacerbated their pain points significantly. The registry has recruited a total of 20,093 donors, of which only 7794 have been human leukocyte antigen typed, with the remaining samples awaiting funding. Out of this small number of typed donors, registry has performed 15 matched unrelated donor transplants for Indian and international patients. As a result of COVID-19, donor attrition was on the rise and showed a peak in 2020. During the year 2020, the number of searches, donor recruitment camps, and donors all decreased considerably. Conclusion(s): The establishment and operation of a stem cell transplant registry necessitate extensive planning and resources. The resource-constrained registries face a number of issues pertaining to effective functioning and future developments. The external support and awareness for the cause can help minimize the pain points of these registries. Copyright © 2022 Indian Journal of Transplantation.

Neither COVID-19, nor cryopreservation, prevented allogeneic product infusion: A report from the National Marrow Donor Program.

Background: The Coronavirus Disease 2019 (COVID-19) pandemic in early 2020 has resulted in an unprecedented level of uncertainty and challenge for the stem cell donor registries. To address these challenges, rapid strategies were implemented by the National Marrow Donor Registry (NMDP) and its network partners. Herein, we aim to report the impact of the COVID-19 pandemic on the collection, utilization of grafts, and short-term outcomes of patients who received stem cell products from COVID-19-positive donors. Methods: NMDP data during the early phase (1 March 2020 through 1 May 2020) of the pandemic were compared to the later phase (1 March 2021 through 1 May 2021). Odds ratios were calculated to determine the impact of the pandemic on graft sources requested by transplant centers (TCs). The Kruskal-Wallis test was used to test the effect of the pandemic on the disease indication, volume of searches, and number of products not infused. Results: Although there was an initial decline in overall donor searches during the early phase of the pandemic, these numbers increased reaching pre-pandemic levels during the later phase. Urgent malignant diseases remained the most common indication for transplant in 2021. The pandemic necessitated cryopreservation of stem cell products due to transportation restrictions as well as clinical uncertainties in managing the virus. Cryopreserved grafts remained the most common requested grafts throughout the pandemic. In the later phase of the pandemic, the total numbers of requests for fresh grafts increased, mostly due to the increase in requests for fresh bone marrow (BM) grafts. As the pandemic continued, TCs became more accepting of cryopreservation, resulting in a reduction in the number of products not infused. Lastly, no short-term deleterious outcomes were noted among the patients who had stem cell products infused from a SARS-CoV-2-positive donor. Conclusion: Throughout the pandemic, the NMDP and TCs worked tirelessly to ensure that patients would receive lifesaving grafts when needed. The data reported here, although limited by small numbers, illustrate that transplantation from donors with COVID-19 is feasible and safe.

OUTCOME OF ADULT HEMATOPOIETIC TRANSPLANT RECIPIENTS AFTER ADMISSION TO INTENSIVE CARE UNIT (ICU): SINGLE CENTRE EXPERIENCE

Background: Intensive care unit (ICU) admission during hematopoietic stem cell transplant (HSCT) is associated with poor prognosis1,2. Published series report a range of ICU admission rates from 24-40% of transplant patients, most frequent reasons involving septic shock, respiratory failure and veno-occlusive disease3. In addition, patients undergoing HSCT are at a high risk of severe morbidity and mortality associated with COVID-194. Aims: The aim of this study was to analyze outcome of HSCT patients requiring ICU admission in our center. Methods: We retrospectively analysed outcome of 752 patients who underwent HSCT in our centre from January/2008 to June/2021. Data were collected from patients' clinical histories. Results: 103 (14%) patients required ICU admission (baseline and HSCT characteristics on table). Median time to ICU admission was 42 days (-2-1765). Seven of these patients were admitted to ICU on two occasions giving a total of 110 consecutive ICU admissions available for analysis. Main reason for ICU admission was respiratory distress (74;67%), mainly due to pneumonia (53%) including a 3% caused by COVID19, pulmonary edema (26%) and pulmonary haemorrhage (8%). Septic shock was second most common cause for ICU admission (26;24%) due to gram-negative bacilli (47%), fungal (15%) gram-positive bacteria (13%), virus (10%) and others/idiopathic (16%). Other less frequent causes were veno-occlusive disease (11;10%), hepatic failure/encephalopathy (8;7%), haemorrhagic complications (6;5%), cardiorespiratory arrest (2%), GVHD (2%), cardiogenic shock (2%). Of the 110 ICU admissions, 37 (34%) required hemofiltration, of which 30 (81%) died;and 77 (70%) required orotracheal intubation, of which 59 (77%) died. During the 110 ICU admissions, 67 patients (61%) died in the ICU;of these, 40 (37%) received unrelated donor HSCT, 36 (33%) sibling donor, 16 (15%) haploidentical and 17 (16%) autologous. Median ICU length of stay of these patients was 13 days (range 1-76). The cause of death was the same reason for ICU admission. Eighteen (16%) patients were discharged from ICU and died prior to Hospital discharge and 24 (22%) survived to Hospital discharge and were classified as post-discharge survivors. Of these 24 cases, 19 (79%) remain alive while the others (5;21%) succumbed to underlying disease or complications post-HSCT. Off note, both patients with COVID19 pneumonia (haploidentical and autologous HSCT respectively) were discharged from ICU and remain alive to date, without major complications. Summary/Conclusion: In our study 14% of transplant recipients required ICU admission, slightly lower than previous reports. Most common cause of admission was respiratory failure, consistent with reported. Mortality rate during ICU admission was 61%;higher death rate observed in allogeneic transplantation and those requiring aggressive ICU treatments such as mechanical ventilation or hemofiltration. Although patients with COVID19 pneumoniae who require ICU admission are usually associated with adverse outcome, in our series they responded successfully to intensive treatment. ICU admission following HSCT is associated with poor prognosis, but should not be considered futile. (Table Presented).

Hematopoietic Stem/Progenitor Cells and Engineering: CRYOPRESERVATION OF UNRELATED DONOR PERIPHERAL BLOOD HEMATOPOIETIC CELL PRODUCTS DOES NOT IMPAIR PLATELET AND NEUTROPHIL ENGRAFTMENT

Background & Aim: During the COVID pandemic the National Marrow Donor Program® (NMDP)/Be The Match® required cryopreservation of unrelated hematopoietic stem cell (HPSC) products prior to initiation of recipient conditioning to minimize risks associated with logistical complications. Transplant centers are still evaluating cryopreservation associated risk factors due to reported concerns on poor postthaw graft quality compared to fresh products. We evaluated the effect of cryopreservation on engraftment outcomes. Methods, Results & Conclusion: Data from patients receiving either unrelated HPSC fresh or cryopreserved products obtained through the NMDP were included in this study. There were 43 fresh infusions during (Table Presented) during 2019 and 54 cryopreserved infusions between January 2020 and January 2022. Neutrophil and platelet engraftments were our primary endpoints. Absolute neutrophil count (ANC) recovery was defined as an ANC of ≥ 0.5×109/L for three consecutive laboratory values obtained on different days. While platelet engraftment was determined as the first day of three consecutive measurements, obtained on different days, where the platelet count is ≥ 20×109/L without a platelet transfusion in the previous seven days. Medians for two unpaired groups were compared by using Mann-Whitney U test. Two-sided p-values < 0.05 were considered statistically significant. Of the total of fresh transplants, 62.8% of patients underwent reduced intensity conditioning (RIC) while 37.2% underwent myeloablative conditioning (MAC). Regardless of the diagnosis category and in accordance with the American Society of Blood and Marrow Transplantation (ASBMT) Standardized Request for Information (RFI), 11.6% of recipients were classified as a high risk, 20.9% as an intermediated risk, 41.9% as a low risk and 25.6% unclassified. Whereas 52.8% of patients who received cryopreserved products underwent RIC and 47.2% underwent MAC;according to ASBMT-RFI classification, 18.9% were considered as a high risk, 24.5% as an intermediated risk, 41.5% as a low risk and 15.1% unclassified. Engraftment characteristics for both groups of patients is summarized in Table I. No statistically significant differences in engraftment were observed. Our analysis suggests that compared to outcomes of fresh product transplantation, cryopreservation does not negatively effect allograft quality in terms of neutrophil and platelet engraftment.

Hematopoietic Stem/Progenitor Cells and Engineering: EVALUATION OF CELL CONCENTRATION, TRANSIT TIME AND CRYOPRESERVATION OF UNRELATED DONOR PRODUCTS ON ENGRAFTMENT

Background & Aim: Prior to the COVID-19 pandemic, allogeneic transplants were typically performed with fresh hematopoietic stem cell (HPSC) products. Unrelated donor (UD) cells are obtained through the National Marrow Donor Program (NMDP). The logistics for coordinating collection, transport, and delivery of fresh products with preconditioning of recipients is complicated under the best circumstances. The pandemic created uncertainty and disruptions in the UD HPSC process. In March 2020 the NMDP required cryopreservation of UD HPSC products, with rare exceptions, prior to patient conditioning. The impacts of cryopreservation on allogeneic HPSC engraftment are not well defined and conflicting outcomes based on transport time and cell concentration have been published. We aimed to determine if cryopreservation, transport time and pre-processing cell concentration negatively impacted patient engraftment. Methods, Results & Conclusion: Methods: Between July 2021 and January 2022, we analyzed UD HPSC products from 24 patients for CD34+ pre- and post-thaw cell recovery and viability based on transit time and pre-processing cell concentration. Transit time, defined as the interval from end of collection to start of processing, was divided into 3 cohorts: 1-20 h, 21-40 h, and >40 h. Pre-processing nucleated cell counts were divided into 2 cohorts: <200 x106 cells/mL and >200 x106 cells/mL. Neutrophil and platelet engraftment data were obtained from the patients’ medical record. Medians for 2 unpaired groups were compared by using Mann-Whitney U test. Three or more unpaired groups were compared using one-way ANOVA with Tukey’s multiple comparisons or Kruskal Wallis non-parametric test with Dunn’s test for post hoc analysis, as appropriate. For paired data a mixed model ANOVA with Geisser-Greenhouse correction was applied. Results: Information regarding patient diseases and product characteristics are shown in Table I. There were no statistically significant differences between the nucleated cell count in the product bag reported by the collection center and those measured at the time of processing. When these parameters were evaluated based on transit time and pre-processing cell concentration, no statistically significant differences were observed. Conclusion: Although our data set is small, the results suggest that transit time and cell concentration of the HPSC product bag does not negatively impact allograft quality and engraftment. (Table Presented)

Impact of Cryopreservation of Peripheral Blood Stem Cells (PBSC) in Transplantation from Matched Unrelated Donor (MUD).

Background: Cryopreservation of PBSC for allogenic hematopoietic stem cell transplantation (allo-HSCT) was implemented due to the current Coronavirus 2019 pandemic. The impact of match unrelated donor (MUD) graft freezing on the outcome of allo-HSCT in terms of hematological recovery, graft versus host disease (GVHD), and survival are still controversial. Methods: In this study, we compared graft composition, clinical characteristics, and outcome of 31 allo-HSCT from MUD cryopreserved PBSC (Cryo Group) with 23 matched-pair allo-HSCT from fresh MUD PBSC (Fresh Group) performed in our center between January 2020 and July 2021. Results: No significant differences were recognized in clinical characteristics of patients, donors, and transplants between the Cryo and Fresh groups except for a better prognostic comorbidity index (HCT-CI) of the Cryo group. In the Cryo Group, the median time from apheresis to cryopreservation was 46.0 h (range 23.8-53.5), while the median time from cells collection and reinfusion was 13.9 days (range 5.8-28.1). In the Fresh Group, median time from apheresis to reinfusion was 35.6 h (range 21.4-51.2). The number of viable (7-AAD negative) CD34+ cells per kg patient infused was significantly lower in the Cryo Group (5.2 ± 1.9 × 106/kg vs. 7.0 ± 1.3 × 106/kg; p < 0.001). Indeed, there was a 36% (11-70) median loss of viable CD34+/kg cells after freezing. All patients engrafted: median time to neutrophil engraftment (>0.5 × 109/L) was 13.5 days (range 12-15) for Cryo Group and 14 days (range 13-16) days for Fresh Group (p = 0.522), while the median time to platelet engraftment (>20 × 109/L) was, respectively, 14 (range 12-18) and 15 (range 12-17) days (p = 0.904). The incidence of grade ≥ 2 acute GVHD was similar in the two groups (56.5% Cryo Group vs. 60.0% Fresh Group; p = 0.832) and no differences in terms of OS (p = 0.090), PFS (p = 0.200) and TRM (p = 0.970) were observed between the Cryo and Fresh groups. Conclusions: In our series, no differences between the Cryo and Fresh groups were found in engraftment, grade ≥ 2 acute GVHD incidence, OS, PFS, and TRM despite a lower CD34+ infused dose in the Cryo Group. Frozen PBSCs could be considered a safe option also for allo-HSCT from MUD but a higher amount of PBSC should be collected to warrant an adequate viable CD34+ post-thawing.

Demand and usage of unrelated donor products for allogeneic haematopoietic cell transplantation during the COVID-19 pandemic: A Canadian Blood Services Stem Cell Registry analysis.

BACKGROUND AND OBJECTIVES: Understanding changes in the demand and usage of unrelated allogeneic haematopoietic cell transplantation (HCT) donors during the COVID-19 pandemic is needed to optimize pandemic preparedness of registry and donor collection services. The aim of this study was to understand the extent to which the pandemic has impacted the demand and usage of unrelated donors and cord blood units (CBUs) at Canadian Blood Services (CBS). MATERIALS AND METHODS: Data regarding stem cell donor interest and product usage for unrelated allogeneic HCT were retrieved from the database at CBS using de-identified anonymous information. RESULTS: Unrelated donor searches for Canadian patients remained unchanged by the pandemic, reflecting stable demand. The number of unrelated allogeneic transplants performed within Canada also remained stable, while the number of cord blood transplants increased, chiefly for paediatric patients. Requests for donor verification typing, a first signal of potential interest, increased from domestic centres during the first 6 months of the pandemic and decreased from international centres, before returning to baseline levels. The proportion of transplants for Canadian patients who used stem cell products procured from Canadian donors increased between 3 and 6 months after the start of the pandemic before returning to baseline and appears to be increasing again more than 1 year after the start of the pandemic. Use of CBUs for Canadian paediatric patients increased and remains elevated. CONCLUSION: Demand for unrelated adult HCT donors has remained stable despite the evolving pandemic with a transient and recurring increased interest and usage of domestic adult donors. Use of CBUs for paediatric patients has increased and remains elevated. Registries and donor collection centres should maintain the capacity to expand services for domestic donor collection during pandemics to offset threats to international donor usage.

A prospective phase 2 study testing high dose post-transplant cyclophosphamide as sole GHVD prophylaxis after matched allotransplant using baltimore-based reducedintensity conditioning regimens and PBSC as source of graft

Introduction: The use of high-dose post-transplant cyclophosphamide (PTCY) has revolutionized graft-versus-host disease (GVHD) prophylaxis and allowed to successfully reconsider haplotransplant in recent years. As this strategy significantly reduces the incidence of both acute and chronic GVHD, PTCY has been thereafter considered not only in matched settings but also as sole GVHD prophylaxis, at least when considering myeloablative allotransplant using matched sibling (MSD) or unrelated (MUD) donors and bone marrow as source of graft. Here, PTCY, as a sole GVHD prophylaxis, was tested in a reduced-intensity conditioning (RIC) setting, using peripheral blood stem cells (PBSC) as source of graft considering that this platform is currently broadly used worldwide in adults. Methods: This prospective monocentric phase 2 study was designed with the main objective to demonstrate the feasibility and safety of using only PTCY (without cyclosporine A nor mycophenolate mofetyl after transplant) in adults (18-70 years old) eligible for a RIC PBSC transplant with MSD or MUD. The Baltimore platform with 2 days of PTCY 50mg/kg/day on days 3 and 4 post infusion was considered as conditioning regimen, using fludarabine for lymphoid disease or clofarabine for myeloid disease. The primary objective was to appreciate the incidence of corticosteroid-resistant acute grade 3-4 GVHD (CR 3-4 GVHD) within 100 days post-transplant. According to statistical rules, patients have to be included in a step by step fashion (3, 3, 6, 15, 15 and 17 patients) for a total of 59 evaluable patients (meaning having received PTCY), in order to stop the protocol soon enough in case of excessive rate of deleterious severe acute GVHD (graded according to Mount Sinai International Consortium). Thus, the trial had to be stopped in case of documentation of > 2 CR 3-4 GVHD for the first 3 patients, >3 CR 3-4 GVHD for the first 6 patients, > 4 CR 3-4 GVHD for the first 12 patients, > 6 3-4 CR GVHD for the first 27 patients, > 8 CR 3-4 GVHD for the first 42 patients and finally as soon as > 9 CR 3-4 GVHD for the last included patients. All patients gave informed consent. The trial was registered at ClinicalTrials.gov Identifier: NCT03263767. Results: The results of the first 27 first patients (males n=17 and female n=10;median age: 59 years old (yo), range: 26-70) are reported here. They were included between February 2018 and November 2020. Diagnoses were AML (N=8), MDS (N=5), CMML (N=2), myelofibrosis (N=5), CML (N=1), DLBCL (N=1), T-cell lymphoma (N=1), Philadelphia positive B-ALL (N=1), CLL (N=1), lymphoblastic lymphoma (N=1) and mixed phenotype acute leukemia (N=1). Donors were MSD in 10 cases and MUD in 17. Only one primary graft failure was documented in a 61 yo MDS patient with active disease at transplant. He is however still alive in response after autologous reconstitution. With a median follow-up of 17.6 months (range: 10-42) for alive patients at the time of analysis (July 2021), 1-year and 2-year survivals were 80.9+7% and 74.7+9%, respectively, for both OS et DFS. GVHD-free/relapse-free survival (GRFS) at 1-year and 2-year was 58.7+9% and 52.2+10%, respectively. Three relapses (11%) and 6 deaths occurred. Deaths were due to acute GVHD in 4 patients (including 1 with sepsis and 1 with SARS-COVID 19 infection) and relapse in 2. Grade 2, 3 and 4 acute GVHD occurred in 11, 1 and 4 patients, respectively, for a total of 59% of grade 2-4 acute GVHD. CR 3-4 GVHD was observed in all of 5 patients with acute grade 3-4 GVHD and 4 died related to GVHD. Moderate/severe chronic GVHD occurred in 5/22 (22.7%) evaluable patients, including 4 still on immunosuppressive therapy at 40, 28, 25 and 16 months post-transplant. Overall non-relapse mortality (NRM) was 14.8% and related to acute GVHD. However, the number of cases conducting to stop the protocol was not reached. Conclusion: PTCY as a sole GVHD prophylaxis is here demonstrated as possible and relatively safe for adults receiving a matched PBSC Baltimore-based RIC allograft. The very good survivals reported he e may be related to a strong GVL effect associated with the high incidence of acute GVHD. However, because of this high incidence and the fact that NRM was related to GVHD after this first analysis, we have now made an amendment to test the addition to PTCY of one day of anti-thymoglobulin (ATG) 2.5 mg/kg on day-2 for the next 32 patients to be included. This second cohort receiving PTCY+ATG as a sole prophylaxis is ongoing.

Assessment of Serology after Sars-Cov-2 Vaccine in Allogeneic HCT Recipients

Introduction: Randomized trials demonstrated ~95% efficacy of SARS-CoV-2 spike messenger RNA (mRNA) vaccines. Patients (pts) after allogeneic hematopoietic cell transplant (HCT) have a variable period of immune deficiency and the impact of diagnosis, treatment regimens, GvHD, and immunosuppression on vaccine (vacc) immunogenicity is unknown. Methods: We performed a retrospective analysis of 149 consecutive pts (Table) who received a SARS-CoV-2 vacc between 12/17/2020, and 5/21/21, and were tested for anti-SARS-CoV-2 S1/S2 antibodies. Serology testing was performed with the Liaison® SARS-CoV-2 S1/S2 IgG assay (DiaSorin) with ≥15 AU/mL defined as a positive result. Pts with prior COVID-19 infection were excluded. Pts received mRNA-1273/Moderna (n= 46), BNT162b2/Pfizer-BioNTech (n= 100) or Jannsen vacc (n= 3). Reactogenicity was not investigated. Demographic and treatment variables were tested for prediction of vaccine response using Chi-square test or Fisher's exact test for categorical variables and two-sample t test for continuous variables. Univariate and multivariable logistic regression analyses with backward selection using Akaike information criterion (AIC) were used to examine interdependence of those variables and odds ratios (OR) with 95% confidence intervals (CI). Results: Pts underwent HCT from a related HLA matched sibling (n=36), related haploidentical (n= 23), or matched/mismatched unrelated donor (n= 89). 93% received fludarabine in the HCT conditioning regimen (data not shown). All pts received a calcineurin inhibitor (CNI) and 76 pts received ATG for GvHD prophylaxis. All pts achieved at least mixed donor lymphoid engraftment (data not shown). Median time from HCT to 1st vaccination was 26 months (range, 3-258 months). Median age at time of vaccination was 61 years (range, 24-78) and 75 (50%) were female. Serology was tested at a median of 37 days (range, 6-119 days) after the second vacc dose. Serology was tested <14 days in 3 pts;all were seropositive. No pt developed COVID-19 during the period of observation. 101 pts (67%) tested positive for anti-SARS-CoV-2 S1/S2 antibodies (vacc responders). Of the responders, the median time from HCT to 1st vacc was 45.5 months (range, 3-258, SD 39.78). Among the 23 pts between 3-9 months after HCT, 26% (n=6) had a positive antibody response, but all were receiving ongoing immunosuppression at time of vaccination. 29% (n=29) vacc responders were receiving prednisone (pred) in the management of cGvHD at the time of vaccination. 48 pts did not mount an antibody response (vacc non-responders). Of the non-responders, 30 pts were receiving cGvHD treatment at the time of vacc, 31 pts were taking pred, and 20 pts were taking CNIs. In univariate analysis, we found a history of prolonged use of pred (>8 weeks) and/or CNIs, on current treatment for cGvHD at time of vacc, and receipt of rituximab in the preceding 12 months predicted for lack of response (Table). Active use of pred and treatment with pred >8 weeks in the preceding 12 months prior to vacc predicted vacc non-response [OR 0.221;95% CI (0.106 - 0.456);p<0.001] and [OR 0.408;95% CI (0.197 - 0.844);p=0.016] in univariate analysis, respectively, however, active use of pred was predictive [OR 0.07;95% CI (0.016-0.304;p<0.001] while pred treatment >8 weeks was not [OR 2.00;95% CI (0.55-7.298;p=0.293] in multivariable analysis. Other significant predictors for non-response in the multivariable analysis include pt use of ruxolitinib [OR, 0.233, 95% CI, (0.067-0.808);p=0.022], and rituximab within 1 year [OR, 0.026, 95% CI, (0.007-0.099);p<0.001]. Discussion: In this study, we found that 67% allogeneic HCT pts developed anti-SARS-CoV-2 S1/S2 antibodies after SARS-CoV-2 vaccination. Predictors of non-response after adjustment for potential confounders, were factors that are expected to suppress immune response including active use of immunosuppressive medications. Consistent with prior studies, anti-CD20 therapy likely impairs humoral response to vaccination. Ruxolitinib also appears to impair response. owever, a proportion of pts being actively treated for cGvHD responded to vaccination and these pts should still be encouraged to receive vaccination in consideration of the COVID-19 mortality risk. Many questions remain including the protective benefit of immune response, the duration of response, and the potential value of booster vaccinations in non-responders. [Formula presented] Disclosures: Rowley: ReAlta Life Sciences: Consultancy.

Orphan disease: a Rare case of Malignant Osteopetrosis

Reports on clinical cases of orphan pathologies, as autosomal recessive type of infantile malignant osteopetrosis, have a great practical importance for scholars. Osteopetrosis may already manifest itself in utero. In early childhood, there is a classic triad of symptoms: increased bone density and fragility, severe anemia. Diagnostics and allogeneic hematopoietic stem cell transplantation at the age of up to 1 year can be cured and significantly increase life expectancy. Bone marrow transplantation is only treatment that has been proven to significantly alter course of autosomal recessive type of osteopetrosis. Inspide of successful transplantation may or-thopaedic, dental problems and their vision rarely significantly improves, however haemopoietic potential is restored and the long term prognosis is favourable. Herein we report a case of patient diagnosed with osteopetrosis and underwent allogeneic hematopoietic stem cell transplantation, with no prior determination type of mutation. Complexity of case: late diagnosis autosomal recessive type of osteopetrosis (at 3.1 years), despite characteristic early clinical manifestations, a protracted preparatory period associated with search for an unrelated donor and COVID-19 pandemic, for allogeneic-hematopoietic stem cell transplantation performed at the age of 4.3 years. In resulting, was engraftment of bone marrow transplant, with restoration hematopoietic func-tion, but with preserved neurological and physical disabilities in a form of psychomotor develop-ment retardation. Allogeneic hematopoietic stem cell transplantation led to restoration hematopoietic function of the graft in this case of late diagnosis osteopetrosis.

Review of Unrelated Donor Cord Blood Transplantation in Children over the Past 3 Decades

Four decades ago, Hal Broxmeyer demonstrated that umbilical cord blood (CB) contained hematopoietic stem cells (HSC) and hypothesized that CB could be used as a source of donor HSC for rescue of myeloablated bone marrow. In 1988, Gluckman et al reported the first successful cord blood transplant (CBT) of a child with Fanconi Anemia using matched sibling CB. This patient survives and 35 years later still has durable hematopoiesis from the CB donor graft. In 1991, Rubinstein et al established an unrelated donor (UD) CB bank and in 1993 the first UD CBT was using a unit from this bank. Since that time, >40,000 CBTs have been performed worldwide. We hypothesized that changes in cord blood banking (increased size, diversity, and quality of banked units enabling selection of units with higher cell doses and closer HLA matching) and in transplantation (less use of steroids, availability of newer therapies for prophylaxis and treatment of graft versus host disease [GVHD], improved antifungal and antiviral detection and therapeutics) have improved outcomes of CBT today. To address this hypothesis, we performed a retrospective study combining data from Eurocord and Duke University in a large cohort of children transplanted with a single UD CB unit (CBU) from 1993-2019. Standard transplant outcomes (overall survival [OS], disease free survival [DFS], acute and chronic GVHD, treatment related mortality [TRM], and relapse) and changes in outcomes over 3 time periods (1:<2005, n=1297;2:2005-2010, n=1735;and 3:>2010, n=1802) were studied. Relative contributions of cell dose and HLA matching to transplant outcomes over time were assessed. A total of 4834 patients (4015 from Eurocord and 819 from Duke) were analyzed. The majority of patients, (59%, n=2839) had malignant diagnoses including 1422 with ALL, 887 with AML and 167 with MDS. Of the 1995 with non-malignant diagnoses, 761 had inborn errors of metabolism, 644 had primary immunodeficiency, 325 had a bone marrow failure syndrome and 206 had a histiocytic disorder. Half of the patients had positive serologies for CMV prior to transplant. The median age of the cohort fell from 5.2 to 3.25 years over time. In patients with malignancies, use of total body irradiation decreased over time. The median total nucleated cell (TNC) and CD34+ cell doses administered were 8.07x10e7 and 6.17x10e5 cells/kg and increased over time. HLA matching and transplantation of patients in earlier disease states also increased over time, p<0.001 for both. The probability of 5-year OS in the entire cohort was 53.48% and improved over time: 42%;57.4%;and 60.4%, in periods 1,2,3 respectively (p<0.0001). OS improved with closer HLA matching, higher cell dose, myeloablative conditioning, and negative pre-transplant CMV serologies. For patients with malignancies, DFS increased and TRM and acute GVHD decreased over time. In contrast, leukemic relapse did not change throughout the years. OS was higher in patients with inborn errors of metabolism and also improved over time with 57.8% surviving before 2005, 69.4% from 2005-2010, and 71% after 2010 (p=0.0141). Similar results were seen in the cohort with immune deficiencies. In the entire cohort, the median time to neutrophil engraftment decreased from 25 days (period 1) to 19 days (period 3). In multivariate analysis for engraftment, a higher TNC dose (p=0.001) up to but not beyond the median cell dose (8.07x10e7 cells/kg), total body irradiation, and the use of ATG improved engraftment. Acute GVHD decreased from 35% before 2005 to 27.1% after 2010 (p=0.0556) while the incidence of chronic GvHD was stable. The use of ATG reduced the risk of acute GVHD and closer HLA matching reduced the risk of both acute and chronic GVHD. In this population of patients receiving high cell doses, outcomes were predominantly influenced by HLA matching and increasing cell dose did not abrogate HLA mismatching. In conclusion, we analyzed the largest cohort of pediatric patients undergoing CBT over the past 3 decades. OS, DFS and engraftment have improved over time accompanied b decreases in TRM and acute GVHD. Relapse and chronic GVHD were stable and remain low. These improvements are explained by the increased availability of high quality banked CBUs enabling selection of closer HLA matching and units with higher cell doses. The numbers of CBTs have decreased in the past decade, but these results support the ongoing use of CBT in children lacking matched related or unrelated donors. [Formula presented] Disclosures: Kurtzberg: Neurogene: Consultancy;CryoCell: Patents & Royalties: Duke licensed IP, and data and regulatory packages for manufacturing and use of cord blood and cord tissue MSCs in the treatment of patients with hypoxic ischemic encephalopathy, cerebral palsy, autism, acute ischemic stroke, COVID-ARDS, and COVID-MIS-C.;Sinocell: Patents & Royalties: Duke licensed IP, data, and regulatory packages for use of autologous and sibling cord blood to treat children with cerebral palsy.;Celularity: Current holder of stock options in a privately-held company. Troy: SinoCell: Patents & Royalties;CryoCell: Patents & Royalties;Bristol Myers Squibb: Research Funding;Synthetic Biologics: Honoraria;Gamida Cell: Consultancy;The EMMES Corporation: Consultancy;The Community Data Roundtable: Consultancy;AegisCN: Consultancy.