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

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.

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.

Real-World Experience of Cryopreserved Allogeneic Hematopoietic Grafts during the COVID-19 Pandemic: A Single-Center Report.

In response to the widespread COVID-19 pandemic, cryopreservation of allogeneic donor apheresis products was implemented to mitigate the challenges of donor availability and product transport. Although logistically beneficial, the impact of cryopreservation on clinical outcomes and graft composition remains unclear. In this study, we compared outcomes and graft composition with cryopreserved versus fresh allografts in the setting of allogeneic hematopoietic cell transplantation (allo-HCT). We retrospectively analyzed the clinical outcomes of 30 consecutive patients who received cryopreserved allografts between March and August 2020 and 60 consecutive patients who received fresh allografts before the COVID-19 pandemic. Primary endpoints were hematopoietic engraftment and graft failure (GF), and secondary outcomes were overall survival (OS), relapse-free survival (RFS) and nonrelapse mortality (NRM). In addition, extended immunophenotype analysis was performed on cryopreserved and prospectively collected fresh apheresis samples. Compared with recipients of fresh allografts, both neutrophil and platelet recovery were delayed in recipients of cryopreserved reduced-intensity conditioning (RIC) allo-HCT, with a median time to engraftment of 24 days versus 18 days (P = .01) for neutrophils and 27 days versus 18 days (P = .069) for platelets. We observed primary GF in 4 of 30 patients in the cryopreserved cohort (13.3%) versus only 1 of 60 patients (1.7 %) in the fresh cohort (P = .03). Cryopreserved RIC allo-HCT was associated with significantly lower median total, myeloid, and T cell donor chimerism at 1 month. OS and RFS were inferior for cryopreserved graft recipients (hazard ratio [HR], 2.16; 95% confidence interval [CI], 1.00 to 4.67) and HR, 1.90; 95% CI, 0.95 to 3.79, respectively. Using an extended immunophenotype analysis, we compared 14 samples from the cryopreserved cohort to 6 prospectively collected fresh apheresis donor samples. These analyses showed both a decrease in total cell viability and a significantly reduced absolute number of natural killer cells (CD3-CD56+) in the cryopreserved apheresis samples. In this single-institution study, we found delayed engraftment and a trend toward clinical inferiority of cryopreserved allografts compared with fresh allografts. Further evaluation of the use of cryopreserved allografts and their impact on clinical and laboratory outcomes is warranted.

Antibody Response to 2-Dose Sars-Cov-2 mRNA Vaccine in Allogeneic Hematopoietic Cell Transplant Recipients

INTRODUCTION Immunocompromised patients have been excluded from initial trials evaluating SARS-CoV-2 mRNA vaccines and there is a critical need to warrant vaccine efficacy in hematopoietic stem cell transplant (HSCT) recipients. In this study, we evaluated antibody responses to 2 doses mRNA SARS-CoV-2 vaccine in allogeneic HSCT recipients. METHODS We retrospectively enrolled successive hematopoietic cell transplant recipients across France who completed the 2-dose SARS-CoV-2 mRNA vaccine (BNT162b2 or mRNA-1273) between January 1 st and July 15 th 2021. All included patients had an available semi-quantitative antispike serologic testing after the second dose (from Roche, DiaSorin, Abbott or Siemens). We excluded patients with a prior COVID-19 confirmed by serology or PCR. For detectable antibody, we calculated the binding antibody units per milliliter (BAU/mL) according to the WHO International Standard by applying conversion factors given by the manufacturers (Kristiansen et al., The Lancet 2021). Antibody response was categorized as “weak” or “good” with a threshold of 264 BAU/mL which has been associated to an estimate of 80% of mRNA vaccine-induced protection against symptomatic COVID-19 in immunocompetent patients (Feng S. et al., medRxiv 2021). We built a multivariate logistic regression model to assess factors independently associated with the absence of antibody response after the second dose of mRNA vaccination. RESULTS Overall, 620 allogeneic HSCT recipients from 12 hospitals across France were included in the analysis (60% male with a median age of 59 years old [IQR 47-66]), most with a myeloid (69%) or lymphoid (26%) malignancies. Donors were matched unrelated for 51%, HLA-identical sibling for 31% and haplo-identical for 18%. Thirty-one percent of HSCT recipients underwent a myeloablative conditioning, while 69% received a reduced intensity conditioning. The two doses of vaccines were given one month apart and the median time between transplantation and the initiation of vaccination was 29 months [IQR 14-58]. At a median of 33 [IQR 27-50] days after dose 2, an antibody response was detectable in 496 patients (80% [95CI: 77 to 83%]). Median [IQR] antibody levels was 243 BAU/mL [29.4-1391]. We classified detectable antibody responses as “weak” in 189 patients (30% [95CI 27 to 34%]) and as “good” in 306 (49% [95CI: 45 to 53%]). In the multivariate analysis including 533 patients (420 with detectable antibodies), factors associated with the absence of humoral responses were a time-interval from HSCT < 12 months (ajusted Odds-Ratio (aOR) 2.8 [95CI 1.6 to 4.8]), absolute lymphocyte count <1G/L (aOR 3.0 [95CI 1.7 to 5.0]), systemic immunosuppressive treatments within 3 months of vaccination (aOR 4.5 [95CI 2.7 to 7.5]), together with the use of rituximab within 6 months (aOR 15.1 [95CI 4.3 to 52.7]). In a subsequent multivariate analysis conducted a subset of 227 patients (170 with detectable antibodies) with available gammaglobulinemia as well as B and T lymphocytes counts, factors remaining associated with the absence of antibody response were only low B-lymphocytes count (aOR 5.5 [95CI 2.4 to 12.3]) and time-interval from HSCT < 12 months (aOR 3.3 [95CI 1.5 to 7.2]). CONCLUSION After 2 dose mRNA vaccination, the majority of allogeneic HSCT recipients developed an antibody response although a significant proportion of these responses may be insufficient. Studies are still needed to investigate the effect of a third vaccine dose in patients with a null or weak humoral response. Disclosures: Loschi: Servier: Ended employment in the past 24 months, Honoraria;Novartis: Ended employment in the past 24 months, Honoraria;Gilead: Ended employment in the past 24 months, Honoraria;AbbVie: Ended employment in the past 24 months, Honoraria;CELGENE/BMS: Honoraria;MSD: Honoraria.

Use of Cryopreserved Allogeneic PBSC Results in Delayed Engraftment and Increased Incidence of Poor Graft Function

Use of Cryopreserved Allogeneic PBSC Results in Delayed Engraftment And Increased Incidence of Poor Graft Function Introduction: During COVID Pandemic, national and international transplant centres agreed to use cryopreserve the donor PBSC as a safer option to deliver allogeneic transplants. Published data suggests that use of cryopreserved allogeneic PBSC is safe and comparable to use of fresh PBSC but cryopreservation of stem cells may lead to cell loss and hence efficacy. During COVID pandemic, use of cryopreserved allogeneic PBSC was adopted as policy on 01/06/2020. This look back analysis evaluates the impact of change in policy. Aims: Evaluate Engraftment time, compare with historical data, blood component support, and use of growth factors Methods and Materials: Data was collected from health records (paper and electronic) and laboratory records. Transplant features and engraftment kinetics were analysed. Results: Group A June 2020 to November 2020, 19 patients [M: 13;F: 6;median age: 50yr (range: 23-69)] who received cryopreserved allogeneic PBSC were compared to 35 patients [M:24;F:11;median age: 59yr (range: 21-71)] receiving fresh allogeneic PBSC for engraftment kinetics. There were no differences between two groups regarding underlying diagnosis (p=0.31), sex mismatch, CMV mismatch, blood group mismatch, reduced intensity conditioning [RIC](p=0.28), type of donor (p=0.98) or use of Alemtuzumab (p=0.88). Median infused Cell dose in group A was 5.3 (3.4-7.16) and in group B 4.9 (1.03-6.85), [p=0.11]. Neutrophil engraftment was significantly faster with fresh PBSC as compared to cryopreserved PBSC (16d vs. 25d, p=0.0025) predominantly with MUD (18d vs. 27d, p=0.009) and RIC (16d vs. 25d, p=0.009). Platelet engraftment to 25 was faster with fresh PBSC (13d vs. 20d, p=0.021) with delayed engraftment in MUD (20d vs. 13d, p=0.006) and RIC (23d vs. 13d, p=0.039). Day to engraftment per unit CD34 was shorter with fresh PBSC for neutrophils (median: 3.2, range: 2.0-7.7 vs. 5.3, range: 2.5-16.7;p=0.006) and platelets (median: 2.4, range: 1.7-25 vs. 3.8, range: 2.2-25;p=0.001) but only for MUD. This suggests 35-40% less efficiency with use of cryopreserved PBSC. There was no difference in the need for transfusion support [RBCs (6 units vs. 3 units, p=0.32);platelets (5 pools vs. 7 pools, p=0.33)]. G-CSF use was higher with cryopreserved PBSC in RIC (54% vs. 20%, p=0.031). Two patients experienced TRM before day 90 (3.7%). At day 90, 17/52 (32.7%) had cytopenia in one lineage and 8/52 (16%) had cytopenia in more than one lineage. Delayed engraftment was observed in 10 of 33 patients (30.3%) transplanted in 2020 and the only significant association was use of cryopreserved PBSC (0% vs. 53%, p=0.001). There was no difference in the incidence of aGVHD, hepatic VOD, microangiopathy and bacterial infections. Numbers are not sufficient to make disease specific comparisons. Conclusion: Cryopreserved PBSC result in delayed neutrophil and platelet engraftment predominantly with MUDS and RIC. Incidence of delayed engraftment and poor graft function is higher. Per unit CD34 dose, cryopreserved PBSC are 30-40% less efficient to achieve engraftment. Delayed engraftment with cryopreserved PBSC especially in MUD raises the possibility that time from harvest to cryopreservation contributes to reduced efficacy. Based on these findings it was decided to infuse higher CD34 dose (6-7x10