Intensity Conditioning Regimen Research Articles

Clinical outcomes of patients receiving three versus four doses of methotrexate with concomitant antithymocyte globulin in match unrelated donor allogeneic stem cell transplant: A single‐center experience

AbstractMethotrexate (MTX) doses on days +1, +3, +6, and +11 after match unrelated donor allogeneic stem cell transplant (MUD HSCT) is a common graft‐versus‐host disease (GVHD) prophylaxis regimen. However, the overlapping toxicity of MTX with conditioning chemotherapy sometimes warrants the omission of the fourth dose of MTX. Prior single‐institution studies showed conflicting results comparing the outcomes of patients who received three versus four doses of MTX, but to our knowledge, the effect of concomitant antithymocyte globulin (ATG) has not been reported. Charts of patients who underwent MUD HSCT between 2009 and 2023 were reviewed. Patients received rabbit ATG (Thymoglobulin), given at 0.5 mg/kg on day −3, 2 mg/kg on day −2, and 2.5 mg/kg on day −1. MTX is given at 15 mg/m2 on day +1 and 10 mg/m2 on days +3, +6, and +11. Severe mucositis was the most common indication for day +11 MTX omission (82%). We identified 292 patients (116 in 3 dose cohort and 176 in 4 dose cohort). Median follow‐up was 23 months (range 1–151). Patients in the 4 doses cohort were more frequently male (68% vs. 50%, p < 0.01), received a reduced intensity conditioning regimen (38.0% vs. 22%, p < 0.01), were older (median 58 vs. 54 years, p = 0.02), and received a transplant in the earlier era (median HSCT year 2014 vs. 2018, p < 0.01). A statistically significant difference was not evidenced between the cohorts for the following outcomes: acute GVHD (aGVHD) (HR 1.1, 95% CI 0.9–1.5), chronic GVHD (cGVHD) (HR 1.3, 95% CI 0.8–1.6), relapse‐free survival (RFS) (HR 1.0, 95% CI 0.6–1.5), non‐relapse mortality (NRM) (HR 1.4, 95% CI 0.9–2.2), and overall survival (OS) (HR 1.2, 95% CI 0.9–1.7). Both cohorts had similar median time to neutrophil engraftment at 14 days. When ATG is incorporated, omission of day +11 MTX does not significantly impact the rate of engraftment or cumulative incidence of aGVHD, cGVHD, RFS, NRM, and OS.

Good engraftment after reduced intensity targeted busulfan-based conditioning and matched related donor hematopoietic cell transplantation in hemoglobinopathies.

Hematopoietic cell transplantation (HCT) is an established curative therapy for transfusion-dependent thalassemia (TDT) and sickle cell disease (SCD). The latest American Society of Hematology guidelines recommend myeloablative preparative regimen in patients under 18years of age. The objective was to demonstrate safety and efficacy of a reduced intensity conditioning (RIC) regimen including high-dose fludarabine, anti-thymocyte globulin, and targeted busulfan as a single alkylator to sub-myeloablative exposures. Between 2012 and 2021, 11 patients with SCD and five patients with TDT and matched related donor (MRD) HCT were included. The median age at transplantation was 8.3years (range: 3.7-18.8years). The median administered busulfan AUC was 67.4mg/L×h (range: 60.7-80mg/L×h). Overall survival was 93.8% and event-free survival 87.5% with one engrafted SCD patient with pre-existing moyamoya disease succumbing after drainage of a subdural hematoma. One SCD patient developed a secondary graft failure and was treated with a second HCT. Myeloid chimerism was full in all other patients with a median follow-up time of 4.1years (range: 2.0-11.1years), whereas T-cell donor chimerism was frequently mixed. This RIC conditioning followed by MRD HCT is sufficiently myeloablative to cure pediatric patients with hemoglobinopathies without the need for additional total body irradiation or thiotepa.

Comparable outcomes of allogeneic peripheral blood versus bone marrow hematopoietic stem cell transplantation from a sibling donor for pediatric patients.

Traditionally, bone marrow (BM) has been preferred as a source of stem cells (SCs) in pediatric hematopoietic SC transplantation (HSCT); however, the use of peripheral blood SCs (PBSC) has recently increased. With advancing graft-versus-host disease (GVHD) prophylaxis, whether the BM is still a better SC source than PB in sibling donor HSCT remains controversial. Here, we compared the results of BM transplantation (BMT) and PBSC transplantation (PBSCT) in pediatric patients with malignant or non-malignant diseases receiving sibling HSCT using a total of 7.5mg/kg of anti-thymocyte globulin (ATG). We retrospectively reviewed children who received HSCT from a sibling donor between 2005 and 2020 at Seoul National University Children's Hospital. Of the 86 patients, 40 underwent BMT, and 46 underwent PBSCT. Fifty- six patients had malignant diseases, whereas thirty patients had non-malignant diseases. All conditioning regimens comprised ATG. Busulfan-based myeloablative conditioning regimens were administered to patients with malignant diseases and approximately half of those with non-malignant diseases. The remaining half of the patients with non-malignant diseases were administered cyclophosphamide-based reduced- intensity conditioning regimens. According to studies conducted at our center, all BM donors received G-CSF before harvest to achieve early engraftment. In all 86 patients (47 males and 39 females), the median age at the time of HSCT was 11.4 (range, 0.7 - 24.6) years. The median follow-up period was 57.9 (range, 0.9-228.6) months, and the corresponding values for those with BM and PBSC were 77 (range, 2.4-228.6) months and 48.7 (range, 0.9-213.2) months, respectively. Engraftment failure occurred in one patient with BM and no patient with PBSC. The cumulative incidence of acute GVHD with grades II-IV was higher in PBSC (BM 2.5%, PBSC 26.1%, p = 0.002), but there was no significant difference in those with grades III-IV acute GVHD (BM 0%, PBSC 6.5%, p = 0.3703) and extensive chronic GVHD (BM 2.5%, PBSC 11.6%, p = 0.1004). There were no significant differences in treatment-related mortality (TRM) (BM 14.2%, PBSC 6.8%, p = 0.453), 5-year event-free survival (EFS) (BM 71.5%, PBSC 76.2%, p = 0.874), and overall survival (OS) rates (BM 80.8%, PBSC 80.3%, p = 0.867) between BM and PBSC in the univariate analysis. In the multivariate analysis, which included all factors with p < 0.50 in the univariate analysis, there was no significant prognostic factor for EFS or OS. There was no significant difference in the relapse incidence between BM and PBSC among patients with malignant diseases (BM 14.2%, PBSC 6.8%, p = 0.453). Additionally, there were no significant differences in the TRM, 5-year EFS, and OS rates between malignant and non-malignant diseases nor between the busulfan-based myeloablative regimen and reduced-intensity chemotherapy using cyclophosphamide. In this study, we showed no significant differences in EFS, OS, TRM, and GVHD, except for acute GVHD grades II-IV, between BMT and PBSCT from sibling donors, using ATG (a total of 7.5mg/kg). Therefore, PB collection, which is less invasive for donors and less labor-intensive for doctors, could also be considered an acceptable SC source for sibling donor HSCT in children.

Efficacy and safety of cladribine in combination with busulfan and cyclophosphamide as an intensive conditioning regimen preceding allogeneic hematopoietic stem cell transplantation in relapsed or refractory acute myeloid leukemia

BackgroundCladribine, an analogue of deoxyadenosine, is used for therapy of hematological malignancies. Cladribine-containing regimen has been recommended as a rescue therapy for relapsed or refractory (R/R) acute myeloid leukemia (AML). Its combination with busulfan plus cyclophosphamide (BuCy), as an intensive conditioning regimen prior to allogeneic hematopoietic stem cell transplantation (allo-HSCT), requires more clinical evidence. This study aimed to explore the efficacy and safety of cladribine plus BuCy administered as an intensive conditioning regimen before allo-HSCT in R/R AML patients. MethodsTwenty-three R/R AML patients, who underwent cladribine plus BuCy intensive conditioning regimen before allo-HSCT, were retrospectively analyzed. The median (range) follow-up duration time of observation was 0.73 (0.08–2.69) years. ResultsThe median (range) returned levels of mononuclear cells were 11.5 (6.1–18.5) x 108/kg and CD34+ cells were 5.5 (3.5–9.3) x 106/kg. The median (range) time of platelet reconstitution was 13.0 (9.0–21.0) days and neutrophil reconstitution was 14.0 (11.0–26.0) days. The incidence of conditioning regimen related toxicity (CRRT) affected 69.6% of patients; all CRRT-affected patients had grade I-II symptoms, including gastrointestinal tract (39.1%), oral cavity (26.1%), liver (8.7%), and kidney (4.3%) CRRTs. The incidence of acute graft-versus-host disease (GVDH) included 30.4% among all patients with 4.3% of grade III-IV acute GVHD, and 34.8% of chronic GVHD. During the follow-up period, 4 (17.4%) patients relapsed, and 6 (26.1%) patients died (cause of death: disease relapse, n = 3; infection, n = 2; GVHD, n = 1). The 1-year and 2-year accumulating event-free survival rates were 66.3% and 53.1%, respectively. The 1-year accumulating overall survival rate was 74.7% and 2-year survival rate was 64.0%. ConclusionCladribine plus BuCy intensive conditioning regimen before allo-HSCT exhibits favorable treatment efficacy with acceptable toxicity in R/R AML patients.

Graft-versus-host-disease prophylaxis with ATG or PTCY in patients with lymphoproliferative disorders undergoing reduced intensity conditioning regimen HCT from one antigen mismatched unrelated donor

Post-transplant cyclophosphamide (PTCY) has been introduced as graft-versus-host disease (GvHD) prophylaxis in mismatched and matched unrelated hematopoietic cell transplant (HCT). However, data comparing outcomes of PTCY or ATG in patients undergoing a 1 antigen mismatched HCT for lymphoproliferative disease are limited. We compared PTCY versus ATG in adult patients with lymphoproliferative disease undergoing a first 9/10 MMUD HCT with a reduced intensity conditioning regimen from 2010 to 2021. Patients receiving PTCY were matched to patients receiving ATG according to: age, disease status at transplant, female to male matching, stem cell source and CMV serology. Grade II-IV acute GvHD at 100 day was 26% and 41% for the ATG and PTCY group, respectively (p = 0.08). Grade III–IV acute GvHD was not significantly different between the two groups. No differences were observed in relapse incidence, non-relapse mortality, progression-free survival, overall survival and GvHD-relapse-free survival at 1 year. The cumulative incidence of 1-year extensive chronic GvHD was 18% in the ATG and 5% in the PTCY group, respectively (p = 0.06). In patients with lymphoproliferative diseases undergoing 9/10 MMUD HCT, PTCY might be a safe option providing similar results to ATG prophylaxis. Due to the limited number of patients, prospective randomized trials are needed.

[Risk Factors of Late-Onset Hemorrhagic Cystitis after Allogeneic Hematopoietic Stem Cell Transplantation].

The clinical data of 300 patients who underwent allo-HSCT at the First Affiliated Hospital of Chongqing Medical University from January 2015 to December 2021 were retrospectively analyzed. The relevant clinical parameters that may affect the occurance of LOHC after allo-HSCT were selected for univariate and multivariate analysis. Then, the differences in overall survival (OS) and progression-free survival (PFS) between different groups were analyzed. The results of multivariate analysis showed that the independent risk factors for LOHC after allo-HSCT were as follows: age≤45 years old (P =0.039), intensified conditioning regimen with fludarabine/cladribine and cytarabine (P =0.002), albumin≤30 g/L on d30 after transplantation (P =0.007), CMV-DNA positive (P =0.028), fungal infection before transplantation (P =0.026), and the occurrence of grade Ⅱ - Ⅳ aGVHD (P =0.006). In the transplant patients who have already developed LOHC, the occurance of LOHC within 32 days after transplantation (P =0.008) and albumin≤30 g/L on d30 after transplantation (P =0.032) were independent risk factors for the progression to severe LOHC. The OS rate of patients with severe LOHC was significantly lower than that of patients without LOHC (P =0.041). For the patients aged≤45 years old and with intensified conditioning regimen, it is necessary to be vigilant about the occurrence of LOHC; For the patients with earlier occurrence of LOHC, it is necessary to be vigilant that it develops into severe LOHC. Early prevention and treatment of LOHC are essential. Regular monitoring of CMV-DNA and albumin levels, highly effective antiviral and antifungal therapies, and prevention of aGVHD are effective measures to prevent the occurrence and development of LOHC.

Clofarabine and High-Dose Melphalan Reduced Intensity Conditioning Regimen for Allogeneic Stem Cell Transplantation

Clofarabine and High-Dose Melphalan Reduced Intensity Conditioning Regimen for Allogeneic Stem Cell Transplantation

Reduced mitochondrial respiration in peripheral T cells after paediatric heamatopoietic stem cell transplantation.

Recovery and functional differentiation of T-cell subsets are central for the development of immune function and complications after allogeneic hematopoietic stem cell transplantation (HSCT), but little is known about the cellular respiration and factors influencing T-cell metabolic fitness during immune maturation after HSCT. We included 20 HSCT patients and analysed mitochondrial oxidative phosphorylation and mitochondrial fitness in peripheral blood mononuclear cell samples collected at days +90 and +180 after HSCT. Phenotypic analysis revealed lower overall T-cell counts, lower CD4+/CD8+ ratio and a skewed distribution of early T-cell subsets at day +90, gradually recovering by day +180. Although ATP turnover in HSCT patients was similar to healthy controls, the spare respiratory capacity (SRC) of T cells, reflecting the available energy reserve, was significantly reduced at day +90 and +180 compared to healthy controls. This reduction in SRC was not correlated with the occurrence of acute graft-versus-host disease (aGVHD), the intensity of conditioning regimens and markers of T-cell exhaustion. We found significantly depressed SRC until six months post-HSCT, but we were not able to identify transplant-related risk factors or associations with the clinical outcome.

Intensified conditioning regimens with total marrow irradiation/etoposide/cyclophosphamide and busulfan/etoposide/cyclophosphamide overcome the impact of pre-transplant minimal residual disease on outcomes in high-risk acute lymphoblastic leukemia patients in complete remission.

Among high-risk acute lymphoblastic leukemia (ALL) patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT), those with positive minimal residual disease (MRD) are susceptible to poor outcomes. Therefore, it is necessary to determine the most suitable preparatory regimen for these patients. Data were analyzed from 141 patients who received allo-HSCT and were diagnosed with high-risk ALL. These patients underwent intensified conditioning regimens, including either total marrow and lymphoid irradiation (TMLI)-etoposide (VP16)-cyclophosphamide (CY) or busulfan (BU)-VP16-CY between October 2016 and November 2022. A total of 141 individuals were in complete remission (CR) before transplantation and, among all patients, 90 individuals exhibited a negative MRD status and 51 patients had a positive MRD status. In patients who tested negative for MRD, the incidence of relapse within a 2-year timeframe was 25.0% (24.8%-25.5%), compared with 32.2% (31.2%-33.2%) in MRD-positive patients; however, this difference was not statistically significant. There were no significant differences in the 2-year disease-free survival (DFS) and 2-year overall survival (OS) rates between the MRD-negative and MRD-positive groups (DFS: 67.2% (57.9%-78.1%) vs. 55.5% (42.6%-72.3%); OS: 69.0% (61.9%-88.2%) vs. 66.7% (53.9%-82.5%)). Furthermore, no notable variations were observed in the occurrence of transplant-related mortality (TRM) and graft-versus-host disease (GVHD) across the two groups. This study reveals the benefits of TMLI-VP16-CY and BU-VP16-CY conditioning regimens in high-risk ALL patients with CR and MRD-positive status. A large-scale prospective clinical trial is warranted in the future.

Subjective Oral Dryness following Hematopoietic Cell Transplantation: A Report from the Orastem Study

Xerostomia, or subjective oral dryness, is a serious complaint after haematopoietic cell transplantation (HCT). Xerostomia is rated as one of the most bothersome symptoms by HCT recipients, affecting quality of life negatively. This sub-study of the Orastem study, a prospective, longitudinal, international, observational, multicentre study, aims to describe the prevalence and severity of xerostomia following HCT. Furthermore, the effect of the conditioning regimen, the type of transplantation and oral mucosal changes related to chronic graft-versus-host disease (cGvHD) in the development of xerostomia were studied. HCT recipients rated xerostomia on a 0-10 scale before the conditioning regimen, several times early post-HCT, and after 3 months, while only allogeneic HCT recipients also answered the question after 6 and 12 months. Furthermore, stimulated whole mouth saliva was collected several times. Linear regression models and longitudinal mixed effects models were created to investigate the influence of risk indicators on xerostomia. In total, 99 autologous and 163 allogeneic HCT recipients were included from 6 study sites in Sweden, Canada, the Netherlands and the USA. The prevalence of xerostomia was 40% before the conditioning regimen, 87% early post-HCT and 64% after 3 months. Complaints after autologous HCT were transient in nature, while the severity of xerostomia in allogeneic HCT recipients remained elevated 12 months post-treatment. Compared to autologous HCT recipients, allogeneic recipients experienced 1.0 point more xerostomia (95% CI: 0.1 - 2.0) early post-HCT, and 1.7 points more (95% CI: 0.4 - 3.0) after 3 months. Allogeneic HCT recipients receiving a high intensity conditioning regimen experienced more xerostomia compared to those receiving a non-myeloablative or reduced intensity conditioning regimen. The difference was 2.0 points (95% CI: 1.1 - 2.9) early post-HCT, 1.8 points (95% CI: 0.3 - 3.3) after 3 months and 1.7 points (95% CI: 0.0 - 3.3) after 12 months. Total body irradiation as part of the conditioning regimen and oral mucosal changes related to cGvHD did not significantly influence the severity of xerostomia. The conditioning intensity was a significant risk indicator in the development of xerostomia, while total body irradiation was not. Allogeneic HCT recipients experienced more xerostomia than autologous HCT recipients: a difference that could not be explained by a reduction in stimulated salivary flow rate or the development of oral mucosal changes related to cGvHD.

Minimal intensity conditioning strategies for bone marrow failure: is it time for "preventative" transplants?

Hematopoietic cell transplantation (HCT) can cure blood dyscrasias and reduce the risk of hematologic cancers in patients with inherited bone marrow failure syndromes (IBMFS). However, because of its high mortality rate, HCT is generally reserved until patients with IBMFS manifest life-threatening cytopenias or myeloid malignancy, at which point outcomes are poor. Screening tests that accurately predict transformation and enable timely intervention are lacking. These unknowns and risks limit the use of HCT in patients with IBMFS, sometimes until significant disease-related sequelae have occurred. A major goal for IBMFS is to reduce cellular therapy-related complications to the point that earlier intervention can be considered before significant transfusion exposure, occurrence of comorbidities, or malignant transformation. In recent decades, disease-specific allogeneic HCT trials have yielded significant improvements in outcomes in IBMFS conditions, including Fanconi anemia and dyskeratosis congenita. This is in large part due to marked reductions in conditioning intensity to address the increased sensitivity of these patients to cytotoxic chemotherapy and radiation. The success of these approaches may also indicate an ability to leverage intrinsic fitness defects of hematopoietic stem and progenitor cells across IBMFS disorders. Now with advances in tracking somatic genetic evolution in hematopoiesis and tailored minimal intensity conditioning regimens, this question arises: is it time for preventative HCT for IBMFS?

Transplant Outcomes for Acute Myeloid Leukemia or Myelodysplastic Syndromes Secondary to Acquired Aplastic Anemia or Paroxysmal Nocturnal Hemoglobinuria: A Report from the EBMT Severe Aplastic Anemia Working Party

Introduction Clonal evolution into myelodysplastic syndromes (MDS) or acute myeloid leukemia (AML) is the most concerning late event among non-transplanted acquired aplastic anemia (AA) or paroxysmal nocturnal hemoglobinuria (PNH) patients, occurring in nearly 10% of cases. MDS/AML secondary to AA differ from primary MDS/AML, presenting with higher risk cytogenetics and poorer prognosis, usually involving abnormalities in chromosome 7 (Gurnari C. et al., JCO 2023). The survival is poor, and the only curative treatment is allogeneic hematopoietic stem cell transplantation (HSCT). We present the HSCT outcomes of secondary MDS/AML following AA/PNH. Methods We have extracted data from the EBMT database for patients with AA or PNH diagnosed after 2010, who later presented a clonal evolution into AML, MDS, or isolated cytogenetic abnormality insufficient for MDS diagnosis according to WHO 2016 classification, who have undergone HSCT after the clonal evolution diagnosis. We have excluded AA/PNH patients with HSCT before clonal evolution, inherited bone marrow failure syndromes, and non-transplanted patients. Our primary objective was to describe the overall survival (OS). The secondary aims were transplant outcomes according to clonal evolution category and conditioning regimen intensity. Results: We have studied 278 patients from 114 different EBMT centers, 250 patients diagnosed with AA, and 28 with classical PNH. The median age at AA/PNH diagnosis was 34.7 (20.5-51.7) years. At first evolution, 153 (56.5%) patients had a diagnosis of MDS, 45 (16.6%) AML, and 73 (26.9%) isolated abnormal cytogenetics insufficient for a diagnosis of MDS (missing data for 7 patients). The median interval from AA/PNH diagnosis to clonal evolution was 30.1 (8.1-67) and 39.8 (21.5-82.6) months for MDS and AML, respectively. The interval from clonal evolution to HSCT was 5 (3-10.2) and 3.4 (2.3-5.1) months for MDS and AML, respectively. We present transplant characteristics in Table 1. With a median follow-up of 5 (4.3 - 5.9) years, the 5-year overall survival (OS) was 65% for the entire cohort. A subgroup analysis did not find a significant 5-year OS difference among groups: 73, 62, and 60% for isolated cytogenetic abnormality, MDS, and AML, respectively (p=0.3, Figure 1). The main causes of death were transplant-related toxicities (66.7% and 75% for isolated cytogenetic abnormality and MDS, respectively) and relapse or progression for AML (43.8%). AML patients relapsed more frequently than MDS patients by 5 years [cumulative incidences of 22 (9-35) vs. 10% (4-17) for AML and MDS (p=0.046), respectively]. The 5-year non-relapse mortality (NRM) was 19 (7-31) and 28% (19-36) for AML and MDS patients, respectively (p=0.3). When stratifying by conditioning regimen intensity, the 5-year NRM was 34% (19-40) for myeloablative (MAC) vs. 18% (9-26) for reduced-intensity (RIC, p=0.025), with similar incidence of relapse in both groups (4 vs 10% for MAC and RIC, respectively, p=0.2). AML patients were more prone to have presented acute graft-versus-host disease (GvHD) by day+100 than MDS or isolated cytogenetic abnormality patients (cumulative incidences of 36, 26, and 14% respectively, p=0.022). Likewise, AML patients had more chronic GvHD (43, 28, and 12% respectively, p=0.008). Graft-failure, GvHD, relapse-free survival (GGRFS) was 71 (61-82), 60 (51-68), and 45% (29-60) for isolated abnormality, MDS, and AML, respectively (p=0.026). Discussion This study is the largest cohort of transplanted patients with secondary MDS/AML following AA/PNH. The major limitations of our study are its retrospective nature, non-adjusted analyses, and missing data on complete cytogenetics. We found a 5-year OS higher than 60% for MDS/AML compared to 45% in the previously published EBMT study (Hussein A. et al., BBMT 2014) and did not find a survival difference between AML and MDS. Interestingly, the main cause of death for MDS patients was HSCT complications. Furthermore, MAC was also associated with a higher NRM. Clinicians should indicate HSCT with discretion for post-AA/PNH MDS or isolated cytogenetic abnormality, considering the transplant toxicity, especially with MAC, and the risk of primary disease progression. For patients with AML and a high risk of relapse, early tapering of immunosuppressive agents and post-transplant maintenance, such as hypomethylating agents and donor lymphocyte infusion, should be considered.

Dynamic Changes in Pre- and 3 Months Post-Transplant NGS MRD Status May Predict the Allogeneic Stem Cell Transplant Outcome of Patients with AML

Introduction: To deal with the high propensity for relapse and substantial genetic heterogeneity of AML, monitoring measurable residual disease (MRD) has become an effective approach to evaluate the response to chemotherapy and to predict relapse. However, the clinical implications of NGS MRD change after allogeneic hematopoietic cell transplantation (alloHCT) are still under investigation. The aims of this retrospective study are to verify whether alloHCT improved the outcome of AML patients with NGS MRD positive status in pre-transplant and to investigate how pre- and post-transplant NGS MRD status changes affect the outcome of patients with AML. Methods: This study analyzed patients of age more than 18 years who underwent alloHCT between 2018 and 2022 at single center. NGS mutation test was obtained at diagnosis, and every 3 months after stem cell transplant for 2 years with synchronized peripheral blood chimerism tests. Requirement for inclusion in this retrospective cohort study was availability of NGS mutation results at pre-transplant and at 3 months, as well as donor chimerism results after alloHCT. Patients with no mutations by NGS at diagnosis and at pre-transplant were excluded. Patients were classified by the NGS MRD status in pre-transplant and at 3 months post-transplant: Positive MRD to Positive MRD (Group A), Positive MRD to Negative MRD (Group B), Negative MRD to Positive MRD (Group C), and Negative MRD to Negative MRD (Group D). Patient characteristics are in Table 1. The Kaplan-Meier method and log-rank tests were used to estimate the survival and to compare the differences in survival. Statistical analyses were performed with GraphPad Prism version 9.1.0 (Prism Inc), Microsoft Excel (Microsoft Corporation). Results: Median follow-up was 21 months (range, 3-66). One hundred sixty-five patients met inclusion criteria. Among these, 104 (63.0%) were MRD positive, and 61 (37.0%) were MRD negative by NGS at pre-alloHCT. Fifty-one of the MRD positive patients (49%) became MRD negative by NGS at 3 months after alloHCT. The conversion rate to MRD negative from positive by NGS was not different by conditioning regimen (myeloablative (MA) 54.3% versus reduced intensity (RIC) 49.2%, p=0.67), or by AML risk group (intermediate 48.9% versus adverse 44.7%, p=0.84). Four years cumulative incidence of relapse (CIR) of each group was statistically different between Group A and the others (Group A 47.3%, Group B 17.7%, Group C 25.9%, and Group D 10.9%, p&amp;lt;0.001), but not different between Group B, C and D (p&amp;gt;0.5). Median OS was 17 months for Group A, 27 months for Group C, but the other groups did not reach. Four-year OS of each group was statistically different between Group A, Group B, and Group D (Group A 21.1% (95% CI: 2.0 - 53.8), Group B 55.2% (95% CI: 38.7 - 68.9), Group C 50.0% (95% CI: 20.8 - 73.6), and Group D 79.3% (95% CI: 63.7 - 94.9), respectively, p&amp;lt; 0.05). Among 12 patients who were MRD positive by NGS in post-alloHCT, but not in pre-alloHCT (Group C), 3 had clinical relapse, at 4 months, 6 months, and 26 months, respectively. Five patients had NGS mutations different from the initial diagnosis. They did not show clinical relapse and maintained 100% peripheral blood lymphoid (CD3) donor chimerism throughout the observation. Conclusion: This study showed alloHCT could convert 49% of pre-transplant MRD positive patients to MRD negative by NGS. However, there were no differences in conversion rate by intensity of conditioning regimen or by AML risk group. Combining pre- and 3 months post-transplant MRD status by NGS could discriminate prognostic subgroups in post-transplant MRD positive and negative group each and may be useful in designing post-alloHCT therapies.

The Area Under Tacrolimus Concentrations on Day 14-28 Is the Independent Predictor of the Development of Chronic Gvhd in Patients without Severe Acute Gvhd after Unrelated Allogeneic HSCT

Introduction: In unrelated allogeneic hematopoietic stem cell transplantation (UR-SCT), chronic graft-versus-host disease (GVHD) is a critical complication that affects not only patients' quality of life but also post-transplant outcome. Acute GVHD is a major risk factor for the subsequent development of chronic GVHD. The combination of tacrolimus and short-term methotrexate (TAC+sMTX) has been widely used as a GVHD prophylaxis for UR-SCT in Japan. Previous reports have shown that tacrolimus blood concentrations early after transplantation are associated with the development of acute GVHD, but not with that of chronic GVHD. On the other hand, among UR-SCT recipients who did not develop severe acute GVHD, the relationship between tacrolimus blood concentrations and the development of chronic GVHD remains unclear. Methods: To examine the association between tacrolimus blood concentrations and post-transplant outcomes, the area under the tacrolimus concentration on day 0-14 (AUTC 0-14) and day 14-28 (AUTC 14-28) was calculated simply as the sum of the area of the trapezoid for the corresponding period ( Figure). Tacrolimus was initiated by continuous intravenous administration from day -1 in all patients, and no patients were switched to oral administration prior to day 28. Short-term methotrexate was administered at 10 mg/m 2 on day 1 and 7 mg/m 2 on day 3, day 6, and day 11. Among all 151 adult patients with hematopoietic malignancies who underwent first UR-SCT with GVHD prophylaxis of TAC+sMTX between 2010 and 2022 at the Jikei University Hospital, the following were excluded from the analysis: developing grade III-to-IV acute GVHD, using prednisolone or methyl-prednisolone ≥0.5 mg/kg within day 100, engraftment failure, death before day 100, and relapse before day 100. Results: A total of 68 patients were included in the analysis. Median age was 50.5 (range, 16-68) years. Twenty-seven (40%) patients had acute myeloid leukemia, and 18 (27%) had acute lymphoblastic leukemia. Fifty-five (81%) were in complete remission/chronic phase/early stage. The donor source consisted of 42 (62%) bone marrow transplantation (BMT), 20 (29%) cord blood transplantation (CBT), and 6 (9%) peripheral blood stem cell transplantation (PBSCT). BMT recipients transplanted from 22 (52%) HLA 8/8 matched donor, 19 (45%) HLA 7/8 matched donor, and one (3%) HLA 6/8 matched donor. CBT recipients transplanted from 15 (75%) HLA 4/6 matched donor and 5 (25%) HLA 5/6 matched donor. PBSCT recipients transplanted from 5 (83%) HLA 8/8 matched donor and one (17%) HLA 7/8 matched donor. Fifteen (22%) patients were administered additional low-dose anti-thymocyte globulin (ATG) as GVHD prophylaxis. Fifteen male patients transplanted from female donors (22%). Thirty-nine (57%) patients received myeloablative conditioning regimen. The median time from UR-SCT to neutrophil engraftment was 19 days (range, 11-34). Regarding acute GVHD, 46 patients (68%) developed none, 13 patients (19%) developed grade I, and 9 patients (13%) developed grade II. The median observation period for all 68 patients was 48.2 months (4.0 years). The 4-year cumulative incidence (CI) of chronic GVHD was 51%, of which 24% were moderate-to-severe. The CI of moderate-to-severe chronic GVHD was not associated with age, disease status, donor source, HLA incompatibility, ATG use, female to male, intensity of conditioning regimen, and grade I-to-II acute GVHD development. AUTC 14-28 &amp;lt;200 was the only risk factor (AUTC 14-28&amp;lt;200: 32% vs AUTC 14-28≥200: 11%; p=0.047). Multivariate analysis also showed that AUTC 14-28 &amp;lt;200 was the independent factor for development of moderate-to-severe chronic GVHD ( p=0.04). In all 68 patients, 4-year CI of relapse was 20%, 4-year CI of non-relapse mortality was 10%, 4-year GVHD-free, relapse-free, survival (GRFS) was 50%, and 4-year Overall survival was 80%, all of which did not differ between AUTC 14-28 &amp;lt;200 and AUTC 14-28 ≥200 groups. Conclusion: In UR-SCT, our data showed that AUTC 14-28 &amp;lt;200 may be an independent risk factor for developing moderate-to-severe chronic GVHD, even in patients who did not develop severe acute GVHD.

Multiparametric Flow Cytometry Based Quantification of the Marrow Hematopoietic Stem and Progenitor Compartment in Post Allogeneic Stem Cell Transplant Recipients with Poor Graft Function to Evaluate Hematopoietic Stem Cell Quality and Predict Clinical Outcomes: A Pilot Study

Poor graft function (PGF) is a poorly defined, commonly occurring (estimated 5 to 27%) 1 and difficult to treat complication of allogeneic stem cell transplantation (Allo-HSCT). Thrombopoietin agonists such as eltrombopag (EPAG) or CD34-selected cell infusions are treatments offered for persistent cytopenias. However, with limited knowledge of pathophysiology, there is a lack of reliable prognostic biomarkers. We aimed to investigate if assessment of the BM hematopoietic stem and progenitor cell (HSPC) landscape by multiparametric flow cytometry (MP-FCM) could help evaluate stem cell quality and predict clinical outcomes in PGF patients. We screened the UHN biobank repository to identify banked BM samples of patients who underwent diagnostic BM aspirate for PGF post allo-HSCT. Patients who had progressive cytopenia in one or more lineages after achieving engraftment while having full donor chimerism were included. Relapse as a cause of cytopenia was excluded. Controls in 1:1 ratio were Allo-SCT recipients with stable counts with banked day 60 BM aspirate. The blinded BM samples were analyzed with a 14-parameter FCM adapted from panels previously utilized to assess HSPC and mature lineages in cord blood xenograft studies (2). We selected 12 each of PGF and controls. The mean age of all recipients was 50 years and donors was 30.5 years. 23/24 cases had AlloSCT for hematological malignancies with 15 having AML or MDS. There were 14 unrelated (9 matched, 5 mismatched) and 10 related (5 matched sibling, 5 haploidentical) donors. Mean cell dose of infused graft was 6.66(± 1.98)x 10E6/kg CD34 cells. The significant difference between PGF and controls were recipient age (median 57y vs 28y), allo-SCT number (3 vs 0 with 2 nd transplant), intensity of conditioning regimen (myeloablative in 16% PGF vs 83% controls), and incidence of ≥ grade 3 acute graft vs host disease (GVHD) (n=3 vs 0). Most common causes of PGF were GVHD (n=6), infections (n=4) and drug effects (n=5). 11 PGF patients were treated with EPAG with 5 patients (A3, B2, B3, B5, C4) showing complete response, 3 (A6, B6, C5) showing partial response, and 3 (A2, A4, C9) showing no response. Patient C1 showed complete recovery without the use of EPAG, while C9, who initially did not respond to EPAG, showed a slow spontaneous recovery almost a year later. Amongst non-responders A2 and A4 received CD34 boost; with A4 showing a good response to the second boost. Analyzing the HSPC population by MP-FCM, we found that the PGF vs control groups show significant differences in the percentage of CD34+CD19+ B-Lymphoid precursors (B-LP) and CD19+ B lymphocytes. The mean ± SD percentage of B Lymphocytes and B-LPs in the PGF cohort were 6.76% ± 0.096% and 0.39% ± 0.005% respectively, while in the control group they were 20.09% ± 0.136% and 1.17% ± 0.012% respectively. When the 50 th centile value of the B-LPs (0.375%) or CD19+ B cells (10.89%) was investigated as a cut off to predict the clinical syndrome, this strategy achieved a 75% success rate with 3 PGF (blue bars) or control (black bars) samples misclassified (Fig1). Next, we investigated if these HSPC fractions could help predict the clinical outcome of PGF cases. The cases A2 and A4 who demonstrated no count recovery and needed CD34 boost lie in the lower quartile of both B Lymphocytes as well as B Lymphoid precursors content (Fig 1 red arrows). Conversely the three PGF cases in the upper 50 centile of these cell populations (patient B3, C4 and C9) all showed either a spontaneous or EPAG induced recovery of counts. We further investigated if the proportion of immunophenotypic CD34+CD38-CD45RA-CD90+CD49f+ long-term HSC (LT-HSC) could provide additional prognostic information (Fig2). Again, patients A2 and A4 had LT-HSC in the lower 50 th centile. Patient C1 who showed a spontaneous recovery of counts without the need of EPAG had the highest proportion of LT-HSCs despite lying in the second quartile of the cohort for both B cells as well as B-LPs. In conclusion, MP-FCM based analysis of the HSPC landscape in PGF marrow could be a robust prognostic biomarker in Allo-SCT patients.

Comparison of Two Reduced Intensity Conditioning Regimens (Baltimore with Clofarabine vs Thiotepa-Busulfan-Fludarabine) in Adults Receiving Peripheral Blood Stem Cell Haploidentical Transplantation for Myeloid Malignancies: A Retrospective Study of the SFGM-TC

Background: Haploidentical transplantation (haploT) has become a routine practice in many centers but the optimal conditioning regimen has yet to be determined. Indeed, the historic Baltimore reduced intensity conditioning (RIC) regimen has been associated with poor outcomes in myeloid malignancies. Two alternative RIC regimens have recently demonstrated promising results in this setting. One of them replaces fludarabine with second-generation nucleoside analogue clofarabine (Clo-Baltimore regimen [CloB], Chevallier et al., Oncotarget 2018) and the other combines thiotepa-busulfan-fludarabine (TBF, Duléry et al., BBMT 2019). Here we compared outcomes in order to determine if one of these two regimens was superior for the treatment of myeloid malignancies. Methods: This was a multicenter retrospective study conducted by the Francophone Society of Bone Marrow Transplantation and Cellular Therapy (SFGM-TC). All consecutive adults having received a haploT after a CloB or a TBF RIC regimen for a myeloid malignancy between September 2013 and May 2023 were eligible. Patients data were extracted from the PROMISE database. CloB consisted of clofarabine 30 mg/m²/day (d) 5 d, cyclophosphamide (Cy) 14.5mg/kg/d 2 d, and 2-Gy TBI on d-2. TBF consisted of thiotepa 5mg/kg 1 d, busulfan 3.2 mg/kg 2 d, a fludarabine total dose of 120 to 150 mg/m². Graft-versus-host disease (GVHD) prophylaxis consisted of post-transplant Cy (2 doses of 50mg/kg), followed by cyclosporine A and mycophenolate mofetil starting on d+5. Some patients received antithymocyte globulin (ATG) 2.5mg/kg/d on d-2. Graft source was exclusively peripheral blood stem cells (PBSC). To minimize bias between the CloB and the TBF groups, a propensity score matching (PSM) was constructed using a logistic regression model that included age, donor and recipient sex, hematopoietic cell transplantation-specific comorbidity index (HCT-CI), disease, cytogenetic risk (European LeukemiaNet [ELN] 2022), previous transplant, use of ATG, and cytomegalovirus (CMV) status, with the nearest-neighbor algorithm, and strict matching of key factors. Matched groups were then compared for time to engraftment (absolute neutrophil count &amp;gt; 0.5 x 10 9/L) and platelet (PLT) recuperation (&amp;gt;50 x 10 9/L), overall survival (OS), progression-free survival (PFS), GVHD-free, progression-free survival (GRFS), non-relapse mortality (NRM), and incidences of relapse as well as acute and chronic GVHD. Results: A total of 329 patients from 25 centers were included, 267 (81%) receiving TBF and 62 (19%) CloB. After PSM, 51 patients remained in each group, with comparable baseline characteristics except for the proportion of previous allotransplants ( Table). Median age was 60 years, and median HCT-CI score was 2. Main diagnoses comprised acute myeloblastic leukemia (AML, n=72 [71%]), including 42% with adverse genetic risk, and myelodysplastic syndrome (MDS, n=22 [22%]), including 25% with high or very high Revised International Prognostic Scoring System (R-IPSS). Thirty-eight (37%) patients received ATG. Time to engraftment was equivalent after both TBF and CloB (19 d vs 19.5 d, respectively, p=0.70), but TBF patients achieved PLT recuperation faster (27 d vs 31 d, p=0.03). Median follow-up was 24 months. Two-year OS, PFS and GRFS were 55% vs 60% (p=0.19), 52% vs 60% (p=0.25), and 37% vs 50% (p=0.15) for TBF and CloB patients, respectively. No differences were observed in terms of grade 3-4 acute GVHD at 3 months (18 vs 20%, p=0.86) nor two-year extensive chronic GVHD (16% vs 8.3%, p=0.25). However, two-year NRM was significantly higher after TBF (41% vs 16%, p=0.003), while relapse incidence was lower (7.1% vs 24%, p=0.02, Figure). In multivariate analysis, CloB was associated with a lower risk of NRM (hazard ratio [HR] 0.31, 95%CI: 0.1-0.7, p=0.008) and a higher risk of relapse (HR 4.03, 95%CI: 1.2-13.9, p=0.03). Finally, in patients aged &amp;gt;60y, two-year OS was significantly lower for those receiving TBF conditioning (39% vs 61%, p=0.02, Figure) due to higher NRM (56% vs 23%, p=0.005). Conclusions: In this retrospective study, a TBF RIC regimen used for PBSC haploT in adults with myeloid malignancies appeared substantially more toxic than a CloB RIC regimen. However, its enhanced anti-leukemic effect suggests that it should be offered to younger patients with no comorbidities or to those with high-risk disease. Conversely, CloB should be proposed for older or frail patients.

Impact of Socioeconomic Disparities on Outcomes in Adults Undergoing Allogeneic Hematopoietic Cell Transplantation for Acute Myeloid Leukemia

Introduction: It is increasingly recognized that racial and socioeconomic disparities play an important prognostic role and contribute to differences in outcomes in adults receiving chemotherapy for acute myeloid leukemia (AML). Structural racism has also been implicated in limiting access to allogeneic hematopoietic cell transplantation (HCT). However, it is unclear to what degree racial and socioeconomic disparities impact post-HCT outcomes of patients with AML in contemporary practice. To address this uncertainty, we investigated the impact of socioeconomic, racial, and non-biologic disparities on outcomes in a large cohort of adults with AML undergoing allogeneic HCT while in first or second morphologic remission. Methods: We identified 1,004 adults with AML (2022 ICC criteria) who underwent allogeneic HCT between 5/2006 and 10/2021 at a single large university-affiliated cancer center. Data was collected on each patient's individual socioeconomic status (SES), including occupation, insurance type, and education attainment. Distance traveled, marital status, household size, country of birth, and religious affiliation were also recorded. Each occupation was classified by the International Socio-Economic Index (ISEI), a standard index of occupational status. Area-level SES was analyzed through the Area Deprivation Index (ADI), a validated measure of socioeconomic disadvantage which corresponds to U.S. census tract measurements. Collected HCT variables include the AML treatment-related mortality score (TRM), pre-HCT flow cytometric MRD status, HLA donor status, cytogenetic risk, conditioning regimen intensity, and incidence of severe acute and chronic graft-vs-host disease. Measured outcomes include non-relapse mortality (NRM), overall survival (OS), relapse, and relapse free survival (RFS). Cause-specific hazard models were used for univariate and multivariable regression analysis and C-statistics were calculated to quantify each model's ability to predict outcomes. Results: In univariate analysis, none of the socioeconomic or non-biologic factors were significantly associated with NRM, and all had poor predictive performance, with C-statistics not exceeding 0.53 for: marital status, larger household size (i.e., patients with children), distance traveled, ISEI, ADI, insurance status, educational attainment, or country of birth. TRM score (P&amp;lt;0.001), non-myeloablative conditioning (P&amp;lt;0.001), reduced intensity conditioning (P&amp;lt;0.001), CR2 (P=0.017) and marital status (P=0.014) were significantly associated with NRM in a multivariable model, but predictive performance of this model was only fair (C=0.69; Table 1). Marital status was only associated with NRM after multivariable adjustment but not on univariate evaluation, possibly because married patients were, on average, older (P&amp;lt;0.001), more likely to be male (P&amp;lt;0.001), and have higher occupational status/ISEI (P&amp;lt;0.001) and TRM scores (P&amp;lt;0.001), with age and sex as likely confounders (Table 2). African American patients (n=14) were found to have worse NRM in both univariate (P=0.036) and multivariate (P=0.024) models, consistent with previously identified racial/ethnic disparities in AML cohorts. Similar results were found for SES and non-biologic variables in regards to OS, relapse, and RFS. Notable exceptions after multivariable adjustment include: ADI was significantly associated with OS (P=0.036) and RFS (P=0.044) and marital status was not significantly associated with OS or relapse. Additional analyses demonstrated that ISEI and ADI were not associated with increased TRM or HLA donor status. Finally, distance traveled decreased in HCT recipients post-2013 (P&amp;lt;0.003), though the number of AML-related transplants remained unchanged. Conclusion: In this retrospective, single center analysis, socioeconomic and non-biologic factors had very limited impact on outcomes following allografting for adults with AML. While reassuring, patients able to undergo allogeneic HCT are highly selected (e.g. need for caregiver, insurance, etc.) possibly accounting for this finding, as could integrated, multidisciplinary cancer care networks and longitudinal care coordination post-HCT. Further research is needed to investigate disparities among HCT-eligible patients and improve access to HCT with a focus on reducing racial/ethnic disparities.

Post-Transplant Cyclophosphamide Eliminates Disparity in GvHD-Free, Relapse-Free Survival and Overall Survival between 8/8 Matched and 7/8 Mismatched Unrelated Donor Hematopoietic Cell Transplantation in Adults with Hematologic Malignancies

Background: Post-transplant cyclophosphamide (PTCy) has become a standard of care for graft-versus-host disease (GvHD) prophylaxis in recipients of human leukocyte antigen (HLA)-matched and mismatched unrelated donor (MMUD) allografts, generating new opportunities for successful hematopoietic cell transplantation (HCT) regardless of patient ancestry. The National Marrow Donor Program (NMDP)-sponsored 15-MMUD study, which used PTCy-based GvHD prophylaxis (PMID 3390526), demonstrated encouraging overall survival (OS) in adult patients receiving MMUD bone marrow grafts matched at ≤7/8 HLA alleles. Currently, the follow-up ACCESS study (NCT04904588) will determine if similar outcomes can be achieved using MMUD peripheral blood stem cell allografts. As part of its 5-year strategic plan, the NMDP aims to determine the extent of differences in GvHD-free, relapse-free survival (GRFS) between 8/8 and 7/8 URD allografts using PTCy and seeks to develop approaches over time to close the presumed gap in URD outcomes. Methods: The primary objective was to compare GRFS between 8/8 and 7/8 URD HCT using the Center for International Blood &amp; Marrow Transplant Research (CIBMTR) database. After analyzing primary results, secondary objectives were added to compare GRFS, OS, and other clinical outcomes among 8/8 URD, 7/8 URD, and haploidentical-related donor (Haplo) HCT. The study included adult patients (age≥18y) with hematologic malignancies (ALL, AML, MDS) undergoing first URD or Haplo HCT between 2017-2020 using PTCy-based GvHD prophylaxis. Kaplan-Meier curves were used to estimate probability of GRFS and OS. Cox regression examined the independent effect of HLA match controlling for other clinical factors on outcomes referenced to 8/8 URD HCT. A priori clinically selected factors considered as possible confounders in the regression model included disease risk index, comorbidity risk, pre-HCT Karnofsky score, conditioning regimen intensity, graft source, donor/recipient CMV serostatus, year of HCT, donor/recipient age and race/ethnicity. Final models were stratified by factors violating the proportional hazards assumption. Factors were eliminated in a backwards fashion if p-values were &amp;gt;0.10 unless inclusion affected the hazard ratio (HR) of HLA match by more than 10%. Interactions were tested against a p-value of &amp;lt;0.01. Results: Table 1 shows demographics for the three patient cohorts: Haplo (n=2772), 8/8 URD (N=1517), and 7/8 MMUD (N=540). Notable differences among the cohorts included: 8/8 URD recipients had younger, predominantly Caucasian donors and were more likely to receive myeloablative conditioning. Haplo recipients had more donor/recipient CMV seropositivity and received more reduced intensity conditioning. Otherwise patient characteristics were similar. Contrary to our expectations, multivariable regression analysis (MVA) showed no significant differences in either GRFS or OS between recipients of 8/8 and 7/8 URD HCT at 1, 2 and 3-years post-HCT ( Figure 1). Outcomes, including relapse and NRM, between 8/8 and 7/8 URD HCT were similar irrespective of conditioning intensity. However, 8/8 URD HCT associated with lower two-year moderate/severe chronic GvHD than 7/8 URD [1.30 (1.00-1.68), p=0.049]. We next compared GRFS and OS among 8/8 and 7/8 URD and Haplo at 3y after HCT. On MVA, GRFS [HR 1.15 (1.04-1.26), p=0.005] and OS [HR 1.15 (1.03-1.29), p=0.013] were significantly better in 8/8 URD compared to Haplo HCT. Differences between 8/8 URD and Haplo appeared to be driven by significantly higher NRM [HR 1.46 (1.22-1.74), p&amp;lt;0.001)] and two-year moderate/severe chronic GvHD [HR 1.28 (1.07-1.54), p=0.007] in Haplo. No significant differences were seen in GRFS or OS at 3 years when comparing 7/8 URD to Haplo. Causes of death among donor types were similar with primary disease relapse/progression, infection and organ failure being the most frequent. Conclusions: Use of PTCy-based GvHD prophylaxis seems to have resolved previously observed differences in GRFS and OS between 8/8 and 7/8 URD HCT. HCT using an 8/8 URD HCT, if available, continues to be the best option for patients lacking a matched sibling donor. Further studies comparing Haplo to 7/8 URD HCT are warranted, but will require larger numbers of 7/8 URD HCT. Both mismatched donor sources substantially increase access to HCT for patients regardless of their ancestry.

Clinical Factors but Not Somatic Mutations Predict for Survival in Patients with Myelofibrosis Undergoing Allogeneic Hematopoietic Cell Transplant: Analysis of the North American Myelofibrosis Transplant Outcome (NAMTO) Study

Introduction: Myelofibrosis (MF) is a clonal hematologic malignancy characterized by constitutive JAK-STAT activation and aberrant cytokine signaling. Allogeneic hematopoietic stem cell transplantation (allo-HCT) remains the only potentially curative therapy in MF. The contribution of disease-, patient- and donor-related factors to allo-HCT outcomes remains to be fully elucidated, as well as the presence of somatic mutations in genes such as ASXL1, EZH2, SRSF2, U2AF1 and IDH1/2 which are associated with worse prognosis in MF patients (pts). In this large multi- center retrospective analysis, we aimed to study the impact of clinical and molecular mutations on transplant outcomes. Methods: This analysis including 498 pts from 11 centers in North America and Canada. Univariate proportional-hazard Cox regression analysis stratified by center was used to assess the association of patient, transplant, and disease characteristics on overall survival (OS). Baseline patient demographic data and disease characteristics were selected as covariates in the multivariate analysis. Results: Pts transplanted between 2002-2021 were included in this analysis. Baseline and transplant characteristics are summarized in table 1. The 1- and 2-year OS was 77% (95% CI; 73-81) and 70% (95% CI; 66-74) and non-relapse mortality (NRM) 19% (95% CI: 17-21) and 23% (95% CI: 19-27), respectively. The cumulative incidence (CMI) of relapse at 1- and 2-years was 12% (95% CI; 10-14) and 16% (95% CI; 12-20). The CMI of acute graft versus host disease (aGVHD) grade II-IV was 31% (95% CI; 27-35) at 3 months and 42% (95% CI; 38-46) at 1-year post-transplant and grade was III-IV 13% (95% CI; 11-15) and 18% (95% CI; 14-22), respectively. The CMI of neutrophil engraftment at 1 and 3 months was 90% (95% CI: 87-93) and 97% (95% CI: 95-95) and for platelets 55% (95% CI: 50-59) and 80% (95% CI: 76-83). Univariate analysis included pts (age and gender), transplant (donor type and conditioning regimen intensity) and disease characteristics (DIPSS, mutations, cytogenetics (CG), blood counts, and spleen size). Hemoglobin &amp;gt; 10 g/dL (HR .5, 95% CI .34 -.73 p=3 x 10 -4) and platelets &amp;gt;50× 10 9/L (HR .59, 95% CI .42-.81, p=.0013) prior to transplant were associated with improved OS. High risk DIPSS was associated with decreased OS (p=0.0002). Mutations in ASXL1, EZH2, IDH1/2, U2AF1 and SRSF2 were not associated with decreased OS in this analysis (Figure 1). However, mutations in ZRSR2 were associated with inferior OS (HR 2.07, 95% CI 1.08-3.95, p=.0252). Lastly, JAK2 which had the most frequent mutations was not associated with OS (HR .0.93, 95% CI .65-1.31). There was no association between the CG risk groups and OS. Splenomegaly, measured radiographically, had no impact on OS but was strongly associated with engraftment (better engraftment defined as HR&amp;gt;1). For platelets, spleen size of 15.6-18.9 cm HR of 0.69 (95% CI .47-1, p=.0489) and size &amp;gt;18.9-22.5 cm HR of 0.48 ( 95% CI .33-.7, p=1x10^-4). For neutrophils, spleen size &amp;gt;19.9-22.5 cm had a HR of 0.68, (95% CI .48-.96, p=.0268) and size&amp;gt;22.5 cm had a HR of 0.65 (95% CI .46-.91, p=.0114). Mismatched unrelated (MMURD) and haplo identical donors had no impact on survival but were associated with delayed platelet engraftment; MMURD (HR .67, 95% CI .47-.96, p=.0298) and haploidentical donors (HR .56, 95% CI .39-.8, p=.0017). In a multivariate analysis adjusted for age, gender, highest DIPSS, donor type and conditioning regimen, platelets &amp;gt; 50× 10 9/L (HR .61, 95% CI .44-.87, p=.0053) hemoglobin &amp;gt;10 g/dL (HR .6, 95% CI .4-.9, p=.0244) and lower DIPSS at the time of transplant were associated with improved OS. Conclusions: In this large multicenter analysis only clinical variables; hemoglobin and platelets, were found to be associated with OS after allo-HCT in MF patients. Somatic mutations associated with poor prognosis were not associated with OS suggesting that transplant can overcome their negative impact. Splenomegaly was associated with delayed engraftment but not OS. Interestingly, using alternative donors (MMURD and haplo identical) didn't have a negative effect on OS, possibly reflecting the use of post-transplant cyclophosphamide for GVHD prophylaxis in recent years. These results highlight the importance of biologic factors in the prognostication of outcomes in MF pts undergoing allo-HCT independent of somatic mutations. Supported by the American Society of Hematology (ASH) and MPN Research Foundation

Optimizing Outcomes with Myeloablative Conditioning in Older Patients: Efficacy and Safety of Precision Engineered Orca-T in Patients > 55 Years Old with Hematologic Malignancies

Background Allogeneic hematopoietic stem cell transplants (alloSCT) offer the only curative treatment for many hematological cancers but carry the risk of significant toxicity including graft versus host disease (GvHD). Additionally, while the use of a myeloablative conditioning (MAC) regimen optimizes disease control, it can increase the complications associated with transplant and non-relapse mortality. Therefore, older patients are often deemed unfit for MAC and relegated to treatment with reduced intensity conditioning (RIC) regimens, which result in a higher incidence of relapse. Orca-T is a high-precision cell therapy biologic that includes stem and immune cells, derived from allogeneic donors, that leverages highly purified, polyclonal donor regulatory T cells to control alloreactive immune responses. The specific subsets selected in the Orca-T manufacturing process retain cells with therapeutic benefit while removing those that pose potential risks, allowing for intensification of concomitant chemotherapy and resulting in overall positive outcomes to date in the phase 1b trial (NCT04013685). To assess the safety and efficacy in an older patient population, we compared outcomes in those at least 55 years old to younger patients treated with Orca-T, receiving chemotherapy-based MAC with tacrolimus as single-agent GvHD prophylaxis. Methods As of 6/02/23, 38 patients ≥18 to &amp;lt;55 (younger) and 25 patients ≥55 years of age (older) received Orca-T as part of a multicenter Phase 1b single-arm trial and had the following diagnosis: acute myeloid, lymphoid or mixed phenotype leukemia in CR/CRi, myelodysplastic syndrome or chronic myeloid leukemia that was in chronic phase. Patients with active disease at the time of transplantation and patients with myelofibrosis were not included in this analysis. Patients received a myeloablative regimen consisting of intravenous busulfan, fludarabine, and thiotepa (BFT) prior to Orca-T, followed by single-agent GvHD prophylaxis with tacrolimus, and had an 8/8 related or unrelated matched donor. Donors were matched via DNA-based high-resolution typing of HLA-A, -B, -C, and -DRB1. Results Orca-T was successfully manufactured at a centralized GMP facility, distributed and infused at study sites throughout the U.S. Vein-to-vein time (i.e. time between end of donor apheresis to start of recipient's Orca-T infusion) was &amp;lt; 72 hours for all patients, majority &amp;lt; 60 hours. Median age was 47 in the younger group and 59 in the older group. The younger group was 50% female, and the older group was 36% female. The percentage that were of Hispanic or Latino ethnicity were 11% in the younger group, and 12% in the older group. 8%, 74% and 11% vs 12%, 44% and 32% had ALL, AML and MDS in the younger and older groups, respectively. A greater proportion of patients in the younger group had a baseline HCT-CI score of 0 (53%), while more had a baseline HCT-CI score of 4 (12%) in the older group. The median duration of follow-up for both groups was 12 months (Table). Disease free survival at 1 year was similar in both groups at 89% in the younger patients and 86% in the older patients (Figure). Modified GRFS* rate at 12 months among patients in the younger group was 86% compared to 77% in the older group. Non-relapse mortality at 1 year was 0% in both of these groups who received BFT MAC. Overall survival was high at 100% and 96% at 12 months in the younger and older patients, respectively. There were two patients &amp;gt; 65 when they received Orca-T; both remain alive without evidence of grade 3-4 acute GvHD, moderate to severe cGvHD, or relapse to date. Only 2 patients experienced grade 3 mucositis (no grade 4-5) and 1 younger patient (2.6%) and 1 older patient (4.0%) required total parenteral nutrition. Conclusions Our analysis suggests that Orca-T cell therapy represents a reduced toxicity alternative to conventional transplant and is well-tolerated by patients 55 and older, with comparable clinical outcomes to those 18 - &amp;lt; 55. In both patient groups, relapse incidence was low, with high GRFS. Remarkably, non-relapse mortality was zero at 1 year with excellent overall survival , suggesting that this regimen could potentially improve outcomes for older patients. An ongoing Phase 3 trial evaluating Orca-T vs. standard of care is currently enrolling throughout the United States.