Relapse Mortality Research Articles

Maintenance Therapy with Chidamide Plus Azacitidine after Allogeneic Hematopoietic Stem Cell Transplantation for High-Risk Acute Myeloid Leukemia Patients

Background: Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is theoretically the only curative option for high-risk acute myeloid leukemia (AML) patients. However, many patients relapse after allo-HSCT, and treatment options are very limited. Azacitidine, a DNA methyltransferase inhibitor exhibits anti-leukemia activity in myeloid diseases. Chidamide, a selective histone deacetylase inhibitor, effectively induces apoptosis of AML cells. They have synergistic inhibitory effect on AML cells when combined together. Therefore, we conducted a multicentre, prospective study (ChiCTR2300067593) to examine the tolerability and efficacy of a combination of both chidamide and azacitidine as a maintenance therapy for high-risk AML patients after allo-HSCT. Patients and methods： Patients ≤ 60 years of age with high-risk AML post- allo-HSCT were enrolled. The high-risk characteristics of AML were defined as one or more of the following criteria: a) Patients with poor prognosis according to the genetic risk stratification assessment of European Leukmia Net (ELN) in 2022; b) Primary refractory or recurrent AML; c) Secondary AML (secondary to MDS or treatment-related AML). All patients received Chidamide 5 mg/d combined with azacitidine 75 mg/m2/d for 5 days. The cycle interval was 6-8 weeks. A total of 6 cycles was recommended. Treatment started as early as 3 months after transplantation. The primary endpoint of this study was cumulative incidence of relapse (CIR). The secondary endpoints included rates of overall survival (OS) and event-free survival (EFS). Survival outcomes were estimated using Kaplan-Meier analysis. Results： Thirty-six patients have been recruited. The median age was 42 years (range, 16-59). Baseline characteristics are shown in Table 1. With a median follow-up time of 412（185-762）days, the 1-year CIR was 12.3 (6.5-18.1) %, the 1-year OS and EFS rates were 100.0% and 87.7 (81.9-93.5) %, respectively. The median OS and EFS time were not reached. Four patients relapsed, two died, and two are still alive and ready for the second transplantation. The most common adverse events (AEs) were thrombocytopenia reaction and gastrointestinal tract reaction. Grade 2 or 3 AEs were observed in 16.7% (6/36) and 25.0% (9/36) of the patients, respectively. No grade >3 AEs were noted. 9 patients (6/36,16.7%) developed grade 3-4 thrombocytopenia, without active hemorrhage. All of them received blood transfusion and thrombopoietin receptor agonist. The median persistence of thrombocytopenia was 3 (2-5) d. Chronic graft-versus-host-disease (cGVHD) occurred in 25.0% (9/36) of patients. Four cases (4/36, 11.1%) were complicated with infection. They were one case of intestinal infection, one case of pulmonary and EBV infections, one case of hepatitis B virus activation and one case of herpes zoster. And all infected patients recovered safely after anti-infection and symptom-oriented treatment. CMV activation was not observed. Non relapse mortality (NRM) was zero. Conclusions： We conclude that chidamide plus azacitidine can be administered safely after allo- HSCT with no evidence of an increased incidence of GVHD, and this combination may decrease the relapse rate in high-risk AML patients. This novel maintenance therapy may be a promising way to prevent relapse in high-risk AML patients.

Dynamics of Immune Reconstitution after Unrelated Allogeneic Transplantation with Post-Transplantation Cyclophosphamide Compared to Classical Immunosuppression with ATG

Introduction: Post-transplant cyclophosphamide (PTCY), in hematopoietic stem cell transplantation (HSCT), is responsible for the success of haploidentical stem cell transplantation and is also being used in matched transplants such as unrelated transplants, with promising outcomes in graft versus host disease (GVHD). However, we lack data on immune reconstitution with this type of immunosuppression, especially in unrelated transplantation. Immune reconstitution is directly involved with post-transplant morbidity and mortality, being related to GVHD, relapses and infections, such as cytomegalovirus (CMV). Objectives: To evaluate global and CMV-specific immune reconstitution after unrelated donor HSCT, comparing the use of thymoglobulin (ATG) or PTCY protocol. Methods: We prospectively included patients undergoing first unrelated donor HSCT with ATG, methotrexate and tacrolimus or PTCY (50mg/Kg D+3 and D+4), mycophenolate mofetil (MMF) and tacrolimus with patient and/or donor CMV IgG positive. Immune reconstitution analyzes were performed by flow cytometry and CMV-specific recovery by ELISPot technique on days +30, +60, +90 and +180 post HSCT. Results: Thirty-six patients were included in this study, 20 in the ATG group and 16 in the PTCY group (table 1). Only 2 patients were 9x10 match, and the others were 10x10 match. All patients were submitted to preemptive strategy of CMV treatment, without the use of letermovir. Regarding clinical outcomes, neutrophilic engraftment was earlier with ATG (median of 12 days), compared to PTCY (median of 16 days) (p=0.0001). There was no difference between the groups in terms of length of hospital stay (median 33 days in both groups), CMV reactivation (70% in ATG and 75% PTCY, p=0.98), acute GVHD grades II to IV (p=0.26) or grades III-IV (p=0.56), and chronic GVHD (p=0.45), as well as relapse (p=0.3), non relapse mortality (p=0.77) and overall survival (p=0.4). Regarding immune reconstitution we observed an initial expansion of monocytes and NK lymphocytes in both groups and a higher increase in CD8+ T lymphocytes was evidenced, with an inversion of the CD4/CD8 ratio (CD4 14.9% vs 15.5% p=0.9 and CD8 49.7% vs 54.5%p=0.5 in ATG and PTCY respectively). We identified a CD4+/CD8+ double-positive T cell (DP) population, which was higher in PTCY group compared to ATG on days +30 (3.5% vs 10.2%, p=0.009), +90 (3.1% vs 12% p= 0.01) and +180 (5.2% vs 13%, p=0.007, in ATG and PTCY respectively ). On day +30 there were higher proportion of T cells (19.9% vs 9.6% p=0.004), B cells (0.76% vs 0.2%, p=0.006) and NK cells (19.2% vs 8.6% p=0.006) in ATG group compared to PTCY and monocytes were higher in PTCY (31.7 vs 44.5%, p=0.02). On day +180 the proportion of B cell were higher in PTCY (6.1% vs 16.6% p=0.014) and the NK cells were higher in the ATG (22.4% vs 14.7% p=0.021) (Figure 1), with higher CD56dim population in ATG group (46% vs 33.6% p=0.0079), while in PTCY there were a higher NK population CD56high on day +60 (40.3% vs 61%, p=0.014). We identified a peripheral expansion of a CD56negCD16posNKG2Dpos NK cell population, which was higher in the PTCY group on day +180 (3.7% vs 13.2% p=0.017). Regarding CMV-specific immune response, we found no difference between the groups on days +30 (5 vs 5 spots/10 4 PBMC p=0.41), +60 (10 vs 6 spots/10 4 PBMC p=0.38), +90 (13 vs 4 spots/10 4PBMC p=0.33) or +180 (7 vs 6 spots/10 4 PBMC p=0.57). Conclusions: In the context of unrelated HSCT, we found no difference in CMV-specific immune response with the use of PTCY or ATG protocol. Post-transplant immunosuppression with PTCY compared to ATG protocol is related to lower levels of T cells, NK cells and B cells on day +30 and later neutrophil engraftment, but with a higher proportion of double positive T cells on days +30, +90 and +180 and a higher proportion of B cells on day +180. At 6 months after transplantation, a proportionately lower number of NK cells, but higher proportion of CD56negCd16posNKG2D NK population was observed in the PTCY group.

A Day 14 Endpoint for Acute Gvhd Clinical Trials

The overall response rate (ORR) 28 days (D28) after treatment has been adopted as the primary endpoint for clinical trials of acute graft versus host disease (GVHD). ORR combines complete response (CR) and partial response (PR) because CR and PR have very similar non relapse mortality (NRM). D28 ORR has some disadvantages: first, physicians usually decide to modify immunosuppression much earlier than D28, and second, NRM does not always correlate well with ORR at D28, particularly for patients who present with intermediate risk or low risk disease. MAGIC serum biomarkers at day 14 (D14) of GVHD treatment have been shown to correlate better with NRM than clinical symptom response (Srinagesh et al, Blood Advances, 2019). We therefore hypothesized that a combination of clinical symptom severity and biomarkers at D14 of treatment would predict NRM at least as well and possibly better than clinical response at D28. We studied 1144 patients from 23 MAGIC sites who were systemically treated with at least 0.25 mg/kg/day of systemic steroids (prednisone equivalents) and had clinical data and serum samples available in the MAGIC database and biorepository. We divided the patients into a training set (n=764) and a validation set (n=380). We used 12-month NRM from the time of acute GVHD onset as the primary outcome of interest. We first trained a recursive partitioning algorithm in the training set to create a response model (MAGIC D14 clinical response) according to overall GVHD grade at both onset and D14 that predicted 12-month NRM and then applied it to the validation set. Patients that either progressed to grade III/IV GVHD, continued having grade III/IV GVHD, or only improved to grade II at D14 from grade III/IV at D0 had high NRM and were classified as non-responders. Patients with grade I/II GVHD at day 0 who had grade 0-II GVHD at day 14 and patients who improved to grade 0/I at day 14 from grade III/IV at day 0 had low NRM and were classified as responders. Although counterintuitive, responders included patients whose GVHD remained at grade II because the 12 month NRM of this group was only 20%. The new clinical model predicted NRM as well as the D28 standard response model in the validation set. When we integrated the D14 MAP biomarker score (low: ≤ 0.290 vs high: >0.290) with the new D14 clinical response (D14 MAGIC integrated response), we observed three response groups of integrated response with strikingly different 12 month NRM (8%, 35%, 76%, p<0.001), in contrast to the D28 standard response (Figure 1A, 1B). D14 complete response required MAGIC clinical response with low MAP; D14 partial response required either MAGIC clinical response with high MAP or MAGIC clinical non-response with low MAP; and D14 non-response required MAGIC clinical non-response with high MAP. The D14 response groups also displayed significant differences in 12 month OS (82%, 58%, 14% respectively, p<0.001) We then compared the D14 integrated response with the D28 standard response for 12 month NRM prediction. This D14 integrated response model was superior for time-dependent AUC (0.78 vs 0.71, P=0.03), sensitivity (0.71 vs 0.54), positive predictive value (0.52 vs 0.48) and negative predictive value (0.92 vs 0.89), with minimal loss in specificity (0.85 vs 0.87) in the prediction of 12-month NRM compared to the D28 standard response model. Using decision curve analysis, the D14 integrated response displayed higher net benefit (correct identification of patients that will experience NRM by 12 months) over the whole range of threshold probabilities/preferences for changing immunosuppression when 12-month NRM was used as the outcome. We conclude first, that the definition of response that uses onset and D14 grades is as accurate as D28 ORR model; and second, that a model using clinical grades and biomarkers on D14 more accurately predicts long term NRM than the standard D28 definition and may be useful as a clinical trial endpoint.

Venous Thromboembolism in Adolescents and Young Adults with Acute Lymphoblastic Leukemia Treated on a Pediatric-Inspired Regimen

Introduction Adolescent and young adult (AYA) patients (pts) with acute lymphoblastic leukemia (ALL) can be effectively treated with pediatric-inspired ALL regimens which incorporate asparaginase (ASP). Asparaginase is associated with increased venous thromboembolic (VTE) complications. We examined the incidence of and risk factors for VTE events as well as the impact of VTE events on outcomes of AYA pts treated on Dana-Farber Cancer Institute (DFCI) ALL Consortium Protocols. Methods We identified pts aged 15-50 years diagnosed with Philadelphia chromosome negative (Ph-neg) ALL treated on 4 multicenter DFCI Consortium protocols (Pediatric 00-001, Pediatric 05-001, Adult 01-175, and Adult 06-254), or treated as per these protocols between 2000-2021. All regimens included an ASP containing induction, 30 weeks of continuous ASP exposure during consolidation and a continuation phase without ASP. The use of a pegylated vs non-pegylated ASP formulation varied between protocols. As ASP exposure is associated with both VTE and survival, it may confound the association between VTE and survival; thus, to ameliorate confounding, all survival associated outcomes were conducted on pts who remained on protocol for at least 1 year (encompassing ASP exposure). Overall survival (OS) and event free survival (EFS) were presented with Kaplan Meier curves and comparisons were made by the log-rank test. Cumulative incidence of VTE, relapse (CIR) and non-relapse mortality (NRM) were estimated by the cumulative incidence method with the appropriate competing risks, and comparisons were made by the Gray test. Cox regression analysis was fit to evaluate the effect of covariates on OS and EFS. Results Among 341 Ph-neg AYA ALL pts aged 15-50 years, 109 (32%) experienced one or more VTE events. The baseline characteristics did not differ between pts who experienced a VTE and those who did not experience a VTE, except for a higher rate of VTE among overweight/obese pts (BMI≥25 kg/m 2, n=56, 38%) vs normal BMI (n=53, 27%, p=0.04) and a lower rate of VTE in patients with hyperdiploid vs non-hyperdiploid karyotype (n=4, 12% vs n=105, 34%, p<0.01). Of the 109 pts with VTE, 9 (8%) experienced sinus vein thrombosis (2.6% in the overall cohort) and 19 (17%) experienced at least one additional VTE. Most initial VTE events occurred during consolidation (n=78, 72%), followed by induction (n=22, 20%), and continuation/follow-up (n=9, 8%). The 2-yr cumulative incidence of VTE was 32% (95% CI, 27%-37%) and was similar between patients who were treated with non-pegylated ASP vs. pegylated ASP (n=43, 30% vs n=65, 35%, p=0.35). The 2-yr cumulative incidence of VTE was higher in the BMI ≥ 25 kg/m 2 group compared to those with normal BMI (38% vs 28%, p=0.035, Figure 1) and was the only covariate associated with increased VTE risk in the univariate regression model (HR 1.49, 95% CI, 1.03-2.17). Among pts who completed ≥ 1 year of protocol therapy (n=220), the 4-year OS was 92%, and did not differ between pts who experienced VTE vs. not (94% vs 90%, p=0.99, Figure 2). Similarly, there were no differences in 4-year CIR (14% vs 11%, p=0.50), NRM (0% vs 3%, p=0.37), and EFS (86% vs 86%, p=0.79). In univariate analysis for OS, obese BMI (>30 kg/m 2), higher WBC, B-cell immunophenotype, and fewer weeks on ASP therapy were associated with worse OS; all remained predictive in the multivariable model. In the uni- and multivariable analysis for EFS, higher WBC and B-cell immunophenotype were associated with worse EFS. Notably, VTE was not associated with worse OS or EFS in all regression analyses. Conclusion Among AYAs treated on DFCI ALL Consortium protocols, VTE events were frequent, occurred mostly during consolidation phase and were more common among pts with overweight/obese BMI vs normal BMI. Sinus vein thrombosis was rare. VTE incidence did not impact CIR, NRM, EFS or OS, suggesting that VTE is a manageable toxicity.

Development of a Modified Prognostic Index for Adult Patients with Acute Lymphoblastic Leukemia

Background:Acute lymphoblastic leukemia (ALL) is associated with inferior overall survival (OS) and progression-free survival (PFS) in adults due to biologic factors and lower tolerance to chemotherapy 1,2. Prognostic stratification is essential to guide therapy intensification and indication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). Recently, a prognostic index 2 integrating measurable residual disease (MRD), white blood count (WBC) and cytogenetic/molecular subtypes has been validated in children and young adults with ALL. However, in adult patients, age, allo-HSCT, other genetic subtypes 3 and center reality, may also play role in prognosis. To incorporate new variables to the pre-established prognostic index 2, a multicenter PFS analysis was performed to develop a modified/adpated risk score. Material and Methods: a multicenter (three Brazilian centers and the Spanish PETHEMA AR-03 trial cohort), retrospective study, reviewed medical charts and database of 398 adult patients with Ph-negative ALL (treated between 2003 and 2022), including risk variables: age, WBC count, cytogenetic/molecular classification, MRD, allo-HSCT, clinical outcomes and follow-up. The prognostic index 2 was calculated individually, then through multivariate analysis the coefficients (HR/OR) to incorporate age and allo-HSCT to the model have been determined. The methods of logistic regression, Cox model, Kaplan-Meier, log rank, ROC analysis and competitive risk regression were used in the statistical analysis. Subsequently, patients were stratified into 3 prognostic risk categories. Results: A total of 398 patients, 77% from the PETHEMA protocol and 23% Brazilian centers; 55.2% males; mean age 38.1 years (range 18-60; 67.4% (268) B-ALL; 31.4% (125) T-ALL; 1.2% (5) biphenotypic ALL. median WBC 22.4x10 9/L; 8.9% with central nervous system involvement; 22.9% high risk cytogenetics. Regarding treatment, 93.9% (373) received pediatric-inspired protocols (AR-03, GRAALL, CALGB, St. Jude TOTALXVI), 6.1% (26) (Hypercvad and others). Regarding the response, 83.3% (309/371) achieved complete remission (CR); CR rate was higher in pediatric inspired versus other protocols: 84.6% vs 57.9% (p 0.006). 45.6% (127/278) reached MRD-neg status after induction and 71.4% (125/175) after consolidation; 21.7% (67/309) underwent allo-HSCT in first remission. After a median follow-up of 3.9 years, 4-year-OS was 42.1% (95%CI 47.2-36.8%) and PFS was 33.4% (95%CI 38.5-28.4%). Cumulative incidences of relapse and non-relapse mortality were: 38.0% and 27.6%, respectively. In multivariate analysis, both allo-HSCT (OR:0.36 95%CI 0.19-0.66 p<0.001) and original 2 prognostic index (OR:2.47 95%CI:1.71-3.55 p <0.001) predicted significantly PFS, so allo-HSCT coefficient has been determined and incorporated to the model. According to this modified prognostic index, patients were stratified into 3 risk groups: low (100/285, 35.1%), intermediate (93/285, 32.6%) and high (92/285, 32.3%) high. At 4-years, PFS was significantly superior in low-risk group (55.9% - 95% CI 65.8-44.5%) compared to the intermediate-risk group (37.3% - 95%CI 47.5-27.1%) and high-risk group (182% - 95%CI 27.0-10.8%), p <0.001. Conclusion: The incorporation of the main risk factors in ALL and the role of allo-HSCT into prognostic index for adults can adequately stratify the PFS of patients into 3 risk categories and could assist in clinical decision-making. Reference 1. Fernandes da Silva Junior W, Medina AB, Yamakawa PE, Buccheri V, Velloso EDRP, Rocha V. Treating Adult Acute Lymphoblastic Leukemia in Brazil-Increased Early Mortality Using a German Multicenter Acute Lymphoblastic Leukemia-based regimen. Clin Lymphoma Myeloma Leuk. 2018 Jun;18(6):e255-e259. doi: 10.1016/j.clml.2018.03.001. Epub 2018 Mar 14. PMID: 29605423. 2. Amir Enshaei , David O'Connor , Jack Bartram , Jeremy Hancock , Christine J. Harrison , Rachael Hough , Sujith Samarasinghe , Monique L. den Boer , Judith M. Boer , Hester A. de Groot-Kruseman , Hanne V. Marquart , Ulrika Noren-Nystrom , Kjeld Schmiegelow , Claire Schwab , Martin A. Horstmann , Gabriele Escherich , Mats Heyman , Rob Pieters , Ajay Vora , John Moppett, Anthony V. Moorman; A validated novel continuous prognostic index to deliver stratified medicine in pediatric acute lymphoblastic leukemia. Blood 2020; 135 (17): 1438-1446. doi: https://doi.org/10.1182/blood.2019003191

Safety and Efficacy of Outpatient Myeloablative Busulfan Conditioning in Allogeneic Stem Cell Transplantation

INTRODUCTION: Busulfan-based regimens are the backbone of myeloablative conditioning (MAC) in allogeneic hematopoietic stem cell transplant (allo-HSCT), particularly for patients (pts) with Acute Myelogenous Leukemia (AML). However, literature on busulfan conditioning administered in the outpatient (OP) setting is limited. Here, we investigate the safety and efficacy of OP busulfan as compared to standard inpatient (IP) administration. METHODS: Pts > 18 years of age who received pharmacokinetically dose adjusted IV busulfan (130 mg/m2 x 4 days) conditioning prior to HSCT between January 2019 and April 2023 at our institution were included in this retrospective analysis. Pts who received non-myeloablative conditioning or who underwent a haploidentical HSCT were excluded. All pts undergoing HSCT were classified as having low-, intermediate-, or high-risk disease by the Disease Risk Index. Pts with AML were classified as having favorable, intermediate, or adverse disease by 2022 ELN classification. CIBMTR guidelines were used to determine neutrophil and platelet engraftment. Oral mucositis was graded per the World Health Organization scale. Clinical grading of acute graft-vs-host disease (AGVHD) was assigned per standard criteria. Adverse events (AEs) were reported in accordance with the CTCAE, v.5. Categorical variables were compared using the Fisher's Exact test. Continuous variables were compared using the Wilcoxon Rank-Sum test. Overall survival (OS) was defined as time from HSCT to time of death from all-cause mortality. Relapse-free survival (RFS) was defined as time from HSCT to time of relapse or non-relapse mortality. The Kaplan-Meier method was used to estimate OS and RFS. Survival differences between cohorts were compared using the Log-rank test. All hypothesis testing was two-sided and conducted at a significance level of 0.05. RESULTS: In total, 54 pts met eligibility criteria; 43 IP and 11 OP. The OP cohort was younger than the IP cohort (35 years vs 47 years median age; p=0.0284). All other patient, disease, and transplant characteristics were similar between cohorts. The majority of pts were male (IP: 56%, OP: 55%) and White/Caucasian (IP: 100%, OP: 91%). AML (IP: 88%, OP: 82%) was the most common indication for HSCT. Most pts were in CR1 (IP: 74%, OP: 89%) and had intermediate risk disease by both DRI (IP: 84%, OP: 64%) and 2022 ELN classification (IP: 62%, OP: 67%). PBSCT (IP: 88%, OP: 91%) and 10/10 MUD (IP: 67%, OP: 45%) were the most common types of HSCT. The majority of pts received a conditioning regimen of Flu/Bu4 (IP: 58%, OP: 55%). The use of PTCy was comparable between groups (p=0.6593). Of the 11 pts who received OP busulfan, 1 had to complete their conditioning IP after experiencing a seizure in the setting of prior meningitis. Between the 2 cohorts, there was no significant difference in the incidence of AEs > grade 2 (p=1), grade 2 AEs (p=0.8695), grade 3 AEs (p=0.7592), grade 4 AEs (p=0.2487), and grade 5 AEs (p=0.6457) within 30 days of conditioning. Incidences of transplant-related GI toxicities, including nausea (p=1), vomiting (p=0.4979), diarrhea/enteritis (p=1), and mucositis (oral: p=0.6102, GI: p=0.2821) were similar. There was no difference in time to neutrophil (p=0.1606) or platelet engraftment (p=0.9742). Length of hospitalization was shorter in the OP vs IP cohort (18 vs 24 days; p<0.0001). During hospitalization, there was no difference in the incidences of neutropenic fever (p=1), infection (p=0.5104), ICU transfer (p=1), or engraftment syndrome (p=0.7076). Number of infections per patient during hospitalization were comparable (p=0.3764). D30 chimerism was similar IP vs OP. Within 180 days of HSCT, there was no difference in the incidence of AGVHD (p=0.5152) or Grade II-IV AGVHD (p=1). Differences in 2-year OS (LR=0.2200) and 4-year RFS (LR=0.3144) were not significant. CONCLUSION: In pts undergoing MAC allo-HSCT with IV busulfan,OP administration shortens the length of hospitalization without delaying engraftment or increasing the risk of toxicity, neutropenic fever, infection, or ICU admission. Additionally, D30 chimerism, rates of engraftment syndrome and AGVHD, and survival were not affected. This makes OP busulfan an attractive option for transplant centers and their pts.

Malignant a-to-I RNA Editing By ADAR1 Drives T-Cell Acute Lymphoblastic Leukemia Relapse Via Attenuating dsRNA Sensing

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy that frequently occurs in children, adolescents, and young adults. Approximately 10-20% of T-ALL patients will experience relapse months or years following remission and will often become refractory to further treatments. The survival of relapsed/refractory patients is very poor, with an overall survival rate of less than a 25% overall survival rate. Relapsed patients often have enriched pools of leukemia initiating cells (LICs) with enhanced pro-survival and self-renewal capacity, suggesting a potential vulnerable population for effective targeted therapies with less toxicity. An emerging research topic in LIC biology is the identification of RNA modifying enzymes that are important for LIC self-renewal and survival. ADAR1 enzymes catalyze the transition of adenosine (A) to inosine (I) in precursor double-stranded RNA (dsRNA). Epitranscriptomic A-to-I RNA editing events are widespread in the cancer transcriptome and are critical for the transition from pre-leukemic cells to fully functional LICs. Compared to myeloid leukemia, the role of ADAR1 in lymphoid progenitor maintenance and malignant transformation is not well understood . A-to-I RNA editing has a wide range of effects on RNA biology including gene expression, splicing, RNA degradation and translation, and miRNA biogenesis and/or 3' UTR targeting. The best documented functional roles of ADAR1 are suppression of the interferon (IFN) response and RNA editing of self-dsRNA to prevent abnormal activation of cytosolic self-dsRNA sensing. Concurrent deletion of the cytosolic dsRNA sensors melanoma differentiation-associated protein 5 (MDA5) and protein kinase R (PKR) is able to completely rescue embryo death and reverse the IFN signatures. Whether editing of immunogenic dsRNA and suppression of aberrant dsRNA sensing pathway could enhance LIC self-renewal capacities is an important question that has not been extensively addressed. In this study, we applied bioinformatic analysis on a large cohort of T-ALL samples to examine the function of ADAR1 in the context of T-ALL LIC maintenance. We found that ADAR1 is highly expressed in ~70% of all T-ALL patients and particularly within the LIC compartment. A thorough comparison of the A-to-I RNA editing landscape between non-relapsed and relapsed T-ALL patient cohorts revealed hyper-editing is associated with both increased risk of relapse and leukemia-associated mortality. A total of 338 under-edited and 1,472 over-edited sites were found in relapsed patients compared to non-relapsed samples. However, there was very little difference in ADAR1 expression and the overall A-to-I RNA editing levels, among various molecular subtypes of T-ALL, suggesting malignant A-to-I RNA editing is a common attribute of relapsed T-ALL regardless of the genetic mutation status. We also performed functional study in a three-dimensional human thymic organoid system and a T-ALL patient-derived xenograft (PDX) model. Depletion of ADAR1 showed striking effects in LIC survival and self-renewal with 50-90% reduction in leukemia growth. Mechanistically, we revealed complex dsRNA regulatory mechanisms of ADAR1 by directing hyper-editing of immunogenic dsRNA and retains unedited nuclear dsRNA to avoid detection by the innate immune sensor MDA5. Interesting, the dependency on ADAR1-MDA5 axis various among patients depending on the cell intrinsic level of MDA5. Collectively, our results show that ADAR1 functions as a self-renewal factor that limits the sensing of endogenous dsRNA. Thus, targeting ADAR1 presents a safe and effective therapeutic strategy for eliminating T-ALL LICs.

Itacitinib for Prevention of Graft-Versus-Host Disease and Cytokine Release Syndrome with T-Cell Replete Peripheral Blood Haploidentical Transplantation

Introduction: Haploidentical peripheral blood allogeneic hematopoietic cell transplantation (PB haplo-HCT) can be complicated by graft-versus-host disease (GVHD) and cytokine release syndrome (CRS). Acute GVHD rates are higher with PB grafts compared with bone marrow, affecting 35-45% of patients and outcomes are poor in steroid refractory cases. Severe CRS occurs in 10-15% of patients receiving PB haplo-HCT and is associated with high non-relapse mortality and one-year overall survival between 25-30%. As interferon-γ and IL-6 are important mediators in both acute GVHD and CRS, we hypothesized that JAK1 inhibition with itacitinib could prevent these toxicities without impairing engraftment. Here we report outcomes from our study of itacitinib with haplo-HCT (NCT03755414). Methods: Patients with AML, MDS, ALL, or NHL in remission undergoing PB haplo-HCT were treated with itacitinib 200 mg/day on days -3 through +100 (first 20 patients) or 180 (second 22 patients), followed by a taper. Myeloablative and reduced intensity conditioning were allowed. GVHD prophylaxis was tacrolimus, mycophenolate mofetil, and post-transplant cyclophosphamide. Primary outcomes were incidence of primary graft failure and incidence of grade III-IV acute GVHD. Secondary outcomes included incidence and severity of CRS, relapse, GRFS, and overall survival. Results: Forty-two patients were enrolled and underwent transplantation on study between November 2019 and December 2022, median days of follow up was 453 days (range 142-1259). The patient population had a median age of 60 years (20 - 73 years) with the majority of patients having AML (AML 60%, ALL 21%), MDS 10%, MF 5%, NHL 4%). All patients with AML, MDS, or ALL were in a complete morphologic remission, although 45% had disease by either cytogenetics, next generation sequencing, or measurable residual disease assay (flow cytometry for AML/MDS, NGS for ALL). There were no cases of grade III-IV acute GVHD. The cumulative incidence of grade II acute GVHD on day 100 was 17.3% (95% CI, 7% - 31%), day 180 was 20.5% and day 365 was 20.5%. There were no cases of severe CRS with 90% of patients having grade 1 CRS and 10% having no CRS. No anti-IL6R or steroid therapy was used. There were no cases of primary graft failure. The cumulative incidence of relapse at 1 year was 10% (95% CI, 3% to 22%) and at 2 years was 14% (95% CI, 5% to 29%). In patients who survived without relapse to day 100, the 1-year cumulative incidence of moderate or severe chronic GVHD was 5% (95% CI 1% - 17%). The refined GRFS at day +180 was 85% (95% CI 69% - 93%) and at day +365 was 79% (95% CI 62% - 89%). Overall survival at 180 days 87% (95% CI 72% - 94%) and at 1 year was 80% (95% CI 63% - 90%). Analysis of peripheral blood mononuclear cells at day +28, +60, and +100, revealed that patients on itacitinib, compared with control haplo-HCT patients, had lower numbers of CD4 and CD8 central memory T cells, lower numbers of CD4 and CD8 naïve T cells, and higher numbers of classical monocytes, nonclassical monocytes, and both myeloid and plasmacytoid dendritic cells. In itacitinib treated patients, T-cell subsets expressed lower LAG3 and PD-1 and higher TIGIT, while monocytes expressed higher HLA-DR, CD80, and CD86. Conclusions: Itacitinib with PB haplo-HCT was safe with low rates of acute and chronic GVHD, without increased risk of relapse or transplant related mortality. Severe CRS was not seen in this trial, and no anti-IL6 or steroid therapy was used. The addition of Jak inhibition to standard PtCy based GVHD prophylaxis was associated with encouraging rates of GRFS and OS on this pilot and expansion study. Patients on itacitinib have unique immune reconstitution characteristics both in terms of PBMC counts and signaling markers within subsets.

Efficacy of Cord Blood Transplantation for the Management of Chronic Myelomonocytic Leukemia: A Registry-Based Study in Japan

Introduction Chronic myelomonocytic leukemia (CMML) is a challenging malignancy that shares characteristics with myelodysplastic syndromes and myeloproliferative neoplasms. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only curative option for CMML. Numerous studies have examined transplant outcomes and prognostic factors; however, the focus has primarily been on bone marrow transplantation (BMT) and peripheral blood stem cell transplantation, while cord blood transplantation (CBT) is understudied. To address this knowledge gap, we conducted a nationwide retrospective study to comprehensively compare the outcomes of unrelated BMT and single-unit umbilical CBT in patients with CMML. Methods Data were collected from the Transplant Registry Unified Management Program 2 of the Japanese Data Center for Hematopoietic Cell Transplantation. The inclusion criteria were as follows: age of 16 years or higher, a diagnosis of CMML, and receipt of the first allo-HSCT between 2013 and 2019 through unrelated BMT from a human leukocyte antigen (HLA) 8/8-matched donor (UBMT group) or single-unit umbilical CBT (CBT group). The primary endpoint was overall survival (OS) after allo-HSCT, and the secondary endpoints included progression-free survival (PFS), cumulative incidences of relapse and non-relapse mortality (NRM), neutrophil engraftment, and graft-versus-host (GVHD)-free, relapse-free survival (GRFS). The impact of CBT versus unrelated BMT on outcomes was evaluated using inverse probability of treatment weighting (IPTW) analysis. In this analysis, the Cox proportional hazards regression model for OS, PFS, and GRFS and the Fine-Gray proportional hazards regression model for relapse, NRM, engraftment, and GVHD were used. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated for all outcomes. The propensity score (PS) was calculated via logistic regression by using the following factors: age at allo-HSCT, sex, cytogenetic risk, disease status, days from diagnosis to allo-HSCT, and year of allo-HSCT. For the CBT group, the stabilized weights were calculated by dividing CBT prevalence by each individual's PS. Conversely, for the UBMT group, the weights were calculated by dividing the 1 minus prevalence of CBT by 1 minus each individual's PS. Results Between 2013 and 2021, 238 patients with CMML underwent their first allo-HSCT. Among them, 50 underwent HLA 8/8 allele-matched unrelated BMT (UBMT group) and 68 underwent single-unit umbilical CBT (CBT group). The median age at allo-HSCT was 58.5 (range: 26-75) years; the median follow-up period for survivors was 1,329.5 (range: 100-1,967) days. Intergroup differences in age at allo-HSCT, recipient sex, hematopoietic cell transplantation-specific comorbidity index, Eastern Cooperative Oncology Group performance status, cytogenetic risk, pre-transplant treatment, disease status at allo-HSCT, conditioning intensity, GVHD prophylaxis, and year of allo-HSCT were not significant. The transplantation outcomes are shown in Figure 1. There were no significant differences in the 3-year OS rate (UBMT: 51.0% [95% CI: 34.1-65.5%] vs CBT: 46.2% [95% CI: 33.2-58.1%]; P = 0.60; Figure 1A). IPTW analysis revealed no significant differences between the CBT and UBMT groups (HR: 1.21, 95% CI: 0.69-2.10, P = 0.51). PFS, relapse, NRM, and GRFS were not significantly different between the groups (Figure 1B-E). The neutrophil engraftment rate at 30 days was significantly higher in the UBMT group than in the CBT group (UBMT: 92.0% [95% CI: 78.9-97.1%] vs CBT: 79.4% [95% CI: 67.5-87.4%]; P < 0.01; Figure 1F). These observations associated with the secondary endpoints were concurrently corroborated by the IPTW analysis. Conclusion Our study suggests that CBT can serve as a viable treatment option, demonstrating efficacy comparable to that of unrelated BMT for patients with CMML. These findings underscore the improved outcomes over time after CBT in patients with CMML, which is a treatment previously perceived as inferior to other donor sources (Itonaga et al., Biol Blood Marrow Transplant. 2018;24:840-48). Further investigations are warranted to optimize transplantation strategies and improve outcomes in patients with CMML.

Comparable Outcome after Busulfan- or Treosulfan-Based Conditioning Regimen in Children Above 4 Years of Age with ALL Undergoing Allogeneic HSCT. Results from the Prospective International Forum-Trial

Purpose: Total body irradiation (TBI) has proved to be the “gold standard” as part of the conditioning regimen before allogeneic hematopoietic stem cell transplantation (HSCT) in pediatric patients with acute lymphoblastic leukemia (ALL). Its superiority over chemo-based conditioning was recently demonstrated in the prospective, international, randomized phase III study, which enrolled 417 patients beyond the age of 4 years transplanted for ALL in complete morphological remission (CR) from either matched sibling (MSD) or matched unrelated donor (MD) (Peters et al, JCO 2021, FORUM study; EudraCT: 2012-003032-22;ClinicalTrials.gov: NCT01949129). The use of either of the two protocol-prespecified chemo-conditioning regimens resulted in significantly worse EFS. Given the unavailability of TBI in some regions/centres and contraindications to TBI in individual patients, we here compare the outcomes of patients who received busulfan (BU) - based regimen vs of those who were given a treosulfan (TREO) - based conditioning in FORUM centres in both randomizing and non-randomizing countries in the years 2013-2018. Patients and methods: Patients ≤ 18 years at diagnosis (median age at HSCT 9.9 years, range 4-19.5), in CR pre-HSCT and with an MSD or MUD were assigned to myeloablative conditioning with fludarabine (FLU), thiotepa (THIO) and either BU or TREO according to country preference. Children transplanted from MSDs received cyclosporine A only as graft-versus-host disease (GvHD) prophylaxis, whereas recipients of MUD HSCT also received short-term methotrexate and anti-thymocyte globulin (ATG). Further details of the transplant procedure have been previously described (Peters C, et al. J Clin Oncol 2021). Results:In addition to the 193 patients from the randomizing countries, the FORUM trial included 115 additional children enrolled in countries where randomization could not occur (for legal or technical reasons). Overall, 180 vs. 128 patients received BU/THIO/FLU vs TREO/THIO/FLU, respectively. There were no differences about the patients' gender, age, and remission status and slight differences regarding donor, stem cell source and MRD status pre-transplant between the two cohorts of patients (see Table 1 for details). Patient's outcomes were updated as of February 20 th, 2023, and median follow-up was 4.2 years (range 0.3 - 9.1). There were neither differences between the 3-year overall survival (OS) (0.71±0.03 for BU/THIO/FLU vs 0.72±0.04 for TREO/THIO/FLU) nor event-free survival (EFS) (0.61±0.04 for BU/THIO/FLU vs 0.55±0.04 for TREO/THIO/FLU, p=NS). Three-year cumulative incidence of relapse (CIR) and non-relapse mortality (NRM) were 0.31±0.03 and 0.08±0.02 following BU/THIO/FLU and 0.36±0.04 and 0.09±0.03 following TREO/THIO/FLU, respectively (p=NS). Only one case of secondary malignancy was observed in the TREO cohort and one case of fatal liver veno-occlusive disease (VOD) in the BU group. No statistical differences were observed regarding the cumulative incidence of both aGvHD and cGvHD between the two groups; 3-year GFRS was almost identical (0.42± 0.04 in the BU/THIO/FLU group and 0.43±0.04 in the TREO/THIO/FLU cohort). There were no differences in OS, EFS, CIR, NRM and GFRS in either CR1 or CR2 patients between the two conditioning regimens. Furthermore, there were no differences in outcomes between countries. Patients given BU/THIO/FLU had a faster leucocyte, neutrophil and platelet recovery as compared to those prepared with TREO/THIO/FLU. Conclusion: Comparable long-term outcomes were observed after BU/THIO/FLU or TREO/THIO/FLU in children with ALL undergoing allogeneic HSCT included in the FORUM trial. Therefore, either of the 2 regimens may be effectively and safely used worldwide in patients > 4 years having a contraindication to or treated in centres/countries unable to deliver TBI.

Epigenetic Profiling and Machine Learning for Enhanced Risk Stratification in Pediatric Acute Lymphoblastic Leukemia

Introduction: Acute lymphoblastic leukemia (ALL) is the most common childhood malignancy with high clinical and biological heterogeneity. Despite advancements in treatment, relapsed patients still face significant mortality rates and long-term complications. Risk-adapted strategies have been implemented to optimize treatment intensity based on prognostic factors. Genomic techniques offer potential for improved risk stratification, but accurate grouping remains challenging. Epigenetic alterations, particularly DNA methylation, have shown promise in tumor classification and prognostication. In this study, we trained machine learning survival models based on DNA methylation signatures to refine risk grouping in pediatric ALL patients. Methods: Clinical annotation and DNA methylation data from pediatric ALL samples were retrieved from the Norlund et al. cohort (n = 763). Age, sex, risk group, and cytogenetic subtype were selected as clinical covariates. The cohort was randomly divided into training (80%) and test (20%) sets. Univariate Cox regression and variable importance analysis were performed to select CpG sites associated with relapse-free survival (RFS) and overall survival (OS). Random survival forest models were constructed using the training set, and their performance was evaluated on the test set using the concordance index (c-index), the time-dependent area under the ROC curve (AUC), and the continuous rank probability scores (CRPS). To assess the generalizability of the risk predictors, we performed external validation using two independent pediatric ALL datasets ( Busche et al., n = 42; and Krali et al., n = 384). Results: The relapse risk predictor (RRP) was constructed using random survival forests based on a signature of 16 CpG sites. The model achieved good predictive accuracy with c-indexes of 0.667 and 0.677 in the training and test sets, respectively. The addition of cytogenetic subtype or age at diagnosis did not significantly change the model's performance. Longitudinal assessment of the RRP revealed its superior performance compared to clinical risk grouping. Combining the RRP with clinical risk grouping improved prognostic accuracy, with a 20-month AUC over 80%. The mortality risk predictor (MRP) was constructed using a signature of 53 CpG sites. The model achieved strong predictive performance with c-indexes of 0.751 and 0.755 in the training and test sets, respectively. Similar to the RRP, the addition of cytogenetic subtype or age at diagnosis did not significantly impact the model's performance. Longitudinal assessment of the MRP demonstrated a higher performance rate than clinical risk grouping at all evaluated time points. Combining the MRP with clinical risk grouping yielded the highest prognostic accuracy. In the external validation of the MRP in the Krali dataset, the MRP score was strongly associated with OS: c-index 0.621, p-value 1.06 x 10 -4. The hazard ratio was 1.073 (95% confidence interval: 1.035-1.112) for each incremental increase in the risk score. On the contrary, a lower reproducibility of the RRP was observed (c-index 0.529), presumptively related to the addition of MRD-driven risk stratification in more recent protocols. Conclusions: Machine learning models built on DNA methylation signatures surpassed the traditional clinical risk grouping both for predicting relapse risk and mortality, while the combination of molecular and clinical factors provided the best prognostic accuracy. Further validation and implementation of these predictors could contribute to personalized risk-adapted treatment strategies for pediatric ALL patients.

Prediction of Graft-Versus-Host Disease (GVHD) in Recipients of Hematopoietic Cell Transplant(alloHCT) from a Single Mismatched Unrelated Donor Using a Highly Multiplexed Proteomics Assay: MHC-Pepseq

Introduction: Graft-versus-host disease (GVHD) remains a major barrier of allogenic hematopoietic stem cell transplantation (HCT). While direct recognition of mismatched HLA molecules is believed to be the major driver of alloimmune T cell response, indirect presentation of mismatched host class I or class II proteins may also contribute to CD4 T cell-mediated GVHD or graft-versus-leukemia (GVL). Using a novel highly multiplexed peptide-MHC binding assay (MHC-PepSeq), we developed a score of HLA-DRB1 restricted and binding allogeneic peptide sequences for each donor/recipient pair in a CIBMTR cohort of mismatched adult HCT recipients with hematological malignancies. We hypothesized that the risk score derived from the MHC-PepSeq assay is associated with the incidence and severity of acute and chronic GVHD. Methods: Using public population allele frequencies (allelefrequencies.net), we identified a set of alleles that covers >95% of HLA genotypes of 3 major US populations (European Caucasian, African American, Mexican Chicano) at 9 HLA-loci (-A, -B, -C, -DRA1, -DRB1, -DQA1, -DQB1, -DPA1, -DPB1) and converted their sequences to 7,744 unique, densely-tiled 15-mer peptides. A highly multiplexed synthesis protocol (“PepSeq”) was used to generate a library of DNA-barcoded peptides of the corresponding sequences, which we used to generate experimental binding measurements of each peptide against 12 common HLA-DRB1 molecules. The resulting data were then used to enumerate DR-binding peptides present in recipient HLA but not donor HLA genotype (“allopeptide score”), for each donor-recipient pair in a cohort of HLA-A, B, C and DRB1 (8/8) matched unrelated donors with a mismatch in HLA-DPB1 and a cohort of 7/8 Class I mismatched unrelated donors. Univariate analysis was used to compare clinical demographics and allopeptide association with clinical outcomes. In multivariable analysis, a logistic regression model was used to analyze aGVHD II-IV at day 100 (primary outcome), and Cox proportional hazards were applied for OS, relapse, chronic GVHD (cGVHD) and non-relapse mortality (NRM) (secondary outcomes). Results: In the 8/8 cohort, 6679 matched unrelated pairs were identified with allopeptide detected in 1563 (30.5%). In the 7/8 cohort, 1133 pairs were identified with allopeptide detected in 156 (15.9%). Patient characteristics were balanced in both cohorts and described in Table 1. In the 8/8 cohort, the cumulative incidence of aGVHD II-IV at day 100 post HCT was 42.3% (95% CI: 40.9-43.7%) in patients with a detectable allopeptide and 45.5% (95%CI: 43.0-48.0%) in patients with non-detectable allopeptide, respectively (p=.069). No significant differences were observed in univariate analysis for cGVHD, NRM, OS. In multivariate analysis there were no significant associations between presence of detectable allopeptide (Y/N) and aGVHD II-IV, cGVHD, OS, and NRM. However, a significant interaction between disease and allopeptide status was detected in the relapse model (P=0.0020), with allopeptide presence associated with a decreased risk of relapse in ALL (HR 0.71; 95%CI:0.54-0.94, p=0.0168) and an increased risk of relapse in AML (HR 1.23; 95%CI:1.05-1.43, p=0.0085). Allopeptide presence was not significantly associated with relapse in MDS (HR 0.89; 95% CI:0.74-1.06 p=0.1901). Adjusted cumulative incidence of relapse is shown in Figure 1. In the 7/8 cohort, cumulative incidence of aGVHD II-IV at day 100 post HCT was 43.4% (95% CI: 40.2-46.5%) and 41.8% (95% CI: 34.1-49.7%) (p=.77) in the allopeptide-detectable and non-detectable groups, respectively. In univariate analysis there were no statistically significant differences noted in cGVHD, NRM, OS. In multivariate analysis allopeptide presence was not significantly associated with any of the endpoints aGVHD II-IV, cGVHD, OS, relapse or NRM. Conclusion: In a large CIBMTR 8/8 and 7/8 matched unrelated donor cohort, allopeptide scores derived from MHC-pepseq were not predictive of aGVHD, possibly due to the limitation of the assay (i.e., low sensitivity, limited to class II presentation - HLA-DRB1 in this analysis) and/or low antigenicity in HLA molecules when indirectly presented as minor histocompatibility antigens. The observed reverse association of allopeptide presence with relapse in AML and ALL requires further investigation, and subgroup analyses for individual HLA-DRB1 presenting allele are currently underway.

Venetoclax-Based Therapy before Allogeneic Hematopoietic Cell Transplantation for Acute Myeloid Leukemia

Introduction The BCL-2 inhibitor venetoclax (VEN) is effective in older patients with untreated acute myeloid leukemia (AML). Few reports exist on the use of VEN as a bridging therapy for allogeneic hematopoietic cell transplantation (HCT) for AML. Previous studies have shown that NPM1 and IDH2 gene mutations are associated with high response rates to VEN therapy. We performed a retrospective cohort study to analyze the efficacy of VEN-based bridging therapy before HCT. Methods We included 46 patients who were eligible for HCT and received bridging therapy combined with VEN between April 2021 and June 2023 at our center. We evaluated response rates to VEN and HCT outcomes. None of the patients received VEN prior to the study. The response rate to VEN was evaluated using the 2022 European LeukemiaNet (ELN) criteria. We estimated overall survival (OS) using the Kaplan-Meier method, log-rank test, and Gray's test for univariate analysis of cumulative incidence of relapse (CIR) and non-relapse mortality (NRM). We used the Cox proportional hazards model for a multivariate analysis of OS. We extracted DNA from the bone marrow or peripheral blood, and analyzed gene mutations using next-generation sequencing (NGS), targeting 70 genes known to be recurrently mutated in myeloid malignancies. Results Of the 46 patients, 32 had de novo AML, 7 had de novo MDS/AML, 5 had secondary AML, 1 had secondary MDS/AML, and 1 had myeloid sarcoma. The median age was 59 (21-70) years. Nineteen were women and 7 had a history of HCT. The regimens combined with VEN were azacitidine in 39 cases and low-dose cytarabine in 7. According to the 2022 ELN risk classification by genetics at diagnosis, 7 were favorable, 11 were intermediate, and 27 were at adverse risk. Nine patients were in hematological complete remission (CR) / CR with incomplete count recovery (CRi) while 37 were not, when VEN was initiated. The maximum response rates among the patients who started VEN treatment in the non-CR group were: 18 with CR/CRi (49%) and no response in 19 (51%). The median time from the first dose of VEN to HCT was 70 (27-315) days. Forty-one patients underwent HCT and 19 (43%) were in CR/CRi at HCT. The reasons for discontinuation of VEN were HCT in 34 cases, failure in 9, and adverse events in 4 (hematological toxicity in 3 cases and infection in 1). Sixteen patients died due to primary disease (n=9), infection (n=5), thrombotic microangiopathy (n=1), and multi-organ failure (n=1). The median post-HCT observation period of survivors was 156 (25-775) days, and at 1-year after HCT, OS was 49.6% (95% CI: 28.0-67.9), CIR was 40.6% (95% CI: 24.1-56.6) and NRM was 15.2% (95% CI: 5.5-29.5). At 1-year after HCT, outcomes of the patients who were in CR/CRi at HCT was better than that of those who were not (OS, 80.8% vs. 26.4%, p=0.002; CIR, 13.4% vs. 61.8%, p<0.01; NRM, 0% vs. 26.7%, p<0.05). In 35 of the patients who underwent the first HCT, the 1-year OS was 88.9% in those who were in CR and 36.5% in those who were not (p=0.015). Thirty cases were non-CR at the start of the VEN regimen prior to their first HCT. This group had a 1-year OS of 57.8% (95% CI, 27.4-79.3). In 11 patients who achieved CR before HCT and 18 others who did not, the 1-year OS rates were 83.3% and 39.9%, respectively (p=0.10). Genetic analysis was performed by NGS in 37 patients before starting VEN, revealing mutations in TP53 (n=9), RUNX1 (n=7), IDH1 (n=6), ASXL1 (n=6), and DNMT3A (n=6) (Fig. 1A). Alterations in MDS-related genes (n=20) and kinase-related genes ( KIT, PTPN11, FLT3, KRAS, n=11) were frequent. Among the patients receiving their first HCTs, the 1-year OS was 0% in the group with TP53 mutations, and 63.9% in the wild-type TP53 group (p=0.04). The OS was worse in patients with mutated TP53 or kinase-related genes (n=19) than those without either mutation (n=15) (Fig. 1B, 1-year OS 28.7% vs. 72.9%, p=0.029). A multivariate analysis of OS revealed that patients who were not in CR at HCT (HR, 25.01 [95% CI, 2.406-259.9], p=0.007), those who previously underwent HCT (HR, 36.81 [95% CI, 4.599-294.7], p=0.035), and those with TP53 or kinase-related gene mutations (HR, 6.311 [95% CI, 1.137-350.0], p=0.035) had significantly lower OS rates. There was no significant difference in OS between the different ELN risk categories. Conclusions Non-CR at the time of HCT, a history of HCT, and mutations in TP53 or kinase-related genes were found to be independent poor prognostic factors for OS after VEN-based bridging treatment followed by HCT.

Favorable Outcomes for High-Risk MDS and Oligoblastic AML with MDS-Related Changes with Reduced Intensity Allogeneic Bone Marrow Transplantation with Post-Transplantation Cyclophosphamide

Introduction: Newer classification systems label myelodysplastic syndrome (MDS) with 10-20% blasts and acute myeloid leukemia (AML) with MDS-related changes (AML-MR) on a continuum as they share common biologic features. The prognostic implication of blast percentage is less clinically relevant particularly in diseases with high-risk molecular features such as MDS/AML with TP53 mutations. The recently introduced Molecular International Prognostic Scoring System (IPSS-M) allows for a more personalized prognosis for MDS patients (pts) than the prior revised IPSS (IPSS-R), but it is less clear if this translates to better therapeutic choices or outcomes for pts. Allogeneic bone marrow transplantation (BMT) remains the only potentially curative approach. Increasingly clinical trials of novel compounds combined with hypomethylating agents (HMAs) have not shown improved efficacy over single agent HMAs, necessitating further study of BMT approaches for durable disease control across the spectrum of disease biology. No uniform approach to the conditioning regimen and GVHD prophylaxis for this pt population has proven superior. In the current study, we describe the outcomes of BMT with post-transplant cyclophosphamide (PTCy) for patients with high-risk MDS and oligoblastic AML-MR, and analyze the prognostic implication of their chromosomal and molecular profiles within the international scoring systems. Patients and methods: This is a retrospective analysis of patients with 5-30% blasts and IPSS-R ≥3 who underwent BMT with PTCy at Johns Hopkins Hospital between 1/2013 and 12/2020. Next generation sequencing (NGS) was performed within 12 months of diagnosis. Kaplan-Meier analysis was performed to evaluate overall survival (OS) and relapse-free survival (RFS). Competing risks analysis was performed to evaluate the incidence of relapse and non-relapse mortality (NRM). Cox-regression models were performed in univariate analyses with false discovery rate adjustment and then subsequently conducted for multivariable analyses to identify statistically significant and independent prognostic factors. Results: Ninety-four consecutive patients (65% male) were identified with a median age of 61 (range 22 - 75) years at diagnosis. Median follow-up was 4.8 years (range 5 days-9.6 years) post BMT. Two-thirds (63%) underwent haploidentical transplantation, and 91% received reduced intensity conditioning with Fludarabine, Cyclophosphamide, and TBI. Median age at BMT was 65 years (range 22 - 76). The median time from diagnosis to BMT was 7.9 months. 52 (57%) received HMA based treatment and 36 (39%) intensive chemotherapy prior to BMT. Graft failure occurred in 6 patients (6.4%) The 5-year OS rate was 53% (95% CI: 43%-65%), the 5-year RFS rate was 47% (95% CI: 38%-59%) ( Figure 1A). The incidence of relapse was 21% (95% CI: 13% - 30%) at 1 year and 31% (95% CI: 21% - 40%) at 2 years after BMT ( Figure 1B). NRM rate in the first-year was 7% (95% CI: 2%-13%) and 11% (95% CI: 4%-17%) in the first two years ( Figure 1B). The incidence of acute GVHD (aGVHD) grades 3 to 4 was 3.2%, whereas chronic GVHD (cGVHD) presented in 12 patients (12.7%) with only 2 patients (2.1%) having moderate to severe disease based on the NIH grading criteria. Univariate analysis showed that higher IPSS-R (HR 1.68, 95% CI 1.39 - 2.04), poor or very poor karyotype risk (HR 7.48, 95% CI 3.49 - 16.02), complex karyotype (HR 3.72, 95% CI 2.01 - 6.88), higher IPSS-M (HR 1.72, 95% CI 1.38 - 2.14), TP53 mutations (HR 6.53, 95% CI 3.36 - 12.7) and RAS mutations (HR 4.96, 95% CI 1.7 - 14.5) were associated with worse OS. IPSS-R was significantly correlated with the patients' response to bridge therapy (OR 1.34, P=0.036). IPSS-R, IPSS-M, poor or very poor karyotype risk, complex karyotype, TP53 and any RAS mutations and response to bridge therapy were independently associated with worse OS and RFS ( Table 1, Figure 1C). Conclusion: This retrospective analysis supports that BMT with PTCy is a durable approach for patients with high-risk MDS and oligoblastic AML-MR leading to high OS and RFS associated with a promising safety profile with low NRM and severe GVHD incidence. IPSS-R, IPSS-M, karyotype and response to bridge therapy are independent predictors of OS and RFS post-BMT. The presence of TP53 and/or RAS mutations defines a sub-group of patients with dismal outcomes representing an unmet need within this patient population.

SMART101 Donor T-Lymphoid Progenitors to Accelerate Immune Reconstitution Post-Haploidentical Peripheral Blood Stem Cell Transplantation with Post-Transplant Cyclophosphamide: SI101-02 First-in-Human Phase I/II

Background and Significance Allogeneic hematopoietic stem cell transplantation (HSCT) is the only curative treatment option for many patients with hematological malignancies, but an HLA-matched donor may not be available, e.g., for ethnic populations under-represented in donor registries. In the absence of an HLA-matched donor, the use of post-transplant cyclophosphamide in unmanipulated haploidentical HSCT (haplo PTCy HSCT) is the favored strategy. However, in vivo T-cell depletion by PTCy significantly impairs immune reconstitution up to 2 years post-transplant, resulting in higher infection-related mortality and relapse rate. SMART101 is a cell therapy using allogeneic CD7+ T-lymphoid progenitors (TLP) produced in culture from mobilized peripheral blood CD34+ cells from an HSCT donor via Smart Immune's GMP manufacturing process. This ex vivo lymphoid niche culture system uses the Notch ligand Delta-like 4 coupled to IgG2 Fc fragment (DLL4-Fc) and RetroNectin® and a specific combination of cytokines, mimicking the initial steps of bone marrow lymphoid and T-cell differentiation. Characterization studies of these allogeneic CD7+ TLPs using single cell RNA sequencing analysis, suggested their high lymphoid commitment and thymic homing potentials. Preclinical in vivo experiments in irradiated adult and non-conditioned neonatal NSG mice demonstrate the capacity of these cells to migrate to the thymus, induce the generation of medullary thymic epithelial cells (TEC) and accelerate the generation of a polyclonal human T cell repertoire. Fig 1 shows the kinetic of cell engraftment and T-cell differentiation for CD34+ cells or CD7+ TLPs. Aims The SI101-02 clinical study (EudraCT 2022-002530-14) seeks to provide proof of concept that SMART101 cells can rapidly complete their differentiation within patient's thymus into naïve T-cells, accelerating the production of polyclonal donor T-cells without GvHD-inducing potential, and reduce the non-relapse and disease relapse mortality post haplo PTCy HSCT. Study Design and Methods This first-in-human, open-label, dose-escalation, two-cohort, multicenter phase I/II study will evaluate the safety and activity of SMART101 infusion (D6) in adult patients with AML, ALL or high-risk MDS eligible for an haplo PTCy HSCT (D0) as standard of care. The study is comprised of two segments. The first is a phase I dose escalation with three dose-levels of SMART101 (1.5 x 10 6, 4.5 x 10 6 and 9.0 x 10 6 CD7+ cells/kg of body weight) to define the recommended dose. The second is a phase II segment that will be comprised of 2 cohorts according to the type of conditioning regimen (myeloablative vs. reduced intensity conditioning). Patients will be enrolled in two consecutive stages following a Simon's 2 stage design, with 9 patients in stage 1 and 8 new patients in stage 2. Each cohort will be analyzed separately. The primary endpoints are the occurrence of unexpected unacceptable toxicity within 14 days after the infusion of SMART101 for the dose escalation segment, with a co-primary endpoint evaluating the activity of SMART101 in term of immune reconstitution (naïve CD4+ T cells ≥ 50/μL by D100) for the phase II segment. Secondary endpoints include the overall safety profile, especially the occurrence of GvHD and graft failure, the incidence of non-relapse/relapse mortality, and a detailed evaluation of the immune reconstitution. The SI101-02 study was initiated in H1-2023 in France and Italy. The study design, major inclusion and exclusion criteria, study treatment specificities, statistical methods and details of the ProTcell platform will be presented. Conclusion SMART101 is the first-generation of allogeneic TLP cell therapy obtained from Smart Immune's proprietary GMP manufacturing platform. The duration and the depth of T cell immunodeficiency post haplo PTCy HSCT is expected to be significantly reduced by the infusion of SMART101 thereby decreasing the non-relapse mortality and morbidity rates and thus improving the overall clinical outcome of this therapy.

Effect of donor age in patients with acute myeloid leukemia undergoing haploidentical hematopoietic cell transplantation vary by conditioning intensity and recipient age.

We investigated the impact of donor age (younger [≤35 years] vs. older [>35 years]) after accounting for other non-HLA and HLA factors on outcomes of patients with acute myeloid leukemia undergoing HLA-haploidentical hematopoietic cell transplantation (n = 790). The effect differed by conditioning-partly related to the differences in the recipient age in myeloablative (MAC; median 46 years) versus reduced-intensity/non-myeloablative conditioning (RIC/NMA; median 61 years) groups. With MAC (n = 320), donor age had no impact on acute graft-versus-host disease (GVHD), but older donors were associated with a significantly higher risk of chronic GVHD (hazard ratio [HR]: 1.6, 95% confidence interval [CI]: 1.10-2.30, p = .02) independent of recipient age and other factors. Donor age had no impact on either relapse or non-relapse mortality (NRM). The impact of donor/recipient age on overall survival changed over time. Older donors were associated with significantly higher late overall mortality (>6 months) in younger recipients (≤ 50 years; HR: 2.2, 95% CI: 1.03-4.6, p = .04) but not older recipients. With RIC/NMA (n = 470), neither recipient's nor donor's age influenced the risk of GVHD. Donor age had no significant impact on the risk of relapse, but older donors were associated with a significantly higher risk of NRM (HR: 1.6, 95% CI: 1.02-2.6, p = .04) independent of recipient age. Older donor age was associated with significantly higher late overall mortality (>9 months) in older recipients (>50 years; HR: 1.66, 95% CI: 1.0-2.67; p = .049) but not in younger recipients. Donor selection based on donor age may require a tailored approach for a particular recipient.

CLAG combined with total body irradiation as intensive conditioning chemotherapy prior to allogeneic hematopoietic stem cell transplantation in patients with refractory or relapsed acute myeloid leukemia.

Refractory or relapsed acute myeloid leukemia (R/R AML) remains the major challenge of AML treatment. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only valid option to achieve cure, but the prognosis is still dismal. We conducted a retrospective analysis for the feasibility of CLAG regimens (cladribine, cytarabine, and granulocyte colony-stimulating factor) combined with total body irradiation (TBI) as new intensive conditioning chemotherapy prior to HSCT in R/R AML. A total of 70 patients, including 21 primary refractory and 49 relapsed AML, were analyzed. Forty-nine (70%) patients had extramedullary diseases, and 54 (77%) patients received haploidentical transplantation. Except for one who died before white blood cell engraftment, all of the 69 evaluable patients achieved measurable residual disease (MRD) negative complete remission. The 3-year overall survival (OS) and relapse-free survival (RFS) rates were 46.0% (95% confidence interval [CI], 33.5-57.7%) and 38.5% (95%CI, 26.8-50.0%). The 1-year cumulative incidences of relapse and non-relapse mortality (NRM) were 38.6% (95%CI, 27.3-49.3%) and 11.6% (95%CI: 5.4-20.3%), respectively. The presence of chronic graft-versus-host disease (cGVHD) showed a trend to be associated with a lower risk of relapse (P = 0.054) and extramedullary diseases with a higher risk of NRM (P = 0.074). Multivariate analyses identified low leukemia burden pre-HSCT (defined as bone marrow blasts ≤ 50%) and cGVHD as independent factors associated with favorable OS and RFS. In conclusion, intensive conditioning with CLAG regimens plus TBI may be an effective and well-tolerated choice for R/R AML patients undergoing allo-HSCT.

Letermovir prophylaxis for cytomegalovirus reactivation in allogeneic hematopoietic cell transplant recipients: Single center Canadian data.

Cytomegalovirus (CMV) is associated with morbidity and mortality following allogeneic hematopoietic cell transplantation (alloHCT). Letermovir is a novel antiviral agent that prevents CMV reactivation in alloHCT patients, with limited data regarding influence on post-alloHCT outcomes. We retrospectively examined 273 alloHCT recipients, 158 in the non-letermovir cohort (NLC), and 115 in the cohort using letermovir prophylaxis (LC). Patients that received letermovir were CMV-seropositive and met criteria for high risk of CMV reactivation. Median start of letermovir was 21 days post-alloHCT, median duration of prophylaxis was 86 days. Letermovir prophylaxis demonstrated a statistically significant reduction in first CMV reactivation (at 200 days post 63.9% in the NLC vs. 35.7% in the LC; p < .001). On univariate analysis at 1 year, overall survival (OS) for NLC was 79.6% and 79.5% for LC (p = .54). Non relapse mortality (NRM) at 1 year for NLC was 12% and 12.3% for LC (p = .69). Cumulative incidence of relapse (CIR) at 1 year was 13.9% for NLC versus 17.1 for the LC (p = .27). On multivariable analysis, there was no significant difference between the two cohorts for OS, NRM, and CIR. Letermovir prophylaxis started at day +21 post-alloHCT reduced CMV reactivation, with no impact on posttransplant outcomes.

Allogeneic hematopoietic cell transplantation for blastic plasmacytoid dendritic cell neoplasm: a CIBMTR analysis

AbstractBlastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematological malignancy with a poor prognosis and considered incurable with conventional chemotherapy. Small observational studies reported allogeneic hematopoietic cell transplantation (allo-HCT) offers durable remissions in patients with BPDCN. We report an analysis of patients with BPDCN who received an allo-HCT, using data reported to the Center for International Blood and Marrow Transplant Research (CIBMTR). We identified 164 patients with BPDCN from 78 centers who underwent allo-HCT between 2007 and 2018. The 5-year overall survival (OS), disease-free survival (DFS), relapse, and nonrelapse mortality (NRM) rates were 51.2% (95% confidence interval [CI], 42.5-59.8), 44.4% (95% CI, 36.2-52.8), 32.2% (95% CI, 24.7-40.3), and 23.3% (95% CI, 16.9-30.4), respectively. Disease relapse was the most common cause of death. On multivariate analyses, age of ≥60 years was predictive for inferior OS (hazard ratio [HR], 2.16; 95% CI, 1.35-3.46; P = .001), and higher NRM (HR, 2.19; 95% CI, 1.13-4.22; P = .02). Remission status at time of allo-HCT (CR2/primary induction failure/relapse vs CR1) was predictive of inferior OS (HR, 1.87; 95% CI, 1.14-3.06; P = .01) and DFS (HR, 1.75; 95% CI, 1.11-2.76; P = .02). Use of myeloablative conditioning with total body irradiation (MAC-TBI) was predictive of improved DFS and reduced relapse risk. Allo-HCT is effective in providing durable remissions and long-term survival in BPDCN. Younger age and allo-HCT in CR1 predicted for improved survival, whereas MAC-TBI predicted for less relapse and improved DFS. Novel strategies incorporating allo-HCT are needed to further improve outcomes.

Primary Mold-Active Antifungal Prophylaxis Decreases the Need for Chest Computed Tomography Scans in Patients with Acute Lymphoblastic Leukemia.

Current guidelines recommend computed tomography (cCT) scans of the chest in children with leukemia following 96h of the onset of idiopathic neutropenia to eliminate pulmonary invasive fungal infections (IFIs). However, cCT exposes some children who are at a very high risk of developing secondary cancers to radiation. We aimed to determine the effect of antifungal prophylaxis (AFP) with voriconazole (VCZ) on the need for cCT scans in children with acute lymphoblastic leukemia (ALL) to eliminate pulmonary IFIs during chemotherapy. We retrospectively screened all patients' data from their electronic charts. Children who were diagnosed as having ALL before February 2013 and did (AFP group) or did not (NoP group) receive AFP were divided into two groups and compared regarding cCT scans and relapse-mortality rates. Ninety-six children were diagnosed before February 2013 and did not receive primary AFP and 146 children were administered VCZ following a diagnosis of ALL. There were no significant demographic differences between the groups. A total of 128 cCTs had been required in 62 children in the NoP group, compared with 64 cCTs in 52 children in the AFP group. The percentage of the patients who had required at least one chest CT scan and the mean number of cCT scans in the NoP group were significantly higher compared with the AFP group. Proven-probable IFIs and relapse-mortality rates were higher in the NoP group compared with the AFP group. Mold-active AFP revealed a significant decrease in the need for cCT scans in children with ALL.