ABSTRACT:Chronic graft-versus-host-disease (cGVHD) is the primary nonrelapse limitation to a successful hematopoietic cell transplantation and is largely treated as a single biological entity. We hypothesized that there exist different biological subtypes of cGVHD. Using the Applied Biomarkers of Late Effects of Childhood Cancer (ABLE) network database, which is derived from the largest pediatric cGVHD cohort worldwide, we applied clustering analysis to subtype patients with cGVHD from the ABLE1.0 and 2.0 studies (51 patients with cGVHD and 158 with non-cGVHD). We found 3 distinct cGVHD subtypes: cGVHD-1 was characterized by an effector memory T-cell, cytotoxic natural killer cell, and early precursor B-cell predominant pattern; cGVHD-2 was phosphatidylcholine, cytokine, and plasma cell predominant; and cGVHD-3 had more naïve CD4+ T cells and naïve regulatory T cells, had later onset, and was the only subtype with measurable T-cell receptor excision circles. We partially replicated these subtypes using metabolomic data from a separate pediatric cohort of the Children's Oncology Group trial ASCT0031 (33 patients with cGVHD and 39 with non-cGVHD). Furthermore, cGVHD-1 was associated with serotherapy (predominantly antithymocyte globulin) exposure, and cGVHD-3 was associated with receiving peripheral blood stem cells from donors, total body irradiation, and no previous acute GVHD. cGVHD-2 was associated with liver involvement and cGVHD-2 and -3 with de novo cGVHD. Overall, none of the subtypes were closely associated with organ involvement. Contrasting each subtype against patients with non-cGVHD, the 3 subtypes shared common markers, all of which were used in our previous cGVHD diagnostic classifier. These findings suggest the presence of distinct biological subtypes of cGVHD that may help guide therapeutic strategies.

This is a consensus-based Canadian review with the primary purpose of expanding knowledge regarding supportive and topical therapies for chronic graft vs. host disease (cGvHD). There is often a lack of confidence in treating certain organ specific manifestations, and access to specialists with organ specific expertise varies across the country. This paper covers information gained from a literature review and Canadian transplanter expertise and will serve as a guide for hematopoietic cell transplant healthcare providers to topical cGvHD therapies accessible in Canada. We will review common symptoms and signs focused specifically on skin, mouth, eye and genital tract cGvHD and on lifestyle modifications and topical treatments as an adjunct to our recent publication on systemic treatment for cGvHD.

In a randomized pilot trial we compared ATG (standard Arm A, 4.5 mg/kg) with ATG plus PTCy (experimental Arm BE, ATG 4.5 mg/kg, PTCy 100 mg/kg). The primary safety endpoint was overall survival at 100 days. We analyzed 79 patients with AML (n=55) or MDS (n=24). Median age (range) was 59 (19 to 74), 47 (59.5 %) were male. Conditioning was either myeloablative (n=49) or reduced intensity (n=30). Donors were 8/8 HLA-matched. Overall survival at 100 days was 95.0% (37 of 39 patients) vs 94.9% (38 of 40 patients) in arm A vs arm BE (p>0.9). In arms A versus BE, serious adverse events (SAEs) occurred in 26 (65.0%) and 25 (64.1%) patients, graft failure occurred in 3 and 1 patients (p>0.9), median (range) days to neutrophil engraftment were 19 (10-45) versus 22 (15-56) days p=0.007), cytomegalovirus and Epstein-Barr virus reactivations occurred in 11 and 7 patients (p=0.45) and in 6 and 5 patients (p=0.29). Overall survival at 12-months was 72.5% versus 75.8% (p-0.79), cumulative incidence at 6 months of relapse was 15.0% versus 15.7% (p=0.88) and of non-relapse mortality (NRM) 7.5% versus 8.0 (p=0.45). The combination of ATG and PTCy can safely be used in phase III trials.

Background: Chronic graft-versus-host disease (cGvHD) is a significant complication in children who have undergone allogeneic hematopoietic stem cell transplantation (allo-HSCT), contributing to long-term morbidity. Belumosudil, a selective rho-associated coiled-coil–containing protein kinase 2 (ROCK2) inhibitor, has demonstrated efficacy in adult cGvHD but pediatric data are lacking. This trial aims to establish the recommended pediatric equivalent dose (RPED) of belumosudil and assess its safety and efficacy in children aged 1 to less than 18 years old. Methods and study design: SchoolROCK is an open-label, multicenter, Phase 1/2, single-arm study investigating a daily orally administered liquid formulation of belumosudil in children with moderate-to-severe cGvHD, which is refractory to or has recurred after 2-5 prior lines of systemic therapy. In Phase 1, participants aged 1 to <12 years will receive a belumosudil dose estimated to mimic the exposure observed in adults after the administration of belumosudil 200 mg tablets once daily. After actual RPED is determined, Phase 2 will assess the overall response rate (ORR) by Week 24 in participants aged 1 to <18 years. Treatment will continue until clinically significant disease progression; relapse of the underlying disease; initiation of new systemic therapy for cGvHD; unacceptable toxicity; or study completion. The study also included a 4-week post-treatment safety follow-up, plus long-term follow-up until death or end of study, whichever occur first. Eligibility Criteria: Key inclusion criteria: Age 1 to <18 years; prior allo-HSCT; moderate-to-severe cGvHD requiring systemic therapy as defined by the 2014 National Institutes of Health (NIH) consensus criteria; prior treatment with 2-5 lines of systemic GvHD therapy; Lansky or Karnofsky performance status ≥60; and body weight ≥8 kg. Key exclusion criteria: Progressive underlying disease; prior exposure to belumosudil; severe pulmonary dysfunction (forced expiratory volume in 1 second ≤39% or lung score of 3); active, uncontrolled infections; significant organ dysfunction; and current use of restricted medications (e.g., strong CYP3A4 inducers, proton pump inhibitors [PPIs] during Phase 1). Participants with progressive underlying disease or post-transplant lymphoproliferative disease within 4 weeks prior to the first dose of belumosudil, active viral hepatitis B and C, history of another malignancy (within 3 years) are excluded. Endpoints:Primary endpoints: RPED determination (Phase 1); ORR by Week 24 (Phase 2)Secondary endpoints: Safety, PK parameters, duration of response, organ-specific response, failure-free survival, overall survival, and time to response Status: The study is in progress. RPED determination in Phase 1 will provide dosing details for Phase 2. Enrollment and follow-ups are also in progress.

ABSTRACT:Allogeneic hematopoietic cell transplantation (allo-HCT) is a curative option for patients with high-risk malignancies and nonmalignant disorders. Long-term survival depends on robust immune reconstitution (IR), which governs overall immune homeostasis and risks of infection, graft-versus-host disease, and relapse. However, despite its centrality to posttransplant outcomes, IR is not consistently monitored across transplant centers, limiting ability to generate meaningful, comparable, and translatable data. This review synthesizes current knowledge on numerical and functional IR milestones after allo-HCT, with a primary focus on flow cytometry-based monitoring of key immune cell subsets. Importantly, early CD4+ T-cell recovery (achieving >50 cells per μL by day 100 after transplant), is supported by strong clinical evidence and correlates with improved outcomes. Although emerging data suggest that additional subsets (CD8+ T cells, natural killer cells, B cells, naïve and recent thymic emigrant T cells, and γδ T cells) may also influence clinical trajectories, further harmonized, multicenter studies are needed to validate prognostic relevance across transplant settings. We propose practical, evidence-based guidelines for IR monitoring, including recommended time points, preferred assays, and flow cytometry panel components. Additionally, we highlight modifiable factors (eg, immunosuppressive drug exposures, graft manipulation) offering interventional opportunities for influencing IR. Harmonized monitoring strategies will support robust correlation between IR and clinical outcomes, guide real-time risk stratification, and facilitate the development of targeted, individualized transplant approaches. Standardization efforts led by consortia and registries are essential for advancing knowledge and optimizing care. We provide a roadmap for implementing uniform IR monitoring to improve outcomes and quality of life for allo-HCT recipients.

Suppression of alloreactive responses is a major limitation to current therapies for graft-versus-host disease (GVHD), as they broadly inhibit immune function, compromising graft-versus-tumor (GVT) effects and protective immunity. CD56brightCD16- regulatory NK cells (NKreg) have recently been associated with improved outcomes in human HCT recipients, but their mechanisms and therapeutic potential remain undefined. We hypothesize that murine NK cells with regulatory function exist and can be harnessed to suppress pathogenic alloreactive T cell responses and mitigate GVHD without impairing cytolytic immunity. To identify candidate NKreg subsets, we analyzed single-cell RNA-seq data from 3-month-old mouse spleens and found distinct NK1.1⁺ clusters. One subset expressed high Cd27 and low Cd11b, lacked cytotoxic genes (Gzmb, Prf1), and expressed stemness markers (Xcl1, Tcf7, Il7r). We focused on this subset due to its transcriptional similarities with human NKregs. Unsupervised clustering from 30-color spectral flow cytometry across murine tissues (liver, thymus, blood, marrow, nodes, spleen; N=2; n=10) confirmed a CD27⁺CD11b⁻ NK cell population. Like human NKregs, the cells have high expression of stemness proteins (TCF7, IL7R), low expression of cytotoxic markers, and high expression of the T-cell inhibitory ligand PD-L1. To assess suppressive function, we co-cultured sorted CD27⁺CD11b⁻ NK cells with proliferation dye–labeled and activated CD4⁺ or CD8⁺ T cells or cytotoxic NK cells. CD27⁺CD11b⁻ NK cells suppressed CD4⁺ T cell proliferation without affecting CD8⁺ T cells or NK cells and did not induce cell death. Cytokine profiling of these assays revealed reduced CD4⁺ T cell–derived IFNγ (p<0.05) and TNFα (p<0.0005). To test whether suppression required direct contact, we used transwell plates. Suppression was observed to be contact-dependent, with reduced effect when cells were separated (p<0.005). (N=2–3; n=8–12). To assess how allo-HCT affects this subset, we used an MHC-disparate GVHD model (C57BL/6J→BALB/cJ), profiling NK cells on days 1, 4, 7, 14, and 21 post-transplant (N=2; n=7–10/group). CD27⁺CD11b⁻ NK cells declined and failed to reconstitute in GVHD recipients (p<0.05). PD-L1 expression also decreased in the periphery and liver (p<0.005). Given the previously observed high PD-L1 expression, we tested whether PD-1–PD-L1 signaling mediated suppression. CD4⁺ T cell co-cultures with PD-1 blockade abrogated suppression (p<0.0005) (N=2; n=10). To evaluate the role of NK cells in GVHD, we first depleted NK and ILC1 cells using the anti-NK1.1 antibody. Depletion increased GVHD scores and reduced survival (p<0.05) (N=2; n=20/group). Using anti-asialo-GM1 to selectively deplete NK cells produced similar results, suggesting the effect is NK-driven (p<0.0005) (N=2; n=20/group). Flow cytometry of recipient tissues revealed increased CD4⁺ T cell infiltration in the blood and liver, a key GVHD target and known homing site for human NKreg cells. To evaluate whether CD27⁺CD11b⁻ NK cells mediate these effects, we adoptively transferred sorted CD27⁺CD11b⁻ regulatory or CD27⁻CD11b⁺ cytotoxic NK cells into allo-HCT recipients with T cell–induced GVHD. First, to evaluate a prophylactic approach, cells were transferred at the time of transplant. CD27⁺CD11b⁻ NK cell transfer improved GVHD scores and survival. To evaluate a therapeutic approach, transfers were performed on day 7 post-transplant, with similarly observed improved GVHD scores and survival. In both settings, CD27⁺CD11b⁻ NK cell transfer selectively reduced CD4⁺ T cells in the periphery and liver without affecting CD8⁺ T cells. To confirm translational relevance, we examined human CD56brightCD16⁻ NKreg cells from peripheral blood in functional assays paralleling the murine experiments. Human NKreg cells similarly suppressed allogeneic CD4⁺ T cells (p<0.0005) while sparing CD8⁺ T cells and NK cells (N=5). Suppression was non-cytolytic, contact-dependent, and partially mediated by PD-1 (p<0.05). These results support functional conservation between murine and human NKreg subsets and their selective targeting of CD4⁺ T cells. In summary, we identify a novel murine CD27⁺CD11b⁻ NKreg subset that suppresses CD4⁺ T cells through a contact- and PD-L1–dependent mechanism. These cells mitigate GVHD by restraining alloreactive CD4⁺ T cells in the periphery and liver, revealing a non-cytolytic, immunoregulatory NK population with translational therapeutic potential.

Graft-versus-host disease (GVHD) is a complication of hematopoietic cell transplantation (HCT) that has a low chance of complete remission and a substantial effect on morbidity and mortality. To better understand how to improve the field of GVHD research, management, and care, the cGVHD Eurograft Initiative organised a European community advisory board of patient advocates, with the assistance of the Lymphoma Coalition, to identify unmet needs. We present the results of this project in this Viewpoint, which identify unmet GVHD needs from the patient advocates' perspectives and provide five key actionable themes to improve GVHD management and care. The identified themes were: the need for reliable and tailored information, increased patient empowerment, access to professional dedicated care, optimal emotional support, and attention to the financial implications of GVHD, with improved communication as an overarching theme. This first step in patient-centred research opens the way to future collaborative initiatives by merging stakeholder perspectives to strive for better care and outcomes after HCT by addressing the most pertinent patient needs.

In 2020, the third NIH Consensus Development Project on Criteria for Chronic Graft-versus-Host Disease (GVHD) Clinical Trials was held with the goals of identifying gaps in understanding, prevention and treatment of chronic graft-versus-host disease (GVHD) and making actionable recommendations that would advance the field. An interim meeting was held in October 2024 to review progress on the 2020 recommendations. Each group was charged with reviewing their previous recommendations, assessing whether the field is on track to eventually achieve the goals, and considering whether recommendations should be modified in light of new data or insufficient progress. This manuscript summarizes the Working Groups' reports and helps define the research agenda for future studies in chronic GVHD. Overall, modest progress has been made on most initiatives. Some studies in progress will address key recommendations and results are eagerly anticipated.

Background Current diagnostic tests for pulmonary chronic graft versus host disease (p-cGvHD) are either invasive or challenging for children to perform. Multiple breath washout (MBW) has been proposed as a feasible and sensitive tool for the diagnosis of p-cGvHD. In this study, we aimed to determine the feasibility and sensitivity of MBW to monitor for p-cGvHD in children after haematopoietic stem cell transplantation (HSCT). Methods This was a prospective, single-center cohort study, recruiting children >3 years of age undergoing HSCT between Feb 2019 and Jan 2024. MBW and spirometry were performed at regular follow up visits out to 2 years post-HSCT. Results 46 children were included in the longitudinal analysis, 5 (10.9%) of whom developed p-cGvHD. MBW success rate was 93.9% (229/244 visits), compared to 78.3% for spirometry (191/244 visits). In children who developed p-cGvHD, compared to those who didn't, peak LCI was higher (12.6 versus 6.8, p=0.0003), nadir zFEV1 was lower (−3.5 versus −0.7, p=0.005) and nadir zFEV1:FVC was lower (−2.4 versus −0.3, p=0.01). The sensitivity and specificity for p-cGvHD were 100%/97.6% for peak LCI, 100%/71.1% for nadir FEV1 and 75.0%/94.7% for nadir FEV1:FVC. In those who do not develop p-cGvHD, longitudinal LCI remained normal or mildly abnormal (LCI<8.0) in 98.1% of visits, compared to FEV1 (z>−1.9) in 90.2% and zFEV1:FVC 95.5% of visits. Conclusions MBW is longitudinally feasible in a post-HSCT population as young as 3 years of age. LCI is highly sensitive and specific for p-cGvHD and may help to distinguish different phenotypes of post-HSCT lung disease.

Although unrelated-donor (URD) hematopoietic cell transplantation (HCT) is associated with many toxicities, a detailed analysis of adverse events, as defined by the Common Terminology Criteria for Adverse Events (CTCAE), has not previously been curated. This represents a major unmet need, especially as it relates to assessing the safety of novel agents. We analyzed a detailed AE database from the "ABA2" randomized, double-blind, placebo-controlled clinical trial of abatacept for acute graft-versus-host disease (AGVHD) prevention, for which the FDA mandated a detailed AE assessment through Day +180, and weekly neutrophil and platelet counts through Day +100. These were analyzed for their relationship to key transplant outcomes, with a major focus on the impact of AGVHD on the development/severity of AEs. A total of 2102 AEs and 1816 neutrophil/pla- telet counts were analyzed from 142 8/8-HLA-matched URD HCT recipients on ABA2 (placebo cohort, n = 69, abatacept cohort, n = 73). This analysis resulted in 2 major obser- vations. (1) Among graft source, conditioning intensity, age, and Grade 2 to 4 AGVHD, only AGVHD impacted Grade 3 to 5 AE acquisition after the first month post-transplant. (2) The development of Grade 3 to 4 AGVHD was associated with thrombocytopenia. We have created a detailed resource for the transplant community by which to contextualize clinical toxicities after transplant. It has identified AGVHD as a major driver of post-HCT Grade 3 to 5 AEs, and underscored a link between AGVHD and thrombocytopenia. This establishes a critical safety framework upon which the impact of novel post-transplant AGVHD therapeutics should be evaluated. This trial was registered at www.clinicaltrials. gov (#NCT01743131). (c) 2024 Published by Elsevier Inc. on behalf of The American Society for Transplantation and Cellular Therapy.

The treatment strategy for children and adolescents with chronic myeloid leukemia in the chronic phase (CML-CP) has evolved from allogeneic hematopoietic stem cell transplantation (HSCT) to tyrosine kinase inhibitors (TKIs). With the advent of next-generation TKIs and new targeted therapies in the CML field, an international pediatric CML expert panel provides recommendations based on the medical literature (including previous pediatric guidelines), national standards, and treatment principles used in adults with CML-CP. Recommendations include diagnosis of the disease and details on managing the initial steps of care of children and adolescents with newly diagnosed CML-CP, including complications such as leukostasis. The treatment recommendations are based on the initiation of therapy with a first- or second-generation TKI according to the allocated European Treatment and Outcome Study (EUTOS) long-term survival score risk group of the patient. The subsequent steps are based on the results of recommended monitoring which can justify a switch to another TKI or a drug in development if there is resistance or toxicity. The panel also provides recommendations regarding the discontinuation criteria for TKIs in children and adolescents in sustained deep molecular response. Allogeneic HSCT is not recommended as the first-line of treatment for children with CML-CP but is to be considered in case of progression to the advanced phase or failure of several lines of treatment. The present treatment and management recommendations are intended to provide advice to clinicians in view of optimizing the care and the outcome of children and adolescents with CML-CP.

The lack of immune tolerance after hematopoietic cell transplantation (HCT) can result in chronic graft-versus-host disease (cGvHD), which is the primary nonrelapse limitation of successful HCT. To date, immune tolerance has been considered a single biological entity, but we hypothesized that post-HCT immune tolerance could develop through multiple pathways. Using the ABLE network database, which comprises measurements of 75 cell populations, 10 cytokines and chemokines, lymphocyte population telomere length, KRECs and TRECs, and 132 metabolites from the largest pediatric cGvHD cohort (n = 241), we applied clustering analysis to patients with primary immune tolerance (PIT; no acute GvHD [aGvHD] or cGvHD) and patients with secondary immune tolerance (SIT; previous aGvHD and no cGvHD) to test whether subtypes could be identified. The evaluation of PIT identified 3 subtypes. PIT-1, associated with postpubertal age, lower thymic output, and increased ST2 compared to PIT-2 and PIT-3, is effector memory T cell-predominant. PIT-2, associated with prepubertal age, normal thymic output, increased B cell development, and longer lymphocyte telomeres, has a naïve T cell-predominant pattern. PIT-3, associated with postpuberty, higher thymic output, and malignancy, is dominated by increased PD1+ regulatory T cells and helper T cells and decreased long-chain acylcarnitine. We partially replicated these PIT subtypes using metabolomic data from a separate pediatric cohort of the Children’s Oncology Group trial ASCT0031 (n = 24 PIT patients). Previously resolved aGvHD had a minimal impact on the overall patterns of SIT-1 and SIT-2 compared to PIT-1 and PIT-2, except for time delays in the expansion of some immune cells. PIT-3 and SIT-3 were dominated by late increases in phosphatidylcholines (lysophosphatidylcholine precursors) and long-chain lysophosphatidylcholines (LYSOC20:4 and LYSOC16:2), respectively. This is the first time that distinct biological patterns of immune reconstitution after HCT are identified, which on validation and potentially could aid the development of future strategies for tolerance induction.

e22000 Background: Inotuzumab ozogamicin (InO) is FDA approved for adult and pediatric (≥1 y) patients (pts) with relapsed/refractory (R/R) B-cell precursor acute lymphoblastic leukemia (ALL). However, InO has been associated with increased risk of sinusoidal obstruction syndrome (SOS), particularly following hematopoietic cell transplantation (HCT). Previously reported post-HCT SOS rates are ~20% in adults and ~20–50% in pediatric pts who received InO before HCT. Methods: This observational, post-authorization safety study used data from the CIBMTR to assess post-HCT outcomes in pts with B-cell precursor ALL who received InO prior to HCT in the US. We report outcomes in pediatric pts ( < 18 y) who received InO prior to first HCT between 18 Aug 2017 and 17 Aug 2022. Results: In all, 52 pts were included (median age 9 y; 54% male; 83% with R/R ALL). Prior to HCT, 17% were in first complete remission (CR1), 40% in CR2, and 42% in CR≥3; 52%, 42%, and 6% received 1, 2, and ≥3 InO cycles, respectively; 46% received InO as monotherapy and 35% in combination with other agents (data unavailable in 19%). After InO, 39/52 (75%) achieved CR and 9/52 (17%) achieved CR with incomplete hematologic recovery; 38/47 (81%) evaluable pts were reported as minimal residual disease negative. Median (range) time from last InO dose to HCT was 1.4 (0.6–12.5) mo. Post-HCT outcomes are shown in the table. Post-HCT relapse of ALL occurred in 21 pts, of whom 7 (33%) died within 18 mo. Of 31 pts without post-HCT relapse, 6 died in remission due to SOS (n = 2), graft-versus-host disease (GVHD), organ failure, infection, or thrombotic microangiopathy (n = 1 each). In all, 16 pts developed SOS (8 mild; 8 severe). Of these, 7 received defibrotide treatment and 7 died within 18 mo (2 with SOS as cause of death). Prophylactic defibrotide was given to 23/52 pts (7/16 with SOS). Median (range) time from HCT to SOS was 10 (6–25) d. Other adverse events occurring in ≥30% of pts 100 d post HCT were viral infection (38%) and acute grade II–IV GVHD (33%). Conclusions: The rate of SOS in this real-world cohort of pediatric pts with ALL who received InO before HCT was similar to prior pediatric clinical studies. Given the high SOS rate and mortality in pediatric pts, careful consideration and pt selection should be exercised when using InO prior to HCT. Further investigation is needed to identify SOS risk factors and strategies for mitigating this risk in pediatric pts. Post-HCT outcomes. Pediatric ptsn=52 Median (range) follow-up from HCT, mo 15.2 (3.3–50.7) 12-mo overall survival % (95% CI) 71 (56–83) 6-mo transplant-related mortality, % (95% CI) 8 (2–17) 6-mo non–transplant-related mortality % (95% CI) 8 (3–17) 6-mo relapse, % (95% CI) 24 (13–37) Continued CR, n (%) 51 (98) Pts with SOS within 100 d, n 16 100-d SOS, % (95% CI) 31 (19–44) Post-SOS mortality among all pts, n (%) 7 (13)

Background: Anti-thymocyte globulin (ATG, or ATLG) and post-transplant cyclophosphamide (PTCy) are used for the prevention of graft-versus-host disease (GVHD). Two ongoing randomized trials (ISRCTN50290131; NCT05153226) are comparing these agents for efficacy and safety, but the safety and efficacy of the combination is unknown and has not been well studied. We conducted a randomized pilot trial of a combination of these agents to assess safety, with the aim of an expansion phase III trial. Methods: Following CONSORT guidelines, we conducted a randomized pilot trial to compare ATG (standard Arm A, 4.5 mg/kg) with ATG plus PTCy (experimental Arm BE, ATG 4.5 mg/kg, PTCy 50 mg/kg x 2) with short term feasibility endpoints at 100 days but otherwise following a phase III design. Patients consented to two years follow-up in anticipation of an expansion to phase III, as described in the CONSORT extension for pilot trials (Abbade LPF et al (2018) DOI 10.1186/s40409-018-0142-2). Overall survival was calculated using the Kaplan-Meier estimate; the log-rank test was used to compare treatment differences. We randomized a pre-planned convenience sample of 79 eligible and transplanted patients. Median (range) age was 59 (19 to 74), 47 (59.5 %) were male. Patients had either AML (n=55) or MDS (n=24) and were transplanted using either myeloablative (n=49) or reduced intensity (n=30) conditioning. Donors, either sibling (n=28) or unrelated (n=51), were 8/8 HLA-matched. The primary feasibility endpoints included: (1) recruitment of the intended sample size, (2) 100-day survival of the experimental arm B to be at least 90% compared with the standard arm A, (3) complete data on 95% of recipients at 12 months and (4) completion of the trial within budget. A variety of secondary endpoints, both efficacy and safety, were included. Objectives 1, 3, and 4 were fulfilled and this abstract describes the safety and efficacy outcomes related to objective (2). Results at day 100: Forty-one patients were randomized to Arm A and thirty-eight patients to Arm BE. At the time of data lock (May 14, 2024), all patients had been followed for at least 100 days. Thirty-nine (95.1%) patients in Arm A and 36 (94.7%) in Arm B survived to 100 days (primary endpoint). Acute graft versus host disease (AGVHD) was reported in 15 and 6 patients in Arms A and BE respectively, of which 6 and 3 had grades II-IV and 3 and 0 had grades III-IV. At 100 days, 3 patients in Arm A and 3 patients in Arm BE were receiving systemic corticosteroids. Serious Adverse Effects (SAEs) were experienced by 31 patients in Arm A and 25 in Arm BE. Graft failure at 28 days occurred in 2 patients in each arm, with all patients achieving engraftment eventually. Median (range) days to engraftment was 19 (13-45) for Arm A and 22.5 (15-56) for Arm BE. Cytomegalovirus reactivations occurred in 10 and 7 patients in Arm A and Arm BE respectively and Epstein-Barr virus reactivations occurred in 7 and 4 patients in Arm A and Arm BE respectively. Results Follow Up: Median follow up of living patients was 23.6 months (range 3.19- 25.92) for Arm A patients and 22.9 months (range 1.64-25.07). Overall survival between the arms was similar at 12-months; 68.9% (standard error (SE) 7.5%) in the standard arm A and 75.4% (SE 7.6%) in the experimental arm BE (p = 0.52). Relapse or disease progression were seen in 7 patients in Arm A and 7 patients in Arm BE. AGVHD was reported in 18 patients in Arm A and 9 in Arm BE (grades II-IV 11 and 5, grades III-IV 5 and 1), with late (>100 days) AGVHD occurring in 3 and 2 cases in Arms A and BE respectively. CGVHD has been reported to date in 7 patients in Arm A and 4 patients in Arm BE, moderate or severe grade in 2 patients and 2 patients respectively. Conclusion: The addition of PTCy to ATG did not result in excessive adverse events in this pilot trial (to day 100), and long-term results remained consistent. The combination of ATG and PTCy can be used safely in future trials to further prevent graft-versus-host disease. Based on the demonstrated safety and feasibility of this combination, and encouraging signals of efficacy, planning for an expansion to a full phase III trial with a primary endpoint of GVHD, relapse free survival is underway.

Background: In patients with AML, EMD can occur in the central nervous system (CNS) or other sites, in addition to bone marrow (BM) disease. Only a few retrospective studies have evaluated the impact of EMD on outcomes after alloHCT for children with AML. We hypothesized that the presence of EMD at AML diagnosis would be associated with inferior outcomes after alloHCT. Methods: The Center for International Blood and Marrow Transplant Research (CIBMTR) database was used to compare the effect of EMD in patients with AML. Based on EMD at diagnosis, patients were grouped as BM involvement (Group I), BM+CNS involvement (Group II), and BM+other EMD±CNS (Group III). The primary outcome was 1year (y) progression-free survival (PFS) with 1y overall survival (OS), non-relapse mortality (NRM), cumulative incidence (CI) of acute and chronic graft versus host disease (GVHD), and CI of relapse as secondary endpoints. Kaplan Meier estimates were used to assess survival outcomes and groups compared using log-rank test; Cox regression was used to identify covariates associated with survival. Results: Our cohort includes 938 children (<21y; 52% male) who received first alloHCT for AML between 2008-2019. All patients were in a morphologic complete remission (CR) and confirmed to have no evidence of EMD at the time of alloHCT. Our study cohort included 630 Group I, 212 Group II and 96 Group III patients. Group III patients were younger at HCT (median age 2.9y vs 10.8y Group I, 10y Group II;), had poor-risk cytogenetics (50% vs 37% Group I, 39% Group II) and a higher pediatric disease risk index (52.1% vs 21.9% Group I, 25% Group II) and poor risk cytogenetics (50% vs 39% Group I, 37% Group II). The majority (63%) of patients had low comorbidity burden by expanded youth malignant HCT comorbidity index (score of 0-1, no difference between groups). While 67.5% of patients received chemotherapy-only conditioning, 32.1% received total body irradiation (TBI) based, and the remaining chemotherapy with low-dose TBI (4.5%) conditioning regimens. Radiation to other sites, including CNS, was reported in 6.7% of the study cohort. Donors were mostly unrelated cords (42.4%), matched unrelated (20.5%), and matched siblings (18%), with the remainder being haploidentical (6.4%) and mismatched unrelated (6.9%)Graft sources included bone marrow (39.8%), umbilical cord blood (46.4%), and peripheral blood (14.8%). GVHD prophylaxis was commonly calcineurin inhibitor-based (89%), with the remainder receiving post-transplant cyclophosphamide-based prophylaxis (6.1%) or ex vivo T cell-depleted grafts (3.2%). At a median follow of 69.8 months (range 3.4-155 months), the 1y PFS of the entire group was 67.4%. The day +100 acute GVHD, 1y NRM, relapse incidence, OS, and chronic GVHD of the entire group was 31.7%, 10.3%, 22.6%, 77%, and 29.6% respectively. Multivariable analysis of factors associated with relapse, after adjusting for disease status (includes MRD), age, and TBI use, EMD was associated with improved survival: Group II: hazard ratio (HR) of 0.697 (95% CI 0.515-0.944; p=0.012) and Group III HR of 0.695 (95% CI 0.459-1.053; p=0.087) compared to Group I cohort. There was no difference in PFS (p=0.21), NRM (p= 0.27), and OS (p=0.90) among the groups. Conclusion: Our results suggest that the presence of EMD with BM at diagnosis did not impact clinical outcomes post-alloHCT. Although this cohort describes a subset of patients with EMD - those who were able to clear EMD prior to HCT and proceed to HCT - we observed that EMD at diagnosis among those who are otherwise able to proceed to HCT does not portend worse HCT outcomes or more relapse. It is possible that, in this setting, the ability to clear EMD prior to HCT was suggestive of chemotherapy-sensitive disease.

This is a consensus-based Canadian guideline whose primary purpose is to standardize and facilitate the management of chronic graft-versus-host disease (cGvHD) across the country. Creating uniform healthcare guidance in Canada is a challenge for a number of reasons including the differences in healthcare authority structure, funding and access to healthcare resources between provinces and territories, as well as the geographic size. These differences can lead to variable and unequal access to effective therapies for GvHD. This document will provide comprehensive and practical guidance that can be applied across Canada by healthcare professionals caring for patients with cGvHD. Hopefully, this guideline, based on input from GvHD treaters across the country, will aid in standardizing cGvHD care and facilitate access to much-needed novel therapies. This consensus paper aims to discuss the optimal approach to the initial assessment of cGvHD, review the severity scoring and global grading system, discuss systemic and topical treatments, as well as supportive therapies, and propose a therapeutic algorithm for frontline and subsequent lines of cGvHD treatment in adults and pediatric patients. Finally, we will make suggestions about the future direction of cGvHD treatment development such as (1) a mode-of-action-based cGvHD drug selection, according to the pathogenesis of cGvHD, (2) a combination strategy with the introduction of newer targeted drugs, (3) a steroid-free regimen, particularly for front line therapy for cGvHD treatment, and (4) a pre-emptive approach which can prevent the progression of cGvHD in high-risk patients destined to develop severe and highly morbid forms of cGvHD.